Mechanical replacement processes in mobile soft calcichorizons ; their role in soil and landscape genesis in an area nearMérida , Spain

G.W.W. Elbersen

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Mechanical replacement processes in mobile soft calcic horizons; their role in soil and landscape genesis in an area near Mérida, Spain

Proefschrift terverkrijgin gva nd egraa dva n doctori nd elandbouwwetenschappen , opgeza gva nd erecto rmagnificus , dr.C.C .Oosterlee , hoogleraar ind eveeteeltwetenschap , inhe topenbaa rt everdedige n opvrijda g 12novembe r198 2 desnamiddag st evie ruu ri nd eaul a vand eLandbouwhogeschoo l teWageninge n

Centre for Agricultural Publishing and Documentation

Wageningen - 1982 Abstract

Elbersen,G.W.W . (1982).Mechanica lreplacemen tprocesse s inmobil e soft calcichor ­ izons; theirrol e insoi lan d landscape genesis ina nare anea rMérida ,Spain .Agric . Res.Rep . (Versl.landbouwk .Onderz. )919 ,ISB N90-220-0810-X , (xii)+ 208p. , 47figs , 16tables ,20 4refs ,Eng. ,Du. ,Sp .an d Fr.summaries . Also:Doctora l thesis,Wageningen .

Amechanica lreplacemen tproces s isdescribe d toexplai n thewa y inwhic h soft calcichorizon sbecom e 'mobile'an d actively penetrate the soil. Thismode l implies thatth ehorizon sar epedogeneti c featureswhic hma y bever y old since they canes ­ capeexposur e m alandscap e subject toerosion .Th e lime theycontai nca nb ederive d tromth eweatherin g strata throughwhic h theyhav epasse d in thecours e of time.Th e processi sinitiate d bysubterranea ngilga ïformatio nwhic h introduces soilmateria l intoth elowe rpar to f thecalci chorizo nwhic h subsequentlymove s thismateria lup ­ wardan d expelsi tfro m thetop .Th etranspor tproces swa sre-create d in thelabora ­ toryan dmonitore db ystere oradiography . Itsdrivin g force isderive d fromai ren ­ closurewhic hoccur supo nwettin g ofcrystallin epowder y lime.Fiel d data from the studyare ahav eyielde d evidenceo f thereplacemen t processan d indicate themai n rnW \^\facf"- Rat*s ofdownwar d movement of thecalci chorizon s havebee n cal- are! rJS- \ th\sa™ °rdero fmagnitud ea srepresentativ e erosionrate s for the arc^oSy^rbrieily^t^:33 ^ "^ ^^ *^^> ^morphology and

InclosureridPat-S: ^^ h°riz0ns> calich*> calcrete,sof tpowder y lime,gilgaï ,ai r izons eenet? of«^te s erosionrates ,carbonat e leaching,petrocalci c hor- ïzons,genesi so fcalci chorizons .

Thisthesi swil l also be pubUshed as AgricuUural Research ^^^ 9]g_

© Centrefo rAgricultura l Publishing andDocumentation ,Wageningen , ,982.

y b e d C f rm b rint h0t0 pri^'microîi^fa:; o ther mea ns w?tr T^^ " ^ ° ' ? P > P " y nermean swithou twritte npermissio n from thepublishers . Stellingen

1. Netterbergha dongelij ktoe nhi jbeweerd eda td einformati edi eka nworde nver ­ kregenui tvisuel ewaarnemin ge nbeschrijvin gva ncalcrete smogelijkerwij szij n grenzenbereik theef te nda tverder evooruitgan gwaarschijnlij kallee ngeboek t kanworde ndoo rd etoepassin gva nmodern egeochemische ,geochronologische ,sedi - mentologischee npedologisch etechnieken .

Netterberg,F . 1969. Theinterpretatio no fsom ebasi ccalcret e types.Th eSout h AfricanArcheol .Buil .2 4 (3/4):117-122 .

2. Brewer'sverklarin gda tcrysti cplasmi cfabric she tsimpel egevol gva nkristal - lisatiezijn ,geld tnie tvoo rd ezacht ekalkhorizonte ndi ei ndi tproefschrif t beschrevenworden .

Brewer,R . 1976. Fabrican dminera lanalyse so fsoils .2n dedition .Wiley ,Ne w York.p .341 .

3. Deui tmeerder ehard ee nzacht ekalklage nbestaand e 'caprockcaliche 'va nd e LlanoEstacad oi nTexa se nNe wMexic oka nnoc huitsluiten ddoo rdegradati enoc h uitsluitenddoo raggradati eworde nverklaard .

Ditproefschrift .

4. Mechanischevervangingsprocesse nkunne nzacht ekalkhorizonte ngedurend elang e tijdi nstan dhouden ,omda the ti ntegenstellin g totd emeest ebodemvormend epro ­ cessengee n 'self-accelerating (endaardoo rterminating )feedbac kprocesses 'zijn .

Torrent,J .& W.D .Nettleton . 1978. Feedbackprocesse s insoi lgenesis .Geoderm a 20:281-287 .

5. Hetfei tda td emeest egoe dgedraineerd egronde nva nhe t 'Altillanura'landscha p vand eLlano sOrientale si nColombi avolgen she tAmerikaans ebodemklassificatie - systeemnie tal sOxisol sgeklassificeer dkunne nworden ,hoewe lzi jee ngroo taan ­ talkenmerke nme tOxisol sgemee nhebben ,i she tgevol gva nbijmengin gva nvulka ­ nischea sui td eAnde si nhe tHoloceen .

Nieuwenhuis,E . &G.W.W .Elbersen . 1972. Algunasobservacione s sobrela sceniza s volcânicase nColombia .Revist aCIA F 1972:7-16 . 6. Eenlineai rgilga ïpatroo nda tnie tzuive rparalle laa nd ehellin ggeoriënteer d is,ka novereenkomsti gd emenin gva nBeckman ne tal .worde nverklaar dal sont ­ staandoo rerosie ,indie nword taangenome nda the tpatroo nzic hi nee ndegra ­ derendlandscha po pd eondergron dheef t 'doorgestencild'.

Beckmann,G.G. ,C.H .Thompso n &G.D .Hubble . 1973. Lineargilgaï .Australia n landformexampl eNo .22 .Th eAustralia nGeographer ,XII ,4 :363-366 .

7. Deinterpretati eva nmonstergebiede no pconventionel e luchtfoto'si s(no gsteeds ) onmisbaarbi jhe tgebrui kva nsatellietbeelde nvoo rbodemkaa rte ringen .

8. Degrot enauwkeurighei dwaarme ehe tAmerikaans ebodemklassificatiesystee md ecri ­ teriavoo rzij ntax adefinieer theef tvoordele nvoo rd ecorrelati emaa rnadele n voord ekaartering .

9. Dete nlast eva nnatuurbehou dkomend ecomponen tva nd eprij sdi evoo rd estorm ­ vloedkeringi nd eOosterscheld eza lworde nbetaal dbestempel tdi tgebie dto the t duurstezeewateraquariu mte rwereld .Worde ndez ekoste nbetrokke no pd egegeven s betreffended emacroscopisch ewaterfaun awaarme ehe tecologisc hmode lva nd eRan d Corporationwerk tda nlaa tzic hbecijfere nda tvoo rd eaanwezighei dva nieder e zeesterva n1 0gra mleven dgewich tee nbedra gva n ƒ1,-moe tworde ngeïnvesteer d terwijlvoo rieder escho lva n25 0gra mƒ 25, -nodi gis .E rbestaa nalternatiev e aanwendingenva ndez efondse nvoo rnatuurbehee rdi eee nhoge rrendemen topleveren .

RandCorporation .1978 . Protectinga nestuar yfro mflood s- a polic yanalysi so f theOosterschelde .Vol .Ill ,assessmen to flong-ru necologica lbalances :a nadden ­ dum (calibrationdata) .Sant aMonica .7 4pp .

Ministerieva nVerkee re nWaterstaat . 1982. Persbulletinno .2647 . 15jun i1982 .

CommissieOosterschelde .1974 . Rapportuitgebrach tdoo rd eCommissi eOoster ­ schelde,ingestel dbi jbeschikkin gva nd eMiniste rva nVerkee r enWaterstaa tva n 15augustu s 1973.Staatsuitgeveri j 's-Gravenhage.19 8pp .

10. Al sui the tvoorwoor dva nhe tManua lo fphotographi c interpretationka nworde n afgeleidda tfoto-interpretati ezowe lee nwetenscha pal see nkuns ti sda nkunne n foto-interpréteursaanspraa kmake no pd econtraprestatieregelin gva nhe tMini ­ sterieva nCultuur ,Recreati ee nMaatschappelij kwerk .

AmericanSociet yo fPhotogrammetry .1960 . Manualo fphotographi cinterpretation , p.vii .

ProefschriftG.W.W .Elberse n

Mechanicalreplacemen tprocesse si nmobil esof tcalci chorizons ;thei rrol ei n soilan dlandscap egenesi s ina nare anea rMérida ,Spain . Wageningen,1 2novembe r 1982. Acknowledgments

Thesoil so fth eMérid aare ahav ebee nth esubjec to fstud yfo rman yyear sfo r studentsan dstaf fo fth eSoi lDepartmen to fth eITC .The yhav e gathered dataan den ­ gagedi nstimulatin gthoug h oftenheate d scientific discussions.Bot h theseactivi ­ tieshav eyielde dusefu lcontribution s whichI gratefull y acknowledge.Th eloya l co­ operationo fm ycolleague si nth edepartmen tmad ei tpossibl efo rm et otak eth etim e necessaryt ocarr you tthi s study. Tom ypromoto r Prof.Dr .Ir .P .Buring hI a mgreatl y indebtedfo rhi ssuppor t fromth ever yfirs tmomen t thatI discusse d thesubjec twit hhi man dfo rhi sguidanc e andconstructiv e criticism. ' I gratefullyacknowledg e thehel preceive d froma grea tman ypeopl e outsidean d insideIT Cdurin gth edifferen t stageso fth einvestigation : - Fromth estaf fo fth eInternationa l SoilMuseu mi nWageningen ,i nparticula rDrs . D. Creutzbergfo rth emicromorphologica ldescriptions ;Dr .Ir .L.P .va nReeuwij kfo r theinterpretatio no fth eanalyse s carriedou tb yMessrs .R .Smaa lan dJ.R.M .Huting ; Messrs.R.O .Bleyer tan dW .Bome rfo rphotographi c work. - Fromth eDepartmen to fRura l Surveyo fth eITC ,Dr .H.G.J . Huizingfo ragro - climatologicaldata . - Fromth eDepartmen to fGeolog yo fth eITC ,Drs .G.J .Kro lfo rgeohydrologica l data,Dr .Ir .N .Renger sfo radvic eo nsoi lmechanica l aspects,Dr .B.N .Koopman sfo r long termerosio nrate san dDrs .D .Kovac sfo rmathematica l aspects. - Fromth eDepartmen to fGeomorpholog yo fth eITC ,Dr .A.M.J .Meijerin kfo rsedimen t yieldestimates ,Dr .R.A .va nZuida mfo rextensiv e referenceso ncalci c horizonsan d Drs.N.H.W .Donke rfo rhel pwit h statisticalproblems . - Fromth eSoi lDepartmen to fth eIT Ci nparticula r Ir.E .Nieuwenhui s forhi scon ­ structivecriticis m fromth ebeginnin go fth einvestigatio nbot hi nth efiel dan di n theoffice ;Ir .E .Bergsm afo rdat ao nsoi l lossan dex-staf fmembe r Dr. Ir.M . Knibbefo rmateria lo nth eRiol aprofile . - Ofth evariou s servicedepartment so fth eITC ,th eLibrary ,th ePhotographi c Laboratoryan dth eDevelopmen tWorksho pan di nparticula rMr .A . 'tHar tfo rth epre ­ cisemanufactur eo fth econtainer sfo rstere o radiography - Ofth eDepartmen to fSoi lScienc ean dGeolog yo fth eL HWageningen ,Ir .H .Rogaa r forhi shel pi nth eexecutio no fth etim econsumin g radiographic experimentsan dfo r hisstimulatin g commentso nthei r interpretation - Ofth eNetherland s Soil Surrey Institute,Dr . Ir.J .Boum afo rhi sadvic eo nth e set-upo fth eexperimen tunde rcondition so funsaturate d flowan dDr .E.B.A . Bisdom formicromorphologica ldat ao n theRiol aprofile . - To theDepartmen t ofZootechnolog yo f theL HWageningen ,fo rputtin g atm y dis­ posalX-ra y equipment and laboratory facilities. A number ofperson shav ebee nwillin g torevie wpart s ofm ymanuscrip t and offer constructive criticism forwhic h Iexpres sm y gratitude: - Prof.Dr .A .Ruella no fth eEcol eNational eSupérieur eAgronomiqu e inRennes , France twicegrante dm e an interview todiscus shi scomment s on themechanica lre ­ placementprocess . - Prof.Dr . Ir.G.H .Bol to f theLaborator y ofSoil s and Fertilizers ofth e LHWage ­ ningen and Dr.Ir .F.F.R .Koenig s jointlyreviewe d theresult s ofm y experiments and offered theircomments . - Dr. Ir.N .va nBreeme no fth e Department ofSoi lScienc e and Geology of theL H Wageningen,wh oreviewe d thecalculation s of therat e of leaching ofcalciu m carbon­ ate. - Dr.W . Salomons of theHare nBranc h ofth eDelf tHydraulic s Laboratory,wh ore ­ viewed the interpretation ofth e stable isotope data of theRiol aprofile . - Dr.J . vanBrake 1o f theLaborator y forChemica lEngineerin g of theDelf t Uni­ versity ofTechnology ,wh o commented onth eresult s of the stereo radiographic ex­ periments and supplied data onth ewettin g ofpowders . - Dr. Ir.P.A.C .Raat s of the Institute ofSoi l Fertility inHaren ,wh o reviewed the theoretical background of theai renclosur ephenomen a incrystallin e lime. I am indebted toman ypeopl ewh ohelpe d invariou s aspects of thepublicatio n of thisstudy : - At ITCMr .E.A .va nLeeuwe n diligently drewth e figures;Mrs .A.R .Morga no f the Publications Department edited the textwit h greatunderstanding ;Mrs .H.R .Rettens - berger,Mrs .M .Völke r andMrs .A.M .va nde r Lindecarefull y typed and type-set the manuscript. - Of the staffo f PUDOCWageninge n inparticula rMr .R.J.P .Aalpol ,wh oresolve d the finaleditoria lpoint s andplanne d and supervised the lay-out. Agradezco alConsej o Superior de Investigaciones Cientificas deEspafi apo r haber mepermitid oy facilitado lainvestigació nefectuad a ene lterritori onacional . Iwan t toexpres sm y gratitude toth eDirectorat e of the ITCfo rputtin g atm y disposal timean d services of the Institute for this investigation. Finallya wor d ofthank s isdu e tom y familywh ohav epatientl y endured my physical andmenta l absence,especiall ydurin g thelas t stageso f thisprojec t and to theman y colleagues andfriend swh o havekep tm e goingb y enquiring frequently and insistently about thewell-bein g of the 'clayballs' . Curriculum vitae

Deauteu rwer dgebore no p1 oktobe r193 8t eEnschede ,alwaa rhi ji n195 6he t einddiplomaHBS- Bbehaald eaa nhe tGemeentelij k Lyceum.I ndatzelfd e jaarbego nhi j zijnstudi eaa nd eLandbouwhogeschoo lt eWageningen .O p2 2januar i196 4studeerd ehi j af (metlof )i nd erichtin gBodemkund ee nBemestingslee rme tal svakke nd eregional e bodemkunde (verzwaard),d ealgemen ebodemkund ee nbemestingslee re nd egeologie .Al s onderdeelva nhe tverzwaard ehoofdva kvolgd ehi ji n196 2ee ncursu si nd etoepassin g vanluchtfotointerpretati e inbodemkaarteringe naa nhe tInternationaa l Instituutvoo r Luchtkaarteringe nAardkund e (ITC)t eDelft . Onmiddelijkn azij nafstudere ntra dhi ji ndiens tva nd eVoedse le nLandbou wOr ­ ganisatieva nd eV Nal sassisten tdeskundig ee nwa swerkzaa mi nbodemkaarteringe ni n Zambia (1964-1965)e nPakista n (1965-1967).I n196 7 tradhi ji ndiens tva nhe t ITC alswetenschappelij kmedewerke re nwer ddoo rdi tinstituu tuitgezonde nnaa r Colombia waarhi jto t197 4werkzaa mwa sbi jhe tCentr o Interamericanod eFotointerpretació n (CIAF)t oBogota .Zij nwerkzaamhede n aldaarbesloege nonderwijs ,onderzoe ke nad ­ visering. Deauteu ri ssind s zijnterugkee ral swetenschappelij k hoofdmedewerker verbonden aand ebodemkundig eafdelin gva nhe tIT Ct eEnschede .Di tinstituu t steldehe msind s de aanvangva nzij npromotieonderzoek ,i naugustu s 1979,i nstaa tee ngedeelt eva nd e hembuite nzij nlestake nbeschikbar e tijd,hieraa nt ebesteden . Hiji sgehuwd ,vade rva ndri ekindere ne nwoonachti gt eEnschede . Contents

1 Aim and progress of the study 1

2 Review of calcic horizons 3 2.1 Typeso fcalci chorizon san dthei rnomenclatur e 3 2.2 Micromorphology g 2.2.1 Terminology 7 2.2.2 Processesan dgeneti c concepts 9 2.3 Typical horizon sequences 11 2.4 Occurrence accordingt oclimati c zones 12 2.5 Genesis 13 2.5.1 Geogeneticmode so fformatio n 15 2.5.2 Pedogeneticmode so fformatio n 16 2.5.2.1 Downwardmovemen t froma surfac e soiltha tcontain s limeand/o rre - 17 ceives limefro maeolia n additions 2.5.2.2 Upward transporto flim eb ysolution s ascending towardsth eaccumu - 18 lation zone 2.5.2.3 Lateral transporto flim e formedo rliberate d fromsourc ematerial s 19 located upslope fromth epoin to faccumulatio n 2.5.2.4 Liberationo rformatio no flim e froma paren tmateria li nth eweath - 19 ering zonedirectl yunderlyin gth ecalci c horizon 2.5.3 Conclusions 20 2.6 Influenceo fcalci c horizonso nlan dqualitie s 21

3 Description of the study area 24 3.1 Location 24 3.2 Climate 24 3.3 Geologyan dgeomorpholog y 30 3.4 Hydrology 34 3.5 Physiographyan dsoil s 35 3.6 Vegetation,lan dus ean dagricultur e 40

4 Observations 42 4.1 Sourceso finformatio n 42 4.2 Methodology 44 4.3 Characterisationo fth esoil s 46 4.3.1 Profiledescription s andanalytica ldat a 47 49 4.3.1.1 ProfileRiol a1 52 4.3.1.2 ProfileArroy o1 56 4.3.1.3 ProfileP 3equivalen tt oE1 8 (ISM) 62 4.3.2 Discussion 62 4.3.2.1 The 'highsoils ' 63 4.3.2.2 The 'lowsoils ' 65 4.4 Crosssectio n 68 4.5 Micromorphology 4.5.1 Description of the 'high soils' with petrocalcic horizons 68 68 4.5.1.1 Petrocalcic horizon 4.5.1.2 Thecalci chorizo nwith cla ynodule s including its lower tran­ 70 sition:th e 'stripedzone ' 4.5.1.3 Theunderlyin gre dMiocen ecla y 72 4.5.2 Descriptiono fth e 'lowsoils 'wit h colluvial influence 72 4.5.2.1 Thesurfac esoi l 72 73 4.5.2.2 TheB horizo no fth ecolluvia l zone togetherwit h its transition towardsth eunderlyin gresidua lhorizo n 4.5.2.3 The IIChorizo ni nloca lweatherin gproduct s ofMiocen e sediments 74 4.5.3 Discussion 74 4.5.3.1 The 'highsoils 'wit hpetrocalci c horizons 76 4.5.3.2 The 'lowsoils 'wit hcolluvia l influence 76 4.5.3.3 Comparisono f 'high'an d 'low'soil s 77 4.6 Additionaldetermination so nlim ean dcla y samples drawn 4.6.1 Thelim esample s ' 4.6.1.1 Results 77 4.6.1.2 Discussion 79 4.6.1.3 Correlation 82 4.6.2 Thecla ynodul esample s 8 4.6.2.1 Results 84 4.6.2.2 Discussion 85 4.6.2.3 Correlation 85 4.7 Stable isotoperatio sfo rth e limeo fRiol a1 86 4.8 Micropaleontology ofth e limeo fRiol a1 88 4.9 Conclusions 88

5 Experiments 90 5.1 Setu p'an dexecutio no fth eexperiment s and measurements 91 5.1.1 SeSett u UTp>o offth theexperiment e emprimonts c 91 5.1.2 Registrationo fth epositio no fth e objects 95 5.1.3 Reconstruction ofth epositio no fth eobject s 95 5.1.4 Executiono fth eexperiment s 100 5.2 Resultso fth eexperiment s 100 5.2.1 Experimentl a 100 5.2.2 ExperimentI I 103 5.2.3 Experiment Ilia 107 5.2.4 Experimentl b 109 5.2.5 ExperimentIIIb 1 109 5.2.6 Experiment IIIb2 110 5.3 Discussion m 5.3.1 Whatcause dth emovements ? 112 5.3.1.1 Gasenclosur e H2 5.3.1.2 Swellingo fcla ynodule s 112 5.3.1.3 Buoyancyo fobject simmerse d inmois tlim e 113 5.3.1.4 Compaction H3 5.3.2 Themechanis mo fth eai rentrapmen tproces s 113 5.3.3 Isth eai rentrapmen tproces scapabl eo fproducin ga sustaine dris e 116 ofobjects ? 5.3.4 Whatfactor sdetermin eth eprocesse stha t leadt one tris eo fth e 120 objects? 5.3.5 Areth eexperimenta lcondition sunde rwhic hth eris eoccurre d com- 122 parablewit hnatura lcondition si nth esoil ?

6 Behaviour of oalo-io horizons 125 6.1 Therol eo fth echemica ldissolutio no f limei nth emobilit yo f 126 calcichorizon s

6.1.1 Thedissolutio no fCaC0 3 129 6.1.2 Computationo fth eequivalen terosio nrate stha tca nb ematche d 129 6.1.3 Theaverag eCC Lpressur ei nth esoi l 131 6.1.4 Representativeerosio nrate s 132 6.1.5 Comparisono fth eequivalen terosio nrate stha tca nb ematche db y 136 thecalci chorizo nwit herosio nrate scommo nfo rth esurve yare a 6.1.6 Conclusion 137 6.2 Mobilityo fsof tcalci chorizon sresultin g fromth emechanica lre - 138 placementproces s 6.2.1 Riseo fcla ynodule san dothe robject s 138 6.2.2 Subterraneangilga îformatio n 143 6.2.3 Amechanica lreplacemen tproces sa sa combine dresul to fth erise - 148 andgilga îformation-processe s 6.3 Factorscontrollin gth emechanica lreplacemen tproces s 152 6.4 Reconstructiono fcalci chorizon swhic hhav ebee nlocall ydamage d 158 6.5 Interruptionand/o rchang eo fth ereplacemen tproces si nsof tcal - 162 cichorizon s 6.5.1 Encounterswit hslowl yweatherabl eparen tmaterial s 162 6.5.2 Surface erosionexceed sth etranspor t capacityo fth esof tcalci c 164 horizon 6.5.3 Changesi nhabitu so fth ecalci chorizo ndu et ochange si nmois - 165 tureregim e 6.5.4 Theproces so fhardenin g uponexposur e 166 6.6 Genesiso fcalci chorizon s 169 6.6.1 Geogenetic:Sedimentatio no flim ei na naqueou s environment 170 6.6.2 Pedogenetic:Replacemen to fmaterial sb ylim ei na chemica lwa y 171 ('épigénie') 6.6.3 Pedogenetic:Replacemen to fmaterial sb ylim edu et oforce s ere- 173 atedb yth ecrystallisatio no fcalcit e 6.6.4 Pedogenetic:Replacemen to fmaterial sb ylim etha tpenetrate s into 174 cracks formedb ychange si nvolum eupo nwettin gan ddryin g 6.6.5 Conclusions 175

7 Implications 176 7.1 Roleo fcalci chorizon si nlandscap edevelopmen t 176 7.2 Datingo fcalci chorizon s 178 7.3 Agriculture 180

7.4 Classification 181

Summary 1g 2

Samenvatting ^g g

190 Resimen

Resume 194

List of tables and figures 198

References 201 1 Aim and progress of the study

Inth eMérid a areai nS.W . Spainsof t calcichorizon so fremarkabl e purityan d thickness occura tdifferen t depthsi nth esoil .Whe nnea ro ra tth elan d surfaceth e upperpar to fthes ehorizon si shardene d forminga so-calle d petrocalcic horizon. Thesof t calcic horizonsan dth epetrocalci c horizonsar eth emai n subjecto fthi s study. Several investigations dealing directlyo rindirectl ywit h these horizons have beencarrie dou tb yth eSoil sDepartmen to fth eInternationa l Institute forAeria l Surveyan dEart h Sciences (ITC),o fwhic hth eautho ri sa staf fmember . The following facts established inthes e studiesar eimportant : - Thecalci c horizonsar eparticularl y well developedo nMiocen e clayswhic h contain calcareous layers.The yar eals o foundo nothe rmaterial s thatd ono tcontai nan y limean dd ono treleas e limei nlarg equantitie s uponweatherin g either.Thes ein ­ clude schist,arkos èan deve n granite. - Calcichorizon s often containnon-calcareou s claynodules ,saprolit e fragmentsan d stonesi npeculia r distribution patterns. - Thepur e calcic horizonsar egenerall y characterised byabrup tan dsmoot h upper boundariesan dabrup tan dirregula r lowerboundarie si nwhic h stressphenomen a occur. Inth estud yo fth ecalci c horizons,th eSoil sDepartmen to fth eIT Cconsidere d thesimilarit yo fthei r characteristics inth edifferen t landscapes.Thi s stimulated effortst oformulat ea theor yo nth egenesi so fthes ehorizon swhic hmigh t have val­ idityfo ral lth eoccurrences .Thi sle dinitiall yt oa stron g inclination towards geogeneticmode so forigi n (Jayaraman,1974 ;Roy ,1974 ;Jung , 1974;Rao , 1975).I n thecours eo fth einvestigations ,however ,a numbe ro fobservation swer emad e that didno ttall y with this typeo forigi nfo rth ehorizon si nthei rpresen t position: - Thelim e occursi nth efor mo fhorizon s parallelt oth esurfac eo fundulatin g landscapeswit ha clea r degradational history. - Mineralogical similarity between soilhorizon s overan dunde rth ecalci c horizon (Mahmood, 1979)fo rth eschis t landscape. Attempts toexplai nth eapparen tmobilit yo fthes ehorizon sb ya pedogeneti c processo fdissolutio nan drecrystallisatio n (unpublished notesb yKnibbe , 1974b) failedupo n testing toaccoun t forth epresenc eo fthes e horizonsnea rth esurfac eo f landscapeswit ha degradationa l history.Th efac t thatth ecalci chorizons ,i festa ­ blishedb ya pedogeneti c processa tall ,coul dremai n intacta to rnea rth esurfac e ofa soi lprofil e subjectt oerosion ,withou tbecomin g subjectt othi s erosiona s well,wa sno tsatisfactoril y explained. Ifa proces s couldb efound ,however ,b y meanso fwhic hth ecalci c horizons couldmigrat e downwardsunde rth eerodin g surface

1 witha velocit y sufficient toavoi d exposure,th epedogeneti c modelwoul d be tenable. Theide atha tth ecla ynodule scoul db e indicative of sucha proces s initiated the research forth epresen t study. Experimentswer ecarrie dou tt ostud y thebehaviou r ofthes e claynodule s and otherobject s embedded ina matri x ofsof t limeunde r alternating moist anddr y con­ ditions. Itturne d outtha ta nupwar dmovemen t of theseobject s through the soft cal­ cicmatri x canb emeasure dunde r certainconditions . Thecombinatio no fthi sfindin gwit h fielddat aregardin g swell and shrink of the soilmaterial s atth e lowerboundar y of thecalci c horizon in the weathering zone,le dt oth edescriptio no fa mechanica lpedogeneti c process.Thi sproces s is capable ofmovin g theentir e soft calcichorizo ndownwar dwit h aspee d sufficient to keeppac ewit hth eerosio no fth elan d surface. Theproces s turnedou t tob eusefu l inexplainin g anumbe ro f soil features in thesurve y area.Hardene d petrocalcic surfacehorizons ,locall y encountered, are ex­ plained asresultin g from failureo fth eproces s tomatc h the erosion rates.Analyse s ofth ereason s forsuc hfailur ehel p toformulat e thecondition s governing the activ­ ityo fth eprocess . Since thecalci chorizon s canaccumulat e limegraduall ywhil emovin g downward, thesearc h forthei rgenesi s canb enarrowe d toth e search for amuc h thinner 'in­ cipient softcalci chorizon' .Th e latterhorizo n isassume d tohav e formed fromse ­ condary carbonates thathav e crystallised inth esoi l andbee n transported mechan­ icallydownwar d towards theaverag e groundwater tablewher e theyhav e accumulated. Themechanica l replacementproces s insof tcalci chorizon s that lendsmobilit y tothes ehorizon smigh thav e important implications forfield s insoi l science,agri ­ culture,geomorpholog yan d archeology. 2 Review of calcic horizons

The literatureo ncalci chorizon si sextensiv e sincei tcontain s contributions fromman y disciplines,th emai n onesbein g geology,geomorpholog yan dsoi l science. Inth elas t decadevariou smonograph swhic hdea lwit h this subjecthav ebee npub ­ lished: Goudie (1973),FA O(1973 )an dReeve s (1976). Iti sno tth epurpos eo fthi s chaptert oduplicat e theseno rt omak ea complet e reviewo fal laspect so fcalcic , horizons,whic hwoul db eoutsid eth escop eo fthi sstud y anyway. Theai mher ei st opresen tbackgroun d informationneede d asa referenc e inth e discussiono fvariou s topicsi nth efollowin g chapters.Thu s certain subjects receive a gooddea lo fattentio nwhil e othersar ereferre dt oi na genera lwa yonly .Termin ­ ologyi sals o treated.

2.1 TYPES OFCALCI CHORIZON SAN DTHEI R NOMENCLATURE

The term 'calcichorizon 'a suse di nthi spublicatio ni sdefine d inSoi l Survey Staff (1975). Itsmos t important equivalents encountered inth eliteratur e are: 'cal- crete', 'croûte calcaire'an d'caliche ' (Goudie,1972ab) .Aristarai n (1971)trace d theorigi no fth elatte rter mespeciall y inN .an dS .America .H ei si nfavou ro fre ­ definingth eter m 'caliche',restrictin g itsus et opedogeneti c accumulations inth e soil.Accordin g toSoi lSurve y Staff (1975)calci chorizon sar ehorizon so faccumu ­ lationo fcalciu m carbonateo ro fcalcium -an dmagnesium-carbonate .Th eaccumulatio n mayb elocate di nth eC horizo no ri na variet yo fothe rhorizons .Minimu m require­ mentsfo rthicknes san dcarbonat e contentar ese taccordin gt oth enatur eo fth e otherminera l constituentso fth ehorizo nan daccordin gt oth echaracte ro fth eun ­ derlyingmaterial .Fo rhar d calcichorizon sth efollowin g fromSoi l Survey Staff (1975)applies : 'Thepetrocalci c horizoni sa continuous ,cemente do rindurate d cal­ cichorizon ,tha ti scemente db ycalciu m carbonateo ri nsom eplace sb ycalcium -an d somemagnesium-carbonate .Th epetrocalci c horizoni scontinuousl y cemented throughout thepedo nt oth edegre e thatdr yfragment sd ono tslak ei nwater. 'Specia ldept han d carbonate content requirementsar ese tfo rlamina rpetrocalci c horizons restingdi ­ rectlyo nbedrock .Fo rhorizon swit h carbonate accumulation thatd ono tfulfi lth e requirementso feithe r calcico rpetrocalci c horizons,th esuffi x 'ca'wil lb eused . Inth ehorizo nnomenclatur e forsoi ldescription ,th eonl ywa yt oindicat ea horizonwit h carbonate accumulationi sth esuffi x 'ca',eve nwhe n thesehorizon s have morphologies dominated entirelyb ythi smaterial .I norde rt oexpres s this,Gil ee t al. (1965)propos eth eter m 'Khorizon' .The yse tne wabsolut e limitsfo rK1 ,K 2 and K3horizon s toindicat e theirdegre eo fdevelopmen ta smeasure db y thepercentag e of theso-calle dK-fabri c (Kfro mth eGerma n 'Kalk')- Theobservatio n that amer e suffix isinsufficien t toexpres ssuc ha distinc tmorpholog y isvalid . Iti sfelt ,however , thata slon gtha t therei sn o concensus onth eprocesse s thatcaus e theformatio n of thisfabric ,soi lscienc ei sno t innee do fmor earbitrar yboundarie sbeyon d those already setb ySoi lSurve yStaf f (1975).A s suchth eK horizo nterminolog ywil l not beuse d inthi spublication .Se eals oth ecriticis m ofBa l (1975b)o f thegeneti c im­ plicationso fthi sterm . Inthi stex tth enomenclatur e of theSoi lSurve yManua l (SoilSurve yStaff , 1951)an do fth eGuideline s forSoi lDescriptio n (FAO,1967 )whic hha sbee nderive d fromthis ,ar eused .Currentl ydraft sar ecirculatin g ofth e 'NationalSoil sHand ­ book'whic hwil l eventually replaceth eSoi lSurve yManua l (SoilSurve yStaff , 1951). Inthi sne whandboo k theaccumulatio n ofcarbonate swil lb e indicatedb y 'k',cemen ­ tationb y 'm'an da petrocalci chorizo nb y 'km'.Thi s terminologywa s firstintro ­ duced inth elegen do fth eSoi lMa po fth eWorl dVol .I (FAO-UNESCO,1974 )an dwa s lateradapte d inth esecon d revisededitio no fth e Guidelines forSoi lDescription . Inth eliteratur e oncalci chorizon s andca-horizons ,numerou s attempts are found tosubdivid eth ephenomen a coveredb ythes eterms .Fo ra revie wse e e.g. Mathieu (1974)an dZuida m (1976).Th ecriteri abelo war euse d forsubdivision . a. Measurable characteristics ofth ehorizon sproper ,i.e . (macro)morphology,car ­ bonateconten tan dhardness :Brow n (1956),Duran d (1959),Gil e (1961),Wilber t (1962),Ruella n (1970),Soi lSurve yStaf f (1975),Netterber g (1980). b. Micromorphology: Blokhuis et al. (1968),Brewe r (1972),Jame s (1972), Siesser (1973),Ba l (1975ab). c. Likea ,togethe rwit hoccurrenc e inth e landscape:Duma s (1969),Lattma n (1973). d. Like a,togethe rwit hag eand/o rdegre e ofdevelopment :Gil e et al. (1965), Gile etal . (1966),Netterber g (1969). e. Like a,togethe rwit hpresume d genesis:Duma s (1969). Ofal lthes esubdivision s thoseo ftyp ea ar epreferre d over c,d , ande .Th e reasonfo rthi spreferenc e liesi nth efac ttha tther ei sn oconcensu s ofopinio n about thegenesi so fth edifferen t types.A s suchag e anddegre eo fdevelopmen t are arbitraryvalues .Positio n inth elandscap ebecome s insignificant ifn o reliable genetic conclusions canb edraw nfro m it.Micromorpholog y isa usefu l tool forchar ­ acterisation,i fsuperimpose dupo nth etype sdistinguishe d according toa . As agoo dan dcomplet eexampl eth eclassificatio no fRuella n (1970)i s given which takesint oaccoun tth eobservation s ofsevera l Frencheart hscientist swh o worked inN .Africa .Ruellan' stranslatio no fhi sow nclassificatio n inFA O (1973)i s given inTabl e 1.Th e following typeso fthi s tablear eo fparticula r interest for thisstud yan dwil lb edescribe d inmor edetai l: 'Concentrationsdiscontinues ' (2)ar ethos eaccumulation s inwhic h thevisibl e concentrationso flim ear eseparate db y zones oflowe r limecontent .O f these the 'amas friables' (2b)hav e thefollowin g characteristics:Thes e arespot s of limeo f Table 1. Main typeso flim eaccumulation saccordin gt oRuella nin :FA O(1973) . The termswritte ni nitalic srefe rt oform so fparticula rinteres tfo rth esur ­ vey area.

1. Distributiondiffus e 1. Diffusedistributio n

2. Concentrationsdiscontinue s 2. Discontinuousconcentration s

a. Pseudo-myceliums a. Pseudo-myceliums b. Amas friables b. Friable accumulations c. Nodules c. Nodules

3. Concentrationscontinue s 3. Continuousconcentration s

a. Encroûtementsnon-feuilleté s a. Non-laminatedencrustation s a1 . Encroûtements massifs al. Massive encrustations al. Encroûtementsnodulaire s a2. Nodularencrustation s b. Encroûtementsfeuilleté s b. Laminatedencrustation s bl. Croûtes bl. Crusts b2. Dalles compactes bl. Compact slabs b3. Encroûtementslamellaire s b3. Platyencrustation s (pelliculesrubanées ) (ribbonedpellicule )

variable shapean dsiz ean do fa whitis hcolour .Thei r limitsma yb eclea ro rdif ­ fuse.The yar eseparate db yzone so flowe rlim e content.Thi s formi sequivalen tt o accumulationso fsof tpowder y lime accordingt oSoi lSurve yStaf f (1975)an dzone s whichsho wthes ephenomen agenerall yqualif yfo rcalci chorizons. Th ewor d 'lime'a s usedi nthi stex tsignifie s calcium carbonatewit ho rwithou tmagnesiu m carbonatead ­ mixed;a meanin g also impliedi nth eSoi lTaxonom ySyste m (SoilSurve yStaff , 1975). Thisi scontrar yt oth esignificanc e attributedt oi ti nth eGlossar yo fGeolog y (AmericanGeologica l Institute,1974) ,whic hattribute s this termt oCa Oonly . Whenever limei nan yfor mi saccumulate dt osuc ha nexten t thatth eorigina l soilcolou ri sobliterate dth eter m 'encroûtement'i sapplied .Lim e contentmostl y exceeds 601b yweigh ti nthes ecases .Th efollowin g formsar eimportan tfo rth epre ­ sentstudy : The 'encroûtements massifs' (3a1).Accordin gt oRuella n (1970)thes ehav ea chalkyo rtuffaceou snature .Thei r structurei sgenerall ymassive ,bu toccasionall y polyhedric.Thei rhardnes si svariabl ebu tgenerall y theyar esoft .The yhav ea homo ­ geneous lightcolour .Accordin gt oSoi lSurve yStaf f (1975)thes ear ecalci chor ­ izons. The 'croûtes' (3b1)hav eth efollowin g characteristics:Accordin gt oRuella n (1970)the ysho wsuperpositio no fhar dbu tno tpetrifie d platyelement swhic hvar yi n thickness froma fe wmillimetre st oa fe wcentimetres .Th elim econten to fthes ehor ­ izonsexceed s 701b yweight .The yhav ea whitis h colour.Th eplat yelement sar eno t continuous,the y interweave (anastomose).Th einterna l structureo fth eelement si s Table2 . Themai ntype so fcalci chorizon so fth esurve yare aaccordin gt oAmerica n (Soil SurveyStaff , 1975)an d French (Ruellan,1970 )terminology .

.discontinuous 'amas friables' •(soft)calci chorizons ' "continuous 'encroûtements massifs ' calcichorizon s laminated 'croûtes ' 'petrocalcichorizon s non-laminated 'dalles compactes '

similart otha to fth e'encroûtement smassifs' .Accordin gt oSoi l SurveyStaf f (1975) theyar elaminate dpetrocalci chorizons . Accordingt oRuella n (1970)th e 'dalles compactes' (3b2)consis to fon eo rsev ­ erallim eplate swhich ar eextremel yhard .The yca nb equalifie da spetrified .The y arei ngenera lcontinuou san dno tverticall y interrupted liketh econstituent so fth e other 'croûtes'.Thei r internal structurei smassiv ean dno tfinel y laminated. Often finecavitie swhich looklik eshrin kcrack sar efound .Th ecolou ri sgreyis han dth e thicknesso fth eindividua lplate svarie s froma fe wc mt oabou t2 0cm .Th elim econ ­ tento fthi styp eo fhorizo ni sgenerall yove r 70%b yweight .I nth eterminolog yo f SoilSurve yStaf f (1975)thes ear epetrocalci chorizons . Forth epresen tstud yth eSoi lSurve y Staff (1975)nomenclatur ewil lb eused , modifyingth eterm sb yadjective swher egreate rdetai li srequired .I ti sno tth e purposeo fthi spublicatio nt opropos e thisterminolog ya sa ne wsyste mo ra sa nim ­ provemento fa nexistin g system.Th eequivalen t termsar egive ni nschemati c formi n Table2 .

2.2 MICROMORPHOLOGY

Themicromorphologica l literatureo ncalci chorizon sca nb eseparate di ntw o disciplines:micropedolog yan dcarbonat epetrography .Thi si sa reflectio no fth ena ­ tureo fth ephenomen ai ncalci chorizons :field so fstud yo nth esubjec tma yspa n bothdisciplines . Pedologists studythes e formationsi norde rt odeciphe rthei rgenesi san dt o characterisecertai npropertie s importantfo ragricultura luse .Petrographer s study bothexpose dan dburie d calcichorizons .Thei rmai nai mi st odefin ecriteri ab y whichcalci chorizon s indicativeo fsub-aeria l diagenesisca nb edistinguishe d from otherformation swit hwhic h theyca nb econfused . Suchhorizon sca nserv ea smarker s instratigraphi ecolumns .Th emai nsourc eo fconfusio nseem st oli ei nthei rsimilar ­ ityt oso-calle dalga lmarin e stromatolites,e.g .Muite r& Hoffmeiste r (1968),Nagte - gaal (1969),Jame s (1972). Theforegoin g impliestha tmicropedolog yoccupie s itselfmor ewit hth eaforemen ­ tioned diffusedistribution san ddiscontinuou s concentrations (types1 an d2ab co f Table1 )whil ecarbonat epetrolog ygive smor eemphasi st oth econtinuou sconcentra ­ tions (3abo fTabl e 1).

2.2.1 Terminology

Themai nautho ri nth edescriptio no fmicropedologica lphenomen ai sBrewe r (1976)wh odevise da syste mwhic hi swidel yused .H edistinguishe s various levelso f organisationi nth esoil .Hi ssyste mi sstrongl ymorphologic ;h eintroduce s criteria sucha schemica lcompositio no fth econstituent sonl ya tth elowes t levelso fhi s classification.Lim ea sa materia ldoe sno treceiv especia ltreatmen ti nhi ssystem . Ifth eso-calle dplasm ai salmos tcompletel ymad eu po fcalcit ecrystals ,it s fabrici scalle db yBrewe ra (fine or coarse) crystic fabric. If,however ,larg e cal­ citecrystal s occurembedde di nnon-calciti cplasma ,the yar etreate da sso-calle d pedological featuresan dcalle d intercalary crystals. Themai noccurrence so flim ei n thesoi lar eclassifie da spedologica l features (whichmay exhibi t crysticplasmi c fabrics).Th emai none si nwhic h limeplay sa rol eare :glaebule s (e.g.lim econ ­ cretions);crystallari a (e.g.intercalar ycrystals) ;cutan s (e.g.calcitans) .Fo rde ­ finitionso fthes e termsse eBrewe r (1976). Severalauthor shav esuggeste d improvementsi nthi sterminolog ywhic hmak ei t possiblet oaccoun tbette rfo rth edifferen t formswhic har eintergrade sbetwee n crystic fabricsan dintercalar y crystals.Ba l(1975a) ,followin gu pa suggestio nb y Mulders,introduce sa so-calle d calcic plasmic fabric toaccoun tfo rcase swher emor e or lessisodiametri ccalciu mcarbonat ecrystal sar eno tclos eenoug h togethert ofor m a crystic fabricbu td oconstitut ea nimportan tpar to fth etota lmass .Othe rauthor s likeFedorof f (1975)rejec tth eus eo fBrewer' ssyste mfo rth edescriptio no flim e concentrationsi nth esoi laltogethe ran dpropos ea separat esyste mfo rcarbonate s exclusively. Carbonatepetrologist s generallywor kaccordin gt oa differen t system.The yde ­ finea numbe ro fbasi celements ,b ymean so fwhic hthe ydefin ea numbe ro fmor ecom ­ plexstructures .Fo ra revie wsee ,fo rexample ,Goudi e (1975).Th ethre emai nbasi c elementsare :

(1) Micrite. Veryfin ecalciu mcarbonat ecrystal srangin gi nsiz efro m1- 4ym .Thi s sizerang ei sgive nb yGoudi e (1975)wh oquote s several authors.Accordin gt oBat - hurst (1971)th eter minclude sbot hinorgani can dbiochemica lprecipitates . Clotted micrite isa fabri cmad eu po fdiscret eaggregate dbodie s (peloids)compose do fmi ­ crite (Bathurst, 1971).Th eFrenc hequivalen to fthi si s 'pâte microcrystalline grumeleuse' whichaccordin gt oDuran d (1959)make su pth efabri co fman yhar dan d softcalci chorizon si nAlgeria . (2) Spar. Amosai co fcrystal s largertha nthos e ofmicrit e (Bathurst, 1971). For neomorphiccrystal sh edistinguishe s microspar mainlyi nth e sizeclas s 4-10 vm and pseudospar mainlyi nth esiz eclas s 10-50um .Othe rterm s frequently encounteredi n theliteratur erefe rt ospecifi c arrangementso fsilt-size d crystals: drusy spar im­ pliesspa r lininga cavity ,whil e flowerspar is applied torelativel y elongated (bladed)crystal stha toccu ri nbunche sa tregula rintervals .

(S) Needle fibres. Thinelongate d calcite crystalswit ha diamete ro fu pt oS p m whichhav emainl ygrow nalon gon eaxis ,rangin gi nsiz efro m 10-300y mar ereporte d byJame s (1972)fo rcalcareou s crusts.H edistinguishe s furthermorebetwee n long ran­ domly orientated needle fibres whichma yfor m felt-likemat s and theshorte r tangen- tially orientated needle fibres whichofte ncoa tparticles .

Folk (1965)develope da cod e systemfo rmethodica ldescriptio no fdiageneti c calciteb ymean so ffour-componen t symbolsi nwhic hth efollowin g characteristics are represented:mod eo fformation ,gros s shapeo fth ecrystals ,crysta l size andrela ­ tiono fth ecrystal st o their surrounding (foundation).Hi s shape classesare : equant, forcalcit ecrystal s thathav e length/widthratio so fles s than 1|:1; bladed, idemfo rratio sbetwee n1^: 1an d6:1 ; fibrous, idem forratio s greater than 6:1. Ofth emor ecomple xstructure s that canb edefine db ymean so fth eaforemention ­ edbasi celements ,th etw odescribe dbelo war eimportan t incalci chorizons .

(1) Laminar structures. These structures arecommo nespeciall y inpetrocalci c hor­ izons.Th eto pi softe ncrowne db ya plat yencrustatio nwhic hMilte r& Hoffmeiste r (1968)classif yo nth ebasi so fmicromorphology .Fo rcalci chorizon si nFlorida ,the y distinguishthre etypes .Th ecrust swhic hoccu ri nth euppe rpar to fcalci chorizons , decreasing innumbe ran dhardnes swit hdepth ,hav e laminarstructure swhic h arede ­ scribedb yJame s (1972).The yar emad eu po fnumerou s alternating light and dark laminaewhic hconsis talternatingl y ofmicrit e andneedl e fibres orientedparalle lt o thelayering .Band so fdrus yspar ,densel ypacke d concentric particles,peloids , flowersparan dclea rspa rma yals ob e included.Jame s observes thatthi ncrust sma y mergewit hconcentri cparticl ecoatings .

(2) Concentric structures. These structures aremainl y foundi nth ehardene d parts ofth ecalci chorizons .The yhav ebee nextensivel y studied since theyca nb e easily confusedwit hmarin eoöid sforme d inturbulen twaters .Th econcentri c structures con­ sisto fsevera lband s ofmicrit eo ro fmicrit e and tangentiallyoriente d needle fibres.Thei rnucleu sma yb ea non-calcareou s grain,a fragmen to fa fossil ,plai n micrite,o rcombination so fthese .Apar t fromwha ti sstate di nth eforegoin gpara ­ graphabou tth econtinuit yo flamina r andconcentri c features,severa l authors offer additionalproo fo fth eformatio ni nth e soilo fthes e structures including Bretz& Horberg,1949 ;James ,1972 ;Siesser ,1973 ;an dHa y& Wiggins ,1980 .Thi s subjecti s furtherdiscusse di nSectio n4.5.3.1 .Thes estructure s arename d diagenetic oöids and intraclastsb ySiesse r (1973)an d spherulitesb yNagtegaa l (1969).Thi s latter term doesno thav eth esam esignificanc e asBrewe r (1964)attache st oit .H edescribe s spherulitesa scrystallari a inwhic h acicularcrystal s radiate froma centre .

Features commonlydescribe d incalci chorizon so fal ltype sar e so-called float­ ing grains ofnon-calciti cmateria l (clasts),e.g . Dapples (1971),Gardne r (1972) and Goudie (197S).Man yo fthes e areofte ncorrode d asmentione db yDegen s& Rutt e (1960) andNagtegaa l (1969).Mor edetail s aboutthi sproces s aregive ni nSectio n2.2. 2 and Section6.6.2 . Gilee tal . (196S)conside r thephenomeno no ffloatin g grains,whic h implies that limeform sa continuou sphase ,th emai n argument for therecognitio no f theK-fabric . Pressure exertedb yth egrowt ho fth ecalcit e crystalsi sth emai npro ­ cessmentione d as thecaus eo fthi s isolationo fskeleto ngrains .Thi si sdiscusse d inmor e detaili nSectio n6.6.3 .

2.2.2 Processes and genetic concepts

The following processes areeviden t from themicromorpholog yo fcalci chorizons :

(1) Crystallisation. This implies the formationo fcalcit ecrystal s froma solution . Several factors influence shape and sizeo fth eresultan tcrystals . - Speedo fformatio n (Bathurst, 1971).Th e slowerth e formation,th e larger the crystals formed.Ba l(1975b )observe si nthi s respecttha t large crystals form slowly intubula rvoid si nsoil swit ha stabl epH ,whil e finecrystal s are formed rapidlyi n soilswit h largep Hdifference swithi nth eprofile ,whe nth esolutio n percolating from theaci duppe rpar t towards thealkalin e lowerpar tbecome s supersaturated. - Presenceo ffin eparticle s that acta snucleatio npoint si sa facto rmentione db y Wieder& Yaalo n (1974).Fo rexample ,th emor e clayparticle s there are,th emor emi - critewil lb eformed . Larger crystalswil l formonl yi fsilicat e clayparticle sar e absent. - Degreeo fsupersaturâtio no fth e solution influencesno tonl y the sizeo fth e crystals becauseo fit s influenceo nth e speedo fformation ,bu t accordingt oBuckle y (1951)als o thefor mo fth ecrystals .Elongate dneedl e fibres,als oknow na s 'whisker crystals',ar e formed fromhighl ysupersaturate d solutions only.Presenc eo fcertai n ionsma y alsoenhanc e the elongated character. Aswel la scrystallisatio no fcalcit e from solutions entering theprofile , transformationo fcalcit e crystals fromon e typet oanothe r occurs.A so-calle d ag­ grading formi sth erecrystallisatio n ofmicrit e tomicrospar .Degradin g formsar e those inwhic ha sparr y fabrici stransforme d intomicrite .Jame s (1972)call sth e latter process 'micritisation'.

(2) Brecciation. Brecciationphenomen a areobservabl ei ncalci chorizon s onmacro- , meso- andmicroscale .The y occur inparen tmaterials ,non-calciti c inclusionsan d informations inth ehorizo n (Bretz& Horberg ,1949 ;Blan k& Tynes ,1965 ;Dapples , 1971;an dJames ,1972) .Jame sapplie sth eter m 'exploded jigsawpuzzle 't o character­ iseth emicrostructure spresen ti ncalci chorizons .Som eo fth ebrecciate d structures ona macroscal ema yb edu et omechanica lbrea ku po fexpose dpetrocalci chorizon s followedb yrecementation .Th emai ncausa lfacto ri nthi sprocess ,however ,see mt o beforce srelate dt oth ecrystallisation .Se efurthe rSectio n 6.6.3.

(3) Dissolution of oaloitia components. Dissolutiono fcalciti ccomponent si sevi ­ dento nth esurfac eo fman yexpose d calcichorizons .Kars tphenomen asuc ha spipe s arereported ,e.g .b yBret z& Horber g (1949)an dGil ee tal . (1966)fo rNe wMexico , USAan db yGoudi e (1975)fo rsevera lregions .Dissolutio nwel lwithi nth ehorizon s mayals ooccur ;thi si s discussedi nSectio n6.5.4 .

(4) Dissolution of non-calcitic components. Corrosiono fminera lgrain sa smentione d inth epreviou ssectio ni nrelatio nt oth e floatinggrain s ispresume d tob edu et o thehig hp Hwhic hca nexis tlocall yan dtemporaril yi ncalci chorizon s (Muiter& Hoffmeister,1968 ;Reeves ,1970) . Substitutiono fquart zb ylim e ismentione db y Degens& Rutt e (1960).Watt s (1980)mention s theinvers esolubilit yrelationshi pbe ­ tweensilic aan dcalcit ea thig hp Hwhic hfavour scalcit eprecipitatio nan d silica solution.Naho n& Ruella n (1975)an dMillo te tal . (1977)describ e isovolumetricsub ­ stitutiono fa variet yo fmaterial sb ylime ,whic hthe ycal l 'épigénie'.Mor edetail s aregive ni nSectio n6.6.2 .Reprecipitate dproduct so fth esolutio no fsilicate si n thefor mo fopa lan dchalcedon yar ecommonl yfoun d inwel ldevelope dpetrocalci chor ­ izons;fo rexample ,Reeve s (1970)mention sthei rpresenc ei n'matur ecaliche' .

(5) Biological processes. Knox (1977),Kahl e (1977)an dHarri se tal . (1979)de ­ scribeborin go fcalci chorizon sb yth eactio no ffungi ,blu egree nalga eo r root- hairso fhighe rplants .Numerou sramifyin g tubesar edescribe db yJame s (1972)a s evidenceo fborin gb yblu egree nalga ei nth euppe rpar t ofpetrocalci chorizon s (Section4.5.3.1) .Tru e (1975)stresse sth erol eo fmicro-organism si n'biocorrosion ' and 'biosynthesis'o fcalcit ei ncalci chorizons .Adolph e (1975)claim stha tcertai n typeso flim econcretion si nth esoi lar e formedb yth eactio no fmicro-organisms . Recognitiono fth eorigina lo rprimar ymineral so fa paren tmateria l ando fth e secondaryproduct s intowhic hthe yar etransforme di sa nimportan tfiel do fstud yi n micropedology.Calcit ei sconsidere d tob ea ver yunstabl eminera lbot hi nprimar y and'i nsecondar yform .Distinctio nbetwee nprimar y andsecondar ycalcit eo nth ebasi s ofth eobservatio no fsingl eisolate dcrystal si sonl yrarel ypossible .Fo rexample , Sehgal& Stoop s (1972)distinguis hprimar ycalcit egrain si na naeolia nsedimen to n thebasi so froundin go fth ecrysta lgrains . Conclusionso nth egenesi so fcalcit ecrystal s aremostl ydraw no nth ebasi so f theiroccurrenc ei npedologica lfeature swhic hma yeithe rb eforme di nsit uo rin ­ herited fromparen trock ,paren tmateria lo rfro mothe rsoils .Wiede r& Yaalo n (1974)

10 distinguish threetype s ofcarbonat enodules : Orthia nodules areforme d insitu ,the y have skeletongrain san d fabricsimila rt oth e surrounding soilmatri x and theyhav e a gradual transitiontoward s it. Disorthia nodules havebee nforme d inth esoi lbu t havebee n subjected tosom epedoturbation .The yhav eskeleto ngrain s anda fabri cre ­ sembling thesurroundin gmatri xbu t theyhav e sharpboundaries . Allothio nodules are thosetha thav ebee ntransporte d towardsth esit ethe ypresentl yoccup y inth e soil. Theyhav e amatri xwhic hdiffer s incompositio n fromtha to f thesoi l inwhic hthe y are incorporated.Blokhui se t al. (1968)describe dvariou s formso fpedogeneti ccar ­ bonate inVertisol s ofth eSudan .The yconclud e thati ngenera lsof tpowder y types sucha sdiffus enodule s andchanne lneocalcitan s arei nsit uformation swhil e the varioushar d anddiscret e typesd ono toccup yth epositio n inwhic hthe ywer e formed. Many concretions showfeature s likemangan swhic h theyhav e acquired inth e zone be­ lowth epresen tchurnin g activity.Thi schurnin gproces s issuppose d tohav ebrough t themupwar d towards thepositio nwhic hthe ypresentl y occupy. Someauthor sclai mtha tth eprogressio ni nth edevelopmen t ofcalci chorizon s iseviden t ina specifi csuccessio n ofform so fcarbonat e (Gilee t al., 1965;Brewer , 1972;Sehga l &Stoops , 1972).The yclai m thatth e general tendency isa n increase of crystal sizewit hage .Wiede r &Yaalo n (1974)d ono tagre ewit h this. Inthei r opinioncrysta lsiz ei smainl ydependen to nth epresenc eo rabsenc eo ffin esilicat e clayparticle s thatac ta snucleatio npoints ,a sexplaine d inth ebeginnin g of this section.

2.3 TYPICAL HORIZON SEQUENCES

Ifal l fourmai n typeso fcalci chorizon so fTabl e 2occu rtogethe r ina soi l profile,thei rnorma l sequence isth efollowing : 1. thindiscontinuou s soilcover ;A orA , 2. non-laminated petrocalcichorizon , 3. laminatedpetrocalci chorizon , 4. continuous softcalci chorizon , 5. discontinuous softcalci chorizon , 6. Chorizo no rC horizon. Cd Horizonsequence swhic h coveronl ypar to fthi snorma l onear ecommonl y found to occur,excep tfo rth efollowing :Th eA orA horizonwhic h isthi nan d discontinuous whenoverlyin g apetrocalci chorizon ,i snormall y thick andcontinuou swhe noverlyin g a softcalci chorizon .Petrocalci c horizonsno t overlying softcalci chorizon snor ­ mallyres t onconsolidate dbedroc k (R)instea d ofo na C horizon .Frequentl yoccurs , e.g.

11 1 1 1 1 1 3 4 5 2 2 4 5 6 3 R S 6 R 6

This lastcas ei sthough tt ob erar e (Ruellan, 1970). Thehorizo ntransition sar egoverne db yrule s (Ruellan, 1970),whic hca nb esum ­ mariseda sfollows : 'Wienin a profile the lime content increases with depth, the boundaries are abrupt or clear. Wien in a profile the lime content decreases with depth, the boundaries are normally gradual or diffuse. 'Th eriche ri nlim eth enex t horizon,th emor e abruptth etransition .Accordin gt oth elas trule ,th ediscontinu ­ oussof tcalci chorizo n (5)ma yhav ea gradua luppe rboundary ,i nth esequenc e 1/5/6. Inth ecas eo fpolygeneti cprofile swhic h showtw oo rmor ecycle so flim eaccumula ­ tionsuperimposed ,thes erule sd ono tappl yi nth econtac t zoneo ftw ocalci chor ­ izons.Th etopograph yo fth ehorizo nboundarie si smostl ysmoot hwit hth eexceptio n ofth etransitio no fth econtinuou s towardsth ediscontinuou s softcalci chorizon . Herew efin dirregula rhorizo nboundarie s (Wilbert,1962 ;Dumas ,1969) .I nth epro ­ filedescription so fChapte r4 thi stransitio n zonei sreferre dt oa sth e'stripe d zone'.

2.4 OCCURRENCEACCORDIN GT OCLIMATI C ZONES

Accordingt oReeve s (1970),wel ldevelope d calcichorizon sd ono tfor mi nari d ori nhumi d climates.I nari d climatesrainfal li sapparentl y insufficientt oallo w forsubstantia laccumulation so flime ,whil ei nhumi dclimate sth eleachin gi scon ­ sideredt ob eto ostrong .Blat te tal . (1972)stat e thati nth eUS A'caliche 'occur s westo fth elin eo f63 5m myearl yprecipitatio ni narea swher eth eaverag e yearly temperaturei shighe rtha n4. 4°C .Summarisin gi tma yb estate d thatcalci c horizons occurwher e leachingi ssufficien tt owas h limeinto ,bu tno tou tof ,th esoil . Apart fromprecipitation ,al lothe rfactor sdeterminin gth edrainag e condition ofth esoi lpla ya role .Lim econten to fth emateria lo nwhic hth ecalci chorizo ni s developedi sanothe r influencing factor:Strongl y calcareousmaterial sma ycarr y cal­ cichorizon seve ni nrathe rhumi d climates.Mediterranea nclimates ,wit hmos to fth e precipitationconcentrate di nth ecoo lseason ,see mparticularl y likelyt odevelo p calcichorizon s evenwher eth erainfal li srathe rlow . Sincepetrocalci chorizon sar ever yresistan tt oerosion ,relict so ffossi l cal­ cichorizon sca nmaintai nthemselve sfo rlon gperiod s afterclimati c changeshav eoc ­ curred.Thi sapplie sparticularl yt omajo rdeser tarea swhic har eno wto oari dfo r theformatio no fcalci chorizon sbu twhic hhav eexperience d moisterclimate s during thePleistocen e (Ruellan,1968 ;Reeves ,1970) . Theaforementione d factorsmak ei tdifficul tt oestablis ha ver y specific cli-

12 matic zone inwhic h calcichorizon sd ooccur . Ingenera l itca nb e stated that the zone inwhic h they are encountered varies from aridt osub-humid .Th emajo r zone in which they still seem tob e actively formed issemi-ari d (Dumas,1969 ;Fran z &Franz , 1969). Ruellan (1968)state s that calcichorizon shav e atendenc y tobecom e thinner andclose r to the surface ifon emove s fromarea swit h aprecipitatio n range of500 - 700mm/y r towards drier zones.I fth e rainfall diminishest o 200mm/y r they tend to disappear altogether.Thic k softcalci chorizon s aremor e common inth emoiste rcli ­ matic range,whil e the occurrence ofpetrocalci c horizons increases progressively to­ wards thedrie r areas.Tropica l climateswit hpoorl y distributed precipitationu p to 1500mm/y r showcalci chorizon s onlimeston e (Florida:Muite r &Hoffmeister ,1968 ; Barbados:James , 1972). Discontinuous softcalci chorizon s aredescribe d as forming under 1400mm/y rprecipitatio n oncalcareou smetamorphi crock s inSenega lb y Leprun & Blot (1978). Fordetail s onth egeographi c distribution ofcalci chorizon s seeGoudi e (1973), FAO (1973)an dReeve s (1976).

2.5 GENESIS

Calcium is the seventhmos t abundant element ofth e earth'scrus t andhydro ­ sphere (Delwiche, 1975).A s suchCaCO ,i sa constituen t ofman yrocks . Inman y other cases inwhic h it isno t aconstituent ,calciu m carbonate isforme d inth eweatherin g zoneupo n liberation ofCa-ion s frommineral s sucha sanorthite ,titanit ean daugite . It isals o found asa result ofth ereductio no fgypsu mb ybacteria l action.Notwith ­ standing these facts,th erelatio nbetwee ncalci chorizon s and thematerial s upon which orwithi nwhic h they areencountered ,i sno talway s properly described by the term 'parentmaterial 'a swil lb e illustrated in thefollowin gparagraphs .

Many authors,e.g .Mathie u (1975)an dVaudou r &Clauzo n (1976)pu t thequestion : 'Arecalci c horizons deposits or soilhorizons? 'Eithe r they ask thisquestio n in thecontex t of calcichorizon s ingeneral ,o r forcalci chorizon s of a specificre ­ giono r location.Th e facttha t theyd ono tagre e onth emai nproces s couldmea n that indeed.severalbasicall y differentprocesse s are tob ehel dresponsibl e for their formation,eac hunde r its ownspecifi ccondition . Itseem shighl y improbable,how ­ ever,tha t formationswhic h ares owidesprea d ina certainclimati c zone,coverin g sucha wid e range ofmaterial s and landscapes and showing soman y striking similar­ ities,woul d notgenerall yhav e onemai nproces s inthei r genesis incommon . It is certain that several differentprocesse shav e affected thecalci chorizon s during their genesis and that several ofthe mma ystil lb e activeconcurrentl y at thistime . Itmus tb e stressed,however ,tha tmos t ofthes eprocesse s aremer emodifier s of the calcic horizon andno tcausal . It isno tuncommo n tofin d inth e literature caseswher e twoentirel y different modes oforigi nar epostulate d fortw odifferen t typeso fcalci chorizon s overlying

13 eachothe r ina sequenc e that isrepresentativ e ofa large area (e.g.Durand , 1959 andRayna l &Gauche rquote db yMathieu , 1975). Itseem smor e logical topostulat e in such instances acommo norigi nfo rbot h andt ohol d amodifyin g process responsible forthei r laterdifferentiation . Stable isotope analyses haveprovide d evidence link­ ingpetrocalci c horizonswit h theunderlyin g soft calcichorizon s insevera l cases (Salomonse tal. , 1978). Inth e literature there is little concensus about themai nprocess .Fo r a review ofth edifferen tmode so forigi npostulate d seee.g . Durand (1959),Mathie u (1975) andZuida m (1976). Themai nproble m seems toli e inth e origino fth e oftenquit e large quantities oflime .I nmos tcase s they are toolarg e tob e accounted forb y simple leaching from thepresen t surfacesoil .Anothe rproble m lies inth eplacemen t ofpur e or almost pure limehorizon swithi nth esoi lleadin g toth equestion : 'Whathappene d to the soilmateria l that formerly occupied the spaceno w takenu pb y the calcichorizon? ' Some authors are inclined on thebasi s ofthes e twoproblem s to answerMathieu' s questionb ystatin g that calcichorizon s aredeposits . Inthi swa yneithe r thequan ­ tityo fth elim eno r itsplacemen t inth e soilbecam e controversial issues,an d argu­ ments aboutth esourc e ofth e lime and the replacement processes of the soil material areavoided .The yar econfronted ,however ,b y theproponent s ofpedogeneti c theories witha numbe ro fargument s infavou ro fthi smod e of formationwhic har edifficul t to counter.Th emai nargument s for apedogeneti c origin ofcalci c horizons ingeneral , apartfro mthei r occurrence inspecifi c climatic zones,ca nb e summarised from Bretz &Horber g (1949),Gil ee t al. (1965),Ruella n (1970)an d Gardner (1972)a sfollows : - Theyar eparalle l toth e topography of thesurface . - Theyhav ea distinctiv emorpholog y and are laterally continuous. - Theyoccu ri nmaterial s ofvariou s compositions and textures. - Theyfor ma developmenta l sequence. - Theyofte nsho w lime accumulations under stones and other objects. - The facttha tther e are gradual lateral transitions between thevariou s types of calcichorizon s isa stron g indication that theyhav e importantprocesse s in their genesis incommon . A factortha tadd s toth econfusio n of thediscussio n istha tmos t authors fail tomentio nwhethe r theyconside r thecalci chorizon swhic h they study as static fea­ turesforme di nth epositio nwhic h theypresentl y occupy,o r asdynami c features ca­ pable oftransformin g themselves fromon efor m intoanothe r and ofmigratin g down­ wards ina downwearin g landscape,adaptin g themselves inth eproces s toth e relief forms asthe yar e shaped.Thi s aspectwil lb edeal twit h inChapte r 6. All theauthor s adhering toth e geogeneticmod e oforigi n apparently adhere rigidly toth estati c concept fromwhic h in fact theyderiv e theirmai n argument. Mostproponent s ofa pedogeneti cmod e seemt od o so too.Onl y in some ofth epedo ­ geneticconcept s isth edynami c character ofth ecalci chorizo n implied:Pric e (1933) asquote d byGoudi e (1973)develop s theconcep t that gradual leaching lowers the zone

14 ofaccumulatio nwhil e erosion lowersth eto po fth esoil .Bret z& Horber g (1949)hav e very similar concepts.Sabelber g& Rohdenbur g (1975)conside rmos t calcichorizon st o havebee n formedi nth esoi lan dexpose db ysubsequen t erosiono fth emateria l from whichth elim eoriginated . Ruellane tal . (1977)impl ya dynami cmode lfo rlandscape s inwhic ha calci chorizo n replacesunderlyin g materials (épigénie). Some authorsprefe r combinationso fth eaforementione d genetic options.I nth e following sectionsa revie wwil lb egive no fth edifferen tmode so forigi npostulated . Inman y casesth eauthor s restrict themselvest oprovin gb ynegativ e demonstration that theirhypothesi si sth eonl yon etenabl eb ytryin gt oeliminat e systematically all otherpossibilities .

2.5.1 Geogenetic modes of formation

Some authors claima geogeneti c formationfo rcertai n specific occurrenceso f calcichorizons .Other sar ei nfavou ro fa mor e generalised applicationo fthi scon ­ cept. Durand (1959)i sa proponen to fgeogeneti c originsfo rcalci chorizons .H e claims that calcareous lacustrine depositsar ea genera lphenomeno ni nAlgeria .H e bases thismainl yo ndetaile d studyo fmineralog yan dgranulometr yo fnon-calciti c grains contained insof tcalci chorizons ,whic hofte nsho wmarke d differencesi n these aspectswit hth ehorizon s over-an dunderlyin gth ecalci chorizons .H econ ­ sidersth ecalci chorizon smainl ya schemica ldeposit si nlake san dinvoke s Ehrart's theoryo fbiorhexistasie ,t oexplai nth etypica l sequenceso fpetrocalci can dsof t calcichorizon s inre dMediterranea n soils.I nsom eo fth ecalci chorizon sh ereport s fossile snail shells.Wit hth eexceptio no fon ecase ,i nwhic hth especie s foundnea r a springwa sindicativ eo fa swamp yenvironment ,h edoe sno tidentif yth especie so f thesnails .Man y completely sterile softcalci chorizon sar epronounce d lacustrine, eveni fthe y showa marke d relationshipwit hth epresen tda ytopography .Fo rsom e formso fcalci c horizonso nslope sh efavour s deposition from runningwaters .No tal l authorsconside rth epresenc eo fsnai l shellsi ncalci chorizon st ob eproo fo fla ­ custrine origin.Arche r& Mäcke l (1973)describ eth epresenc eo fgastropod si ndamb o calcretei nZambia .The yrejec ta lacustrin e originfo rthes ecalcretes ,however , sincea tleas ton eo fth especie so fsnail swa sfoun dt ob eo fterrestria l origin. A numbero fauthor s apply concepts similart othos eo fDuran d toa variet yo f occurrenceso f 'croûtes calcaires'i nth eMediterranea n environment.The ypropos ela ­ custrine,palustrine-lacustrin e orothe r sedimentarymode so forigi nmostl y related tochange s inth esedimentar y cycles.The yofte nmentio nth epresenc eo fsnai l frag­ ments,withou t identifying thespecie si norde rt obac ku pthei r claimo fa genesi s underwe tcircumstances : Wilbert (1962)advocate sa lacustrin e originfo rsof t calcichorizon s inleve l positions.Fo rsof t calcichorizon si nnon-leve lposition sh eadvocate s depositioni n rivercourses .H estate s thatth eobserve dpoo rcrystallinit yo fth elim e contained

15 inthes ehorizon si sproo fo fthei rgenesi sunde rwe tcircumstances . Noureddine (1979)describe squaternar y calcareousmud s deposited inbasin s inth eBeqa' a valley inLebanon .Vog t (1979)describe s 'croûtescalcaires 'whic har ei nhe ropinio nsedi ­ mentso fth esam e typea svalle ybotto m travertines,fo rthre equaternar y riverval ­ leysi nMediterranea n France.Ballai s& Vog t (1979)describ e sedimentationo flim ei n swampyenvironment sa sth emod eo forigi no f'croûte scalcaires 'o fsom e quaternary piedmontsi nAlgeria .Thes ehorizon sar efoun do nslope so f2- 3 %whic hth eauthor s attributet otectoni cmovement s postdating theirdeposition .Tiha y& Vog t (1979) de­ scribe 'croûtescalcaires 'fro mtw oold-quaternar y glacisi nAlgeri aa scalcareou s swampdeposits .

2.5.2 Pedogenetie modes of formation

Leaving apartfo rth emomen tth eproble mo fth ereplacemen to fth esoi l material by limewhic hi sdeal twit hi nSectio n 6.6,th epedogeneti emode so forigi nca nb e subdivided accordingt osourc ean dmod eo ftranspor to fth elime .Th equestio no f whetherth ecalci chorizon sar econsidere dt ob edynami co rstati c cannotb eavoide d inthi sdiscussion .Case scoul d existi nwhic hn omod eo ftranspor to flim e towards thecalci chorizo nnee db eenvisage d sinceth edynami c horizonca nb eassume d tob e moving towardsth elim ean dno tvic eversa . Modeo ftranspor tan dsourc ear eno tindependen t factors sinceth eassumptio no f a source impliesth eassumptio no fa mod eo ftranspor ti naccordanc ewit hth epos ­ itiono ftha tsourc ei nrelatio nt oth epositio no fth ecalci chorizon . The following sourcesar efrequentl y assumed inth eliterature :horizon s over­ lyingth ecalci chorizo nwhic har erecipient so flim e contained inaeolia nmaterial s depositedo nth esurface ;horizon s and/or strataunderlyin g thecalci chorizon ; ma­ terialsa tth esurfac e locatedupslop e fromth epoin twher eth ecalci chorizo ni s

1„~„.- _j

Asmod eo ftranspor t fromth eaforementione d sources towardsth ecalci c horizon, mostauthor s assumewate ra sth eagen t thatcarrie sth elim ei ndissolve d forma sbi ­ carbonate.Th esolution s canmov e downward,upwar do ri na latera l sense.Alternativ e modeso ftranspor tfo rlim ear eilluviatio no fcarbonat eparticle s (Gile,1977 )an d diffusion.Th elatte rmod eo ftranspor ti streate db yReeve s (1976)wh oconclude s thati ti sprobabl yno ta nimportan t factori nth eformatio no f'caliche' .Bertouill e (1976)mention s transporto fcolloida l CaCO,particle sdu et othermophoresis . Such colloidsca nfor mb yprecipitatio n froma bicarbonat e solution.Th etranspor tpro ­ ceeds fromcolde rtoward swarme rzones . Themos t commoncombination so fsourc ean dmod eo ftransport ,encountere d inth e literature,ar ediscusse di nth efollowin g sections,togethe rwit hth eoptio ni n whichn otranspor tha st ob eassume d sinceth ecalci chorizo nmove s towardsth e sourceo fth elime .

16 2.5.2.1 Downwardmovemen t from asurfac e soil thatcontain s lime and/or receives lime from aeolianaddition s

Ifth e amounts of limeaccumulate d insoil s are relativelymino r they canb eas ­ sumed tohav ebee n leached from thehorizon spresentl y overlying the accumulation zone.Thi s is illustratedb y computations ofJenn y &Leonar d (1939),a squote d by Reeves (1976),wh oestablishe d arelationshi pbetwee nprecipitatio n and depth ofcar ­ bonatehorizon s insoil s ofKansa s and Colorado (USA).Arkle y (1963)improve d upon Jenny's techniqueb y taking intoaccoun t excesso fprecipitatio n overévapotranspi ­ rationan dwaterholdin g capacity of thesoi l inorde r tofin d themea ndept h of leaching.H e established agoo dcorrelatio nbetwee n this lattervalu e and the depth ofth ecarbonat ehorizon s for soils fromCaliforni a andNevad a (USA).Al l thesere ­ lationships hold true,however ,fo rrelativel yyoun g soilsonly .Whe napplie d to oldersoil swit h thicker carbonate accumulations,complication s arisedue ,fo rex ­ ample,t oth e influence of thecarbonat e onth epermeabilit y ofth ehorizo n and lack ofdat a aboutth e climate ofth epast . Inthos e soils,moreove r the amount of calcite accumulated iss o large that one cannot assume itt ohav ebee nprovide d solelyb y the soilmaterial s presently overlying thecalci chorizon . Inorde r toaccoun t forth e discrepancybetwee n the amount oflim ean d thethicknes s of theoverlyin ghorizo n in suchcases ,man y authors assume thataeolia naddition s toth esurfac e soilhav e taken place.Th emagnitud e ofaeolia naddition s tosoils ,especiall y for areas bordering greatdeserts ,i swel ldocumente d both forth epresen t andpast .Lim eofte nmake s up animportan tpar t ofthes ematerials .Th e following authors arequoted :Buring h (1960)fo r Iraq,Yaalo n &Gano r (1973)abou taeolia ndus t and lime ingeneral ,Sidh u (1977)fo r Indiaan dMacleo d (1980)fo rGreece . The following authors arequote d asbein g infavou r ofdownwar d leaching of lime towards the calcichorizon .Man y assume aeolianaggradation s toth e surfacesoil . Gilee t al. (1966)postulat e forNe wMexic o (USA)th e formationo f animper ­ meable zone at thedept ho ffrequen twettin gb yunsaturate d flow.Th e limes ode ­ posited 'plugs'th ehorizo nan dcause s the formation ofa zonewher e percolating water accumulates.Evaporatio n ofthi swate r leads to the formationo fa har d lami­ nated crust.Thi s formationwil lgro wupwards ,i nth eproces s gradually lifting the overlying soil. Lattman (1973)discusse s cases fromNevad a (USA).H e favours apedogeneti c ori­ ginan d indicates carbonaceouswindblow n sandan d silt,deposite d onth e topo fth e profile,a s themai n sourceo f lime.Fo rfan sbuil t of 'non-carbonate detritus'h e finds the strongest cementationdownwin d ofplayas ,hig h incarbonates . Ina later article (Lattman &Lauffenburger , 1974)h e suggests thatarea sdownwin d ofmajo r out­ crops of gypsiferous rocksals ocarr ythic kcaliche . Inhi sopinio ngypsu mca nb ere ­ duced in the soilb ybacteri awhic h leadsultimatel y toit stransformatio n to CaCO,, incorporating CO,fro m thesoi l and liberating H2S. According toReeve s (1970)wh odiscusse s caliche fromTexa s andNe wMexic o

17 (USA),sof tcalci chorizon s formwher esoluble s fromth euppe r zonear ecarrie d down­ wardan dprecipitated ,whe nsoi lmoistur e isremove db y évapotranspiration.H e admits thatsom ecapillar yris ema ycontribut e inthi sstag e too.Induratio nwil l takeplac e veryslowly ,du et oth egradua lincreas e in limecontent .Rapi d indurationwil lre ­ sulti fth esof tcalci chorizo n loosesmos t oral lo fit ssoi l cover.Onc e thehor ­ izonbecome s 'plugged',th eproces smentione db yGil e et al. (1966)wil l takeover . Brown (1956)consider sth eworldwid epresenc eo fa zoneo fcalciu m carbonateen ­ richmenta tth ebas eo fpedoca lsoils ,a sstron gevidenc etha tC horizons and 'caliche'ar egeneticall yrelated . Inth eLlan oEstacado ,Texa s (USA)h e findsa per ­ fectgradatio ni nundisturbe d sectionsfro mnon-calcareou s orver yslightl y cal­ careous topsoil,dow nint oth e 'caliche'.Thi sh eregard sa s strongproo f thatth e whole 'calichecomplex 'i sth eresul to fidentica l orver ynearl y identicalprocesses . Hepostulate sa naeolia naggradatio no flime-containin gmaterial s ashavin g provided thelime .H ebase sthi s largelyo nproo fb ynegativ edemonstration ,invokin g the fact thatth erock so nwhic h thecalich eha sbee n found tores tvar y fromCretaceou s lime­ stonest onon-calcareou ssandstones . Gardner (1972)studie da similarcas e fromNevad a (USA)and reache d a comparable conclusion.H ecalculate dth eag eo fa thic kcalci chorizon ,takin g intoaccoun t the limecontaine d inairborn edus tan drainwater . Blümel (1979)assume saeolia naddition s toth esurfac esoi la son e of the sourceso fth elim efo rcase s inS.W .Afric aan dSpain ,i nwhic hcalci c horizons overliematerial sou to fwhich hardl yan y lime canb e liberatedb yweathering .

2.5.2.2 Upwardtranspor to flim eb y solutions ascending towards the accumulation zone

A commonmechanis mo ftranspor tenvisage d iscapillar yrise .Othe roption s are a fluctuatinggroundwate rtabl ean dth epumpin gactio no fth evegetation .Man y authors indicate thatcapillar yris eo f limewoul d imply transporto fal lkind so f soluble saltsalso .Thi swoul dcaus e salinisation andalkalinisatio n ofth eprofile .Lac k of evidenceo fthes eprocesse s isuse d asa nargumen t against thismod e of formation. Thefollowin gquote sfro mth e literature areo finterest . Goudie (1973)compute d that 1m ofcalcret e couldb e formed in360 0year s if 240 cmo fwate revaporate d annually,derive db y capillary rise froma groundwate r that contains 150g/ m carbonate. Netterberg (1969)describe d the zoneso flim ecemente d gravels and sands,ove r 9m thick,o fth eVaa lrive ri nS .Africa .H econsider s their thickness toogrea tt o assumepedogenesi s inth estric tsens eo fth eword .Th e limewa sdeposited ,i nhi s opinion,b ya fluctuatin gbu tsteadil ydroppin gwate rtable ,unde rsemi-ari dcon ­ ditions. Mathieu (1974)quote sa remar kb yYankovitc hwh oput s forward that limewhic h is dissolvedb yrainwate rdeepe r inth eprofil ewil lb e leftbehin d at ashallowe r depth

18 after thewate rha sbee ndraw nu pb y thevegetation . Boulaine (1966)invoke s therol eo fth evegetatio n inbringin g dissolved limeu p towards theaccumulatio n zone.H ecite s calcified roots asproo fo f this.

2.5.2.3 Lateral transport of lime formed or liberated from sourcematerial s located upslope from thepoin t of accumulation

Thisrefer s to transport of limemainl y inth e formo fa solution over andunde r thesoi l surface andoccasionall y inth e formo fa suspension over the soil surface. The following literature quotes areo f interest forthi smod e of formation. Ruellan (1968)find sn o relationship between thickness and lime concent of cal­ cichorizon s and those of theoverlyin ghorizon s insoil s fromMorocco .Fo r cases where calcichorizon s are foundo nmaterial s thatd ono t contain lime andd ono t lib­ erate calciumupo nweathering ,h econclude s that limemus thav ebee n transported lat­ erally from sources availableupslope .H e tested thisrelationshi p and found itvali d overdistance s ofsevera lkilometre s inth emor e arid areasbu t overten s ofmetre s only insub-humi d areas. Dumas (1969)presume s that thelim ewhic hconstitute s theuppe rhorizo n ofa se ­ quence ofpetrocalci c and soft calcichorizon s inS.E . Spain cannotb ederive d by leaching of the overlying soil.Neithe r doesh e find evidence of transportupward s of lime from the lowerhorizons .Thi s leadshi m toth econclusio n that lateral transport oflim ethroug h theoverlyin g soilha sprovide d themateria l forth epetrocalci c hor­ izon. Gigout (1960)consider s lateral transport of limea son e of thesource s for cal­ cichorizon s inN .Africa . Wilbert (1962)describe s laminated petrocalcic horizons fromMorocc o as surface formations.H epresume s surface flowo fwater s chargedwit h lime tob e thesourc e of this formation.H e admits that inth ecas e oflaminate d petrocalcic horizons overly­ ingsof t calcichorizons ,th esourc eo fth e limema yhav ebee n the softcalci chor ­ izons. For lime incalci chorizon s ofS.W . Africa and S.E. Spainwhic hoverl ynon - calcicmaterials ,Blüme l (1979)take svariou s sources intoaccount .H emention s lat­ eral surface transport of limederive d fromcarbonaceou s rocksupslope ,bot h in sus­ pension and insolution .Pluggin go fth e soildu e toinfiltratin g limewoul d render theprofil e impermeable and aid inprovokin gmor e runoffc.q . lateral lime transport.

2.5.2.4 Liberationo rformatio no f lime froma paren tmateria l inth eweatherin g zonedirectl yunderlyin g thecalci c horizon

Asmentione d before,thi smod e of formation envisagesn o transport towards the calcichorizo n as iti sassume d that thishorizo nmove sdownwar dwit h the weathering front into theparen tmaterial . Iti sdiscusse d indetai l inChapte r 6.Thi smod e of

19 formationi ssuppose dt ob eaccompanie db yremova lo fth eweatherin g products from thesurfac esynchronou swit hth edownwar dmovemen to fcalcic horizon san dweatherin g front.A ssuc hi ti smostl yreferre dt oi nth eliteratur ea sa degradationa lmod eo f formation.Th efollowin gquote sfro mth eliteratur ear eo finteres ti nthi scontext . Lattman (1973)favour sfo rS .Nevad a (USA)th ehypothesi so fcarbonaceou s aeolianmateria la sth emai nsourc eo fcarbonate ,a smentione di nSectio n 2.5.2.1.H e reports,however ,'Th e extentan ddevelopmen to fcementatio nar egreates to nfan s composedo fcarbonat ean dbasi cigneou sroc kdetritus ,les so nfan sbuil to fsilici - oussedimentar ydetritus ,an dleas to nfan scompose do faci d igneousroc kmateria l' . Incomparin gth ecalciu mconten to fweathere dan dunweathere d localandesite ,h edi d notfin da significan tdifference ,which le dhi mt orejec tth ehypothesi s thatth e rockmateria li sth esourc efo rth elime .H eadmits ,however ,tha tth erelatio nbe ­ tweenroc ktyp ean ddegre eo fdevelopmen to fth ecalci chorizo ni sno tproperl yun ­ derstood. ForMorocco ,Wilber t (1962)an dRuella n (1970)repor tcalci chorizon so nrock s thatd ono tcontai nlim ebu td ocontai ncalcium ,e.g .basalt san dals ocertai ngran ­ ites.Boule t& Paque t (1972)repor tsimilarl yo na 'granito-gneissà amphibole 'whic h formsth eparen tmateria lfo rVertisol swit hcalcareou snodule si nHaut eVolta . Gardner (1972)treat s 'caliche'fro mNevad a (USA)develope di na nalmos tcarbon ­ ate-freealluvia lsand .H ecalculate s that 36.5m o fthi smateria li sequivalen ti n limeconten tt oth elim econtaine di nth ecaliche .Had thi ssam eamoun to flim ebee n derived fromcalciu m liberatedo nweathering ,ove r9 0m o fmateria lwoul d have been needed.H ediscard sth ehypothesi s thatth esan di sth eparen tmaterial ,however , sinceth eresidu eo fthi sweatherin gi sno tpresen tan dn oexplanatio nfo rit suni ­ formremova lca nb egiven . Fora cas ein .N .Africa ,Gigou t (1960)show s thatcalci chorizon sca ndevelo p duet oth eweatherin go fcalcareou s sandstones.Th eproces sma yfirs tlea dt oa nen ­ richmenti nlim ean dsecondl yt oinduratio no fthi s lime.I ncertai n casesa har d crusti sforme ddirectl yupo nth eweatherin grock . Blank& Tyne s (1965)repor tth eformatio no fsof tpowder y lime,b yi nsit u weatheringo flimeston ei nTexa s (USA).The ytrie dunsuccessfull yt osimulat eth e process,which the ycal l 'chalkification',i nth elaboratory .The yrepor t thatth e softpowder ylim ei sno tbrough ti nfro moverlyin g soilo rrock sb ymigratin gwater , buti sdu et oi nsit udissolutio nan dreprecipitation ,which transforms coarse cal- cit eint omicrocrystallin e calciumcarbonate . James (1972)report sth esam efo rsub-aeria lweatherin go flimestone so nBar ­ bados.Importan tevidenc ewhic hh enote si sth epresenc eo ffossils ,als o contained inth elimeston erock ,withi nth esof tlim elayer .

2.5.3 Conclusions

1. Therelationshi pbetwee ncalci chorizon san dth ematerial swithi nwhic ho ro nto p

20 ofwhic h they areencountered , isno t alwaysproperl y characterised by the term 'par­ entmaterial' . Inman ycase s 'hostrock 'o rjus t 'underlying stratum' are tob epre ­ ferred over 'parentmaterial 'whic h implies astron g genetic relationship. 2. There isa stron g tendency amongst researchers tofavou rpedogeneti c modes of origin formos t calcichorizons ,ove rothe rtheories . 3. Many authors considervertica lprofil e sequences ofcalci c horizons asgenetical ­ lyrelated , theirpresen t differences being due to laterdifferentiation . 4. Amongst an important group ofAmerica n earth scientists,ther e isconcensu s on a model inwhic hmos t thick 'caliche'complexe s overlying avariet y ofrock s inth e S.E.US A owe their origint oaeolia n aggradation of lime-containingmaterials . 5. French soil scientists generally favoura lateral transport of lime,i norde r to account forcalci chorizon s inposition s where surface soilan d underlying material are incapable of supplying it.

2.6 INFLUENCE OF CALCIC HORIZONS ONLAN D QUALITIES

The following definition ofth e term 'land quality' isgive nb y FAO (1976): 'A landqualit y is acomple xattribut e of land,whic h acts ina distinc tmanner ,i n its influenceo n thesuitabilit y of land for aspecifi ckin d ofuse' . Themai nuse s con­ sidered are theproductio n ofcrops ,o f feed foranimal s and ofwood . Soilmaterial s fromcalci chorizon s have some application outside agriculture too.Netterber g (1975,197 8an d 1980)report s andclassifie s theutilit y of thesema ­ terials forroa d building.Duran d (1959)mention s theirus ea sbuildin g materials and asra wmateria l for the localmanufactur e ofburne d lime. Artiola & Fuller (1980)describ e theus eo f limestone asa liner for landfills consisting ofmunicipa lwaste ,i norde r toslo wdow n themigratio n ofcertai nmetal ­ lic cationswhic hwoul d cause soilpollution . Soilmaterial s fromcalci chorizon s can bepresume d to serve the samepurpose . Recently important commercial uraniumdeposit s havebee n found inW .Australia , asmineralisation s incaliche .Deposit s ofuraniu mmineral s related tocalich e are also reported from theUS A (Reeves, 1976).Accordin g toNetterber g (1980),non-pedo - genic calcretes are themos t favourable foruraniu m occurrence. In the following paragraphs arevie wwil lb e giveno f thewa y inwhic h thepro ­ perties of thedifferen t kinds ofcalci chorizon s influence,singl y or incombi ­ nation,th e land qualities for agriculturaluse .

Availability of nutrients This quality depends on thevolum e ofsoi l incontac twit h theroo t system and onth epresenc e and solubility ofth evariou snutrient s inth e soilmass . Petrocalcic horizons are largely impenetrable for roots,an d restrict theirgrowt h to the generally shallow surface soil overlying thehorizon .Sof t calcic horizons arenormall y overlainb y athicke r surface soilan d are themselves pen­ etrable forroots .Th enumbe r ofroot s found isgenerall y low,however ,probabl y due

21 toth erelativel yadvers echemica lconditions .Th ehig hpH ,generall yaroun d 8.2, re­ strictsth eavailabilit yo fnutrient st oplan troots .O fth emajo relements ,N an dP mayb eadversel yaffected .Nitroge ni nth efor mo fammonia ,o ri nform s thattrans ­ formt oammonia ,wil lb eineffectiv ei fsurficiall y appliedt ocalcareou s soilsdu e toth evolatilisatio no fNH 3 (Fuering, 1973).Applie dP i squickl y transformed into insolubleforms .O fth emicro-elements ,Fe ,Mn ,B ,C uan dZ nma ybecom e deficient (Jacob& Va nUexkiill ,1963) .I npur ecalci chorizons ,relativel yfe wnutrient sca nb e stored,sinc ea nexchang ecomple xi slacking .Lim ei nsmal lquantitie si sbeneficia l formos to fth ecommo ncrop so fMediterranea n areas.I flim ei spresen ti nlarg e quantities,however ,i tha sa detrimenta leffec to nth enutrien t statuso fth esoil . Assuc hdiscontinuou s softcalci chorizon sd ono teffec tth enutrien t statuso fth e soilt osuc ha nexten ta scontinuou sone sdo .

Availability of moisture Availabilityo fwate ri smor eadversel yaffecte db ypetro - calcichorizon sa tshallo wdepth ,tha nb ysof tcalci chorizon swhic hnormall y occur ata greate rdept hi nth eprofile .Petrocalci chorizon sar eslowl ypermeabl eo rim ­ permeable.Thi slead st ostagnatio no fwate ro nto po fth ehorizon ,followe db yrun ­ offan devaporatio n losses.Root spenetrat eth ehorizo n onlywit h utmost difficulty, inorde rt oreac hlowe rhorizon smoistene db ygroundwater .Thi s appliesmainl yt o suchperennial sa solive san dgrapes ,whic hca npus h their roots downt ogrea t depths throughcrack si nth epetrocalci chorizon .Th esof tcalci c horizoni spermeabl ean d canstor elarg equantitie so fwate rdu et oit srelativel y fine texture (Durand, 1959).Massou d (1973),however ,foun d thatcalcareou s soils tendt ostor e consider­ ablyles swate rtha nnon-calcareou s soilso fth esam etexture .Thi sma yb edu et oth e influenceo flim eo nth eformatio no fsoi laggregate so rt oth ecoverin go fcla ypar ­ ticlesb ylime .

Availability of oxygen Theavailabilit yo foxyge nt oth eroo t systemso fplant si s negatively influencedb ystagnatin gwate ro nleve lpetrocalci c horizons. Especially inMediterranea nclimates ,i nwhic hmos to fth eprecipitatio n fallsi nth ecoo lsea ­ son, this causesroo tdamage .Sof t calcichorizon sar egenerall ypermeabl ean dadmi t air. Abundant soft limei nsurfac ehorizon s induces slakingo fth esoi lupo nwetting , thusblockin g soilaeration .

Workability of the land (ease of cultivation) Petrocalcichorizons ,withi nplowin g depth,hav ea negativ eeffec to nth eworkabilit yo fth esoil .N oprope r seedbedca n beprepare dfo rannuals ,whil edus tmulchin go fperennial sbecome s ineffective.Wher e petrocalcichorizon soccur_at_shallo wdept h 'specialmeasure shav et ob etake nfo r theplantin go fperennials .Re^ToT-th e crustb ysubsoilin gwit hheav y equipment ismentione d fornewl yplante dvineyard si nAlgeria .Fo rtreecrop si ti sconsidere d cheapert oresor tt oth eblastin go fplantholes ,wit h special agricultural explosives (Durand, 1959).

22 Resistance to soil erosion Ifa thi nsoi lcove r ispresen t onto p ofa petrocalci c horizon,thi swil lb eerode dver yeasil ydu e torunof fprovoke d by the impermeability ofth eunderlyin g horizon.Petrocalci c horizonsprope rar ever y resistant toerosion . Thismean s that the sediment yield from exposedpetrocalci c surfaceswil l be low.Th e slaking effect of limeo ntopsoils ,a smentione d before,als oha sa detrimenta lef ­ fecto nth eresistanc e toerosion .Conservatio nmeasure s sucha s theconstructio n of terraces arehampere db y thepresenc eo fshallo wpetrocalci chorizons .

Adequacy of foothold Shallow soilsoverlyin gpetrocalci chorizon s dono tpresen t an adequate foothold forplants .Thi s isespeciall y serious forperennials .A s suchth e measuresmentione d inforegoin gparagraph s todestro y thepetrocalci c horizon,ar e alsoessentia l toassur e afoothol d fornewl yplante dperennials .

Conditions for germination Petrocalcic fragments,formin g arubbl e layero n thesur ­ face,adversel y influence germination conditions formos t annualcrops .Thi s ismain ­ lydu et oth efac ttha tfin e seedsfal l awayto odeepl ybetwee nth ecoars efragments . The surface crust,whic hform so nto po f soilsric h insof tpowder y lime,du e to slaking inwe tconditions ,i softe na caus e forpoo rgermination .

Itma yb e stated thatpetrocalci c horizonswhic hnormall y occur at shallow depth,seriousl y affect thedifferen t landqualities . Inman y cases thismean s that theus e of the landsha st ob erestricte d tograzin g or forestry.A s fara sth e cul­ tivationo fcrop s isconcerned ,preferenc e isgive nt operennial s overannual s on landsunderlai nb y thesehorizons . Soft calcichorizon swhic h occurdeepe r inth eprofil ehav ea lessdetrimenta l effect.Th emai nhazar d isthei rrapi dhardenin g duet oexposur e orothe rcauses .I n thiscontex t it iswort hmentionin g thatRichte re tal . (1978)foun d that anextreme ­ lyrapi dhardenin g ofa sof t calcichorizo ntoo kplac eafte r the introduction ofir ­ rigation incombinatio nwit hheav y applications oforgani cmanure .

23 3 Description of the study area

3.1 LOCATION

Theare ai ssituate di nth ecentra lpar to fBadajo zprovinc ewhic h formspar to f theregio ncalle dExtremadur ai nS.W . Spain.Mérid ai sth ecentra l towno fth earea . Iti slocate droughl y7 0k meas to fBadajo zan dapproximatel y35 0k msouth-wes to f Madrid.Th earea ,a sshow ni nFig .1 ,lie sbetwee n 6°05'an d6°3 1'longitud ewes to f Greenwichan dbetwee n 38°47'an d38°57 ' latitudenorth . Theare ai ssituate dbetwee nth etown so fMont ij o (westo fit) , Mirandilla (northo fit) , Guarena (inth eeast )an dSolan ad elo sBarro s (southo fit) . Iten ­ compassesth ewester nextremit yo fth eSierr ad eSa nServan .

3.2 CLIMATE

The climate of the study area is typically Mediterranean, being characterised

Fig.l. Location of the study area in Spain in relation to the towns of Mérida, Badajoz and Madrid and to the Guadiana river.

24 mainlyb ywar m dry summers andcoo lmois twinters .Accordin g toMeig s (1962)thi s is due toth e fact thatmos t of therainfal l isassociate dwit hwesterl y storms thatre ­ sult from the southwardmovemen t ofth epola r frontdurin g thewinte r season.Th e summer drought isrelate d toth eapproac ho f thedr y sideo f theoceani c highs. According toth e classification ofKoppe n& Geige r (1932)th eclimat e isCsa . In thissyste m thesymbol srepresen t the following: C:war m temperate (average temperature ofth ecoldes tmont h isbetwee n +18°Can d -3°C) s:dr y season inth e summer a: average temperature of thewarmes tmont h exceeds 22°C According to theclassificatio n ofThornthwait e (1948),th eclimat e of the study area issemi-arid .Thornthwait e defines a so-calledmoistur e indexas :I m= (100s -6 0d)/ n inwhic hth esymbol smea nth e following: Im:moistur e index s:precipitatio n surplus overpotentia l évapotranspiration d: precipitation deficit frompotentia l évapotranspiration n: totalwate rnee d ortota lpotentia l évapotranspiration Onth ebasi s ofth edat ao fFig .2 i tca nb ecalculate d that themoistur e index for thesurve y area is -20.8.Thi smean s thatth eclimat e classifies inth e semi-arid class (between-2 0an d -40),ver yclos e toth eborde rwit hth e sub-humid class (be­ tween -20an d+20) . According toUNESCOFA O (1963),th e climate ismeso-Mediterranea n of theaccen ­ tuated type. Inthi sterminology ,a Mediterranea n climate is aclimat ewit h adr y period of 1-8 months,coincidin gwit h theperio d of the longest daylight.Th eMedi ­ terranean climate isfurthe r subdivided onth ebasi s ofth e 'xerothermic index' (i.e. index ofho tweathe r drought).Th e xerothermic index isth e sum ofth emonthl y in­ dexeswhic h are foundb y subtracting fromth etota lnumbe ro fdays ,th eday swit h raintogethe rwit hhal fth eday s offo g and dew.Th e resulting total ismultiplie d by a factor derived fromth emea natmospheri c humidity. The qualification of accentuated meso-Mediterranean correspondswit h axerothermi c index that fallsbetwee n 75an d 100. For theneares tmajo rmeteorologica l station,Badajoz ,th e attenuated thermo- Mediterranean climatewit h axerothermi c indexo f 100-125,applies . Theneares tmajo rmeteorologica l stationwit h full coverage ofdat a isfo rth e survey area Badajoz-,It sdat a arereporte d inTabl e 3fo rth eperio d 1934-1960. Castillo &Beltra n.,(1973 )repor t for this same station forth eperio d 1931-1960sev ­ eralagro-climatologica ldat awhic h arequote d inTabl e 4. For two stationsnea r thewester n and southern limits of thestud y area,preci ­ pitation, temperature andpotentia l évapotranspirationdat aaccordin g to Thornthwaite (1948)ar e available forth eperio d 1957-1966.Th e data arereporte d by the Instituto Nacional de InvestigacionesAgraria s inMadri d andpertai n toth e stations Lobon (6°41'west ,38°51 'north ;altitud e 232m )an dAlmendralej o (6°26'west , 38°41' north; altitude 336 m). From theaverage s ofthes e twostation s awate rbalanc e dia-

25 TCC) P and EPT (mm)

Y//A Surplus of P over EPT (S) . Mean monthly air temperature (°C)

I | Use of stored moisture (U) U= 150 trim \ P mean monthly precipitation i c I I Deficit of moisture (D) U= 10C mm- / . I -

U = 5 i f

/ S= 150 r /~~- -U- i — S- 50 r

"N^^ZZ^

^E X:

M

Fig. 2 Water balancediagra mbase d on theaverag eprecipitatio n and evapotranspi- ration forth estation sLobo nan dAlmendralejo ,fo r theperio d 1957-1966.Th eaverag e ofth e meanmonthl y airtemperature s for thesetw o stationsha sbee n indicated too. Thep o tential évapotranspirationha sbee ncompute d according toThornthwait e (1948). Inth e graph itha sbee n indicated,ho wmuc hmoistur e surplus (S)result s from the winter rainsan ddurin gwhic hperio d thjsmoisture ,i f stored inth e soil,ca ncom - pensât efo r theexces so févapotranspiratio nove rprecipitatio n in the summer period .Th e totalsurplu so fabou t 150m m isuse d up (U)b y thebeginnin g of July.

gram (Fig.2 )ha sbee nconstructed .Th eaverag emonthl y temperatures are also indi­ cated.Th egrap hshow sho wmuc hmoistur esurplu sresult s from thewinte rrain san d duringwhic hperio d thismoisture ,i fstore di nth esoil ,ca ncompensat e for theex ­ cesso f évapotranspirationove rprecipitatio ni nth esumme rperiod . Itca nb econclude dfro mth ediagra mtha tth emoistur e regime isxeri c according toSoi lSurve yStaf f (197S)fo ral l soilstha td ono t receive importantamount so f runofffro madjacen t areas.Fig .2 show s that the total amounto fsurplu swate r for thewinte rmonth si sabou t 150mm .I f thisamoun twer e storedi nth e soil itwoul d not lastlonge rtha nth een do fJune .A tleas t threemonth s followthi speriod , duringwhic hth epotentia lévapotranspiratio nexceed sth eprecipitatio n and the soil moisturecontro lsectio ni sconsequentl ydry .Durin g thewinte ra tleas t 2\ monthso f excess followth epoin twher e 75m mo frai nha sbee nstore dan d atwhic h the soil moisturecontro lsectio ni ssuppose d tob ecompletel ymoist .Th e totalperio do fex - 26 60 ja 0) m • H ß U M-1 CA •H 0) O W J= O m ro m ro co n>i 6- S r- — ß o- 00 N in m > o 4J Öui-H •H J3 cd J= U 60 VJ « cd ~ LH — •H tu ß >-t /-* CO ^O CF\ VJ > O 3 JS — ~ CN CN — « cn ~ m cd 6 T) ^

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ja (-1 CD 0) 4-1 6 0) ja ja cd CO CD ja 0 S 0) S* 3 4J o 01 ja ß i-H 60 o. u cö c>d . 3 3 3 Ol cj o> S •- ) < C/Î O s 27 Fig. 3. Landtypes of the survey area

Hills of Ordovician quartzi and silicious slates Undulating landtype onP a granites and gneisses Undulating to rolling landl on Paleozoic schists

• A Undulating to rolling landl on Miocene arkoses E3 F Undulating landtype on fii sandy Miocene clays Roads Railroads

Urban areas ~*£ River courses X7 Site Cross section A u E

28 tes f I jyj Gently undulating to undulating landtype on Miocene clays

île« przv] u Dissected plateau on Plio-Pleistocene "Rana" deposits N i• ., •i j Nearly level sand covered Pleistocene planation '•-'' • '^ surface on mixed materials

^ffi,] y Nearly level landtype on Holocene deposits of the Guadiana valley

For a description of physiography, parent materials, soil and calcic horizons of these landtypes see Section 3.3 and 3.5

Site 1= Riola 1 Observation site: Site 2 =Arroy o 1 Site 3 = Arroyo 2 Site 4 =Arroy o 3 For the location of profiles PI, P2, P4 and P3 =E l8 see cross section AE.

29 Table4 . Agroclimatological data forBadajo z (seeTabl e3 )coverin g theperio d 1931-1960 asreporte d byCastill o &Beltra n (1973)

Averageabsolut eminimu m temperature of thecoldes tmont h (January) - 1.5C

Averagemaximu m temperatureo f thewarmes t 6month s (May-October) 29.0C

Entirelyfrost-fre eperio d 5.9month s

'Leaching rainfall' (excesso fprecipitatio nP ove rpotentia l evapo- 160m m transpiration E+ for theperio d thatP > E )

'P/Eratio ' (averageannua lprecipitation/ditt o potential evapo- 0.46 transpiration)

+ Potentialévapotranspiratio naccordin g toPenman .

cesso fprecipitatio nove rpotentia l évapotranspiration,whic h corresponds moreo r lesswit hth eperio ddurin gwhic hpar to fth econtro l sectioni smoist ,amount st o about5 months .Th emea nmonthl yai rtemperatur eha sbee n includedi nFig .2 .Thi s servesa sth ebasi sfo restimate so fth esoi l temperaturea t5 0c mdept h accordingt o SoilSurve y Staff (1975).I tca nb econclude d thatth emea n annual soil temperature isbelo w22° Ca t5 0cm .Furthermor ei tca nb ededuce d thatmea n summeran dwinte r temperaturesvar yb ymore than5° Ca tthi sdept han dtha tth emea n annual temperature isove r8° Ca tthi sdepth .Th econclusio n that,o nth ebasi so fth eabove-mentione d data,th emoistur e regimei sxeric ,applie st oal lsoil sfo rwhic hprofil e descrip­ tionshav ebee ninclude di nthi stext ..Th eVertisol s amongst themhav ea xeri c mois­ tureregim eo nth ebasi so fth eperio d duringwhic h theircrack sar eope nan dclose d whichcorrespond swit hth eperio d duringwhic h theirmoistur e control sectionsar e dryan dwe trespectively . Shallowsoil s likethos ewit hpetrocalci chorizons ,tha t areno tcapabl eo fstorin g 150m mo frain ,ar edr yi nth esunnie rfo rperiod s which exceedth eon eindicate dwit hD i nFig .2 .The yd ono tfulfi lth erequirement s fora n aridicmoistur e regime,however ,du et oth eprecipitatio n distribution patternfo r thearea .Consequentl y these soilshav ea xeri cmoistur e regime too.Knibb e (1974a) comest oa simila rconclusio nfo rth esoil so fth eadjacen tMontij o areao nth ebasi s ofth eclimatologica ldat afro m thisstation . Specialmanagemen tpractice sar ei nus ei nth earea ,i norde rt oconserv e mois­ ture.A ssuc hth eamoun to fmoistur e storedi nsoil swit ha goo d moisture-holding capacity,ca nb eincrease dt ovalue sa shig ha s30 0mm .Th eefficienc yo fthes e measuresfo rvariou scrop sca nb eevaluate d ina theoretica lmodel .Thi swil lb e treatedm Section3.6 .

3.3 GEOLOGYAN DGE0M0RPH0L0G Y

me geologicalhistor yo fth estud yare aa sdescribe db yPannekoe k (1968), IGME

30 (1970)an dVa nDorsse r (1974)i sbriefl y summarised asfollows . Inth e Paleozoic eraa largegeosynclin eexiste d inwhic h severalmaterial swer e deposited. The following formations of interest for thesurve yare adat e from this period: Cambrian limestones andOrdovicia nquartsite s and slates.Late r in thePaleo ­ zoicthes ematerial swer e subjected to intense foldingan d faultingwhe n theywer e influencedb y theHercynea n orogenesis.Intrusio no fmostl ygraniti cmagm a occurred synchronously, leading toth eformatio no f largebatholith s and causingbot h regional andcontac tmetamorphis mo fman yrock so fth earea . During theMesozoi cdownwearin gprevailed ,leadin g toth e formation of anero - sional surface,fro mwhic h only somemajo rmountai n rangesprotuded . Inth eTertiar yperio d of theCainozoi c era,thi splai nwa s subject totrans ­ gressions and regressionswhic hwer e separated bymino r tectonicdisturbances ,fol ­ lowedb yrenewe dbas e levelling.Accordin g toolde r literature,th e sedimentation started in theOligocèn eperiod . Findso f fossilremain s ofmammal s have led toa n updating of theonse t ofth e sedimentation toth eVindobonian ,whic hbelong s to the MiddleMiocen e (IGME, 1970). Inthi sperio dheav ymarin eclay swer e deposited, fol­ lowedb y terrestrial arkosewhic h intur nwa s coveredb y sandy claysan dheav y clays during thenex t transgression.Th eclay sar eseparate d fromth earkos eb ydiscor ­ dances. Bothma y contain limean d assuc har ereferre d to inth e literature asmarl s (IGME, 1954ab). Theuppe ron e of these clayscontain sver yconsiderabl e amounts of limei nit s top.Thi s limei sgenerall y considered by geologists tob e of sedimentary origin.Accordin g toPere zMateo s (1955),wh o investigated themineralog y of theTer ­ tiarydeposit s ofth eGuadian abasi ni nExtremadura ,th earkos e isautochtonou swhil e theuppe r clays are allochtonous andhav ebee n transported tothei rpresen t position byrivers .Gehrenkempe r (1979)attribute s the limeconten t ofMiocen e sediments near Talaverad e laRein a (approximately 150k mN.E .o fth e survey area)t oth eweatherin g ofplagioclas e ingranodiorite s nearby.Th e total thickness of theMiocen e sequence isvariabl ebu t thefollowin g averagethicknesse sca nb egiven : - claysunderlyin g the arkose 80m , - arkose grading fromcoars e tofin e6 0m , - clays overlying the arkose 30m . The end of theTertiar yperio dwa smarke db y erosiveprocesse swhic h led toth e formationo fa nerosiona l surfacewit ha gradua l slope towards thewest .O n thissur ­ face thecoars e terrestrial deposits ofth e so-called 'Raha'wer e laiddow ndurin g theUppe r Pliocene.Gehrenkempe r (1978)report s forthi smateria l thicknesses that vary froma fewmetre s to 17m inarea snort h ofth eMonte sd eToled onea r Talavera de laRein a and south ofth e samemountai n rangenea rGuadalupe . Inhi s opinion the Rahawa s formed as anaccumulatio nglaci s inthre ephase stoward sth een d of the Pliocene,du e toa climati c change towards slightlymor ehumi d circumstances which caused déstabilisationo fth eolde rweatherin gproduct s ofth emountai nranges .Thi s caused the initiation ofth eRah aformatio na smudflow-lik emas smovement s close to themountai n fringe.Thi swa s followedb y torrential dynamicsmainl y inth emiddl e

31 parto fth eglacis ,whil ea mor eregula r formo falluvia l sedimentationende d the processan dshape dth erafi aplain .Thi smod eo fgenesi si sreflecte di nth edistri ­ butionpatter no fth erafi amaterial si nth esurve yare awhic hca nb edistinguishe di n so-called 'mountainrafia' ,consistin go fmainl yangula r stonesalon g themountai n rangesan d 'normalrafia' ,whic hconsist so fmainl yrounde d stonesan d gravelswhic h areextensiv ethroughou tth eres to fth earea .Th e'mountai nrafia 'ha sbee ncalle da 'fanglomerate'b yPannekoe k (1968).Va nDorsse r (1974)report sa thicknes so fu pt o 7m fo rrafi adeposit so fth esurve yarea . Duringth eQuaternary ,degradationa lprocesse s accompaniedb yloca ldepositio n prevailed,th elatte rmainl yi nth eGuadian avalley .Variou sprocesse scontribute dt o thedownwearin gan d incisiono fth ePliocen esurface .I ti squit eprobabl e thatre ­ liefinversio ndu et oth ehig hresistanc et oerosio noccurred ,sinc emos to fth e thickestan dbes tconserve drafi aremnant sno woccup yhig hposition si nth e terrain althoughthe ywer edeposite di nleve lo reve nslightl ydepresse dposition s (asvalle y deposits).Mino rtectoni cevent shav econtribute dt oth e shapingo fth erelie fdurin g theQuaternary .Th epresen tlandscape so nTertiar ymaterial sdispla ysevera l fault systemswhe nviewe do nai rphotos . Inth efollowin gparagraph sa descriptio ni sgive no fth eunit srepresente do n thelandtyp ema po fth estud yare a (Fig. 3), thatreflect s thegeologica lhistor ya s outlinedi nth eforegoin gpart .Thi sdescriptio ni smainl ybase do nth e geological compilation (IGME,1970) ,supplemente db ysom eadditiona lfiel d information.A pro ­ blemi nth eus eo fth ecompile d geologicalma pi stha tth eorigina l sheetshav eno t beenupdate dprio rt othei rmatching .Thi s leadst odifferen t interpretationso fth e samephenomen ao nthi smap .A ssuc hth elegen dshow sarkoses ,e.g. ,bot hi nth eOli ­ gocènean di nth eMiocene ,whil eth enewe rconcept srestric t themt oth eMiocene . Thiswa stake nint oaccoun tan dcorrecte dwhe nextractin g thegeologica lequivalent s ofth elandtype so fth esurve yarea .

(Q) Hi IIB of Ordovioian quavtzites and silioious slates Theywer eforme db yth eHer - cyneacyn norogenesis .Nea rGuaren asmal lhill sconsis to fthes ematerial swhil eth e majomaj runi ti sforme db yth eSierr ad eSa nServan .Thi si sa nerode dope nanticline . Associateddebri sslope san deve nsom emino rarea so fmountai nrafi ahav ebee nin - eludedi nthi sunit .

(G, UndulaUng landtype on Paleozoic granites and gneisses Underthi sheadin gth e granitesan dgneisse so fth estud yare aar ecombined .Sinc e theyar erelativel ysimi ­ lara nchemica lcomposition ,the yar etreate da son eparen tmateria l forth e soilso f theare a Thelarg ebatholit hN.W .o fMérid aconsist saccordin gt oIGM E (1954b)o f calclcalka l grmiteo fth e^ micatype jwit ha dominmc eQ fbiotit e^ ^sco_

In lilit"fi"; :rathS rCOarSe -Srained> hanging tomicrogranite s locallywithi n thelimit so fth ebatholith .Mahmoo d navol A* -U tainingbetwee n4 0an d4 5• ,T , * *re Presentative samPle as C°n' and4 5, felspar sb yvolume ,o fwhic hmor e than2/ 3 arealkali - 32 felspars.A mino r intrusionS.E .o fMérid ao nth elef tban ko fth eGuadian arive ri s ofa fine-graine d typeo fgranite ,accordin gt oIGM E (1950).Th egneissi cuni t lies northo fValverd ed eMérida .O nth egeologica lma pthi suni ti sinclude di nth e granodiorites.Accordin gt oMahmoo d (1979)i tconsist smainl yo fmedium-graine d orthogneissan dsom e interlayeredmedium -an dfine-graine d gneissfo rwhic hh edoe s notcommi thimsel ft oa classificatio ni northo -o rpara-gneiss .H edescribe sa sam ­ plewhic h showsroughl y equal felsparcontent ,highe rquart z content and lowermic a contenti ncompariso nwit hth eabove-mentione d granite sample.

(S) Undulating to rolling landtype on Paleozoic schists Thislandtyp econsist so f intermediatean dbasi cmetamorphi crock san doccur sa sthre eunit s:a larg eon eex ­ tending northan deas tfro mMérida ,o nth egeologica lma pmarke da sgranodiorite ,an d two smallerone s alongth esouther nban ko fth eGuadian ariver ,o nth egeologica lma p markeda sMiocen ean dPliocene .Mahmoo d (1979),wh ostudie da cros s section from Proserpina Lake (situateda t5 k mnort ho fMérida )t oValverd ed eMérida ,foun dth e largeuni tt oconsis to fth efollowin gmaterials :fine-graine d hornfelsic schist, medium-grained hornblende schist,medium -t ocoarse-graine d amphibolite,th elatte r locally overlainb ysecondar y carbonate rockan darkose .Th eunit s southo fth erive r have lostmuc ho fthei r originalMiocen ean dPliocen e coversan dsho wschist sa to r nearth esurface .

(A) Undulating to rolling landtype on Miocene arkoses Thisunit ,southwes to fth e Sierrad eSa nServan ,encompasse sth eare awher e arkose formsth emai nparen tma ­ terialfo rth esoils .O nth egeologica lma pi ti sshow na sundifferentiate d Miocene. Itconsist smainl yo fmedium -an dcoarse-graine d arkose.

(F) Undulating landtype on fine sandy Miocene clays Thisuni tcover sth eare anort h ofth eSierr ad eSa nServan ,aroun dth evillag eo fCalamonte .O nth egeologica lma p iti sshow na sundifferentiate d Miocene.Th emateria l isa fin esand yclay .Th esan d issimila r inminera l compositiont oth esand so fth earkose .Th euni tca nb econ ­ sidereda sintermediat e betweenth eM an dth eA units .I ti sdistinguishe d from those becauseo fit sdifferenc ei nrelief ,lim econten tan dsoi lmantle .Thi s fine sandy Miocene clayi sfrequentl y foundunderlyin gran aplateaus .Th eR uni tjus tnorth-wes t ofCalamont ei sunderlai nb yit .Dissectio no fthi suni texpose sth emateria l inth e slopes.

(M) Gently undulating to undulating landtype on Miocene clays Twounit ssout ho fth e Guadianarive rar eindicate db ythi ssymbol ,show na sundifferentiate d Mioceneo nth e geologicalmap .The ybelon gt oth edee pclay so fth eUppe rMiocene ,whic har echarac ­ terisedb yth epresenc eo flarg eamount so flim ei nth euppe rfe wmetres .This ma ­ terial,whic hth egeologist scal l 'caleno',i sth emai nconcer no fthis study .O n this subjectVa nDorsse r (1974)quote sCoqu e (1962),wh ofavour sa naeolia n source

33 forth elim ei nsimila rdeposit s fromTunesia .

(R) Dissected plateau on Vlio-Vleistocene 'Rafla' deposits Inthi sunit ,whic hi slo ­ catedalon gth esouther nsid eo fth ebroa d Guadianavalley ,on efind s theclose d com­ plexeso fcoars ematerial scalle d 'Rana'an dgenerall ydate da stransitiona l between thePliocen ean dth ePleistocene .Mos to fth estone san dgravels ,whic har erounded , areembedde di na matri xo fsan dan dcla yan doccu ra slenses .Accordin g toVa n Dorsser (1974)th emineralog yo fth esand so fthi sdeposi ti sver y similart otha to f thesand so fth earkose .Th ecomplexe sno wstan dou ta spartiall y dissected plateaus whichprobabl yow ethei r formationt orelie f inversion. Goosene tal . (1973)describ e similarrelie finversion sfo rRaiî aoverlyin g Paleozoic rocks.O nth egeologica lma p theunit sar eshow na s'arcilla s areniscosas' (clayswit h sandstone cobbles)o fth e Pliocene.

(I) Nearly level sand-covered Pleistocene planation surface on mixed materials This symbolrefer st oa gentl y slopingplai nwhic hi spresen t over long stretches ofth e southernmargi no fth eGuadian avalley .I ti smos tprobabl ya nold ,mainl y erosional surface,forme di nmostl yredeposite dmaterial s fromth eTertiar y hinterland.Th e surfacei scovere db ysan dwhic hvarie si nthicknes s froma fe wdecimetre s toove r onemetre .Accordin gt osevera l authors (Goosene tal. , 1973;Va nDorsser , 1974; Datiri,1976 ;Nieuwenhui s &Trustrum , 1977)th esan di so faeolia n origin.Th egeo ­ logicalma pinclude smos to fth eT unit sunde rPliocen e 'arcillas areniscosas'whil e parti sinclude di nth eundifferentiate dMiocene .

(7) Nearly level landtype on Holocene deposits of the Guadiana valley Thisuni t coversth ematerial s that fillu pth evalle yo fth eGuadian ariver .Th echaracte ro f thematerial s suggests thata considerabl e parti sno tt ob ecalle d Guadiana alluvium proper,sinc e iti smostl yo floca l origin.Pleistocen e andHolocen e degradationo f theTertiar y landscapesalon gbot h sideso fth erive rha ssupplie d thebul ko fthes e materials.The yvar y fromheav y clayst osand san dgravels .Th egeologica lma p classifies thisuni ta sQuaternar y alluvium.

3.4 HYDROLOGY

The main river of the area is the Guadiana, which, with its major tributaries, normal y carries water throughout the year. Most of the smaller watercourses are

»11 I"", S tte SWmeT- ™S aPPlleS t0 the St— °f the ^ous «* PeS md t0 the TertiM7 ClayS aS W611 rr^z^iS)"f d ht 01o fth equartsit ehiiis ; >**—»»— «*** those Learns that— potenU^for'r^vty* ^ "^ ^ ^^ °*£ e^ ^« thatth e potentialfo rth eutilisatio no fgroundwate ri srathe r low.A ssuc hth ecit yo f

34 Mérida drawsit swate r supplyfro mtw obarrage swhic hhav ebee noperativ e since Roman times. Irrigationwate ri sdraw ni nlarg equantitie s fromth eGuadian a riverwhic hi s regulatedb ya nelaborat e systemo fbarrage si nit suppe rcourse . Beforeth eGuadian a riverwa sregulate db yth eaforementione d structures itha d aver y irregular regime,du et oclimati c factorsan da poorl yprotecte dcatchment . Discharges couldvar y from less that0.2 0m / si na ver ydr ysumme rt oove r 1000 0 m/ sa smeasure di nth ewinte ro f1947 .Th eaverag e discharge overth eperio d 1936- 194Swa s12 8m /s .Al lthes evalue swer emeasure dnea r Badajozaccordin gt oIGM E (1950, 1954a).A pea kdischarg eo f1 000 0m / si sequivalen tt oa discharg eo fap - 3 _2 proximately0.1 5m /s.k m catchment.I fthi stendenc yi sdisplaye db ya majo r river, itsmino r tributariesmus t showi ti na mor epronounce dway ,especiall yi fth estor ­ agecapacit yo fsuc hcatchment s islow .A ssuch ,th estream so nigneou san dmetamor - phicrock swil l dischargemos to fthei rwate ri nth efor mo fdirec t runoffan dlittl e ornon ei nth efor mo fdelaye d dischargeo rgroundwate rdischarge .Th esam e applies toth eMiocen e clays,whic hma ystor e somewate ro fth efirs train si nthei rcracks , butwhic h showa hig h directrunof f lateri nth erain ywinte r seasonwhe nth ecrack s areseale dan dth eimpermeabl e charactero fth ecla yprevails .Petrocalci c horizons accentuate thisbehaviour .Th earkos e landscapeswil lprobabl y showmor edelaye d dis­ chargean dgroundwate rdischarg e sinceth einfiltratio nan dpercolatio ni nthi sma ­ teriali sexpecte d tob esomewha thigher .Th einvers erelationshi p betweenper ­ meabilityo fmaterial s influencingth eeffectivenes so fth estorage ,an dpea k flows measured isdemonstrate db yHalasi-Ku n (1973)an dMeijerin k (1977).Th edensit yo f thedrainag enet si shig ho ngranit ean dgneiss ;o nth eothe rmaterial so fth esurve y areai ti srathe rvariable ,sinc eth etime-dependen t incisionha sno tproceede dt o allareas .I nth eMiocen e clayarea ,mos tvalley s showrathe r flatbottom si npar t duet oinfil lb ysediment s fromth einterfluves .Othe r landscapes generally showval ­ leytype swit hmor epronounce d forms.Fo rmor edetail sreferenc ei smad et oSectio n 3.5.

3.5 PHYSIOGRAPHYAN D SOILS

Inthi s sectiona descriptio ni sgive no fth ephysiograph yan dsoil so feac h unito fth ema p(Fig .3) .Typ ean dlocatio no fth ecalci chorizo ni nth esoil so f theseunit si sgive ni nth edescriptio no feac hlandtyp etoo . Thema po fFig .3 wa scompile d from severalphot o interpretationan dfiel d stu­ dies carriedou ti nth eare ai nth eperio d 1974-1980.I twa slocall y completedb yth e authorb yth einterpretatio no faeria lphotograph s (scaleo f1 : 3 3000 ,1956) .A sa basema pa blow-u po fth e1 : 20 000 0topographi cma pserved .

(Q) Ullis of Ordovioian quartsites and silicious slates Thisuni tinclude sth e quartsitic ridges togetherwit h theirdebri s slopes.Thei rrelie fi scharacterise da s steeplydissecte d forth eridges ,an dhill yfo rth edebri s slopes.Th eunit sar e

35 mostly devoido fan ysoi lcove ran da smiscellaneou s landtypes theywoul d qualifya s Rock landan dRubbl e landrespectively . Limei scompletel y absent from thesema ­ terials.

(G) Undulating landtype on Paleozoic granites and gneisses Thegneissi clandscap e canb edistinguishe d tosom eexten t fromth egraniti c one,i nhavin gwide ran dshal ­ lowervalley san di nbein g less intensely dissected,resultin gi na gentl y undulating topography.Th esoil so fthes e landscapesar egenerall y shallow,coars e texturedan d non-calcareous.Xerochrept san dXeropsamment s (typican dlithi c subgroups forboth ) arecommo nsoil so nth edivide san dslope so fthi s landscape.Th evalley s areoccu ­ piedb yth etypi can daqui c subgroupso fthes e same soils.Occasionall yi nth egran ­ itean dmor ecommonl yi nth egneis s areas,thes e soilsar eassociate d with Haplo- xeralfs:aqui csubgroup s inth evalle ybottom san dth etypi c subgroups elsewhere. Mahmood (1979)report sth epresenc eo fsom ever y limited areaso fsoi lo nbot h gran­ itean dgneis swhic hhav ea continuou s soft calcichorizon ,bu twhic hma yb ehardene d locally.Th elim eeithe rpenetrate s theunderlyin g saproliteo rlie so nto po f the saprolite.I nth egranit e area thiswa sobserve d nearth etransitio no fth eM land - typean dals oclos et oa limeston e outcrop,whil eth eobservatio ni nth egneis s area wasmad ei nth ecentr eo fth eunit .

(S) undulating to rolling landtype on Paleozoic schists Thefine-graine dschist s generallyhav ea gentl yundulatin g topographywhil eth ecoarse-graine d ones showa n undulatingt orollin g topography.Th edegre eo fdissectio n isles so nth efine ­ grained ones thano nth ecoarse-graine d ones.Th econve x topsma yhav e calcic hor­ izons,som eo fwhic h show induration.I nthi scas eXerochrept so fth ecalcixerolli c andoccasionall y petrocalcic subgroupsar eth esoils .Chromoxerert san dHaploxeralfs , mostlyo fth etypi c subgroups,ar efoun di nthes eposition s too.I nmor e strongly dissected landscapesmos t topsar enon-calcareous .Xerochrept s andHaploxeralfs , of­ teno fth elithi c subgroup,ar efoun d here.Th eslope s generally show relatively shallowsoil swhic hen di nstrongl y calcareous saprolitei nth ehighe r reaches:Xero ­ chreptso fth elithi cvertic ,paralithi c vertic andlithi c subgroups. Lower downo n the sameslopes ,deepe rnon-calcareou s Chromoxererts andXerochrepts ,bot ho fth e ypxcsubgroup ,occu ri n concavepositions .Xerorthent so fth etypi c andaqui c sub- upshav ebee nfoun di nth evalle ybottoms .The yma ycontai n limebu td ono tsho w calcichorizons .

'LT^ t0V°Tg landtWe °nMi0aene aVk0SSS This ™* comprises therela - Z IZ f"11: ar0UndArr0y °^ Sm S™ ^ «liefi sgenerall y 0UtCT0PSl n MgherreaCh6 S be rnTZ gef " ^ " ^ S-l y rollingan d genialym ea T " "" ^ ^ ^ ^ S°ils° f ^ escape «« or! S" Tl t0fln eteXtUTe d^ m°St *•*-- calcareous.MoÜ tar - outcropsm thehighes treache so fth elandscap ear ecrowne db ypetrocalci chor -

36 izons.The ycarr yth eshallowes t soils:Xerochrept smainl yo fth epetrocalci csub ­ group.Th eslope shav emainl ydiscontinuou s soft calcichorizon swhic hbecom econti ­ nuous locally.Thei rsoil sar eXerochrepts ,mainl yo fth ecalcixerolli csubgroup . Fluventic Xerochreptsar efoun di nfootslope san dcolluvia l terraces.Chromoxerert s ofth etypi csubgrou poccu ri nbotto mpositions .

(F) Undulating landtype on fine sandy Miocene clays Thisunit ,whic hi st osom eex ­ tent similart oth eM unit ,differ sfro mi ti namoun to flim epresen ti nth elandtyp e andi nth echaracte ro fth esoils .Lim ei susuall ypresen ta sdiscontinuou s soft cal­ cichorizon so ra sconcretions .Ther ei sn oconcentratio no flim ea tshallo wdepth s inth ehighes tpart so fth elandscape .Th esoil sar egenerall yfin e texturedan dma y containvariabl e amountso fgravel san dcobble srelate dt oadjacen tran alandscapes . The stones oftensho wver ycharacteristi c distributionpattern swhic hma yow ethei r formationt oa combinatio no fgilga îan dslop eprocesses .Simila rphenomen awer eob ­ servedi nth eT an dR unit si nth esoil sunderlyin ga san dcove r (Nieuwenhuis& Trustrum, 1977).Th emai n soilsar eXerochrept so fth ecalcixerollic ,verti can d typicsubgroup san dHaploxeralf so fth ecalci c subgroup.I nlo wposition sChromoxer ­ ertsmainl yo fth etypi csubgrou par efound .

(M) Gently undulating to undulating landtype on Miocene clays Thelandtyp eca nb e describeda sa dissecte dplateau .Th evalley sar emostl ybroa dan dgentl ysloping . Theinterfluve s oftenhav e slightlyelevate d edges.Thei rcentra lpart scontai nman y closeddepressions .I nothe rplace sconve xridge s formth eremnan to fth eforme rpla ­ teausurface .Th esoil sar emostl yfin et omoderatel y finetextured .Th eplatea u edgesan dconve xridge sar echaracterise db yrelativel y shallowsoil swit hpetrocal ­ cichorizons :Xerochrept smostl yo fth epetrocalci csubgroup .Mos tslope ssho wcon ­ tinuous softcalci chorizons :Xerochrept smostl yo fth ecalcixerolli c subgroup.Val ­ leybottom san ddepression sar echaracterise db yChromoxerert s (mostlytypic )an d their intergrades towardsth eInceptisols :verti c Xerochrepts.Thes e soils generally havediscontinuou s softcalci chorizon sa tgreate rdepths .Thi sdistributio npatter n isillustrate d inFig .1 0b yth ecros s sectionA Ean db yth eai rphot o (Fig. 4).

(R) Dissected plateau on Plio-Pleistocene 'Rana' deposits Thisuni tgroup ssom e weaklyt omoderatel ydissecte d remnantso fa platea uupo nwhic hdeposit so fRan ao f variable thickness coverarkos eo rsand yMiocen eclay .Locall y someaeolia n sands formth eto po fthi s sequence.Th etopograph yi snearl y levelt ogentl yundulatin gi n thecentra lpart san dundulatin gt orollin g alongth edissecte d edges.Her eoutcrop ­ pingran a gravelprotect sth esurfac eagains tfurthe r erosionan dcause sth eforma ­ tiono fth echaracteristi c 'ranashoulder' .Th esoil so fth ecentra lpart so fthi s unitar emainl y coarseove r finetextured .The yar emostl ynon-calcareou s inthei r upper layersan dma ysho wdiscontinuou s softcalci chorizon s and/or discrete lime nodulesa tdepth .Th emai nsoil so fth enearl y levelsurface sar eVertisol so rAlfi -

37 m a S Arroy de san servan in whichmos to f thi\Lst5SoL ::ri7oL?ntrrt:d T I ,° lighttone so nth e rZm Z t \™ ridges and Plateau edgeswhic h showu pa s tiono fth ethre eprofiïe sI fr^" 1?" h°rizonS at °r ™* thesurface .Th eloca - cated.Profil eE U"o f '4 -^T ^S** °fth e «°ss sectionA Eha sbee nindi - j-ig.4 1 xsindicate dtoo .

38 solscovere db ysan dwhic hclassify ,accordin gt oth eSoi lTaxonom y systema sThapto - XeralficXerorthents ,Aqui cXerorthent san dTypi cHaploxeralfs. Th evalley swhic h havea sandfil lhav eXeropsamment smainl yo fth eaqui c subgroup.Nea rth eedge sver y gravellyHaploxeralf san dRhodoxeralf soccu rmainl yo fth etypi c subgroup,whil eth e slopesar echaracterise db yver ygravell yTypi cXerochrepts .

(T) Nearly level sand-covered Pleistocene planation surface on mixed materials This uniti sfoun d alongth esouther n limito fth eGuadian avalley ,i tshow sa ver ygentl e slopetoward sth eriver .Th esurface sar ecovere db yan aeolia nsan dcove ro fvari ­ ablethickness .Th etextur eo fth ecove rvarie s from sandt osand y loam.Th eunderly ­ ingmaterial swhic hvar yi ntextur e frommoderatel y finet ofin eofte nsho wa charac ­ teristicmicrorelie fwhic hi sblankete db yth esan d cover.Consequentl yth esoil s vary fromcoars et omoderatel y coarseove rfin etextured .Th edee pcoars e textured soilsclassif y eithera sXeropsamment so ra sXerorthents ,in bot h casesmainl yo fth e aquic subgroup.Th edee pprofile si nth eslightl yheavie raeolia nmantl eclassif ya s Xerochreptsmainl yo fth etypi c subgroup.Whe nth eunderlyin g terracemateria li s closert oth esurface ,Thapto-Xeralfi cXerorthent s togetherwit hHaploxeralf sar e found,whic h showth einfluenc eo fth esand ycove ri nthei r tops.Th eaeolia ncove r isnon-calcareou sbu tth eunderlyin g terracemateria l contains lime.I nsoil sde ­ velopedmainl y from thismateria la tdepth so fabou t1 m ,eithe ra discontinuou s soft calcichorizo ni spresen to rdiscret e limenodule sar efound .Combination so fthes e twofeature sar eals oencountered .

(V) Nearly level landtype on Bolocene deposits of the Guadiana valley Thevalle y surfacei sinterrupte db ynumerou s abandoned channelsmos to fwhic hhav ebee nfille d upi nlevellin g operationsfo rirrigatio npurposes .Th evalle yca nb edivide d into rathercoars e recentalluvi aalon gth epresen tbranche so fth eriver ,an dth eolde r valley fillwhic hi sheavie rbu tlocall yshow sa naeolia nsan d cover.Bot hunit sar e crossedb ynumerou schannel swhic hanastomos e irregularlyi nth eolde rvalle y fill andmeande rparalle lt oth epresen tstreambed si nth erecen t alluvia.Th esoil so f therecen tpar tar emainl ymediu mt ocoars e texturedan dweakl ydeveloped .N olim ei s present.Th emai n soilsbelon gt oth etypi can daqui c subgroupso fth eXerofluvents , Xerorthentsan dQuarzipsamments .Xerochrept smainl yo fth efluventi c subgroupar eal ­ sopresent .Th eolde rvalle y fill showsHaploxeralf san dChromoxererts ,bot hmainl y ofth etypi c subgroups,togethe rwit htypi cXerorthent swher eth esan dcove ri spro ­ minent. Locallyth eproportio no fVertisol st oAlfisol s increases towardsth eedge s ofth evalley .Th eolde rvalley-fil lpar to fth elandscap eshow scalcareou s soilma ­ teriala tdept h combinedwit hdifferen tproportion so flim enodule swhic h forma cal ­ cichorizon .Accordin gt oGoose ne tal . (1973)th enodule sar eo ftw otypes :autoch ­ tonousan dallochtonous .

39 3.6 VEGETATION,LAN DUS EAN DAGRICULTUR E

Accordingt oUNESC O (1970)th eare ai smappe da s'formation so fth eMediter ­ raneanevergree noa kstage' .Thi ster mrefer st oth e'potentia lvegetation' ,whic h meansth evegetatio na si twoul db ewithou tth einterventio no fma nan danimals . The holmoa kfores t (Queraue ilex) isa nope nfores twit hshru bundergrowth .Onl ysom e patchesremain ,an dthes ehav ebee nturne d intosemi-natura lvegetatio nlocall ycall ­ ed 'dehesa'.Thes edehesa sforme dfro mth eorigina levergree noa kfores taccordin gt o Spiers (1981)a saresul to fgrazin gan dburning .Som eoa ktree swer eretaine dan d periodicallyprune dt ostimulat eacor nproductio nwhic hserve dfo rth efattenin go f pigs.Th ecutting swer euse dfo rcharcoa lproduction .Mos to fthes epasture swer e usedm a5- 8yea rrotatio nwit hon eyea ro fcereals .Thes edehesa sar eno wprogres ­ sivelyeliminate di norde rt ogiv ewa yt omechanise dfarming .Eve no nth epoore r product^ arSbeln gClearS d n°W ln0rde rt 0Pl» t Eucalyptus speciesfo rwoo d

Dryfarmin gi spossibl ei nthi sare aonl ywhe nspecia lmeasure sar etake nt o conservemoisture .Th efollowin grotation so fannual soccu r (RuralSurve yStaff ,

- Cleanfallo wo r'barbech olimpio' .Thi simplie stha twintergrai n (wheat,barley , oatso rrye )i sgrow never yothe ryear .A ssuc hth esyste mi sals ocalle d 'ahoy vez' .

Ct0ber harVeSt6dl nJUn S rJU1 f f Il nTsYhM " ° ^ ° ^° ^ ^°™g /ear-Th e SgraZS dt m the£al 1WhS nth Slm d 1Stille d la"ofo " ;nUI,S Stillag e1S PraCtiSS d - alio!maximu m nexïT^^r7tyea ri norde rt oconserv emoistur '™ eb y'dus tmulchina "**« ' N™, * tillth efal lo fth e sownan dth ewhol ecycl erepeat sitself. ' " ' W ^ *"* " - Thecultivate dfallo wo r'barbech osem i11pHn ' ru- • -,• theaforementione dwintergrai ncrls i t 7 ^ ***th e r°tati°n °£ d inthi scas eth egrai T ubbt I! d ^ ** *tolerant "ops. - springo fthelx tye ^ CL"Ï ^JT" ^ ^ SUnflowe ro rmelon s are sown.Th ecultivatio no fthes ecron si« ,a ' ordert omak eopt^a lus eoHc«™ " * ^^ **""" ^ * n iveiyin o^r™::: s2 :::t™ r ™ -—- are, however, often found on soils which eto^^ °* ^^ ^ ^

Huizing (1979) has made a study of te Toc f * T^ '""**' servation measures on yields of -en above-mentioned water con- data fromMérida, supplemented «7-T™ "^ * ^ "^ * USed -teorological n stract a waterbalJ d™ ^l °T° from the station Talavera to con- & the retical model (1979) and Doorenbos &Pruit t (WTT^T ° of Doorenbos & Kassam C mPUted yieU de result due to moisture deficiency i 't7 ° ^ P^sion that will The yield reduction is expressed Vari°US StagSS °£ dereloP>nent of the crops. is » Kassam (1979) as: ,taijnum ^^ "/^ ^fined by Doorenbos yield for a high producing variety adapted to Table 5. Yield depression asa percentage ofY m (Doorenbos &Kassam , 1979), duet o moisture deficiency fora number ofcrop/soil/managemen t system combinations forth e Mérida area according toHuizin g (1979).

CroP Storage capacity Rotation Yield depression(% ) in thesoi l(mm )

wheat 300 clean fallow 0 wheat 300 cultivated fallow 40 wheat 150 cleanfallo w 35-40 wheat 150 cultivated fallow 40 barley, vetch and oats 300 cleanfallo w 0 barley, vetch and oats 300 cultivated fallow 0 bar1ey , vetch and oats 150 cleanfallo w 0 barley, vetch and oats 150 cultivated fallow 0 grapes 55

thegive nenvironmen twit hgrowt h factorsno tlimited' .Fo rth ecomputatio no fth e reference évapotranspirationh euse dth eradiatio nmethod .H econsider stw osoil s witha moistur e storage capacity,i nth eroo t zoneo fth ecrop sconsidered ,o f13 0 and30 0m mrespectively .Workin gwit hmedia nmonthl y rainfalldat a (rainfall thati s exceeded once everytw oyears) ,h efind sth eresul treporte di nTabl e 5.Fo rwhea ti t turnsou ttha tth ecritica lperio d fallsi nth einterva lMarch-June .Th emai nconclu ­ sioni sthat ,o fth etw omoistur e conservationmethod s considered,th eclea n fallow onlymake s senseo nth esoil swit hth elarge rwater-holdin g capacities.Fo rgrape sn o particular soilwa sconsidere d sincei twa sassume d thatthi scro puse dal lprecipi ­ tation.Th eresul t shows thatth eclimat ei sno toptima lfo ra maximu mproductio no f grapes.I tmus tb eremarke di nthi srespec t thatth equalit yo fth eproduc twa sno t taken intoaccount . The only areawher e irrigated farmingi simportan ti sth eGuadian avalle yan d itsimmediat e surroundings.Th emai nannua lcrop sgrow nunde rthi s farming typeare : sugarbeets,wheat ,sorghum ,rice ,fodde rcrop san dmaize ,a swel la spotatoe san d othervegetable so fman y typesan dtobacco .Th emai n annualcrop sar epears ,peaches , apricotsan dapples . The averageyield so fth emajo r cropso fth eare avary ,dependin go nth elan d qualities,fro m1- 2ton/h afo rdry-farme dwhea tan dfro m1-2. 5ton/h afo rdry-farme d barley. Sunfloweryield s approximately 1ton/h a (dry-farmed),whil eth eyiel do f grapes (unirrigated)varie s from3.5-1 0ton/ha .Irrigate dwhea tan dbarle ybot hyiel d approximately4 ton/h aan dirrigate dmaiz ebring sapproximatel y9 ton/ha .Thes e data arederive d fromMarsoed i (1981).

41 4 Observations

Theare arepresente do nth ema p (Fig.3 )form spar to fa zon e around the cityo f Méridawhic hha sserve dfo rfiel d studieso fth eSoil sDepartmen to fth e ITCsinc e 1966.Severa lM.Sc .these shav ebee nwritte no nvariou s aspects,an d the areaha s beenth esubjec to fintensiv e soilmappin g fortrainin gpurposes .Th emateria l thus gatheredha sserve da sbackgroun d informationfo r thispaper ,particularl y thosedat a related toth eMiocen ecla y landtype (M),wher emos to fth e investigationso fthi s studyhav ebee ncarrie d out.Th e following approachha sbee nchose nfo r the treatment ofal lthes edat afro mdifferen tsources . InSectio n4. 1a detaile d accounto fth e informationuse di sgive ni ntabula r form.Th emethodolog y applied inal ldetermination s andobservation si streate di n Section4.2 .I nSectio n4. 3profil edescription s and standard analytical data for3 sitesselecte d asrepresentativ e arepresente d anddiscussed .Referenc e ismad et o theothe rprofile sno treproduce di nthi stex ti faspect srelevan tt othi s studyvar y significantly.Sectio n4. 4 containsa cros s sectiono fth eMiocen ecla y landtype(M ) showing thespatia lrelationshi pbetwee nth esoil streated .I n Section 4.5 the main featureso fth emicromorpholog yfro mth emateria l available are listed and discussed. InSectio n4. 6 specialdetermination so nlim ean dcla ynodul e samples carried out for thisstud yar e listedi ntabula r forman ddiscussed .I n Section4. 7 datao nstabl e isotope ratioso fthre e lme samples fromprofil eRiol a 1ar e reported.Micro - paleontologicalanalyse so fthes e samesample s arefoun di nSectio n 4.8.I nSectio n 4.9a numbe ro fconclusion sar edraw n fromth e informationcontaine di nth ediscus ­ sionso fth evariou saspects .Th eexperiment scarrie d outwit hmaterial scharacter ­ ised inSectio n4. 6 aretreate di nChapte r5 .

4.1 SOURCESO F INFORMATION

Table6 list sal lmateria lrelatin gt oth eMiocen ecla y landtype (M).Th eana ­ lyticaldat afo rth eprofile sreporte d jointlyb y Roy (1974)an dJayarama n (1974) are basedo nanalyse scarrie dou ta tth eLaborator yo fPhysica lGeograph y and Soil Scienceo fth eUniversit yo fMsterdam ,whil ethei rmicromorphologica l studieswer e carried outa tth eMicromorpholog yDivisio no f theNetherland s SoilSurve y Institute in^eninge n (STIBOKA).Th eanalytica ldat a for theprofile s reported jointlyb yRa o ml" g C974 )Wer SCarri6 d °Ut^ thSSam SlabOTat0 ^i nA-stexdam .The ^ WZT TriPti0nSWSr e^ atth e ^mational SoilMuseu m (ISM)i n Wageningen.Micromorpholog yo ftw oadditiona l samplesdraw n forthi s studywa sde -

42 Table6 . Sourceso finformation .Th etabl e indicatesth eauthors ,number , classificationan dlocatio no fth eprofile s aboutwhic h informationwa s available.Informatio nfro mth eProfile s PI,P2 , P3an dP4 include sde ­ scriptionso fassociate d deepaugerings .I nth ematri xa cros s (x)indi ­ cates that informationi spresen tan da poin t (.) indicates thatinforma ­ tioni slacking .

Jayaraman (1974) Jung; (1974) and and Roy (1974) Rao (1975)

(O > > > hd •Ö M tfl •-a H. t-i ti ti to W U) j> 0 >-i i-i ti S t—» o 0 o II tu vi vi V! M 0 0 O •—OD _ tO u>

X TJ X m CD ft) 3" Vi fD (U ET VI 3* Vi n> re i-l rt H rt ti T3 l-( I-) tl -Ö i-i >o reir viQi i-l rt |J O M O * 9 H- o o Q H« 9 ' 0 H- o i-l O 0 o o 3 o O H- 3 O B o B n n o C o 3* o 0 3* X O o 0 3- n n » ri m X n rt> X X X i-l M ft) w fD f-> r» ii f» m ft rt> t-» •ö o t) O tl •ö o tl i-i i-i fl> 1 •a o rt H' rt H- rt t- n> ro m f-T H* o O ff)h t-1 tl ti fi o rt rt rt rt O

Location siteo nth ema p(Fig . 3) 1 2 3 4 ABCDE

Profiledescriptio n

Analytical data

Granulometric analysis pH (H20an dCaCl 2 orKCl )

Electrical conductivity

Organic carbon percentage

Calcium carbonate equivalent

Gypsum

Exchangeable cations

Cationexchang ecapacit y(CEC )

Base saturation(BS )

X-raydiffractio no fcla y

Micromorphology

scribeda tth eIS Mtoo . Jungan dRao' sprofile ,P3 ,i sth eequivalen to fProfil eE1 8o fth ecollectio n ofsoi lmonolith so fth eISM .O fth eanalyse sreporte dfo rE18 ,granulometr yan dX - raydiffractio nwer ecarrie dou tb yth eIS Mwhil eth eremainde rwer edon ea tth e

43 Royal Tropical Institute (KIT) in Amsterdam. New samples were drawn up to a depth of 540 cm from profile Arroyo 1. These were subjected to X-ray diffraction by the ISM in order to study the clay mineralogy ofth e subsoil. In order to facilitate comparison of the X-ray diffraction data ofth e two laboratories, they are,all rated according to a four point scale as indicated on the data sheets. Special determinations on lime and clay samples as listed in Section 4.6 were carried out by the author in the ITC soils laboratory. In Section 4.7 there are stable isotope analyses ofIk e samples ofth e Riola 1 profile, which were carried out atth e Physics Laboratory of the University of Groningen by W.G. Mook. Micro- paleontological analyses ofth e same Riola samples (Section 4.8) were carried out by A.C. van Ginkel of the Institute for Geology and Mineralogy of Leiden University. For the location of the profiles and sample sites ofth e area see the map (Fig. 3), the aerial photograph (Fig. 4)an d the cross section (Fig. 10), which carry the corresponding site numbers and profile numbers.

4.2 METHODOLOGY

Under this heading the methodology for obtaining all determinations and other operations such as profile description, classification etc. isdescribe d briefly.

onomv sZTTT °f the S0US- Pr0£lleS WSre ClaSSlfied aCCOTding to the Soil Tax- ( SmVey Staff 1975) Cl TL I ' - ^ -^ationS were updated accordingt o the approved amendments to this system of May 5 1978

Soil Lm! tSOriPUOn- ^ Pr0£lleS W6re deS^bed aCCOTd-g to the Guidelines for ha^e n^nrV™ ' 1%7)- ^ *™ Produced in Sections 2.1an d zo have been added to clarify some features

to remTiXf T^ ^ * *" ^ ^ £^™ ™> treated in order rganiC matt6r llme fraCti n PI tw bv 1 I ° ** - ^ ° — than 50 m was ipiit in two by means ofsieving , while the fTOrH™, -c- »ith sodi« carbonate/sodi» JLtjL^ f '"" ^ S° m ™S ^^ pipettemetho d frac «»»s,av „a silt,m ti^z^z™ :i* °" " makeu p 100% . Theresul t i* \ fractions in order to PBTh e oü i lt\ PreSS6d" aWeigh t %(maS S fraction). pa. lnesoi lwa s shakenwit hH 70a ta rati o „f i., c t whichth ep Hwa sdetermine db ym eans ofa 2 T ' *" ^ ^ with0.0 1 mol/1CaC l . electrode.Th eprocedur ewa s repeated Electrical conductivity (EC) Thi=- expressed asmS/c ma t2S°C . meaSUr6di nth e satoation extract and Organic carbon percentaqe (C 7) TM method (Black,1965) ,excep tfo rProfile" ^^t 61"***1 accordingt oAllison s- s 6qUlValentt 0Profil e thisprofile ,th edat af romth eRoya lT r T " ™- *<* minesorgani ccarbo naccordin gt n ,1, „*!? InStltutear e reported,whic hdeter - * «*«- »,a «^r;™::^ ^ «- ««*. <»«>. -*,.»« 44 Calcium carbonate equivalent (CaCOg%). Thiswa sdetermine daccordin gt oth e methodo fScheible r (volumetrically).Th edat ao fProfile s P1,P 2an dP 4o fJun g (1974)an dRa o(1975 )wer edetermine d gravimetricallyaccordin gt oWesemae l (1955). Theresul ti sexpresse da sa weigh t %(mas sfraction) . Gypsum. Thiswa sdetermine db yprecipitatio nwit haceton ean dmeasure dturbidi - metrically. Exchangeable cations. Cationswer edisplace db ya solutio no f1 mol/ 1NH.OAc . Forcalcareou s soilsth eammoniu macetat e solutionwa sbrough tt op H8. 2prio rt oth e extraction.Despit e thisprecautio n someC aion sno tderive d fromth ecomple xwer e determinedi nth esolutio na sanalytica ldat ashow .A ssuc hth edeterminatio n should ratherb ecalle d 'extractablecations 'whe ndealin gwit hcalcareou s soils.Th edat a areexpresse di nexchang eequivalent sa smmol/10 0g soil . Cation exchange capacity (CEC). Thesample swer esaturate dwit hN a bytreatmen t with sodium acetate.Subsequentl yth eN a wasdisplace db ytreatmen twit h ammonium acetate (buffereda tp H8. 2i nth ecas eo fcalcareou s samples).Th edisplace dN a was determinedan dexpresse di nexchang eequivalent sa smmol/10 0g soil . Base saturation (BS). Thisfigur ewa scompute db ydividin gth esu mo fth eex ­ changeablebase sb yth eCEC ,expressin g thisrati oa sa percentage .Figure s exceeding 100wer erounde dof ft o10 0 %,assumin g thatth ediscrepanc ybetwee nth efigure swa s duet ofre ecalciu mcarbonat ei nth esample . X-ray diffraction of the clay fraction. Wetsample swer emounte do nglas s slides,drie dan danalyse db ya Philip sdiffractometer .Th esample swer e irradiated withC oradiatio nan dscanne dove ra nangl eo f2 9= 2 to2 9= 3 2. Th econtent so f eachminera li nth ecla ywa sestimate d fromrelativ epea k intensities.Th econtent s wereexpresse da s- t oxxx xfo rcla ymineral san d- t o+++ +fo rothe rminerals ,(x ) and (+)refe rt ointermediat e cases.Trace sar eindicate db ytr .whil ea questio n markindicate s thatth epresenc eo fa minera li sno tcertain . Liquid limit (LL). Determinationswer emad eo na numbe ro flim e samplesaccor ­ dingt oth eAST M (1954)procedure .Th eliqui d limitswer eascertaine db yon edeter ­ minationi na rang e between 15an d4 0blow san dcorrecte db ymean so fa nomogra m (Olmstead, 1949).O feac hsample ,mois tconsistenc ywa sdetermine d according toth e Guidelines forSoi lDescriptio n (FAO, 1967). Bulk density. Bulkdensit yo flim esample sha sbee ndetermine db ymeasurin g weightan dvolum eo fundisturbe d samplesdraw nb ymean so fsampl erings .Bul k density ofcla ynodule sha sbee ndetermine d fromth edat aacquire di nth emeasuremen to fth e coefficiento flinea rextensibility .Th ebul kdensitie sar ereporte da sB D(dry )fo r thevalue s derived fromweigh tan dvolum ei na noven-dr y condition.Fo rth ecla ynod ­ ulesamples ,a bul kdensit yi nsaturate d conditionwa sals ocalculated ,b ydividin g the weight in saturated condition byth evolum ei nthi s condition.Thi svalu ei s in­ dicateda sB D (sat.)+.Fo rth elim esample sth esam evalu ewa scalculated ,fo rtw o extremecases ,fro mB D (dry),assumin ga certai nspecifi cweigh tfo rth esoli d phase (Section 4.6.1.2).Th esam eapplie sfo rth ebul kdensitie si nmois tconditio n taken

45 fromth elim ea tth een d ofExperimen tI I(Sectio n 5.2.2 and Table 14)an d reported asB D(moist ). It must be stressed that BD (sat. ) and BD (moist) do not refer to weight dry/volume saturated and weight dry/volume moist respectively, which are the meanings commonly attributed to these ratios in the literature. Inthi sstud yth e needwa sfel tfo ra bul kdensit yo fcla y and lime thatwoul d be ablet opredic t the behaviouro fthes etw omaterial s relativet oeac hothe ri nsaturate d andmois t con­ dition (seeChapte r5) . Grain size of oalcite crystals. Anestimatio no f the average grain sizeo fth e crystals inth elim esample swa smad eb ymean so fapétrographi emicroscope . Forthi s purposepreparation swer emad eo fth edrie dmaterial .Th e fraction smaller than0. 5 mmwa ssprinkle d thinlyo na nobjec tglas s coveredwit hheate d Canadabalsam . Thees ­ timationswer ebase do nth emeasuremen t ofth e long and theshor t axiso fa limite d numbero fcrystals . Coefficient of linear extensibility in saturated condition (COLE sat.). Theco ­ efficiento flinea rextensibilit ywa smeasure d fora numbe r ofcla y nodules,whic h werecoate d indr yconditio nwit hSARA Nresi naccordin gt oBrashe re tal . (1966). Weightan dvolum ewer edetermine d indr y state,the nth ecoatin gwa s scratchedt o al­ lowmoistur et openetrat e afterplacin g theobject so nawe t sponge.Whe n constant weightwa sreached ,volum ewa sdetermine d again.Volum edetermination s weremad eo n thebasi so fweigh t lossupo n immersion inwater .Volume s andweight s were corrected bydeductin g thepar tcorrespondin gt oth eSARA N coatingwhic hweigh s1. 4g/cm 3 (Bouma, 1977).COL E (sat.)wa scalculate d as thecubi c rooto fth erati oo fth esatu ­ ratedove rth edr yvolume ,minu s1 (Grossma ne t al., 1968). Fercentage of water-stable aggregates of the lime. Inorde rt oevaluat eth ein ­ fluenceo fth edegre eo faggregatio no fth e limeo nth e liquid limito fth esamples , wetsievin gwa s applied.Sample swer ebrough tt oth e liquid limit,the npu t througha 50y msiev eb ymean so fvibratio nunde r theapplicatio n ofwater .Afte ra 2 0minut e treatmentunde rstandardise d conditions,th eresidu ewa sdrie d andweighed . There ­ sulti sexpresse d asa weigh t %(mas sfraction) .

Micropaleontology. Sampleso flim ewer edesintegrate db ytreatmen t with H202 and studiedunde ra binocula rmicroscope . Stable isotopes. The stable isotopes C13 and0 18wer edetermine d bymean so fa massspectrograph .Thei r fractionationrate s areexpresse di n°/o oi nrelatio nt oth e standardsample :th ePede ebelemnite . Micromorphology. Large size thinsection swer e prepared using the techniqueo f

Jongerxus& Heintzberge r (1972).The ywer e studiedunde ra pétrographi emicroscope . Mosto fth eterminolog y applied isaccordin gt oBrewe r (1976).

4.3 CHARACTERISATION OFTH ESOIL S

Ofth ematerial sliste d inTabl e 6,thre eprofile s havebee n selected forrepro ­

ducel nthi stext .Riol a1 an dArroy o 1ar erepresentativ eo fth e -high soils'o f

46 p.- S. !*>,••••-

B21c.iiri

lW2ca

»23(\

•'•tB3>'

Fig. 5. Profile Riola 1.Th ephotograp hwa s takeni nth enortheaster n corner of the pit. Someoverburde n ispresen t on thesurfac ewhic h isvisibl e justunderneat h the pole.Th e surface soil,laminate d petrocalcic horizon,continuou s softcalci c horizon and its transitionvi a a 'striped zone'toward s theunderlyin g Miocene clay,hav e beenindicate d with their corresponding horizon symbols. (Photocourtes y ofM . Knibbe.)

theplatea uedge san dfro mth etop so fth eridges .Riol a1 wa sintensivel y studiedb y Jayaraman (1974)an dRo y(1974) .Unfortunatel y thisexposur ewa sn olonge r available forth einvestigation so fth epresen tstudy .Mos tsample sha dt ob edraw n fromArroy o 1whic hresemble s Riola1 closely .Notwithstandin gth efac ttha tProfil eArroy o3 classifies differently fromRiol a1 an dArroy o1 a tsubgrou p level,thi sprofil ei s notconsidere dt ob ebasicall ydifferen ti ngenesi s fromth eothe r two.Ther ei s hardeningo fth ecalci chorizo ni nthi sprofil e too,bu tno tt osuc ha nexten ttha ta continuous petrocalcichorizo ni spresent .Profil eP3 ,whic hi sequivalen tt oProfil e E18o fth eISM ,ha sbee nselecte da sa representativ e exampleo fth e'lo wsoils 'o f valleysan ddepressions .

4.3.1 Profile descriptions and analytical data

Forth ethre eprofile sreferenc ei smad et ophotograph si nwhic hth ecorrespon ­ dinghorizo n symbolshav ebee nindicated .Fig .5 show sa genera lvie wo fth eProfil e Riola1 .Fig .6 show sdetail s from thissam e soil.Fig .7 i sa genera lvie wo fPro ­ fileArroy o 1,detail so fwhic har eshow ni nFig .8 .Fig .9 show sa photograp hmad e

47 l .»•*,; •'..:'. ••' •;•«• "» •-.•' *. *••*-. il . 'f' '

/•'.••

zo^^inPro fl fRiol» 6,T Sltl0n •'th e S°ft Calcic horizon towardsth e'stripe d desinegrate d io uv L»s a"°!,lndi?ates thepoin twher ea 'cla ypillar 'ha s CUy n duleS Each SeCti n f the.easurin g£ s £dp erepresent eS îso1 ™ 0 cm fP.(Phot W ^ ocourtes ^ yo fM .Knibbe.° ') ° ° ofth esoi lMonolit hE1 8whic hrepresent sProfil eP3 . t™ f\Tre\SOilS haVe C°ntinuous so£t cal"chorizon so fwhic hth elowe rboundar y nT tet Trlyin§ Clay 1S lrregUlar °rbr °ken- ^ foll-- te™ areuse dt o xndxat eth efeature srelate dt othi s'striped 'transitio nzone :g LLay yvllavs arelarg eelonmfp H H,,,iwi - theunderlyin ghorizon . " ^ VemCally miented and COlmeCted t0

wS lZS. are Smller Clay b°dieS SeParatSd fr°m the c1^ Pillasb ycrack sfill -

- CZœ/ nodules arestil lsmallp- r m-,-;„i , 1 latd throat the ovenyi„8 c * 1 ' f™* ^ *"»«• ">** °<™ '» »solute s.» , * and ln the "*« »erlying horizons. iMr de ri ft the p me a th.„:,:: ,r ::z:z^ d r " ™ ^ ™ ^ -"*

48 4.3.1.1 Profile Riola1

Site information Soil Classification Petrocalcic Xerochrept. Dateo fexaminatio n May 1973. Authorso fdescriptio n M. Jayaramanan dD.K .Roy . Location App.8 k msout ho fArroy od eSa nServa no nth eArroyo - Almendrajelo road (Riolawin e factory pit). Site 1o n map (Fig. 3). Elevation App.30 5m abov ese alevel . Landform i. Physiographic position Levelt oconve x 'mesita'summit . ii. Landformo fth esur ­ rounding country Moderately undulating. iii. Microtopography Nil. Slope Less than1 %. Landus e Arable landwit h olivesan dgrapes . Climate Semi-arid.

General soil information Parentmateria l :Miocen e clay. Drainage :Wel l drained. Soilmoistur e condition : Dry. Deptho fgroundwate r table :Mor e than4 m . Presenceo fsurfac e stones orroc k outcrops :Man ypetrocalci c fragments;n orocks . Erosion :Moderat e sheet erosion. Presenceo fsal to ralkal i : Nil. Human influence :Plowing .

Brief description of the soil Moderately deep,wel l drained dark reddishbrow n surface soilwit hyellowis hred , claysub-soi lo fmediu m structural development;overlyin g alaminate d petrocalcic horizonwit h many large sub-rounded tosub-angular ,non-calcareou s claynodules ,fol ­ lowedb ya calci c horizonwit h large claynodules .Belo w25 0c mth ecalci c horizon appearsa salternat e stripes,mor eo rles sverticall y oriented with non-calcareous redcla y lumps,a swel la scla yo freduce d greycolours .Re dheav y claywit hmanga ­ nesecoating s appearsbelo w32 5cm ,wit hwel l developed prismatic structurean dpro ­ minent slickensides.

49 Description of soil horizons

0-25 cm Darkreddis hbrow n (5YR3/4 )moist ,yellowis h red (5YR3/6 ) dry,clay ; Ap moderate,fine ,sub-angula r blocky;commo nmediu m limeconcretions ; slightly sticky,slightl y plastic,friabl emoist ,slightl yhar ddry ; common,fine ,tubula r pores;commo nmediu m roots;calcareous ;gradual , wavyboundary . 25-40c m Yellowishre d (5YR3/6 )moist ,clay ;strong ,mediu m sub-angular blocky; Al fewmediu m limeconcretions ;slightl y sticky,slightl y plastic,fir m moist;common ,fin e tomedium ,tubula r pores;few ,fin eroots ;cal ­ careous;clear ,wav yboundary . 40-100c m Petrocalcic horizon,laminated ;few ,fin ean dmediu m roots;many , B21cam large,rounde d tosub-rounded ,non-calcareou s claynodules ;gradual , wavyboundary . 100-250c m Calcichorizon ;pinkis hwhit e (5YR8/2 )moist ,many ,large ,non-cal - B22ca careouscla ynodules ;abrupt ,irregula r boundary. 250-325c m Calcichorizo nwit h claypillar swhic hbrea ku p into clay lumps;calci c B23ca materialan dcla yappea ra salternat estripe smor eo r lessverticall y oriented;cla y lumpsnon-calcareous ;calci cmateria l in soft powdery form;phenomeno no fpseudo-gle ywit hcla yo freduce d greycolours ,al ­ ternatingwit h softcalci c stripes;clay :moderate ,coars e angular blocky;sticky ,slightl y plastic,ver yfir mmoist ,har d dry;fe wcoars e roots;clear ,irregula r boundary. 325-450c m Red (2.5YR5/6 )moist ,heav y clay;strong ,coarse ,prismatic ;stripe s B3 of softlim ealon g cracks;sticky ,slightl y plastic,ver y firmmoist , harddry ;prominen t slickensides;manganes ecoating s over clay;non - calcareous.

50 Analytical data

Particle sizedistributio n (um)weigh t Depth (massfraction ) Horizon (cm) c.san d f.san d silt clay Texture 2000-250 250-50 50-2 2 Ap+ A l 0-40 5.0 12.0 20.5 62.5 Clay B21campetrocalci c material 40-100 n.d. n.d. n.d. n.d. n.d. B21camcla y nodules 40-100 1.2 10.0 23.0 66.5 Clay B22ca calcic material 100-250 n.d. n.d. n.d. n.d. n.d. B22ca clay nodules 100-250 2.9 22.5 33.5 41.0 Clay B23ca calcicmateria l 250-325 n.d. n.d. n.d. n.d. n.d. B23ca clay lumps 250-325 0.5 4.0 13.5 82.0 Clay B3 325-450 0.5 4.5 13.5 81.5 Clay

CaC0„ pH EC 3 Horizon mS/cm % (mass % (mass H20 CaCl. fraction) fraction) 0-40 n.d. n.d. 19.5 40-100 (ca) n.d. n.d. 94.4 40-100 (cl) n.d. n.d. 5.7 100-250 (ca) n.d. n.d. 94.0 100-250 (cl) n.d. n.d. 0.2 250-325 (ca) n.d. n.d. 85.9 250-325 (cl) n.d. n.d. 5.7 325-450 n.d. n.d. 0.5

X-raydiffractio no f thecla y fraction Horizon smec- palygor- kaoli- vermi- tober- quartz tite skite nite culite morite 0-40 x(x) xx(x ) tr (+) 40-100 (ca) n.d. n.d. n.d. n.d. n.d. n.d. 40-100 (cl) n.d. n.d. n.d. n.d. n.d. n.d. 100-250 (ca) (x) xx 1 (+) +(+ ) 100-250 (cl) xx XXX tr ++ 250-325 (ca) (x) XXX ? (+) 250-325 (cl) X xxx(x) tr (+) (+) 325-450 (cl) n.d. n.d. n.d. n.d. n.d. n.d.

Symbols: xxxxabundan t xxx common xx small x very small These terms apply to therelativ e quantities of clayminerals .Th e samerang e applies fornon-cla ymineral s indicated by+ .Bracket s indicate intermediate caseswhil e tracesar e indicated by tr.A ?indicate s that thepresenc eo fa minera l isuncer ­ tain. (ca)= calciti cmateria l (cl)= claye ymateria l n.d. =no t determined = content 0

51 4.3.1.2 ProfileArroy o1

Site information Soilclassificatio n Petrocalcic Xerochrept. Dateo fexaminatio n June1973 . Authorso fdescriptio n Jayaramanan dRo y(supplemente db yElbersen , 1981). Location A roadcu to nth eArroyo-Solan ad elo sBarro s country road,6 k msouthwes to fArroy od eSa nServan .Sit e2 o n map (Fig. 3). Elevation Landform About 270m abov ese alevel . i. Physiographicpositio n ii. Landforrao fth esur ­ :Leve lt oconve x 'mesita'summit . roundingcountr y iii.Microtopograph y :Moderatel yundulating . Slope : Nil. Landus e :Les s than1 %. Climate :Arabl e landwit holives . : Semi-arid. Geneva! soil information Parentmateria l Miocene clay. Drainage Welldrained . Soilmoistur econditio n Slightlymoist . Deptho fgroundwate rtabl e More than3 m . Presenceo fsurfac estone s orroc koutcrop s Manypetrocalci cfragments . Erosion Slight sheeterosion . Presenceo fsal to ralkal i Nil. Humaninfluenc e ,Ni lapar tfro mroutin ecultivation .

Brief general description of the profile Shallow,wel ldrained ,yellowis hbrown ,silt ycla y loam surface soiloverlyin ga hard,indurate dan dlaminate dpetrocalci chorizon ,whic hi sunderlai nb ya soft ,pow ­ derycalci chorizo ncontainin gnon-calcareou s claynodules .Stripe so fsof tcalci c material alternatingwit h clay 'pillars'for mth etransitio n towardsth eunderlyin g Mioceneclay .Th eMiocen e claycontain s lijiiepocket su pt oa dept ho fa tleas tS m . As suchi tqualifie sa sa discontinuou s softcalci chorizon .

52 1 f•- • - ••• •'-. ..il-4 v *..1,• * -, . .v<-'••-. .•.•'• - 'N Vil^..V!.? :.-•-• O'..' - - V .^ . * ÎV» : ^ÏV:

BSS-li. rW^ÏUi.^«™™"»"»"!'""*•*"**• * Fig. 7. Profile Arroyo 1. A thin surface horizon overlies a laminated petrocalcic horizon inwhic h several clay nodules areembedde d (arrow). Underlying thepetro ­ calcic horizon isa continuous soft calcic horizon which contains clay nodules. This horizon merges viaa 'striped' transition zone into theunderlyin g Miocene clay.I n the photograph this horizon sequence isindicate d byth ecorrepondin g horizon sym­ bols.

. • ••- .(321 c

i-V-

i-on symbols ofFig . 7ar eindicate d in thephoto .

53 Description of soil horizons

0-16 cm Yellowishbrow n (10YR5/4 )mois tan d dry,cla y loam;weak ,fin esub - Ap angular blocky structurebreakin g into crumbs;slightl y sticky,non - plastic,friabl emoist ,slightl yhar d dry;commo npetrocalci c frag­ ments;commo nver y finean d fewfin e tubular pores;commo nfin ean dfe w veryfin eroots ;calcareous ;abrupt ,smoot hboundary . 16-55c m Pinkishwhit e (7.5YR8/2 )moist ,whit e (N9/0 )dr y petrocalcichorizo n B21cam consisting ofvariou s laminated sub-horizons;th edegre eo f cementation deminisheswit hdept han dvarie s from indurated in theto p to strongly cemented atth ebottom ;th ehorizo ncontain s few,larg e (1-5 cm),hard , massive,partiall y rounded and partially angular non-calcareous clay noduleso fa yellowis hre d (5YR5/6 )moist ,pin k (5YR7/3 )dr ycolour ; thenodule shav ea lim ecoatin g and showthi npatch y black cutanso f manganesecompound so nsom eo f their faces;fe wfin ean dmediu mroots ; diffusewav yboundary . 55-140c m Pink (5YR8/3 )moist ,whit e (N9/0 )dry ,calci chorizo nconsistin go f B22ca softpowder y limewit hman yweakl y cemented to strongly cemented par­ tiallybroke nlim efibres ;th ehorizo ncontain sman y largecla ynodule s anda tth etop so f intruding claypillar s fewcla y lumpswhic hvar yi n sizefro m2- 7 cm.Bot hnodule s and lumpsar ehard ,massive ,partiall y rounded and partiallyangular ,non-calcareou s and of ayellowis hre d (5YR5/6 )moist ,pin k (5YR7/3 ) drycolour ;the yhav ea lime coating and showthi npatch y tobroke nblac k cutanso fmanganes e compoundso n mosto f theirfaces ;clea r irregularboundary . 140-300c m Reddishyello w (7.5YR7/6 )moist ,pink-pinkis hwhit e (7.5YR 8/3)dry , B23ca limewhic hform sa discontinuou s softcalci chorizo n inth efor mo f 'stripes'alternatin gwit h 'pillars'whic hconsis t ofre d (2.5YR 5/6) moist,pin k (5YR7/4 )dr yclay ,th ecla ypillar shav ea strong coarse angular tosub-angula r blocky structurewhic hbreak su p into strong mediumangula rblock y elements;th e structural elements of thecla y pillarsar emassiv e and show thinbroke nwhit e (7.5YR 8/1)mois tan d dry,cutan sprobabl y ofbleache d clayo nthei rpe d faces together with thinbroke nblac k cutanso fmanganes e compounds,th e elements arenon - calcareous;ver y fewver y fineroots .I nhorizonta l section thelim e 'stripes'for ma roughl yhexagona l patternbetwee n thecla y 'pillars'; intersecting slickensides areabundan t inth ecla y and common inth e lime; locally,concentration s ofreddis hbrow nmottlin g occur inth e limeofte naccompanie d bycementation . 300-540+c m Darkre d (2.5YR3/6 )moist ,clay ;mixe d with somelim e (auger sample). B3

54 Analytical data

Particle sizedistributio n (um i)weigh t% Depth (mass fraction) Horizon (cm) c.: sand f. sand silt clay Texture 2000-:25 0 250-50 50-2 2 Ap 0-16 5 .5 27.5 31.5 35.5 Clay loam B21cam 16-55 n .d. n.d. n.d. n.d. n.d. B22ca 55-140 n,,d , n.d. n.d. n.d. n.d. B23ca calcicmateria l 140-220 n,.d , n.d. n.d. n.d. n.d. B23ca clay 140-220 1 .0 5.0 48.0 46.0 Siltycla y

pH EC C CaCO. 3 Horizon H„0 CaCl„ mS/cm % (mass % (m;1S S ^ fraction) fraction) 0-16 7.8 7, .2 n.d. 1.10 55,. 3 16-55 7.7 1, .5 n.d. 0.29 82,. 6 55-140 7.7 7. .6 n.d. 0.17 86,. 9 140-220 (ca) 7.8 7, .4 n.d. 0.06 82,. 5 140-220 (cl) 8.3 7, .6 n.d. 0.06 7,. 0

X-raydiffractio n of the clavfractio n vermi- chlo- mixed Horizon smec­ palygor- kaoli- juartz tite skite nite culite rite layer 0-16 xx(x ) xx(x) x(x) - - tr. 16-55 (ca) XX xxx(x) tr. tr. tr. - 16-55 (cl) XX xxx(x) X X - tr. 55-140 (ca) xx(x ) xx(x) tr. - tr. tr. 55-140 (cl) XX xxx(x) tr. X - - 140-260 (ca) xx(x ) xxx(x) tr. - - tr. 140-260 (cl) xx(x) xxx(x) x(x) - tr. tr. tr. 420-430 xxx(x) xx(x ) x(x) - - x 490-500 xxx(x) xx(x) x(x) - - X 530-540 xxx(x) xx(x) x(x) — X

Symbols: xxxxabundan t xxx common xx small x very small These terms apply toth erelativ e quantities of clayminerals .Th e samerang eapplie s fornon-cla ymineral s indicated by +.Bracket s indicate intermediate caseswhil e traces are indicated bytr . (ca)= calciti c material (cl)= claye ymateria l n.d. =no t determined = content 0

55 4.3.1.3 ProfileP 3equivalen tt oE1 8 (ISM)

Site information Profilenumbe r :E1 8 (ISM)equivalen tt o P3. Soilclassificatio n :Typi cChromoxerert . Dateo fth eexaminatio n :Jun e1974 . Authorso fth edescriptio n :Creutzber gan dVa nBaren/Ra oan dJun g (Theuppe r6 6c m ofth edescriptio no fCreutzber g andVa nBare nwa s used.T othi sth elowe rpar to fth edescriptio no fJun g andRa owa sattached .Thi spar twa schecke dan d correc­ tedagains tmonolit hE1 8b yElbersen) . Location :Abou t30 0m nort ho ffarmhous e 'LaCora' .6 k mwes to f Torremegia,provinc eo fBadajoz ,Spai n (DEi ncros s section,Fig .10) . Elevation 292m abov ese alevel . Landform i. Physiographicpositio n Broadvalle ybottom . ii. Landformo fth esur ­ roundingcountr y Undulating. iii. Microtopography Nil. Slope Almostflat . Landus e Arable landwit holive san dgrapes . Climate Semi-arid.

General soil information Parentmateria l Miocenecla y (colluvialmaterial) . Drainage Moderatelywel ldrained . Soilmoistur econditio n Dryu pt o1 5cm ;mois tbelow . Deptho fgroundwate rtabl e Notreache dwithi n2 m (4m i nawel l 500m nort ho f profile). Presenceo fsurfac estone s orroc koutcrop s :N ostones ;n orocks . Erosion :Nil . Presenceo fsal to ralkal i :Nil . Humaninfluenc e :Periodi charrowing .

Brief description of the soil Thisprofil econsist so ftw onan-<= -a ^ n -, sitionalzon ea ta dept ho f5 2 , ^ VPP" *"* WMch me^esvi aa ^an - i S s ProfilesRiol a , Jtr0 2 "T !*^ *** ^« toth eclay so f redfin etexture dsurfac eso u T *** °** * Pr°me ^ * yell°Wish withmoderat estructur e^ J ^ ^ & *** reAdish bro™ finetexture d sub-soil andshow mgman yintersectin gslickensides _ A discontimous 56 softcalci chorizo nwhic h includesver yman ycla ynodule san doccasiona l slickensides formsth euppe rpar to fth ere dclay .Th elim econten to fth esof tcalci c horizonin ­ creaseswit h depthan dth ehorizo nturn s intoa continuou s softcalci chorizo nwit h manyre dcla ynodules .A ta dept ho f11 5c mth emateria l changest oa heav ywell - structuredre dcla ywit h gleyphenomen aan dprominen t slickensides.Larg epocket so f soft limemak e thisa discontinuou s softcalci chorizon .

t

:?•*

f i • 1 a *.« i

i \ *.-*••*•• k — '£'•"••.* •"* • 'M

Fig. 9. Monolith E18o f ProfileP 3 showinga colluvia luppe r partwit h strongverti c propertiesoverlyin g acontinuou s softcalci chorizo nwit hre d claynodule sdevelope d inre d Miocene clay!Th ehorizo n symbolso f theprofil edescriptio ni nSectio n 4.3.1.3hav e been Indicated inth ephotograph . (Photocourtes y of the ISM.)

57 Description of soil horizons

0-3 cm Yellowish red (5YR 3/6) moist and dry, clay; moderate tostron g medium Apl crumbs; very sticky, very plastic, very friable moist, slightly hard dry; very few small gravels ofcalcareou s and quartz nature; slightly re : n f e Md feW medium roots ab 3-15 cm Yenn T 57: ^ ; rupt wavy boundary. :e (5YR 3/6) moist and Ap2 anlulZV t . dr?, clay; massive to weak fine sub- 1 y:/erj StlCky' Very Plastic, very friable moist, slightly y V£ry few ver flne a ' ^ tubular pores; very few small gravels of medium I qUa/^ natUre; sli%htly calcareous; common fine and few 15-42 cm medium roots; gradual smooth boundary. B2 Dark reddish brown (2.5YR 3/5) moist and reddish brown (2.5YR 3.5/5) /S "°d?rate fin? bl0<*y; very sticky, very plastic, firm moist, pores ' common intersecting slickensides; few very fine tubular ii v Y""615 °f calcareous and q«artz nature/less than in US; and Very few medi root w";y boundary '^^ "^ ™ ^ ««dual

52 Cm a k d b ? m0iSt reddish fa BB" L y witn m:nv d T- ""^ ^ ^ rown (2.SYR 3.5/5) very s Îckv yv ?" -°arSe red m°"les' cla^ moderate fine blocky; Ilicken £;. f Y PlaSt^' fi™m°"t, very hard dry; many intersecting ' Llcareouî and f TY ^ tUb"lar P°reS; Verv few small gravels of few medium root^ ,* ^^ ^ than in B2 = calcareous; few fine and W3Vy 52-66 cm itd ^ 5YR l/7\ ' ^ boundary. many medium di BCca mottle; clav- ^" ^ ^J' "^ stinct reddish yellow V6ry plaStic friable ist hardry; ewV«y fineTb "^ ^^ ' ™ ' roots- diffuL VZ lit ^lar P°reS; str°"8ly calcareous; few medium B3 6 into the BCcTho^™ ? "^ ^ ^"^^ ™t.ri.l'i. tonguing nc?caCm î/^aïcS/Se}2^5-57,6? m°iSt Clay; feW fine ^»t red (2.5YR 7 fine structure very iSvL: Df T^ ** -b-angular blocky few very fine Ld fi™\T? plaStlc' extremely firm moist, hard dry; fine rot e a „I"1" P°T: Str°ngly calcareous; few very B3 material- soft nowd?-lnaS °f 3 diamet« of 1-2 cm filled up with ual smooth boundary " ™ P°CketS *"* 6l°ngated patcheS' grad" «-115 cm Light red to red (25YT ? <\ K/c\ 5 5 5/6) IIC2ca occurs .n noduleS^ ™2 : »?»'. clay; dusky red (10R 3/4) clay angular and sub-angular v „ w "h 6Xhlblt a moderate tostron g medium Y structu sticky, very plastic f re set in a lime matrix; very iSt feW ery fine strongly caLar^s 'vlrTf w^: V / tubal« poresl on the clay nodules- f«, =r , •," ! dark f«ro-manganese cutans smooth boundary! s^ckensides which do not intersect; abrupt 115-200 cm Dusky red finp i;/\ 25 cm) pockeï of^eTÄf Ïht^ a1"™»** *'» large (4x Pockets of soft lime up to 1S ° , moist colom' CCur ; hard Ca encountered; numerous slickensides ^,° . C03 pieces are also prominent; the cleavage faces «Meeting at various angles are nese cutans and with white lime Shlnln§ and coated with ferro-manga-

58 Analytical data

Particle sizedistributio n (ym)weigh t% Depth Horizon (massfraction ) (cm) c.san d f.san d silt clay Texture 2000-250 250-50 50-2 2 Apl Ap2 0-15 11.4 13.5 19.9 55.1 Clay B2 15-27 11.6 13.5 19.1 55.7 Clay B2 27-42 11.7 12.4 19.0 56.9 Clay B3 42-52 10.9 11.9 18.9 58.3 Clay BCca 52-66 7.2 8.0 17.2 67.5 Clay IIClea 66-82 3.8 4.9 14.4 76.9 Clay IlClca IIC2ca 82-102 2.7 5.5 16.2 75.6 Clay IIC2ca IIC3ca 102-118 2.0 3.6 15.8 78.6 Clay

pH EC CaCO,CaSO , Exchange equivalents(mmol/l00g soil) 3 4 BS Horizon Exchangeable cations H 0 CaCl mS/c m Z -CEC 2 2 JC a K Na Sum (mass,fractions ) 0-15 8.2 6.7 0.23 0.41 0.2 44.0 0.9 51.8 46 .3 100 15-27 8.0 6.1 0.14 0.38 36.8 0.4 43.7 41,. 3 100 27-42 8.0 6.3 0.22 0.32 0.3 36.9 0.3 43.9 43 .8 100 42-52 8.3 6.8 0.23 0.29 6.2 36.8 0.2 43.5 41 .3 100 52-66 8.4 6.9 0.26 0.25 30.0 31.1 0.2 36.8 31,. 7 100 66-82 8.7 7.2 0.23 0.16 56.6 25.4 0.2 29.7 24,. 0 100 82-102 8.7 7.2 0.28 0.06 50.8 24.0 0.2 28.9 24,. 5 100 102-118 8.7 7.4 0.22 0.03 69.8 18.5 3.2 0.1 21.8 17,. 0 100

X-ray diffraction of the clay fraction Horizon smec- palygor- kaoli- vermi- illite quartz tite skite nite culite

0-15 xxx tr. tr. (+) 15-27 xxxx tr. tr. (+) 27-42 xxxx tr. (+) tr. 42-52 xxx x x tr. 52-66 xx x(x) tr. + 66-82 xx XX tr. 82-102 xx XX tr. tr. +(+ ) 102-118 xx XX tr. tr. +

Symbols: xxxxabundan t xxx common xx small x very small Thhese e terms apply to the relative quantities of clay minerals. The same range applies fo r non-clay minerals indicated by +. Brackets indicate intermediate cases while tracesar e indicated bytr . n.d. =no t determined = content 0

59 C C n f iOCene landt e Fig!]°; nd F?g!4? The cross sIcHo ^ yP - The location isindicate d in riginal pubUshed b JunS (1974)an dR ao (,975)a ta mod i eseile"Id H>•* *T •" ° ? ther explanation isfoun d inth etex t Addltlonal informationwa s inserted.Fur -

60 CROSS SECTION ABCDE

Soil and/or colluvium

m Red clay Soft lime

Indurated lime

Clay nodules and lumps

Soft lime pockets

Limit of augering

Assumed continuation of horizon boundary

Derived from profile 1

Derived from deep augering number I

Additional data inserted in the cross section

o 50 100 150 200 250 VERTICAL SCALE IN cm • 300 350 • 400 -450 • 500

'fi %%'Sj ---•-_--•- • 0 HORIZONTAL SCALE IN METRES ut

61 4.3.2 Discussion

4.3.2.1 The'hig hsoils '

Theprofile sRiol a 1an dArroy o1 o fwhic h thedescription s are reported here, arediscusse d indetail .Simila rprofile s (Arroyo3 an d P4)wer e studiedt ochec kth e validity ofth econclusion so nRiol a 1an dArroy o 1. Thehorizo nnomenclatur eo fthes eprofile s should reflect the genetic historyo f thesoils .A ssuc hth enomenclatur e isdifferen t from the oneuse db yth e original authors.Th emai nproces so fth eB horizo n isconsidere d tob e the carbonate accumu­ lation,whil ecla yilluviation ,a seviden t from themicromorpholog y (Section4.5.1.2 ) isconsidere d importanti n its lowerpart . Texture. All samples arerelativel y fine textured,bu t somevariation si nsil t andcla yconten td ooccur .Sinc edispersio nproblem s cannotb erule d outi nthes e highlycalcareou s soils,i ti sno t clearho wmuc h importance shouldb egive nt othes e differences.Th e lowest sampleso fth eprofile s areeithe r clayo rsilt yclay .Vari ­ ationsi n textureo fth eorigina lMiocen e clayar e also reported for deep augersam ­ ples inwhic heve nsilt yan d fine sandy layersoccur .Th evariou s kinds ofcla y bodiesencase di nth ecalci c andpetrocalci c horizons showa simila rvariatio ni n siltan dcla ycontent .San dconten ti slo wi nal l samples.Th econten to fbot h fine andcoars e sandshow sa tendenc y to increase towards thesurface .Surfac e soilsar e somewhatcoarse rtexture d thanth eunderlyin gMiocen e clay forbot hprofile s report- ed Calcium carbonate equivalent. The limeconten to fth eprofile si shigh . Calcic andpetrocalci c horizonshav ea conten to fove r8 0%. Th eunderlyin g Miocene clayi s non-calcareousi n the interioro fit sstructura l elements.Th e samehold s truefo r thecla ynodule s and lumpsencase di nth e calcic andpetrocalci c horizons.Whateve r calcium carbonatei sfoun d inthes e samples isprobabl y derived froma fillin go f smallcracks .Surfac e soilsd ohav ea rathe rhig h limecontent .

pH. TheP H (H20)measure d inmos t samples ismos t likelyrelate dt oth e high limecontent sreported .Th eP Ho fa solutio n opent oth e atmospherei nequilibriu m witha soli dphas eo fCaC0 3i s8.3 .Highe rvalue sprobabl y indicate that insufficient t™ wasallowed toreac h thisequilibrium . Lowerp Hvalue s couldb edu e tobufferin g byorgani cmatter .Th e lowerp H ofsom ecla ynodule s isprobabl y relatedt othei r lacko flime .

Organic carbon percentage. Theorgani c carbonconten to fth ehorizon so fprofil e Arroyo i h ratherMg h ^ ^ ^ ^^ ^ ^ ^ withdept hbein g less than0. 2 %belo w 55cm . mineraiZ TT"" "' ^ "^ ^^ ^ Pr°£UeS ™ ^ *^« in ^Y t u uTtr 6rPalyg0rSMtd e b°tarh ePreS6n tin ^P — Cities eti "'T Paly80rSkiteSeem St 0haV eit S -™ concentrationi nth e calcichorizon ,an d smectitei n thedee p sub-soil.Thi s can indicate that palygor-

62 skiteform s inth e calcic horizonpossibl y atth eexpens e ofsmectite .Th epalygor - skite (named attapulgite inJayaraman' sdata )i scommonl yreporte d asa neoformatio n incalci chorizon s (Ruellan, 1970;Scholz ,1972 ;Naho n &Ruellan , 1975;Redondo , 1975;Gras , 1975;Mathie u et al., 1975;Watts , 1980).Th e facttha t asmal l decrease inpalygorskit e inth e surface soils iseviden tcoul dmea ntha t thisminera l isun ­ stable inenvironment s with a lower lime content. (Thismatte rwil lb ediscusse d in moredetai l in theparagrap h oncla ymineralog y ofth e 'lo wprofile s' ,i n Section 4.3.2.2.)Whethe r all thepalygorskit e isa neoformatio n inth e calcichorizon s or is atleas tpartiall y inherited from theparen tmateria l isno testablished . The deepest samples ofProfil e Arroyo 1stil lsho wconsiderabl e amounts of limederive d from crack fills,admixe d so that thepalygorskit e present inthes e samples couldjus t as wellb e formed under the influence of the lime,o rb e inherited from theparen tma ­ terial.Th e swell and shrinkbehaviou r ofth esoi lmaterial s canprobabl y beattri ­ buted entirely to the smectite present.Kaolinit ei spresen t insmal l tover y small amounts inProfil eArroy o 1an d astrace s only inProfil eRiol a 1.Vermiculite ,chlo ­ ritean dmixe d layermineral s arereporte d asver y small amounts ortrace s in some samples ofProfil eArroy o 1only .Thes e differences canb e indicative ofmino r vari­ ations inth eMiocen eparen tmaterials .Takin g intoaccount ,however ,tha t data arecompare d from two different laboratories about concentrations close toth e limit ofdetectability ,no tmuc hweigh t should begive nt othis .Th e sameapplie s to the minordifference s in theamoun t ofquart z reported.Tobermorit ereporte d for some layers ofProfil e Riola 1refer s toa calciu m silicate thatcoul dhav e formed locally inth ecalci c horizon.Th epeak s fromwhic h thiswa s concluded, 0.115 nm and 0.610 nm,coul dwel l be indicative,however ,o fmixe d layermineral s similar to those iden­ tified inProfil eArroy o 1.

4.3.2.2 The 'lowsoils '

Profile P3 =E1 8 ofwhic h thedescriptio n isreporte d here isdiscusse d inde ­ tail.Simila r profiles (P1,P 2 andArroy o 2)wer e studied tochec k thevalidit y of theconclusions . The soils of thedepression s andvalle ybottom shav e thefollowin gpropertie s in common:The y areheav y textured and showverti c characteristics.Al l arecolluvia l in nature in the surface soil. Inth e closed depressions thecolluvia l layer isove r 1m thick,whil e thismateria l measures around 70c m inth evalleys .Th edarke rcolluviu m overlies red clays similar to theone sunderlyin g the 'highsoils 'o fth eplateau. Locally,sand y arkose-like layers areencountere d ata dept h ofsom emetres .Al l soilshav e calcic horizons mostly ofth ediscontinuou s softtype . Texture. The colluvial materials areal lfin etextured .Th eunderlyin g red clay showscla y contentswhic h aresomewha t higher.Ther e isa clea rdifferenc e inbot h finean d coarse sand content between thecolluvia l layers and theunderlyin g clay. Calcium carbonate equivalent. The colluvialmaterial s arecalcareou s but their

63 CaC03content sar erathe rlow .Th etransitio n towards there dcla yshow shighe rcar ­ bonatecontent san dqualifie sgenerall ya sa discontinuou s softcalci chorizon .Th e colluviallayer ssho wsom esmal lpetrocalci c fragmentswhic hd ono t showu pi nth e limecontent ,sinc ethe yd ono tfor mpar to fth efin eeart hfraction .

pH. Thevalue smeasure d inH 20generall yhav ea tendenc yt oincreas ewit hdepth . Nowhered othe yreac hth ep Ho f8.3 ,however .A ssuc hthe yremai n lowertha nthos e measuredi nth e 'highsoils' .Th evalue sdepen do nth eCaCC Lconten tan dorgani cmat ­ tercontent .The yca nb eshow nt ohav ea stron gpositiv ecorrelatio nwit hth elim e contentan da stron gnegativ ecorrelatio nwit hth eC %.A ssuc hth ehig horgani cmat ­

terconten tan dth elo wCaC0 3conten to fth ecolluvia l layersprobabl y accountfo r theirlowe rp Hvalues . Organic carbon percentage. Thisi srelativel yhig hi nth ecolluvia lmaterials , consideringth eclimat eo fth earea .I tdecrease swit hdept han dreache s levelsgene ­ rallybelo w0. 2 Ii nth ere dclay .Profil eP 2form sa nexception .I tshow sa nunex ­ pectedlyhig hC %i nth esub-soi lwhic hdoe sno tmatc hwit hit sothe r characteristics sucha scolour ,p Hetc .I ti sconsidere dt ob eaccidental . Electrical conductivity ofth esaturatio nextrac to fthes esoil sshow svalue s whichindicat enon-salin esoils . Gypsumwa steste di nProfil eE1 8an dwa sshow nt ob eabsen ti nal lhorizons . Exchange capacity and bases on the complex. Thecatio nexchang ecapacit yi sex ­ pressedpe r10 0g soil ;a ssuc hth elo wvalue s forth esample so fth e lowerhorizon s canb eattribute dt oth ehig hlim econten to fthes esamples .I fth eCE Ci scompute d per10 0g clay ,correctin g forlim econten tan ddeductin g thecontributio no fth eor ­ ganicmatte ra ta rat eo f4. 5mmo lexchang eequivalent spe rg C ,onl ya smal lvaria ­ tioni sfoun dbetwee nth edifferen thorizon so fth eprofile .Th evalue svar yi nthi s casefro ma maxie mo f8 1mmol/10 0g cla yfo rth eto psoi lt o6 5mnol/10 0g cla yfo r someo fth ecalci chorizons .Thes evalue ssee mt ob ei ngoo d agreementwit hth ecla y mineralsuit eo fth ematerial .Th emai ncatio no nth ecomple xi sCa ,whil ea smal l percentagei stake nu pb yMg .Monovalen t cationsoccu ri nnegligibl e quantities. The totalo fth eexchangeabl ecation si sslightl yi nexces so fth evalue s foundfo rth e CEC. Thisi sprobabl ydu et oth edissolutio no ffre elim edespit e thefac t thatth e extractionswer ecarrie dou twit ha solutio nbuffere da tp H8.2 .Th ebas e saturation isconsequentl yreporte da s10 0%. X-ray diffraction of the clay fraction. Theprofil eshow sa clea rdistinctio n betweenth ecolluvia l topwit hsmectit ea sth edominan tcla yminera lan dth ere dcla y presenti nth eunderlyin gcalci chorizon s inwhic hpalygorskit ean dsmectit ear e iTrvTTl 1JnP°rtant- ™S 1S alS°re£leCte di nth eswe1 1- dshrin kbehaviou ran d ar Z, r , ^T***** Pr°flle ?"*• Smallquantitie so rtrace so fkaolinit e It is T thePr0file -* artZVarie fS ™traCe Sto cl-ly identifiable 72ZZ^^z^^ "f X SUr£aCeSOi l Sme traC6C0UapseS °f' illite'— identifieo f2: 1dminerals possibl-yre - -s -erelation - highsoils 'seem st oappl yher e too:Palygorskit e accompanies

64 thepresenc e of large quantities of lime.I teithe r formsth eweatherin g product of theparen tmateria l inth epresenc e of limeo ri s inherited from it.Bigha me t al. (1980)stat e thatpalygorskit e canb e expected toprecipitat e togetherwit h calcite ina nenvironmen t relatively lowi nM gwhil e sepiolitewil lb e theprecipitat e inth e presenceo fdolomit e athighe rM g levels.Watt s (1980)treat sth e formation ofpaly ­ gorskite incalcrete s indetail .H ementions ,fo rcalcrete s fromSout hAfrica ,tw o modeso fformation :neoformatio n aftero rdurin gcalcit eprecipitatio n and transform­ ationfro mmontmorillonit eunde ruptak e ofMg .Th esmectit e thatdominate s inth eup ­ percolluvia l layers seems tobe ,a t leastpartially ,a produc t ofpedogenesi s ato r nearth esurface . Its formationprobabl y continued during thetranspor tphas e andaf ­ terth edepositio n of the colluvium,sinc e iti spresen t inquantitie shighe r than thoseobserve d in theuppe rpar t ofth e 'highsoils 'whic har epresume d tohav e been thesourc e of the colluvialmaterials .Palygorskit e ispresen ta s tracesonl y inth e colluvialmaterials . Itprobabl ydi dno tresis t theweatherin g conditions thatper ­ sisted inthes ematerials .Bigha m et al. (1980)conside rpalygorskit e ametastabl e mineralwhic h is degraded andultimatel ydestroye db y sufficiently intensepedogen ­ esis. Inon e case they found evidence thatdiscret e smectite isformin g from the weathering products ofpalygorskite .Considerin g thequalitativ e character of theX - raydiffractio n analyses,th eMiocen eparen tmaterial s inth esub-soil s ofbot h 'high'an d 'low'profile s couldwel lb eidentical .

4.4 CROSS SECTION

Thecros s section (Fig. 10)wa sredraw nafte ra norigina lpublishe d byJun g (1974)an d Rao (1975).Additiona l field informationwa s inserted,whic h led tosligh t modifications.Bot hhorizonta l andvertica l scaleswer e changedb ymean s ofa nH P 984SBdes k topcompute r towhic h aplotte rwa s attached.Th eorigina lcros s section wasbase d onaugering s todepth s of 100-120 cma t6 m intervalsbetwee nA and Ban d at1 2m intervalsbetwee n B and E.Som edee paugering swer e inserted too.Th e surface configuration of thecros s sectionwa s based onmeasurement swit h a tacheometer. The cross section represents thematerial s encountered infou rclasses : - soiland/o r colluvium (witho rwithou t soft limepocket san dcla y nodules), " redcla y (with orwithou t soft limepockets) , " soft lime (witho rwithou t claynodule s and lumps), - indurated lime. The red clay of theparen tmateria l isdistinguishe d fromth esoi lmaterial s and alluvia on thebasi s of colour.Th e soilmaterial s andcolluvi avar y inmois t colour fromyellowis h brown and dark yellowishbrow nt oyellowis hred .Th emois t colours of thecla yvar y from light red tored ,dar kre d anddusk yred . Inth e transition zonebetwee n soilo rcolluviu m and theunderlyin gmaterials , redcla ynodule sma yb e found embedded inth esoi lmatrix .TTie ysee mt ofor m the Parentmateria l fromwhic h the overlyingsoil sweather .Whe nencountere d ina rela -

65 tively fresh andeasil yrecognisabl e state theyar e indicated in thecros s section. Inth ecros s sectionn o indication ismade of claynodule s embedded inth epetrocal - cichorizon ,no ro floos epetrocalci c fragmentspresen t in thecolluvia lmaterial . The lime inth ecros s sectionwa s distinguished inth e augerings on thebasi s ofit s colour,reactio n and consistency. Thedistinction smade inth e cross section are for the largerpar t based onvis ­ ualestimate s ofth eproportio n of thedifferen t constituents in the augersamples . Especially theestimate s onth erelativ e proportions of limean dcla y or soil areim ­ portant sinceth edistinctio nbetwee n soft lime (withcla ynodules ) and clay or soil (withlim epockets )depend s on it,th e former implying that lime forms a continuous phase and the latterimplyin g thatsoi l orcla y forms acontinuou sphase .Auge rob ­ servationshav ecertai n limitations forthi sdetermination , since apart from thevol ­ umeratio ,th edistributio npatter nmus t alsob eknow nbefor e one candecid ewhic ho f thetw ocomponent s forms acontinuou sphase . Bystudyin g thedat acontaine d inth edescription s of theprofile s and deep augerings,i tca nb econclude d thatJun g (1974)an d Rao (1975)fixe d their limit somewhat arbitrarily atapproximatel y 50 %b yvolume . Ifth ebul k density data of limean d clay (Section 4.6) are taken into consideration,thi s coincideswit h 50% limeb yweigh tu p toa dept ho f about 120c man dwit h about 65 %lim eb yweigh t ata deptho f 250c m (duet o compaction). Horizonswit hconsiderabl y less than 50 %lim eb yvolum e can stillb e considered ascontinuou s softcalci chorizon sprovide d the lime occupies thevoi d system. Iti s indeed frequently found insample s that limefro m thevoi d system dusts allnon-cal - citicconstituents .Takin g this into account itseem s that thecriterio n of 50 %lim e byvolum e couldb e lowered to 30o r 40 %b yvolum e for those caseswher e the limeoc ­ cupies thevoi d system.Nevertheless ,i norde r tomaintai nuniformit y of criteria, the 501nor mwa suse dwhe n inserting theadditiona ldee p augerings DAVI I and DAVII I andth ecorrecte d Profile P3 (=E18) .Additionall y itma yb ementione d that thisnor m coincidesreasonabl ywel lwit h limecontent s reported ascommo nb y Ruellan (1970)fo r 'encroûtements'whic h according toTabl e 2ar eth eequivalen t ofcontinuou s soft cal­ cichorizon s inthi spublication . Tosu mup ,i ti sstate d that the layers identified inth e cross section as lime correspond tocontinuou s softcalci chorizon swhil e the soil and clay layers with limepocket sgenerall y correspond with discontinuous soft calcichorizons .

The following general conclusions are drawnwit hregar d tocalci c horizons (Fig. 10):

1. Thecontinuou s softcalci chorizo n seems toexten d laterally across almost the wholearea . 2. Gradual transitions occurlaterall ybetwee n thedifferen t types ofcalci c hor- ïzons.

3. Inal lplace swher e the lowerboundar y of thecontinuou s soft calcic horizon is

66 observed,th etransitio n towardsth eunderlyin g clayoccur svi aa discontinuou s soft calcichorizon . 4. Inth edepression sth econtinuou s softcalci chorizo n liesdeepe rbelo wth esur ­ facetha ni nth eres to fth elandscape . 5. Inth edepression sth econtinuou s softcalci chorizo ni soverlai nb ya disconti ­ nuoussof tcalci c horizon. 6. Inth edepression sth econtinuou s softcalci chorizo ncontain smor ecla ynodule s thanelsewhere . 7. Inth ehig hposition sth euppe rpar to fth econtinuou s softcalci chorizo nmerge s intoa petrocalci c horizon onlywher ea relativel y steepslop ei snearby .Thi s takes placealon gth erim so fth eplateau snex tt oth edeepe rdissection san do nisolate d highridges . Theonl yexception st othes erule sar eforme db yth edepressio no fD AVI ,th e smallhummoc kbetwee nD AI Van dP 3an db yth eare aaroun dD AVIII .Fo rD AV Ilim e pockets occupying between3 0an d4 0 %o fth evolum eo fth ehorizo nar ereporte dbe ­ tween19 0c man d32 0cm .A ssuc hther ei sonl ya gradua lan dn oprincipl e difference betweenth ecalci c horizono fthi sdepressio nan dthos eo fth esurroundin g area.Th e smallhummoc kbetwee nD AI Van dP 3ha smuc hmor ei ncommo nwit hth ebotto mo fth e surrounding depression thanwit hth ehighe rplateaus ,sinc en opetrocalci c horizoni s presentan dsinc eit scontinuou s soft calcichorizo ni soverlai nb ya discontinuou s softcalci chorizon .Dee p augeringD AVII I shows thatth eapparen t lacko fa continu ­ oussof tcalci c horizoni nthi spar to fth ecros ssectio nindicate db yJun g (1974) andRa o(1975 )i sincorrect .I nrealit yProfil eD AVII I showstha t eventw olayer s (100-140c man d190-21 0 cm)qualif yfo rcontinuou s softcalci chorizons ,i fth e5 0 % limeb yvolum e criterioni sapplied . Comparingth eaforementione d conclusions1- 7wit h thosementione d inSectio n2. 3 takenfro mth eliterature ,th efollowin gi sevident :Fo rth ewhol e crosssectio nwit h theexceptio no fth evalle ybottoms ,th ehorizo nsequenc ei sa norma lone .T oal l thesecase son eca nappl yth erule : 'When in a profile the lime content increases with depth, the boundaries are abrupt or clear. Whenin a profile the lime content decreases with depth, the boundaries are normally gradual or diffuse. ' Thevalle y bottoms seemt ob ea nexception ,sinc eher eth elim eaccumulation s first increasean dthe ndecreas e graduallywit h increasingdepth .Th eprofil eo fth e valleybotto m inSectio nA Bsuggest sa splittin gu po fth econtinuou s soft calcic horizon intotw osuc hhorizons ,i nth elowe rslope .Th euppe ron echange s intoa dis ­ continuous soft calcichorizo n towardsth emiddl eo fth edepressio nwhil eth elowe r oneremain s continuous underth ewhol edepression .Thi s interpretationo fth eavail ­ abledat ai sshow nb yth edashe d linesi nFig .10 .A simila r tendencyt ospli tu pi s alsoeviden ti nD AVI Ian dD AVIII .I nothe rvalle yprofile s sucha spli tu pint otw o continuous soft calcichorizons i sno tevident .I ti sprobabl ymor ecorrec ti nthos e «ses toassum e that towardsmos tvalle ybottom sth ethic kcontinuou s soft calcic horizonsplit su pint oa discontinuou suppe ron ean da continuou s lowerone .

67 4.5 MICROMORPHOLOGY

4.5.1 Descriptionof the 'high soils' with petrooaloio horizons

Micromorphologicaldat aar eavailabl efo rthre eprofile so fthes e soils from Jayaraman (1974)an dRo y(1974) :Riol a1 an dArroy o1 (bot hPetrocalci c Xerochrepts) andArroy o3 (Calcixerolli c Xerochrept),indicate da sSite s 1,2 an d4 respectivel y onth elandscap ema p(Fig .3) .Additiona l sampleso fth epetrocalci can dcalci chor ­ izonso fArroy o1 hav ebee ncollecte dfo rthi sparticula r study.Dat aobtaine d from thesesample sar eindicate db y'o.s. ' (ownsample) .O fth ecalci chorizo nbot hundis ­ turbedan ddisturbe dsample swer ecollected ;se eals oSectio n4.6.1. 1 andFigs .1 5 and 16.Th edat aar epresente d separatelyfor : - Petrocalcichorizon . - Calcichorizo nwit hcla ynodule s includingit slowe rtransition :th e'stripe d zone'. - Theunderlyin gre dMiocen eclay . thephenomen aobserve dar etreate di ngroup saccordin gt oprocesse san dmorphology .

4.S.1.1 Petrocalcichorizo n

Thethi nsection s showa grea tvariet yo fcalciti cmaterials .Zone swit ha mono ­ tonouscrysti cfabri c (pseudospara sdefine db yBathurst ,1971 )alternat ewit hzone s ofa crypto-crystallin enatur e (clottedmicrite) ,brecciate d zoneso fapparentl yre - cemented fragmentsan dconcentri c features.Occasionall y claynodule sar eenclosed . Dtssolution phenomena of the lime. Calcitecrystal swit hdiffus e edgesar e re­ ported.Zone so funifor mcoars ecrysti c fabric showeddissolutio nphenomen aalon g voidsm thefor mo fcrystal swit hfraye dedge s (o.s.).Th efraye d edgesca nb edis ­ tinguished fromgrowth so nth ecrysta lb yth efac ttha t theysho wextinctio ni n polarised lightparalle lt oth eres to fth ecrysta l (Fig. 11).

Rearystallisation phenomena of lime. Claynodule sar ereporte dt osho wa calcit e coating.Void swit hextensiv e lublinite (calciteneedl e fibres)formation sar eindi ­ cativeo fm situformatio n (o.s.). Cracks filledi nb ymor e recent carbonatesar e reported.I ti sno tclear ,however ,whethe r localrecrystallisatio no rmechanica lre ­ distributionprio rt oth ehardenin go fth epetrocalci chorizo ni sth ecause . Erection Zonesar efoun dwhic hconsis to fangula r fragmentso fmicrocrystal - (os. ) ' haVea febriC di£ferent fr°m that °fth es -™iingcalci c disJsIT^f °0mPOnentS (Cla8tS md °lay h0dies)- Few ***** g-ins arefoun d mn tv °T8'l nth SCalClt emtrl X °£th e*-** * ^ents. Morecorn ­ ed Pi ref ^ theCla y n°dUleS- S°me °fth S*-t z grains^howa netche d " I v7d C0UUb eindiCatlV e °fChemiCa l dissol-ion (o.s.).Th ecla y claynodule sma yb elocall ysubjec tt odissolutio n too.Th ec acit e crystals

68 "J-

t.

1 3 1

•, t: v * •Oi.-I 'W Fig- 11. Dissolutionphenomen a inth ecoars ecrysti c fabrico fth ecalcit e that makesu pa nimportan t parto fth epetrocalci chorizo no fProfil eArroy o 1a ta dept h ofapproximatel y 10c mbelo wth eto po fthi shorizon .Th earrow s indicatefraye d edgeso fth ecalcit e crystals alongth evoids .Photograp h takenwit h crossed polar- isers. (Pseudospar inth eterminolog yo fBathurst , 1971.)(Phot ocourtes yo fISM. )

: Ksr '- '••s-: *.ÏI.J' • 3

Hg. 12. Diagenetic oöids from the upper part of_the petrocalc"horizo n of Prof lie Arroyo 1. The concentric structure is clearly visible in some of them They consist of calcite and clay. Photograph made in normal light. Photo courtesy ISM.

69 surroundingth ecla ynodules ,however ,d ono t showan ypreferre d orientationrelativ e toth enodule san dboundarie s arerazor-sharp . Cutans of non-calcitic materials. Mangansar ereporte d tooccu r inth epore sen ­ counteredi nth eencase dcla ynodules .A fewvoid s inth e laminated topo fth ehor ­ izonsho wchalcedan s (o.s.). Laminar features. Several layerswhic hca nb edifferentiate d onth ebasi s ofth e grainsiz eo fth eenclose dclast san dcla ynodule s arereported .Band sdifferin gi n typeo fcalci c fabrican dcolou rwer esee n (o.s.). Concentric features. Layerso fsub-spherica lsand-siz e carbonateparticle scon ­ sistingo fconcentri c laminaeo fCaCO jsurroundin ga nucleu s ofdifferen tmateria l arereporte da soölithi c layers.Simila rphenomena ,whic h included clay inth econ ­ centriclamina e (o.s.),wer esee n (Fig.12) .Spherulite sa sdefine d by Brewer (1976) canals ob eobserve d locallyi nth e laminae (o.s.). Pores. 'Wormburrows 'whic hconfin ethemselve s toband s inth euppe rpar to fth e horizonar ereported .Simila r featureswer e found inth e angular fragments ofth e brecciated layer (o.s.).

4.5.1.2 Thecalci chorizo nwit hcla ynodule s including its lowertransition :th e 'stripedzone '

Themateria lconsist smainl yo funiform ,wel ldeveloped ,silt-sized ,calcit e crystals (pseudospara sdefine db yBathurst ,1971) ,randoml yoriente d and forminga coarsecrysti cfabric .Th emateria lencase scla ynodule s ofvariou s sizes.Ther ei s evidenceo fdislocatio ni nth efor mo fshea rplanes ,especially ,i nth e 'striped zone'.Locall yth ecalcit egrain sar eboun d togetherint osand-size d elements (o.s.). Recrystallisation phenomena of lime. Recrystallised lime,finel ydisperse d in thematri xhavin gaccumulate d inpores ,crack san d rootchannel s isreporte d forth e upperpar to fth ehorizon .Lublinit e (calciteneedl e fibres)i spresen tespeciall yi n ProfileArroy o 1.I ndisturbe d sampleso fth ecalcit esprinkle d inCanad abalsa m (Fig. 16)i ti sfoun d thatth esilt-size d calcitecrystal s arecommonl y coveredb y micrite (o.s.). Thesegrowth sconfin e themselves toth euppe rreache s ofth esof t calcichorizo ndirectl yunderlyin g thepetrocalci chorizo n (o.s.). Similarphenomen a areals oreporte db yJayarama n (1974).A secondarycalcit ecoatin g along thewall so f cracksi ncla ynodule s isreported . Impregnationo fth eedge so fthes ecla ybodie si s alsomentioned .

_ Evidence of mechanical disturbance. Along theedge so fcla y lumpsdifferen t orientationo fcla yi sobserved .Dislocatio nan duneve ndistributio n ofdifferen t ypeso fcalcit ei sreported .Linea rfeature swhic h locallysho wevidenc eo fshearin g inth efor mo fcrushe dcrystal s (Figs. 13an d 14)ar e indicative ofmechanica l dis­ turbance o.s.). Orientationo fth emai naxi so fcalcit ecrystal s along slickensides wassee nlocally . 6

Non-calcitic components. Mosto fth equart zgrain swhic h occurar e found inth e

70 'ISM

J"-I: Shea r Planeo r slickensidei nth esof tcalci cmateria lo fth e'striped ' . L,Tr°M f Pr°file Arr0y° 'a t Sdept h °f 26°Cm - The slickensidei svisibl e Pedinr t u t?c °™ects severalvoids .Th earro windicate sa quart zgrai ntrap - J-ntn eshea rplane .Th ephotograp hwa stake ni nnorma l light.Phot ocourtes yISM .

r

: • •< *•-- • - -vi.1 yfi ••• •• ,-. , •- . .-«-''. •-.'•^;-,r-'.v,T ÏSM' .•»' :v .• '- •• .•' . -- - •^..Ni . . V

xg.14 . Detail fromFig .13 ,showin ga quart zgrai n (whitearro wi nFig .13 )trap ­ ped m ashea rplane .Severa lcalcit ecrystal sappea rt ohav ebee ncrushe dagains t quartzgrai ndu et odifferentia lmovemen talon gth eplane .Photograp h takeni n normal light.Phot o courtesyISM .

71 claynodules ,whil eonl ya fe war econtaine d inth elime .The yd ono tsho wclea r signso fpitting .Dissolutio nca nno tb eexcluded ,bu ti fpresen t iti smuc hweake r thani nth epetrocalci chorizon . Cutans. Fleckedstriate d ferri-argillanswhic har emediu m thickan dsometime s disruptedar ereporte dt ooccu ri ncrack san droo tchannel so fth ecalciti cmatrix . Thecla ynodule san dlump ssho wmangan salon g rootchannel s andpore san dferri - argillans alongcracks ,whil eremnant so fferri-argillans ,ferran san dmangan sar e foundintegrate di nthei rmatrix . Animal activity. 'Animalburrows 'ar efoun di nth ecalci c horizono fProfil e Arroyo3 only . Other features. Brown impregnations,probabl yo firon ,ar efoun d locally inth e calcichorizo n (o.s.). Limited amountso fcla y appeara sstreak spresse d intoth e slickensideso fth elime .

4.S.1.3 Theunderlyin gre dMiocen e clay

Themai npar to fth emateria li smad eu po fdens e clayey substances. Evidence of mechanical disturbance. Isolated calcite crystal concentrationsar e reportedalon gpe dboundaries .A largenumbe ro fcrack s isfound .Th ematri x isre ­ portedt oconsis to fcompacte d clayeymaterial . Non-calcitic components. Abundant quartz grainsar epresen t inth ecla ymatrix . Cutans. Yellowishre dferri-argillan s arereporte da scommo n along thecrack si n combinationwit hmangan san dcla ycutan sa tth epe dboundaries .

4.6.2 Description of the 'low soils' with colluvial influence

Ofth e'lo wsoils 'representativ e ofth evalley san ddepression s dataar eavail ­

ablefro mfou rprofiles :Arroy o2 ,P1 ,P 2 andP 3(identica lt oE18) ,al lo fwhic h classifya sTypi cChromoxererts .The yar eal lsituate d incros s sectionA Ewit hth e exceptiono fProfil eArroy o2 whic h occupies Site3 o nth ema p(Fig . 3).Al lfou r profiles,whic hconsis to fa colluvia luppe r layeran da napparentl y local lower layer,ar esubdivide dfo rth edescription.int othre e zones: - Thesurfac e soil. - TheB horizo no fth ecolluvia l zone togetherwit hit stransitio n towardsth eun ­ derlyingi nsit uhorizon .

- TheII Chorizo ni nloca lweatherin g productso fMiocen e sediments.

4.5.2.1 Thesurfac esoi l

The thinsection so fth esurfac esoi lhav ea unifor m appearance. Finely divided

tribT rtter \ KiStribUted thr°Ugh0Ut theminera lmat -ial- Th- homogeneous dis­ tributioioni sprobabl ydu et oanima l activitywhil e churningma yals ohav e playeda

72 role.Stres s induced plasmic fabrics are common,especiall y around embedded quartz grains.

4.5.2.2 TheB horizo n of thecolluvia l zonetogethe rwit h its transition towards the underlying residual horizon

Thishorizo nha s aver y heterogeneous aspect.Th ecolluvia lmateria l shows ava ­ rietyo fcontrastin g enclosures:petrocalci c fragments (pedorelicts),pocket s ofsof t limeman y ofwhic h are superficially hardened due to limeredistributio n and,es ­ pecially inth e transition zone,re dcla ymasse s ofvariou s sizes andshapes . Organic matter ispresent ,mostl y infinel ydivide d formthroughou t thematrix , locally iti sconfine d toanima lburrows . Stress features. Features related topressur evar y frommoderatel y developed biréfringentplasmi c fabrics toclea r stress features along cleavage lines,dra g phe­ nomenaan d intersecting slickensides. Evidence of clay illuviation. Fewcla yskin soccu ralon g largecracks .Par to f them seem tohav e beendestroyed ,sinc e somepapule s arepresen t too.Mos t cutansob ­ served inthes ehorizon sma yb e due to localcla yredistributio n andno t to illuvia­ tionsens ustricto . Animal activity. Clear signs ofanima l activity arepresen t inth e formo f channels insom e ofwhic h lubUnit e (calcit eneedl e fibres)i spresent . Petrocalcic fragments ofbot h rounded and sub-angular forman d ofdifferen t sizesar e always coated by laminae ofapparentl yrecrystallise d lime.Som eo fth e fragments are entirely laminated andsom eenclos ediscoloure d claymasses . Inon e case 'oölithic grains'ar esee n ina fragment . Pockets of soft lime occur inal lprofiles .The yar emostl yringe db y layerso f fine,probabl y recrystallised, limewhic hma yals openetrat e inchannels .A senclo ­ sures,speck s and smallbodie s ofre d clay are encountered. Red clay bodies, oftenmor e orles srounde d inshape ,occu rvaryin g insiz e from

100 m to 5mm . They areespeciall y common inth e lowerpar to fth eB horizon .Som e carryconcentri c rings of CaCOj. Theyar epartiall ydiscoloure d and somesho wneoman - gans. Evidence of mechanical disturbance. The lowerpar to fth eB horizo no f Profile P3 (=E18 )show s evidence ofmechanica l disturbance,probabl y the resulto f swelling andshrinkin g of the clay.A ver ycontrastin gmixtur e ofre d anddiscoloure d clay withcalcit e is found.Th ematerials ,thoug h intricatelymixed, sho wshar pbound - aries. 4.5.2.3 The IIChorizo n in localweatherin gproduct s ofMiocen e sediments

Themateria l is acompac tnon-porou s redcla ywit henclosure s ofcalcite ,som e discolouration and stress features.Petrocalci c fragments (pedorelicts according to

73 Brewer's 1976terminology )ar eabsent . Stress features arecommo ni n the IICo fal l threeprofiles .Pressur efeatures , locallystriate dextinctio npattern so f theclay ,shea rplane s and 'micro-tectonics' arereported .Extensiv e cracking occurs.Alon g thecrack sredistributio n ofcalcit e andgle yphenomen ai nth e formo fdiscoloure d clayar eevident . 'Flow'o fcalcit e aroundstabl elump so fre dcla yan do fre dcla y incalcit ei sreported . Evidence if elay illuviation. Intw oprofile s someevidenc eo fcla y illuviation isfoun di nth efor mo fcutan si nlarg ecracks .Papule s areno tpresent . Animal activity. Indicationsar efoun d inP 3only . Lime pockets arepresen ti nth efor mo fmasse s consistingo fcrystallin e lime whichalternat ewit hre dclay .Speck so f redcla yar e founda sinclusion si nthes e limemasses . Red clay bodies occurwhic hca nb edistinguishe d from thesurroundin g redcla y matrixb yth efac ttha tthe yar esurrounde db ycalcit e (clay lumps). Gley phenomena arecommon .Discoloure d claywit h sharpboundarie s along cracks hasbee nmentione d already.Redistributio no firo nan dmanganes ei sevident .Impreg ­ nations inth efor mo fneomangan s arecommon .

4.5.3 Discussion

4.S.3.1 The'hig hsoils 'wit hpetrocalci c horizons

Dissolutionan drecrystallisatio nprocesse so flim ear eapparentl y still active inth euppe rpar to fth esoil .Thi s indicates thatth epetrocalci c horizoni sforme d bychemica lredistributio no flim e inth eoriginall y softcalci c horizon.Additiona l evidencefo rthi si sfoun d inth egradua l transitiono fth epetrocalci c horizont o theunderlyin gsof tcalci chorizon .Thi sgradua ltransitio ni sconsisten twit hth e facttha tth echemica lredistributio nprocesse s decreasei nintensit ywit hdepth .

Thislas tfac tfit swit hth eexpecte d distributionpatter no fH ?0an d C0? inth epro ­ filem relationt oth esurface ;bot ho fwhic h substances thatar eessentia l forth e chemicalredistributio no flime .

_Tnc^l0Wing f6atUreSPrSSen tl nth SP^alci c horizonar ementione d byJaya - ^man (174 )a sproo fo fthi s layer's sedentary origin: laminar features,concen -

tr ue': : • m bUrr0WS- m thSSef °™S'h —' -edescribe di nth e and2 2 2) C0M t0Petr0Calci c an»Tda asT product d T s o7fpedogeneti c-processes ' " . *"*<** - general

do inth epotro -** **„,.tte, Jz^jzi^iTr- r: ™ " astomose. character of fibres which interweave and an-

74 Concentric features The 'oölithicgrains 'ar estrikingl y similar tophenomen a that bothSiesse r (1973)an dJame s (1972)describ e asformation s that originate inth e petrocalcic horizonb ypedogeneti c processes.Siesse r inparticula r takesgrea tpain s toprov e that any other originmus t beexcluded .Ha y &Wiggin s (1980)repor t for a petrocalcic horizon nearWickieup ,Arizona ,th e following: 'Mosto f the laminar lay­ ersar eoverlai n by a layero foöid sbetwee n 1an d Sc m thick.Th e laminar and over­ lyingoölithi c layers parallel thehillslopes ,cuttin g across thenea r horizontal bedding inth e alluvium.' They claim thatth eroundin g ofth eoölithe swhic h contain someopa l and occasionally some sepiolite,i sdu e tosurfac e tensions ofgel s from thesematerials ,whic hcause d a thinning ofth ecoatin g overth e angular corners of theenclose d nucleiwhe n theconcentri c layerswer edeposited .Ha y& .Reede r (1978) claim thatoölithi c textures canb e formeddu e toreplacemen t ofcla ycoating s around sandgrain sb ymicrite . From theaforementione d datath econclusio n canb edraw n that thephenomen a described inth epetrocalci c horizons of theMérid aregio nwoul d rather qualify fordiageneti c oöids as definedb y Siesser (1973).

'Worm' burrows James (1972)ha spublishe d microphotographs ofa patter no f circular tubes ina petrocalci c horizon that isver y similar toth eon edescribe d aswor mbur ­ rowsb yJayarama n (1974). Only adifferenc e insiz e isnoticeable .James' s data are derived from a sample taken atexactl y the sameposition :a fewcentimetre s below the topo fa petrocalci c horizon.H e offersproo f that these tubes areth eproduc t ofth e activity ofborin g algae.

Drawing onth e abovementioned evidence itmus tb econclude d thatth e features aremor e likely tob e proof ofa pedogeneti c origino fth epetrocalci chorizo n than ofa geogeneti c origin. It is admitted that thesubjec t ofmarin e oöidsversu sdia ­ genetic oöids is a controversial one inth e literature and onecoul dpossibl y quote otherpublication s thatproclai m these features asexclusivel y sedimentary. The lat­ terconclusio n would not,however ,mea n thatth epresen tpetrocalci c horizonha s to beconsidere d a geogenetic feature.Rathe r theoölithe swoul d intha tcas eb econ ­ sidered as lithorelicts (asdefine d by Brewer, 1976). Dissolution ofnon-calciti cconstituent s occurs,bu tonl y ona limited scale.I t seems tob e restricted to thepetrocalci c horizon,wher e solutionphenomen a of quartz grains togetherwit h probable products ofthi sprocess ,chalcedans ,ar e found. Dissolution, in the sense ofdestructio n ofclay ,canno t be ruled outbu t is difficult toprove . Boundaries between clayan d limear e alwaysrazor-sharp . Inth e caseo freplacemen t ofcla y by lime onewoul d expect transition zones and specific orientation of lime along thecontact .Non e ofthes e areobserved ,however . Inth e horizon that forms the transitionbetwee n soft lime and theunderlyin g -d clay, the 'smearingout 'o f small claynodule s trapped inshea rplane s isevi - dent. It isconceivabl e that.theclay ,sprea d outthinl y inth e limematri x tends to

A- , 0 „r riav forth e argillans m the underlying disperse.A s such itma y form the source ofcla y torui e <* t, 75 horizon. Thefac ttha tth ecla ynodule scontaine di nth epetrocalci chorizo nhav elac ko f limean dpresenc eo fremnant so fmangan si ncommo nwit hth eunderlyin gcla yindicate s thatthe ydescen dfro mthi sclay . Itmus tb estresse dtha tth epetrocalci chorizo nseem st ob eto oimpermeabl et o allowlarg eamount so fwate rt opercolat eint oth edeepe rcalci chorizon san dth eun ­ derlyingclay ,whil eth egroundwate rtabl ei stoo.lo wt omoiste nthes ezone sfro mbe ­ low.A ssuch ,gle yphenomena ,stres sfeature sdu et oswel lan dshrin ko fcla yan d clayilluviation ,ar econsidere da sfossi li nth elayer sunderlyin gth epetrocalci c horizon.Th efac ttha tthe yhav ebee nwel lpreserve dca nb eproo ftha tth ehardenin g ofth epetrocalci chorizo ni sa relativel yrecen tphenomenon .

4.5.3.2 The'lo wsoils 'wit hcolluvia linfluenc e

Thatcolluvia lmateria loriginate sfro mth e'hig hsoils 'ca nb ederive dfro mth e facttha ti tcontain spetrocalci cfragment swhic har ever ysiMla rt oth epetrocalci c t—H f°rth S' hlgh S°ilS' (laminati°n «* in° n—e - 'oölithic hen oV ', r, aredif£eren t£r0 mth ehar dr0Und6 dlim ef r«s ^er *™ * Ikt sb - :CÎ Pr°bably f°med l0Callyb y ™tric ****** of softlim e t0 S me Ped0tuAati n YaaÏon;: Z ° ° Cdisorthicnodule sa sdefine db yWiede r&

acted'bTth?"^10111 SV6r yWSa kl nth SCOllUVia lla ^- " isProbabl ycounter - -lows!L tV e C Pr°CeSSeS WhiChar SeVlden tl na1 1 *™ I-^es studiedo fth e

better^e??011Phen0me m° 1Mef 'SUC h" rlng S° lim£ e— d °^ects,ar e dSPth Sl nth6S eS ilStha nl n P iH thHT " ° * » '^ -ils'.Thi si s h s c o c T7 °rganiCmatt6 r C°ntent °fth S ^^ serial whichi s 2 agS COnditi n alS s^Z5ZeZ [0 ° "*«*«* °^ -™* . si.cethes e subjectt oseasona lvariation si nmoistur econtent . 4.5.3.3 Comparisono f'high 'an d'low 'soil s

C 0 :stres s phen«e„a („gane5e iv„mtian„ , , ™ ™" " features, gle y d «age„ , „. lesser «t™!»;™ "™^°"- <*•>*>». * «* **.*. Similart othos ei nth e'h ih -i betweenth ecolluvia lmateria lan dth e^ ^ n°dUl6S ^^ ^ ^ transition zone commonwit hth ere dcla ydeeper^ n tht rT^ matSrials'hav e seve^ featuresi n ' fvi m tneChorizon . Adifferenc ebetwee nth er PHH » r ^ thefac ttha t„s tprocesse d ^n t lm' ** * ,hl8h•»« = is £»"taä longeractiv ei nth elowe rhorizon so fthe^il! . S°"S "h"eaS"*" '* "° ° Luc uign soils. 76 4.6 ADDITIONAL DETERMINATIONSO NLIM EAN DCLA Y SAMPLES DRAWN

The objecto fthes edetermination swa st ocollec tmor edetaile d informationo n thepropertie so fmaterial s thatmak eu pth esof tcalci chorizon s:th elim ean dth e claynodules .Fo rthi spurpos eth einvestigation swer emainl yconcentrate d onth e siteo fProfil eArroy o 1.Her ebot h limean dcla ynodule swer esample da tvariou s depths.Undisturbe d ring sampleswer e takeno fth elime ,whil eth ecla ynodule s could besample d inundisturbe d formwithou t suchprecautions . Undisturbed ring sampleso flim ewer e alsotake n fromothe r sites indicatedo n thema p(Fig .3) .Th epurpos eo fthi ssamplin gwa st oestablis hwhethe r extrapolation ofth efinding so fth eArroy o 1sit ewa sjustified . Inth esamplin go fth elime ,car ewa stake nt oselec tpur e lime samples avoiding concentrationso fcla ynodules .Thi swa ssuccessfu li nth eArroy o1 soi lbu ti nth e other.soil scontaminatio nwit h clay couldno tb eavoided .Stron g contaminationo fth e limeb yfinel ydivide d clay aggregatesmad e extrapolationo fth edat ameasure dfo r purelim edifficult . The following properties weremeasure d (methodologyi nSectio n4.2 )o nth erin g sampleso fth elime : - CaCOjpercentage , - liquid limit:LL , - bulkdensity :B D (dry), - percentageo fwater-stabl e aggregateso fa diamete ro fles s than5 0urn , - average equivalent sizeo fth ecalcit ecrystals . Forth ecla ynodule sth efollowin gpropertie swer emeasured : - bulkdensity :B D(dry )an dB D (sat.)+, - coefficiento flinea r extensibility: COLE (sat.).

4-6.1 The lime samples

4-6.1.1 Results

In.Tabl e7 th eresult sar egive no fth eaforementione d determinations.Al lexpe ­ rimentswer e carriedou to nth esam e ring samples.Bul kdensit ywa smeasure d fromth e ring samples afterdrying .Th econten to fth ering swa sthe ndivide d intoon esampl e

forCaC0 3 determination,on esampl efo rcalcit ecrystal-siz ean don esampl efo rth e determinationo fth eliqui d limit.O fth elas tsample ,th epar tno tuse dfo rth eex ­ perimentwa swet-sieve d forstabl e aggregates,whil ewe tconsistenc ywa s determined °nth eportio n fromwhic hth emoistur epercentag ea tliqui d limitwa sdetermined .

77 co •r 3 P-I PM PM PH PK Pu Pu PH CU P-I PL, P-. P-I PH pL, On p., p-i Pu P-I P-< 4-1 O CO co co CO CM G O o S3 S 53 S W rS S ^ S S » rZi CO !3 P-i P-. •rl co co co CU >> 4H CO CO CO CO CO co en co CO CO CO CO CO CO CO CO co co u >•. CU 60 eu S CO •H 4-1 N O *3 J3 S3 B S ,3 S3 tHÏ3r32 s a S ÎS co co CcOo CcoO 1c3o C/l 'H HCO «HS OH CO •3 -o 4-1 S 4-1 T3 O cd o) C »f! T3 CU CO 4J 6•0 u• CO H M CJ H o r3 ^ « 0) 0 pH 4-> i-l u• CU 3 HP,> fi « C 0) ,43 3 X ,3 H CJ •o a- eu H N eu •a •H CO /-^ co • eu C0 4-1 3 H «•HO 13, 1,3 O HJ ^ «H cd *~* •H ^ CJ c•r B& mioo o in o o o o o io m o u~> u-i m m o o o m g Mi Ö C PI 4J CQ iH W ^ <- -d- -H O COH G u"> O, pu iH 4-1 -SH O m i-i A fi VJ CO &•« CU o iH •g 3 -O t>S 4-1 60 3- 3 »H CO 60 • CU PK CD 3 fi CU cd o r- CO rJ O* 60 4J 4-1 en o- o o o CTV vo "3 -H 60 4-1 T3 H T3 T3 * O CM rH cd n) C CO 4-1 A cjnr m r-, •<]- —H CM —- en — 0> O CTi vO — • • fN IN IN •! O. S r-)^ H CJ S co O •H cd ^^ 0) O Ë • 4J co >VJ> 1-4 Cl) 3-^ co TJCO O. CJ eu 00 CM CTi o o co CO LO CM CTI v£5 O 0> v£> v£> m CO IN co O vD Ol •—• S O « IJ ^ Sü r- CO r- 3 P3 fi Se O eu U ^ 0 •H r4 10(0 0 ^DO N N n \o o n N vï in LO \D O CM CO IN m -, cd G -O fi o u u O cd c o o N CU ri «w rH CO •H W 4-1 O CM — r- \o oo ^ F- fN LTI ao vO N CO ^ o CM WON O co co co CTCT»i CT * 0\ IN |N in MD CO co r- NT ,cn LH ö 0„ «'H co • x* LH O rö o 3 rH bO 0 N fis ?0 cu CfiJ co •H CI] -H t-i 1-1 60 • co !>, CJ Pu 4J CU rH |N O W i-H cd o cu 3 CÖ Ö rH 0 CO 0 c 0) MH CU UH •H -3 - eu M O LH tl > .Û Nf 1-1 'H rl bflrl u CU N Ai 4J a eu 60 C a o p, CU O a -H u CU rH M—1 •rH' O 4J -Û fi CO «H CO ßH HJ W CJ CU 4J •H 4-1 -H CO •r i O ÎTJ 4J 3 rH CO CU • co co n3 cu CM W co CO CJ •P eu UH 1^ er CO o O 0 O •H 0 - CU -a 3 ? p 4J O >, >> 0 * CO >> cd O o o o O rH 4-» co G U co •i H fi u fi 3 u ÙO H M eu eu M-t CU CO "O i-l f», 4-1 u eu o •H Cd 4-1 u •H H CU CU O cd XI N 4-1 M3 ß 4J.r4 3 ia CU -O T5 < > G C 3 -H M co o •r4 < tu fi G CN 0 3 3 3 ^ >>-rl CM CM CM 0) « fi 4-1 •i H & COU LD 3 ü CO eu 60 a) vO gCJ U CJ B r3 eu aj eu y co o cd 4-1 •i H eu Ue aCJ e u CJ •p 4-1 O o PU cu •H QJ rH eu U •H •H •rH 4J O 4-1 4-1 4-1 O.T3 O CA •i-l •r-t CO o o o CM CO ° C CO co CO CO — •H •iH >r4 CM CM — — o Cl • CO •d Ü44 eu r^ G rH O co 4-> o cd eu eu rl cu M O CJ co J3 rH eu t—i F 4J &J J3 -O >, CU fi r^. • o — o o O — H co •du« O cd 3 o — —. — o — o en « CM r- co 3

78 4.6.1.2 Discussion

CaCO? percentage All themeasure d contentsar ehig han dal lsample swit hth eposs ­ ibleexceptio no f those fromSit e Sar edraw nfro mhorizon stha tqualif y forcontinu ­ oussof tcalci chorizons .Th edat a fromArroy o 1sho wth ehighes tpercentage swhic h increaseslightl ywit h depth.Thi s increase doesno t signifytha t claynodule s are morerar edeepe r in theprofile ,sinc e thesample swer edraw ni nsuc ha wa y thatcla y noduleswer e avoided. Inth e samples fromGuaren a (Site7 )thi swa sno tpossible .Th e lowerlim econtent s of these samples aredu e toth e inclusiono fcla ynodules .Th e samplesfro m the other sitesow e their low limecontent s tosmal lcla y aggregates whichoccu rdisperse d throughout the limemass .

Liquid limit (LL) The liquid limitsdetermine d aregenerall y low.The ydecreas ewit h depthi nth eArroy o 1profil e andbecom eremarkabl y lowi nth edeepes thorizon .Th e materials of the lowesthorizon s qualify interm s ofth eBurea uo fReclamatio n (1974) as 'quicksilt',a highl yunstabl ematerial .I twa s founddurin g thedetermination s thatth epur e lime samples changed rather abruptly from thesoli d toth e liquid state,whil e samples contaminated by finelydivide d claydi dno tsho wsuc ha nabrup t change.A strong decrease inth evolum eo fth edr y limepowde rwa snote dupo nwet ­ ting.

These observations indicate thatth e crystallinecharacte ro fth e lime is the maincaus e for thisbehaviour .Upon wettin g thecalcit ecrystal s tendt oadher e to eachothe rb ymean s ofver y thin filmso fwate rbetwee nthei rcrysta l facets.Th e filmsar ever y thin if thecrystal s areclea nan dperfec t inshap e (Fig. 15).Thi s explainswh y thedeepes t samples ofProfil eArroy o 1showe d liquid limitsa s lowa s 17.Apparentl y thatwate r contentwa s sufficient to lubricateth ecrystal s inorde r toallo wthe m tomov e relative toeac hothe rwhen subjecte d toshocks .Stron gdefor ­ mations ofobject s formed from the limea tthi swate rconten tar eno tpossible ,how ­ ever,withou t breaking them,a s iseviden t fromth enon-plasti c consistencyo fth e samples.Th enon-stick y consistency indicates thatth e limegrain sadher estrongl y to eachother . Higher liquid limitswer emeasure d forsample s fromth euppe rpar to fth e calcic horizono f ProfileArroy o 1.Thi s isprobabl ydu et oth e facttha t thecalcit e crys­ talsher e are coatedwit h small growthso fmicrit e (Fig. 16),whic hpreven ta perfec t fito fth ecrysta l facets.Highe r liquid limitsfo rcla ycontaminate d samples are Probablydu e to the samephenomenon :th ecla yparticle spreven ta perfec t fito fth e crystalfacets .Thes e liquid limitsar e tob econsidere d asnon-representativ e ofth e ***i nit snatura l state,i nwhic hpur e limecontain srelativel y large fragments of «**• Themixin g of themateria lprio r toth edeterminatio no fth e liquid limit caus­ edth econtaminatio n of the calcitecrystal sb ycla yparticles .

79 ~%r)

•;\

S y« v ISM i O'

Fig. 15. Uniform silt-sized calcitecrystal smak eu p themateria l of thelim e 'stripes'o fProfil eArroy o 1a ta dept ho f 180cm .Th elim ewa s loosely sprinkled intoCanad abalsam .Th ephotograp hwa s takeni nnorma l light.Phot o courtesy ISM.

.*•*•. ' y'h.

*•' i hlhfm

l t ' V" | ' -.. 1.. _ i ! *. f { T. 1 .1 . t 'f O ' ; ••V Ü 1 Ô ; :,' L K •\.'vïJ ÎSHJW '. W' < *

'

- T'AJiV'rïj¥r°'illli

Fig. 16. Silt-sized calcitecrysta l from thesof tcalci c horizono f ProfileArroy o 1a ta dept ho f8 0cm .Th ecrysta l iscovere d bygrowth s of secondary calcite.Th e photographwa s takenfro ma sampleo f lime thatwa s loosely sprinkled inCanad abal ­ sam.Polarise d light shows thecalcit egrai nhal f extinguished while themicrit e growths lightup .Phot o courtesy ISM.

80 Bulk density [BD (dry)] Thebul kdensitie s increasewit hdept hi nProfil eArroy o 1. Theyvar y from 1.18g/c m to1.8 6g/cm 3.I fth enon-calciti cmineral sar econsidere d tohav eth esam e specific weighta slime ,por evolume so f5 6 %an d3 1 %respectivel y arecompute dfo rthes e sampleso nth ebasi so fa specifi cweigh to fcalcit eo f2.71 0 g/cm (Weast, 1974). Ifthi spor e spacei sfille d entirelywit hwater ,bul kdensitie s of1.7 4g/c m and2.1 7g/c m respectively resultfo rB D(sat. ).+Thes ecorrespon d withmoistur e contentso f4 7 %an d17 1b yweigh t respectively.Th egenerall y lower valueso fth ebul k densityfo rth esample s fromth eothe rprofile sar ea tleas tpar ­ tiallydu et oinclusio no fclay .

Percentage of water-stable aggregates Ofth esample suse dfo rth edeterminatio no f theliqui d limit,whic h accordingt oAST M (1954)norm sha dbee nsieve d overa 42 0u m sieve,th eremain swer ewet-sieve d overa 5 0ur nsiev ei norde rt oseparat eth esingl e calcitecrystal s fromth elim eaggregates .Thi s limitwa schose no nth ebasi so fth e dimensiono fth ecomponent s derived frommicroscopi c observation.Th eprocedur e adopted (20minute s wet-sieving undermoderatel y intensevibration )le di nmos t cases toa clea reffluent .Onl y clay-rich sampleswit hdispersio nproblem sma yno thav e beenseparate d completely (thesample swhic har estick yan dplastic) .Th econten to f water-stable lime aggregates showsa clea rdecreas ewit hdept hi nProfil eArroy o 1. Thissquare swit hth emicroscopi c observation thataggregate sconsistin go fsilt - sizedcalcit e crystals boundb ysmal l (micrite)crystal sdecreas ei nnumbe rwit h depthi nth eArroy o 1profile .

Average equivalent size of the calcite crystals Inth eloosel ysprinkle dsample s measurementswer emad eo na numbe ro fdiscret e calcitecrystals .Th eaggregate swer e observedbu tno tcounted . Sinceth elim ewa srathe runifor ma rang efo ra limite d numbero fcrystal swa sestablished .Th elon gan dshor taxe so feac hcrysta lwer e measured.Th erati oo fth elon gan dth eshor t axisvarie s from1. 7t o2.6 .N orela ­ tioni sfound betwee n thispropert yan dan yothe rpropert yo fth elime .O naverag ea ratioo f2.2 5i sfoun d forth eArroy o 1profile .Thi s implies thatthes ear e'blade d crystals'i nth eterminolog yo fFol k (1965) (Fig. 15). Ml crystalsar eassume d toconsis to flo wMg-calcite .N ostainin g testswer e donesinc eX-ra y diffractiono fsample s 98, 101,103 ,104 ,112 ,11 4an d11 7showe da totalabsenc eo fdolomite . Forth ecomputatio no fth eequivalen taverag esiz eo fth ecalcit ecrystal sth e borageo fth emea no fth elon gan dshor taxi swa scalculate dfo ra limite d numbero f estais. Thismean s that crystalswit ha nequivalen tdiamete ro f5 0y mwil lpas s trougha 5 0y m sievei fvibratio n puts their longaxi sperpendicula rt othi ssieve . ^e data show thatal lcrystal s fiti nth esil tfractio nan dtha tthei rsiz e tondst odecreas ewit h depthi nProfil eArroy o1 .Th esil t fractionseem st ob ea co *onsiz e category for lime in the soil.Meeste r (1971an d1973 )report sth esiz e actiono fth elim eo fa numbe ro fprofile s fromKonya ,Turke ya sfin esil t (mainly

81 2-8 ym).Abed i& Talibudee n (1974)foun d thatsilt-size d carbonatewa smor e commoni n theuppe rhorizo no fth eolde rsoil so fa caten atha tthe y studied inAzerbaijan - Iran,whil eclay-size dcarbonat ewa smor ecommo ni nth euppe rhorizo no fyounge r soils.Massou d (1973)report s largeamount so flim ei nth esil t fractiono fsand y clayloa msurfac esoil so fth eNil edelt ai nEgypt .Netterber g (1980)publishe sdat a onth eparticle-siz edistribution so fsom e 'powdercalcretes 'o fSout han dSouth-Wes t Africa.Th emajorit yo fhi ssample sconsis t forth emajo rpar to fth esil t andfin e sandfraction .Thi smateria li snormall y indicatedb yth eter m sparitei ncarbonat e petrology. Inundisturbe d samplesth egrain s forma (mostl ycoarse )crysti c fabrici n theterminolog yo fBrewe r (1976).Th egrai nsiz ecoincide swit h theon e forvados e silta smentione db yBlat te tal . (1972).Micrit egrowth s (Fig. 16)ar eobserve do n crystalsfro mth euppe rhorizon so fth eprofil eonly ,a sreporte di nSectio n4.5.1.2 .

4.6.1.3 Correlation

Table8 show sth eproduc tmomen t correlation coefficients calculatedbetwee nth e differentpropertie so fth esample so fProfil eArroy o1 an d theirrelatio nwit h depth.Computatio no fa correlatio ncoefficien t forth epropertie so fal l the lime samplesreporte di nTabl e8 i sconsidere d tob e superfluousdu et oth e fact thatth e samplingwa sno taccomplishe d according tounifor mcriteria .Moreove r theparameter s measured areexpecte d tob e influencedb ydifferen t factorsi nth edifferen tpro ­ files,whic hmake scorrelatio ntest smeaningless .Th e significancewa sverifie db y performinga two-side dt tes to nth ecorrelatio ncoefficient .

Withth eexceptio no fth erelatio nbetwee nCaC0 3 %an d theliqui d limitan d CaC03 %an d % stableaggregates ,al lcombination sproduc e correlation coefficients thateithe rqualif ya sprobabl ysignifican t( P<5 t )o rsignifican t (P

82 Table8 . Correlation betweenfiv epropertie s of 14lim e samplesfro mProfil e Arroyo 1an d their correlationwit hdepth .Th epropertie s areliste d inTabl e7 . Thesymbol s in thematri x have thefollowin gmeaning : n =numbe ro fobservations , r= correlatio ncoefficient ,t = Student's tvalue ,P =probabilit y levelo fer ­ rorwhe nconcludin g that thecorrelatio n issignificant ,expresse d asa percent ­ age(two-side d distribution).

CaC03 % LL BI) (dry) St. agg. X Eq. size Depth >5 0u m C. (

n = 14 n = 14 n = 14 n = 14 n = 14 r = -0 .52 r = 0.71 r= -0.32 r= -0.67 r 0.54 CaC0 X 3 t= 2.10 9 t 3.53 t= 1.17 t= 3.13 t = 2.21 not si;gn . P < 1% not sign. P< 1% P < 5%

n = 14 n= 14 n = 14 n = 14 -0.81 r= 0.59 r= 0.79 r = -0.82 IX r = t = 4.79 t= 2.56 t= 4.42 t = 4.94 P < 1% P< 5% P< \X P < 1%

n = 14 n= 14 n = 14 r= -0.62 r= -0.83 r 0.87 BD(dry ) t= 2.72 t= 5.09 t = 6.13 P < 2% P < 1% P < 1%

n= 14 n 14 St- agg.% r= 0.63 r -0.68 >5 0u m t= 2.83 t 3.19 P< 2% P < 1%

n 14 Eq.siz e r -0.83 c cr. t 5.23 P < 1%

- Iti samazin g thatth ecorrelatio n coefficient foundfo rth erelatio nbetwee n

CaC03conten tan ddept h isno thigher .I ti sals ounclea rwh yth ehighes t limecon ­ tentsar eno tfoun di nth eto pinstea do fth ebotto mo fth esof tcalci chorizon .Thi s isstrang e sincemicromorphologica levidenc e suggests thatth eaggregatio n c.q.th e receipto flim ei sstronges t inth eto po fth ehorizon . - Theliqui d limit reflects theeffec to fth eaforementione d properties,al lo f whichrelat et odepth .A ssuc hi ti snorma lt ofin da relatio nbetwee n liquid limit anddepth . Themutua l relationships found betweenth e5 propertie s reflecti npar tth ere ­ lationwhic h eacho fthe mha sindividuall ywit hdepth .I fth edat aha dbee n acquired ina nexperimen t inwhic h each couldb evarie d undercontrolle d conditions,t o »easureit seffec to nth eothers ,analysi so fvarianc ewoul dhav ebee nth etoo lt o travel their mutual relationships.I nth epresen t set-up thisi sno tindicate ddu e *>th e'desig no fth eexperiment 'a sperforme db ynature .Unde rth epresen t condi­ tionsi nwhic hn ovariable sca nb especifie d asdependen to rindependent ,partia l correlationmethod swhic hmeasur e interdependence only,ar eindicate d (Snedecor

83 Cochran, 1974). This approachi sjustifie di fth eassumptio nhold s true thatan yva ­ riableha sa linea rregressio no nth eothe rvariable so ro nan ysub-se to fthem ,wit h deviations thatar enormall y distributed.

Thepartia lcorrelatio n coefficientbetwee ntw ovariables ,eac ho fwhic hi scor ­ relatedwit ha thir dvariable ,ca nb ecompute d ifth esimpl e correlation coefficients betweenal lthre ear eknown .Th epartia lcorrelatio n coefficient measures that part ofth ecorrelatio nbetwee nth etw ovariable s thati sno tsimpl ya reflectio no fthei r relationwit hth ethir dvariable . Whenth emutua lrelation sbetwee nth efiv epropertie so fth elim ear ethu spuri ­ fiedo fth e'dept heffect' ,w efin d that onlyon esignifican t correlationi sleft , namelyth eon ebetwee nbul kdensit yan dCaCO ,content :Fo ral lothe r 'correlations' iti sconclude d that,fo rth epresen tnumbe ro fsamples ,n osignifican t correlation canb eproven .

4.6. 2 The clay nodule samples

4.6.2.1 Results

Fora batc ho fcla ynodule s fromdifferen t depthso fth eArroy o 1profil e (Site 2), bulkdensity ,B D(dry )an dB D(sat. )+,an dcoefficien to flinea r extensibilityi n

Table9 . Propertieso fcla y nodules fromProfil e Arroyo I. Batcheso fsample s weredraw n from threedifferen tdepths . The following properties were determined: bulk density indr y condition- B D (dry), bulk density insaturate d condition- BD (sat.)+,an dcoefficien to flinea r extensibility insatu ­ rated condition- COL E (sat.).Th emethodolog yo fthes edeter ­ minations isgive ni nSectio n4.2 .

Sample Depth BD (dry) BD (sat.)+ COLE (sat.) number g/cm3 g/cm3

1 1.33 1.70 0.02 2 1.26 1.62 0.05 3 100-120c m 1.28 1.64 0.05 4 1.29 1.66 0.04 5 1.2 9 1.66 0.05

1 1.27 1.65 0.03 2 1.24 1.6 6 120-140c m 0.03 3 1.28 1.72 0.02 4 1.29 1.67 0.04

1 1.37 1.69 0.04 2 260c m 1.33 1.66 0.05 3 1.40 1.69 0.05 4 1.37 1.61 0.08

84 saturated condition, COLE (sat.), were determined (Methodology in Section 4.2). Table 9 summarises the results.

4.6.2.2 Discussion

The range of values of BD (dry) is rather limited. There seems to be a tendency for this property to increase with depth. No such tendency is apparent for the BD (sat.) values, which have a narrow range also. For the COLE (sat.) values a larger range is evident. This range extends on either side of the value 0.03 which according to Franzmeier &Ros s (1968) separates soils with dominance of smectite from soils in which this clay mineral is not dominant.

4.6.2.3 Correlation

Productmomen t correlation coefficientswer e computedi nth esam ewa ya sde ­ scribedfo rth elim e samples.Correlatio ncoefficient swer e computedfo rth ethre e properties,mutually ,an dfo ral lthre epropertie swit hdepth .Th et tes twa sper ­ formedo nth eresult si norde rt ochec kth esignificanc eo fth erelationship s found. Table1 0summarise sth eresults .A significantpositiv e correlationi sfoun dbetwee n BD(dry )an ddepth .A sdiscusse d forth elim esample s this signifies thatthi spro ­ pertyshow sth einfluenc eo fon eo rmor edepth-dependen tpedogeneti cprocesses .I ti s mostlikel ytha tth eincreas eo fbul k densitywit hdept hi scause db yth eproportio ­ nalincreas ei noverburde nwit h depth.Ther ei sa significan tnegativ e correlation betweenB D (sat.)+ andCOL E (sat.). Thisi st ob eexpecte d sinceth eswellin gdimin ­ ishesth ebul k density.

la^ 10. Correlation between threepropertie s ofcla ynodule so fPro - Ue A«oyo 1an d their correlationwit hdepth .Fo r themeanin g ofth e symbolsse eTabl e 8an d Table 9.

Depth BD (dry) BS (sat.)+ COLE (sat.) = 13 n = 13 n =1 3 n r= 0.83 r = 0.19 r = 0.42 (dry) t= 4.92 t= 0.64 t= 1.53 1% notsign . notsign . P< 13 n =1 3 n = r =-0.7 3 r= 0.003 (sat.)H t= 3.55 t= 0.011 p <1 % not sign. n= 13 r= 0.51 COLE( sat.) t= 1.96 not sign.

85 Allothe rcorrelation s turnou tt ob enon-significant .Th eclu et othi s lacko f correlationma yb eth ewid erang ei nCOL E (sat.)value sbetwee nth edifferen tcla y nodulesregardles so fdepth .Th efollowin gfactor scoul db eresponsibl efo r this (Franzmeier&Ross ,1968) : amountof clay, soil fabric, absorbed cations andkind of clay. Differencesi namount of clay betweenindividua lcla ynodules ,s olarg ea st o accountfo rdifference si nCOL Eo fu pt o40 0 %,ca nconfidentl yb eexcluded .Th e lack ofcorrelatio nbetwee nB D(dry )an dCOL E (sat.)indicate s thati ti simprobabl etha t differencesi n soil fabric aret ob ehel dresponsibl e either.Thi s leavesdifference s in absorbed cations andi nkind of clay aspossibl efactor sresponsibl efo rth edif ­ ferencei nswellin gbehaviou ro fth ecla ynodules .A subsequen t checko nth ecla y mineralogyo fsom eo fth enodule suse dt odetermin eth epropertie s listedi nTabl e9 hasshown ,however ,th efollowing .Th enodule s froma dept ho f26 0c mar eal lver y similari ncla ymineralog ydespit eth efac ttha tthe yrang ei nCOL E (sat.)fro m0.04 - 0.08.Th ecla ynodule sfro ma dept ho f100-12 0c mha di ngenera l lower smectitean d somewhatlowe rpalygorskit econtent si ncompariso nt oth enodule s from26 0cm . The variationsi nsmectit econten tbetwee nth eindividua lcla ynodule sfro ma dept ho f 100-120c mdi dno tsho wan yrelatio nwit hth eCOL E (sat.)value smeasure d either. Thesefinding sd ono tsuppor tth eclai mtha tcla ymineralog yi sth ecaus eo fth edif ­ ferencesi nCOL E (sat.).Thi s leavesabsorbe d cationsa sa las toption .Difference s inth erelativ eamoun to fM gion spresen tca npossibl yaccoun tfo rth edifference si n COLE (sat.)measured .The ycoul dals oaccoun tfo r someo fth edifference si ncla y mineralogysinc eM gion spla ya rol ei nth etransformation so fsmectit e intopaly ­ gorskitea smentione di nSectio n4.3.2.2 .N odat aar eavailable ,however ,t overif y thisassumption .

4.7 STABLE ISOTOPERATIO SFO RTH ELIM EO FRIOL AI

Jayaraman (1974)report so nstabl eisotop eanalyse scarrie dou to nthre esample s oflim edraw na t80 ,20 0an d45 0c mdept hi nth eRiol a1 profil e (Site 1). There ­ sultso fth edetermination s (letterfro mW.G .Moo kdate d 21-12-1973)ar eindicate di n Table11 . Theresult sar eexpresse da sth erelativ edifferenc ebetwee nth eisotop erati o measuredan dth eon eo fa standar d sample:Th ePeede ebelemnit e (PDBstandard )whic h

Table 11. Stableisotop eratio sfo rthre elim e samples fromProfil eRiol a1 .

Samplenumbe r Depth 613PDB (°/oo) 6,8PDB (°/oo)

Riola 7372 80c m -8 . .86 -3 . .19 Riola 7373 200c m -8 . .27 -2 . .5 7 Riola 7374 450c m -9 , .20 -3 .62

86 issuppose d torepresen t averagemarin e carbonates.Th erelativ e difference isex - presseda sa °/oo . This isdon e forbot hth eratio sC (versusC )an d0 (versus 016). Salomons (1975)an d Salomons &Moo k (1976)hav epublishe d adiagra m inwhic h theyindicat ewhic h 613-618 combinations are typical forsoi lcarbonate s ofth e tem­ peratezone . Ifth evalue s ofRiol aar eplotte d inthi sdiagra m theyfal lrathe r closet oth eperimete r indicated astypica lfo rsoi lcarbonates .Fo rth eRiol asam ­ plesth e 613value s are about 2°/oohighe r and the 618value s areabou t 5%o higher.

The 613value s of C02 insoi l airupo nwhic hth eaforementione ddiagra m isbase d

areno trepresentative ,however ,fo rari dareas .Th e C02 ofth esoi lai ro fari d

areasi sno tdeplete d in C13,relativ e toatmospheri c C02, tosuc ha hig hdegre ea s thesoi lCO ,o f thehumi d temperate zone.Th ecaus eo fthi s liesmainl y ina differ ­ enttyp eo fphotosyntheti c cycle of theplant s inthes eareas .Thi s isexplaine d by Salomonse t al. (1978).Dat a onthi sphenomeno n aresupplie db yMagarit z &Amie l

(1980)fo r C02 of Israeli soils.Lowe rorgani cmatte rcontent so fari dsoil smus tal ­ sob etake nint o account,sinc e thispresumabl y allowsfo ra large rcomponen t ofat ­

mospheric C02 inth e soil air of theseregions .Considerin gthes e factsi tca nb eex ­ pectedtha t the 613value s of theRiol a samples arewithi nth erang ecommo nt o soil carbonates inthes eareas . Indeed inth e literature several 613value s are foundfo rcalci chorizon so fdr y regionswhic h are similar to those ofth eRiol asamples :Manz e &Brunnacke r (1977) reportabou tcalci chorizon s fromAlgeri awhic hhav e 613value so fth esam erang e as theRiol asamples .Thi s similarity applies tocalci chorizon s forwhic hthe yclai m Plioceneag e andals o forhorizon s forwhic h theyclai mol dQuaternar y age.Th e authorsstat e that the data refer to soilcarbonat e andno t togroundwate rcarbonate . Salomonse t al. (1978)repor t on anumbe ro fcalcret e samplesfro mdifferen tpart s of theworld . Fromamongs t their samples,thos e from Italyan d Francesho w 613value s veryclos e to those of theRiol asamples . The 618value s of the Riola samples are,a sha sbee nmentioned ,relativel y high forsoi lcarbonate s in general.Manz e &Brunnacke r (1977)stat etha tth e61 8value s ofMediterranea n soil carbonates are ingenera lhighe rtha n those ofMid-Europea n soilcarbonates .Th e Riolavalue s are still toohigh ,however ,i fcompare d toth e averageisotopi c composition ofSpanis hrainwate ra sreporte db ySalomon se t al. 0978). This lattervalu e for 618 is -4.5°/oowhic h leadst oa nexpecte d 618fo rsoi l carbonateso f -4.8°/oo.Highe rvalue s thanthos eexpecte d forsoi lcarbonate s indi­ te inth e opinion of Salomonse t al. (1978)tha tth ecarbonate shav eno tbee n form­ edb yprecipitatio n from abicarbonat e solutiondu et o losso fCO, ,a si scommonl y ** case,bu t due to evaporation of thissolution .The ysuppl ydat ao nanothe rpro ­ filei nSpai nwhic h showshighe r 618value s thanar et ob eexpecte d onth ebasi s of theaverag erainwate r composition and attribute thisdeviatio n toth eevapontiv e genesiso f the soil carbonates.The y finda n argument forthi shypothesi s m the strongcorrelatio nbetwee n the 618an d 613value so fthes ecarbonates .I t is mteres-

87 tingt onot etha tthos esam evalue sfor th eRiol a sanples showa highl y significant correlationtoo . (Productmomen tcorrelatio ncoefficien to f0.999.' )I tshoul db e takenint oaccount ,however ,tha tonl y3 sample swer emeasured . Ifth e61 3value so fth ecarbonat eo fth eparen tmateria lar eknow nan dth e 613

valueo fth esoi l C02i sals oknown ,th e61 3o fth enewl y formed carbonatesca nb e computed.O nth ebasi so fthes edat aa nestimat eca nb emad eo fth epercentag eo f soilcarbonat e thatha sbee nrecrystallised ,usin ga formul apublishe db ySalomon s& Mook (1976).Unfortunatel yfo rth eRiol aprofile ,a numbe ro fdat aar elacking .I ti s interesting,however ,t omak ea nestimat eo fth epercentag eo frecrystallise d carbon­ atesi nthi sprofile ,o nth ebasi so fth efollowin g assumptions: - 613o fth ecarbonat eo fth eparen tmateria l (p.m.)i s0°/o o (ancientmarin ecar ­ bonate).

- 613o fth eC0 2o fth esoi li s-21°/o o (thevalu emeasure d asa naverag efo rsoi l

C02 inIsrae lb yMagarit z& Amiel , 1980). Onth ebasi so fthes edat ai tca nb ecompute d thatfo rRiol ath enewl y formed soilcarbonate swil lhav ea 61 3valu eo fapproximatel y -9°/oo.Mie non eintroduce s 515 thesedat aint oth eformul ao fSalomon s& Moo k (1976) P= Ç soil- 61 3p.m. )x 1nn ..... , ' (613ne w -61 3p.m. ) 100, m combinationwit hth e61 3value s actuallymeasured ,on eobtain svalue sfo rP whichvar yfro m9 2 %t o10 2 %. Thismean stha ti fth eRiol acarbonate swoul d originate from ancientmarin ecar ­ bonatesi nth eMiocen e clay,the ymus thav ebee n subjectt ocomplet e recrystallisa- tion.

4.8 MICROPALEONTOLOGYO FTH ELIM E OFRIOL A1

Jayaraman (1974)report so nmicropaleontologica ldetermination s carriedou to n threesample sdraw ni nth eRiol a1 profil epi ta tdepth so f80 ,20 0and 45 0c mre ­ spectively,^ e sampleswhich wer e studiedunde ra binocula rmicroscop e turnedou tt o beentirel y sterile.Thi sresul tmake sa sedimentar yorigi no fth elim erathe rimpro ­ bable.Marin e carbonateswithou tan ytrac eo fmicrofossil sar eparticularl yunusual . Completerecrystallisatio no fa forme rsedimen tcoul dpossibl y also accountfo rth e absenceo ffossils .

4.9 CONCLUSIONS since^T 'high SOllS' Sh°W " h°riZOn SeqUenœ WhlCh iS entire1^ Frenetic in origin a The chemical and physical characteristics of the materials over and under the calcic horizons are very similar.

Lfe^nt?10 'T0" arS laterally C°ntinU0US «* Sh0w S-dual transitions of the ZlZlT5' a diStÜ1Ct relati0n t0 the land Surface «ith which they c. Thecalci chorizo nha s a stable isotopecompositio nwhic hclosely ,resemble s the oneo fsoi lcarbonates . d. Nofossil swer e found inth e samples studied. e. Themicromorpholog y of theprofile s doesno trende ran yevidenc e fora norigi n differentfro mpedogenesis .

2. The 'lowsoils ' arever y similar toth e 'highsoils' ,excep tfo rth e following: a. Theiruppe rpar t consists of acolluvia l layerderive d frommateria l ofth esur ­ faceo fth e 'highsoils' . b. Thepedogeneti c processeswhic h areeviden t inth e 'lowsoils 'ar e largely active whileth esam eprocesse s are fossile inth e 'highsoil s' ,wit h theexceptio no f the redistribution of lime insolution ,whic h isstil l active in- an ddirectl yunde r- thepetrocalci chorizon .

3. Onth ebasi s of themateria l contained inthi schapte rn oconclusio no nth e ori­ gino fth e lime isdraw nyet .

89 5 Experiments

Theobservation so nth eunusua l distribution patternso flim ean dcla yi nth e calcichorizon s of,e.g. ,profil eArroy o 1an dRiol a 1a sillustrate d inth efore ­ goingchapter ,hav earouse d interest inth ebehaviou ro fth ematerial s when brought intoclos e contact undernatura l conditions.Experiment s were designed toverif y possiblemovement so fcla ynodule san dothe r objects,embedde d ina sof t lime matrix whichi ssubjec tt operiodi cwettin gan ddrying .Experiment so fa simila r nature carriedou tb ySpringe r (1958)wit h stones embeddedi nso-calle d vesicular desert soilmaterial shav edemonstrate d suchmovements .Sinc e displacements,i fdetectabl e atall ,wer e supposedt ob eo fa rathe rlo worde ro fmagnitude ,accurat e measurements hadt ob edevised . Lime samplesmainl y fromprofil eArroy o 1wer e drawn from different depths, togetherwit h claynodul e samples.Thes e claynodule swer e embedded together with leadpellets ,gravel san dpetrocalci c fragmentsi ndifferen t combinations inth esof t limematerial san dsubjecte dt ocycli cwettin gan ddrying . Apart fromth evariatio ni norigi no fth elim ean dth enatur eo fth eobjects , the following treatmentswer e introduced inth eexperiments ,a ssummarize d inTabl e 13. - Grainsizeo fth elim e samples:Variou s fractionso fth elim e sampleswer e pre­ pared,b ymean so fdr ysieving .Th esiz e classesuse di nth edifferen t experiments arementione d inTabl e 13. - Packingo fth elim ea tth einitiatio no fth eexperiments :I nmos t cases,th elim e was givena dens epackin gb ypourin gi tint owate ri norde rt oavoi d consolidation duringth eexperiment .I non ecas eth elim ewa sinserte di ndr ystate . - Confiningpressure :I non eexperiment ,a pressur ewa sexerte db ymean so fa lea d weighto nth elim e surface duringth ewettin gan ddrying ,i norde rt osimulat eth e effecto fth eoverburde npressur ei nth esoil . - Moistening: Inmos t casesth emoistenin go fth emateria lwa seffecte db ymean so f anascendin g flow,unde rsligh tpressure .I non ecas eth emoistenin gwa seffecte db y meanso fa descendin g unsaturated flow.Th epurpos eo fth eascendin g formo f moisteningwa st oreduc eai renclosure ,whic h occurswhe n moistening isattempted , ina descendin gmode ,b ypourin gth ewate ro nto po fth elim e surface.Fo ra descrip ­ tiono fth efor mo fmoistenin gunde rnatura lcircumstance s seeSectio n 5.3.5. Forth eregistratio no fth emovements ,transmitta l X-ray techniqueswer e used. (Attemptst orecor dth emovement so fth eobject si na mechanica l way,b ymean so f small rodsattache dt othem , failed.)Stere o radiographyan dphotogrammetri c

90 techniqueswer e applied toreconstruc tth epositio no fth ecentr eo fgravit yo fth e variousobject swit h sufficient accuracy.Fo rthi spurpos eth eobject sha dt ob e markedwit h small lead cylinders. Thepositio no fth eobject swa srecorde d relativet oa referenc e frame,a t variousstage s duringth edifferen t moist-dry cycles,t owhic hth eset-u pwa ssub ­ jected.I nmos t experiments,displacement swer e measuredan dplotte di ngraph s againsttime .Th egenera l patternwa ttha tth eobject s roseupo nwettin gan dfel l upondrying .I nsevera l cases thisle dt oa smal lne tgai ni nheigh tfo reac hcycl e andi nsom eothe r casest oa smal lne tloss . Casesi nwhic hth eobjec t oscillated aroundit spoint so fdepartur ewer e also encountered.Latera lmovement so fth e objectswer e also evident. Someadditiona l determinationswer emade .I non eexperimen tth eheav eo fth e limesurface ,whic h became evident during several experiments,wa sregistere db y meanso fa lever .Bul k densityo fth elim e afterth eterminatio no fthi s experiment wasals odetermined . Analyseso fth emovemen t pattern,represente di nth egraph so fth edifferen t objectsunde rvariou s conditons,gav ea ninsigh t intoth eprocesse s responsiblefo r themovements .Stud yo fth eX-ra y images,i ncombinatio nwit hth ebul k density data andth esurface-heav e data,mad emor e specific conclusionspossible .

5.1 SETU PAN DEXECUTIO N OFTH EEXPERIMENT SAN DMEASUREMENT S

5-1.1 Set up of the experiments

Plexiglass containers about1 3c mx 7 c mx 1 5c mi ndimensio nwer e constructed (Fig- 17).Fou r cylindrical leadmarker swer e insertedi nth efron tan di nth ebac k windowso fth econtainers ,suc h thatth esquar e formedb ythes emarker so nth ebac k coincidedexactl ywitl ith eprojectio no fth e square formedb ythe mo nth efront . The bottomo fth econtaine rwa scovere dwit ha laye ro fabou tS c mo fclea ncoars e sand, intowhic ha perforate d tubewa splaced ,t oallo wfo reve nmoistenin gdurin gth e experiment.Lim ewa sdeposite d overth esan di na laye ro fabou t9 cm .I nmost ^ experimentsa unifor man ddens epackin go fth elim ewa sattaine db yfirs tpourin g thlsmateria l intowater . Claynodule swer e marked inth efollowin gway .Tw oholes ,wit ha diamete ro f 2 m, weredrille d approximately perpendiculart oeac hother ,intersectin g closet o «iecentr eo fgravit yo fth ecla ynodul e (Fig.27) .Tw osmal l leadcylinder swer e Verted into each hole. Petrocalcic fragmentsan dstone swer emarke d similarly by Cueing leadmarker s tothei r surface accordingt otw operpendicula r axes through their centr eo fgravity . 1 , Whileth econtaine rwa sbein g filledwit h lime,th emarke d objectswer eplace d inthi slaye ro fmaterial ,togethe rwit h some leadpellets .

91 r I e

"* -'>•->.,..

•M "'- »••.» "-A *".•

*'

^^îi'j R?c^anëular Plexiglass container inus efo rExperimen t Illb.Th econtaine r istille d witha layero fclea n coarse quartz sand intowhic ha perforate d tubei s IT \ «7 °^ *•-* Sand'Um e has been P°ured int° «hichvariou s marked objects are embedded Thelim e surfacei scovere d byporou smateria l (ground brick).A narro w indicatesa lea d marker inth efron t windowreferenc e frame

92 : - -ee­ 2 lt•.„'"•I fe1 ^ •

*"as ;'•*>. . . ---Fi

..ilS

•h

Fig- 18. Mock-up of image formation during radiography simulated with normal light For this purpose the lime has been removed and a clay.nodule which was embed^ ™ £ has been placed on a rod. The film (A) was placed against ^^^"^îLe (Arrow tainer. The lead markers of the back window are in contact with the film pi£^

93 rr •.».-7*'• UT-pa

CA/A C .Vff

i/ . /-•« ?

;

d

Fig. 19. Dodged printo fX-ra y imageNr .577 L Mpft h ^ T. pair), representing ExperimentI Ti n ^ i- • hand Ph°tographo fth estereo - shadowso fth ebac kwindo wmarker s (a b THT™" ^ ^ °f the '' th<^ le- The ront wlndoH d )allo wth econstructio no fth P i=J L I ,V- markers (a',b' , c', beenmarked :CN R= cla ynod ue Sg h ° CNL" M^' 'TV "Th e f°UowinS ob^s ^ clay n dule left U =lea dpelle tleft .Th elea dmarker , L~ J ? > LR= lea dpelle t right, centreso fgravit yo fth ecla ynoduïe sar eM 1 "^ ChaMels bored ^ough the ofth epositio no fth ecentr/ ^ „1 L*"^16"1? vls^le andallo wth econstructio n

visiblemainl yi nth p„ L " (Fig'27 )*A concentrationo frou t underneathth ecla y nodules;the yar ea nV* ^ °L^e Ume- Fewvoid s canb esee n sand surfaceca nb edistinguishe d in the iL! ""* horiz °«al direction.Th e eum theimag ejus tunderneat h thelin e d'c'

94 S.1.2 Registration of the position of the objects

The position of the enclosed objects was recorded during the different stages of the experiments, by means of stereo X-ray photographs. These were made by placing the X-ray film against the back window of the container and exposing the object from the front to radiation (Fig. 18). Table 12 supplies the technical data on the radio­ graphy. The object was encased in lead slabs in order to diminish backscatter. In order to obtain a stereo-effect, the container was moved between exposures over a distance of 10 cm perpendicular to the axis of the cone-shaped X-ray beam. The resulting photos, of which a positive copy is reproduced in Fig. 19, show the lead markers as dark spots due to the absorption of the X-rays by the lead (transparent spots in the original photos and dark spots in the positive copies). The markers of the back window of the container were in direct contact with the film and as such show no displacement. The markers from the front window and those from the encased objects are displaced due to the divergent character of the X-ray beam (Fig. 18). The displacement would be radial from the centre of the reference square if the photo was taken by aiming the axis of the X-ray beam on this centre. In order to obtain a stereo-effect, however, two photographs were made, a left and a right one. The left hand photograph was taken by exposing the container to the X-rays from a point left of the centre of the reference frame, resulting in a displacement^ of the shadows of the front window markers and object markers towards the right. This is evident in Fig. 19. The reverse holds true for the right hand photograph. s-3.3 Reconstruction of the position of the objects

By means of a construction, the true projected position of the objects relative to the markers of the back window could be determined. Fig. 20a shows the construc­

tie 12. Technical data on radiography.

Vipment Philips-Rotalix F0Cal =POt 0.3 mm 100 kV 15 mA Variable;generall y 2second s 50c m (from focus tofilm ) Kodirexan d Kodak Definix (bothenvelop epacked )

ono fobject s 6c mo f limepacke d ^i^^«^^^

95 tiono fth etru eprojecte d positiono f thecentr e ofgravit y of a leadpelle t(LL) , made forX-ray s 577R an dL (Photo57 7L isshow ni nFig . 19).Fig . 20bshow sth e constructionapplie d toa cla ynodul e (CNL)o fth esam ephoto-pair . The following isth edescriptio n of theconstructio n showni nFig . 20a:Firs t theintersectio n i(L)o fth ecentr eo fth eX-ra ybea mwit h the filmwa s constructed for thelef than dphotograp h (L).Fo r thispurpose ,a sheeto f transparent material wasplace dove rth ephotograph ,upo nwhic hal l themarker s of frontan dbac kwindow s ando fth eobjec twer etransferred . Intermittent lineswer e drawn through themarker s ofth efron twindo w a'(L), b'(L),c'(L )an dd'(L )an d their counterparts of thebac k windowa ,b ,c an dd.-Th eextensio no fthes e lines coincided inon epoint ,whic h is the intersection ofth ecentr eo fth eX-ra ybea mwit h the filmplane .Thi spoin t functioneda sth e isocentre i(L)o fth e lefthan dphotograph .Al l displacements in thisphotograp h areradia l tothi s isocentre.No w a linewa s drawn from thisiso ­ centrethroug h thecentr eo f gravity Z1'(L)o f leadpelle t LL.Th e tracingwa s then transferred toth erigh t handphotograp h andoriente d according toth e identical contactpoint s ofth ebac kwindo wmarker s a,b ,c an dd .Next ,th eprocedur e was repeated ina n identicalway ,tracin g intermittent linesa'(R)a ,b'(R)b ,c'(R) c and d'(R)d tofin d isocentre i(R)fro mwhic h a linewa s drawn to the centre of gravity Z1'(R).Th eprojecte dpositio no f Z1wa s found atth e intersection ofth e lines drawn fromth e isocentres i(L)an d i(R)t oZ 1' (L )an d Z1'(R)respectively . Fig. 20bshow sa simila rconstruction ,no wapplie d inorde rt ofin d the true projectedpositio n ofth ecentr eo fgravit y (Z2),o f claynodul e CNL,o f X-ray stereopair 577RL .Tw otransparencie swit h thedat acopie d from thephoto swer e superimposed inorde r topoo l the information.Th e construction of the isocentres, i(L)an d i(R),wa s identical totha tdescribe d forFig .20a .Fo r the claynodule ,th e centreo fgravit yha d tob econstructe d fromth e imageso fth efou r leadmarker s (two ineac ho fth e twohole sdrille d throughth ecla ynodule )o nbot h films.Fo r this purposecrosse swer edraw nthroug h thesmalle r squareswhic h form theprojectio no f thecylindrica lmarkers .Thes ecrosse swer econnecte db y lines,whic h intersect in thepoint s Z2'(R)an d Z2'(L),whic hrepresen t thepositio n of Z2i nth erigh tan d lefthan d imagerespectively .Th etru eprojecte dpositio no f Z2wa sno wfoun da tth e intersectiono fth e line thatconnect s i(L)an d Z2'(L)wit h the line that connects i(R)an d Z2'(R)- Thisconstructio n isa nadaptio n ofa techniqu e called radial triangulation, commonlyuse d inth erectificatio no faeria lphotography ,se eVisse r (1968). Stereo radiography applied tosoil s isdescribe d byBoum a (1969),Krinitzk y (1970),Rogaa r & Boswinkel (1978)an dRogaa r (1980). Theconstructio nmetho d employedha s ahig hdegre e of accuracy for thosepoint s thatwer edetermine d fromfou rothe rpoint s (centres of gravity ofth e larger objects),mino r discrepancies tended tocance l eachothe r out.Fro mth e excellent coincidence ofth e fourline s determining the isocentre and the fact that upon repetition,th econstructio n turned out tob ewel l reproducible,i tcoul d be con-

96 b'ILI

dim (j'iLi c'(R) c'IU

Kg. 20a. Construction of the projected position of Lead pellet LL (Zl) of Stereo- Pair 577 LR, of Experiment II, in dry condition at the end of the 11th cycle (see Flg. 19), The explanation of the radial triangulation procedure is in the text.

Kg eprojecte d positiono fCla ynodul eCN L

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99 eluded,tha terror swer e lesstha n0. 2m mfo rrecorde dmovement s ina vertica l direction.Error si na horizonta ldirectio nwer e sometimes greater,i fth etw oiso ­ centres fellbot hclos et oth elin e throughth eobject st ob emeasured . Poorinter ­ sectionsresulte di nsuc hcases ,whic haffecte dth eaccurac yi na horizonta l directionbu twhic hdi dno taffec t the accuracyo fmeasuremen t ofth eris ean dfal l ofth eobject si na vertica l direction

5.1.4 Execution of the experiments

Theexperimenta lse tup swer e carried througha numbe ro fcycle so fwettin gan d dryingan dphotographe d intermittentlya tth edifferen t stages.A cycl ei nthes e experiments signifiesth etim e interval betweenth emomen to fwettin gth econtent so f thecontaine ran dth emomen ta twhic hdryin go fthes e contentsi scomplete . Wettingwa smostl ycarrie dou tfro mth ebotto mup .Wate rwa sadde dt oth e sandlaye ra tth ebotto mo fth econtainer .Th eflo wwa s controlled,i norde rt oavoi d anupwellin go fwate ralon gth etube .I npractic e this resultedi nmaintenanc eo fa headtha t fluctuatedbetwee n0 an d1 0c mabov eth esan d surface.Thi s resultedi na flowo fabou t 100enr/h .A nexceptio nt othi streatmen twa sExperimen t lb,whic hwa s moistened fromth eto pdow nb yunsaturate d flow,throug ha gypsu m crusto nth e surface.Mos tcontainer s received about80 0g o fdr ylim ean d40 0g o fdr ysand ,t o whichi ntota l approximately 300cm 'wate rwa sadde di neac hcycle . Aftermoistening ,th econtainer swer e left approximately 1day .Thi swa s followedb ya dryin gperio do fabou t3 week si na stov ea t50°C .Th edryin gwa s monitoredb ymean so fweighing .I nal lexperiment sth econtainer swer ehandle d with care,especiall y thoseo fwhic hth econtent swer ei na mois t state,i norde rt oavoi d shocks thatcoul ddistur bth earrangemen to fth econstituents . Intota l9 8X-ra yphotograph swer etake nan d4 8triangulation swer emade .

5.2 RESULTSO FTH EEXPERIMENT S

Table1 3summarise sth eexperimenta l conditionsan dth eresult si nth efor mo f movement registeredfo rth edifferen t objects.Additiona lparticular swil lb egive n for thoseexperiment s onlytha tdeviat e fromth estandar d set-uptreate di nth efore ­ goingsection .

5.2.1 Experiment la

Thisexperiment ,whic hwa scarrie dou twit ha lim e sample fromwhic h onlyth e fractioncoarse r than2 m mwa s removed,showe da ne tdownwar dmovemen to fal l the enclosedobjects .Th eexperimen tdeviate d fromal lth eother si nth efac t thatn o consolidationo flim ewa sundertake nprio rt oth eexperiment ,b ypourin g this materialint owater .Th eresult sar eshow ni ngrap hfor mi nFigs .21 aan d 21b.

100 Fig.21 awa s drawnt oexplai nth emod eo frepresentatio nuse di nFig .21b , 22, 23an d28 .I tshow sth emovement so fon ecla ynodul e only.Th emovement so fth e centreo fgravit yo fcla y nodule (CNR)o fExperimen t laar eplotte d againsttime , duringth efirs ttw ocycle so fthi s experiment.O nth ey-axis ,th emovemen ti nm mi s showno na namplifie d scale.Th ex-axi s showsth etim ei ndays .I tca nb eseen ,tha t theobjec tros e rapidly uponth emoistenin g that initiatedth efirs tcycle .I twa s founda tapproximatel yth esam e level after some dryingha dtake nplac ean dte n days hadpassed .Whe n dryingwa scomplete ,afte r3 5days ,a tth een do fth efirs tcycle , theobjec tha dgon e down againan dwa s approximately levelwit hth epositio ni nwhic h itstarted .A tth emoistenin g that initiatedth esecon d cycle,i tros e rapidlyt o aboutth esam eheigh ta sattaine d inth efirs t cycle.Afte rte nday so fdryin go fth e secondcycl eha dpassed ,i tha dlos t abouthal fo fth eheigh t gaineda tth emoist ­ eningstage .A tth een do fth esecon d cyclewhe n dryingwa s complete,th ecentr eo f gravityo fth ecla ynodul eha dfalle n belowth eleve l occupieda tth ebeginnin go f theexperiment .

À/CNR

MOIST progressive drying * a The 5iji \ vertica-rtical movementlmovement so sf Clao fCla y noduly nodule (CNR)_oe (CNR)off t^^dicated'inln P indicated in thefig - 1 «Sl.—*.,^, uuring^ th thefirse firs t ttw twocycleo cycle s os ofthf th eexperimee experime n n. *A» ^ nta ^t which^th e 'a ?ycl ei nthi s case signifies thetim e interval between the ^ llnSo fth econtaine r starts andth emomen t atwhic h drying

101 InFig .21 bth emovement so fal lth eobject so fExperimen t laar eplotte d against time.I tca nb esee ntha tal lobject s roseupo nwettin gan dfel lupo ndrying . The totalexten to fthi smovemen twa s1-1. 5m mfo rth ecla y nodulesan dabou t0. 5m m forth elea dpellets .Ever ycycl e showeda smal lne tdownwar d movement.A tth een do f the second cycle,th erigh than d claynodul e (CNR),ha dfalle n belowit sorigina l level.Bot h leadpellet s (LLan dLR )wer e backa tzer oan dth elef t hand claynodul e (CNL)wa sstil l situateda t0. 4m move rit sleve lo fdeparture .Afte r sevencycles , all fourobject sha dfalle nbelo wthei r zero levels,a sindicate d inTabl e13 , Column7 . TheX-ra yphotograph so fth edr yconditio n showa narro w void aroundan d especially aboveth ecla ynodules. Som e cracksi nth elim emas s showu ptoo .Thes e features disappeared almost completely fromth eimag e uponmoistening . Vesicles formeddurin gth eexperimen ti nth euppe rpar to fth elime .Thes e vesicles remained visiblei nth eX-ra yphotograph s takeni na mois t condition. Itwa snote d thatdurin g thisexperiment ,moistenin gwa ssomewha t slower thani nth eothe r experiments.Thi s

progressiv,, drying

Fig. 21b. Thevertica l ) n LR) f uuies68 (CNR and Se ex eri(LR) °of ^P^^^a^'^^L^L^^Experiment Ia.'piMt^"*' "V .. >— v-(CNLw )-an ^ d Lea^- d pelletr— s . . Plotted against time, during the first twocycle so £

102 was due to the fact that the set-up of Experiment la did not include a perforated tube to distribute the water throughout the sand layer. This made the infiltration from the feeder tube directly into the sand, much slower.

5.2.2 Experiment II

In the course of this experiment a net rise of all objects was noted. Fig. 22 shows the positions of all objects in dry condition, at various moments during the experiment, plotted against time. It can be seen that after an initial fast rise, the process stabilized and the average curve becomes almost a straight line. No sign of decline of speed of rise can be observed in the last of the eleven cycles. The effect per cycle seems to vary considerably. Cycle 7 was very effective, whereas Cycle 8 was an ineffective one, but this was followed by some very effective cycles. Differences between objects are present. The performance of clay nodule (CNR) was clearly higher than that of the other objects.

>;CNR

LR :T LL , * CNL

10 H Cycles of appr. 25 dayseac h

?!*•22 . Thevertica l movementso fth eobject so fExperimen t ^'^^n^oUed 1 ^ during 11cycles .Th eobservatio n pointsar etake ni n ^ # ^ m ly l £** indicate interpolations since X-rays wereno t "ken = trlght . nodule left,CN R= cla y noduleright ,L L= lea d pelletleft , 103 InFig .2 3severa l observationso fth efirs ttw ocycle s indry ,mois tan d intermediatestage shav ebee nplotte dagains t time.Th egenera lpatter n showstha t aftermoistening ,ther ewa sa rapi d riseo fal l objects.Afte r this therewer emino r movementsupward so rdownward sdurin gth efirs tte nday so fth edryin g cycle.Whe n thedryin gcontinued ,al lobject s generally fell,Th eonl y differencei nth ebehav ­ iouro fcla ynodule san dlea dpellet swas ,tha tth eamplitud eo fth emovement so fth e former,wa sgreater . Incomparin gth efirs ttw ocycle so fExperimen t II(Fig .23 )wit h thoseo f Experiment la (Fig.21b) ,i tca nb esee n that apartfro mth esimilarit yi nth e peneralpatter no fmovements ,a smentione d above,a nimportan t differencei nth e behaviouro fth eobject si sevident .Th eobject so fExperimen t IIsho wa smal lne t gaini nheigh ti neac hcycle ,whil eth eobject so fExperimen t lasho wa smal lne t loss.Th etota lamplitud eo fth emovement so fth eobject so fI Ii sconsiderabl y greatertha ntha to fth eobject so fla . Thetrajector yo fth eobject so fExperimen t IIi sshow nte ntime senlarge di n

70 Days

CYCLE 1 CYCLE 2 Fig. 23. Thevertica lmovement so f theobject so fExperimen t IIplotte d against time during thefirs ttw ocycles .Th econdition srepresente d inchronologica lorde r are:dry-moist-moist-dry-moist-Tnoist-dry .CN L= cla ynodul e left,CN R= cla ynodul e right,L L= lea dpelle t left,L R= lea d pelletright .

104 Fig. 24. As already mentioned theaccurac y of the construction formeasurement s in vertical direction is higher, than that formeasurement s ina horizontal direction. Part ofth e observed movements in a horizontal direction may be due to this effect. It is, however, beyond doubt that horizontal movements of the objects did occur since the registration errors in a horizontal direction, are not larger than 0.5 mm. In the course of Experiment II, it was noted that a considerable amounto f vesicles became trapped in thelime , which caused this material to increase involume . Consequently a device was installed, to measure the heave of the surface of the lime mass, by amplifying the movement by means of a lever. Fig. 25 shows the movementso f the lime surface during thelas t four cycles of the experiment, plotted against time. For each cycle thehorizonta l time scale has been subdivided into two parts,th e first one into hours to represent therapi d rise that occurs upon moistening, and the second one, ofa much smaller scale, to represent the movements of the surface during the remaining period of thecycle . Irrelevant differences in length of the cycles, (due toth e fact that thecontainers , once dry, were not always remoistened immediately), are notshow n here. Each cycle is represented by a standard block. It can be seen that theinitia l heave varied from cycle to cycle and that small downward movements often followed. Inal l cases part of the heave was produced, apparently by the rise of the temperature, just after placing the set-up in the stove for drying. Study of the X-ray images (Fig. 19), shows theformatio n of prominent voids

2 3 4 5 6 7

;lQy nodule left Lea d pellet Iett ICNLI ILL]

J^S. 24. Trajectory of the centres of gravity of clay ™?" "0^ition is indicated b ect «Périmen.- t I„I enlarged_„,_ . Th...e. positioposition oof ththe °objectJ *.s ™xn-ox •_s^. indicate^ d bbyy a& croscrQSsS (x(x)) . b y aa point- < \. „^ *„„•.-,•„„ „f „Hiprts in dry condition xs inu .„a„r lines - Point (.); the position of objects xn dry conai ion# Intermittent lines cumbers indicate the number of cycles passed for eacn p indicate the ^e interpolations of intervals for which no X-rays were taken. Section of movement. 105 cvciJ öf lut heaVe.°f the surface °f the lime of Experiment II, during the last four ent scaïL ™rferTnt- EaC\?y?le has been subdivided into two part! with différ­ ents tne remaL^ f*T IS ?1V^ed int° h0Urs' the second Part (crossed) repre- sample was intrl^ H • ^ ^^ ^ dat6S) ' Arrows indicate the ^ent at which the due o expansion of th1,3 "T ^ drying' which led to some hea^ immediately, cycle It is cW ,t t tapped air. The solid bars indicate the net heave per wS-ovL-tf^tSlur^elf^^occTif^c S ^ ^^ ^

aboveth ecla ynodule si ndr ystate .I nth ecours eo fth eexperiment ,som eo fthes e voidsseeme dt o'disintegrate 'int onumerou ssmal lvesicle swhic hals odevelope di n abundance,independentl yo fthes evoids .Th evesicle sappeare di nincreasin gquantit y duringth ecours eo fth eexperiment .The yrestric tthemselve sa sFig .1 9show salmos t exclusivelyt oth elim eoverlyin gth ecla ynodules .Unde rth ecla ynodule shardl yan y voidsar evisible .Th evesicle sincreas ei nsiz efro mth esurfac edownward .The yar e roundnea rth esurfac ean dbecom eincreasingl yhorizontall yplane dof fwit hdepth . market;,5 "i'™' ^ BEaSUra«lts ™> ^e ofth epositio no fth elea d I riment ^"^ ^ ' * "**t 0 ******* theamoun to fswellin gdurin gth e :~: !aUe :f_ C0LE ^ — *-d whichar esimila rt othos ereporte di n foUn dbe bew en £ f t ^*' ^^ ™° *-n differentcycle san dals o - J aX\S the Sme Clay n°dUle M thS^ ^ Sincesom elea d d S " thelrb0ringS '^ SlnCeSOm S <**-iule stende dt o c during the experiment the d e :; r > ~ »^c^ t be C0Uld h be n u s r T ' —' ascertainedtha tmos to fth eswellin go f P alm St inStant Mt h H ' ° -ouslyupo nwetting . endo fExperimen tII ,un dlsturbedrin g^ ^ ^ ^ ^ ^ ^ 106 ? B

E • „f „rmitvo ftw ocla ynodule s ïndi- Fig.26 . Reconstructed positiono fth ecentre so fgr a y^ ()> rf ^ ?l te y catedb ya cros s (x)an do ftw olea d pellets indicated *sand surface (EF)i n ofth eheav e indicator (AB),an do fth eaverag e level 01 ^ d) ^ the end ma relationt oth ereferenc e frameo fth ebac k window ™

i, vfo r changesi nbul kdensit ydurin g overan dunde rth ecla y nodules,i norde rt ochec x *^^ remoisted inth e theexperiment .Th esample s were taken afterth econtaine r ^ ^ ^ samples samewa ya sha dbee n done during theexperiment , [lor z l

SeeFi§ '26 ° • ,th estar to fth eexperiment ,lim e from Inorde rt odetermin e thebul k densitya ttn e ^ ^ ^^ .^ ^^ thesam e fractiono fth esam e samplea sused fo rEx Pe™ moisture contents Fromthis ,rin g samples were drawn.Tabl e 14show sbul kde n '^^ ^^ ^ andpor evolum eo fth elim e samples.Fo rth edeterminatio n o ^ ^ specificweight o flime , 2.71,wa stake na srepresentativ e

faction.Thes e figures arediscusse d inSectio n 5.3.3.^ concentric cracks,

Uponremoval ,th ecla y nodules showeda numbe ro main^^ & vesicular probablyth eresul to ffas t moistening. Insom e cracKs, structureha dpenetrate d (Fig. 27).

5.2.3 Experiment Ilia

• A t witha H * sample thatha dbee n obtained This experiment whichwa s carriedou twi t signifleantne tris efo rcla y byaugerin gan dwhic h wasno tsieved ,di dno tyi e a ^^ ^^ ^^ aduleso rfo rlea d pellets.Th eexperimen twa s abandoned 107 itwa ssee n that movements causedb yth esecon d moistening, brought allth eobject s backt oth esam e height that theyha dreache d inmois t condition during thefirs t cycle.Th eamplitud eo fth emovemen twa ssmal l compared with thato fExperiment sI I and Illbl. It shouldb estate d thatth esampl eca nhardl yb equalifie d as 'natural' since

Table 14. Bulk density (BD,se eSectio n 4.2),moistur e contentan dpor e volume of thelim eo fExperimen t IIa tth een do fth e11t hcycle .

Source Sample BD BD Pore Moisture content no. (moist)"1" (dry) volume (v/v) (w/w) Lime poured inwate r 1 1.42 47% 2 1.45 46% Over thecla y nodules 1 1.2 0 0.92 66% 28 30 2 1.20 0.92 66% 28 30 Under thecla y nodules 1 1.70 1.35 50% 35 26 2 1.69 1.34 49% 35 26

périment.Th efractur e shows thf^ °f,ExPeriment H that fractured during the ex- b red throu h the (Arrow 1)int o which the leadl r Ir°^^ ^ ° S -«re ofgravit y crack(Arro w2) .Vesicle sar evisibl e ^t^^i Ume haS Pirated intoth e arevisibl ei nth elim etha tpenetrate d (Arrow3) . 108 the auger that took it ground up several clay nodules, which caused the admixture of rather large quantities of clay to the lime. This probably influenced the properties of the lime in moist condition, as shown, e.g., by the deviating liquid limits of clay-rich lime samples, reported in Section 4.6.1.1. On X-ray photographs it can be seen that during the experiment, voids formed around and especially above the clay nodules in dry condition, and disappeared in »ist condition. The overall cloudy appearance of the images indicates that from the start the heterogeneous mixture enclosed more air, than in the other experiments.

5.2.4 Experiment lb

This experiment involving moistening from the top down by means of unsaturated flow, was carried out to evaluate the effect of this process on the behaviour of various objects encased in lime. The objects in this case were two clay nodules and a rounded piece of quartzite gravel from the rafîa deposits (Unit R), which are common in the survey area, as indicated in the map (Fig. 3). For this purpose, the set-up was identical to Experiment II, except that the moistening took place through a gypsum crust on the surface, over which a constant head of approximately 1 cm water was maintained (see Bouma, 1977). In order to avoid local saturation of the sample, the bottom of the container was perforated, covered by porous material and placed m dry sand during the moistening. , During the two cycles that the experiment was run, no movement could be detected, » the centres of gravity of the clay nodules, nor in that of the rana gravel, prison was made between the dry state at the start and the dry stat°* ^ °f the second cycle. Intermediate images were not available. Since no e seen, the experiment was discontinued after the second cycle.

5>2-S Experiment Illbl

The set-up for this experiment was identical to that of Experiment H, except ** the source of the lin* and the nature of the embedded objects (see ^bl 1 )• Ane t rise was noted for all objects enclosed, which measured 4.2 m to ^ CW nodule, 3 mm for a rana gravel and S mm for a petrocalcic rag* «* -ddle. These results were obtained in five cycles (movements shown^ ^ ** the positions recorded in a moist state at *e vitiation o^ ^ ^ ^^ it can be seen that, just as in Experiments la and U, a ^ dement upon drying. This measures about 1 mm for the clay nodu

Petrocalcic fragment and only 1/4 mm for the rana gravel. ^nt wMch At the end of the fifth cycle, a modification was made m exp Was then continued under the number IIIb2.

109 SSL

Cycles Fig. 28. Thevertica lmovement s of theobject s ofExperiment s Illbl and IIIb2plot ­ tedagains t time.A considerabl eris efo ral lobject s is evident during thefirs t fivecycle so fExperimen t Illbl.Th epositio no f theobject s inmois t condition shortlyafte r theinitiatio no f thefift h cycle is indicated byhollo w symbols.A t theinitiatio no f thesixt hcycle ,th e set-upwa s changed and Experiment IIIb2 started.A heav yweigh twa splace d on the surfaceo f the limewhic h caused sub­ sidenceo fal lobject sdurin g the sixthcycle .Fro m thepositio n of theobject sa t theendo f thenint hcycl e iti seviden t thatth e subsidencemus t have continueda t \ "™ rate for some timeafte r the sixthcycle .Th efollowin g objectsar e shown:P M= petrocalci cfragment ,middle ;CN R= cla y nodule,right ;S L= ran a

5.2.6 Experiment IIIbB

Atth een do fth efift hcycl eo fExperimen t Illbl,a lea dweigh to f4. 5k gwa s placedo nth elim esurfac ei nth econtainer .Thi scause da pressur eo f7 5g/cm 2, whichi sroughl yequivalen tt oth epressur ei nth esoil ,a ta dept ho f5 0cm .Th e weightwa sapplie ddurin gth eful lcycle .I twa sonl yremove dwhe nth econtaine r hadt ob etransporte di na dr ycondition .Specia l arrangementswer e madet oassur e fastdrying ,despit eth eweigh to nth esurface .Fo rthi spurpose ,th elea dweigh t was separated fromth eto po fth elim esurfac eb ya laye ro fporou smaterial , (groundbrick) ,throug hwhic hai rwa sblown ,i norde rt oensur e fast evaporationo f moisture.I nthi sway ,i twa spossibl et ocaus e this samplet odr ya squickl ya s thosewhic hha duncovere dsurfaces . Hieexperimen twa scarrie do nfo rfou rcycles .Th eeffec to nth einclude d objectswa sa ne tdownwar dmovemen to f2. 5m mfo ral l(Fig . 28).Despit eth efac t thatn oarrangement sfo rdetaile dmeasurement so fcompactio nwer emade ,i tcoul db e observed thatth esurfac eo fth elim ewen t downabou t2 mm ,whic hi ssimila rt oth e

110 fall of the encased objects.

5.3 DISCUSSION

The experiments summarised in Table 13 were set up originally, as stated in the introduction of Chapter 5, to verify the occurrence of movements of objects contained inlim e subjected to wetting and drying, and to confirm that these could be measured. When this was ascertained, five new questions arose, namely: 1. What causes the movements? 2. What is the mechanism of the process (es)? 3. Are the process(es ) that cause these movements capable of producing a sustained rise of objects? 4. Which factors determine the process (es)? 5. Are the experimental conditions under which the rise occurred comparable with natural conditions in the soil? The min cause of the movements can be identified. Furthermore it is possible toprov e that the rise measured is not due to some temporary phenomenon but represents a sustained upward movement. The answers to the other questions, however, include an element of speculation, for the following reasons. Time is the main limiting factor in most attempts to reproduce pedogenetic Processes in the laboratory. This weighed especially heavily in this particu ar «se, since an attempt was made to approach natural conditions as closely as Possible. This implied that in the experiments drying was performed at temperatur ** higher than 50°C, which made the minimum duration of one cycle about y • Despite the fact that some of the experiments lasted for periods up to one year, their duration was too short to solve all questions satisfactorily. ^ ^^ Each of the individual experiments was carried out with the purpose o a specific assumption. If it became apparent that the assumption had to e re^ted, a new one would be formulated and the experiment would be adapted ** - The expiations given in the following part have emerge gra ^ ** course of the investigation. As such the set-up of the sequence F **1 have been different, had the testing been started with these id a ^ P°int of departure. This explains a lack of certain useful data such a , -g-,

^e-heave measurements during Experiments la and Ilia. insu£ficient to The six variations introduced into the experiments are ay ^ *** the large number of factors and their interactions which evi n ^ J^ r^- More experiments of a longer duration would be needed to set **!«*. The five questions will be treated in the following section .

111 5.3.1 What caused the movements?

Optionst ob econsidere dt oaccoun tfo rth emovement s registeredar etreate di n thefollowin g sections (5.3.1.1-5.3.1.4).

5.3.1.1 Gasenclosur e

Gasenclosur edoe s indeed occur,i nal lexperiments ,tha t showedupwar dmovemen t ofobjects .Proo ffo rthi sca nb efoun di nth eappearanc eo fvesicle sin th ecours e ofth eexperimen tan di nth edecreas eo fth ebul kdensit yo fth elim edurin gExperi ­ mentI I(Tabl e 14).Th efac ttha ta ga si sresponsibl efo rth esurfac eheav ei sals o clearlydemonstrate db yth etemperature-relate d additionalheave ,indicate db yarrow s inFig .25 .Th eX-ra yphotograph s offerclea rproo fo fth egradua l increaseo fth e gasaccumulatio ni nth ecours eo fth eexperiment s (seee.g .Fig .19) . Itcanno tb erule dou ttha ta smal lpar to fth ega si sCCU ,whic hi sforme db y theH ion si nth ewater ,whic hreac twit h CaCO,.Th equantitie s cannotb elarge ,how ­ ever,sinc eonl ysmal l amountso fH ion swer eavailable ,i nth ewate ruse d formois ­ tening,an dsinc ebicarbonat ewoul dhav e formedi fth eC0 ? pressureha dbee n locally raisedto omuch .Notwithstandin g this,th eproces sma yb ewort hmentioning ,sinc ei t couldexer ta primin g functionon othe rprocesse so fga senclosur e (personalcommuni ­ cation,Va nReeuwijk , 1980). Releaseo fair ,absorbe don th elim e surfacesi ndr ystate ,upo nwettin gca n conceivably contributet oth ega senclosur ephenomen a (personal communication, Koenigs, 1982). Paletskayae tal . (1958),suggeste d thatth ereleas eo fCO ,durin gth edryin g ofa bicarbonat e solution,cause svesicl e formationi ntaky r soils. Entrapmento fair ,du et oirregula rwetting ,seem st ob eth eonl y otheroptio n availablet oaccoun tfo rth ega senclosur ephenomen aobserved .Thi sproces swil lb e discussedi nSectio n5.3.2 .

5.3.1.2 Swellingo fcla ynodule s

Swellingo fcla ynodules ,i seviden tin th emovement s registeredi nth efirs t cycleso fExperiment s laan dI I(Fig .21 ban d23) .Th egenerall y greater amplitude ofmovemen to fth ecla ynodule scompare dwit hth eothe robjects ,mus tb edu et o the swellingan dshrinkin gwhic hcause sris ean dfal lo fthei r centreso fgravity . Thisprocess ,however ,doe sno tlea dt oa consistentl yhighe rne trise ,i nth e variousexperiments .I nl ai twa sapparentl y totally ineffective.Sinc e rigid objects likestone san dlea dpellet swer e foundt oris e too,swellin go fth ecla y nodulescanno tb eth emai nproces sresponsibl efo rth erise .I ti spossibl e that theswellin gbehaviou ro fth ecla ynodules ,i nconjunctio nwit h otherprocesses ,

112 would in the long run cause these objects to rise more rapidly than the rigid ones. Theexperiment s offer indications, that this may be so, (e.g., the performance of the right hand clay nodule of Experiment II, after 11 cycles as shown in Fig. 22).

5.3.1.3 Buoyancy of objects immersed in moist lime

Buoyancy of objects immersed in moist lime was suspected to be the mam process responsible for the rise, at the initiation of the experiments. The experiments have shown, however, that there was also a rise in various objects, of abul k density, much higher than that of the moist lime, such as, e.g., lead pellets and quartsitic rafia gravels. The moist bulk densities of lime developed at different heights in the container during Experiment II are summarized in Table 14. prison with those of clay nodules (Table 9) shows that in dry state these are lower than the moist bulk densities of the lime, except for its upper layer. The »ist bulk densities of the clay nodules, however, are approximately equal to the »ist bulk densities of the lime of the lower part of the container. It is conceivable that in the initial stages of a cycle, when the lime was moist but tne day had not yet absorbed all the water it could take, the buoyancy effect combined with the shrinkage of the nodules contributed to their rise, provided that oca liquifaction of the lime allowed for the displacements. Buoyancy cannot accoun for the rise of all objects, however.

5,3-1.4 Compaction

*• ^t ohiprts was evident faction, leading to short-lived downward movement of objects, * the results of some experiments (la and Illb). Its effect may be pies -nain extent in all relts. The net rise of objects and the ne heave^the s «ace is always the balmce between whatever compaction occurre an Processes operating in the opposite sense.

5'3-2 The mechanism of the air entrapment process

Review of all the options considered, leads to the cone usion^ ^ ^ ^ Pr°cess to be held responsible for the movements of all types o

entrapment. This process will be considered in more detail. ^ compress this Water entering a capillary will expel the air centaine ^ ^ ^^ ^ air if it cannot escape. The maximum pressure (A Pmax) w ^ ^^ this «ay, can be calculated for round capillaries by means o f0I*la for capillary rise as given, e.g., by Hillel (1980).

A p = (2 y cos o)/r

113 inwhich : AP = pressur e difference betweenwate runde r themeniscu s and air over it Y =surfac e tension; 72.7mN/ m forwate r at 20C a =contac t angle;0 °fo rpur ewate r incontac twit h inorganic substances r =radiu s ofth e capillary The assumption ofa contac t angleo f0 °implyin g completewettin g is also usedb yBol t &Koenig s (1972)fo ra soil-wate r system. They approximate thevalu e ofA Pma xfo ra 1u mcapillar y as 1.6 bar andus e therelatio n 1.6/rt ofin d the APma x inba rfo rcapillarie s ofwhic h the radius (r)i sexpresse d inym . whetherth eA Pma xfo rai rcompresse d in acapillar ywil l indeedb e reached depends,a sBol t &Koenig s (1972)poin t out,o nth e lengtho fth ecapillary . Water entering acapillar y fromtw o sidesma ycompres s the occluded airt o a spherical bubble inth emiddl ewher e the twomenisc imee t andbecom e stationary. The APma x willno tb ereache d inth ebubbl e ifth ecapillar y isno t longenoug h toallo wfo r sufficient compression. Ifsuc ha bubbl e is formed,th epressur e on the capillary wallreturn st o zero.T osummariz e itma yb e stated that APmax for asingl e round capillary depends onth eradiu s ando nth e ratiobetwee n radius and length.Th e smallerth eradiu s the largerA Pma xprovide d thatth erati oradius/lengt hi sals o smallenoug h toallo wsufficien t compression to takeplace ,t oreac h APmax before abubbl e isformed . Fora plat e capillary the formulatha texpresse s APma xha s tob e modified. Sinceth emeniscu s insuc ha capillar ydoe sno thav e aspherica l shapebu t takes thefor mo fa semi-cylindrica l trough,i tca nb ederive d that fora plat e capillary ofwidt hd an dassumin gcomplet ewetting ,A Pma x= y/ 1d - Thisi shal fo fwha t APma xwoul d be fora roun d capillarywit h aradiu s equal to \ d. Therelatio n y/\ à indicates theA Pma xtha twoul db ereache d ifth e compression ofai r tookplac e ina plat e capillary open onon e side only.Wher eplat e capillaries occurbetwee n thecalcit e crystals of thepowder y lime (see Section 4.6.1.2), thecompressio nmode l ismor e complicated sincewate r enters from all sides. Insuc ha cas ea nelliptica l orcircula rbubbl ewil l formbetwee n theplates . Thisbubbl e isbounde d onal lside sb y ameniscu s ofsemi-cylindrica l shape.Fo rthi s situation therelatio n AP= T / (1/R1 + 1/R2) isvali d (seee.g .Hillel , 1980),i n whichR 1 represents theradiu s ofcurvatur eperpendicula r to theplate s and R2 the radius ofcurvatur eparalle l toth eplates .I nth ecas e ofpur e crystalline limea perfect fito fth ecrysta l faces canb eexpecte d as suchR 2wil lb ever y large in comparison toR1 . During thecompressio n ofth ebubbl e R1 remains constantbu t R2re ­ duces somewhat.Notwithstandin g the latterfac t it seems justified toneglec t the term 1/R2whe nestimatin g theorde ro fmagnitud e ofth epressur e thatdevelop s inth e plate capillaries. Inthi scas eth eequatio nreduce s toA P= y/\â, which isvali dfo r plate capillaries openo non esid e only.B ymean s of this formula itca nb e calcu­ lated thatpressure swil ldevelo pwhic hrang e from 1.6 to 16ba r forplat ecapil ­

lariestha trang e inwidt h (d)fro m 1t o0. 1 m.

114 In the following paragraphs a model will be developed which describes air enclosure in the peculiar void system of the lime for those experiments that produced a net rise of the objects. Asmentione d in the discussion of the liquid limit of the lime (Section 4.6.1.2), the crystalline character of the calcite grains has a strong influence on the behaviour of this material. Upon moistening of the lime by pouring it into water, as was done in Experiment II and IIIb1, the calcite crystals tend to arrange themselves in packets of grains which adhere to each other by means of a thin water-film between their facets. These packets of crystals pile up randomly to form astructur e with larger voids. Upon subsequent drying a structure results which doesno t show a continuous distribution from large to small pores but in which two different void systems can be recognized, namely a system of extremely narrow planar voids inside the crystal packets and a system of much larger voids between the crystal packets. Upon remoistening this pore system behaves as follows. Water enters the larger pores rather rapidly. A certain amount of air is occluded in this pore system ue toth e fact that water enters the pore network from different places and blocks the exit for air trapped in the system. Water will also enter the narrower voids but this wetting is much slower, since according to Bolt & Koenigs (1972) the flow resistance in narrow pores (0-1u m class) exceeds the effect of the larger pressure deficit m this sys e . TMseffec t retards the build up of pressure in the system as part of the air ^ gelled from the narrow voids in order to 'pump up' the larger vol s. ^ P^t of the narrow pores will, however, occlude air between the crysta a

«ad moistening of these planar voids allows for ^f^^ Q£ air Perimeter of the planar voids via the wider pores. As a resui , between the crystal planes will take place. _ ^ ^ ^e ARna x of the wide pore system is governed by the diameter o • Dointivelv modest lowest neck of this system which contains a meniscus. Relativ y usures result which lead to dislocations of the lime ^^^J^ la^s of the container. The dislocations result from the failure ^ ^ P°«s in the upper zone where the overburden pressures are modes . ^ ^ n *row planar voids between the crystals aids the dislocations si ^ discussed ll*rication for movements of the crystals along their contac p , ^ ^^ ^ ln laV action 4.6.1.2. Deeper in the lime mass the number of ^J^^ due t0 ls occluded with a pressure sufficient to cause failure decrea ^ ^ the larger overburden. In most instances the compressed air wi ^ ^ optional cases is the smallest pore neck of the system son ^ J**** for a A Pmax sufficient to overcome the larger overburde p

^ about failure. s mQSt o£ the permanent ^is behaviour of the large pore system probaoiy explains the su«ace-heave due to increase in volume of the lime mass. 115 relativelystee pbul kdensit ygradien testablishe di nth e lime during ExperimentI I (Fig. 26an dTabl e 14).Als ocontributin gt othi s steepnessi sth e fact thatth e largevoid scollaps ei nth edeepe rlayer sbu t areconserve di nth euppe rlayers . Theobservatio ntha tmos to fth esurfac eheav e occurred relatively abruptlyon e ormor ehour safte rth ewettin gha dbee n initiated confirms thenecessit yo f moistening theplana rvoid san dlowerin g theliqui d limito fth e limebefor e dislocationsca nb eproduced . Thewettin go fth enarro wpor esyste m causesa neffec twhic hdiffer s from thato fth elarg epor esystem .Wate renterin g from all sides into thenarro wplana r voidsbetwee nth ecrysta l facetswil lcompres s the airu pt oconsiderabl epressure s (probablyi nth eorde ro fsevera lbar s sincewidth so fth eplana r voidsi nth eclas s 0.1-1 ymar et ob eexpected) .Th eare ao fth eplana rvoid si sver y large comparedt o itswidth ,a ssuc hA Pma xwil lb ereache d inmos tcase swel l before the air iscom ­ pressed toa spherica lvolum ei nth emiddle .Th ecompresse d airi nth ebubble swil l tendt odissolv eint oth ewate ra tarat eproportiona lwit h the gaspressure .Th e facttha tonl ya smal lpar to fth esurfac eare ao fth ebubble si si ncontac twit hth e liquidslacken sth epac eo fth edissolution .Notwithstandin g this last fact,hig h pressurebubble swil lprobabl yb erathe r shortlived. Theeffec to fth eocclude d airbetwee nth ecrystal s upon the limemas s isa s ows.Th ecrysta lpacket swil lexpan d somewhati na naccordion-lik e fashioni n adirectio nperpendicula rt oth ecrystal s thatboun d theplana rvoids .Sinc eth e crystalpacket shav ea rando m arrangement,force swil lb eexerte di nal ldirection s y theseaggregates .Th ecalcit ecrystal sbecom e temporarily separated fromeac h otherb yai rcushion shel d inplac eb ymenisc i thatac t like 'springs',th etota lre ­ sembling theai rsuspensio nsyste mo fa vehicle .Th eresul to fth emulti-side dexpan ­ sioni seviden tm themovement so fth eobject sa sillustrate di nFig . 24.Upo nwet - thüf 1 I"""6maS Sth e °bJeCtS m°Ve ina1 1 Sections except downward.Th ereaso n thatdownwar dmovement sar eabsen ti sth efac t thatcompressio no fth eunderlyin gma ­ terialswo ud tak ea greate rforc etha nuplif to foverlyin gmaterial . measure- . * ^^ ^^ WMch isi nP art reversible.Th emaximu mheav e ^asured ineac hcycl ei sth etota lo fth eheav edu et oth e coarsepor e system LTZ ZZVTS) mdt 0th efin epor esyste m(th ^hout the lime fine„J ! , S WhlCh iS risible is probably mainly due to the SyStSm t0 a l6SSer 6Xtent t0 C0lla tLoo tnthe ccoars" r7e° pore system ^ . P- "f larger voids related deats? IS tke UiV entrapment proeess copule of producing a sustained vise of dir the iZeZlZ^Z^T' WGredU e S°lely t0th elnCreaS e °f the V°1Ume °£ that its inroortanr. "^ Pr°œSS W0Uld be short-lived. It would mean ance, as a natural process would be very limited. The fact that the

116 heave, according to Fig. 25, did not show any signs of diminishing after 11 cycles. doesno t mean that the process would have lasted indefinitely. If the bulk density had continued to lower, a moment would have come, when the reduced amount of solids could no longer support the void structure and collapse of voids would have xcurred. An equilibrium would then have established itself between the creation ofvoid s and their collapse. In fact the heave diagram shows that collapse on a small scale has already taken place during every cycle. If the rise of the objects were due solely to the increase in volume of the lime, it would stop once the equilibrium was established. These considerations make it important to know, whether the bulk density decrease was indeed the only process active in the experiments. Comparison of the bulk densities measured at the end of Experiment II, with that which existed at the initiation of Experiment II (Table 14), taking into account the rise of the objects registered, makes it possible to settle this question by a simple calculation. In Experiment II, the average rise of all the objects registered (see Table 13), can be computed to be 7.4 mm. At the end of the experiment, their centres o gravity were situated at an average of 44.5 mm above the sand surface, whereas at thebeginning , they were situated at 44.5 mm- 7.4 mm = 37.1 nm over the sand sur ac (Fig. 26). If the rise of the objects were to be entirely due to the increase of M* of the underlying lime mass, which, encased in the container could only expa « a vertical direction, then the product of average distance between ejects and « surface and average bulk density before and after the experiment, wou d have * equal. This is clearly not the case. Product before the experiment started . _. • t_ j /i/i ç Y 1 ^45 = 59.9. It can oe x U35 = 53.2. Product after the experiment finished. 44.5 x I.M calculated that the decrease in bulk density during 11 cycles accounts

iZjmmx 1.435 ,n , rare = 39-6™ 0f the distance to the sand surface at the- end of the experiment this ^S^ "" - v\ f. „ mflv the only conclusion that can LK- 39-6 m = 4.9 mm, unaccounted for. Consequently the y ^ ^.^ dra** is that at the end of the experiment, more lime particles P fr °m the underlying sand surface than before the experiment. ^^ n Q£ 7A m> Of the total average rise of the objects registered m bxpe ^ ^ ^ ^ ^ the vo1 net average rise, which was not due to increase in ™^ ^ ^ ^ o£ 0.5 W 11 c c cycles. This means that the average net rise per ? ^^ = 2.5 mm. The regis- m -TCie ris e due to decrease of bulk density was 7.4 mm- . ^.^'^ the lime. Un- te red surface heave must be due entirely to decrease in u ^ available. An fortunately, for Experiment II, for all 11 cycles, no heave ^_^ ^ ^ ^ Relation, however, can be made from the last fou r eye , ^^ ^ Mistered heave was 7.25 mm (see Fig. 25). For 11 cycles 117 -j- x7.2 5m m = 19.9m m

Thechang eo fth ebul kdensity ,o fth euppe r 54mm ,enable s thecalculatio n ofthi s distance atth ebeginnin go fth eexperiment :

54m mx 0.92 ,„ , 1.435 =34 '6 ™

Thismeans ,tha to fth etota lheav eo f 19.9mm ,5 4m m - 34.6m m = 19.4m m hasbee n accounted for.Th eremainin g 19.9m m - 19.4m m = 0.5m mmus tb edu e toth edecreas e ofth ebul kdensit yo fth e lowerhal fo f thelime .Thes e 0.5m m differs from the 2.5 mmactuall ycalculated .Th edifferenc eprobabl y lies inth e fact that thebasi so f thecomputatio nwa s anextrapolation . Ifincreas e involum e ofth e limebelo wth eobject swa s thesol e cause of theirrise ,th eamoun to flim ebetwee n theobject s and thesan d surfacewoul dhav e remained constant.Thi s leadst oth econclusio ntha tanothe rproces smus thav e beenactiv e inorde rt oaccoun t forth efac t thatmor e limeparticle s separate the objects fromth esan d surfacea tth een do fth eexperimen t thana tth ebeginning . Thisadditiona lproces s isver yprobabl y theresul t ofth e largely reversible accordion-effect ofth ecalcit ecrystals .A model for thiswil lb e treated inth e nextparagraph . Upondryin go fth e limemas s thecrysta lpacket s contractagai n andmos t small limeparticle sretur nt oth epositio n theyoccupie dbefor e the enclosed air forcedthe mapart .Som edislocations ,mainl y shifting ofcrystal sparalle l toeac h other,ma ynot ,however ,caus eal lsmal lparticle s toretur nt othei rorigina l positions.Th echance s thatlarge robject sretur nt othei rorigina lposition s is nuchsmalle rsinc ether ei sver y littlelikelihoo d that theorigina lvoi dwhic h theypreviousl yoccupie dwil lb ereconstitute d ondrying .Th e larger the object andth emor e irregular itsshape ,th esmalle r thechanc e that theorigina lvoi d willb ereconstituted . Ifonl ya fe wo fth eman ycalcit ecrystal s thatbounde d thisvoi d failt otak eu p theirorigina lpositions ,th e large objectwil lno t fit andcanno tretur nt oit sorigina lvoid .Consequentl y thewettin g anddryin g ofth e limemas swil lproduc ea ne tdisplacemen t of the largeobject .Sinc eupo nwettin g allobject smov e inal ldirection s exceptdownward , (asmentione d inSectio n 5.3.2),consolidatio no fpar to fth emovement s of the largeobject swil l include in themajorit y ofth ecase spar to fth eupwar d component (seeFig . 24).I nothe rwords , therei sa ne tris eo fth elarge robject s from themajorit y of theirdisplacements , majority ofthei rdisplacements .

Theaforementione dproces sha sa clos eparalle l incertai nsievin g procedures

m themillin gtechnolog y ofcereals .Accordin g toLenige r& Beverlo (1971) TZl ^ 8r0Und Pr°dUCt 1S ^^y P«fe™d with arathe r thick layer flouro nth esieve ,unde rth einfluenc eo f theshakin g of thesiev e asortin g

118 processtake splace .Thi s causes coarsean dirregula rparticle st oconcentrat ea t thesurfac eo fth elayer ,whil e finean dsmoot hparticle s concentratea tth ebotto m ofth elaye ri ncontac t withth esieve .Thi s separation takesplac e irrespectiveo f themes hwidt ho fth esieve .Th eexplanatio no fth esortin gproces si sth esam e astha tgive nfo rth eobject s encasedi nlime :coars ean dirregula rparticle s standles schanc eo freturnin g tothei rorigina l levelsinc e smallan dsmoot h particlesfil lu pth espace s thatthe yformerl y occupied. Theprocesse s active inth elim eexperiment ,ar esimila rt othos eresponsibl e forth eformatio no fcertai n desertpavements ,whic h regeneraterapidl yupo n removal,a sdiscusse db ysevera l authors,includin gCook e& Warre n (1973),Bale s& Péwê(1979) ,Jessu p (1960)an dSpringe r (1958).Th elatte r testedth eproces s experimentally,wit h soilmaterial s derived fromdeser t soils,wit ha vesicula r structurewhich ,thoug h similart olime ,lac ka fin eplana rvoi d system.H e demonstrates that stones embeddedi nmateria l fromthes e soils,wil l gradually riset oth esurfac ei fth etota li ssubjecte dt owettin gan ddrying .H emeasure d ane tris eo fpebble so fu pt o1. 1cm ,i n2 2cycle so fwettin gan ddrying .Hi s explanationo fth ephenomeno ni sa sfollows : 'Wemigh tpostulat e that through swellingo fth esoil ,th eston e islifte d slightly.A sth esoi lshrinks ,crack s areproduce d aroundth eston e andwithi nth esoil .Becaus eo fit slarg esiz eth e stonecanno t fall intoth ecracks ,bu tfin eparticle sma yeithe r fallo rb ewashe d intoth ecracks .Th ene teffec ti sa nupwar ddisplacemen to fth estone. 'Springe r notedth eai renclosur e phenomenonan dpropose sth efollowin gmechanism : 'Upon becomingmoist ,th eparticle s belowth esurfac e appearedt obecom e rearrangedan d closelypacke dwit hai rmovin g fromth edisappearin g mediumsize dpores ,int oth e largerspace sno wcreated .' Springer's postulate aboutth ecrack sproduce d aroundth eston edoe sno t holdtru efo rth eexperiment swit h lime,sinc eth eX-ray s showclearl ytha tn o voidsar eproduce d around rigid objects sucha sstone san dpetrocalci cfragments . Hisexplanatio no fth eai renclosure ,bein gdu et ocollaps eo fth emediu msize d Poresdoe sno thol d truefo rth elim e either.Th eexperiment shav e showntha tth e bulkdensit y lowered,wherea s accordingt oSpringe rcompactio no fth ewhol emas s occurred. tob ea continuou s one,i f Iti sunclea rwh ySpringe r considersth eproces s heassume s collapseo fsmal lvoid sa sth edrivin gmechanis mo fai renclosure .H e doesno tbeliev e thatth eproces s stops oncea certai namoun to fcompactio n(du e tolos so fai rthroug hth esurface )ha stake nplace ,sinc eh eals ostate s 'Repeatedwettin gan ddryin g causeda continua l rearrangemento fsoi lpart i «* -ids.- m springer's experiments,th edrivin g forceo fth emechanis m isn t thecollaps eo fvoids ,bu tapparentl yth ecapillar y forcetha t dnvesairut thesma nvoid s int0 the larger oneS) uponmoistening .Th eproces swhic hh e «Hies isprobabl y active onlyu pt oa relativel y shallowdept h in h so1 His "««rials lacka fin eplana r void systeman da ssuc har esuppose dno tt odevelo p

119 pressures thatca ncop ewit ha larg eoverburde no fsoil . Itmus tb eremarke d thatSpringe rdrie dhi s samplesa t90° Cwhic hmean s that a largepar to fth eeffec tmeasure dwa sdu et oth etemperature-relate d expansion ofai ri nth evoids .Thi sunnatura l effectwa smuc h lesseviden ti nth eexperiment s ofthi s study,i nwhic hdryin gwa sperforme d ata temperatur eo f5 0C only . Only abouton ethir do fth etota lheav eca nb eattribute d toth etemperatur e effecta sca n besee ni nFig .25 . Forth ecla ynodules ,Springer' s explanation aboutth eformatio no fvoid si n thedr ystate ,whic h fillu pdurin gth enex twetting ,coul d indicatea nadditiona l process thatha st ob etake n intoaccount .I nthi s case,however ,th eformatio no f voidswa sdu et oshrinkag eo fth ecla ynodule san dno tt otha to fth elim emass . Thefillin gu po fvoids ,i spartiall ydu et oexpansio no fth elim emas san d partiallyt oswellin go fth ecla ynodule sunde rth einfluenc eo fwetting . Inth e longru nthi scoul d leadt oa greate rris eo fth ecla ynodule s compared withth e rigid objects.Som e indicationso fthi shav e beentreate di nth eforegoin g section.

5.3.4 What factors determine the processes that lead to net rise of the objects?

Theresult so fth eexperiment sa sdiscusse d inth eforegoin g sections indicateth eimportanc eo fth efin eplana rvoi d systemo fth elim efo rth eai r enclosureproces san dth eresultin g riseo fth eobjects .Severa l factors which playa rol ei nthes eprocesse s havebee n identifiedan dwil lb etreate d inth e followingparagraphs . Important factors influencingth eestablishmen to fa nextensiv e fine planar void systemca nb ederive d fromth eexperiment san dfro mth edetermination s ofth e liquid limit (Section 4.6.1.2).Th epropertie so fth elim ewhic hwer eo fgrea t importancewere :uniformit yo fth ecrystals ,lac ko fgrowth so nth ecrysta l surfacean dpurit yo fth ematerial .Thes e factors influence directly thewa yth e crystalsfi ti nth elim emass .Th ebette rth efit ,th elowe rth eliqui d limitan d thegreate rth eai renclosur ean dne tris eo fobject si nth eexperiments .Lac ko f netris ei nExperimen t Iliawa sprobabl ydu et ocontaminatio no fth esample sb y clay.Lac ko fne tris ei nExperimen t lacoul deithe rb edu et oth epresenc eo fa considerable amounto fcoars e cemented limeaggregates ,o rt oth efac t thatth e samplewa sno tproperl y consolidatedwhe nth emeasurement s started. Packingo fth e limei sa facto ro rprim e importancefo rth eestablishmen t ofa nextensiv e fine planarvoi d system.Al lexperiment s thatproduce da ne tris eo fth eenclose d objectswer e subjectedt oconsolidatio nb ypourin gth edr ylim e intowater . Whetherai renclosur ean dris eo fobject swil loccu r dependso nth ewa yo f moistening (provided thatth elim efulfil sal lth econdition s described inth e foregoingparagrap han dha sbee nproperl y consolidated).Experiment s thatwer e moistenedb ysaturate d flowshowe dth eaforementione d processesbu tthe ywer eno t provokedb yunsaturate d flow (Experiment lb). Slowmoistenin g probably leadst o

120 escapeo fal l air from the pore system. Whether themovement s that areproduce d inth e limemas s lead tone tris eo f theobjects ,depend so nth e behaviouro fth e limemas s during the air enclosure process.Dislocation s during thisproces s prevent theretur no fth e objectst o theirorigina l level and causea ne t rise effect.Suc hdislocation s are facilitated bylo wliqui d limits (see Fig. 27)whic h intur ndepen d onth esam e characteristics thatcause d thedevelopmen to fth e fineplana rvoi d system. Overburden pressurei sa facto r that seemst ohav ea stron g influenceo n the airenclosur eo fth e coarse pore system. The experimentshav e showntha t decrease ofbul kdensit y duet ofailur eo f the capillariesa sth eresul t ofth e relatively modestpressure s builtu pi nthi s system, ismainl yrestricte d to theuppe r5 c m ofth econtainer s (Table 14).Th emovement s related to the fineplana rvoi d system occurthroughou t the limemas sa sth e experiments have shown.Th e influenceo f muchlarge roverburde n pressureso nth e airenclosur e inth e fineplana rvoi d^ systemca nonl y be assessedo ntheoretica l considerations,sinc e thedat a acquired inExperimen t IIIb2 are inconclusive where this aspect isconcerned .Thi si s becausen oX-ray s were taken to covera complet emoist-dr y cycleunde rth e influenceo fincrease d overburden. The only conclusion thatca nb edraw nfro m this experiment is that apparently theapplicatio n ofth e overburdenpressur e caused consolidationo fon e or othero fth e two layers between theobject s andth e bottom ofth econtainer . This conclusion isbase d onth eobservatio n that thesinkin go f theobject s and the surface was approximately equal,i.e. ,abou t2 mm .Thi s ^ consolidation effect superseded any othermovement s thatma yhav e takenplac e in thelim emaS s during the four cycles that the experiment lasted (Fig.28) .Th e Pressuretha t canb e expected tobuil du p inth e fineplana rvoi d systemha s been quantified inSectio n 5.3.2 and iso fth e ordero f4 bar ,considerin gwidth so f theorde ro f 0.1 m for theplana r voids.Eve nwhe n taking into account that these Pressures only act onpar to fth e surface ofth ecalcit e crystals,i tmis tb e concluded that overburden pressures equivalentt o theweigh to f severalmeter so soilmateria l can be exceeded.

Inth e literature some information is found regarding air enclosureleading toth eformatio n ofvesicula r structures.Non e ofth e studies,howeve r deals wUh thebehaviou ro fcrystallin e materialswhic h is largely governed y^ j „ -hnfailur eo f the coarser v°idsystem . They rather dealwit h air enclosure due to failure P°res,a phenomeno n mainly restrictedt oth e surface soil. ,11 t-Pnnmsoils 'fro m semi-aria areas Volk& Geye r (1970)describ e what they call foam * Morocco,Spai n and S.W. Africa.The y state thatvesicle s form,a ta c r ;r:«epthi nrth ^e soil.antheyd thenma slowl y^y mov furthereupward , through '^c*^^^^« ^^^^ wMch ft*help st orearrang e the skeleton grains. ******* * witha speed lsrapi denoug h topermi t air enclosure.Dryin g should takep i 121 sufficientt ofor ma har dcrus ta tth esurfac e rapidly,bu tslo w enought opermi t upwardmovemen to fai rbubbles ,throug hth eplasti c soilmas s upwards,befor eth e systemsolidifies .Accordin gt othes e authors,th efollowin g conditionso fth e soilmateria lar ea prerequisit e forai renclosur e uponwetting : 1. Highsil tan dfin esan d content (40-70 %)an dlo wcla y content. 2. Lowliqui d limitan da ver ynarro w intervalbetwee nth emoistur e contentsa t whichth ematerial sbehav ea sliquid s andsolid s (thesoil s they describe tendt o 'flow'ove rcliff san dproduc e 'draperies'). 3. Tendencyt ostron g crusting,t ofor ma barrie r thatprevent s airescape . Evenane t al. (1974)carrie dou texperiment s similart oSpringer' s (Section 5.3.3),t oexplai nvesicula r features fromth esoil so fth eNege v desert.Thei r experiments,unde r laboratory conditions,aime da tth eformatio no fvesicula r structuresi na variet yo fsoi lmaterials ,subjecte d towettin g anddrying .T o simulateth eformatio no fvesicula r structuresunde r stones,the y introduceda modificationi nth eset-u pb yplacin ga petr idis h overth ematerials .Thi s preventedth eescap eo fai rupo nmoistening . Good vesicular structures formedi n thesoi ldirectl yunderlyin g thedish ,afte r 20-25cycle so fwettin gan ddrying . Non-covered surfacesdi dno tdevelo pvesicula r structures,du et olos so fai r throughth esurface .Loess ,fin esan dan dcoars e sandwer e tested, thefirs ttw o ofwhic hforme dgoo dvesicula r structures,whil eth ecoars e sand performedpoorly . Tneirinterpretatio no fth ecaus eo fth eformatio no fth evesicle s is, the expansiono fenclose d air.The y alsostat e thatth ephenomeno nma yb eenhance db y theheatin go fth eenclose d gassesdu et oth edail y temperature cycle,unde r narrai ions.Asimila r^ ^ ^^. ^ ^^ & ^^

whoregi sere d surfaceheav ei ncruste d soils,i nwhic h therei sa slo wai r exchange (m theorde ro f0. 5mm) . Thisi sdu et odail y differences intemperatur e n^rarid^r"^ "^ « «* «* «* ^*** *° f5 «*> ^ uons undevM the d uwith ^aZZ:rzTsif * ~— »*°* conä^r^lCr^ Wil1 be reStTiCted t0 a COT*™ bet««« experimental -^^LZ:;7z,T;^ rai —• «•*—-- rise an PreSented in SeCti pedimentst oth epro^ 1^ !" °" ^' *» byone . m thefore goingsection ,wil lb ereviewe don e ofexp^e^a lc^itie T ZT "T ***** C°nditi°nSPr0babl ymatChe S ^ conditions (asderive d fromth ebul lH "*"* "^ ** ****** "^ natUTal f ?)i S inth esam B thatindicate db yth ebul k den > T "^ ° ^ """ " Thebul kdensitie so fT**"* 1*3** develoP^ duringExperimen tI I(Tabl e14) . ofth elim eo fProfil eArroy o1 a t26 0c meve n exceed those 122 established at the initial stage of Experiment II. Anegativ e influence of admixture of coarse lime aggregates on packing, air enclosure and the resultant rise of objects may be inferred from a comparison of the results of Experiment la with those of Experiments II and Illb in which these coarse fragments in the fraction 0.5-2 urn had been removed by sieving (Table 13). Ms observation could in turn lead to the conclusion that Experiments II and Illb are not representative of natural conditions in the soil, since coarse fragments had been removed from the natural samples. In Section 4.9, however, the conclusion was drawn that pedogenetic processes are fossile in the high soils of which the ime samples had been derived. As such the sieving of the samples prior to the experiments does not create 'unnatural' samples, since the rise process is supposed to have been active under natural conditions before chemical redistribution of lime created the coarse aggregates that are nowadays found in the calcic horizons. Moistening under natural conditions is probably characterised to a great extent by unsaturated flow. Uneven distribution of percolating ram water m th calcic horizon, through the cracks of the overlying Vertisol, is to be «*«**• with the coming of the first heavy showers of the wet seasons. Also to be expect

is the phenomenon of unstable flow, due to wetting front ^^'^^ in a transition between the clay and the underlying silt-sized lime. is r n ^ saturated flow surrounded by a cynu wetting pattern of columns which have a core of saturate o£ der of unsaturated material (see Hillel, 1980). It seems that a ««^^

infiltration types can be expected under natural ««^^^ is worth noting tion types are similar to those of the experimental conditi ^ ^ ^^ that more air enclosure can be expected under natural ^ _ takes place from the top down, than under laboratory conditions «»its, except lb, moistening took place from the bottom up.^ ^^ ^ ^ The question arises as to whether the net rise o ^ ^ ^^

experiments can be qualified as representative o ^ ^ ^ £.ne circumstances. As mentioned in Section 5.3.4 t P ^ ^^ Pore system can be expected to be high enough tonat ^ ^ ^ ^

equivalent to several meters of soil material. ^ ^^ ^ ^^ & ^^

Planar pore system should be considered a ^^^orizons compared with that stronger rise is expected to occur in thick soft ime

measured in the experiments. be expected under natural Temperatures during drying were higher than^ o ^ ^^ ^^ ^ ^^ Q£ ro£l conditions in the deeper layers of the soil P ^ ^ ^ di££erence. the total heave evident in Fig. 25 may be attribute ^^^ ^ ^.^ pgr cycle cal_

In conclusion, it may be stated that the value^o ^ ^^ ^^ which is pr0.

culated in Section 5.3.3 for Experiment II represen ^ ^ ^^ ^^ ^ justi£ied

bably exceeded in most cases under natural conditions i ditions which, except by the fact that the experiments have been cai ^ ^^ ^^ layers, simulate for the temperature effect and the cumulative effect o thoseo fth esoi l inth enatura l environmentwhe nth eris eproces s occurred.Theo ­ reticalconsideration s implytha tthi sconclusio nmus tb evali d for calcichorizon s ofa dept h ofu p tosevera lmetre s inth esoil .

124 6 Behaviour of calcic horizons

In this chapter some processes active in the calcic horizons of the study area are treated, taking into account the results of analyses, experiments and surveys of the foregoing chapters. These processes are verified by field observations made in the survey area and by data from the literature on comparable regions. The field data for this chapter are mainly derived from the Miocene clay landtype. Some evidence from other landtypes is introduced when warranted by conditions sufficiently similar to those of the Miocene landtype . Certain terms in this section are written in italics in order to indicate that they will be used as standardised terminology throughout Chapter 6. One of the aims of this chapter is to formulate an acceptable theory on the gen­ esis of the calcic horizons of the survey area. This genesis is not the starting point but the conclusion of the discussion. The point of departure is the question. 'How can soft calcic horizons become mobile in order to maintain themselves for a ^ long period in an eroding environment without falling victim to erosion themselves. . In order to answer this question a model is tested in Section 6.1 in which it assumed that dissolution in its upper part and recrystallisation in its lower par , / • , i intn the soil. This test shows causes the calcic horizon to move downward (migrate) into uie a ^^ ^ that chemical dissolution processes cannot be expected to act fast enoug un e conditions of the survey area to propel the horizon downward with a speed high enough to escape exposure by erosion. u-^*-= mntained Section 6.2.1 contains field evidence of the ^ process of ^J^f « a soft calcic matrix as observed in the experiments of Chapter . ^ ^^.^ the objects that rise upwards through the ^.^ """ ^ trials ac- zone. There is evidence that swelling and shrinking of the ciay y -«ed by the infilling of the cracks by lime causes the ƒ.— of >*

— 9il9a relief. This process brings about the formation o cUy V ^

P-rude lnt0 the soft calcic horizon and which upon « ^ ^ *oduce material into the soft calcic horizon. These clay lumps break p^ ^ a <*¥ nodules which rise up through the calcic horizon and ^omltion is called The - Nation of the rise process and t*^^^ration of the soft cal- Mechanicalmeohanioal replacementy>e„1.„,om*nf. process process. It leads to a downwa ci-lcc horizonhorizon. rontrol the downward mi- c - c -t-hP factors which control ui<=

Section 6.3 contains an analysis of the tacL ^^ illustrates their combined gration of the calcic horizon. A model is formulât t i ^ ^ downward mi e«ect under natural conditions. Computations show that grationo fth ecalci chorizo nexceed sth espee d computedi nth echemica l dissolution modelan di scapabl eo fmatchin gth ecommo nerosio nrate so fth earea . Thequestio no fho wa calci chorizo nreconstitute s itself afteri tha sbee nlo ­ callydamage di streate di nSectio n6.4 . Field evidenceo floca ldamag et ocalci c horizonsi sreviewe dan dexplaine do nth ebasi so fth emechanica l replacementmodel . Severalfactor sma ycaus ea disruptio no fth emechanica lreplacemen tproces si n thesof tcalci chorizon .Fiel devidenc eo fdisruption so fvariou s typesi spresente d anddiscusse di nSectio n6.5 . The implicationso fth emechanica lreplacemen tproces sfo rth egeneti c concepts onth esof tcalci chorizo nar ereviewe di nSectio n6.6 . Sinceth esof tcalci chorizo n canaccumulat e limeo nit swa ydownward ,th esearc hfo rit sgenesi sca nb enarrowe d toth egenesi so fa muc hthinne r 'incipient continuous soft calcic horizon 'whic h startsth emechanica lreplacemen tprocess. Fo rth egenesi so fthi shorizo na numbe r ofoption s fromth eliteratur ear ereviewed .I ti sconclude d thatth emos t likely process initiatingth eformatio no fthi shorizo ni sth eilluviatio no flim eparticle s formedb yevaporatio no fbicarbonat e solutionsi nlarg e cracks,toward sth eaverag e levelo fth egroundwate rtable .

6.1 THEROL EO FTH ECHEMICA LDISSOLUTIO NO FLIM EI NTH EMOBILIT YO FCALCI C HORIZONS

Thissectio ndeal swit hth equestio no fwhethe rchemica ldissolutio no flim eca n givesufficien tmobilit yt ocalci chorizon si norde rt omatc h representative erosion ratesunde rpresen tan dpas tcondition si nth esurve yarea . InSectio n2. 5a revie wi sgive no fth evariou s existing theories onth egenesi s ofcalci chorizons .Al lauthor si nfavou ro fa pedogeneti c origin assume thatth e dissolutionan drecrystallisatio no flim ear efactor s influencingth eformatio n process.Mos tauthor s agree thatfo rthic k calcichorizons ,especiall y ifforme do n ori nmaterial swhic hd ono tconsis tfo ra larg epar to fCaC0 3,a larg e time span willb enecessary .Gardne r (1972)compute s agesbetwee n0. 4x 10&y ran d2. 5x 1(>6 yrfo rth eformatio no fa thic k 'caliche'. Large timespan sar eassume db yauthor si nfavou ro faggradationa lan ddegra - dationalmode so forigin .I nth ecas eo fth eMiocen e clayi nth eMérid a area,th e aggradationalmode li sdiscarded ,sinc e geological evidence shows thatth eMiocen e clayshav ebee nsubjec tt oconsiderabl e erosion since their deposition (Section5.3) . Thisraise sth equestio no fho wcalci chorizons ,afte r theyhav ebee n formed,ca n remainintac t over largeperiod so ftim ewhe nth esoi li nwhic h theyar econtaine di s subjectt oerosio na tth eto pan drejuvenatio na tth ebottom . Forth eMérid acas ea degradationa lmode li steste di nwhic hi ti sassume d that a calcichorizo nkeep spac ewit ha downwearin g surfaceb ydissolutio na tit sto pan d crystallisationdeepe rdown .Author swit h similarconcept sar equote d inth epen ­ ultimateparagrap ho fth eintroductio no fSectio n 2.5.Th ecas ei steste db ycalcula ­ tingth emaximu mrat ea twhic hlim eca nb edissolve d (seeFig .29 )an dsoi lmateria l

126 [CuHmol/U Ig [Col

.2.0'

.2.2-

-2.4-

.2.6-

.2.8

-3.0-

.3.2-

-3.4-•

-3.6- .4 -J -* -' Ig PCO, PCOilborl

Kg. 29. D issolution of CaC03 by water at various C02 pressures. The concentration [Ca] in mol /I is plotted as lg [Ca] against P C02 in bar as lg P C02 for two dif ferent temp eratures. The dotted line represents lg [Ca] = 1/3 g C02 - 2.13 for 25°C while the solid line represents lg [Ca] = 1/3 lg P C02 - 2.03 for 10°C.. Activ ities equal to unity are assumed. The two crosses (x) show the «tor , de to this assump tion on the basis of values from Lindsay (1979) for the 25°C case. It xs evident tha t these errors are small up to values of P C02 of 0.1 bar.

Equivalent 50% |ime erosion raies 150. mm |m/10!yr] 50>,

PC02lbQr'

2 3 4 56789 3 4 56789 . 2 3 4 5678 1 u ,0OOx 1x "HTl0" ' " Àlô x *>°" im* ' u the liberation of non- '/?. 30. Equivalent erosion rates which can be matcnea y hi plotted ealc Equivalent erosion rates which can be matche J eaching, plotted "ic solid,_T-,s out of .calci - c. horizon.-_• s whic,j,,'i.ihi dxssolv dissolvee du ouec i-u x (]/3 ^ p ^ _ consequently liberateda tth eto po fth ecalci c horizon,i norde rt ocompensat efo r soil lossesdu et oerosio na tth esurfac e ('equivalenterosio n rate').O nth ebasi s ofthi ssimpl emode li nwhic hth erecrystallisatio no flim edeepe r downi sno tquan ­ tified,conclusion sca nb edraw na si sdescribe di nSectio n 6.1.6.Th eso-calle d 'equivalenterosio nrates 'whic hca nb ematche db yth eaforementione d processar e calculatedfo rtw otemperatures :10° Can d2 5C ;fo rtw ocomposition so fth ecalci c horizon: limepercentage s (byweight )o f5 0 %an d8 0 %\an dfo rtw oleachin g inten­ sities: 150m man d30 0m mpe ryear .Al lcase sar econsidere dfo ra rang eo fCC U pressuresvaryin g from1 t o100 0x th eatmospheri c C07 pressure.Th eresult sexpres - 5 sedi na rat eo fm/1 0 yrar eshow ni nth efor mo fa grou po fcurve si nFig .30 . Theserate sar ecompare dwit hvariou spas tan dpresen t erosionrate s reported inth e literaturean dwit hestimate so fpresen tan dpas t erosion ratesi nth esurve yarea . Thesedat aar esummarise di nTabl e 15. Theteste dhypothesi si sver y similart oth eon epropose db yKnibb ei na nunpub ­ lishednot e (1974b).H eclaim s thatth elim eo fbot hth eMiocen ean dth eSchis tland - types originates from theseparen tmaterial sb ya gradua l concentration duringth e

Table 15. Summary ofpresen t and past erosionrate scompute d for soilmaterial s ofa n averagebul kdensit y of 1.5g/cm 3 from the sedimentdat areporte d inSectio n 6.1.4.

Erosionrat e Subject Source Conditions (m/105yr )

1.7 Very largearea s Holmes (1965) Average long-term (100 million years) erosion rate converted from rock-(BD 2.5 g/cm3) to soil-(BD 1.5 g/cm3) erosion 133 22Italia ncatch ­ Gazzolo &Bass i From suspended sediment data re­ mentswhic h total (1964) ported as representative for catch­ 28318km 2 ments that consist for 70% of easi­ ly erodible rocks. From a relation­ ship based on 22 catchments varying in size from 226-8186 km2, mainly located in Mediterranean climates. 58 RioGuadajir a Table 16o f Estimated by means of an empiric31 catchment (816 this section 2 regression model of Jansen & km )representa ­ Painter (1974) for present day con­ tivefo r the ditions in the survey area: 450ira " surveyare a precipitation and 'steppe' vegeta­ tion. 141 id. id. Idem for conditions which deviate from the present ones in precipita tion (800 mm) and vegetation (f°r~ est) . 33-80 LandtypeM o f Bergsma (1980) Derived from soil loss predictions thema p (Fig.3 ) from an erosion hazard classifica tion partially according to the universal soil loss equation.

128 downwearing of the surface. He assumes a CC>2 pressure of 15 times the atmospheric pressure and reaches the conclusion that the calcic horizon must have gone through at least 35 cycles of dissolution and precipitation while the surface was wearing down, during the last 1 million years.

6.1.1 The dissolution of CaCO^

The dissolution of CaC03 in the soil is governed by the partial pressure of C02- The following relation is valid for a pure system under equilibrium conditions at a temperature of 25°C:

lg [Ca] = 1/3 lg P C02 - 2.13

In this formula [Cal is expressed as nmol/1 and P CC>2 as bar. For the derivation of this relation in the carbonate/bicarbonate system see Bolt (1963). Substitution in this derivation of the values corresponding to 10°C for the solubility coefficient of

C02 (Durand, 1959) and the first and second dissociation constants for H2C03 and t e solubility product for CaC03 (Kharaka & Barnes, 1973), leads to the following rela­ tion valid for a temperature of 10°C:

lg [Ca] = 1/3 lg P C02 - 2.03

These two relationships are graphically represented in Fig. 29.

«-Î-2 Computation of the equivalent erosion rates that can be matched

f. 1 1 it is riossible to calculate the On the basis of the equations of Section 6.1.1 it is possi iiber_ suivaient erosion rates to be matched by the dissolution of calcic non «ing insoluble material included in them. For this simplified mode in rallisatlon 0£ CaC03 lower down in the profile, disregare te fo^ ^ b °n* in raind. ^e thickness o£ the layer of material liberated oy ^ C«3 is proportional to the.amount of water leaching the.calcichoru^ ^ -ely proportional with the bulk density of the material 1* **> of lime to non-calcitic solids in the calcic horizon The concent ha* + \ r rem /I This leads to the following to be converted from mol/1 to grammes o± Lauyx- ^ equiva- »rabined factor by which the [Ca] has to be multiplied m order lent erosion rate that can be matched, in cm/yr: P xC SITS

e symbols have the following meaning: _ 2 P = Annual amount of water leaching the calcic horizon m 129 C= 100;Th econversio nfacto rfro m [Ca]i nmol/ 1t oth e equivalent amounto fCaCO , dissolved ing/1 . B= 1.5;Th ebul kdensit yo fth e liberated solids.Compar e Table9 fo r thebul kden ­ sityrang eo fth ecla ynodules . S= Numbero fgramme so fCaCO jt ob edissolve di norde rt oliberat e1 go fnon-cal - citicsolids . Multiplicationo fth eformul ab y 1000convert s thedimensio no fth e conversionfacto r fromcm/y rt om/1 0yr :

A= 100 0S-^- Ç Bx S

Fora cas ei nwhic h 150m mo frainwate r leachesa calci chorizo nwhic hconsist so f 80 %lim e (whichmean s that4 go flim ehav e tob edissolve di norde rt oliberat e 1g ofnon-calciti csolids) ,th efollowin gequatio nresult s for the equivalent erosion rate:

1000 ^TTTT1 [Cal= 25 0 tea]m/10 y5 r

Forleachin ga t25°C ,substitutio no fth epertinen trelatio n for [Ca] leadsto :

250x 10(V3 lgP C0 2- 2.13 )m/1o5y x

Dittofo r 10°C:

3 250x 1 0 tV !g? C02- 2.03 )^ 5 ^

Similarlya conversio nfacto r (A)o f50 0result s for 300m mwate r leachinga calci c horizono f8 0I lim econtent .Leachin gintensitie so f15 0m man d 300m mfo rcalci c horizonstha tconsis to f5 0 %CaC0 3 byweigh t leadt oconversio n factors (A)o f 1000 and 2000respectively . InFig .3 0 theresult so fthes ecomputation s areplotted , leadingt oa grou po f curvestha tsho wth eequivalen terosio nrate st o bematche do na linea r scale,plot ­ tedagains tth eP C0 2o na logarithmi cscale . Underth epresen t circumstances,leachin gneve rexceed s 150m ma t levelsite s Tl tI ralnPenetrateS - *>* of theleachin g takesplac ea ttemperature so f about1 0c sinc ewinterrain spredominat e (seeFig .30) .Th e lime contento fth ecal ­ cichorizon so fth eMiocen e landtypeso fth esurve yare avarie s from about 50-80i .

Z are!'b1 ^ analytlCal** *° f* *SOi l P™files <* Section 4.3.1.)A ssuc h tteare abetwee nth ecurve smarke d (10°,8 0» lime ,15 0mm )an d(10° ,5 0 Xlin« ,15 0 ^represents themaximu meffec to fdissolutio nt ob eexpecte d forpresen t daycir - mTic^:, 0tÜerCUrV6 S °fFlg - 3°ar eadd6 dt 0 illustrateth eeffec to f cli­ maticcondition swhic hma yhav eprevaile di nth epast .

130 Thefollowin g factorswhic hwoul d lowerth eequivalen terosio nrat etha tca nb e matchedar eno tquantified : - Dissolutiono flim e dependso nth egrai nsiz eo fth ecrystals ;give nth edominanc e ofsil tsize d crystalsi nth ecalci c horizonso fth e survey area,th esoi l solutions canb eexpecte dt ob eundersaturate d comparedt oth ecalculate dvalues . - Additionso flim e from other sourcest oth esurfac e suchas ,e.g. , lime contained inaeolia ndust ,ar edisregarded . - Allpedogeneti c processes that counteractth erelativ e downwardmovemen to flim e sucha shomogenisatio nb ybiologica l and/ormechanica l actionan ddownwar dmovemen t ofsolid si nsuspensio n (e.g.cla y illuviation)ar edisregarded .

Factorsno tquantifie d that could speedu pth emigratio nproces so fth e horizonare : - Ionpai r formation involving Ca++ andMg ++ enhances solubility.Thi s effecti s expectedt ob erelativel y unimportant,sinc eal lcalcit ei sprobabl yo fth elow-M g typean ddolomit ean daragonit ewer eno tfoun di nth eX-ra y diffractiono fth e materialo fth esurve y area. (Other soluble saltsar eabsen ti nth ecalci chorizon s ofth esurve y area.) - Transporto fCa ++ througha diffusio nproces si na moist calci chorizo nunde rth e influenceo fa C0 ? pressure gradientbetwee nto pan dbotto mo fth ehorizo ni sno t considered,sinc eth econcentratio n gradiento fC0 2 overthi sdistanc e issuppose dt o below .I ti sknow n thatdiffusio nprocesse spla ya nimportan trol ei nth etranspor t ofmaterial si nth esoi l overver y shortdistance swher econcentratio ngradient sar e high,suc has ,e.g. ,th efonctio no fconcretion san dpetrifie d roots.Anothe rargu ­ mentagains tth ei^ortanc eo fdiffusio nprocesse si nth etranspor to fCaCO jm the soili sfoun di nth efac t that diffusion tendst oheighte nth e CD, concentration m thezon ewher eth eCaCO ,precipitates ,whic h countersth eprocess .A furthe r(in ­ direct)argumen t againstth eimportanc eo fdiffusio no fcarbonate s isfoun d inth e goodrelationshi p demonstratedb yJenn y& Leonar d (1939)betwee ndept ho fcarbonat e accumulationan dprecipitatio nan db yArkle y (1963)betwee ndept ho f c^b°^^^ elationan ddept ho fleaching ,a smentione di nSectio n 2.5.2.1.I tmus t e s*e *atthes eauthor s foundth erelationshi p disregarding several factors ^J™*™

* -ist soilcondition san dC0 2 concentrationi nsoi lair ,whic har eo f ^anœ **th ediffus a process.Additionall yi tma yb estate d thatReeve s (1976)discusse s andreject sa diffusio nmode lfo rcalcret eformation .

•1-3 The average C0~ pressure in the soil

re The literature contains reportso fa rang eo fC0 2 partialP ^es inso i .

131 State that inth eroo t zoneth econcentratio ni smaxima l andmeasure sa tleas t 15x thato fth eatmosphere .Fo rdee p groundwaterso fhumi d temperate regions,however , Blatte tal .repor t thatconcentration s ofu pt o100 0x tha to fthe atmospherehav e been found.Lindsa y (1979)use s 10x th e atmospheric concentrationa sa commo n reference level for soils.Jenn y (1980)report s 10x the atmospheric concentration

ofC0 2a sa naverag e forsoi lair .Rightmir e (1967)assume si nhi s radiocarbonstud y

ofcaliches ,C0 2 concentrations ofu pt o5x th e atmospheric concentration forari d areas. Itseem sjustifie d toregar d 10x th e atmospheric concentrationa sa goo d

average C02 concentration forsoi lair ,fo r conditionso fth e study areaunde rwhic h leaching takesplace .I nplace s temporarily higher concentrations may occur,due ,

e.g.,t oreleas e ofC0 2 absorbed on lime surfaces.These effects,however ,ar ever y short lived.The ypla ya rol ei n the initial stages ofwettin g only,a sdemonstrate d byCallo te ta l (1978). Inth e field during spring,p Hvalue s lower than 7.6wer eno t

measured.Th eP H valueo f7. 6 canb ecalculate d fora solutio ni ncontac twit hsoli d

CaC03i n equilibriumwit ha CO. ,partia lpressur eo f1 0x th e atmospheric C02pressure . Waterlogged conditions accompaniedb yhig hbioti c activity,whic h could produce

higher C02 concentrations,ar ever y short-lived inth e survey area too. Introductiono fthi sCO. ,concentratio n inFig .3 0show s that the equivalentero ­ sionrate s thatca nb ematche dvar y from 0.3 m/10S yr,fo rcalci c horizonso f8 0 % limecontent ,t o1. 3m/10 5y rfo rcalci chorizon so f5 0 %lim e content,bot hunde r presentda ycircumstance so f15 0m mleachin ga t10°C .

6.1.4 Representative erosion rates

Unfortunately datao nerosio nrate sbase d onmeasurement so fsuspende d sediment yxeldso fcatchment so fth eare aar e lacking.Th e equivalent erosion rates thatca n

theCalCi Ch0rlZO nar SCOnpare dWit hth e 1in Tabl 71 et 15),instead : fellowü« data (assummarize d - Long term geological erosion ratesfor larg e areas - Measured present dayerosio n -rat« c climbs A» • Ac °mcon, Parable catchments inMediterranea n climates,derive d fromsuspende d sediment datao friver s - Erosion ratecalculate d fornresen t ,w • f S tati catctat „e„th estud y„ ea ZZX "™°" " "— " - Erosion „f«, , ^cordingt oa nempirica l formula, erosion rate accordingt otJi Ae o J- g climatemoiste r than the^ s ~£T J «"— «*-*" * - Erosion ratesderive d from si & ***** ™^™- ationpartiall y according to Zun 7 "T^^ *"" " ^^ ^ ^^ 1978)applie d to landtypeM o fth esurve y area'^ ^^ ^^ &Smlth ' Long termgeologica l erosion rat*« f years,base d onmeasurement so fth e P6ri0dS " *" °rder °f 10° miUi°n ando nth erat eo fexposur e ofH i T^ °f Sedinent dischargedb ylarg e catchments xposureo fdiamon dpipe si nSout hAfric a are estimatedb yHolme s 132 (1970)a tapproximatel y 1m/1 0 yri nterm so funweathere drock . 2 -1 Fig.3 1show s suspended sedimentyield si nt/k m.y r for1 0semi-ari dan d1 0 sub-humidN .Africa n catchments reportedb yHeusc h& Milliès-Lacroi x (1971).Th e catchmentshav e been selected fromthei rdat ao nth ebasi so fth esimilarit yo fth e parentmaterial swit h thoseo fth eMérid a studyarea .Th echoic ewa srestricte dt o marls,calcareou smarl san dmarl-schis t combinations.Th etota lare arepresente db y thesemi-ari dcatchment s is5960 2k m andth etota lare ao fth esub-humi d catchments is4376 4km . Themea n annual suspended sedimentyield s areplotte d againstth e catchmentsize so nlogarithmi c scales.Th e well known linear relationshipbetwee nth e logarithmo fth ecatchmen t sizesan dth elogarith mo fth esedimen tyield si seviden t forbot hclimates . (Theproduc t moment correlation coefficientfo rth esemi-ari ddat a

Suspended sediment yield t/km". yr"'

Rio Guadajira

10000-

8000

6000.

4000-j

2000

1000-1 eoo|

600

400-

500-

Catchment arealkmj —| !

i-- qhit)betwee nmea nannua l sus- • Regression linesrepresentin gth erelation s v ^ scale. Thedat arepre - sedimentyiel dan dcatchmen t sizebot hplott e Maereb.Th e catchments '0semi-ari d (o)an d. 0sub-humi d(• ) catchments fromj-he^j ^.^.^ „ sub-humid <*) c-tcb-en« ^ ^ ^ ith with selected from Heusch &Milliës-Lacroi illiès-Lacroix (19/x (197U U°" °" z"combinations) ,„- - i .V Estimate Estimates fos fr th n t ons survey area (marls, calcareous marls andmar l sc facilitate comparison: 450 «* survey area from Table 16 have been indicated too to facili Precipitation as (-) and 800m ma s (-.-)• 133 is -0.72,whil e itmeasure s -0.87 for the sub-humid case.)Th e region between thetw o regression lines inth egrap h isrepresentativ e for the survey area,sinc e theloca l climate isa boundar y casebetwee n semi-arid and sub-humid (Section 3.2).Th eRi o Guadajiracatchmen twhic hi srepresentativ e ofth e study area and forwhic h the sedimentyiel dha sbee nestimate d bymean s ofa n empirical formula is indicatedto o to facilitate comparison.Th edat a consistently showhighe r sediment yields forth e sub-humid case than forth esemi-ari d one.Thi s fitswit h the general relationship established byWilso n (1973),betwee nsedimen t yield and precipitation,base d on 1500catchment s around theworl d re-calculated toa unifor m size. He states that contrary toth ewel lknow n relationship ofLangbei n &Schum m (1958), the sediment yield increaseswit h theprecipitatio nu p to avalu e of 750mm .A t higherprecipita ­ tions,th esedimen tyiel ddecrease s due to thewell-know n fact that increasedpreci ­ pitationpromote sth egrowt ho fa vegetatio nwhic hprovide s cover andprotect s the ground from theful lforc eo fth eerosio nprocesses .Langbei n &Schum m (1958)claime d thatthi swoul d cause adecreas e insedimen tyiel d from approximately 300m mupwards . Gazzolo &Bass i (1964)repor tfo r 22 Italiancatchments ,mainl y inMediterranea n climates,totallin g 28318km 2 andvaryin g insiz e from 226-8186 km2, a relationship betweensedimen tyiel d insuspende d forman d %are a taken inb y easily erodible rocks.Thi srelationshi pwa s established disregarding the effect of catchment sizeo n sedimentyield .Fo rcase scomparabl ewit h therepresentativ e catchments of thesurve y area (approximately 70 %easil y erodible rocks),the yrepor t avalu e of 740m / km .yr .Thi svolum e ofmateria l resulted fromdivisio n ofweigh t of the sediments % 2-1 by abul kdensit y of 2.7g/c m .Th eequivalen t amount of 2.7 x 740 = 1998 t/km .yr fallsbetwee nth etw oregressio n lines ofFig .3 1 for a large range of catchment sizes Jansen &Painte r (1974)develope d linearregressio nmodel s for sedimentyiel do f catchments fordifferen tclimati c zoneso fth eworld ,base d on anumbe r ofparameter s found tohav ea significantrelationshi pwit h the sedimentyiel d of the catchments used forthei rmodels .Fo rth eRi oGuadajir acatchmen t therelationshi p whichhold s forrelie f lengthratio s >3 m/k man dC climate s according toTrewarth a (1943)ap - plier\1i p c•s

lgS = 3.05 5- 1.125 lgA +0.58 5l gH + 1.104 lgR +3.05 6 lg P+ 3.053l g

Inwhic h thesymbol shav eth efollowin g meaning: S = suspended sedimentyiel d int/k m .yr 2 -1 A = sizeo fth ecatchmen t ink m 2 H = altitudeo fth ecatchmen t inm above sea level R = relief/lengthrati o inm/k m P = precipitation inmm/y r V = factorrepresentin g naturalvegetatio n groups:deser t = 1,stepp e = 2,gr a 3,fores t= 4 .

134 Table 16. Sediment yield estimated for the Rio Guadajira catchment representative for the survey area, under present and past conditions according toa n empirical regression model of Jansen & Painter (1974).

Size Altitude Relief/Length Precipitation Vegetation Sediment yield A(km2) H (m) R (m/km) P (mm/yr) V S (t/km^.yr ')

816 700 7.35 450 3 (steppe) 874 816 700 7.35 800 4 (forest) 2108

Table 16 summarises the result ofth e aforementioned formula applied to the Rio Guadajira catchment which isrepresentativ e of the Miocene clay and Schist landtypes of the survey area. The Rio Guadajira passes less than 1 km from the southwestern tip of the survey area. The table shows the suspended sediment yield in ton/km .yr for present day circumstances as well as for a case which isassume d to have higher pre­ cipitation and a forest vegetation and which may represent conditions of the recent past. The results plotted in Fig. 31 show that the present day case, 450 mm precipit­ ation and a vegetation cover qualified (due to human influence) as steppe, falls very close to the line ofth e semi-arid data. The case for an assumed precipitation of 800 mman d forest vegetation plots intermediate between the sub-humid and semi-arid data. The same tendency of increase ofsedimen t yield from semi-arid to sub-humid according to Wilson (1973) iseviden t here. Iti s interesting to note that according to Gehrenkemper (1979), a natural steppe vegetation also existed mlarg e areas the Mediterranean during the early stages of the Wurm glaciation. Taking into account that the model of Jansen & Painter (1974) was developed from catchments ceding 2 5000 km in size but is applied in this case to a catchment of approximately 800 km , the coincidence with the N. African data can be qualified as quite ™*^' Bergsma (1980) reports estimates for erosion hazard of several landtypes n the «rida area partially based on the universal soil loss equation. For h area co ciding with the unit Mo f the map (Fig. 3) he reports an estimate of - soil loss per ha per year. The erosion hazard is the soil loss that is P take place under present day conditions oflan d use and management. His esUma „2 -1 This seems to concur well witn equivalent to erosion rates of500-120 0 t/km .yr . This

<*«ti-te s _de by _ of «he Sirica! — —^ ^/cLidU

«- »o C^ila CÄ »der ^ ^ »"^ —*' thatno tal lth emateria l actuallyerode d doesleav e

0m™-iral formulasar eboun dt ob e Naturallyth eerosio n rate estimatesbase do nempi. i ^ ^ ^.^ ^ objectt osom e considerable error.A sa n"PP^" " risonwit h actually theerosio nrate ,however ,the yar en odoub tvalid ,a stheir ^ P i nA N Africal^cll(-'<* l*c*•, measureddat afo rsimila r conditionsi nItal yan d . s capacityo f escaping Sincei ti sth epurpos e heret ojudg eth ecaxc i 135 exposure due to erosion by migrating downward in the weathering zone, all values quoted so far in this section have to be converted to the erosion rates of soil ma­ terial. Abul k density of 1.5 g/cm3 for this material, which is the basis of the cal­ culation in Section 6.1.2, is used for this purpose. Table 15 lists the erosion rates converted by this factor. For the erosion rates based on sediment yield of catchments, the factor sediment delivery ratio has to be drawn into the comparison. This factor is defined as sedi­ ment yield/gross erosion. The delivery ratio quantifies the proportion of the total sediment produced in the catchment that actually leaves this area. The lower the de­ livery ratio, the larger the quantity of sediment that settles inside the catchment. The larger the catchment, the stronger the influence of this factor as can be seen from the slope of the lines of Fig. 31. The difference between the upper value of the estimate by means of the universal soil loss equation, which measures gross erosion, and the estimate for the Rio Guadajira shows this sediment delivery effect too. For calcic horizons outside the valley bottoms of the catchment, gross erosion is a de­ termining factor irrespective of the fact that part of its products settle in the valley bottoms. Gross erosion determines whether calcic horizons are stripped bare of their soil cover or not. As such the erosion rates determined on the basis of sus­ pended sediment,yiel d of catchments have to be increased proportional with the in­ verse of the sediment delivery ratio to express their effect for the calcic horizons. ^ is not easy to quantify the sediment delivery ratio. Comparisons between sediment yield and estimates by means of the universal soil loss equation are normally used rathe/h?11113036' ^ ^ ^° GUadajira' the sed™ent delivery ratio is probably ^ded flßh' SlnCe m°St °f the flne textured ^terials leave the catchment in sus- pen e^ orm. No estimate of the sediment delivery ratio is made, however. For the

whicTmat thS PreS6nt StUdy ^ 1S Su££icient t0 indicate that gross erosion rates based oTsed-f0r ^ ^^^ °f Calcic horizons are always larger than the rates m e ment yieldS s should be rat05 . t ^ ' ™ taken into account when considering the rates of Table 15 which are based on suspended sediment yield. •

0» 1, o COîTtpCXP'LsOYl Of-1 -hin " ' hovi?n„ ,-x t savaient erosion rates that can be matched by the ealcic n WUh eV°8i0n «*»• — for the survey area

mtche^Ty^e c^T" ^ * ^ " ^ *" e^uivalent eTOsi°n **** " * 3 md 1 tors mentione d in Secti^Tons ö ^ ^^ * ^ ° "»S «*** ** "*** **" Only the -1-2 and 6.1.4, the following result is obtained:

lution process Z^TcT^ ^'^ """^ rates C£m h& natched * ** ^ soil for the most f PaTtlal preSsure of 10 x the atmospheric pressure in the horizon of 50 %. ^^^ Case of ™ ™ leaching and a lime content of the calcic

ceeds the equival t& & ^ the'Rio Guadajira under present day circumstances ex- er0S10n rate to be matched by the dissolution process under con- 136 ditionso f15 0m mleachin gan d5 0 %lime ,fo ra C0 2 concentrationo f1 0x tha to fth e atmospherea t10°C ,b ya facto ro fapproximatel y4 0x .Th erat ecompute dfo rth eRi o Guadajiraunde r circumstances whichma yrepresen tth erecen tpas texceed sth erat et o bematche db yth edissolutio nproces sunde rcondition so f30 0m m leachingan d5 0 % limefo ra CC Lconcentratio no f1 0x tha to fth eatmospher ea t10°C ,b ya facto ro f

approximately5 0x .Assumptio no fth eimprobabl yhig h C02 contento f10 0x tha to f theatmosphere ,lower s these factorsfo rth eabovementione dtw ocase st o2 0x an d2 5 xrespectively .O nth ebasi so fthi sth elim edissolutio nmode li srejected . Theassume d higherprecipitatio nvalue saccompanie db yfores tvegetatio nma y wellb erepresentativ efo rth ePost-Glacia lwar mperio di nth eMediterranea na smen ­ tionedb yFrenz l (1967).Fig .3 0shows-tha ta shif tfro mwinter -t osummerrai nha s littleinfluenc eo nth eamoun to fleachin g sinceth etemperatur ecurve so f2 5C an d 10C ru nclos e together. Forth etestin go fth elim edissolutio nmode la sth esol ecaus efo rth edownwar d migrationo fth ecalci c horizon,ther ei sn oneed't odra wth elarge rclimati cvaria ­ tionso fth ePleistocen e intoth ecomparison .Th eduratio no fth ePost-Glacia lperio d islon genoug ht oallo wa rejectio no fth elim edissolutio nmodel .

6-1.6 Conclusion

Iti sno tnecessar y totes ta mor e complexdissolutio nmode lo fcalci chorizons , inwhic hth elim ei ssuppose dt orecrystallis ei nth elowe rpar to fth ehorizo ni n ordert ob edissolve d againi nth enex t cyclewhe ndissolutio nexpose si ta tth etop , sinceth efollowin g conclusionsca nb edrawn .

Thedissolutio no flim ei na soi l solutioni nequilibriu mwit ha C0 2 partial Pressureno wcommo ni nsoi l air,doe sno tcaus ea continuou ssof tcalci chorizo n o migratedownwar dwit h enough speedt oescap eexposur eb yerosio nunde rth eprese n conditionsi nth esurve y area.Thi si seviden t fromcalculation so fsuspende d sedi-

*»*yiel do frepresentativ e catchments. it ^

Ifio npai r formationdu et ointeractio no fM g andL a ^ ++ ^ havea nenhancin g effecto nth emobilit yo fcalci chorizons ,diffusio no t influenceo fa CO ,pressur e potentialwoul d alsohav ea nenhancin g effect.Th ec o- 2 v -, ' TA h,0 laraelvoffse tb yth ecombina - hnedeffec to fthes etw ofactors ,however ,woul db elargel yott s . atu_a_

tiono ffactor s that tend t0 decreaseth emobilit yo fcalci chorizons : underu f *« ofth esolution ,addition so flim et oth esurface , *»^™ fe^ "* iHuviationo fnon-calciti c solids.I ti shighl y improbable that et*-f -H thesefactor swoul d ™t toa nincreas eo fth eequivalen terosi e„» s ^ thecalci chorizo nca nmatch ,b ya facto ro f40 ,whic hwoul db eneede d

*e conclusiono fth eforegoin g paragraph in ^

Iti shighl y improbable thatprevailin g conditions tn PXClusivelyvi a —ey areacause dth ecalci chorizon st ohav esufficien tmobility ,exclusivel y thedissolutio nprocess ,t oescap e exposureb yerosion . If chemical lime transport had been the only process responsible for the down­ ward migration of the well-developed soft calcic horizons of the survey area, they would long ago have been caught by the prevailing erosion. This would have led to much more widespread exposure, hardening and subsequent destruction of these horizons than is witnessed in the present situation. Additionally it may be stated that the assumption of a geogenetic origin of the calcic horizons (Section 2.5.1) would not invalidate the foregoing conclusion. The same downward migration would have to be assumed to explain why calcitic materials deposited in some period between the Miocene and the present, happen to be found now all over the area mostly within 1 m of the surface of the soils. The fact that the foregoing calculations show that the leaching process is too slow to account for the downward migration of the calcic horizon, does not invalidate Knibbe's (1974b) postulation entirely. His assumption that the lime originated from these parent materials may still be valid, if there is another process with a speed sufficient to account for the migration of the calcic horizon synchronous with the wearing down of the surface.

6.2 MOBILITY OF SOFT CALCIC HORIZONS RESULTING FROM THE MECHANICAL REPLACEMENTPRO ­ CESS

Inthi ssectio na nalternativ e forth edissolutio n modelo fSectio n 6.1 ispre ­ sentedb ymean so fwhic hth esof t calcic horizons canmigrat e downward. Inthi smode l subterraneangilga îformatio n along the lower boundaryo fth e soft calcichorizo nin ­ teractswit hth eris eproces s inside thjshorizon .Togethe r they constitute themech ­ anicalreplacemen tproces sa si sillustrate di nFig . 38.Th e two constituentproces ­ seswil lb etreate dseparatel yi n thefollowin g sections.

6.2.1 Ri8e of clay nodules (and othev objects)

Thisproces sha sbee nstudie d indetai li nth e experiments described inChapte r •Fig .3 8depict sth eproces sunde r naturalcircumstance si na schemati c form.Th e conditionsunde rwhic h iti s operative arediscusse d inSectio n 5.3.4.I n thefiel da nume ro ffact s (1-7)hav ebee nobserve d which indicate that thecla y noduleshav e indeedrise nthroug hth esof tcalci chorizon.

0) Thedistributio npatter no fth ecla ynodule si nth e Riola1 profile ,a sdraw nb y tobbe (1974b),show stha tth e claynodule s decreasei nsiz ewit h the height overth e si7 b v fr°mWMC h theyiSSUe '™ iS Size dilution is indicativeo faprogres - UP fth SCl3 y n dUleS as the rise covPrrl ° ° y "PW"**. Thelarge rth edistanc e pheno- menoT' K' ^ ***^ ^ SUbiected t0we «ing and drying. The samepheno - not undernn wa tks observe h di n theArroy o1 pro Y° fiiprofilee. Counting- Countings and sizs anedmeasurement sizemeasurement swer es wer e undertakenen,becaus becaus emosmos t 1alarg™,e „cla i ynodule s desintegrate. . d intoman y smallerone s ^ upon

138 Fig. 32. Transition of the soft calcic horizon awards the v y ngperoclcx^ horizon of Profile Arroyo . (Site 2) The photo covers the horizons betwe & ^^_ cmdepth . The visible part of the knife measures 13 • The ™™ the tration of clay nodules which have been hampered in their upw* hardening of the petrocalcic horizon.

removal from the profile. This fact is probably due to the long exposure to which they have been subjected in the roadside cut.

(2) Fig. 32 of Profile Arroyo ! shows indications of interaction between rising clay nodules and the formation of lime fibres. Apparently the clay nodules were

-»-wip "/TT:

f

.*i

•::-4-- '

I Fig- 33. Profile^yo 1. Two arrows indicate a ^j^^/^ whence rise b ^d of dark coloured clay nodules. The lime I ID sJndstU1. Process of the clay nodules had come to a virt 139 •V

1 i«

* . =*»

r\ ••'-• «

./

mMWÉMjlhtfcaiat«IBte

Fig.34 . Claynodule svaryin gi nsiz efro m 0.5-1.5c mtake n froma sof t calcichor ­ izon ina nexposur eo fMiocen e claya tSit e7 (Guarena ). Th e characteristic surface of theclaynodule s withbot hangula r androunde d edges indicates that theygraduall y broke_upwhil emovin g upwards through thelime .Th enodule s were isolatedi nth elim e anddi d notfor mclusters .

risingwhe nth euppe rpar to fth eoriginall ysof tcalci chorizo nbecam eexpose dan d startedt oharde ni nplaces .Th ephotograp hshow stha tband so frisin gcla ynodule s werehampere di nthei rmovemen tan dwer eforce dt ofollo wa narro wpassage .I nFig . 33i ti sshown ,however ,tha ta lim efibr ecut sthroug ha ban do fcla ynodule swith ­ outcausin gan ydisturbance .Thi scombinatio nshow stha tth eslackenin go fth espee d ofth ecla ynodul eris ean dth einitiatio no floca lhardenin gwer esynchronous .Th e formationo flim efibre sdu et ochemica ldeposition ,continue dafte rth eris eo fth e claynodule sha dbecom einsignificant .

(3J Theshap eo fth ecla ynodule si sevidenc eo fthei rgradua ldésintégratio no n theirwa yupwar d (Fig.34) .Th ecla ynodule softe nsho wa sub-rounde dshap ewit hbot h roundedan dplan eo rangula rfaces .Th eroun dface sar eprobabl ythei rorigina lcon ­ tourswhil eth eplan ean dangula rface shav eforme ddu et othei rbreakin gu pdurin g therise .

(4) Severalcla ynodule sar epartiall ycovere db ydar kiro nan dmanganes ecoatings .

S 5 largeL er°cla?!"rcla ylump swhe T nthe ^ywer "e

prominenti nthi szon ea s reVe b ^ * ^ ^^ ^^ *" ^ Pr me 10 descriptions.Asimila rty " a ° " ^ ** n**™*» ***' accostfo rcarbonat egl ^ 1 " ^ * """" * *' ^ "ll aboveth ea w „ -\. Ymangan swh ichar efoun di nVertisol swel l aDoveth egle yzon em whic hth wn^. „ ave ac,uiredthss e mgms ass^to the glaebulest L 4;T ;? ™ ' enl nth esoi ldu et ochurning .Thi sproces sma y 140 : -1J

fi. * •

Fig. 35. Roadside cut at Site 5, south of the village of Arroyo de San Servan.Th e abrupt smooth boundary between a soft calcic horizon and the ^er^f J^*^, has a slope of 1% from the left to the right of the photo in ^"f^^r to road (away from the observer). The boundary owes itsabrup t ^^^J™^. a very active mechanical replacement process which expels the clay from the lime. The calcic horizon is overlain by a surface soil of 40 cm.

either imply that the glaebules rose relative to the surrounding clay matrix (like the clay nodules inrelatio n toth e lime) ortha t clay and glaebules rose simultane- ously as adisturbe d mass.

(5) The fact that the clay nodules are non-calcareous inthei r interior (profile de­ scriptions of Section 4.3.1), notwithstanding the fact that they are ^™£ • • +Kic matprial under alternat- "»st pure lime, indicates that their residence trme m this material ^ ing wet and dry conditions cannot be long. This implies arelativel y ig P their rise upward through the lime. Those encased ino r under P^ocal^c ho ns *ay have occupied such positions much longer without becoming calcareous dense petrocalcic horizon prevents moistening once it has forme .

«O The abrupt smooth upper boundary ofth e ^^^J£££°S<*- rally described inth e literature (Section 2.3), is consia y ^ ^ ^^ ^ roc Pulsion ofcla y nodules from the lime matrix by the rise P ^- 35 showing

« «rlH, „_*. of tMs W of horizon**£ » H™ Arroyo * S„ S,„„. a Profile ina road cut located approximately 15UUm a . expulsion of

The o„ly £easible explanation f0r this abr.pt ^^tJd Live Ice bio-

*ay from the soft calcic horizon. The expulsion must be ^^ .£ .t were slw logical homogenisation would obliterate the f^^ ^ ^ as £ollows:

* «active. Alternative explanations (a) and U ^ by ^^ 6(a) Slow movement ofhorizon s relative toeac h otne 141 (1970)a son eo fth ereason s forth e accentuation ofth euppe r horizonboundar y of softcalci chorizons .I nthi sparticula r case it isno t probable that thecontac ti s a shearlaye rsinc e theslop e of thehorizo nboundar ywa smeasure d tob e only 1%. 6(b) Anotherpossibilit y ist oassum ea sedimentary origin for the calcichorizon . Inthi scase ,however ,th ecalci chorizo ncontain s only 45 %lim eb yweigh twhil eth e rest ismad eu po fcla ynodules .I tseem shighl y improbable that such amixtur ewoul d havebee ndeposite d (recently)i na quie tenvironment .

(7) Thefac ttha tai renclosur eha soccurre d is indicatedb y the lowering ofth e bulkdensit y ofth e limewit hdecreas e indept h asreporte d inSectio n 4.6.1.1.Fre ­ quentoccurrenc e ofvoid s (vacuoles)i sreporte d for soft calcic horizons ofAlgeria n soils,e.g. ,b yDuran d (1959).

Inth e literature anumbe ro fprofile s aredescribe dwhic h showsimilarit ywit h thefeature s ofth eProfile sArroy o 1an d Riola 1 (1-5).

(1) Gile& Peterso n (1966)describ e themorpholog y of the so-called Khorizons .The y mentiontw opolygeneti c soilso nth eMid-Pleistocen e laMes a surface along theRi o GrandeValle yi nsouther nNe wMexico ,USA :th eRotur a soil and the Cacique soil,bot h ofwhic hhav eK horizons .Fro mth edescription s the following is quoted. For the Roturasoil : 'Atit suppe rmargi n theK horizo n contains a few spheroidal inclusions ofweakly calcareous ornon-calcareous ,reddis hbrown ,somewha t stickymaterial , which suggest incomplete engulfmenta tB thorizo nped sb yupwar d encroaching carbon­ ate'. For theCaciqu e soil: 'Itgrade s acrossa clearboundar y to a K1 horizoncon ­ sisting ofa carbonate-whitene d matrixenclosin gnumerou s spheroidalmasse s ofred ­ dishbrown ,slightl ycalcareou s tonon-calcareou s stickyBt-horizo nmaterial .Thes e inclusions lenda cellula rappearanc e and are suggestive of engulfmentb y carbonate ofa pre-existin g Bt-horizon'.

(2) Gardner (1972)mention s a 'somewhatlump y ornodula r structure'fo r the topo f thecalci chorizo nwhic h forms the transition zonebetwee n anoverlyin g petrocalcic horizonan d theunderlyin g sandyparen tmateria l of soils fromMormo nMes a County, Nevada,USA .H estate s thatbot h thepetrocalci c and the calcic horizonhav e ahighe r clayan d siltconten t thanth eunderlyin gmaterial .

(3) Netterberg (1980)describe s a 'powdercalcrete 'o nDwyk a shale inwhic hscatter ­ edpocket s ofcla yderive d fromth eunderlyin gmateria l occur.Th eunderlyin gweath ­ ered shale isfissure d andshattered .Man y fissures are filledwit hpowde r calcrete.

(4) Wilbert (1962)publishe s aphotograp h of aprofil e from Chaouïa Berrechid,Mo ­ rocco,tha tshow sa strikin g resemblancewit h Fig.5 o fRiol a 1.Translatin g fromth e Frenchan daddin gbetwee nbracket s the terminology given inSectio n 2.2.1 yieldsth e

142 following description: 'A laminar zonal crust (laminar petrocalcic horizon) covers a chalky or tuffaceous, stratified deposition (continuous soft calcic horizon), con­ taining some small soft clay pebbles. The total rests on a clay loam with big calcar­ eous spots (discontinuous soft calcic horizon) which have been subject to the pheno­ menon of 'mowing' through solifluction on the slope from left to right in the photo­ graph. The total represents the Moulouyen resting on a loam which is strictly Villa- franchien. Under this total, deposits from the pluvial period called Saletien.' The clay pebbles are probably equivalent to the clay nodules of the Riola and Arroyo pro­ files; the more so since they are found overlying a striped zone similar to the one of Riola 1. The author does not give an explanation of the genesis of the 'clay peb­ bles'. He shares Durand's (1959) opinion that most soft calcic horizons are due to deposition under wet circumstances. As such he considers the whole profile as an as- semblage of several different deposits.

(5) Distribution patterns of stones and other coarse constituents in the calcic hor­ izon are often chaotic in comparison with normal sedimentary structures. Such distr - bution patterns are indicative of the rising up of objects through the calcic hor­ izon. Brown (1956) reports similar phenomena. He expresses the following opinion for the origin of the chaotic distribution: 'The complete mixing of elastics found i caliche is best explained by soil animals and plants aided by altematang w and ry , • -f.-;™ r-r-arVs and by the thrusting ac periods which caused opening and closing desiccation cracKS ai y companying freezing and thawing'.

s-2-2 Subterranean gilgaî formation

The processes of soil formation in heavy cracking clay soils of tropical an *• ^«t and dry climate which lead to me sub-tropical regions with an alternating moist ana axy ^ ^^ (1965),

formation of Vertisols are well known and extensively descri e , "^^ Q£ cracks Soil Survey Staff (1975) and Young (1976). cesses sucras ^ ^ ^ ^

*at open and close due to swelling and shrinking, ate elements are evident

lief, churning and the development of slickensides an ^ particuiarly well landtyP throughout the study area. In the Miocene clay ^th thick so£t calcic hori-

expressed and they also affect the sub-soils of soils ^^ QÎ ^ clay mderly. z°ns. in these cases, interaction of the swelling an ^ ^_^ condition causes

ing the soft calcic horizon with the movement of this ^un ^ descriptions so

the formation of an unusual horizon configuration, n ^^s tMs process in a

far, this is indicated as the 'striped zone'. Fig. 38 * "^.^ 6<2<3)< In the schematic way. It is described step by step in t s -striped zone' that the formation or uic r survey area there are numerous indications tnau ^ „wnrelief in normal Ver- i. r „ on-rfnre eilßal microiej-ici has much in common with the formation of a suriac g formation. H „A cnhterranean gHgal iul,ua ^sols. As such the process has been called SUL. ^ al hypothesis of gilgai

According to Hallsworth &Beckman n (1969): e ^ rewetting the material does formation is that the soil cracks on drying, and t at on 143 notretur nt oit sorigina lposition. 'Th eagreemen ti nth eliteratur eo nth emai n processes thatfor m (surface)gilgaî ,i sreflecte di nth edescriptio no fth eVerti - solsi nth eSoi lTaxonom ySyste m (SoilSurve yStaff ; 197S).Th emai nstage smentione d are: - Formationo fa crac kpattern . - Materialdrop sint oth ecrack sunde rth einfluenc eo fsurfac eprocesses . - Swellingo fth ecla yo nmoistenin gwhic hresult si nth ebuildin gu po fpressure , duet oth einfille d cracksand/o runeve nwettin go fth eprofile . - Releaseo fth epressur ei na nupwar ddirectio nb ydeformatio no fth ecla ymas si n apatter nrelate dt oth ecrac kpattern . This leadst oth echaracteristi csurfac emicrorelie fcalle d gilgaî.I tlead st o the formationo fgrove dshea rplane scalle dslickenside san dtypica lbicuneat eo r lenticularstructura l elements,al lo fwhic har euse da sdiagnosti c criteriafo r Vertisols.Th efallin gdow no fth esoi lmateria lint ocrack s leadst ocycli cmove ­ mentso fth esoi lmass ,whic har ecalle d churningo rpedoturbation . Acharacteristi cdifferenc ebetwee nth eformatio no fsubterranea ngilga îan d surfacegilga îi stha tth eforme rcanno tlea dt oreal ,complet e churningo fth euppe r soil layerssinc eth ecla ypillars ,whic har eequivalen tt oth emound so fth esurfac e gilgaî,brea ku pvi acla ylump sint ocla ynodule swhic hdisappea r fromth ecycl eb y risingu pthroug hth ecalci chorizo na sillustrate di nFig .38 . Paton (1974)i son eo fth efe wauthor swh odisagre ewit hth egenerall y accepted opiniono nth eformatio no fgilga îmicrorelief .H edescribe shorizo n transitionsi n heavycla ysoil swhic hindicat etha ttongue so fth eunderlyin gcla ypenetrat ei nth e overlyingcla ylayer .H ecall s thesetongue s 'fingers'o r 'mukkara'.H efavour sloa d castinga sth emai ncaus eo fthi shorizo nconfiguratio n sinceh edoe sno tfin dcrack s inth eunderlyin gclays . Thehorizo npatter no fth eRiol aan dArroy oprofile s showssimilarit ywit hsom e exampleso fPaton .Ther ear enumerou s indications,however ,tha t thisi scause db ya gilgaiproces si nth esens eo fSoi lTaxonomy .Th efollowin g aspectsma yb econsider -

- Thecrack sclearl ypenetrat eth ecla ylayer ,whic hshow s abundant evidenceo f pressurean ddislocatio ni nth efor mo fslickenside san dwedge-shape d structuralele - ments.

- Theoccurrenc eo fslickenside si nth esof tlim efil lo flarg ecrack s (Fig. 36),i s a strongindicatio no fpressur eexerte do nthi smaterial . - Theaforementione d featuresar eeviden ti nth emicromorphologica ldescription s too. Evidenceo fshearin gb yforce ss ostron gtha teve ncalcit ecrystal swer ecrushe d isreporte d inSectio n4.5.1.2 .

rp- ^ inmTn °fllm e int°CraCk S is also clea^y demonstratedb yExperimen tI I lig. 27) m whichI* * penetratesa cracke d claynodule .A neve nmor e strikingex ­ ampleo flim epenetratio nint oa layere dMiocen e depositwa sencountere d inth esur ­ veyarea .Fig .37 ashow sa profil ewhic hi slocate da tSit e8 nea rGuarena ,whil e

144 **ir V" KV C"*- sTP*.." ''*wT !|„M

j*.. L.2Z.M' . L.z? : .*.$ F-2* d \[n '~ \ ï ?s M '' [.. 27 •' "•s- s ^ ?K k,. ' " ' f. ?3 ï. LJ:I i • *

r>- i i CQi't-p H The lime which Jb36.. DetaiDetail frofrom ththe stripestriped zonzone ouof. Profil""•-•"e- Riola 1 [^Jj^„lickenside^ sn -indicatinndicating gth e has penetrated the cracks of the Miocene clay shows clear s ^^ ^ ^^ ig considerable pressure exerted by the clay but resisted By • 5 ^ &) _ photQ from the B23ca horizon which occurs at a depth ot Z5U w^ courtesy M. Knibbe.

Fig- 37b shows details fro, that profile. The Serial is for the majorert moder­ ately coarse textured, but contains fine textured layers. The san ym a e so- vertical cracks, while thefin e textured layers have split up^^^ gular blocky structural elements. Soft powdery lime is present in e «d between the angular peds of the horizontal fine textured layers. ^ ^ irately coarse textured material between the fine ^ ^ & ^ high than 0.1 % lime. The fine textured layers and the vertical matprial is vir- *» -tent, as can be estimated visually. The fact ^^£Zt ^ 8 tually non-calcareous, indicates that the lime was P«* ^ J^ ^ cracks and

^ons it presently occupies from the overlying calcic ^^ ^ probably the ac. n°t in solution through theporou s sandy materials. ^ penetrating twn of soft powdery lime which when moistened becomes a ^ ^^ ^ ^ ^ Uye trough the cracks into thevoid s of thefin e textured ™ ^^^ mistening and 'jerks' its way stepwise into these voids byliquifyin g upo ^ ^ textured subsequently resisting thepressur e exerted byth e ^"^J.^ t0 the one u- layers as these aremoistened . This form of penetration is i lustrated in Fig. 38. ion . . qnf the irregular lower boundary (Sect: In the literature, several descriptions ot t ^ ^^ tQ 2-3) of soft calcic horizons contain references to featur those in the soils from theMérid a area: 145 t.

1 \ •*..*•• f.

',

Fig. 37a. Profile ina roa d cutalon g the southernban k of thecana l del Zujar,ap ­ proximately 200m easto f thespo twher e iti scrosse d by theroa d fromGuaren a to the^railway station (Site8 i nFig .3) .Th eprofil e showsa remnan t of a softcalci c horizon,indicate d bya whit earrow ,whic hha s infiltrated theunderlyin g stratai n aver yunusua lway .Th ehamme r included asa referenc e is3 0c m long.

1, l •' |.,»j^H^'J••° '^"t•^^î"^:g-••

"3

v I *- y?fawfal,jiiMf „ ,-_•_ «„ —1i~ ./

Fig. 37b Detailfro mFig .37 awhic h shows thelim e ina crack of the sandymate r ial (arrowa )an d betweenth eangula r fragments of theclaye y stratum (arrow b). The black arrows inFig .37 a

146 147 - Reeves (1970)describe svariou s structures foundi nth econtac t zoneo f'caliche ' andunderlyin gmaterial .H e offers asa nexplanatio n forth e irregular boundary the following sequenceo fevents :drying ,fracturing ,bucklin g and subsequent fillingo f theresultan tvoids .Th emateria l thatfill s thevoid s andmake s the deformations permanent isvados e silt.Thi smateria lwhic h consistso fsilt-size d calcite crystals isconsidere d asver ymobil eb yBlat te tal . (1972)wh omentio n itspresenc ei nth e voids ofman y rocksa sa sedimen t thatpost-date s the formationo fthes evoid sb y dissolution. - Durand (1954)mention s limemasse s inth e crackso fa clay . - Dumas (1969)discusse sa 'stripe d zone'wit hvertica ltraces . - Gilee tal . (1966)describ eroug hprism s coatedwit h thin layerso flamina rcar ­ bonate. Ruellan (1968)state s thati na simila r zone the lime accumulationi sinfluence d byroo tsystems . - Mathieu et al. (1975)describ e the infiltration of 'calcitemud 'i nth e cracked substratum underlying calcichorizons .

Itseem s thati nth eMérid aregio n thesubterranea n gilgal formation isno tre ­ strictedt oth e zones ofMiocen e clay fromwhic hmos to fth eevidenc e for thesepro ­ cessespresente di nth e foregoing sectionsha sbee ndrawn .Ver y similar phenomena havebee nobserved , e.g., onweatherin g schists,arkose s and limestones. Thewidesprea dpresenc eo fthes ephenomen a throughout thedr y climatic zoneso f theworl d canb e explainedb yth e fact thatmos t claymineral s formedi nth e presence of lime areo fth e2 : 1 lattic e type and showa hig h swell and shrinkpotential . Poorcrystallinit y ofcla ymineral si n the formative stagema y alsoenhanc e theswel l and shrinkpotentia lo fth eweatherin g zone.Moh re tal . (1972)describ e Vertisolsi n kaolimticmaterial swhic how e theircharacteristic st oth e latter factor. Other factors thatma y aid thepenetratio no flim ei nth eweathering zoneinde ­ pendento fswel l and shrinkar echemica l replacement (épigénie)an d the force exerted by crystallising lime.Thes e factors arediscusse di nSection s 6.6.2 and 6.6.3 re- spectively.

6.2.3 A mechanical replacement process as a combined result of the rise- and gilgaî formatton-processes

^combined effecto fsubterranea n gilgaiformatio nan d claynodul e rise isre -

presened m Flg.3 8i nwhic h theproces si sschematicall y condensedt ofiv ecycles , eacho fon eyear' sduration .Th e first twocycle shav ebee ndivide d into four seasons each.Th e sequencei sdescribe d asfollows - la. The initial situation inmid-w^ter . Bothlim ean d clay aremoist .

1' T T m eaTly" • ™SH œ haSdrie d °ut first duet oevaporatio n from the top. ^s has ledt osom edecreas e involum eo fth e lime (seeChapte r 5) and 148 Hg. 39. Horizontal cut of the striped transition zone between the soft "lcic ho izon and the Miocene clay at a depth of 260 cm in Profile Arroyo 1 at bite t. lime-filled cracks show a roughly hexagonal pattern which is similar to face patterns. The rounded shape of the lime pockets is due to £"£" J*?W for­ *en the lime penetrated the cracks. This process is called 'subterranean gilgai mation'.

toamino rsubsidenc eo fth esurfac e soil. fc-Th esituatio ni nmid-summer .Th edryin gha sproceede d intoth ecla y layer,re ­ ntingi n losso f volumeo fth ecla ymass .Th e surfacesoi lha ssubside dan danet ­ worko fshrinkag e cracksha sforme di nth eclay .I nprojectio nthes ecrack ssho wa agonal patterna si seviden ti nFig .3 9whic h showsa horizonta l coupeo fth e

Gripedzon eo fth eArroy o1 profile . . „omni<._ S "• Tnesituatio n in autumnwhe n thefirs train shav e fallen.Th e1 ™ *» ™» t-edl eading t0 air enclosurC; local liquifactionan dremouldin g especially^na r ^ ^ voidswhic h have filledu pwit h lime. Inth eschemati cdrawin g itha sb e n ^ thatth eincreas ei n volumeo fth elim edu et oai renclosur ewa scom pn s e f °rb yth esubsidenc e causedb y the infillingo fth ecracks .A ssuc hth esurfac e ha, s— -°tm0Ved- . ,. Mien to moisten the whole 2a. *• The situation in mid-winter when sufficient ram has fal en ^ Pr°file. After the lime had moistened and filled the cracks, the clay I ^ sl«ly permeable) started to moisten and swell. The voids, however, ^ ^ s1** the li.e (after some compression) resisted the exerted pressure

<* the mgular calcite grains trappedi n the c^.^^^^t the gram pressure. Evidence of this is shown, e.g., m Fig- • hetweQn the cracks in Plastic clay changed shape, releasing the pressure by rising up the fon» of pinars. Heaving and deformation of the overlying 1* n,ass caus soil - - - - surface to return to its original level. 149 2b. Thesituatio n inearl y summer.Th e limeha s dried out and the surfaceha ssub ­ sided slightly. 2c. Themid-summe r situation.Th e clayha s dried out and the cracks have reopened. Voidshav e formedbetwee nth e lime fillan d thewall s of the cracks.Th epillar shav e cracked andhav e splitint ocla y lumps.Th e surfaceha s subsided due to thedecreas e involum eo fth eclay . 2d. Thesituatio n inautumn .Th e limewa s remoistened by the first rains resulting inai renclosure ,loca lliquifactio nan dremoulding . Thevoid s along thewall s ofth e crackshav e filled in,whil eminut e quantities of limepenetrate d between the lumps. Thesurfac e soildi dno tsubsid e since the infilling of the crackswa s compensated forb y theai renclosur e inth e lime. 3a. Themid-winte r situation.Th ecla ywa smoistene d andha s swollen.Th ecla ypil ­ larshav eextende d furtherint oth e limemas s since the lime in the cracks resisted thepressure .Th ecla y lumpsmove d relative toeac h other andmor e limeentere dth e cracks thatseparat e them.Th esoi l surfaceha sreturne d again to its originalpo ­ sition. 4a. Themid-winte r situationafte r onemor e fullcycl e haspassed . The crackshav e penetrated further intoth ecla y and thecla ypillar s protrude further into thesof t limean dhav ebroke nu p intocla y lumpswhic h intur nhave separated into claynod ­ ules.Th e latterhav ebecom e subject toth eris eproces s in the soft lime. 5a. Themid-winte r situation afteron emor e full cycleha spassed . The crackshav e extended furtherdownwar d and thepillar shav ebee n largely brokenu p via claylump s intocla ynodules .Th e latterhave rise nan d havealmos t reached the surface soil. 6a. Themid-winte r situation after onemore full cycle has passed. The processes haveproceede d furtheran d somecla ynodule shav ebee n expelled from the softcalci c horizonan dhav ebee n incorporated intoth e surface soilwher e they desintegratean d mixwit h thesoi lmaterial .

Iti seviden t thati nth e field theeffec t ofeac h cycle ismuc h smaller than indicated m Fig.38 .Th e starting point aspresente d indrawin g 1adoe sno t existi n reality (seeSectio n 6.6.4).Th e schematic representation,however ,give s animpres ­ siono fth e interactiono fth egilga îformatio n and theris eproces s as they occuri n thenatura l environment (documented inSection s 6.2.1 and 6.2.2). Themechanica l replacement processwil l lead toa n increase in thickness ofth e surfacesoi la smore andmore clay isadde d to it.Consequentl y the calcic horizon willmigrat edownward . Ifsurfac e erosionremove s soilmateria l from the surfacesoi l andthes e lossesar ecompensate d forb y claynodule s frombelow , thewhol e system willmigrat e downward.Th e lattercas e isrepresente d in Fig. 43,whic h dealswit h deformationo fstructure s due tothi smigration . For theM landscape ofth e survey area thedownwar d migration canb e derived tromproo fb ynegativ e demonstration,a smentione d inSectio n 6.1.6: Ifn o process existed tocaus e thedownwar dmigratio n of the calcic horizon synchronous with the downwearmg of the land surfaceb y erosion,th ecalci c horizons of this landscape

150 would all have been stripped bare of their soil cover. This would have led to a much morewidesprea d hardening of the calcic horizon than is witnessed in the present situation, and soft calcic horizons not crowned by petrocalcic horizons on their tops wouldb e virtually absent. Of the two options open for such a migration, namely the chemical transport of lime and the mechanical replacement process, the chemical dis­ solution is ruled out in Section 6.1 since the speed of this process is not in pro­ portion with the erosion rates estimated by various different means for the M land­ scape. The mechanical process can cause a migration speed of the calcic horizon which is of the same order of magnitude as the rates of erosion estimated. This aspect is treated quantitatively in Section 6.3. Due to the downward migration of the soft calcic horizon, cases may arise in which the calcic horizon contains objects 'non-related' to either the material pre­ sently overlying and underlying this horizon. The 'residence time' of objects con-^ tained in the fine crystic matrix of the soft calcic horizon depends mainly on their size (Chapter 5). Objects the size of the calcite crystals will probably not be ex­ pelled at all, while larger objects rise up in the horizon. Large stones may not rise as fast as clay nodules of similar dimensions as suggested by the result of Experi­ ment nibi of Section 5.2.5. As a result fine-grained mineral constituents probably accompany the horizon for extended periods while it migrates downward. Larger objec accompany it for shorter periods, before they are expelled from the top of ^hor­ izon. The result of the temporary enclosure of objects of all sizes may e a d the course of time, the mineral suite of the calcic horizon becomes ^™ r resU that of both the overlying and underlying horizons. This can ^™he calcic accumulation of minerals from different parent materials through w i horizon has passed. In such a case the calcic horizon contains sane additional erals not present in the overlying or underlying horizons. ^ ^ ^ ^ v Nomineralogica l investigations have been carried out to ^>^^ ^ veri£ied 1-dscape in the Mérida area. In the literature, however i ^ ^ -tn reference to soft calcic horizons m Algen d scri d ^ ^ ^ t«*d in Section 2.5.1. He supports his thesis h characteris-

Pomting to deviating mineralogy and to the large var at di££erences in min- fc« of the quartz grains of these horizons. Brown ( *>J P ^^ ^^ «al composition between 'caliche' and overlying soil. ^ ^^ y^izen- unrelated et st0ne al. (1954) who report the presence of rounded Y^0sited by £ast-flowing t0 the substratum and conclude that lime and stones were ^^ ipoorly sorted wa oî ters. Lattman (1973) reports a high degree ^^ ^ in 'the surface layer' ion-calcareous fan deposits possessing over 50 % of pe ^^ ^^ ^ pebbles may

« 'extensive and well-developed lime cementation'. He ^^^ ^ excluded> how-

^e initiated the cementation by developing lime ^.^.^ ^ are now being ever, that the pebbles have been contained in the calcic derated due to dissolution of the lime.

151 6.3 FACTORS CONTROLLINGTH EMECHANICA LREPLACEMEN T PROCESS

Bothth eaforementione dprocesses ,ris eo fobject san dsubterranea n gilgaifor ­ mation,whic h togetherconstitut eth emechanica lreplacemen tproces sar edependen to n alternatingwe tan ddr ysoi l conditions.Onl yi ntha tpar to fth esoi li nwhic hthes e conditionsprevai lca nth ereplacemen tproces s takeplac ean dth ecalci c horizonmi ­ grate.Th esoi lmaterial sar esubjec tt oupwar dmovement .Thei rrat eo fproductio n alongth eweatherin g fronti so fcours ea limitin g factorfo rth etranspor to fma ­ terial.Th ecalci chorizo ni srestricte d init smovement ;i ti sencase d betweenth e soilsurfac eo nth euppe r sidean dth eweatherin g fronto rth eaverag emea n ground­ water table,whicheve ri sshallower ,o nth elowe rside . Ina landscap ei nwhic hequilibriu m exists,th espeed swit hwhic hth esoi lsur ­ face,th eweatherin g frontan dth egroundwate rtabl emigrat e downwardar eequal .Tem ­ porarily,disturbance so fthi sequilibriu mma yoccur ,whic hmodif yth esiz eo fth e zonei nwhic hth ecalci chorizo nmigrate s downward. Factors determining therat eo f migrationo fth esoi lsurface ,th egroundwate r tablean dth eweatherin g frontar ea s follows: - Thesoi l surfaceo fan ylandscap e generallyerode sa ta spee d determinedb ycli ­ mate,vegetation ,soi land/o rparen tmateria lan dtectoni c eventswhic h shapeth e landscapean ddetermin eth erelief . - Agroundwate r tableestablishe s itselfi nth esoi la ta certai n distance fromth e surfacea sth eresul to fth edevelopmen to fa nequilibriu mbetwee n additionan dre ­ movalo fwater .I nmos tcase s thisresult si na groundwate r tablewhic h reflectsth e surface reliefi na generalise d form.Change si nadditio no fwate rar emostl yrelate d tochange si nclimate :amount ,distributio nan dfor mo fprecipitation ,togethe rwit h changes inth evegetatio nwhic hresul t from this.Change s inremova lar emostl ydu e tochange si nth edissectio npatter no fth elandscape :change s indepth san dintri ­ cacyo fth epatter nan ddownwearin go fth edivides . - Inth ecours eo ftime ,othe rparen tmaterial sma yb eexpose db yerosion ,leadin g toth eformatio no fdifferen t soils.Suc hchange sma yaffec tth epermeabilit yo fsoi l andparen tmateria lan dinfluenc ebot hth eadditio nan dth eremova lo fgroundwater . - Theweatherin g frontproceed sdownwar da ta spee dmainl y controlledb yparen troc k andclimate .Th edept ho fth egroundwate r table alsoplay sa role ,sinc eweatherin g underth egroundwate r tablei sminimal ,compare dwit hweatherin g over it.Th eweath ­ eringprocesse sar egenerall ymos t activei nth ezon ei nwhic h groundwater fluctu- ates.

- Limepenetrate sth eweatherin g zonea smentione di nSectio n6.2. 2an dexert sa n acceleratxnginfluenc eo nbot hphysica lan dchemica lprocesses .Severa l authorsclai m this Goudie, 1972).Youn g (1964)describe s fracturingo fsandston e cobbles embedded incaliche .I nhi sopinio nth emai ncaus eo fth efracturin gi sth eforc e exertedb y thecrystallisin g calcitewhic hi sfe db ya bicarbonat e solutioni nth epores .Th e

samephenomeno ni sreporte db yCapolin i& Sari (1975).Se eals oSectio n 6.6.3.Naho n

152 et al. (1977) state that calcic horizons are capable of digesting fossile latérite crusts• As a consequence of the accelerating influence of the calcic horizon on the weathering, it is common to find the lower boundary of the calcic horizon coinciding with the weathering front, which in turn is positioned generally close to the average gromdwater table. If the weathering front maintains a reasonable distance from the soil surface, the soft calcic horizon retains its original characteristics, if it can mtch the speed with which the system moves down. (Exceptions to this case are dealt with in Section 6.5.) . Various types of calcic horizons can be observed in the study area. They vary in thic^ss, composition and depth and in the type of horizon boundary which they share with overlying and underlying horizons. The main types that occur have been described in Chapter 4. In many cases the various types show gradual lateral transitions (Fig. 10) which suggest that different types descend from each other. This is explained by adynami c model which shows how a calcic horizon is subject to changes in morphology and depth in the course of time (Fig. 40). This figure illustrates how the calcic^ horizon reacts to the movements of weathering front, groundwater table an

*. in . landscape with a surface which is being worn down in ^^^ Ms gives a schematic representation of the fate of a pro P ^

is indicated by an arrow in the cross-sections of the landscape; ,. ctim by sents time and the y axis represents the distance covered in a downwar U« X respectively: the soil surface, the top of the soft calcic horizon, tte o« *

soft calcic horizon which coincides with the weathering ^J^.^ ^ the

groundwater table. The figures under the graph correspond o sections ^ par- re resented different erosion cycles, which have been P "" ^^ horizon will ent material is assumed to be easily weatherable, so m ^ ^ initiated by head- ev051 rapidly follow a falling groundwater table. The °^ ^ groundwater table ward erosion of the drainage system, which causes a incision of the drainage throughout the area. Downwearing of the divides follows t e m

WayS' • -nitrated in the model (Fig. 40):

The following sequence of events is musti* ^ ^ ^ ^^ down 1 - In the initial situation there is equilibrium. The sur a ^ ^ nodules that s lowly. Losses of material on the surface are "^^J^. o£ the caicic horizon r cm ise through the soft calcic horizon. (The clay nodule ^^d close tQ the average « relatively low.) The bottom of the calcic horizon is si groundwater table. _ e drainage system is taking 2 - An erosion cycle has been initiated. Incision o ^ ^ ^^ Sur£ace erosion Plaœ, leading to a rapid fall of the groundwater ta e^ ^^ ^ ^ ^^_ re CtS has not yet increased much. The calcic horizon * Jo{ clay_ It expands in thick­

er table by an increase in the upward transportation ^^ ,bloated. by the clay ness equivalent to its dilution by the clay nodules. continuous lt consumes and whose former space it invades. -ICI c Bottom of soft calcic horizon which equals the weathering front (for simplicity representeda s astraigh t line) d Average groundwater table t Position of profile

Fig.40 . Adynami cmode lfo r thebehaviou r ofa softcalci c horizon thatmigrate s downunde r thesurfac eo fa landscap e subject tovariou s cycles of erosion.Tim ei s plotted onth ehorizonta l axis.Distanc e covered ina downwar d directionb y thesoi l surface,th ecalci c horizonan d theaverag e groundwater tablear eplotte d onth e verticalaxis .Th e schematiccros s sectionsa t thebotto m of thefigur ecorrespon d innumbe rwit hth evariou s situationso f thegraph .Detaile d explanation isfoun di n thetext . v

softcalci chorizo nma ychang e temporarily intoa discontinuou s soft calcic horizon (Section 6.5.3). 3. Surface erosiondu et odownwearin go fdivide si sno wincrease dan da ne wequi ­ libriumi sestablished .Th ehighe r losso fsurfac emateria l iscompensate db ya nin ­ creased transportationo fcla y throughth ecalci c horizon.Th ebotto mo fth ecalci c horizonha sno tbee nabl et okee ppac ewit hth erapidl y falling average groundwater tablean di sfurthe rseparate d fromit . 4. Theincisio no fth edrainag e systemha s reached base level.Thi s leadst oa de ­ creaseo fth espee da twhic hth egroundwate r table fallsan dth ecalci c horizoni s catchingu pwit h it.Th etransportatio no fcla y throughth ecalci c horizondiminishes . Thecalci chorizo n itselfdiminishe si nsiz ea si tpurifie s itself fromth elarg e quantitieso fcla ynodules .Th esurfac e erosion startst odiminis htoo . • Ane wequilibriu m hasbee nestablishe d betweenth ereduce d surface erosionan d

154 thereduce d transportation of clay. The bottom of the calcic horizon is situated close to the groundwater table again. 6. A new erosion cycle has started. Incision of the drainage system causes the groundwater table to fall. The bottom of the calcic horizon follows and the transpor­ tation of clay through the calcic horizon starts to increase. Surface erosion has not yet accelerated. 7. Surface erosion has increased and can just be matched by the increased transpor­ tation of clay through the 'bloated' calcic horizon. in nature a number of variations and complications of the aforementioned model »y occur. In the contact plane of lime and parent material a perched water tab ema y establish itself. TMs may control the downward movement of the calcic horizon during the period it persists. Another complication may arise from the establish^ of a so-called 'dead horizon' which is a dry zone that separates the ^^T part from the groundwater-moistened lower part of the calcic horizon, complication will be dealt with in Section 6.5.3. Ihe model of Fig. 40 is an illustration of the boundary condition^ which —nts of the soft calcic horizon in long-term perspective are^ ^^ natural conditions in a landscape subject to degradation ^ petrocalcic hor- in those parts of the Miocene clay landscape that are no ^ , r T- /in hprause groundwater taDiea uons corresponds with Situation 3 of Fig. 40 bee P ^^ ^^ o£ deeply in the last few thousand years. This du ^ ^^ re_ the natural vegetation which has increased run-oti ai ^ discontinuous soft *arge (Section 3.4). Locally this has induced the formation o^ ^ ^ ^^ ^ ^

calcic horizons. All variations covered by the model o ig. ^ ^ ^ £Q1_ cross section Fig. 10. Other evidence that backs up this mode

lowing paragraphs. r short lateral intervals In the Guarena cut (Site 7) it was noted tnar ^ ^^ horizon. They

there were marked differences in habitus and depth of * ^^ ^ top o£ the so£t coincide with the presence or absence of a petrocalcic ^o ^ ^ ^^ horizon is rese calcic horizon: where the petrocalcic horizon is P ^c horizon is absent, the 6 Pwe and not deeper than 120-150 cm. Where the P "^"^ m cm. These differ-

calcic horizon is full of clay nodules and its dept is in depth and

ences occur over a lateral distance of only ^ ^^ ^ local hardening of

habitus of the soft calcic horizon have probably arisen^ ^_ ^ ^ ^ in£ntra. etrOCa ** calcic horizon (Section 6.5.4). Where the P ^rizon could not follow a calcK Wono f rainwater almost impossible, the soft no petr0Calcic horizon im- rapidly falling groundwater table on its way down. e ^ ^ ^^dwater table Peded the infiltration, the soft calcic horizon cou ^ ^^

downward, becoming 'bloated' by the lime it consume ^^ with soft calcic

The relative abundance of weakly developed soi ^ ^ ^ ^ ^^ horizons

bizons on slopes in many landtypes (Section 3. ) s ^^.^ Q£ the slopes. The have moved down in the profile, synchronous witn V. weakprofil e developmentmake s itimprobabl etha t sufficient timeha s passed toac ­ count for the limeaccumulatio n inthes eprofile s by otherprocesses ,e.g .b y crys­ tallisation from laterallymovin g groundwaters. Coque (1955)describe d acas e inTunesia ,i nwhic hdownwar d bending ofcalci c horizons towards the limitso fdrainag eway s isevident .Thi s indicates thatcalci c horizons followth egroundwate r table,whic h isdraw ndow nb y local incision. Ruellan (1968)describe swea ktrace so fhydromorphis ma s acommo n feature of calcic horizons.Thes ehav eals obee nobserve d inth eRiol a andArroy o profiles,i n the lowerpar t ofth e softcalci chorizon .The ysuppor t the fact that thebotto m of thecalci c horizon,whic hcoincide smostl ywit h theweatherin g front,i s oftenfoun d near the average groundwatertable .

Beforemakin g anestimat e ofth espee dwit hwhic h the soft calcic horizons can movedownward ,th eproces s sketched inFig .4 0mus tb e examined critically. Thevelo ­ citywit hwhic h thecalci chorizo nmove sdow ndepend s on twoprocesse s: subterranea n gilgaî formation and rise ofclod s ofweatherin gproduct s produced by it.Th e riseo f materials can onlyoccu r ifth egilgaî.formatio ndetache s them.Th e continuity of thisprocess ,however ,i sno tdependen t onth eremova l of itsproducts .Thi s isil ­ lustrated inPoin t 2o fth ediscussio no fFig .40 ,whic h shows that inextrem e cases continuous softcalci chorizon sma ybecom e discontinuous. Ifth egilga î formationac ­ celerates to aspee dwhic h iss ohig htha tth eris eproces s cannot transport thepro ­ ductsupwar d sufficiently quickly,th esof t calcichorizo nbecome s cloggedwit hth e weathering products.Al lupwar dmovemen twil l stop ifth e fragments come into contact with eachothe ran d forma 'skeletalstructure' .Thi sdoe sno tmean ,however ,tha t themovemen t of thecalci chorizo n stops.Th e swelling and shrinking of the claycon ­ tinues.Th e soft limecontinue s tofil lth ecrack s thatar e formed in theweatherin g zone,bu t thefragment s ofweatherin g products contained in the limecanno t follow andar e leftbehind .Th eresul t istha tth ecalci chorizo n leaves its 'skeletal structure'behin d andcontinue s itsdownwar dmigration .Th eproces s bymean s ofwhic h the limemigrate s involves apartia lreplacemen t of theunderlyin gmateria l which differs fromth emechanica l replacementproces s towhic h thismateria l is subjected by themigratio n ofa continuous softcalci chorizon .Th e discontinuous soft calcic horizondoe sno tentirel y rework thehorizo n throughwhic h itpasses ;i t onlywiden s itsfissure s temporarily.A s suchth eproces s should ratherb e called 'active v^e- tratum'. Fig. 41 illustrates claynodule s leftbehin d by acalci c horizon inwhic h theyforme d askeleta l structure. Inothe rcase s itha sbee n observed that skeletal structures consisting ofpetrocalci c fragmentshav ebee n leftbehind .Whethe rdiscon ­ tinuous softcalci chorizon sca nreconver t intocontinuou s softcalci c horizons is discussed inSection s 6.5.3 and 6.6.4.

The complexrelationshi pbetvee nth eris eproces s and the gilgaî formationa s discussed inth eforegoin gparagraph ,ha s tob e takenint o accountwhe nmakin g anes -

timateo f the speedwit hwhic h thesof t rain> i,„• -u uiesot t calcichorizo n canmov e down.Th econtribu - 156 m,

•'«0,-V*. . y 41. DetaiTof soiTmonolith El. of the ISM.The P^^rap^representsjhe^art beween 35 and 50 cm depth. Several clay noduleV h' horizon The clay nodule in a clayey matrix. They form the parent material of this n • ^ ^ ^ location ien 'he middle of the upper part of the photograph has a ^ been left behind f Profile EH has been indicated in Fig. 4. The clay nodules ha ^ ^ V * calcic horizon which followed a rapidly falling groundwater tesy ISM.)

*» « the rise process t0 the „nt of the ^^^J^,^ flying the results of the experiments of Chapter 5. Under rises of morere tha than nth the emeasure measured dvalue values sar are eprobable probable. . _ ^ ^ different ob- r In Sectectioi n 5.3. ' ' 3-*- it was concludeI..J»J dtha that tth the ene net t average rise ^ ^

*** was in the order o£ 0.5 m per cycle. This means that by ^ was ...e order of 0.5 mm per cycle, mis i— ^ ^ ^ ^^ o£ the rai^_ ,. . . . - . • ^-„ ^n,.m at a speed that is tne y •calci ;alcicc hori horizoz n is capable of migrating down at a spee ^ density data 0115 rise and its content of clay nodules. Taking into acccun ^ ^ ^

«ported in Section 4.6, the lime content by weight, as use i ^^'^ are as equal to the content by volume, since the bulk densities o movement Si^ar, at depths of about 1 metre in the profile. The following are d: found: luine- 1/5 x 0._5 . nm.= _ 0. n1 1 ™,/vrmn/yr. calcic horizon with 20 % clay nodules by vo um . Q Sm= 0.25 mm/yr. F°r a calcicalcic chorizo horizonn wit withh 5 050 t tcla clayy nodule nodules sb yby volume volume. : / / Thes'esee valuevalues correspond with 10 -an d ..25 .m/10 ^/ln5 5y r^ respectiv respectivelye ^ . correspond with 10 and 25 m/10 yr f calcic horizons remain °nly by means of the rise process can continuous so Only by means of the rise process can continuous so ^ ^ ^ ^ transport Sinuous while travelling downward. Aprerequisit e for 151 7 capacityo fth eris eproces s exceedso rmatche sth esuppl yo fsoi lmateria l intoth e calcichorizo nb yth egilga î formation.Th erate so fmovemen t calculated applyt o suchcases .The y show thatth erat eo fmovemen to fcontinuou s softcalci chorizon si s ofth esam eorde ro fmagnitud ea serosio nrate s commoni nth esurve y area (Table15) . Ifth erequiremen t thatth esof tcalci chorizo nremain sa tleas tpartiall y continuous whilemigratin g downi sdropped ,muc h larger rateso fmovemen tar epossible .Th e speedwit hwhic ha discontinuou s softcalci chorizo nca nactivel ypenetrat eth ecla y isgoverne db yth ecrac kvolum e available.Thi s speedcanno teasil yb equantifie dbu t iti sprobabl e thata discontinuou s softcalci chorizo nca neasil y followa fallin g groundwater tabledownwards ,provide d thatmoistenin g ofth elim edurin g eachwinter - seasoncontinues . Summarising,i ti sconclude d that continuous softcalci chorizon sca nmatc hth e erosionrate s commoni nth esurve y area,whil e discontinuous soft calcichorizon sar e capableo fexceedin g these rates.

6.4 RECONSTRUCTION OF CALCICHORIZON SWHIC HHAV EBEE NLOCALL YDAMAGE D

Occasionally iti sobserve d inth efiel d thatcalci chorizon sar einterrupte d locally.A fe wexample swil lb egiven .Tw ogenera l typesca nb edistinguished : - Onit swa ydownwar da calci chorizo nencounter sa nobjec twhic hi sunweatherabl e orslowl yweatherable .Whe n this objecti sby-passed ,a loca l interruptiono fth e calcichorizo nresults . - Sometimesth ecalci chorizo ni sbreache d locallya sa resul to fgull y erosion. Whenth egull y fillsup ,a 'plug'o fmateria l interruptsth econtinuit yo fth ecalci c horizon. The facttha tsuc h 'scars'ar eonl yrarel y foundi ncalci chorizons ,whil een ­ counterso fbot h typesmus thav ebee nnumerou si nthei r longhistory ,i sa stron gin ­ dication thatthe yar eabl et oreconstitut e themselves.I nbot hcase sth escar sar e 'repaired'b ylatera lmovemen to flim ewhic h closesth egap s synchronouslywit hth e downwardmovemen to fth ewhol e system.Thoug hneve r fluidi nit sentirety ,th ebeha ­ viouro fth esof tcalci chorizon ,whe nviewe d intime ,ha smuc hi ncommo nwit hth e behaviouro fa liquid .Th etendenc yt ofor mabrup tuppe rboundarie s ison eo fth e properties itha si ncommo nwit ha fluid .Anothe ri sth elatera lmovemen to fcalci c materiali nth eprofile .Th ereaso ni stha t locallyan dtemporaril yth ecalci chor ­ izoni si na flui dstat e (asdemonstrate d e.g.b yFig .2 7an dFigs . 37ab). Fig.4 2show sa profil ewit ha sof tcalci chorizo ni nth eproces so fby-passin g an unweatherable object.Th eobjec ti nthi s casei sa dik eo ffine-graine d basicin ­ trusiverock ,whic hform sa so-calle d lamprophyrei na bod yo fcontac tmetamorphou s hornfelsic schist justN .o fMérida .Th ecalci chorizo nactivel ypenetrate s thehorn - felsic saprolite,fro mwhic h several fragments havebee ndetache d andar econtaine d inth ehorizon .Th eaverag e lime contento fth ehorizon ,a smeasure d fromtw osample s oneithe r sideo fth einclusion ,wa s7 6 %(mas s fraction).

158 • y*-.- •?•.•. •* ••• • til H- ••i1

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Fig. 42. Adik eo f fine-grained material (lamprophyre) isbein gby-passe d bya sof t calcichorizon .Th efine-graine d basicmateria l isles sweatherabl e thanth erock s which itintrude s (hornfelsic schists). Green saprolite from schist ispresen ta sa continuous phasebelo w theweatherin g fronta t 170cm .Fragment s ofthi s saprolite occur inth e softcalci cmateria l oneithe r sideo f thedike .Th ephotograp hwa s takeni na n excavation at theparkin g loto f theMérid a football-field indicateda s Site 6i n the Schist landtype (Fig.3) .Eac hbloc k of themeasurin g taperepresent s 10cm .

Exampleso f'repair 'o fdamag e inflictedb yerosio ngullie son a sof tcalci c horizonca nb efoun di nth eexposur eo fMiocen eclay ,alon gth eroa d towardsGuarena , inth eextrem eeaster ncorne ro fth esurve yare a (Site 7). Inthi scu tsevera lstruc ­ turesar epresent ,representin gvariou sphase so fregeneratio no fcalci chorizon s whichhav ebee n incised locallyb ygull yerosion .Th einfille dgullie sar eby-passe d byth ecalci chorizo no nit swa ydown .Th elim epenetrate s laterallyunde rth egull y bottoman dcause scharacteristi cdeformatio npatterns .A ta late rstag e limepene ­ tratesth egull y fill,whic hma ylea dt oa tota ldisruptur eo fth eorigina lstruc ­ ture.Th eproces si sschematicall y reconstructedin Fig .43 .Th efollowin g stepsar e distinguished: 1. Theinitia lsituatio ni sstable :surfac eerosio nan dcla ytranspor tthroug hsub ­ terraneangilga i formationan dcla ynodul eris emaintai nan equilibriu mresultin gi n a slowdownwar dmovemen to fth eentir esoi lsystem .

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160 2. Anerosio ngull yha s dissected the soilan dha s cutthroug hth e softcalci chor ­ izonan d into the transition zoneo fthi shorizo nwit hth eunderlyin g clay.O nth e flatbotto m stones are deposited. 3. Thegull y is filledu p by asedimen t ofsand yclay .Th e slowdownwar dmovemen t of thesurfac e and of thecalci c horizoncontinues . (Therema yhav ebee nsom e local hardening ofth e limepreviou s toth efillin g ofth egully ,bu t toavoi d complicating thecase ,thi sha sno tbee n indicated.) 4. Thedownwar dmigratin g calcichorizo npasse s thegull ybotto m and the limestart s tomov e laterally into cracks inth ecla ymas sunderlyin g thegully .Thi scause s an increase involum e of thewedge-shape d claymasse sunde rth egully .Thes ewedges , which increase involum e byreceivin g more limewit h everycycl e ofwettin g anddry ­ ing,exer t apressur e on the overlying stone layer,whic h consequently curvesup ­ wards.Th e filling of thegull yha sbee ncomplete d nowan d thesurfac e iseven .Lim e alsostart s toente r the sandycla yplu g laterally along thegull ywalls .Thi s causes somevolum e increase,whic h isreflecte d ina sligh tdeformatio n ofth eshap eo fth e gully.Loca lhardenin g of the limeretard s the influx intoth eplug . 5. The limeproceed s furtherbot hdownward s and laterally.Th eexpandin gwedge s of cracked clayreceiv emor e lime.A t their sides they looseonl ysmal lamount so fcla y inth e form of claynodules ,sinc e these aremainl y trappedunde r thegully .Th e force exerted results ina strong deformation ofth eston e layer,whic hmark s the former gully bottom. Through thegull ywall smor e limepenetrate s thesand ycla yplu g subjecting it tomor e deformation. Surface erosion shavesof fan ysurfac erelie f that results from thesedeformations . 6. The expanding claywedge s fromeithe r side ofth egull ybotto mhav eno wproceede d sofa runde r the gully that they almostmee t inth emiddle .A t their sides theyar e gradually 'eatenup 'b y theproces s ofcla ynodul e formation.Th ecla ynodule smov e toth e surface.Lim eno w starts tomov e through thecurve d stone layer intoth esand y clayplug ,subjectin g it to furtherdeformation . Fig.4 4illustrate s asituatio n in theGuareh a cutwhic h isrepresente d by this stage of theprocess . 7. The expanding claywedge s havemet .Lim e entering the sandy clayplu gcause s a strong deformation of thisplug .Sinc e the supportwhic h thecla ywedge s offered at thebotto m has largely fallen away,th epressur e inth eplu g isno wn o longerre ­ leased towards the surface,bu t towards theadjacen t soft lime,leadin g to further deformation of the stone layer. 8. The claywedge s under thegull yhav eno wbee ncompletel y removedb y the migrating softcalci c horizon. Limecontinue s toente r the sandy clayplug ,whic hrespond sb y further expansion inal ldirections .Th e limecontent ,insid ean d outsideth eston e layer,tend s toeve n out.Eventuall y thetota l gully fillwil lb e expelled atth e surface and eroded. Fig. 45 illustrates a stonedistributio npatter n inth eGuaren acut ,whic h matches Stage 8o fth efigure . Notal l erosiongullie s incising calcichorizon s areassume d topas s through the

161 t

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Fig.44 ._ Th ecurve d stonelaye r indicated byarrow s forms thedeforme d bottom ofa gullywhic hdissecte d a softcalci chorizo n inMiocen e sediments at Site 7nea rGua - rena.Theprocesse s responsible for thepresen tconfiguratio nar e explained inFig . 43,o fwhic h Stage6 represent s thepresen tdegre eo fdevelopment .Textur ean d lime contento f thematerial sove ran dunde r theston e layerdiffe r significantly.Auger - lngsi nth eadjacen t field confirmed thatth efeatur eha sa n elongated shape.Eac h block on themeasurin g taperepresent s 10cm .

aforementioned Stages1 t o8 .Onl ydee pgullie swil lru nthi sful l sequence;shallow ­ erone sma yno tge tfurthe rtha nStag e6'befor ethe yar edischarge d fromth ecalci c layer.Thi sapplie st oth egull yi nFig .44 ,whic hwil lno tdefor mt oreac hStag e8 . Originallyi twa smuc hshallowe r thanth egull yshow ni nFig .45 .

6.5 INTERRUPTIONAND/O R CHANGEO FTH EREPLACEMEN TPROCES S INSOF T CALCIC HORIZONS

Theprocesse sresponsibl efo rth emigratio no fth esof tcalci chorizo nca nb e interruptedfo ra variet yo freasons .Suc hinterruption sma ylea dt ohardenin go fth e horizono rt oa chang eo fit shabitu sfro mcontinuou st odiscontinuous .Thes echange s mayb epartia lo rcomplete .Th echang ei nhabitu sma yb ereversible .Th efollowin g sections treatth ecase stha tar edistinguished .

6.5.1 Encounters with slowly weatherable parent materials

Ifo nit swa ydownward ,th esof tcalci chorizo nmeet sa kin do fparen tmateria l that1 S notreadil yweatherable ,th esuppl yo fweatherin gproduct swil ldiminish .I n thiscase ,th esuppl yo fmateria lupward sthroug hth esof tcalci chorizo nwil lno t keeppac ewit hth edownwearin go fth esurface ,whic hwil l leadt oit sexposure .The n

162 f-

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ig.45. ^ The irregular stone layer indicated byarrow swa smarke d withchal k inth e leidprio r to thetakin g of thephotograp h tobrin gou t thisdetai lmor eclearly .I t forms theremnan t of the stonybotto m ofa nerosio ngull ywhic hha sbee ndeforme dan d isno wi nth eproces s of being expelled by thecalci chorizo n intowhic h itha dcu t itsbed .Fig . 43 explains the stages of theproces s thatcause s thedeformation .Th e presentda y situationconform swit h Stage8 o f it.Th ephotograp hwa s takena ta roa d cuti nMiocen ecla ya t Site7 nea rGuarefla .Remnant so fhar d limelayer s ina lalmos t vertical positionar epresen t justoutsid e theston e layer inth euppe r lefthan d corner.Ever y blocko f themeasurin g taperepresent s 10cm .

importantchange soccur .I na relativel y shortperiod ,th ehorizo nbecome shardene d andimpermeable .Fo ra descriptio no fth ecausa lprocesses ,se eSectio n6.5.4 .A petrocalcichorizo nform san dthi s increasesrun-off ,leadin gt oa genera llowerin g ofth egroundwate rtable .A si ti shighl yresistan tt oerosion ,i tbring sth eerosio n ratedow nt oapproximatel y zerofo ran extende dperiod .Th edestructio no fth epetro ­ calcichorizo ni sa slo wprocess ,i nwhic ha mechanica lbrea ku pdu et ophysica l fac­ torsplay sa majo r role,a smentione db yLattma n (1973)an d(1977) .Recementatio no f theproduce drubbl ema yoccu ran dprolon gth edestructio nperiod . Inth eMérid aarea ,a goo dexampl eo fth einterruptio no fth eprocesse si sfoun d m thearkos e landscape.I nvirtuall yever ycas ei nwhic hth earkos esurfac ei sex ­ posed,th emateria li sintersperse dwit hpetrocalci c fragments,fro mwhic hi tca non ­ lyb edistinguishe db ymean so fa han d lens.Th eexplanatio ni stha tth esof tcalci c horizon,whic hdevelope din th eUpper-Miocen eclaye ymaterial ,migrate ddownward san d "itth eresisten tMid-Miocen e arkose,on whic hi thardened . Locally,a smentione di nSectio n3.5 ,calci chorizon shav eals obee nfoun do n topo fgranit ean dgneiss .The yprobabl ydescende dont oth eaci drock sfro manothe r overlyingmateria l (probablyMiocene) ,whic hha ssinc ebee nremove db yerosion .Upo n itsremoval ,i tlef tbehin dth ecalci chorizo ni nth econtac tplan ewit hth ene wpar -

163 entmaterial .Th e topo fthi shorizo n isusuall y hard,whil e soft lime ispresen ti n the crackso fth esaprolite .

6.5.2 Surface erosion exceeds the transport capacity of the soft calcic horizon

Ifth eris eproces so fweatherin g products through the soft calcic horizoncan ­ not keeppac ewit h therat eo fdownwearin go fth e surface,th e soft calcichorizo n will finallyb eexposed .Thi smigh toccu r ifextremel y high erosionrate spersis tfo r some time and/ori fther ear edrasti c climatic changes,whic h diminish the transport capacityo fth esof tcalci chorizon .Accelerate d soil erosion isprobabl y themai n causeo fthi sphenomenon .Unde rnatura l conditions,tectoni c eventsmigh t alsoinduc e it locally.Drasti c changesi nth eamoun t and distribution patterno fth eprecipita ­ tion leading toa nincreas eo fth erun-of fa tth e expenseo finfiltration ,ca nals o bring about theexposur eo fth e calcichorizon .I nal l these cases,rapi d hardening of the surfacean dreduce dpermeabilit y and infiltration result. Whether theentir e calcichorizo nwil l fossilise,o ronl y theuppe rpart ,de ­ pendso nth egroundwate rregime .I fth egroundwate r table continues tob e fedb yin ­ filtration ofrainwate r intoth eadjacen t non-hardened surfaces,i tma y fallslowl y enought oallo wa smal lpar to fth e lower soft calcic horizont ofollow .I fth ehard ­ eningo fth esurfac e occurssynchronousl y over large areas,th e fallo fth eground ­ water tablema yb e sorapid ,tha tn opar to fth e calcic horizonwil lb eabl et ofol ­ low it.I fth efirs tcas eapplie sa split-u po fth e calcic horizonresults . It isindee d commoni n theMêrid aare at ofin dpetrocalci c horizons underlainb y softcalci chorizon swhic har econtinuous ,thes ei ntur nbein g underlainb ysof tcal ­ cichorizon swhic h arediscontinuou s (Fig.10) . Inth e literature,doubl e andeve nmultipl e calcic horizons are frequentlyde ­ scribed. Someo fthese ,e.g. , theprofil erepresente d onpag e 135o fRuella n (1970), couldwel lb e theresul to fsuc ha split-up . Inth eMiocen e clayarea ,som eexposur e and subsequent hardeningo fcalci chor ­ izonsha s takenplace .Th ephenomeno n isquantifie d inth edescriptio no fth esoi l distribution pattern,a sdescribe d inSectio n3. 5 and illustratedb yth ecros ssec - horizfFlS '1 °' Theaeria l Ph°t0graphshow ni n Fi8- 4show sth e e*P°sed PetrocalciC orizonsm very lighttones .A compariso no fth e aerial photograph and thecros s sectionshow stha tth epetrocalci c horizons arerestricte dt oth erim so fth einter - fluvesborderin g thevalle y sidesan dt osom e isolated ridges.Th eligh t greyarea s troÏÏc 7 °UtCr0PS° Wethel r relatively üght colour tonet oth epresenc e ofpe - œsses^Th ^^^^ dispersed throughout the landscapeb yplowin g and erosionpro ­ cesses, ever y light-toned areas indicate the truepetrocalci c horizons,forme di n the zoneswher e erosionha sbee nstrongest .Th e valleypatter ni srelate dt o fault

causedT t6db yJUn g 0974)'bU tth e e*P°sure ofth ecalci choriz0n Sh3 Sbee " y rOS10n mainl rinn „ .^ ' y brought aboutb yhuma n disturbanceo fth e naturalvegeta ­ tion.Rapi d incisiono fth evalle y system duet otectoni c causes,ma y have setth e

164 stagefo rthi sman-induce derosion .

6.5.3 Changes in habitus of the calcic horizon due to changes in moisture regime

Asmentione din Sectio n6.3 ,th econtinuou ssof tcalci chorizo nma ychang eit s habitust obecom ea discontinuou s softcalci chorizon ,whe nchange soccu ri nit s moistureregime .Whethe rth eentir ehorizo nconvert st othi s formo ronl ypar to fit , dependson th ewa yi nwhic hth emoistur eregim echanges . A rapid fallo fth egroundwate r tablema ycreat ein th eprofil ea so-calle d 'deadhorizon' .This ,accordin gt oBuring h (1979),i sa n'alway sdry 'zon ebelo wth e rain-moistenedpar to fth eprofil ewhic hoccur sa tshallo wdept hi nari dregions .I n semi-aridregion si tma yb epresen ta tgreate rdepth .Thi s zone separatesth erain - moisteneduppe rprofil epart sfro mth egroundwater-moistene d lowerpart s (Franz& Franz, 1967). Ifa dea dhorizo ni screate dwhic hoccur si nth emiddl eo fa continuou s softcalci chorizon ,th eeffec twil lb ean interruptio no fth elin kbetwee nth egil ­ galformatio ni nth egroundwater-moistene d zonebelo wan dth eris eproces si nth e rainwater-moistenedpar t above.Whe nthi s linki scut ,th elowe rpar to fth ecalci c horizonwil lbecom e discontinuousdu et oth eamoun to fsoi lmateria l introducedwhic h isno tremoved .Th emiddl epar tin th edea d zonewil lremai n immobilefo rth etim e beingan dth euppe rpar twil lpurif y itselfcompletel yo finclusion ssinc eth eris e processi nth erain-moistene d zonecontinuou sbu ti sno tfe db yne waddition sfro m below. Iti sinterestin gt oconside rth emovemen to fth eentir esyste m includingth e dead zone ina degradin g environment.Th esurfac ewil lb elowere db yerosio nan dcon ­ sequentlyth erainwater-moistene d zonewil lals ob elowere dan dpenetrat eth euppe r parto fth edea d zone.Th edea d zonewil li ntur nlowe ra sth egroundwate rtabl e falls.Th eresul ti stha tne wsoi lmateria l formerlycontaine di nth edea d zonei s workedu ptoward sth esurfac e soilb yth eris eprocess ,whil eth edea d zonepene ­ tratesan d^mobilise spar to fth ediscontinuou s softcalci chorizo nbelow .Whe nth e movemento fth esyste m continuesth euppe rrain-moistene d zonewil l alsopenetrat e thediscontinuou s softcalci chorizo n imnobilisedi nth edea d zone.Th esoi lmateria l ofthi s zonewil lno wb eintroduce d intoth econtinuou ssof tcalci chorizo nb ya gil ­ galformatio nproces s thatresume sit sactivit yan dwil lsubsequentl yb edischarge d fromthi shorizo nb yth eris eprocess . The foregoing discussionshow stha tth epresenc eo fa dea dhorizo ni na profil e doesno tnecessaril ypreclud eth emovemen to fsof tcalci chorizon sb ymean so fth e mechanical replacementprocess .Th eeffec to fth edea d zonei srestricte dt osepar ­ atingth edirec t linkbetwee nth egilga lformatio nan dth eris eproces san dactin ga s a temporarystorag e zonefo rth esoi lmaterial s thatar ebein gmove dt oth esurface . Tneestablishmen to fth edea d zone,however ,affect sth eappearanc eo fth ecalci c horizon,whic hwil l convertit slave rpar ti na discontinuou s softcalci chorizo nse ­ parated fromit scontinuou suppe rpar tb ya zon erelativel ypoo rm lime. 165 Iti sconceivabl e thatthic k discontinuous soft calcichorizon s reformt obecom e muchthinne r continuous softcalci chorizons .I fth eaverag e groundwater table stabilisesfo ra certai nperiod ,th elime ,unabl et omov e further downward,wil lac ­ cumulatea tthi s level.Th eswellin gan dshrinkin g activei nthi s zonewil lprogres ­ sivelydischarg e claywit hth eaccumulatio no flim ea tthi s level.Give n sufficient time,thi sma ylea dt oth ereconstitutio no fa continuou s soft calcichorizon . Asmentione d inSectio n 6.3,severa l observations inth esurve y area indicate thata dilutio nproces so fth esof tcalci chorizo nha stake nplace ,e.g. ,th ecros s sectionshow ni nFig .10 .I tconfirm sth eobservatio no fRuella n (1970)tha tbetwee n thedifferen t typeso fcalci chorizon s therear egradua l transitionswhic h occur laterallyan dvertically .H econclude s fromthi stha tth edifferen t typeso fcalci c horizons descend fromeac h other.H especificall ymention sth eformatio no fcontinu ­ oussof t calcichorizon s fromdiscontinuou s calcichorizon so fth esam e type.Hi s statement implies thatreconstitutio no fcontinuou s softcalci chorizon s fromdiscon ­ tinuous softcalci chorizon si spossibl ei nsom ewa yo rother .

6.5.4 The process of hardening upon exposure

Exampleso fexposur e leadingt ohardenin go fcalci c horizonsar enumerou s inth e literature.Gil ee tal . (1965)observ e thattruncatio no fa profil ewit ha plugge d (calcic)horizo n offerscircumstance s favourablefo rth edevelopmen to fa lamina r horizon,sinc ei tbring sth eplugge d (calcic)horizo nwithi nreac ho fmor e frequent wetting.Yaalo n& Singe r (1974)discus sth eformatio no fa nindurate d calcic horizon onsof tchal krock san dstat e thatth elamina r crustca nfor m sub-aeriallywithou ta n overlying covero fsoil . Gigout (1960)mention s thatonc eth esof t calcichorizo ni s exposedb yerosion ,thi smaterial sharden sa srainwate r flows overit ssurface ,caus ­ ingdissolutio nan drecrystallisation . Lattman (1973)describe s 'casehardening' ,whic hi sa non-pedogeni c formo fce ­ mentationo nvertica lan dnea rvertica l exposures.I ti scause db ysurfac e water whichflow s over theseexposure san ddissolve s fine-grained calcareousmateria lan d redepositsi ta scement .I tca nestablis h itselfi na fe wyear s onlyan di taffect s variousdifferen tmaterials .H edistinguishe s 'casehardening ' explicitly fromth e developmento fpetrocalci chorizons ,whic hh esuppose st ob eforme d inth ewa yGil e postulates,a streate di nSectio n 2.5.2.1. Reeves (1970)make sa simila r distinction between slow indurationo fpetrocalci c horizons according toGile' sproces san drapi dregiona l indurationan dformatio no fa laminar zonewhic hoccur swhe ncalich ebecome splugge d orwhe nth eto po fi ti s ex­ posed.Accordin gt ohi mthi srapi d indurationwil l startwhe nonl ya thi nsoi l layer remains overlyingth esof tcalci cmaterial .H estates : 'Nodeepl y buried laminated zoneha sbee nobserve di nth estudie d areas thatdoe sno tsomewher e exhibit evidence ofpas texposure' .B ythi sh eimplie s that laminatedpetrocalci c horizonsca nonl yb e formeda to rnea rth esurface .H equote sth efollowin g reasonsfo rth esof t calcic

166 horizon toremai n softwhe nno t incontac twit h thesurface :A writte n communication byGil etha t this isdu e to insufficientcarbonat eaccumulation .A writte ncommunica ­ tionfro mBlan kwh obelieve s that thecalich eremain s softbecaus eo f the frequent presence ofmoisture ,whic hcontribute s tosolution ,rathe r thanprecipitatio n of the carbonate.Hi s comment onthi s lastobservatio n istha t itcontradict s theobserva ­ tiontha tmoistur e on thesurfac edoe scaus e induration.

Inth esurve yare a itwa s observed thatexpose dcut so f softcalci chorizon s hardensuperficiall y ina ver y short timewhe nexpose d tosurficia lwetting .Fo rex ­ ample,a profil e dug ina softcalci chorizo ni na roadsid editc h in 1973wa s found tohav eundergon econsiderabl e surficialhardenin g in 1979.Hardenin g ofroadsid e cutswa smentione d alsob yRuella n ina remar kmad edurin g thediscussio no f Menillet's (1975)paper .O nth eothe rhan dvertica lo roverhangin g roadsidecut stha t nevermoiste nwer e found toretai n softcalci chorizon s forextende dperiods ,e.g. , theprofil e shown inFig .35 .Thi scombinatio no ffact sindicate stha thardenin gwil l takeplac e only ifbot hwate ran dcarbo ndioxid e (fromth eatmosphere )ar eavailabl e tomak echemica lredepositio npossible .Thi s islogical ,sinc e theformatio no f sol­ uble Ca(HC03)2 canonl y takeplac e inth epresenc eo fthes e twosubstances .I nperma ­ nentlywe t circumstances,n ochange s affectth esof tcalci chorizo ndu e tolac ko f

C02. Inpermanentl ydr y circumstances,n ochange saffec tth e softcalci chorizo ndu e to lacko fwater .Onl y inth e intermediatecases ,i nwhic hbot h ingredientsar epre ­ sent,doe sredistributio no f limetak eplace .Thi smean s thatoptimu mcondition sfo r hardening are found ato rnea r thesurface ,wher emoistenin g isfrequen tan dwher e

atmospheric C02 isfreel y available.Unde ra shallowtopsoil ,thes econdition sar e

fulfilledwhil eadditiona l C02 isavailabl e from thedeca yo forgani cmatter .Deepe r inth eprofil emoistenin gwil lb e lessfrequent ,whil e thediffusio no fatmospheri c

C02 towards these sites isslower .Hardenin gma yno ttak eplace ,o rma yb ever yslow . Where thetranspor tprocesse s inth esof tcalci chorizo nar eactive ,th eproces s ofhardenin gwil lb echecked .Th e limemas s isthe nconstantl yagitate ddu et oth e actiono fth eweatherin gproduct s (aseviden t inth emicromorphology ,Sectio n 4.S). A certainamoun to frecrystallisatio no fth e limewil lundoubtedl yoccur ,bu tbefor e thisredistributio n canbuil dbridge sbetwee nth e spargrain so fth esof tcalci chor ­ izon,th e 'churningaction 'ha smove d themrelativ et oeac hother .A s suchspa r grainsca nb e expected togro wevenl y onal l sideswhe nsubjecte d toa slo wredistri ­ butiono f lime.Th e fact thatNetterber g (1980)report stha t 'powdercalcretes 'ar e onlyt ob e found onto po fclay s andweathere dmudrocks ,coul db ea nindicatio ntha t the 'churningprocess ' isindispensabl e ifth ecementatio no f lime ist ob eavoided . Several soils inth eare asho wevidenc eo fth ecounter-activit y ofth etw o aforementioned processes inthos esof tcalci chorizon swhic hhav estalle dnea rth e surface. Fig. 46 shows acla ymas s trappedunde r thehardenin gpetrocalci chorizon , parto f thecla y seemst ohav ebee nforce d intoa narro wvertica lvoid .A ver ysimi ­ larcas e ismentione db yWatt s (1977),wh odescribe sdiapiri c foldsdu e toth eupwar d

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Fig. 46. Detail of thesof tcalci c horizono fProfil eArroy o 1(Sit e 2) Dark- colouredband so fcla y nodules havebee nhampere d inthei r upward movement by the localcementatio no f the light-coloured calcichorizon .Th earro wpoint s toa cla y mass thatha sbee nforce d intoa narro wvertica lvoid .Th ehamme r which servesa sa reference hasa length of 30cm . '

injectiono fswellin g clays intoa pre-existin g calcrete.Severa l softcalci chor ­ izonsi nth eare acontai ni nthei ruppe rpart sman ybroke nplat ypetrocalci cfrag ­ mentswhic hconceivabl yow ethei rgenesi st oth eformatio no fhar d fibreso fredis ­ tributed limewhic hwer e laterbroke nup ,whe nth e'churnin gprocess 'resume dit s ac- tivity. Many authorswh oclai mtha tth eformatio no fthic kpetrocalci chorizons ,con ­ traryt osurficia lhardening ,i sa ver y slowprocess ,bas e thisclai mo nth efac t thatsuc hthic kpetrocalci chorizon sar efoun do nol dsurface s only.Thi si sa dangerousconclusion ,sinc ecaus ean dresul tcoul dwel lb emixe dup :surface swit h thickpetrocalci chorizon sar eofte nver yold ,sinc epetrocalci chorizon sar es ore ­ sistantt oerosion .Th ebes targumen tfo rslo wformatio no fthic kan dofte nlaminate d petrocalcichorizon si smor e likelyt ob efoun di nth enatur eo fth ehardenin g pro­ cess.A ssoo na sth esurfac e layerha shardened ,it spermeabilit yt obot hwate ran d airbecome simpeded .Thi smean stha tth efurthe rth ehardene d zonegrows ,th elowe r thepermeabilit ybecome san dth eslowe ri tgrows . _ ,Th e formationo fthic klaminate dpetrocalci chorizon si sa comple xproces swhic h involvesmor e thansimpl edownwar d leachingo flim edissolve di nth euppe rlayers . Apparently,dissolutio no flim eals otake splac ewel lbelo wth esurface ,afte rwhic h thesolutio nma yb esucke dbac kb ycapillar yactio nt oth esurfac ewher ei tevapo ­ rates Yaalon& Singe r (1974)repor ttha tth ehighe rporosit yo fth elowe rnar i (lime

crusts)i sdu et osolutio no ffin eCaC0 3 fragments.Siesse r (1973)report s similar phenomena.H eha sobserve dunfille dpor espace sdirectl yunderlyin ghardpa ncalcret e

168 beds.I nhi sopinio n this suggests thatth esuppl yo fupwar d drawncarbonat ewa sar ­ restedbefor eth evoid swer e filled. Asdescribe d inSectio n4. 5th elamination so fth epetrocalci c horizonsee mt o beth eresul to fredepositio no flime .I ncertai n layersth elim epercentag e increas­ esan dconsequentl y theconcentratio no fclast s lowers,whil eth erevers eapplie st o other laminae.Th eforc e exertedb ycrystallisin g calcite (Section6.6.3 )probabl y playsa rol ei nthi sprocess .Brow n (1956)write so fthes ebands : 'Theonl ydiffer ­ encebetwee nth eband san dth emateria l theyenclos eappear st ob ei nth ehighe rper ­ centageo fcemen ti nth ebands .Thes eband s apparentlyhav en orelatio nt osequentia l depositionbu thav e formed insecondar y fracturesan dope n spaces.N omean swer e foundt ocorrelat e themwit hth espatia l orientationo fth especimens. 'Experimenta l evidencefo rth eformatio no fcalcit e fibresi na san d columni spresente db yDumon t (1975). Sabelberg &Rohdenbur g (1975)postulat e thatth eformatio no ffibre si ncal ­ careousmaterial s owesit sorigi nt oai renclosure ,whic hprevent svertica l infiltra­ tiono fwate ran dforce sth esolutio nt osprea dou ti na horizonta lplane .

6.6 GENESIS OF CALCIC HORIZONS

Inthi s texta distinctio ni smad ebetwee n calcichorizon s (accordingt oSoi l Taxonomy)whic har econtinuou san dthos e thatar ediscontinuous .I nth efirs tcas e softpowder y lime formsa continuou s phasewhil ei nth esecon dn ocontinuou sphas eo f thismateria l ispresent .Thi sdistinctio ni simportan t sinceth emechanica lreplace ­ mentprocess ,consistin go fsubterranea n gilgaî formationan dth eris eprocess ,ca n onlyac twhe n continuous softcalci c horizonsar epresent .Discontinuou s softcalci c horizonsca nmigrat eb ymean so f'activ epenetration 'bu tthe yd ono tcaus e complete displacement ofth elayer s throughwhic h theypass .Th eminimu m requirementsfo rth e firstproces st otak eplac ear eth epresenc eo fsoi lmaterial swhic h swellan dshrin k seasonallyan dth epresenc eo fa calci chorizo nwhic h contains sufficient lime(o f suchpurity ,grai nsiz ean dcrystallinit y thati tdisplay sa lo wliqui d limit)tha t -afte rth eformatio no fth esubterranea n gilgaî- a continuou sphas ei sforme db yi t inth euppe rpar to fth ehorizon . If,a tleas tfo rth econtinuou s softcalci c horizonso fth eMiocen e clay,th e mechanical replacement processha sbee n furnishedwit h sufficient evidence,th e searchfo rthei r genesisca nb enarrowed . Itca nb econcentrate d onth eprocesse s thatcreate dth econdition s underwhic hth ereplacemen t couldb einitiated . Ifth ecalci c horizonmaintain s itselffo ra lon gperiod ,escapin g erosionan d accumulating lime steadily fromth eweatherin go fth estrat a throughwhic hi tpasse s (Sections 2.5an d6.1.6) ,th esearc hca nb erestricte dt othos eprocesse s thatiniti ­ ate thisphenomeno nan d'prim eth epump' .Th ever ymagnitud eo fth elim eaccumula ­ tions thatha spuzzle dman yresearcher si nthi s fieldi nothe rareas ,doe sno tfor ma problem inth ecas eo fth eMiocen e clayo fth eMêrid a zonei fthes ehorizon sar e vieweda sdynami cphenomen a insteado fstati c features.N osource sothe r thanth e

169 Miocenecla yhav et ob econsidere dt oaccoun tfo rth e amount oflim epresent . Themechanica lreplacemen tproces sca nb eactiv ei ncontinuou s softcalci chor ­ izonswhic har emuc hthinne rtha nth epresen tone sfro mth esurve yarea .Th econti ­ nuous softcalci chorizo nwhic h justfulfil sth eminimu mrequirement sfo rth egilga î formationan dth eris eproces sa saforementione dwil lb ecalle d 'continuousincipien t softcalci chorizon' . Thevariou smode so fgenesi spropose di nth eliteratur e (Section2.5 )wil lb e reviewed criticallyi nth esearc hfo rth eprocesse s thatcoul d formsuc hhorizons .I n thisrevie wth e form ofth eaccumulatio ni sconsidere dt ob emuc hmor e important than the source ofth elime ,sinc eth etota lquantitie srequire dfo rth econtinuou sinci ­ pientsof tcalci chorizo nar esuppose da tan yrat et ob emodest .Th erevie w includes processes thatlea ddirectl yt oa continuou shorizo nan dthos ewhic h leadvi aa dis ­ continuoust oa continuou s softcalci chorizon .Fig .4 7show sth emai noption si n schematicform .Th efou roption sar ediscusse di nSection s 6.6.1-6.6.4. Conclusions aresummarise di nSectio n 6.6.5.

6.6.1 Geogenetia: Sedimentation of lime in an aqueous environment

Depositiono flim ei na lacustrin e environmenti sa mod eo fformatio nwhic hca n accountfo rpur econtinuou s softcalci chorizons .Suc hdeposit sar eapparentl yexten ­ sivei nN .Afric awher e theyar edescribed ,e.g. ,b yCoqu e (1962)fo rTunesi aan d Durand (1959)fo rAlgeria .Fo rTurke y theyar edescribe db yMeeste r (1971).(Se e furtherSectio n2.5.1. )Suc hdeposit s couldconceivabl ypla yth erol eo fincipien t softcalci chorizons ,startin gth emechanica lreplacemen tproces s afterth een do f thelacustrin ecycle . Inth ecas eo fth eMiocen eclay ,thi sorigi ni sno tprobable ,sinc eth efollow -

Geogenetic Pedogenetic Sedimentation of Chemical deposition of lime from a lime in an aque­ solution in voids (pores and/or cracks) ous environment followed by or synchronous with ZZL Replacement of materials Replacement of materials Replacement of materials by lime in achemica l by lime due to forcescre ­ by lime that penetrates way ('épigénie') ated by the crystallisation into cracksforme d by of calcite changes in volume upon wetting and drying

Continuous incipient soft calcic horizon

Fig. 47. Schematic presentationo f thevariou s options for theformatio no f acon ­ tinuous incipient softcalci chorizon .

170 ingfact shav et ob etake n intoaccount : - Fossilremain s haveno tbee n foundi nth ecalci chorizons .Al lfeature s described inth emicromorpholog y canb eexplaine db ypedogeneti c processes.Th efac t that macro-fossilsar eabsen t could stillb eattribute dt othei r expulsiona tth eto po f thehorizon. Bu tmicro-fossil swhich ,du et othei r size,ar eno tsubjec tt othi spro ­ cess,wer eno tfoun d either. - Theextensio no fcontinuou s softcalci chorizons ,no tonl yi nth epresen tda yMio ­ cenecla y landscapebu tals oi nman y different surrounding landscapeso fa completel y differentnature ,make sth elacustrin e hypothesis improbable. - Stable isotope ratiosfo rth ecarbonate so fth eRiol aprofil e indicate thatth e carbonates,i fo fsedimentar y origina tall ,hav ebee nrecrystallise d inth esoi l (Section4.7) .

6.6.2 Pedogenetic: Replacement of materials by lime in a chemical way ('épigénie')

The formationo fcalcit ei na finel y dispersed formthroughou tth esoi lmas si s acommo nphenomenon . Such lime accumulationsar ecalle d 'distributions diffuses'i n theterminolog yo fRuella n (1970).Th elim eprecipitate s asCaC0 3 froma solutio n which contains calcium bicarbonatei nionise d form.Th eprecipitatio nma yb einduce d byth eevaporatio no fth esolution ,upo nwhic h calciumbicarbonate ,whic hcanno tex ­ isti nsoli d form,convert st ocalciu m carbonate,wit h losso fcarbo ndioxide . Changesi nth epartia l pressureo fcarbo ndioxid ei nth esolution ,e.g. ,du et otem ­ perature changes,als o affectth esolubilit ya sdemonstrate d inFig .29 .I ti sas ­ sumed thatth efirs tcrystal sar eforme d inth esmal lvoid s thatconstitut eth epor e spaceo fth esoi lmass .A ssuc ha conten to fmor e thanabou t4 0 %b yvolum ema yb e difficultt oattain ,sinc emos t soilsd ono thav emor epor e space.Th efillin g ofth e pore spacewil lprobabl yno tlea dt oa lim econten thig h enought oinitiat eth emech ­ anicalreplacemen t process.I norde rt oarriv ea thighe r limecontents ,thi sdeposi ­ tionmus tb eaccompanie db yothe rprocesse sb ywhic hth eamoun to flim ei nth ehor ­ izon increasesan dth eamoun to fclast sdecreases . This section reviewsth erol eo fth echemica l replacement processo fnon-cal - citic solidsb ylim ei nth etransformatio no fdiscontinuou st ocontinuou s soft calcic horizons.Th erol eo fth eforc eo fcrystallisatio n exertedb ycalcit ei streate d m Section 6.6.3.

The solutiono fsilicat emineral si sa ver y slowproces swhic hca noccu ronl ya t veryhig hp Hvalues .Th ep Ho fa solutio ni ncontac twit ha soli dphas eo fCaCO ji s governedb yth epartia l pressureo fC0 2- Callote tal . (1978)measure dth evariatio n overa perio do ftim eo fth ep Ho fsevera l lime samples thatwer emoistene dm con­ tactwit hth eatmosphere .The y found thatwithi na fe wminutes ,a p Ho fapproximat ey 9.5wa sestablished ,whic h graduallydecrease d inth ecours eo fsevera lhour st o8.4 , which they consider indicativeo fequilibriu mwit hth eatmospheri c C02 concentration.

171 The influenceo fsevera lfactor so nthi sproces swa s investigated. Itturne d outtha t

C0? absorbed onth esurfac eo fth ecalcit eparticle s isa nimportan tcontrollin g fac­ tor.Anothe r factor isth edegre eo fdilutio no fth esystem ,o runde rdynami ccondi ­ tions,th espee do fpercolation .Th ehighes tp Hvalue swer ereache db yrelativel y coarse-grainedcalcit e (lowamoun to fC0 2 absorbed)an d strongdilution .Suc hcondi ­ tionsca nb eexpecte d incalci chorizon s forshor tperiod sonly .Th e zone inwhic h theyar eexpecte dt ooccu r lieswel lbelo w theroo t zonewit h itshig h C02 pressure. Degens &Rutt e (1960)mentio n thepresenc eo fcorrode dquart z and felspar grainstogethe rwit hsom e secondarysilic ai na calci chorizon .The yexplai ntha tth e highp Hwhic hresult sfro mth esaturatio no fbicarbonat esolution s inthes ehorizon s hascause d thesephenomena .The yclai m thatquart zan d felspars arereplace d 'meta- somatically'b ycarbonates . Nahon& Ruella n (1975)repor ta nexchang emechanis mo fsilicate s and lime ina profileo nmar l inSenegal .Th ephenomeno nwhic hthe ycal l 'épigénie'consist s in symmetricreplacement .Highe r inth e soil limereplace s quartz,cla yan ddolomit e while lower inth esoi ldolomite ,attapulgit e (palygorskite)an dquart zar eformed , replacing thecalcite . Millote tal . (1977),Millo t (1979)an dRuella n (1980)clai mtha t 'épigénie'i n thesens eo fisovolumetri creplacemen to fnon-calciti cmineral sb y calciteoccur si n manydifferen tmaterials .The yfin devidenc eo fthi sproces s inschists ,granites , quartsites andargillite so fbot hmicromorphologi can dmacromorphologi cnature .Thi s process isfoun d tohav etw oconcurren tmode s ofoperatio ni nth esam e soil. Firstly, theroc kmineral stransfor m toclay swhic h intur nar e 'epigenised'b y calcite.Se ­ condly,th ecalcit ereplace s theroc kmineral sdirectly .Th emechanis mo f there ­ placementproces s and theremova l of itsproduct sar eno tye tproperl yunderstood . Corrodedsilicat emineral sar efeature scommonl yreporte d incalci chorizon s (Section 2.2.2).Thei r frequentoccurrenc ecoul d justa swel lb eproo f of long periodso fresidenc e inth ehorizon s inwhic hthe yar e found,a so frapi d corrosion ofth egrain sdu et oth ehig hp Hvalues . Thefollowin gha s tob etake n intoaccoun twhe n trying toexplai nth e formation ofth e incipientcontinuou s softcalci chorizo nb y localchemica lreplacemen t of silicatesb ylime . - Theproces swhic hgenerate shig hp Hvalue sonl y lastsfo ra shor tperio d andpro ­ bablyoccur s onlyonc ea year . - Theproces srequire s ahig h initialCaCO ,concentration .

- Theproces s isfavoure db ycoarse -rathe rtha nfine-graine d calcitedu e to its C02 absorption ina dr ystate . - Ifth eproces s occurs iti sassume dno tt orestric t itselft oa ver ynarro wzon e inth e soil.

172 6.6. 3 Pedogenetio: Replacement of materials by lime due to forces created by the crystallisation of caleite

Lime accumulating inth evoi d systemo fa soi la sdiscusse di nSectio n6.6. 2ma y expelnon-calciti c solidsb ymean so fth eforc e exertedb ycrystallisin gcaleite . Thisforc eplay sa rol ei nth eformatio no fcalci chorizon saccordin gt osevera l authors.Apar t fromth edat ao nweatherin gi nSectio n 6.3,th efollowin gi simpor ­ tant. Yaalon& Singe r (1974)stat etha tvolum eexpansion ,becaus eo fth egrowt ho f carbonate cement,i spossibl ean dcommo ni nunconsolidate d sediments,bu ttha tthi s processwa sno tobserve di nth eformatio no fa lim ecrus t fromchalk . Watts (1980)state s thathig hsupersaturatio noccur swit hrapi d evaporationan d isa requiremen tfo rdisplaciv ecaleit ecrystallisatio ni ncalcretes . Boulaine (1978)quote sa nexperimen tb yC .Ple tprovin g thatcarbonates ,jus t likesulphates ,ar ecapabl eo fpushin g thepre-existin g elements asidewhil ecrystal ­ lising.H edoe snot ,however ,giv ea literatur ereferenc efo rthi sexperiment . Inth eSoi lTaxonom y System (SoilSurve yStaff ,1975 )th efollowin g statement regardinga petrocalci c horizoni sfound : 'Gravelsan dan dsil tgrain shav ebee nse ­ paratedb yth ecrystallisatio no fcarbonate si na tleas tpart so fth elamina rsub - horizon'. Brown (1956)acknowledge sth erol eo fth eforc eo fcrystallisatio ni ncertai n specific casesbu tdoe sno twan tt oappl yi tt orandoml yoriente dcaleit ecrystals , sucha sthos e thatcommonl ymak eu psof tcalci chorizons .H enotes : 'Someinvesti ­ gatorshav edemonstrate d thisforc ei nth elaboratory ;bu tapparentl yn oon eha s showntha ta grou po fCaCO ,crystals ,i na naqueou smedium ,randoml y orientedi n spacean dfre et ogro wi nan ydirection ,wil l growi noppositio nt oconstrictin gob ­ jectsrathe r thani nth edirectio no fleas tresistance' .Brown' sargumen ttha ta mas s ofnon-aligne d crystals couldno tb eexpecte dt ogro wpreferentiall yi noppositio nt o a constricting forceneed s commento ntw opoints . - Crystals generallyhav ea preferenc efo rgrowin galon ga certai naxi s (Section 2.2.2).A differen tconcentratio ni si nequilibriu mwit hth edifferen tfacet so fth e crystal.Whethe ro rno tthe ychang e thishabi twil ldepen do nth edegre eo fsuper - saturationan dth econstrictin gforce . - Eveni fa mas so fcrystal swhic hdoe sno thav ea preferre dorientatio ngrow swith ­ outan ypreferentia l direction,a poin twil lb ereache di nwhic hth eoveral leffec t ofthi smulti-side d growthwil lb eth ebuildin gu po fpressure . Wieder& Yaalo n (1974)stat etha tnon-carbonat e claypresen ti na lim enodul ei s partially expelledt oth efringe so fth enodul ean dint oth ematrix .A similarobser ­ vationi smad eo nth eeffec to fth eforc eo fcrystallisatio ni nglaebule sb yTru e (1975). Concerningth erol eo fth eforc eo fcrystallisatio ni nth eformatio no fcontinu ­ ousincipien t softcalci chorizons ,th efollowin g shouldb etake nint oaccount .

173 - Iti ssuppose dt ob ea relativel y slowproces swhic h onlytake splac ei nth epre ­ senceo fsupersaturate dbicarbonat esolutions . - Theproces si sno tspecifi cfo rcertai n limited zonesi nth esoi lprofile .

6.6.4 Pedogenetia: Replacement of materials by lime that penetrates into cracks formed by changes in volume upon wetting and drying

Inth eforegoin gtw ocases ,depositio no flim ethroughou tth evoi d systemwa s considereda sa prerequisit efo rth eformatio no fcontinuou s soft calcichorizons . Hereth eaccen ti so nchemica ldepositio no flim ei nth elarge rvoids . Thedepositio no ffine-graine d calcitei nlarg ecrack san dvoid si sa commo n phenomenoni ncalcareou s soils.Th ebicarbonat e solutioni nth esoi lmatrix :i sdraw n by capillary forcestoward sth ewall so fth evoids ,wher ei tevaporates .Thi sproces s ismor eappropriat et oth elarge rrathe r thanth esmalle rvoids ,sinc eth eevapo ­ rationi nth elarge rone si sstronger .A filmo ffine-graine d calcitei sforme di n thiswa yi na crac keac hdr yseason .Result so fstabl e isotope analysiso flim e sam­ ples fromProfil eRiol aindicat e thatevaporatio nha splaye da rol ei nth eprecipi ­ tationo fth elim e (seeSectio n4.7) . Transporti nsuspensio no fth ecalcit e crystals formedi nth elarg ecrack si s expected,whe nth efirs trai no fth ewinte r seasonwashe s downthroug hthes epassag e ways.Th elim ei nth ecrack sca nb eexpecte dt odescen dt oa specifi c levelcontrol ­ ledb yth egroundwate r tablewher en ocrack s occur.Suc htranspor to ffin e silt-sized calcite crystalsi sreporte db yBlat te tal . (1972): 'Themateria lknow na svados e silti sfoun di nth evoid so fman ycarbonat erock s thatar esubjec tt oweathering .I t fillsbot horigina lan dnewl yforme dvoids. 'Sinc emicro-crossbeddin gha sbee nob ­ servedi nthi nsections ,Blat te tal .presum ei tt ob edeposite db ywate rwit hvelo ­ citiesi nexces so f4 0cm/sec .Thes evelocitie sar eprobabl yattaine db ywate rwhic h movesdow nthroug hth evados e zone,fro mth eexpose d surfacetoward sth egroundwate r table. Whenth elim eaccumulate si nth elarge rvoid sjus toverlyin gth eaverag e level ofth egroundwate r table,a replacemen tproces si sinitiated ,provide dth ecrack s openan dclose .I na proces ssimila rt otha tillustrate d inth efirs ttw ostage so f Fig.38 ,lim ewil l 'jerk'int oth ecrack swhic hexten du pt oth eaverag e groundwater table,forcin gth esoi lmateria lt odefor mi norde rt oaccomodat eth epressure s that itcreate sb yit sswelling .Graduall ymor e limework sit swa ydow nt othi snarro w zone,jus toverlyin gth eaverag egroundwate rtabl ean dmor e soilmateria lwil lb eex ­ pelled fromthi s zoneunti la continuou s softcalci chorizo ni sformed . Concerning thisprocess ,th efollowin gha st ob etake nint oaccount . - Itwil lb eoperativ eonl yi nsoi lmaterial s that swellan dshrink . - Theproces sma yconcentrat econsiderabl e amountso flim ei na relativel y narrow zonei na rathe rshor tperiod .

174 6.6. 5 Conclusions

Forth eMiocen ecla y landtypeunde rcondition ssimila rt oth epresen t onesi n thestud yarea ,th eproces s sequenceo fSectio n6.6. 4ha sle dt oth eformatio no fin ­ cipientcontinuou s soft calcichorizons .Thi sproces si sth efastes tan dmos teffi ­ cientwa yt oconcentrat e limei na narro w zone.Th eothe rtw ooption sar eles spro ­ bablefo rth etransformatio no fdiscontinuou s calcichorizon st ocontinuou s ones. Chemicalreplacemen to fnon-calciti csolid san dreplacemen to fsolid sb ycrystallis ­ inglim ear ebot h slowprocesse swhic har eno tspecifi ct oa narro w zonei nth esoil . Consequentlymuc h limeha st ob eaccumulate di nth evoid so fa thic k layero fsoi l beforeth elatte rtw oprocesse sca ntak eeffect .I na landscap e liketha to fth eMio ­ cenecla yi ti st ob eexpecte d thaterosio no fth esurfac esoil swil lcatc hu pwit h theaccumulatio n zonesbefor eeithe ro fthes etw oprocesse s takeseffec tan dform sa n incipient continuous softcalci chorizon . Forth egenesi so fcontinuou s softcalci chorizon si nmaterial swhic hd ono t produce largeamount so fswellin g claysupo nweathering ,i nlandscape sno tsubjec tt o suchstron g erosiona stha to fth eMiocen eclay ,chemica ldissolutio no fnon-calciti c solidsand/o rcrystallisatio n forceso flim ema yb eimportan t factors.Thes ema yb e active,e.g. ,i nth esaprolit e zoneso fth eschis t soilsa smentione di nSectio n 6.2.2. Iti sconceivabl e thatsuc hprofile sar e'hybri dcases' :Penetratio no flim e intoth eweatherin g zonei smainl ydu et ochemica lreplacemen to rt oth ecrystallisa ­ tionforces ,bu ttransportatio no fchunk so fdetache d soilmateria lthroug hth esof t calcichorizo ni ssimila rt otha to fth ecla ynodule so fth eMiocen ecla yprofiles . Theprofil eo fFig .4 2ma ywel lrepresen t sycha 'hybridcase' . The geogenetic alternative treatedi nSectio n6.6. 1i sconsidere d improbable takingint oaccoun tth edistributio no fcontinuou ssof tcalci chorizon s throughout thelandscape so fth esurve yarea .

175 7 Implications

7.1 ROLEO F CALCICHORIZON S INLANDSCAP E DEVELOPMENT

Theactiv erol eo fcalci chorizon si nshapin gth erelie fo fdr yarea sha sbee n stressed recentlyb yRuella ne tal . (1977)an dNaho ne tal . (1977).The yclai m that chemicalreplacemen to fnon-calciti c solidsb ylime ,épigénie ,play sa nimportan t rolei nth elowerin gan daplanatio no fsurface si ndr yareas ,vi ait sregulatin gef ­ fecto nth eadvanc eo fth eweatherin g front.Thi sprocess ,however ,i sslo wwhil eth e detailso fit soperatio nan dth eremova lo fit sproduct sar estil lunclear .Combi ­ nationo fthi sproces swit hth eris eproces so fth ecalci chorizo na sdiscusse dbe ­ foreaccount smuc hbette rfo rth erelativel y fastaplanatio no flandscape sunde rdr y conditions ('hybridcase' ,Sectio n 6.6.5). The épigéniewoul dac ta sa precurso rfo rth eothe rprocess. Saprolite s could conceivablyb eforme d rapidlyb yth echemica lreplacemen tproces s actingi nfissure s and alongth eboundarie so fth eminera l grainso fth erocks .I nthi scas e onlya minorpar to fth etota lvolum eo fth erock woul dhav et ob ereplace db ylim ei norde r tocreat ea saprolite .Th eris eproces so fth esof tcalci chorizo nactin gupo nth e saprolite fragments subsequently transports largequantitie so fthi smateria l towards thetopsoi lt ooutweig hth eeffec to ferosio no nth esurface . Deeppenetratio no flim eint osaprolite s of,e.g. ,th eschis t landscapewa sfre ­ quentlyobserve di nth esurve yarea .Transpor to fsaprolit efragment s towardsth e surface soilo fthi s landscape througha calci chorizo ni sevident .Deepl yweathere d granites overlainb ya thic kmantl eo floos emateria lar ever y commoneas to fth e surveyarea .I nmos t instancesth edeepl yweathere d granitesan dthei r overlying soilscontai nfai rquantitie so flim ewhic hma yhav ebee nth eagen t that formedth e deepsaprolites .Th elim ei nth egranit ean dschis t landscapesma ywel l havebee nin ­ herited frommaterial s previously overlying theserock swhic hhav ebee ncompletel y removedb yerosion ,i nth esam ewa ya sth elim eo fth epetrocalci chorizon so fth e arkose landscapei ssuppose dt ob einherite d fromth eMiocen e clayformerl ycoverin g this landscape.Thi si sexplaine di nSectio n 6.5.1.

Therol eo fth ecalci chorizo ni nlevellin g landscapesca nb ereverse dwhe nth e softcalci chorizo nbecome s exposedan dharden s locally.Th ehorizo nno wact sa sa shieldo nth esurfac ewhic heffectivel yprotect s itfro m erosion.Continuatio no fth e erosioni nadjacen tparts ,wher en oexposur ean dhardenin gha soccurred ,wil l cause thehardene dpart st ostan dou ti nth elandscape .Thi sma ywel laccoun tfo rth ewa y

176 inwhich ,i nth eMérid a area,th eedge so f theplateau s inth eMiocen e clay landscape standout .Par t ofth e locallyrollin g reliefo fth earkos e landscape isconsidere d tob edu e toth eprotectio n afforded toit s topsb y thepresenc e ofa petrocalci c horizon. Inth e literature,th erol e ofth epetrocalci chorizo na sa protectin g agent of surfacesi softe nmentioned ,e.g. ,Duma s (1969)an dLattma n (1973).Ther e isa widel y spreadmisconceptio n that,sinc epetrocalci chorizon s areofte nfoun do n topo folde r surfaces,the ymus tnecessaril yb e older thannon-hardene d calcichorizon s inadja ­ centlandscape s (whichcontinue d toerod e after thepetrocalci chorizo nha dfossil ­ isedth eothe rparts) . Iti sclea r that inconcludin g this,caus e andresul tar e easily confused.

Petrocalcichorizon sma y assertthei r influenceo nlandscape s forver y long periods.Multipl ecalci chorizon s areevidenc eo fvariou scycle so fdegradatio nan d aggradation.A well-studied case is the so-called 'caprockcaliche 'overlyin g the mainlynon-calcareou s Ogallala formation inth eLlan oEstacad o ofW .Texa san dE .Ne w Mexico (USA).A smentione d inSectio n 2.5.2,Brow n (1956)an dReeve s (1970)ar ei n favouro f anaggradationa lmod e offormatio nwhil e Price (1933)an dBret z &Horber g (1949)advocat e adegradationa l onefo r thecaprock . Browndescribe s this formation inth efollowin gway : 'Calicheunderlie s the soilso fth enortheaster n LlanoEstacad o assingle ,double ,o ri na fe wplace smul ­ tiplelayers ,eac h consisting ofrelativel yunindurate d calichegradin gupwar d into the indurated caprock'.Bot hBrow nan d Reevesconside r thegenesi so fthi scomple xa s entirely aggradational.Th eargument s forthi smod e offormatio nar etha taeolia n contributions of limear ecommo n inthi senvironmen twhil eth emateria lunderlyin g thecaproc k isofte n incapableo f supplying it.Degradationa lmode s offormatio nar e excludedb y Brown sinceh eexpect sdegradatio n to leadt osealin g ofth e carbonate layerwhic hwoul d prevent furthermigration . Introduction ofth econcep to fa mobil esof tcalci chorizo nwhic hmigrate sdown ­ wardyield s amor eplausibl e theory on themod e offormatio no fthi s layeredcalich e complex.Sof tcalci c horizonswhich procee ddownwar d incalcareou s aeolianmaterial s cankee pahea d ofth eerodin g surface andaccumulat e limei nth eprocess .Th eharden ­ ing ofthi s layerwil l occur after itha sbee nexposed . Ifth ecalci chorizo nen ­ counters on itswa ydow nunweatherabl e orslowl yweatherabl ematerial ,i twil lsettl e onto po f itan dharde nsuperficially ,formin ga caprock .Thi scaproc k iscapabl e of protecting itself fromerosio ndurin g longperiods .I twil lmaintai nitsel funti lag ­ gradationo fne wcalcareou s aeolianmateria lburie s it.A ne w softcalci chorizo n forms inthi smateria l andmigrate s downwardunti l ithit sth eunweatherabl eunderly ­ ingcaprock .A s soona s thishappen s itssurfac ebecome sexpose d andharden ssuper ­ ficially tofor m thenex t caprocko fth e sequence.I nthi swa y subsequentcycle so f aggradation and degradation, whichma y tiei nwit h theclimati cvariation so fth e Pleistocene,leav e theirresidue sa sa serieso fhar d andsof tcalci chorizon ssuper -

177 imposedo nth eOgallal aformation ,eac hcycl ebein grepresente db ya sof tcalci chor ­ izonan dit suppe rhar dcaprock . Thismode lreconcile sth edegradatio nfavoure db yPric ean dBret z &Horber gwit h theaggradatio nadvocate db yBrow nan dReeves .I texplain s satisfactorilyal lth eva ­ riationsi nappearanc eo fth ecalich ecomple xa sdescribe db yBrown .A ssuch ,thicke r calichesi nth evalley sar eexplaine db ymor eaggradation ,whil eloca labsenc eo fon e membero fth esequenc eca nb eexplaine do nth eunderstandin g that locallyn oaggrada ­ tiontoo kplac ei ntha tparticula r cycle.Th esilicat ei nth evariou s calichesi s probablya remnan to fth elas tsoi lmaterial s trappedi nth ehorizo n afterit s top hardened. Applicationo fth emode li nwhic haggradatio nan ddegradatio n alternatemake s thedatin go fth elowermos tcaproc ka sPliocen equestionable .I fth efirs t calcic horizonha dlowere d itselfo na Cambria nrock ,i twoul dno thav ebee nCambria n either! An interestingparalle lfo rthi salternatin g aggradationalan ddegradationa l modeo fformatio ni sforme db yth eobservatio no fSabelber g& Rohdenbur g (1975)fo r calcichorizon si nMorocc oan dSpain .The yclai mtha tthic kcalci chorizon sar emost ­ lypolygeneti can dar edu et oa n 'accumulationeffect 'i nwhic hsevera l soil-forming phaseshav econtributed ,whic hma yhav e actedi ndifferen t climaticcycles .The y statetha tofte ni tca nb eshow ntha tthic kcalci chorizon s splitu pint oa numbe ro f separate soils,eac hwit hit sow nthinne rcalci chorizon . Watts (1980)probabl yrefer st osimila r caseswhe nh emention sfo rKalahar i cal- cretes: 'Compositeprofile srepresen trecurrin g episodeso fcalcret e formation.The y mayb eidentifie db ya stacking ,wit hoverlap ,o findividua l calcreteprofiles. '

Insummar yi tma yb estate d thatlim ei sa ver y tenaciouscomponen to fland ­ scapesi ndr yregions .I tma yescap eerosio ni nsof tconditio nb ymean so fth emech ­ anicalreplacemen tproces san dharden swhe neventuall ycaugh tu pb yth eerodin gsur ­ face.I tresist serosion ,whe nhard ,fo rlon gperiods .Whe nfinall ydissolve dit s productsma yre-for mt obecom ea mobil e softcalci chorizo nagain .

7.2 DATING OFCALCI CHORIZON S

Theabsolut edatin go fcarbonate so fcalci chorizon sb ymean so fth eC1 4metho d isunreliabl edu et oth efollowing . Incorporationo fCC u from livingmatte ri ncar ­ bonatesupo nformatio naccount sfo ronl yhal fo fth etota lC i nthes esubstances ,th e remainderbein gmad eu po fmuc holde r 'dead'C ('limestonedilutio neffect 1).A ssuc h theirC1 4age sca nb eexpecte dt ob eon ehal flif e (app.557 0yr )to oold .Thi si s discussed,e.g. ,b yWilliam s& Polac h (1971).Recrystallisatio no fcarbonate s causes incorporationo frecen tcarbo nan dmake sC1 4age so fcarbonate sto oyoung . Comparisono fC1 4age so fcarbonate swit h C14age so forgani c substances from thesam ehorizo nshow stha tlate rcontaminatio no fcarbonate swit hrecen tC generall y

178 outmatches the limestone dilution effect,a sdat a fromBowle r &Polac h (1971)show . Assuc hmos t carbonate C14age s turnou tt ob e tooyoung .Thi seffec t isth emor eex ­ aggerated thewette r theclimate .William s &Polac h (1971)mad e similar comparisons forth e arid zonean d found inthi s case the limestone dilutioneffec t dominant over latercontaminatio nb ymor erecen t C,whic hcause d carbonate C14age st ob e tooold . Netterberg (1969)an d (1978b)define s theag eo fcalcret ea sth eag eo fth eon ­ seto fcalichification .H epropose d carefulselectio no fcarbonat e samples inorde r todistinguis h thevariou sphase s ofth eproces s evident ina horizon . Carbonate-based C14date so fcalci chorizon s aremostl y interpreteda sbein g ac­ curate onlyrelativ e toeac hothe rwithi n oneprofile .Gil ee tal . (1966)us e such data inthi s sense andWilliam s &Polac h (1971)repor t several sequences inthi s form.Th e general tendency found istha tth e limefro mcalcret eprofile s increases in agewit hdepth . From this theconclusio nca nb edraw ntha tcalcrete sgro wfro mth e bottomupwards .Th eyounge r ageo fth euppe rpar t canals ob eattributed ,however ,t o theincorporatio no fmor e recent C inth eto p layerswher erecrystallisatio nproces ­ sesar e active. One sequence fromGil ee t al. (1966)an d twofro m thosereporte db yWilliam s & Polach (1971)sho wa n agereversa l atth ebotto m ofth e sequence.Thi s isa nexcep ­ tiont oth e tendency of increaseo fag ewit hdepth . Inth e interpretation ofcarbonate-derive d C14date s itseem sworthwhil e tocon ­ sider thepossibilit y thatth emechanica l replacementproces s isactiv eo rha sbee n active in thehorizo no fwhic h the samplewa s derived.Th e aforementioned profiles withag ereversal s could,e.g. ,b e interpretedver ywel lb yassumin g thatthi spro ­ cessha sbee n active during theformation .Thi syield sth efollowin gmodel .I fcal ­ ciumcarbonat e isrelease d froma paren tmateria l overlainb y asof tcalci chorizon , part of this calciumcarbonat ewil lrecrystallis e inth eweatherin g zone,incorpo ­ ratingmoder nC from soil-CD,.A largepar to fth emateria l fromth eweatherin g zone is,however ,transporte d by themechanica l replacementproces s ofth ecalci chorizo n towards the surface soil.Her e itweather s andrelease s theres to fth eol dcarbonat e which incorporatesmoder n soil-CO,a s itdissolve s and leachesdow ntoward sth euppe r part ofth e soft calcichorizon . Inthi swa y it ispossibl e toaccoun t forth eentir e sequence of carbonate C14age swhic h increase inag ewit hdepth ,bu tdecreas e inag e at thebotto mo fth ecalci chorizon . Other effects ofth emechanica lredistributio nprocesse s tob eexpecte dar e homogenisationo flim e inth esof t calcichorizon ,leadin g tounifor m carbonate ages forth eentir ehorizon .Contrarily ,upwar d expulsion ofcarbonat eaggregate s cemented bymor erecen trecrystallisation s may leadt oa nenhancemen t ofth eapparen tyouth - fulnesso fth euppe rpar to fth ecalci chorizon . All theaforementione d facts shouldb egive ndu econsideratio nwhe n interpreting carbonate-based C14dates . An importantprincipl eo frelativ edatin g inth eeart hscience s istha ti nun ­ disturbed sequenceseac h layerpost-date s thatwhic h itunderlies .Furthermore ,ob -

179 jectsencase di nundisturbe d sequenceso flayer sar euse dt odat ethes e layers.Th e mechanical replacementproces s activei nmigratin gcalci chorizon sha st ob etake n intoaccoun twhe napplyin g this. Surfacesoil sconsistin go fmaterial s expulsedb yunderlyin g softcalci chor ­ izonsma yno teasil yb erecognise da s 'disturbed'.No rma yobject splace di nthes e horizonsb yth esof tcalci chorizo nb eeasil yrecognise da soriginatin g fromdeepe r layers.A ssuc hi ti sconceivabl etha tfailur et orecognis eth eeffect so fth emech ­ anicalreplacemen tproces so fsof tcalci chorizon s leadst oerror si nrelativ e dating.Whe ndeterminin gth eage so fcalcretes ,base do nth eag eo fartefact s found ino ro nto po fthe m (e.g.Netterberg ,196 9an d1978b) ,th einfluenc eo fth eafore ­ mentionedphenomen ashoul db echecked .

7.3 AGRICULTURE

Thedegre eu pt owhic hma ni sresponsibl efo rth edeterioratio no fth esoil so f theworl dcanno tb eassesse d everywherewit hcertainty .I ti sdefinitel yno tcorrect , inth ecas eo fcalci chorizons ,t otak eth emode lo fa mobil e softcalci chorizo na s thestandar d caseunde rnatura lconditions .Thi swoul d implytha tal lpetrocalci c horizonsconsequentl ywoul dhav et ob econsidere da santhropogenic .Th eoccurrenc eo f oldmulti-layere dpetrocalcic sal love rth eworl da sdiscusse di nth efirs t section ofthi schapte ri sclea revidenc etha tpetrocalci chorizon sca nfor mwithou thuma n intervention.Yaalo n& Singe r (1974)showe dtha tpetrocalci chorizon smus thav ebee n commoni nIsrae li nRoma ntime ssinc eth emateria lwa smine dfo rconstructio npur ­ poses.A smentione di nSectio n 2.4,th efac ttha tth epetrocalci chorizon sar e in­ creasinglycommo ntoward sth eari dclimate s alsoshow stha t theyar enatura lpheno ­ menaunde r specificcircumstances . Themode lo fGil ee tal . (1966)i nwhich ,a smentione di nSectio n 2.5.2.1,th e petrocalcichorizo ni sth enatura lend-produc to fgradua lpluggin go fa soi lhorizo n by infiltrating lime,doe sno tsee mt ob euniversall y acceptableeither . Itseem sprobable ,especiall yi nth etransitiona lzone sbetwee n sub-humidan d semi-arid climate,tha tman ypetrocalci chorizon soccu r thathav e formed from soft calcic horizons,du et ointerruptio no fth eequilibriu mbetwee n surfaceerosio nan d theupwar d transporto fmateria lb ymean so fth emechanica lreplacemen tproces si n thesehorizons .Huma ninterferenc ewit hth enatura lvegetatio nmus thav ebee nth e main cause.I nth eentir eMediterranea nthi sma yhav ebee na nimportan tfacto ri nth e wellknow ndeclin eo fagricultura lproductio n towardsth een do fth eRoma nera . Identificationo fthos earea swher e thisha sno thappene d yet,bu twhic har ei n dangero fsufferin gth esam eprocess ,seem simportant .Soi lconservatio nmeasure si n sucharea scoul d turnou tt ob ehighl yefficient .The ynee dno tsto perosio nentire ­ ly.Rathe rth eai mshoul db et omak e suretha t soilerosio ndoe sno tsupersed eth e threshold ratea twhic hth eequilibriu mbetwee nth emechanica lreplacemen tproces s anderosio ni sbroken .Measure stha tenhanc e infiltrationo frainwate rhel pt omain -

180 tainth eequilibrium .Moistur e conservationmeasure sa squantifie d inth emode lo f Huizing (1979) (Section 3.6)d ono tonl yserv e agriculturalproductio nbu tals ocon ­ tributet oth emaintenanc eo fth eequilibriu m sincethe ydiscourag eerosio nan dsti ­ mulateth eactivit yo fth esof tcalci chorizon .

7.4 CLASSIFICATION

Themechanica lreplacemen to fmateria lb yth esof tcalci chorizon si sa pedogen - eticprocess ,th eactivit yo fwhic h shouldb ereflecte d innatura l soilclassifica ­ tionsystems . Iffurthe r studyo fth eredistributio nphenomena ,unde rnatura l circumstances hasyielde da bette runderstandin go fth edifferen t influencing factors,a sub ­ divisiono fsof tcalci chorizon s shouldb edevise d accordingt oth eactivit yo fth e process. Factors thatca nb eidentifie d are:moistur eregime ,groundwate r regimean d grainsize,purit yan dliqui d limito fth elime .I tseem sadvisabl et odistinguis h continuousan ddiscontinuou s softcalci chorizon s sinceth erelativ eproportion so f limean dsoi lar eimportan tparameter si nth ereplacemen tprocess . Itma yb epossibl et osubdivid eth epetrocalci c horizons intothos e formeddi ­ rectlyb yth eproces so fpluggin g describedb yGil ee tal . (1966)an dthos e thatow e theirorigi nt oexposur eo foriginall ymobil e softcalci chorizons .Typ ean ddegre e ofconservatio no fth eenclosure s seemst ob ea nimportan t criterionfo rthi sdis ­ tinction.

181 Summary

A field studywa scarrie dou t ina nare a situatedaroun d thecit yo fMérid a in Badajozprovinc e inth esouth-wes to fSpain ,wit h themai npurpos e ofexplainin g the presenceo fdifferen ttype so fcalci chorizons a to rnea rth esurfac eo f landscapes whichar esubjec tt oerosion . Theare ai spar to fth ecatchment.o fth eGuadian arive rand ,apar t from the levelvalle yo fthi sriver ,consist smainl y ofundulatin g landscapes ongranite , schistan dTertiar ydeposits .Th e soilspredominantl yclassif ya s Inceptisols,Alfi - solsan dVertisols .Sof tcalci chorizon sbot ho f thediscontinuou s andcontinuou s typesan d locallywit hhardene d topsoccu rfrequentl y inth esoil so nTertiar y sedi­ ments.The y areals opresen t onschis tan dar e locally encountered onth egranite . Theare aha s forth elarge rpar tbee nstrippe do f itsnatura lvegetatio nan dha sbee n broughtunde ragriculture .Som earea sar eno wbein g irrigated.Th eclimat e istypi ­ callyMediterranean ,semi-ari d tending towardssub-humid . The investigationconcentrate d inth efirs t instancespecificall yo na nundu ­ latingMiocen ecla y landtype,a cros ssectio no fwhic h (Fig.10 )reveal s that the calcichorizon sfollo wth erelie fan dar e laterallycontinuou s thoughthe y showdif ­ ferentform swhic hgraduall ymerg e intoeac hother .I nessenc ether ear e twoprofil e types: 1. Thetop san dplatea urim shav ea thi nsurfac esoi loverlyin ga continuou scalci c horizon.Th euppe rpar to fthi s ishardened .I tmerge svi a anirregula rboundar y into anunderlyin gdiscontinuou scalci chorizo nconsistin g ofmasse s of softlim e inMio ­ ceneclay .Th e transitionzon ebetwee nth econtinuou s anddiscontinuou s calcichor ­ izoni scharacterise db y slickensidestha toccu rbot h inth ecla yan d inth elime . Claynodule s ofwhic h theinne rpar t isno ncalcareou sar e foundbot h inth esof tan d hardlime . 2. Soilso fth evalle ybottom sdiffe rfro m theaforementione d type inth epresenc e ofa thic k colluvial surfacesoi lan d inth eabsenc eo fhardenin g inth e lime.Th e otherphenomen a (irregular lowerboundary ,slickenside san dcla ynodules )ar eals o present inthes eprofiles . Sampleso fbot hsoi l typeswer edraw nfo ranalysi s andmicromorphologica lin ­ vestigations.A swel la sroutin eanalyses ,othe rtest swer ecarrie d outa sfollows . The liquid limito fth e limewa sdetermine d and found tob ever y low.Bul kdensit y wasdetermine do nundisturbe d sampleso fbot hlim ean dcla ywhil eo fth ecla ysample s thecoefficien to flinea rextensibilit y (COLE)wa sdetermined .Furthermore ,o nsom e limesample s thestabl eisotop ecompositio nwa sdetermine d and thepresenc e ofmicro -

182 fossilswa s investigated.Th eresul to fth elatte r investigationwa snegative .Th e position inth e landscape ofth ecalci chorizons ,th eresult s ofth eanalyse s and the studyo f themicromorpholog y showtha ti nth epresen tcas e thesehorizon sar epedo - geneticfeatures .I ti sshow ntha tsurfac esoil san dcla ynodule s arebot hderive d fromth eunderlyin gMiocen eparen tmaterial . Laboratory experimentswer ecarrie d outon th elim ean dcla ynodul e samples in ordert o studyth ewa y inwhic hthes ematerial sbehav ei nrelatio n toeac hothe r undercircumstance swhic hmatc h those inth e soil,an d toexplai nth ephenomen aob ­ served.Fo r thispurpose ,cla ynodules ,stone san dhar dpetrocalci c fragmentswer e embedded insof t limean dalternatel ydrie dan dmoistened .Th eresult swer eregis ­ teredb ymean s of stereoradiography .Th eradiograph s showedtha tal lobject sros e uponmoistenin g and fellupo ndrying . Ina numbe ro fcase sthi sle dt oa ne tris eo f theobjects .Th edrivin g forcebehin d thesemovement scoul db eshow nt ob e thepres ­ sureo fai r enclosed inth ecrystallin e limea sa resul to fmoistening .I ti sclea r thatth e largeobject sregardles s ofthei rconstitutio nar emor eincline d toconserv e theascendin g componenttha nth efin eparticles .The ytherefor emov eupward srelativ e to the surrounding finelime . Onth ebasi s of the field observations andth eresult so fth eexperiments ,th e following explanationfo rth egenesi so fth eobserve dhorizo nconfiguratio ni sgiven . Whenfin ecrystallin e limeoverlie s swelling clayan d thesyste m issubjecte dt o moistening anddrying ,a nirregula r transitionbetwee nth etw omaterial swil ldevelo p whichca nb e interpreted asa subterranea ngilga lmicrorelief .Upo ndrying ,crack s form inth ecla y intowhic h limeflow supo nremoistening .Thi sproces s leadst oth e introductiono fcla yint oth esof tcalci chorizon ,sinc eth e limetha tflowe d inre ­ sists thepressur e exertedb y the swelling clay.Th ecla y thenform sprotrusion s into the lime.Thes eprotrusion so r 'claypillars 'brea ku pint osmalle rfragment swhic h oncepresen t inisolate d form in.th e limecom eunde r the influenceo fth eris epro ­ cessre-create d inth eexperiment .Th ecla ynodule sar eno wtransporte dupwar d through the calcichorizo nan d expelled atit stop ,s otha tthe yadjoi nth esurfac e soil.Th eresul t ofthi smechanica l replacementproces s isa downwar dmovemen to fth e entirecalci chorizo n (Fig.5 an dFig .38) . Thisproces s isfossil ei nth ecalci c horizonswit hhardene d topswhich ,du e tothei rimpermeability ,d ono tmoiste nany ­ more. Incalci chorizon swhic hhav eno thardene d theproces smus tstil lb eactive . Comparablephenomen awer elocall yobserve d incalci chorizon s inothe rlandtypes . Undernatura lcondition san equilibriu mestablishe s itselfbetwee nth elowerin g of thecalci chorizo nan d thesimultaneou supwar d transporto fsoi lmateria l toth e surface soil inherent inthi so nth eon ehan dan d onth eothe rhan dth eerosio nt o which thissurfac esoi li ssubject .Disturbanc e ofthi sequilibriu mca nlea dt oth e exposure ofth ehorizo nwhic hresult s inhardenin gan d fossilisation ofth eentir e system. (Thelatte rha soccurre d inth eprofile salon g theplatea uedge so fth eMio ­ cenecla y landtype.)A disturbanceo fth eequilibriu mca nals o lead toa chang e in habituso fth ehorizo nfro mcontinuou s todiscontinuous . Ifo nit swa ydow nth ehor -

183 izonhit sunweatherabl e ordifficultl yweatherabl emateria lth eequilibriu m is disturbed anderosio ncause sexposur ewhic h isfollowe db yhardening .Example s of calcichorizon stha t 'foundered'o narkos eo rgranit e arefoun d inth earea .Loca l 'damage'o fth ecalci chorizo ndu e toincisio no ferosio ngullie s orb y encounters withunweatherabl evein so rdike s is 'repaired'b y thehorizon ssinc e thelim e is ablet oshif t somewhati na latera ldirectio nwhil emoving down . Comparisono fth eestimate s oferosio nrate s inth eare awit h thoseo f therat e ofdownwar dmovemen to f thecalci chorizo nshow s thatthes ear eo f thesam eorde r of magnitude. Iti sprobabl e thatth ecalci chorizo n indiscontinuou s form isabl e to developconsiderabl y largerrate s ofdownwar dmovemen tan d assuc h isabl et o stay ahead ofa considerabl y strongererosion .I na nalternativ emode l inwhic h thelow ­ eringo fth ecalci chorizon swa s assumed tob e dueentirel y toleachin g (dissolution followedb ycrystallisatio na tgreate rdepth )i tcoul db e calculated thatth e dis­ placemento fth ecalci chorizo nwa squit eunabl e tomatc h theestimate d erosionrate s ofth earea .Th edissolutio nmode l istherefor erejecte d asth emai ncaus e for the downwardmovemen to fth ecalci chorizon so f thearea . Since thecalci chorizo nca naccumulat e limefro mth ematerial s ittraverse s on itswa ydown ,th eexplanatio no fth epresen tthic kcontinuou scalci chorizon sma yde ­ partfro m theassumptio ntha tthe ystarte d theirexistenc e longag o asmuc h thinner horizons.Fo r thegenesi so fthes e 'incipientcalci chorizons 'a numbe r ofoption s arediscussed .A s themos tprobabl emanne r ofdevelopment ,th efollowin g is assumed. Calcite crystals thatfor mever ydr yseaso na sefflorescence s incrack s ofheav y clay soilsar ewashe ddow nb y thefirs train so fth efollowin gwe t seasont oth ebotto m of thesecracks .Swellin gan dshrinkin g of thecla y ininteractio nwit h liquifactiono f thelim e lead toa gradua lreplacemen t ofth ecla yb y lime,a sdiscusse dunde r the formationo fth esubterranea ngilga îrelief .A s such,finall ya tth eleve lwher e all cracks end,a continuou s softcalci chorizo n isforme d froma discontinuou s one.Thi s horizonstart sit smovemen tdownward swhe nth egroundwate rtabl e lowersi nerodin g landscapes. For theformatio no fa n 'incipientcalci chorizon' ,othe roption s sucha sgeo - genetic sedimentation,replacemen t ofsoi lmateria lb y crystallising limean dchemi ­ calreplacemen t ofmateria lb y limear econsidere d tob e lessprobabl e inthi sparti ­ cularcase . Thedescribe dmechanica l replacementproces sha s implications fora numbe ro f disciplines,a sfollows . 1. Iti sa nimportan t factor inth egenesi s of landscapes inwhic h softcalci chor ­ izonshav ea planatin g influenceo nth erelie fbu twhe n locallyhardene dbrin g about theopposite .Th ewell-know n 'caprockcaliche 'fro mth eLlan oEstacad oo fTexa san d NewMexic owhich consist s ofsevera l softan dhar d limelayer s canb eexplaine d as resulting fromsevera lcycle so faggradatio nan ddegradation . 2. Theproces s shouldb ekep t inmin d ininterpretin g C14dating so fcalci chor ­ izons.Th e ability ofth ecalci chorizo n toplac e objectsderive d fromunderlyin g

184 formations inth e soil overlying thehorizo nwithou t the latterhavin g tob e con­ sidered as 'disturbed'ha s importancefo rdating s thatar ebase d onthes e objects (archeology). 3. Iti s important torealis e that erosion in landscapeswit hsof t calcic horizons maybecom ever y noxious for agriculturewhe na certai n thresholdvalu e is exceeded. Ifth eerosio nrat ebecome s so large thatth eequilibriu m inth ereplacemen t process isdisturbed , exposure followed by irreversiblehardenin g of the limewil l occur. 4. Theproces s should be incorporated insoi l classification. Thispublicatio n also includes aliteratur erevie w ofcalci chorizon swhich ,be ­ sidesnomenclatur e andmicromorphology ,contain s information onhorizo n sequences, occurrence inrelatio n to specific climatic zones,geneti c andagricultura laspects .

185 Samenvatting

Eenveldstudi ewer duitgevoer di nee ngebie d gelegenron dd esta dMérid ai nd e provincie Badajozi nhe tzuidweste nva nSpanje ,me tal svoornaamst edoe ld eaanwezig ­ heidt everklare nva nverschillend e typenkalkhorizonte naa no fnabi jhe toppervla k van landschappendi eaa nerosi eonderhevi g zijn. Hetgebie di sdee lva nhe tstroomgebie dva nd erivie rGuadian ae nbestaa tbuite n hetvlakk eda lva ndez erivie rvoora lui tglooiend e landschappen,o pgraniet ,schis t enTertiair e afzettingen.D egronde ndi ehiero p ontwikkeld zijnbehore nvoo rhe t grootstedee lto td eInceptisolen ,d eAlfisole ne nd eVertisolen .Zacht ekalkhorizon ­ tenzowe lva nhe tdiscontinu eal she tcontinu etyp ee nlocaa lme tverhard e top,kome n veelvuldigvoor i nd egronde no pd eTertiair e sedimenten.Z ezij noo kaanwezi go pd e schiste nworde nlocaa lo pgranie t aangetroffen.He tgebie di svoor he tgrootst edee l van zijnnatuurlijk evegetati eontdaa ne ni ncultuu r gebracht.Enig e gebiedenworde n geirrigeerd.He tklimaa ti stypisc hMediterraan ,semi-arie d tenderend naarsub - humied. Hetonderzoe kconcentreerd e zichi neerst e instantievoora lo pee nglooien dMio - ceenkleilandscha pwaarva nee ndwarscoup e (Fig.10 )toon tda td ekalkhorizonte nhe t reliefvolge ne nlateraa lcontin u zijn,zi jhe tda tz everschillend evorme nvertone n diegeleidelij ki nelkaa rovergaan .I nessenti e zijne rtwe eprofieltypen : 1. Detoppe ne nplateaurande nhebbe nee ndunn ebovengron dwaaronde ree ncontinu e kalkhorizont aanwezig is.He tbovenst edee lhierva ni sverhard .He tgaa tvi aee non ­ regelmatigegren s overi nee nonderliggend ediscontinu ekalkhorizon tbestaand eui t zachtekalkmassa' si nMiocen eklei .D eovergangszon e tussend econtinu ee ndisconti ­ nuekalkhorizonte nword tgekenmerk tdoo rglijvlakke n (slickensides)di ezowe li nd e kalkal si nd ekle ivoorkomen .Kleiknolle nwelk eva nbinne nkalkloo s zijnworde nzo ­ weli nd ezacht eal si nd ehard ekal kaangetroffen . 2. Dedalbodemgronde nverschille nva nd evoorgaand ei nd eaanwezighei dva nee n dikke,colluviale ,bovengron de ni nd eafwezighei dva nverhardin gva nd ekalk .D ean ­ dereverschijnsele n (onregelmatigeondergrens ,glijvlakke ne nkleiknollen ) zijni n dezeprofiele neveneen saanwezig . Vand ebeid ebodemtype nwerde nmonster svoo ranalys ee nmicromorphologisc hon ­ derzoek getrokken.Naas td eroutine-analyse swerde nd evolgend ebepalinge ngedaan . Vand ekal kwer dd evloeigren sbepaal ddi euitzonderlij k laagblee kt ezijn .He t volumegewichtwer daa nongestoord emonster sva nzowe lkal kal skle igemete n terwijl vand ekleimonster soo kd elineair euitzettingscoefficien t (COLE)wer dbepaald . Tevenswer daa nee naanta lkalkmonster sd estabiel e isotopensamenstellingbepaal de n

186 werd onderzocht ofmicrofossiele n aanwezigwaren .He tresultaa tva ndi t laatsteon ­ derzoekwa snegatief .Ui t de landschappelijke liggingva nd ekalkhorizonten ,d eana ­ lyseresultaten end emicromorphologi e blijktda tdez ehorizonte n inhe t onderhavige gevalpedogenetisch e vormingen zijn.Oo kblee kda td ebovengronde ne nd e kleiknollen beideva nhe t onderliggendeMiocen emoedermateriaa l afstammen. Metmonster sva nkal ke nkleiknolle nwerde n laboratoriumexperimenten uitgevoerd teneindehe tgedra gva ndez emateriale n tenopzicht eva nelkaa rt ebestudere nonde r omstandigheden overeenkomendme tdi e ind ebode me nz oee nverklarin g tevinde nvoo r dewaargenome nverschijnselen .Hierto ewerde nkleiknollen ,stene ne nhard ekalkfrag - menteningebe d inzacht ekal ke nafwisselen dgedroog d enbevochtigd .Doo rmidde l van stereoradiografiewer dhe tresultaa thierva ngeregistreerd .D eröntgenfoto' stoonde n aanda tall evoorwerpe nopwaarts ebeweginge nmaakte nbi jbevochtigin g enneerwaarts e bijdroging .Di t leidde inee naanta lgevalle nto tee nnett ostijgin gva nd evoor ­ werpen.D edrijvend ekrach tvoo r dezebeweginge nblijk tnaa rko nworde n aangetoond luchtinsluiting ind ekristallijn e kalk te zijntengevolg eva nbevochtiging .He t is duidelijkda t degrot eobjecten ,ongeach thu n samenstelling,mee r geneigd zijnd eop ­ gaande component tebehoude nda nd e fijnedelen .Zi jbewege n zichdaardoo r opwaarts tenopzicht eva n dehe n onringende fijnekalk . Op grondva nd eveldwaarneminge n end eresultate nva nd eexperimente nword t de volgendeverklarin g voorhe tontstaa nva nd ewaargenome nhorizontconfigurati e ge­ geven.Al s fijnekristallijn e kalk op zwellende klei ligte nhe tsystee mword tbloot ­ gesteld aanbevochtigin g endrogin g zalzic htusse nd e tweemateriale n eenonregel ­ matige overgang ontwikkelendi eka nworde ngeïnterpreteer d alsee nondergrond s gilgaï microrelief. Bijdrogin g ontstaan scheureni nd ekle iwaari nd ekal kbi jherbevochti ­ gingvloeit .Di tproce s leidt totd e introductieva nkle i ind e zachte kalkhorizont omdatd e ingevloeide kalk,d edoo r de zwellendekle iuitgeoefend e drukweerstaat .D e kleivorm tda nuitstulpinge n ind ekalk .Dez euitstulpinge n of 'kleipilaren'breke n ind ekleiner e fragmentenop ,welk e eenmaalgeisoleer d ind ekal kaanwezig ,onde rd e invloedva nhe t inhe t experimentnagebootst e stijgproces komen.D ekleiknolle nwor ­ denn udoo r dekalkhorizon t omhoog getransporteerd enaa nd ebovenzijd euitgescheide n zodat zij zichbi j debovengron dvoegen .He tgevol gva ndi tmechanisc hvervangings ­ proces isee nneerwaarts ebewegin gva nd egehel ekalkhorizon t (Fig.5 e nFig . 38). Ditproce s is fossiel ind ekalkhorizonte nme tverhard e topdi e tengevolgeva nhu n ondoorlatendheid nietmee rbevochtigen .I nd eonverhard e kalkhorizontenmoe the tpro ­ cesno g actief zijn.Vergelijkbar everschijnsele nwerde n locaali nkalkhorizonte n in andere landschappengevonden . Ondernatuurlijk e omstandigheden stelt zichee nevenwich t intusse nd edalin g vand e kalkhorizont enhe tdaaraa n inherente transportva nbodemmateriaa lnaa rd e bovengrond aand e enekan te nd eerosi ewaaraa ndez ebovengron d onderhevig isaa nd e anderekant .Verstoringe nva ndi tevenwich tkunne nleide nto tblootleggin gva nd e kalkhorizont hetgeenresulteer t inverhardin g enfossilisati eva nhe tgehel esysteem . (Dit laatste heeft zichi nd eprofiele nlang sd eplateaurande nva nhe tMiocen eklei -

187 landschapvoorgedaan. )Oo kka nee nverstorin g vanhe t evenwicht leiden totee nver ­ andering vand ehabitu sva nd ehorizon t vancontin unaa rdiscontinu .Al s de horizont onderwegnaa rbenede no pee nonverweerbaa r ofmoeilij kverweerbaa rmateriaa l stuit wordthe tevenwich tverbroke n entreed t expositie door erosie,gevolg d doorverhar ­ ding,op .Voorbeelde nva nkalkhorizonte n die zoo p arkose ofgranie t 'gestrand' zijn worden inhe tgebie d aangetroffen.Local e 'beschadiging'va nd ekalkhorizon t doorin ­ snijdingva nerosiegeule n ofdoo rontmoetinge nme t onverweerbare aders ofgangen , wordendoo rd ehorizon t 'gerepareerd'omda td ekal k zichtijden s deneerwaarts ebe ­ wegingva nd ehorizon t ookenigermat e lateraalka nbewegen . Vergelijking van-schattinge nva nd e erosiesnelheid inhe tgebie dme t dieva nd e daalsnelheid vand e kalkhorizont toont aanda tdez eva ndezelfd e ordeva n grootte zijn.He t iswaarschijnlij k datd ekalkhorizon t indiscontinu evor mno g aanzienlijk hogeredaalsnelhede n kanontwikkele n en zoee nno g aanzienlijk sterkere erosie kan voorblijven. Inee nalternatie fmode lwaari nd e dalingva nd ekalkhorizonte n geheel aaninspoelin g (oplossing gevolgd dooruitkristallisati e opgroter e diepte)wer d toe­ geschrevenko nworde nbereken d datd edalin gva nd ekalkhorizon t inhe t geheel niet instaa twa sd e geschatte erosiesnelhedenva nhe tgebie d teevenaren .He t in- spoelingsmodel wordtal shoofdoorzaa k voord eneerwaarts e beweging vand e kalk­ horizontenva nhe tgebie ddaaro mverworpen . Aangezien dehorizon t op zijnwe g naarbenede nkal kka naccumulere nui t demate ­ rialendi ehi jdoorloop t kane rvoo r deverklarin gva nd egenes eva nd ehuidig e dikke continue kalkhorizontenva nworde nuitgegaa nda tdez ehu nbestaa n langgelede n als aanzienlijk dunnerehorizonte n zijnbegonnen .Voo r degenes eva n deze 'incipient cal­ cichorizons 'worde nee naanta l optiesbesproken .Al smees twaarschijnlijk e vormings­ wijz eword t devolgend e aangenomen: Kalkkristallen die zichiede r droog seizoen ind e vormva nuitbloeiinge n insplete nva n zwarekleigronde nvorme nworde ndoo r de eerste regensva nd edaaropvolgend e natte tijdnaa rbenede ngespoel d totd ebode mva ndez e spleten. Zwel enkrim pva nd ekle i inwisselwerkin gme tvervloeiin gva n dekalk , leidde totee ngeleidelijk evervangin g vankle idoo rkalk , zoalsbi jd evormin g van hetondergronds e gilgaïreliefbesproken . Zodoende ontstaat uiteindelijk ophe tnivea u waar de spleteneindige nui t eendiscontinu e eencontinu ekalkhorizont . Bij daling vand egrondwaterstan d ineroderend e landschappenvang tdez ehorizon t zijnbewegin g naarbenede naan .Ander eoptie svoo rhe tontstaa nva nee n 'incipientsof t calcichor ­ izon',t ewete ngeogenetisch e sedimentatie,verdringin g vanbodemmateriaa l door ter plaatsekristalliserend e kalk enchemisch evervangin gva nbodemmateriaa l door kalk, worden alsminde rwaarschijnlijk evormingsprocesse n beschouwd voor het onderhavige geval.He tbeschreve nmechanisc hvervangingsproce s heeft devolgend e implicaties voor eenaanta lvakgebieden : 1. Het isee nbelangrijk e factor ind e landschapsgenesewaarbij dekalkhorizonte n in zachte toestand eenvervlakkend e invloed ophe trelie fuitoefene nmaa r in locaalver ­ harde toestand juisthe t omgekeerde bewerkstelligen. Debekend e uitmeerder e harde en zachte kalklagenbestaand e 'caprock caliche'va nd eLlan oEstacad o inTexa s enNe w Mexicoka nal sresultaa tva nmeerder e cycliva naggradati e endegradati eva nhe t landschap terplaats eworde nverklaard . 2. Bijd e interpretatieva nC1 4dateringe nva nkalkhorizonte ndien tme the tproce s rekening teworde ngehouden .He tvermoge nva nd ehorizonte no mobjecte nafkomsti g van onderliggende formaties ind ebovengron d teplaatse n zonderda tdez e laatsteal s 'verstoord'moe tworde nbeschouw d heeftbelan gvoo rdateringe ndi e zicho pdez evoor ­ werpenbasere n (archeologie). 3. Het isva nbelan g zicht erealisere nda terosi e inlandschappe nme t zachtekalk ­ horizonten zeer schadelijkka nworde nvoo r de landbouwal sbepaald e grenswaarden overschredenworden . Indiend eerosiesnelhei d zogroo tword tda the tevenwich t inhe t vervangingsproces onderbrokenword t treedt expositie gevolgddoo r irreversibelever ­ hardingva nd e kalkop . 4. Ind ebodemclassificati e dienthe tproce s eenplaat s tekrijgen . Depublicati ebeva t tevens eenliteratuuroverzich t betreffende kalkhorizonten datnaas tnomenclatuu r enmicromorphologie ,informati ebeva t overhorizont-sequen ­ ties,voorkome n inafhankelijkhei d vanspecifiek eklimaatzones ,genetisch ee nland ­ bouwkundige aspecten.

189 Resumen

Unestudi od ecamp ofu e llevadoa cab o enun a zonaubicad a alrededord e la ciudadd eMérid ae nl aprovinci ad eBadajo ze ne lsuroest ed eEsparïa ,co ne lpropo - sitoprincipa ld eexplica r lapresenci ad ediferente s tiposd ehorizonte scâlcico se n o cercad e lasuperfici ed epaisaje ssujeto sa laerosion . La zonahac epart ed e lacuenc ade lRi oGuadian ay fuerad e lallanur aaluvial , deest erî oest a formadaprincipalment epo rpaisaje sondulado s sobregranitos ,es - quîstosy deposito s terciarios.Lo ssuelo s seclassifica npredominantement ecom o In- ceptisoles,Alfisole sy Vertisoles .Horizonte scâlcico sblandos ,d e lostipo sdescon - tînuousy continuou sy localmenteco ntope sendurecido s ocurrenco nfrequenci ae nlo s suelossobr e losdepósito sterciarios .Estâ nprésente stambié nsobr eesquîsto sy han sidoencontrado s localmentesobr egranitos .L azon ah a sidodesprovist ae ns umayo r parted e lavegetació nnatura ly dedicad aa laagricultura .Alguna s zonasestâ nahor a bajoriego .E lclim a estïpicament eMediterrâneo ,semiârid oco ntendenci ahaci asub - hûmedo. Desdee lprincipî o lainvestigacio ns econcentr é especîficamentee ne lpaisaj e ondulado dearcilla smiocenas .U ncort ee né l (Fig. 10)révél aqu e loshorizonte s câlcicos siguene lreliev ey son lateralmentecontînuo sn oobstant e quemuestra n formasdiferente sy se fundengradualment e entre si. Essencialmenteha ydo s tiposd eperfiles : 1. Lascima sy lasmârgene sd e lasmesita stiene nu nsuel osuperficia ldelgad o yacente sobreu nhorizont ecâlcic odescontïnuo .L apart e superior seencuentr aen - durecida.Po rmedi od eu n limiteirregula rs econviert ee nu nhorizont ecâlcic odes ­ contïnuo subyacente elcua lconsist ee nmasa sd eca lbland ae narcill amiocena .L a zonad etransicio nentr ee lhorizont ecâlcic ocontinu oy descontïnu oest acaracteri - zadapo r 'espejulas' (superficiesacanalada sy lisas)présente se n laarcill ay enl a cal.Tant oe nl aca lbland acom oe nl adura ,s eencuentra nnódulo sd earcill a cuya parte interiorn oe scalcârea . 2. Los suelosd e losfondo sd e losvalle sdifiere nde ltip oarrib amencionad oe nl a presenciad eu n suelosuperficia lcoluvia lpotent ey e nl aausenci ad eendurecimient o de lacal .Lo sotro sfenômeno s (limiteinferio r irregular,espejula sy nódulo sd e arcilla)estâ ntambié nprésente se nésto sperfiles .Muestras d eambo stipo sd eper ­ filesfuero ntomada spar aanalisi s einvestigacione smicromorfológicas .Junt o conlo s analisisd erutin as eefectuaro notra sdeterminaciones :E l limited e liquidezd e la cal fuédeterminad oy result ómu ybajo .L adensida d aparente fuéestablecid asobr e muestrasn odisturbada sd earcill ay ca ly almism o tiempo seobtuv oe l Indiced e

190 dilataciónlinea l (COLE)d e lasmuestra sd e arcilla.Ademâs ,£u édeterminad al acom - posiciónisotópic aestabl e de algunasmuestra sd eca ly inspeccionada lapresenci a de microfosiles.E lresultad od e estaultim a investigaciónfu enegativa .L aposiciö nd e loshorizonte s câlcicos ene lpaisaje ,lo sresultado sd e losanâlisi sy elestudi od e lamicromorfologîa ,demuestra nqu e éstoshorizontes ,de lpresent ecaso ,so nféno - menospedogenéticos .H a sido establecidoqu e lossuelo ssuperficiale sy losnódulo s dearcill afuero nderivado s delmateria lmiocen osubyacente . 3. Sobremuestra s deca ly nódulo sd earcill afuero nejecutado sexpérimente sd e laboratóriopar a estudiar lamaner ae n lacua lésto smateriale ss ecomporta nmutua - mentebaj o condiciones semejantesa lasencontrada s ene l sueloy explicar asîlo s fenómenosobservados .Co nest eproposit ofuero nenterrado snódulo sd earcilla , Piedrasy fragmentespetrocâlcico sduro se nca lbland a locua lfu éhumedecid oy secadoalternativamente .Lo sresultado s fueronregistrado spo rmedi od eestereoradio - grafîa.Lo sradiograma smostraro nqu e todos losobjeto s subierona lhumedecers e y descendierona l secarse.Est e condujoe nu nciert onumer od ecasos ,a un asubid a netad e los objetos.S epud ocomproba rqu e lafuerz amotri zd eésto smovimiento sfu e laprêsio nde l aire incluidae n laca lcristalin acom oresultad ode lhumedecimiento . Es evidentequ e losobjeto s largos,indiferente sd es uconstitución ,so nmâ s aptes paraconserva re lcomponent eascendent equ e laspartïcula s finas.Po rest arazo nas - ciendene nrelació na laca l finacircundante . Enbas e de losobservacione s decamp oy losresultado sd elo sexpérimentes ,s e présenta la siguiente explicaciónpar a lagenesi sd e laconfigurai , dehorizontes , observada. Cuando laca l finacristalin a sobreyacea arcill adilatabl ey e lsistem a estasujet o ahumedecimient oy secado,s edesarroll aun atransició nirregula rentr e losdo smateriale s lacua l sepued e interpretar comou nmicroreliev egilga lsub - terrâneo.A l secarse,s eforma ngrieta s en laarcill adentr od ela scuale s fluyel a cal alrehumedecerse .Est eproces o llevaa laintroduce d dearcill ae ne lhorizont e câleicoblande ,y a que laca l incorporadarésist el aprésió nejercid apo r laarcill a dilatante.L a arcillaform aentonce sprotusione sdentr od e lacal .Esta sprotusione s o 'pilares de arcilla's eagrieta nfernando fragmente smâ spequeno s loscuale sun a vezprésente s enform a sueltae nl acal ,estâ nsujeto sa lproces od eascens orepro - ducido ene l expérimente.A continuai losnódulo sd earcill aso n transportas haciaarrib a atravé s delhorizont ecâleic oy expulsadosa llimit esuperio rdémanera , que sejunta n alsuel o superficial.E lresultad od eest eproces od e sustituco n mecânicae su nmovimient od ehundimient od e todoe lhorizont ecalcic o (Fig 5y Fg . 38). Esteproces o es fosile nhorizonte s câlcicosco ntope sendurecido s1 eu s debidoa su impermeabilidad,n ovuelve na humedecerse .E n loshorizont es ca l ^e no seha nendurecido ,e lproces o debese r aunactive .Fenómeno scomparable s fueron observados localmentee nhorizonte s câlcicosd eotro stipo sd e tie"^ Bajocondicione s naturales seestablec eu nequilibri oentr ee l hund—

horizonte câleicoy el transporte simultanéed emateria ld esuel ohaci a ^*>0 suelo superficial loqu e esinherent ee nest ehundimiento ,d eu n ladoy po rotro ,

191 erosiona lacua lest asujet o elsuel osuperficial .L adisturbació nd e esteequi ­ libria-pued eocasiona r laexposició nde lhorizont e lacua lrésult ae ne lendure - cimientoy fosilizaciónde l sistemaentero . (Loultim o ocurrióe n losperfile s al o largod e lasmargene sd e lasmesita sde l tipod etierr ad e laarcill amiocena. )L a alteraciónde lequilibri opued e llevar tambiéna u ncambi oe ne lhabit ode lhori ­ zonte,d econtinu oa descontînuo .S ie ns uhundimient oe lhorizont e tocamateria l no meteorizableo dificilment emeteorizabl e elequilibri o sepierd ey laerosio n ocasiona suexposició n seguidapo r enduréeimiento.Ejemplo sd ehorizonte scâleico s 'zozobrados'e narcos a agranit o seencuentra ne nl a zona.Lo s 'dafios'locale sd e los horizontes câleicosproducido spo r laincisio nd ecârcava sd eerosio no encuentros conveta so dique sn ometeorizable s son 'reparados'po r loshorizonte sy aqu e laca l esapt apar amovers ealg oe nsentid o lateralmientra s seest abajando . Lacomparacio nd e lasproporcione sd e erosiond e la zonaco n lasde l hundimiento delhorizont e câleicomuestra nqu eesta sso nde lmism o ordend emagnitud .E s probable quee lhorizont e câleicoe nform adescontînu a seacapa zd edesarrolla r proporciones dehundimient omuch oma selevada sy d eest aform a igualara un aerosio nmuch oma s fuerte.E nu nmodel oalternativ oe ne lcua le lhundimient ode lhorizont ecâleic o fué atribuîdo completamentea lixiviación (disoluciónseguid apo r cristalizacióna mayo r profundidad)s epud ocalcula rqu ee ldesplazamient ode lhorizont e câleicoer aabso - lutamenteincapa zd e igualar lasproporcione sd e erosionestimada spar a la zona.E l modelod e disolucióne spo res orechazad o comocaus aprincipa l delhundimient o de loshorizonte scâleico sd e lazona . Puestoqu e loshorizonte scâleico s soncapace sd eacumula rca ld e losmateriale s queatravies a ens uvi ahaci a abajo,l aexplicació nd e losprésente shorizonte s câl­ eicoscontînuo sy potentes ,pued eparti r de lasuposició nd equ e éstos se iniciaron hacebastant e tiempocom ohorizonte smuch oma sdelgados .Par aexplica r lagenési sd e êstos 'horizontescâleico s incipientes's ediscut eu nnumér od e opeiones.Com o la manerama sprobabl e seasum e lasiguiente .Lo scristale sd ecalcit aqu e seforma ne n cadaestació nsec acom oeflorescenci ae n lasgrieta sd e suelos arcillosospesado s son lavadoshaci a elfond od eesta sgrieta spo r lasprimera s lluviasd e la siguiente estacionhûmeda .L aexpansio ny contracció nd e laarcilla ,actuand o juntoco n la licuefacciónd e laca l llevana un asustitució ngradua ld e laarcill apo r laca lcom o fuédiscutid obaj o laformació nde l relieve gilgal subterrâneo.As ï finalmente,e ne l niveldond e terminantoda s lasgrieta ss eform au nhorizont ecâleic obland oy con ­ tinuoa parti rd eu nhorizont e descontînuo.Est ehorizont e inicias uhundimient o cuandol acap afreâtic adesciend ee n lospaisaje ssujeto sa l aerosion . Para laformació nd eu n 'horizontecâleic oincipiente 's econsidera notra sop ­ eionescom o sedimentacióngeogenética ,sustitució nd emateria lde l suelopo r calcita cristalizantey sustituciónquîmic ad emateria lpo rcal ,com omeno sprobable s enest e casoparticular . Elproces od esustitució nmecanic adescrit atien e implicacionespar au nnumer o dedisciplina s enl asiguient eforma :

192 1. Esu n factor importante en lagenesi sd epaisaje s en loscuale s loshorizonte s câlcicosblando s tienenun a influenciaaplanant e sobre elrelieve ,per o cuando local- mente estânendurecido s causane l efecto contrario.E l conocido 'caprockcaliche 'de l LlanoEstacad o deTexa sy Nuev oMexic oe lcua lconsist e envaria s capasblanda s y duraspued e explicarse comoe lresultad o devario s ciclosd e agradacióny degrada - ción. 2. Hay queda r ladebid a atencióna lproces o citadocuand o seinterprete n dataciones C14d ehorizonte s câlcicos.L aaptitu d delhorizont e câlcicopar aemplaza r objetos derivados de formaciones subyacentes ene lsuel osobreyacent e alhorizont e sinqu e pueda considerarsee lultim ocom o 'disturbado',tien e importanciapar a lasdatacione s basadas en éstos objetos (arqueologîa). 3. Esmu y importante saberqu e laerosio ne npaisaje s conhorizonte s câlcicos blandos setornar âmu yperjudicia lpar a laagricultur a alexcéde rcierto svalore s limites. Cuando laproporció nd e erosions e incrementa tantoqu edisturb a el equi- libriode l proceso,s epresentar â laexposició n seguidapo r elendurecimient o irre­ versible. 4. Elproces o debe incorporarse en laclasificació nd esuelos . Estapublicació ncontien e tambiénun areseiï aliterari asobr ehorizonte s câlcicos lacua lcomprend efuer ad enomenclatur ay micromorfologîa ,informacio nsobr e secuencias dehorizontes ,ocurenci a enrelació na cierta s zonasclimaticas ,aspecto s genéticosy de laagricultura .

193 Resumé

Uneétud ed eterrai nfû texécuté edan sun e zone situéedan s les environsd el a villed eMérid adan s ledepartemen td eBadajo z au sud ouestd e l'Espagne dans lebu t d'expliquer laprésenc ed edifférent stype sd'horizon s calciques (croûtes calcaires) présde-o uâ-l asurfac ed epaysage s sujeta l'érosion. La zonefai tparti ed ubassi nversan t de larivièr e Guadiana constituées ­ sentiellementd epaysage sondulé s surgranits ,schiste s etdépôt s tertiaires,sau f lavallé ealluvial ed e larivière .Le s solsson tprincipalemen t classés enIncepti - sols,Alfisol se tVertisols .De shorizon scalcique s friables de type continu etdis ­ continu avecde spartie s superieureslocalemen t endurcies apparaissent fréquemment dans lessol ssu r lesdépôt stertiaires . Ilss eprésenten t aussi sur les schistese t localementsu r lesgranits .Dan scett erégio n lavégétatio nnaturell e a en grande partie laissé laplac eà l'agriculture. Quelques zones sontmaintenan t irriguées.L e climattypiquemen tméditerranée nes t 'semi-arid'ave cun e tendance 'sub-humid'. Audébu t l'étude étaitconcentré e spécifiquement suru n typed e paysage d'argiles miocène ondulées,don tun ecoup e (Fig. 10)transversal e arévél é que les horizons calciques suivent lerelie fe tson t latéralement continusbie n qu'ilspré ­ sententde s formesdifférente s quifusionnen tpe u àpeu . Ily a essentiellementdeu x typesd eprofils : 1. Les cîmese t lesbord sde splateau x ontu nso l superficielminc e sous lequels e trouveu nhorizo ncalciqu econtinu .L aparti e supérieure estdurcie ;ell e fusionne viaun e limite irregulieree nu nhorizo ncalciqu ediscontin u sous-jacent consistant ende sama sd echau x friabledan sd e l'argile miocène.L a zoned e transition entre l'horizon calciquecontin ue tdiscontin u estcaractéris é par des surfaces deglisse ­ mentqu is eprésenten t à lafoi sdan s l'argile et lachaux .De s nodules d'argile dont laparti e internees tno ncalcarifèr e existent à la foisdan s lachau x friable et dure. 2. Lessol sde sfond sde svallée sdiffèren tde s typesmentionné s ci-dessus enpré ­ senced'u n solsuperficie l colluvial épais ete n l'absence de durcissement dans la chaux.Le sautre sphénomène s (limite irrégulière inférieure,surface s de glissement etnodule sd'argile )son tégalemen tprésent s dans cesprofils . Des échantillonsde sdeu x typesd e solson tét érelevé spou r analyses etétude s micromorphologiques.Parallèlemen t auxanalyse sd eroutin e d'autres tests ontét é exécutés coimesuit .L aImit e de liquiditéd e lachau x aét édéterminée et savaleu r s'estavéré e trèsbasse .L adensit éd e lemass e aét édéterminée sur des échantillons inaltérés àl afoi sd echau xe td'argile ,alor s quepou r les échantillons d'argile on

194 a déterminél ecoefficien td'extensio n linéaire (COLE).D eplu spou r certains échantillons dechau xo na détermin é lacompositio nd'isotope s stablese t recherché laprésenc ed emicrofossiles .L erésulta td ecett edernièr e étude étaitnégatif .L e positionde shorizon scalcique s dans lepaysage ,le srésultat s desanalyse s et l'étuded e lamicromorphologi e montrentqu edan s leca sprésen tce shorizon s sontde s phénomènespédogénétiques . Iles tmontr équ e les solssuperficiel s et lesnodule s d'argile sont tous lesdeu xdérivé sd umatériau parenta lmiocèn e sous-jacent. Des essaisd e laboratoire ont étéeffectué s avecde s échantillons de chauxe t de nodulesd'argil e pour étudier lecomportemen td ece smatériau x entre euxdan sde s circonstances analogues àcelle sdan s leso le tpou rexplique r lesphénomène sob ­ servés. Dans cebu tde snodule sd'argile ,de spierre s etde s fragmentspétrocalcique s durs ont été enrobés dansd e lachau xfriable ,pui s alternativement séchéee thumidi ­ fiée. Lesrésultat s ontét éenregistré spa r stéréo-radiographie.Le sradiographie s ontmontr é que tous lesobjet smontaien t sousl'effe td e l'humidification etdescen ­ daient sous l'effetd uséchage .Dan su ncertai nnombr ed eca s lerésulta t se traduit parun emonté ede s objets.I la ét émontr équ e laforc eagissant eprovoquan tce s mouvements estdu e à lapressio nd e l'airemprisonn édan s lachau x cristalline sous l'effetd e l'humidification. Iles tclai rqu ele sobjet sd egrand e taillequell equ e soit leur constitution ontdavantag e tendanceà conserve r leurcomposant e ascendante que lesparticule s fines.Pa rconséquen t ils sedéplacen tver s lehau tpa rrappor t à lachau xfin e environante.

Sur labas ede sobservation s deterrai ne tle srésultat sde sessais ,l'expli ­ cationsuivant e aét édonné epou r lagenès ed e laconfiguratio nde shorizon sob ­ servés.Quan d de lachau x finecristallin e recouvred e l'argilequ igonfl ee tqu el e systèmees tsoumi s àl'effe td'humidificatio n etd e séchage,un etransitio nir ­ régulière sedévelopp e entre lesdeu xmatériau xqu ipeu têtr e interprétéecomm eu n microrelief gilgaî souterrain.E nséchan t ils eformer ade sfissure sdan s l'argile dans lesquelles s'écoulera lachau x sous l'effetd eréhumidification .C eprocessu s conduità l'introduction d'argile dans l'horizon calciquefriable ,puisqu e lachau x quis'écoul edan s lesfissure srésist e à lapressio nexercé epa r l'argilequ igonfle . L'argile formealor sde sprotubérance sdan s lachaux .Ce sprotubérance s ou 'piliers d'argile'cassen t enfragment splu spetit squ iun e foisprésent s sousform e isolée dans lachau x subissent l'influence duprocessu sd emonté erecré édan s l'essai.Le s nodulesd'argil e sontalor s transportésver s lehau tà traver s l'horizoncalciqu ee t expulsésver s lehau td esort e qu'ils fusionnentave c leso lsuperficiel .L erésulta t de ceprocessu s de substitutionmécaniqu e estu nmouvemen tdescendan td e l'horizon calciqueentie r (Fig.5 e t Fig.38) .C eprocessu ses t fossiledan s leshorizon s cal­ ciquesave cde spartie s supérieuresdurcie squ in e s'humidifient plusd ufai td e leur imperméabilité.Dan s leshorizon scalcique squ in'on tpa sdurci sl eprocessu srest e probablement actif.De sphénomène s semblableson tét éobservé s localementdan sde s horizons calciquesdan sd'autre s typesd epaysages .

19S Dansde scondition snaturelles ,u néquilibr es'établi tentr el'affaissemen t de l'horizoncalciqu ee t letranspor t simultanéver s lehau td ematéria ud uso lver s le solsuperficie l d'un côté (lesdeu xphénomène s étant liés)e tl'érosio nà laquelle ce solsuperficie l estsoumi sd'autr e part.De sperturbation sd e cetéquilibr epeuven t conduire àl'expositio n dece thorizo ndon t lerésulta t estu ndurcissemen t etun e fossilisationd u système entier. (Cettedernièr es'es tproduit e dans lesprofil s le longde sbord sd eplatea ud upaysag ed'argil e miocène.)Un eperturbatio nd e l'équi­ librepeu tauss iprovoque ru nchangemen t de '1'habitus'd e l'horizond e continuver s discontinu.S idan sso nmouvemen tver sl eba s l'horizonrencontr eu nmatéria uno n méteorisableo udifficilemen tméteorisable ,l'équilibr e estromp ue t l'érosionpro ­ voque l'exposition quies tsuivi epa r ledurcissement .De s exemplesd'horizon s cal- ciquesqu ion t 'couléà fond 'su r arkose ougrani ton tét é trouvésdan s larégion . Des 'dégâts' locauxd e l'horizoncalciqu edu s à l'incision deravine sd'érosio n ouà la-rencontred e 'dikes'o ud efilon sno nméteorisable sson t 'réparés'pa r les horizonspuisqu e lachau x estcapabl ed e subirun e translation latérale toute ns e déplaçantver s lebas . Descomparaison sd'estimation s devitesse sd'érosio n dans larégio nave c celles de lavitess ed emouvemen tdescendan td e l'horizoncalciqu emontren tqu e celles-ci sontd umêm eordr ed egrandeur . Iles tprobabl e que l'horizoncalciqu e enform e dis­ continuees tcapabl ed edéveloppe rde svitesse sd emouvemen tdescendan tbie nplu s grandes etains id e supporterun e érosionbeaucou pplu sforte .Dan su nmodèl e alter­ natif où l'abaissement de l'horizoncalciqu eétai tdu eentièremen t àu n lessivage (dissolution suivied'un ecristallisatio n àplu s grandeprofondeur )o na p u calculer que ledéplacemen td e l'horizoncalciqu en epouvai tpa sd u toutégale r lesvitesse s d'érosion estiméesdan s larégion .L emodèl ed edissolutio nes tdon crejet é comme causeprincipal ed'affaissemen t deshorizon scalcique sd e larégion . Comme l'horizoncalciqu epeu taccumule rd e lachau xà parti rde smatériau xqu'i l traverse^aucour sd e sonmouvemen tdescendant ,l'explicatio n deshorizon s calciques continues épaisses s'écarted e l'hypothèse àsavoi rqu e leurexistenc e acommenc éi l y alongtemp sà parti rd'horizon s beaucoupplu sminces .Pou r lagenès ed ece s 'inci­ pient calcichorizons 'u nnombr ed'option s sontdiscutées .L'explicatio n laplu spro ­ bable sur ledéveloppemen t est lasuivante .De scristau xd ecalcit equ i seformen tà chaquesaiso nsèch ecomm ede sefflorescence sdan s lesfissure sd esol strè sargileu x sontemporté sver s lefon dd ece s fissurespa r lespremière spluie sd e la saison humide suivante.Dilatatio ne tretrai td e l'argilee n interaction avec laliquefac ­ tiond e lachau x setradui tpa ru n remplacementprogressi fd e l'argilepa r lachaux , comme ila ét édiscut é sous laformatio nd u reliefd egilga î souterrain.Ainsi ,a u niveauo ù toutes lesfissure s se terminent,i l seform eu nhorizo ncalciqu e continu friableà parti rd'u nhorizo ndiscontinu .Ce thorizo n commence sonmouvemen tdescen ­ dantquan d lanapp ephréatiqu ebaiss edan s lespaysage s soumisà l'érosion. Pour la formationd'u n 'incipientcalci chorizon' ,d'autre s optionstelle squ e lesédimenta ­ tiongéogénétique ,l asubstitutio nd umatéria u duso lpa rd e lachau x cristallisante

196 etsubstitutio n chimiqued ematéria upa r lachau xson tconsidérée s commemoin spro ­ bablesdan s ce casparticulier . Leprocessu sd e substitutionmécaniqu edécri ta des implicationspou ru ncertai n nombred ediscipline s commesuit : 1. C'estu nfacteu r importantdan s lagenès ede spaysage sdan s lesquels leshorizon s calciques friableson tun e influenceaplanissant esu r lerelie fmai s lorsqu'ilsson t localementdurcis ,il sproduisen t l'effect contraire.L e 'caprockcaliche 'bie nconn u dans leLlan oEstacad od uTexa s etNe wMexic o composéd eplusieur scouche sd echau x friablee tdur epeu t êtreexpliqu écomm erésultan td eplusieur scycle s d'accumulation etd edégradation. 2. Leprocessu sdevrai t êtrepri sen considératio ne ninterprétan t lesdate sde s horizons calciquespa r leprocéd é duC14 .L'aptitud e deshorizon scalcique sd e 'placer'de sobjet sdérivé sd e formationssous-jacente sdan s leso lcouvran t l'horizon sansqu e cedernie r soità considére rcomm e 'perturbé',a un e importance quand ils'agi td edétermine r lesdate sbasée ssu rce sobjet s (archéologie). 3. Pour l'agriculture iles t importantd eréalise rqu e l'érosiondan sde spaysage s avecde shorizon scalcique sfriable sdevien ttrè snoci f siun ecertain evaleu r limite estdépassée .S i lavitess ed'érosio ndevien ts igrand equ e l'équilibre dans lepro ­ cessusd e substitutiones tperturbé ,i ls eprodui tun e expositionsuivi epa ru ndur ­ cissement irréversibledu chaux . 4. Leprocessu s doitêtr e incorporédan s laclassificatio nde s sols. Cettepublicatio ncompren d aussiun e étudebibliographiqu e sur leshorizon s cal­ ciquesqui ,en plu sd e lanomenclatur ed ed e lamicromorphologie ,contien tun ein ­ formationsu r lesséquence sde shorizons ,le scirconstance sdan s lesquelles ilss e produisente nrelatio nde s zones climatiques spécifiquesde saspect sgénétique se t agricoles.

197 List of tables and figures

Table1 Maintype so flim eaccumulation s 5 2 Maintype so fcalci chorizon si nFrenc han dAmerica nterminolog y 6 3 Climatologicaldat aBadajo z 27 4 Agroclimatologicaldat aBadajo z 3Ü 5 Yielddepressio ndu et omoistur edeficienc y 41 6 Sourceso finformatio n 43 7 Propertieso fsample sfro msof tcalci chorizon s '° 8 Correlationbetwee npropertie so flim esample s °3 9 Propertieso fcla ynodule s °4 10 Correlationbetwee npropertie so fcla ynodule s 85 11 Stable isotoperatio so flim esample s 86 12 Technicaldat ao nradiograph y 95 13 Summaryo fexperiment san dthei rresult s 98 14 Bulkdensit yo flim eo fExperimen tI I 108 15 Summaryo fpas tan dpresen terosio nrate s 128 16 Sedimentyiel destimate dfo rth eRi oGuadajir a ^"

Fig. 1 Locationma p 24 2 Waterbalanc ediagra m 26 3 Landtypeso fth esurve yare a 28 4 Airphotomosai c 28 5 Generalvie wo fRiol a1 profil e 47 6 Detailsfro mRiol a 1profil e 48 7 Generalvie wo fArroy o1 profil e 53 8 Detailsfro mArroy o1 profil e 53 9 Monolitho fProfil eP 3 57 10 Crosssectio nA E 60 11 Dissolutionphenomen a inth epetrocalci chorizo no fProfil eArroy o1 69 12 Diageneticoöid si nth epetrocalci chorizo no fProfil eArroy o1 69 13 Shearplan ei nsof tcalci chorizo no fProfil eArroy o1 71 14 Detailsfro mshea rplan eo fProfil eArroy o1 71 15 Uniformsilt-size dcalcit ecrystal sfro mProfil eArroy o1 80 16 Micritegrowth so ncalcit ecrystal sfro mProfil eArroy o1 80 17 Rectangularplexiglas scontaine ro fExperimen t Illb 92 18 Mock-upo fimag eformatio ndurin gradiograph y 93

198 Fig. 19 Dodged print ofX-ra y imageN r 577L 94 20aConstructio n ofth eprojecte d positiono f leadpelle t 97 20b Construction ofth eprojecte dpositio no fcla ynodul e 97 21aTh evertica lmovement s ofcla ynodul eo fExperimen t la 101 21bTh evertica lmovement s ofcla ynodule s and leadpellet s ofExperi ­ 102 ment la 22 Thevertica lmovement s of theobject s ofExperimen t IIdurin g 11 103 cycles 104 23 Themovement s ofth e objects ofExperimen t IIdurin g thefirs ttw o cycles 105 24 Trajectory of the centres ofgravit yo fcla ynodule s and leadpel ­ lets ofExperimen t II 106 25 Theheav e of thesurfac e ofth e limeof -Experimen t IIdurin gth e last four cycles 107 26 Sampling of thebul k density ofth e limea tth een do fExperimen t II 108 27 Detail of a fractured claynodul e inwhic hlim eha spenetrate d during Experiment II 110 28 Graph showing thevertica lmovement s ofth eobject s ofExperiment s Illbl and IIIb2 127 29 Dissolution ofCaCO ,b ywate ra tvariou s C02 pressures 127 30 Equivalent erosionrate swhic hca nb ematche db yth eliberatio no f non-calciticsolid s outo fcalci chorizon swhic hdissolv e 133 31 Relationbetwee n sedimentyiel d andcatchmen t size 139 32 Detail fromProfil eArroy o 1; cla ynodule shampere d inthei rupwar d movementb y thehardenin g ofth epetrocalci c horizon 139 33 Detail fromProfil eArroy o 1; lim efibr eintersectin g aban d ofcla y nodules 140 34 Claynodule s froma calci chorizo n inMiocen e clay 141 35 Abrupt smoothuppe rboundar y ofa sof tcalci chorizo n ina roa dcu t nearArroy o de San Servan 36 Detail from ProfileRiol a 1;slickenside s inth elim etha tpene - 145

trated thecrack s 146 37a Penetration oflim eint oa layeredMiocen edeposi talon g thecana l

37b"clnfror n Fig. 37ashowin g limetha tpenetrate d inth ecrack san d 146

the clayey strata . u7 ** • „F thP interaction ofsubterranea ngilga i 14/ 38 Schematic representation ofth euiteract-Lu u formation andcla ynodul e rise 39 Horizontal cuto fth e 'striped zone'o fProfil eArroy o1 40 Schematic representation ofsof tcalci chorizon s m landscapessub - ject tovariou s erosion cycles

199 Fig. 41 Detailo fmonolit hE11 ;cla ynodule s formth eparen tmateria l for 157 thesoi l 42 Soft calcichorizo nbypassin g adik e inschis t 159 43 Schematicrepresentatio no fth e stages inwhic h asof t calcichor - 160 izonbypasses ,deform s andexpulse s aninfille d erosion gully 44 Deformed infilled erosiongull y ina calci chorizo nnea rGuaren a 162 45 Stronglydeforme d remnanto fa nerosio ngull y ina calci chorizo n 163 nearGuaren a 46 Detail fromProfil eArroy o 1;cla ynodule shampere d inthei rupwar d 168 movementb y thehardenin go fth ecalci chorizo nfor mdiapiri cstruc ­ tures 47 Schematicpresentatio no fth evariou s options forth eformatio no f 170 a continuous incipient softcalci chorizo n

200 References

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