Radiolarians and Tethyan Radiolarites from Primary Production to Their Paleogeography

Chapter48

RADIOLARIANSAND TETHYANRADIOLARITES FROM PRIMARYPRODUCTION TO THEIR PALEOGEOGRAPHY

Patrick De Wever CNRSUM 1761,Laborûtoire de Géologie Musé m Natiowl d'Histoire Naturelle

FlançoisBaudin, JacquesAzéma, and Eric Fourcade CNRSUM 1761, Départementde CéoloqieSédimentairc UniveÆitéPierre et Marie Curie Park, France

I. INTRODUCTION

Paleogeographyis establishedusing mainly plate kinematicsand unfolding mountainbelts, but basinalpaleodepths are definedusing specific facies, among which radiolaritescan provide key information. The commoneqlJatioî rqdiolqrites = deep oceanic âasir is obviously too simple to be correct; and to infer from the geologicalmessage (e.g., radiolarites),the original,environmental, biological sig- nalrequires a goodknowledge of the successivefilters that have changed it andthe originatorsof thesesignals (e.9., the radiolarians). Thebiology of thegroup, as far asfeeding and ecology are concemed, must be takeninto account;in effort,the present-dayradiolarians hold the key to the past. The resultsof such studieshave made it possibleto documentprecisely paleo-

The Ocean Basinsanil Mareins, volume8: The TethysOcean, editedby A E. M. Naim ?t dl. Plenum Press.New York. 1995. Itttd'ltlhrrltl ltl|dkrlllrllrI thtrl(.k | )(, t\(,vo,{,t /r/ It||rthhr'lruN

l)irlhyrrcr'yon l!rhysMcs.z.ie ()l ccntralcapsulc in thc lilc ol radiolariansThe rrrr|,s.llrr.rrrri, r.csulr ol.rhis srr(ly ir rhcidcnri lllustrillcsthc ilttl)(nlirtlcc lhc Iicuti.rurrtl l.crrli.n.l upwcllirgs skclctondepends on the centralcapsule (Hollande and i, t'c.cc., arr'ingrhc M.*,;nl Wcstrcss thc li rn tion ol lhc siliccous c(fualiontkl/.)/.r.ik,.r is the only pafi of interestto the micro- ubulklun!uutt.i(ttt, hccausc: thcy cxisl ilt itn ufwclin! lirr,iunrct.1960). 1'his siliceousskeleton cnvilonntcnt.lhis vcrysinrpliliccl statcnrcntrùrst bc rnrtlificd by lukilgsome othcf pulconk)logist. pafantctcrs. with seawaterand suchas dissolution and diagcnesis, into accorttrf. The skeleton,included within the cytoplasm' is not in contact Radiolariansarc ntarine protozoarians ,l.hcy during the cell life Skeletal growth is disconttnuous; . witha siliccoustcsf. naveexlstc(l not cxposed to dissolution sinccthc Canrbrian and conrprise ,l.hcy altematewith stases'Periods of silica precipitationare a largenumber of specics.,r, olienare founrl phasesof rapid skeletogenesis In rocksothcrwisc unlirssilifèrous. physiology than on the environment(Matsuoka' 1992)' andtheir strutigraphic valuc is vcryhrgh, espc_ ttrnr" d.p.nà"nt on the cell ciallywhen they arc thc onlyfbssils present. They were disrcgardcd lbr stratigraphie purposesfbr a longtinrc, bur havebeen srudied thoroughly:;ince the 1980s.Thcir 0. BiologY uniqueassociation with ophiolites allowsdating of f"rloA, of active,oceanrc spreading(and crucial times of l, Reproduction conrinentaldrift). Becausc of thedifficulty rn extrac hng radiolariat'rom siliceous rocks, nev- the first zonâtionsof the Mesozoicwere pro Many aspectsof the reproductivecycle of radioladansrcmain unsolvedl posedonly duringlate l9?0s, first with partitionand sporogcncsis' theCretaceous, then lbr theJurassic, antl crthcless,two typesof multiplicationcan be recognized: laterfor the Triassic. interpretedby Kling (1971)as a f, tlimorphismobserved in someradiolarians is oi gcncritlionsin thc rclllo- rcxu l dimorphism that could result from an alternation (1977)'Inultifliclliu) l)y ductivecycle (as in foraminifera).Accortling to Hanson ll. THE SILICEOUS pLANKTON: in nsw cclls CYTOLOGY, BIOLOGY, flrsion may occurbefore the secretionof a new skclcton AND ECOLOGY OF RADIOLARIANS

2, Nutrililtt Â. Oeneral Châracteristics wlth prcy or llacliolariansarc floating predators They await ritndonl contact Itadiolariansbelong to the class in the environmentThe captureis by meansof filopodes' of Actinopotls. They arc characterizedby tlrc whh nutritivepanicles plcscnccof a capsularmembrane, which within the ectoplasm'They are omnivores' and feed on a wide physically separatescctoplasm from enckr 0tt(l prcy is ingested lllsrr. They incluclesymbiotic algae polycystines, organisms: silicoflagellates, tintinnids' other protozoans' in their cytoplasm. wrttr thcir Vût'icty ol tnicroscopic siliccousskeleton, are forms as large ând active as copepods' etc' the only radiolarianss./. preservcdu, iorrli, presenlly. tlirrtorirs.algac, bacteria' and possibly nllx)ngpolycystines, the Nassellarians (zooxanthellae) also contribute to râdiolarian nutrition Radio- are the mostcliversified, but Spumeltariuns iyrrrbiotic irlgac sccntto be for relatively long periods the most abundant(Lombari and Bowden, l9g2). Int'ilrn c,uttui,ting algal symbionts are able to exist thealgae' glllt,uttu|1,ur"nt, nutrition,as long aslight is availableto sustain "*tclnal seemsto be ancient' becausediver- ll. Cellutar Organization 1'h$ struiS inlcldcPcnrlcncewith the symbionts is the llty,,t nr.ii,,lariun*,tndphytoplankton, notably the acritarchs-dinoflagellates' A relationshipexists between the centraicapsule (basis lirr thc brokrgicirl lltttl('lltt(trlglnrrrl gcologictl time (Anderson,1983)' classilication)and the skeleton(basis of the paleoniologicalclassilication;. Thcl. lorc. thesctw(, typL,sol clussilicutionsirre not tulirlly iidcpcn.lcnt. ll, lleokrgy Iladiolar.iansarc all marine, and most Iivc irulutc,lintlivitluals, our sorrrr. s1'tccicsarc colonial.Sontc ol-these ". tltdiotarirtttsilrc prcsentin all the oceansand open seas' cobnies arc as big as 5 nr and includcnlrrrv lixr'lrtrivclytttittittc, spccintcnswithin a conrnton.gelatinous lnlss. F-oIi",rtate.l inttivi.lu ts, lhc cytrr plirsrrris suslaincd by thc skclctalcrcmcnrs. l. ll,'ttlirt' IltÈ.crilttitl eirpsrrlc.eonristing ol.encklplasnr (!tnd its inclusi{)ns), 'l'llcy to ltlachto floating ., nuctcusillrl |{ tt r | | r t I t t t I t t t t r tttr'||llr\ivf' lhrlllilll!|rl pllllisltIs irtcablc r.. irx.l)rir\r,rs lIllrtc(l hy rlrc cirpsuliu nrcnrbranc.An inclividualtlrirt l]irs hr\l ('vrfytl',1 lntl llr(.ccnlritl ||h|e{lr|||||x'i||||||||||||1.||!||lt||||x.|||||l|||vv{,||iC||||l|||v(|||(.||ls(|.1()|l|2()()to350m cir'srrlcis itblclo rcgcncril(call thc Inissi'l.l tlx'(olltftll trl wllielt vrllicswilh l)itrts.lllt\ f iIlrrrlk'r tttrlt lrr' tr'lrrlr'rllrt I'tl' tlltllol{'N' ,l,]::']':|''',.'l|]/t|n/lIl'.|l'1|l,|t{|t('|||ll|ll(1l|n'|ll|f|l|(.l|!nh|w'|s([l|di'i||iiU|sw||i.|i'(||! llll(l(lllllllrrl llellv- lnlrtlttrtl tcl[t||rlhrlll('(t,|llxlllrlhrltlltlllllrfl'llll llllrrl'rhVlllll('ll( rll\rtrttfl{'lnlfrl lrrfllvlloll (t't l, Urelttrl rlerteltt | vtlllll l lllrll[ll t'ltlr'lllr ^LllvÈ, (lccpelwlttcrs (luring storllN), l{&lioluli rtscxisl itt ll ;r'crictltrltty ttccntts, liltrtt ltolcs lo thccqtlltl(,t, httl lhcit' 2. Iltulioluriun l)ixtributiotr lhundttnccvutics, ln gcncrttl,rtuliolttlitrrt rlislribuliott (lhcys lhc sllnlclilws it$th(tsc C()nlrollingplankttltt: wittct tltllstics,clirnrllc, lItitudc' tlcpth' hydrrtlogiccttnditittns As fbr other planktonic organisms,radiolarians occur in profusion whcre nutri (0,g,, tcrnpcraturc)and thc abundanccol llutricnts(trxnc than thc uvailabilityol' ment ls abundant. Becauseof their symbiosis with algae, radiolarians are mosr Therelbre,thc long-stândingclaim ol a connectionwith volcanistrt abundant lllicu in watcr). near the lower limit of the photic zone, circa 50_200 m (Fig. l). Radio h clroneous. larianslive in the upper part of the water column. They do not require a-deepocean, Radiolariansaccumulate in abundancein sedimentswhere productivity is hiSh but are found in deep-watersediments because they are able tà reach significant the suprajecentwater column, in divergent-waterzones (where cold, nutricnt-rich depthsafter death. In Wutcrascends into the photic zone), such as in pedequatorialzones, polar belts, and some continental margins where upwelling is active Quantityper m3ol waterfiftered In rec€nt sediments(Miocene-Present), the radiolarian abundanceat a sitc is 5000 10(m10000 )^ oonnectedeither to high- or low-standsof sea level (e.g., South Atlantic coast ol1 Afiica, WalvisRidge; Diester-Haass et al.,1992:Hay and Brock, 1992).Hcncc' heightof the sealevel is important only in the modifications it induc€sin currcnl the variations (silica abundanceversus nonabundance,high versus low scll associatedwith the upwetling. Moreover, radiolarian location can migratc with timel therefore, the local sedimentaryrecord also can migratc understandthis generaltrend, it is necessaryto take global phenomenainto In brief, sealevel \ariation and silica abundanceprobably are connected this abundance,but the prime factor is the existenceor absenceof upwelling Radiolarian associationsshow a latitudinal distribution. It also is possible to 7 tivtng speclmens surfacefrom subsurfaceassemblages. In sedimentsbelow upwellings (e.g,, NNI Discordedsketetons a mixture of fauna systematically occurs the cold- and warm-water offPeru. where Arctic watersare mixed with tropical ones;De Weveret cl., 995), or as surface and subsurfacewaters mix off Somalia (CatJletet al., 1992). in work on o the chancesof depicting tropical Tèthyan versus boreal fauna from radiolaritesare almost null, becauseradiolarite facies result from

SILICEOUS SDDIMENTS: TAPHONOMY OF RADIOLARIANS

Fourmajor processes control the evolutionof a biogenicooze from its initial to its present state: (l) supply of biogenic material, (2) dissolution ol material during settling, (3) dilution within the sedimentby other comPonents biogenic or not), and (4) diagenetic hansformation of the initial pro-

Fig. L An exampl€of radiolarian death,an individualtest is at leastpartially dissolved during the settline âbundânceversus depth in the equatoriâlpacific (accordingt0 After Petrushevskaya,I 971 Thenumber ). of radiolariaoccurring at thissite can differ considerably from othcr subsequentlywhile it lies on the bottom and, finally, within the sediment. places,but the curveshape remains similar (e.g.. Caseyetal.,1979; TâIahashi.lggl). settling, testsare laterally disPlacedby currents.Popova (1986) calculatesa lhtrl(k lh W(,v0rdr at. Rrdiolâri1ùrs l|nd ltthlltl R||dli)hrltts 213

possiblc hofizontrldisplilccnrcnt in r'cc lcstsofas muchas 2500 km in rnc wcstern Pacific. However,observations are opposcdto calculations.Most radrolarianset_ tlings occur in fecal pellets (with other consequencesfor dissolution);theretore, the horizontal displâcement is restricted. Also, currents have different dlrections al different depths.The horizontal displacementsmay, therefore,be almost neglected. but it remains true that buried radiolarians assemblages(taphocenosis) are sym- migies, not thanatocenosis,* and absolutelynot paleobiocenosis. Chemical and physical characteristicsof tests vary according to taxa (King, E 19'77),and so does the dissolution affecting them; hence, a species_selectiveeffecr .c exists (Swanbergand Bjorklund, 1992). ,'positive 230 Sedimentspreserve species with a preservationpotential,, and aver_ age the backgroundvariations, such as seasonalvariations. Robustforms and thosc of spec ies of blooms are overrepresentedin sedimentswhen comparedto the common plank_ ton (Swanberg and Bjprklund, 1992). The number of individuals and speciesarc lessimportant in sediments(and a/ortiori in the rock) than in the caseofplankton, a difference that is more important when planktonic individuals are not abundant (Fig. 2). On each side of the equator,the ratio of individuals in plankton to those in sediment pacific, decreasesrapidly. In the Central the loss is 257o at the equator. where plankton ggEo is abundant; but it represents rrcar 25. latitude, where thc plankton is slightly lessabundant (Renz, 1976).This drasticdiminurion resultsfron) a6 dissolution Ê1? Et6 E$ E11Eo E? Ëa Ez E1 sltos during their fall in the water column. Within continental margin sedi 82 Erg ments, radiolariansgenerally are scarceor absent,dituted by an important detrital input that, moreover,acts as a silica pump. On the continentalplatform (e.g., off thc United States;Kling, 1978), radiolariansexist in surface sediments,but disappear with depth. On the contrary theseorganisms may be abundantin relatively shallow basinsclose to a shoreline, where chemical conditions that favor their preservarxrn 8ô Numberof species prevail and detrital input is low (e.g.. the SantaBarbara Basin of Califàrma, where anaerobic, laminateddeposits rich in radiolariansand other microfossils are deoos / ràô6 ited at a depth less than 500 m; Kling, 1979). Other examplesare found in Nrrr ?s 3??7 8Jl wegian fjords (Swanbergand Bj6rklund, 1992). e 2'r 2s $l \33 Abundant radioladansand foraminifers frequently sharethe samegeographical water domains, but in sediments there may be a great contrast where siliccous (a) I'iB. 2. I)istribution of râdiolariansin the equatorialPacific (adaptedfrom Renz' 1976): plankton' fossils may be preserved,and calcareousones are not. Such a contrast is excrrr (l lo 300 watcr depth. The upper scalerepresents the latitudes (bart; the studied sites are located by plified in the sedimentsof 'r the Atlantic when comparedto those of the pacilic arrrl |'(,i ls'lhcsitcsâlsoarclocatedonthelowerscâle,whercthenumberscorrespondtothenumberof Indian (Figs. rlr.ic\ ((livclsity)i(b)su itccscdiments (same sites). The numberofspeciesisgiven inthe lowerpart of oceans 3,4). In the latter, the deep waters are silica_richand carhorl tht, tlre (tirocl cou]plriron ofboih curves is difficult becauseof different unit systems, ate-poor(estuarine-type, of authors).Conversely, the Atlantic deep Ii(.t$tc. wittcrs lirv(n.llx. tlr lrùltirnr\ ^ltlxnrfillol rrxrxirrrttttts rrn(l lhc ,lcncrrt shapeof thc curves can be used- The tr€nds are similar' but preservationof calcareous organismsthat arc citrb(nrittc_rich(thc anticstuitrincol tl[.tf t|'l| \hilt(ll l)('||l1'll|ti|t(l(.ithf(lUsuroul(lhclheinflucnceoflhetùrbulentcurrentsinthevicinity lagoonaltype of Bcrgcr, t970). 1 N ll',th lM\ rlr'rw tr r[\'tr'rl\r' In nhlrrt(hrtrtcon cilch sidc of the equâtor, ând the abundancein 'r! t$rlt ||. t rl,r r,,t,.rrrol|r vr,lv xrrr'|lrl,kllv thnr lh(t io phnkltnl.'[hc planktonicsignal is transmittedbut * l}c lcfr "thiut:tt([0n(' Iily ft which(lcllLlrn!I l Wt' prrli r lo r(.stri(Ithi\r.(r.|t lItrn,,,( tl'1,tr,,.\tlhrttrÊrF,rtt!ttr{lltllvtrr}trrgr,tlrr,rrarrar

.re, ilF* Solutlonrate 14 '!6 18

fenpetaturc'C ôlo1020 1,,,, l trl 1,," 1,,',1,'., ""rr "'l" Saturationrcte 10 1ô 20 2ô 30

250 500 .10 f1 l- llO-20 f l2O-4O f-- 40-60 r.Tt , 60 umol/l 750 1000 B 9l s * r-3

I Rdte of dissolved sllicd

T--] .5 li-...l 5 10 i:lrrl - 10 - 50 lE l , SO % v\^.\.^/v Costal l?.t- upwe ing Fig- 3. Relationships betweenplanktonic silica and silica content in seafloorsediments (adapte{:i fiorn Lisitzin' 1985):(a) disrriburion ofdissolvedsirica in theuppermosr r00 m ofthe sealnorttrem winter) i. pg si at l-r; (b) amorphoussirica (chiefly diatoms, frustures and radiolarianskeretons; rn surtacr, sedimentsin percentof dry sediment(in carbonate_freesediment).

lutionrate A. Dissolution I of Tests 1æO sil ice r-r

Dissolutionsusceptibility depends on the particlesize, temperature, pressure, protective the "vamish"coating the tests(organic or adsorbedions), the degreeol. crystallogrâphic Tenpercturc order, etc. The relativeorder of increasingdissolutlon suscep_ tibility for siliceousorganisms is as follows: sponges,spicules, radiolarians, sil_ icoflâgellâtes, anddiatoms. In zonesof averageproductivity, one_third to one_hall. 5000 of theprimary, biogenic sirica produced reaches thebottom, while this ratio rs uD to in the seawatercolumn (after Hurd' 1972) two-thirds Fig. 4. Solutionprofile of biogenicsilica versus depth in zonesof high productivity.At the water-sedimentinterface, the siiicr dissolution is aboutthree times greater than in sediments.The global balance is that 211 l'rlrhk l)c Wcvrr rl {/. ll0rll{rlîrlrrll.rrtttd l(lhrrrll llllllhllll lll'r

lcss than l% ol thc silica lixcd by pllnktorrieolgurrisnts in surlirccwiltcrs is Drc servedwithin the geologicalrccord.

L Dissolution in the lVater Column

Dissolution has a selectiveeffect in different taxonomic groups (Riedel, l95l{; Renz, 1976). The shell-wall ultrastructure is made of granules (Lawson e/ a/., sr c6 1978), and their distdbution and densiry within the skeletonmay profoundly influ m enceskeletal porosity, clêv resistanceto dissolution,and diagenetictransformatlons. Th( LrrHoLoGy I detailed chemical composition may differ in different species(King, tg75, lgjj). m porosrty The physical and chemical characteristicsalso differ for difierent taxa. The mosl delicate structuresare dissolved first. It is trivial to say, therefore, that the thinnOf shells will be dissolved first. The first parts to dissolve are the last that werc precipitated(Bj6rklund and Goll, 1986). The average residencetime of a free radiolarianin the zone ofbiologic produc- LITHOLOGY COIIPOSITION tion (the upper 200 m of the water column) is from two weeks to one and one-hâll months (Takahashi, 1983). The duration of the settling process for a free tesl requires from two weeks to 14 months PËæ in a water column of 5000 m (Takahashi. F_I 1981). Laboratory expedmentshave shown (Johnson, 1974) that important dissolu F- l*il tlon occurs after a few hours. Forty-five weight percent of a test is dissolvc(l between0 (Wollast, and 1000m 1974).The dissolutionof a free test may occur rn il AÊDIIETT ROCr few hours to a few days (Vinogradov and Tsitlin, l9g3). OPAL A OPAL GT OUARlZ During settling, radiolarian testsmay be protectedftom dissolution ii they JIc duringdiaBenesis ln embeddedin fecal pelletsor organic aggregates(Casey 5, l,itholoByrrodiflcation and components parting in a siliceoussediment et c/. , 1979).This samerypc strongporosry |icdirrrcrl(lcfi part).the lithology is subhomogeneous-During diâgenesis' one nores a ol' sedimentationalso is invoked for diatoms (Schrader, l97l). The observation more silica-rich places The ir nsc(nrcchanical and chemical compâctions)and silicâ migràtion to lhe vcry important, in slighdy more because,at least in some basins, most of the sedimentationoccurr iiliccoùs parls arc transfbrmedin priority; therefore,the silica is fixed CoNersely' ofclays' andsilica migrates towards lh t way (e.g., the SantaBarbara Basin; Dunbar and Berger, lggl; Bermudcs: cy lcvols.thc kirrcticsof transformationsis diminished because in silica;clâycy layers are still impoverishedin.silica. Diagenesis.enhanced original Asperet al., 1992).According to Banett (1982), the settling velocity for ri'richcdflaccs a free rcst in coDrposition.The finâl resultis a duâlfacies consisting of chen/shales' ol averagesize (50 to 250 pm diameter)ranges from 15 to g50 miday in a fluitl ol up to 20Eoclay content.According to Takahashi( lgg l ), this settling vades from l(l to 400 m/day. For Vinogradov and Tsitlin (1983), the settling velocity for a rree lcsl lh rr ol tlissolution. When bioproductivity is high, the first dissolvedorganisms is estimatedat about 100 m/day, while it reaches1000 m/day when it is embctklt.rl lhc wltcr in silica; consequently,this water becomesless effective against is within fecal pellets. tcsts. llcsitlcs this effect, when productivity is high, the sedimentationrate at The rate of silica dissolution is higher in surface waters (in the upper 5(X)trr , urxlskclclons âre buried rapidly; hence, they are less subject to dissolution 1000 m; Fig. 5) and does nor increasewirh deprh (Leinen, 1979; Hurd antj lirl wrrtcr so(lin)cntintcrface. This explainswhy skeletonsarc betterpreseryed and ahashi,1981; Tàkahashi, 1983); contrary to what is known fbr carbonatcs.rncrc r\ higlr prrxluctivity zoncsand why variâtionsof quantity betweenplankton no silicacompensation depth. As thesefew remarksclc rly show,thc chancc litt rl rïcor(l is inlplilicd (llcnz, 1976). tiee testwill be depositedis small, but it (locs|()t clrrrrrpcgrcnlly with (lcuh.

2. Disx tttionin tht,Sadint'ut llhrgr,rtt,ttlx ('..lcr (1977, ,lltr, l()7ll)w.s tlr' llrhr ixrllxx l, rll*w llltl r(t'urr,rff .r (|rr.rl ,ll,r!r,rr,.tt,ltl',lrx! t|l rllil $rlÊ trrttrlrir' irrllIc r,r'tlglctllly by thc con]posl- pc lurrcerrl hiol,lt'rri(silir'rr qr,rllrrrr, g r lr *{r l $li tgtllh l hlrlrrrllrtr vlty vrl rrr rllh rr \, r rll'rllr'rrllc, ttl lllllÈl lrl lll{'lxrhlr,t'rlitttt'ttl tttxl hy its pcrrrlcbility 27tl ltûtrlck l)0 W€vcret û1. Rtdh rrrlr||r' nd 'ltlhyrrrrllrr(lhtlrrrlkr 1. Transforme on oJ thc Siliut phutes Porosity (%) Biogenic silica is amorphour lAmo,el;us"0,,,;";, ;;î;$,:ïi;;:ï:i,iJ I îïj;Jlil."ll,ïi.'liil fi:Ï ilî:li'Ëiil+',;.:;o;3.'1:* ;;;;;; ;o;;i"Jl,'I", r"p,,pr,".",1, .';.#; ;iË'ii,i1ïfl1,ti:Hij;j",JïH"J: 70 % sllical - I lï*,,:""r0 ;"ffi I ,i:fli:ilJ":[i:H':Ëi1"ffi 40 % silica--'-l I ii.;;,il,,i ::l'ïiï :l'-"""''s's'nni',,"î',liuËiïun*.,0*" i:j::,:j,ii:"anosrlrca concentration. :i:Jffl,:îïl"ïffîï:fr:jilf Thesolubility ot.rlfl"" utroi. r"".,,r."îïi" sotidphase and. for very smalt crysrais. " "ryon,r". :ll.^ "_1," ,.;;*. ;;;..a"anz is rhe tempera'|ureand ;il'::riï:jl"ri,î iï;:ïffi: "{"ce surraceprissure, thus. Transformation sotubility 1982).A decrease opal A-opâl cT ofradiolarianstests with;t^Î::i-": 1n9t' Iastner, in ractrhat the ageprobabrv isdue to rhe 'r;;;;l; ;:i ililii::f if"georogicar diasene'[icphases (Murara and :îï#:î:lI rn:T::i'"'': older or deepersediments' and porcelanites prevail"J:i!;ï:[J:l in tr;"t";;; r;;t;;;Prwdr In sedimentary duariry is *" .","î' rocks, o"ili,liiriji"i,î:,.d:radiolr j.1ï#H tn^ ,: because"iî'practicalty u"o,r.*n,*"o"r.o-i"rîo,îT"n ïï:Jîî occ(,ntel.'.r].ï:rT.more and o*o.,,"0, morediflerentiated with rime r figr- o rusrraredby Z. OLiîi, modrficationis rhediatomires of theMonterey eàÀîir* verystishrty iô"i.rT#r, whichare compa.t"a.,ne.etr,ey a.e ;il.:;ï,;rratrted, (D rD.'rrurcd:::j:::::: l*and wetr bur differenfiated(1,::L ;hi," r)ccur.rcd(carison ;ô;il;"i,ur"n"r,, nu. andDouglas, ":oouring rb(,rrr0 k) lgll) o"ri".rol,îi ui,ca migrates r00cm during ,n" ,,î:^.1Tr:, #;;:i ltoun(l l0 cm during il Ë Ë,r,una ueuin rheopal CT to_quartzkansfo;mution -'i' 1dJu, tflt;. Siti"u r'- :i',i:';'"i,'iiÏifl.ï,].,Xl.llf:tt''e'"""i'"'",,,.',ii,l'i"l-.,., rr*, Transformation rpove shed original differences opal CT - quartz consi

2. Por

Silica phasetransformations ï:î:ll,,ï,,aif,lrnlli,:":"..ffiar :l::,ïi::îa,:"î.îïli_iit" il,;;ïi,,;;;ilii,i:"1',;,ï.,i:ïll::',,îîi.:,ïJÏ ::::::occlcilscl:(voluntc)lt*1.'. ïïiiJ; at mocler- coltcspo|dst() n rcductron ltll t, s,lrr,rrrlttr rlrt lt Iltt( t tin.(liulornilccous rocks ând diagen€tic equivalenh in ortlyont.rlirrtcttni(nl: lhc lxrroilty tickltcsri. tk' lrrrrt,rlrlr,|lthl tllrirrrt ,lllll ltltltllll) Io itrrliviLltrlrlllrycrr. în llb|'|lplrcductioÛ in porosilyis âssociated lrânsforma- 'l*:i*iïiiii,,lliiïlï:ijliïlltï1,l.îlîilïï:,1;:ïi,ïuii,ï|l,lt,j'Tl,,iÏ,,I;i[it;,tJi,li,j,iïi,i,]iï:tvlthol|| lr îl lhr lwrrllll Illllq0tr rrlirllllrllarnr\'lxll sliSlltly(litlcrcnl lcnlpcfitturcs fi)r thc xt sll rrl rllll$lt]rll| r'rrrlrtrll|nr r(ll lr',lllllll n torrtptrttrtivtlyhl\rll(l olpo()rily rcduction llrttr 'onc t ltr,rLdi, r, lullIJ

,d-e Itororllv lhtrorit' llllrllll l)hlgttl$ihi

I\n0|'rly l)croIllnr(ll('ll lltcl('l ("1' 1() Olnrl oprl ( l' Ollrl-A |o Opat Quartz ^ ^ u0 x5.0 .p-oË: x 3.8 '70 28 x l.l x3.2 >

Duration of PhaseTransformations transformations' ln addition to pressureand temperature,time favorsboth opal (Paleozoic and Mesozoic) and , cherts are more prevalent in older sediments UTAL the OPAL CT OUAFTZ in mgrerecent (Cenozoic). Based on resultsfrom 37 DSDPlegs' opal-CTis estimatedto occurat temperaturesof25-50" iliJ;,-:'|j""]ï:il.iïï:îfi1';1"#'.::Iï:'lon ors'lriceous\edimen6 dunns rhe opai A toq,,,,,, rnof opal-Ato Êrom moderatesedimentation rates' and 5-10 Ma in in rhechert, 85%in theinrtial sediment to almosro'|i takes 20 Ma in areasof low to (;') #{rrdrmmjshes to quartz transtor- -ù;.;;;;;; of high sedimentationrates (Kastner, l98l) The opal-CT Keene' 1975 Tàble I provides n ocÀrs within 40-50 Ma (basedon resultsfrom 32 DSDP legs; ' some numbersfo r a range of original silica content and the conr of average,oceanic heat flow and.moderate sponding decompactionfactors. ; Fig. 9) when depositedin areas mdioladtes were depositedprob- From porosity variations, o"nà,ion ru,"r. The heat flow where Tethyan . . a compacdonof 60gohasbeen ricb proposedfbr siticrl (and the oceaniccrust young)' but the sedimentationrate was low to sedimentsin Califomia (Isaacs, r-ssrf. e*",Iy was high u;."_" of Late Jurassic silica phases probably occurred from the study of a silicified woo ",,iiiirvr, o."o"r*, :rate. ihe transformation just the matn 50 and 100 Ma later (Late Cretaceousto Paleogene), before d;-'';;1*il';Tffi::i,:,ff occurs fust in #ï:,::lïJi,H"1fl,,,1ï:îi1îï: phasesthat folded them. The mineralogical ftansformation in shales,where the diffusion rate is lower (see above) Themean silica content ofradiolarites g5Zo beds and then liesbetween and95% (Steinberg (/ limestonesprobably is the at., 1983;Gursky and îhe oriein of the radiolarian"nests" known in some Schmidt_Effins,1983); the."f".", ;" of 7o-807o* ;;;;;;rage porosiry pellet accumulationon the ocean floor' anda final of t-4qo can^.beâccepted. t of fecal Applyin; it that affecta radioladantest (disso- abovegives ?s : 5.02. (with = pt'= "-[rîrity In conclusion,all the possiblemodifications A Bo%.. t%:):;;i;:':-3ii "tung.,, diagenesis'death) Pr :4%) 1w,t r. in the water column, Proximity to the sedimentinterface' for radiolarites(i = mrcknessof sediment; : 10Ea,=_original z, rhicknessof roctil for a skeletonto be preservedare nearly zero' espe- P. porosity;p, : finai porosrty.). so great that the chances the test from the rock in the laboratory with hydro- ro oemore precise, we takeinl Ly when the etching to free pindos- say that all radiolarian skeletonsobserved by o,onosridiil;ô;ï;:::ïH iiJl"* .",,:I acid is added. ihur, on" can For the chertbeds (wirh :i'f ï.TîîH, :ï micropaleontologistare miracles! 95ZoSiO". 4 cm thick),,h" d""";;;i;;;ior rl":n"t:: is s andl (402oof biogenicSiOr, o.s f:: c_ thick).The originalbeddrng was 4/0.5, but 20l1. This nor altemationis comparableto the diatomites Formation of the Montercv WITHIN THE GEOLOGICAL SERIDS t,.it"ro.-uiion (c",'t,ofo,ig;;"'t;;. i;;r;ï;^ RADIOLARIANS ffi;i::lijifrJn:î#i:;l3,l,ili;;il:; with millime- Radiolaritess.s. (the interbeddingof centimeter-thickchert beds +Notethât elsewhere. ftequent Samrheinand Fausèr (1993) beds), becauseof their bathymetric significance and their radiolarian havemeasured a porositvof 75Eato shale . mudsin Eastuo";;.;;;il-";:-t 85Eat:nl reconstruc- .y""1:g-l-1lï,.r:1, ation with ophiolites, are of great importancefor paleogeographic .:,hod of catcutarion,Samthein and Faugères are' r.âsrhLentratAdanlic. 0993) propos€da radiolarianmud ol dating tÀe oceanic crust and proposing geodynamicsmodels- with a final rhicknessone-tourth to one,fifth for -They of its initial thickness.The fact(x.s formation' subsidence'and indeed, very good markers for studying ocean margin q) È40 o ÀF ot ^ù o, E () \:r.s..o)."u *È -60 o$ot\--- -ëË 80 3000

Pù Distancefrom subductionzone at 5 cm,/yr convergencerate v9 t;::':'"imentation ;:i l; diâsramrrom initiar deposirion roincorpinr EÉ "Iiiffffi;'î;,i:'iiy.""oiirffi ;.; abovef31*i1;a "1i ïï:ï":i.":*[,'"i1"*"ffi:"#U":,Sfl:; thecatcium carbonak comDensarion o"p,t l,f:*ilill ô.; subsided 6.o,oo ,o-iï ni"l. iiii ,rà'j',"" *"r"* below rhe CCD, and ontv ;iliceo ,,n, ï-Y::tn"..:oJo":.-iffi;','i:iilïi"i!.;'ii:.;::,,:mliiï*,î,iîî;,î,i.iilï In sedlmenlationrate. Distancefrom a mid tn"î1 a uniformicmlvr rate Aller 60Ma' it mou.. in,o,h" u"".",iollïi:10j" lt' ".tt"ltg sprearlrrtl ,"ai..n,rr*"ry',oi"i"ffi;,;;il:i:i"'.",i;iïlliT,îiililiîî""iîîhl'âîlil"y:lllli Ëz resurtsrû surfâceerosion and decreasineo_"-o]l..ioil" ilil;;ïil:ï;nary eslimâtedusing the low heatflow valueslssociatea prisnr*p *ittr srrUauciionzone.._a. ,"r"ii,"r,f," erosronalter 100Mâ, rheremperature *,,f sr:lrts.rode"r"-u.". fU" " "prif, È!! _p-tonglJ f.ioà oïià bu.,u,", f,irf, ::iT:fii"Jïli:i;i,:i:'r',iï:tiriî*" sorurionand o'"t derivedi,v -"i-"ïio"*,'r."ins However, directdaring was not possibleunril recenrly, sedrmentsl]Lll1i1 do becausethcsc notcontain the usual fossils useà in stratig.upty (io-.-u_iilfa.r, fossils),and until nunn,, recently,dates were dispersed through"ouirÉà,"iJ"îU,0,,"g."0,l, o\ gl periods A. Favorable for RadiolariteDeposition

From recent oceanic sedimentsand sedimentspreserved in folded mountairl ranges,it is apparentthat siliceoussedimentation occurreOat-.*îrriT*"n.. ," ,n. folded rangesall over the world, Jurasslc radiolaritescertainly are the best known [|lo tstr|yltl ll$l|ll||l||i||el 'l'he trppct .ltttrtssiewits u ltctirxl lirvolrrhlrto lrrdiolulilicsclirrrcrrtuliç1, l,lrr. abundancc lifllrIlioI ((lirtort|lt(.N)urxl in lhu ljitxrli (MirrcuncMcdilcrrancu tliol p'csc'vctrirr r'.cks thilt pcritxr h.s rcd ro scvcrirl hypotheses. 'adiora'ians 'r' ) unrl.lLrnnsic lurliolrrlilcs ol lhc Alps and Apcnnincs,thc contributionof The most convincingrinks ratliorarianrrloonrs to inlpo ant nutricnrs inputs as the riliccouscontcnt is ol lhc sut|rcor(lcr ol nl gnitudc.Below the activeupwelling resultof upweling. such ûn intcrprcliltionnrakcs scnsc. fbr radi. larianswere probably Sonralia,a scdinrcnlllior)ultc ol tl.5 m/Ma (Cauletcr al., 1988,1992) is found. theonly organismsable to usesilica at thattimc; diatoms havc existed in abundance scdimqntsshow washing nd rcworking indexesconnected to currents(Caulel only since the Upper Cretaceous(Burckle, 1978).This intcr, pretaton, nevertheless, tl,,1992\. Exactlythcs mc phcnomenaand comparable mtes (I1.5 m/Ma) were may be inadequate,because radiolarians behave as othcr planktonic organisms, lirr radiolarianmuds in theeastem Atlantic (Samthein and Faugères, 1993), but where the most impofiant factor is the abundanceof nutrienr. not the abundanceof ()l l)crulhe recentsedimentation rate is around100 miMa (Schrader.1992). silica. A scenarioin which transgressionsare assocratedwith a significant input of organic matter and a radiolarian bloom has been proposedby Steinberg(1981) for Ori Rinal SedimentationRate : Precision? the main epochsof silica deposition. It should be noted.thatil reducing environment favors the nondissolutionof silica. The combinatronof sev_ Comparing radiolaritesand modem sediments,there are various uncartainties eral factors probable, is such as upwelling activity bringing nutrients rn abundancc consider: thickness, decompaction, age assignment, and chronostratigraphic and a changein the carbonatecompensation depth (CCD) resulting from a specral Iactors. Their cumulative effects infoduce significant vadations in the esti- sea level, etc. In the Atlantic ofi of South Africa, most of the silica production The following example is applied to the radiolarites depositedduring the occurredduring glacial or interglacialperiods (Diester_Haassei a/., 1990; Hay aml Malm, a paleontologically establishedage. The presentthickness is 60 m. Brock, 1992). Hence, in older sediments,no unequivocalrelation can be consid_ ,lJ. The numbersare realistic, they are thoseapplied to all Tethyanradiolarites. ered, but the most important is strong upwelling activity. In sedimentaryrocks, n dill'erencesbetween the diverse,chronoskatigraphic scales for that periodare high concentration of silica now is admitted as a traduction of very fertile surfacc Hinte(1976)-20 Ma; Harlandet al. (1982)-25 Ma; Odin(1982)-28 Ma; waters, and almost always is connectedwith the most active part of upwelling ûndGradstein (1985)-25 Ma; Westermann(1984)-24 Ma; Odin andOdin (Thiede and Jûnger, 1992; Ganison. 1992). 990)- l9 Ma. Thesenumbers provide the two possiblelimits for the durationofthe (if we supposethe initial rimespan is well established)-19and28 Ma (29ïa). B. Sedimentation Rates of Radiolarites Thus, the sedimentationrates would represent60 m/ 19 Ma : 3. I m/Ma for tninimal duration, and 60 m/28 Ma = 2.2 m/Ma for the maximal one. The l. Rate Evaluation sedimentationrate has to be consideredwith a factor of 3.2 to 5 (to The evaluation for the silica content). Hence, the above difference becomesgreater (see of sedimentarionrate must be precededby the direct dating ol. the beginning II A). and end of a radiolarite episode;hence, sedimentation rate evaluati.n is dependentupon Onc could as well use the range provided by one of the authors with the the ability to date radiolaria. The averagesedimentation rate ol radiolarites is between uncertainties.For examole. if we consider the ranee of the Malm as 2 and l0 m/Ma, but it is quite difficult to comDarerarcs proposedby several by Odin(1994), one obtains 154 :! 5 to 135a 5, thatis to sayfrom 159to authors,because the radiochronologicalscale used for carcuh- with minimumduration representing 9 to 29 Ma. tions generally is unknown. In generar, the rate I t() 140to 130 maximumand of iadiolarite accumulation is : comparableto those c lcufationof sedimentationrates would. therefore, be 60/9 6.66 and6O129 in nutrient-rich, present_dayoceans (Kling, 1978; De Wevc| and Origlia-Devos, 1982). 2,1, (s!'cTable Il B).

TABLE IIA 2. Comparison with Modern Sediments SedimentationRates According to ahe DecompactionFactors Using Differenl To comparesedimentary rates in the Mesozoicwith modern sedimenrs,one nirs Scalesfor the Malm to usea correction factor tied to the loss ofporosity, which is imponant in silica_riclr rocks (lsaacs,l98l; Isaacs Sedimentâtionrate et al., l9g3; Fig. 7). When sedimentatiol I)ccompaclion rates, the sediment has "o-pu.ing to be comparable(before thcir conrparison);they need t{r 3. I rn/Ma 2.2 lx,lll{a havcthc santccomponents present in thc s nlc pt1)p(n,ti(nrs.inrlccd, in rnecontcll ].2 9.9 nVM.r 'l porilryscdirrrcnts trr'thc 'l],JMa cuI'o[ c.lifruri.. rrswcI uriirr tru. sctrirlcnrsr' ar(. 15.5ntMa | | m/Ma 'rtrcr

.ru 2ll6 lhlrl( k lh Wov(r d, /t. Rrdkrhrlûnrrnd'lrlhlû llrdhlùrll0r

r Iltt Similarbctldctl rudirrlulilei could rcsult liom differentprocesses. They could Sedimcntûtktn^Bt,DRutcs to the Decompaction occur in the samclocality .rl dillbrcntpcriods of time or at the sametime; conse- làctors U$lng^c(ordlng Odin\ Scales for thc Matm quently,they obscure thc variousphenomena. Shales and chert beds may be related to water-cunentdeposition; some sedimentary structures visible in radiolaritescor- SeJimenlation Decompaction rarc tespondwell to very slow deep-watercurrents. factor 6.66 nlMa 2.1 r,],lMa

2l .3 rf'tMa 6.7 ll:.lMa Laminated Deposits 5 33.3 nVMa 10.5 n/Ma Radiolarian depositsoften show laminae. Some of them are unquestionably with redeDosition.Other laminae reDresentseasonal variations and are. This calculationunderlines the precision . exolained as marine varves. The radiolarian-richmember of each varve mav we can expect when we comparepast sedimentsro modern ones. It signifies that seasonalupwelling, and the clay-rich membermay reflect yearly runoff. This a differenceeqJ io'o, *J, ,nun u fu.,o, of 5 is meaninglesswhen the parametersof calculationsare imprecisc, the casefor the Monterey Formation, older sedimentsof the SantaBarbara Basin andGarrison, 1981; Soutar er al., 1981)and those of theGulf of Califor- C. Stratification at depthsranging from 300to 1200m (Schraderet al., 1980).Other laminated are explainedby an alternationof warm and cold cunents (e.g., Pliocene l. Bedded Cherts in Sicily; Riedel and Sanfilippo, 1978). In the Monterey Formation, three Generally,the effects(bedding, cycles are identihed (Pisciottoand Garison, 1981):the first-order cycle lamination)can be observed,and one glimpses some of the vectors (contourites, turbidites, seasonalvariations and laminae 0.4-0.8 mm (compactedthickness) thick; the diagenesis)i.r"f""à; i", most of thc trme, one can only guess the real causes(e.g., cycle, with a 12- to 200-yeartime span,has laminae I to 20 cm thick; cyclic variations of climates) ol. stratification. Some of thesevarious elementsare listed below. the third-order cycle, with a 1800- to 3750-yeartime span, has bands I to 5 m (a) Bedded Cherts, Ribbon Radiolarites, Laminated Cherts. Radrolarite beds often alternateregularly witb siliceous shales. Severalprocesses m-f exptain tli* bedding: diageneticsesresadon of silica Climatic Control from i"i i"ny ;bi;;;;;nllur, ,li""or* mud; successiveepisodes of high and low production àf radiolariià-uÀg a constanr Diagenesisand water-currentdeposition may createthe ribbon aspectof radio- sedimentationrate of muds; episodesof increasingdeposition or.uoio-rlun, water ou" u, , but these beds probably are limited where an intemal variation already curents while mud sedimentationis constant, or, conversely,episodes ofhigh Thus, the bedsemphasize a preexistingdiscontinuity; for example, Tethyan mud depositiondue to water currentswhile the sedimentation.ué ofîdiol.iun, constant. i,, beddedchens from Creecemay correspondto a variation of the rotation of the Earth (with the equinoxesprecessions in the Milankovitchtheory of Diagenesis. Diagenesis ,^*(!,)-!r*-.lhens. .antt occurs in rhe bedded_chcrl , climatechanges; De Wever,1987). An astronomiccontrol of climatealso is rormatron,as evidencedby the important loss ofporosity and its conelative reducc,l for siliceousdeposits by Munay and Prell (1992)for Plio-Quaternary thickness.For example,diatomites (of the Monterey Formation, Califomra; and (1992) Pisco Formation, peru) rhc in the Owen Basin, and by Shimmield for northwestAfrica. These are massivewhen still made of opal O,'U* ,rr",,rr"O ,rn",, mcntion that silica accumulationsconespond with a 23,000-yearcycle and transformedto oparcr (Fig. 6). Duringthe mineralou"rr.Àuuo"'uio corrclatcd with upwelling activity. the forcing processof the primary planktonic tion,rhe silica-richlayers further are enriched, "".0r. *nif" tn" poo.".t on"i'ur" irnp,,u bcinc tied with orbital constraints.Slisht modifications of planktonic vity lcud to major modifications in numbet and diversity of radiolaria rn Variationof Bioproduction .. !"h1tu" VersusDctrùal Inputs. I.1tmacr rtl $cdinrcn(s(Rcnz, 1976). This amplified variation is effective during di- (.1978),^_!.! Steinberg ct (lgg3), al. and othersconsi(lcr thrr t c.tr-r,'nO"intcrt depositcd cO**"," lgËnciirilnd nl[y cûuscan altemationof radiolarian-richbeds with azoicshales. scparateiy,one input constant, thc'rhcr rrighry .rihric.ccnrri,,,, vur.i,hrc, lltnlcri irr bctklctl chcrt ihen could correspondto low productivityperiods (De ycrc lluctuatinghi.pnxlucliviry .1. rrtl'rlurl.nr, llofro::d:..11) e'rrsr'rri 1{cvcr.l9lt?), (lcpo$ilk'n:(2) tluctuuting wrtcr-curr.rt, r,.rllrl'1., (lFlrrrl,f,u,,..,,,,ri ',rc 't.c,rv 'l'hlr (lc'o$iti(nli(.1) ,,,,'r,,,.,u .f"u dorrhlc(nllflnccltrc t lny conlc lionr u mud with slightvariations in its ll'ct,.ti'* w'trr.(.'rr'lt, rr*rrlrle,rrrlliirtt, r,.r*tunt lr,*iltcrrrrrrc !$l( er) r vorrttrrlli! ItrlxIll0[ to l r rltcrnûtionol purcsiliccous and calcareous

.n* .ffi*. lhlrh,k l)r.W(vrr rl dr. In(l lfthyllll larrllllrltl llrr 'Ihc 'l'rill{rli(N4i(]ccrrc M""t:]]lÏ::il:'t'" uppcl.lrrrirssic wrrs rr |t.rrrrrllrtvolrlrll.to rrrtliolulilic sctlirr tcrrtirt iotr. lll, y lirrrruliott(rhrrlorrrllrcl runl ill thr' abundanceol radi0laliarts irt to(,ks0l llxtt pcrirxl Al|rt'i:l Ir'cscr.vctl htrs lcd l0 scvc tl llllos) andilll. rurirssicrrrrir\ir\ ri(lrr'|lilrrrfhr'Nrrrr""'r'! rrl thr' 1 l, 1|'":']'i*',,:ll::l:]:llll',ll:ii;illclow thc activcupwclling hypotheses.The most convincirrglirrls rltliolrrlirrnhkxuls lo itnp(n1iu)tlutricrr\ ol lltr'r'tttttI'ottIt'r't tiliccouscontcnl i* ""rxttitudc inputs as the resultof upwclling. Such rn intcfl)tctittionrrrrkcs scnsc, lirr nulio Sonralia,ascdirttcttrirriorr rllr ol x :rrrr/Mtr.(('irulctl-']^...t^1i.lll3],r.s,i;,l]i; (caurct larianswere probably tttdcxcsconnectcd tocurrcnts theonly organisnrsahlc to uscsilica at thattimc; diatonlshirv(, ;l::iÏiiJ"::ffi'*;*;;'';;';';i';;.,'king existedin abundanceonly sincethe UpperCretaccous (Burckle, nu,'nl{r::fj:^lÏ l9?8). This inrt.r teeL)ssz).Exactlv Ex.octLJthcrrr! sa'ncia"'lv plrcnun'"r"''"-. - j 1.,[ ' I and::T: Faugères, i :.t.?:'Hl1993)'but Ï:: pretation, nevertheless,may be inadequate,because radiolarians behave as o rcr in theeastern Atlantic (samthein ndlirr radiolarianmuds 1992) planktonic organisms, is around100 m/Ma (Schrader' where the most impofiant factor is the abundanceof nutric t, r)l Pcruthe recent sedimentatlon rarc not the abundanceof silica. A scenarioin which transgressionsare associatedwitll rl significant input of organic matter and a radiolarian bloom has proposcd : Precision? been hy Original SedimentationRate (1981) Steinberg for the main epochsof silica deposition. It should be noted thirl ir therc are vadous uncertainties radiolaritesand modern sediments' reducing environment favon the nondissolutionof silica. The combination ol srv Comparing tntcKn€ss' dt"otpu"uo"'ue'vxrPq!!'"-'' ug"."*icl-::ll-ioauce-significant eral factors is probable, such as upwelling activity bringing nutrients in abun

.-* l'rh.l(k l)(. Wov(r. .t Radiolârites ql Rsdiolariâns ând Tethyân Ittls. l,llchrlodilication ol thc irritiirlsiflrrl (rlurirrNsctlirrcntation, 2 ateas with water upwelling' as in dia8"""t't) productive (300 mg C"," m a-r) are irssocrltcdwith an anrplilicationol lScllrrclulrlior,. ,, i;;;i;; in i'Ln,utsherves or** T:i:ï11 orsanicmatter resuit fromï:"ll::';,:::- high plank- ;t;;";; ;;il,t* and marine D. Domain of Radiolarite Deposition 1e86; Diester-Ha us"t ot' tl?t.l:l)?li^l^ *i"u, it""n^nt' ." They;J]1'; are 'l'ytc not alwaYsren lain associatedin sediment'-^ l. und Dimensiotlsof Basins et at., lgg2), but do in the following cases: Radiolaritic basins are rather small and locally restricted and correspon(l- , California' associatedwith speciliclicoeriodsinsmallhqci". Â-.^..linût'ôrhÂi.,-ti-^-^:^-^ ! I r(, of the Monterey Formation' periodsin smallbasins. According ro theirdimensions, rheir pr : . Miocene diatomites loxlIDllvlrl"l (Garrison and Douglas' continentsand their lithostratigraphiclithôcrrâiiorâ^1,i. ."rt'ino rh.-..- r^^-*^, r- - content of organlc muu"' und Phosphates set,iù,,f,"yurlt dç I..""ol;'u.,îiru!;dleoln areas-- J":iÏl'llisuch as trlt,. a high bfocks .tVeyer 1983\ on an extensional margin (e.g., Morocco,-. De et ql., .rr 198| ; Isaacset Ql.. fSiS, ,,,,,1tr Peru (Ochoa' 1980); and off Lagonegro,Italy, De Wever I . diatomites of the Pisco Formation' and Miconnet,l9g5). The lu.g"r, o..urr"n... .:,,,,1, Miocene spondto relativelysmall channers(e.g., the pindos-olonos (Suesset al', 1986) zone is circa 8()(r Peru r anoxic event such as the Aptian-Albian f200 km in length x 100 200 km in width: Cecca et . iifi"" o"o*n, connectedwith an al., 1993\. time (Marcuc- 1987) or during Cenomanian-Turonian beds (Coccioni e/al ' 2. Deposition Depth ci ct 41., 1991)in ltaly deposits in Costa Rica (Hcin ct n/ ' . ôr"iul"ou. and Paleogenesiliceous Fossilradiolarians occur in facieslhat represent an extremely widc ri r,,(,,.. Rad and Rôsch, 1974) tlcpositional 1983;Von depth.lndeed, these organisms, as otherpelagic fuunu, as Domanikin Russiu(Ornriston' 19931 i,,'.i,,,1t . i,rrc" O"p"rn, of Paleozoicknown low-waterdeposits such as the TithonianSolnhofen "^ir, Limestones(Gcrnùr v), t,. 1993) which VishnevskaYa, sedimentologyand macrofbssilsindicate a shallow_waterorigin Spain' and ltaly ('Illurow and Kuhnt' 1Sf,,,,,*,'1'l . C"nr."niut ':pf,tanites"in Morocco, l(X)3:Barthel, 1970),and the MontereyFormation and SantaBarba-ra .,",1,,,,,,u,. 1990) ((itlilinlia), 1986: Kuhnt et aI , which are closeto the coastand at a d€pthofaround.5(X) "schistes à Posidonies"' tonian Zone in rrrtKl,rrpr . Several horizons of the Jurasstc lt)77,19711:Pisciotto and Danelian and Ganison.lggl). Hence, it is nor.justified,u,,.,,,ui,lt, 1988; Baudin and Lachkar' 1990; (Baudin e' cl ' wltlercnvironment to all depositsbearing radiolarians. If we conrparc rir(trrrlilttrt\ ""t*"id"s 1990) wltlr rrrrxlcrn Baudin, deposits,good candidatcsior equivalent enuironnrcnt. ilrc rrr(.srrr.. time Such lltttirulrrlJasin (Califomia), the are not found associatedmost of the slopcoll BajaCalilornia (Mcxico), ,1," r1,,1,..,,;; ;; Orll nic matter and radiolantes (lttttyttttts(Sonora, Baja California, by severalfactors: Mcxico),and thc Uppcr Slopcs.li .t ( .llnrl e(nrtrul(lictionmay be explain ttltdl)isco (Peru), off equatorialAliic (Sarnthcinanrl F.augùr.cs.l9().1), 111111 1111ç Bogdanov n*" Owcn . ct as a diluent of the organic matter' llasin. At thescplitccs, bott(nn llnlinirtcd clcpusits arc not (lccl)(5{It silic may :t-lllYto) particles {,t|lt[l the TOC/SiO2 ratio in suspended i SInta Brrbar basin.3(X)_13(X) showtr lhill in nrodem sedlments' rrron Guayntas l]asin antl .lfXt Xtttt r Pacific' the rrrr||ç when productivity increases'in the Central Irûllwcstcrn IntlianOccan; tnglc, lglt t ) (itt surlircc)dccrcases Formation' California (Donegan and ( irrll ol ('alilolnia and the Monterey (irrnptrison l9ll2l /\plin at al 1992)' l{. wilh l)epositsAssrrilted with Radiollriles Selrttttfct, ' in organic matter becauseof.their deposi- . l{n(li{tlrrlilcsillso tllily bc depleted al 1992)' as as their low |, Ilulioltritr',t t OtR uiI Mt tt,t. wutcr tlcpths (Von Breymannst ' ii,,,, ., u*'*, 'well were not doesnot meanthat the sediments 'llrc lxt(' ltl l('(lilllclllilll(nl:yct' ttlls IniltllrvIr'.rrrr'ri.'rrr'.r'irri( ir trrc . is the casefor red clays In(.rcrrrriry, || | r | | | | | | |. | | i || | | | | tlrc lirrrc'ol thcil dcposition;it also tttr'ttlsis (l ''racr ,,,guuu |l,ft tlt ttrttittly f lo vl i(l \ llto |,r l|l Itrr.ll l t, ttrit,rosr,rlrjr,,| during settlingor at the waÉr- | II | | | li I r , | | | , tri. luf,lt (hFrrrri(l|l tlcf is rccyclcd Lll lN0tr itt(lt tn lrlr1, p,111.1qrrlpr ,, tllotl,',, rllttrrllrrpr,lllr,rr, rllitlorttr ittxl I t.,Ilrttttt,ttl l|lllIlt' l l0lr'l lll{ l' lltr'V lrrtttt llt{, lr'rl(, ,tf.tlx,t rrl tlrr,lrrrrrlrltrrl, l,lrl, l*t*tt\, rrl lltr,'y111;111,;,,1 ;1;. . r|lrillr|rrrlrltll toh'itt lltc Itcsctvalittnt]l l{ttrlirrlltlrtttrltt'prll rl || | r , |t || | | ! | | pt|{htrFtrrl rrt i,,",,rUt l'".:lgi:::.::i 1l | | Élttth 5trtltr,tllr rtrrtt|,r. ,,rrr r'rtt ",,, .u"t"'*"''' *,l"lil.::l n[!llt lltr,\ lrlt ur,rr. I rlt lltËFHiF||, p "' lt::lÏ:1,.ïlJ;ltt lllc oxygcn lrrrrlr ltrtlÉtrl ltsHlltl tlt I\lprrrrrt, llIlFa i-l;;iii;'*,ï,'';;'lf||llrtlllr rlrtlllrl'lï l\ vrrv :l:l:::::rfltl,il ivr whF,r.tx*rrrrÉrn, rr'r rrrllrr tApltu ot ,,1, I'ltl!l lhF drl drÈrHrfirlrÉdnd tFrÉ'l|Érg r r',rtrrrrr, w[lrlr rug ttJltËlll 0t lllP lltle|rllllËl .ft ".# zttl lhlrl(k l)c w(.vcri'l rr, ll[dlolrrlrtl|i rurd li lhrnrr ll||'ll'rlIr lhlr

lt;rsitlsill . Organicmatter preseryation varies greatly cluring dirgcncsis, and interprctrl lhcoccitn lowaltl llrt rlillrrll(l{ll, M(lhrcco;l'agoncgrtt, llllly) l{il(liolilrintr tionsof bioproductivitybased on it shouldbe carriedout with caution(Aplirr nrrtlltctnMonrcco rlriArrlc(l rrotlhwllr(l duling thc Midtllc Uppcr'lutilssic' sllllAcsl- ()l lisllic et al., 1992). lltI sc(tinlcntationon lillc(l blockswith a progressivc,oorthwil[(l lirnllillion fHults(f)c \Neveret t ..1t1351.The diachronismol the lirst ladiolalitusdcposits To conclude,there is a relationshipbetween organic matter and silica, but thcrl' (ll urngartnct' hlcntilictlin Lagonegro(De Weverand Miconnet' 1985)andArgolis is more than one parameterthat regulatestheir abundancein sedimentaryrocks, arttl blocks ol' l9l{4) rcprcsentthe samekind of phenomenon:deposition on tiltcd their identity and importance are not yet well identified. Both result from higlr thc dillcrcncc hllFin ir formation.In other cases,the variationscorrespond to productivity, but conditions of preservationare not the same; they have not bcrrr lJ sin ând Trcnto b€twccnbasins and plateausol seamounts[e.g., Lombardian associatedsystematically in sedimentaryrocks. (Galacz'l9{14: Flulclu,northern ltaly (Baumgartner,1984); Bakony Hills. l-lungary lrct.al ql., 1985;De Wever,unpublished data)]. The first radiolaritedqposrts arc 2. Comparison with Deep-Sea,Red Clays synchronousin the Mediterraneanand Alpine tlomains,but their maxlmurn times This diachronicityin siliceous Radioladtes,most of them red, havebeen compared to pelagicred clays. It now gcncrallyoccurred during Oxtordian of the MontereyFormation This is commonly admittedthat this compadsonis incorect, andthe only common featurr ntîtion also is known in the diatonlites resulto[ the positionof thesesites with is the color; the trace elements,clay content, components,etc., are different. iorrin the latteris interpretedas the to thc centersof upwelling at thc time of deposition (\Nhite at al , 1992)' 'l'hc gcnc|algcometry of Tèthysat that time (an eastwardopen triangle) pro- 3. Radiolarites and VoL'anic Rocks upwcllingson the westernside and led to the developmentof a clockwisc, The proximity of radiolarites and volcanic rocks has been emphasizedmarry : gyrc (De Wcverand Thiébault,l98l) This trianglewas prcsenttrom thc times, and a genetic associationhas beenproposed by severalgeologists, becausc rl ol Nco.-'lèthysduring thc Penniirn.During Triassic and Jurassic periotls, thc seemedsimple to connectthe enrichmentof seawaterwith silica and the needof this ic urcl oPcncdlncl sprcîdto thcwcst Thisschenrcfits wcllwiththe progresslvc componentby radiolariansto build their skeletons.This simple and direct connc( ol |ltliolaiitc sc(linrcntittionIl1)Dr cast to westduring thc Triassicand Jurassic (1982), ol tion is merely a striking coincidence.Indeed, if it were the case, siliceousplanktorr [rklitiotrto llrc cilttsssquotçd by Jcnkynsand Wintcrcr the absence should proliferate along midoceanicridges such as the mid-Atlantic spreadingccl in lhc Atlanlicdouririn can bc cxplaincdby thc lackofstrong upwelling irl tcr. They do not (Fig. 3). Radiolariansare profusewhere nutrient is abundant.Wl)irl hnnir rrrrrllhc Stciltdislilncc ol this basinhrrn thc zoncof upwelling' radiolariansneed is energy to pump the silica from sea water. ln the chain radio Irr '|'itIrorti;rttIin)cs, tit(liol ritc sctlimcntrlionsuddcnly ccased and was r{'r- larians-radiolarites, plankton is the first link, with dissolution and diagenesistlrr' bv thc sc(litlrr:l itlion 1)lcitrh(nliltcs. Although this changcwas widcsprcad' others.Volcanism allows sea water to be lessdepleted in silica (almyrolyse)arul, fl ltc irirxrl rrr..t.r.ssit|ityir r)lirj0t orrc, lrcctrtrsc wc know thatonly slightmorliliclt- consequently,less aggressiveto biogenic silica. Volcanism does not favor ratlirr larian life; it favors its preservation I. irtlltc lilc r'rrtuli(iolrscitlt pttxlttce slf(tll8 rrx)(lilicnti()ns in thc planktrtnic lilt' (i('r lil Nitlorltcr(s. wllcr('lllchiotttltss prrttlttclion is nxrdilicclby a lactot ol lll,nr(orlitt[llrrlltltlrt'tittttl ('ltitvcz. l()1{(rl llcinzc artcl Wclcr, 1992: lrrttt V. TETHYAN RADIOLARITES rp lo r lx(irtt rrl .t{}.ttttottlitlPloN4((;owllt,l(''ti4l l)isiasrlrr/,l9ll(r)i Irrrrl in sc(linlcnt(l{cllz, iI lri'rrilr(x1tt rIttr'Iitrtt. wltitlt lrrrstttl rrrttIlilicd cllccl A. Diachronism of Appearance, Synchronism lr,/fr, l)('W{v('1,lr)X,}lt ). of the Disappearance of Râdiolarites (tltl lltr,rr, ,lttlrFr.,, rtttV ltttv('ltt1'll wrrrlrlwirlr'.lrlll wr lltke illl(l ilcc(nltllollly ( In early radiolarite studies,iÎ appearedthat the main sequenccsl'tcllrrrllt'rl lr' llrr' tlItn, lx,r Ittt{' lrlllv\ ( ltt||tttt' itltlrrtttttt, M('xiro), lltcl( llrr txl 'rttl,,lrlr' (l('ltillrI Jurassic,confirming the classichypothesis on the agcol lhcsc(lcFrsils. SttLcr',,',tt, E l tr!tlrr,rhh.rl!vitlr lrl'rpr'||l' ,.rrlirx'r1,,rltt|. trr IIt| rItIttItorrlry illIlll l('!,llll('lllltlltl worksthen preciselydated their baseand thcir loll. irrrl (||xrtrcnlc(l ir rIirr('Irrorrr',rrr lgdhtlntlX tlr,l(rqlth IUrxltllrrtll'Il{ l r f h r'ltr llljllltrtl lllllV llllVr for the earliestradiolarite scdiDrcrll tiorl artrlrt st'rt,lr'|ll\||r lor llrtir lrrl llrr'., I lrt tlrf lI r.t llr.lh. lrh, r,r r,q Irr.vtrrttirlVIlt|lxr\frl llli' W'vrt ttttrl variationscorrcsponcl to (lilli'rcnllilt(.rl lrlorl ||ri||l!l r |'l ir rlrvfIr|Ill!. lIr il|l'Il 111,lr)fi11, l{tt tlrtn||[ri rttil tr tFr-rllrl UI l lrrll! r lrct'llx' ll'llltrrll lllltllph' xq lll llx'Irllr, occ n (l)c Wr,:vr.lr,/ a/,, lr)ll5) lr s rlf r,,r'r,lltl.v I tlr:tll||lrll|| rtàlt(.lr lrlr}l lr[|l Ëli|lItF trr{tltl lIrvF ltrrlr.rri,rl tlxr rlit!rttlll! ril Irilr !Frllllli'tll{, .:,sriff#' Iolrkl l)r, Wr.v.,ri,t rr. rrtd li.lht{n llnrllrlnr lh,r

,lttussi(ll(l y,llUl(.t sc(lur.c(,i\irr is.ltttctlInrsir\ {Vitl'lq.l, (itur's.s), whiclt i\ tlccI crrorrghl() l)rcv(.rlsrlirr.orrs strlirl|crrls lrlnr) bcing swcpt way by surlàce n(llillccltsc,'lltctcltrrvr.bct slrrrlktwrcrrsirr llrir/.' f \tlùr!tltr.liiussic..l.hus. tlrr, runrllitlal culrcrrts rrrllrr.low tlrc ('('l) l(] void dilutionby carbonatecompo- llcllcrrictcct'rrisrrr Pnrhrrhly wrrs inr(lc(llnr(' r. rrr.rlrl!rrll rhr. ,r'r,,urgraphic conrri (rlthouSh il is krrowr lhat ('('l) is highly variablein depth and may be liortsas litt s M0nrc0, lltc srtrklflrtlisrrltIr.rrrrrrrr,,, r,l rtll lltr. Ilt(li(rlantcsIn llx. y shallow in placcsol high productivity,rising more than 2000 m off of uppcnlx)st.lurilssicntity hc cxIlairrerlby it rl rrlrr,( lt{ pf l r.it.cttlationdue ro ir whsrc upwcllingis uctivc). latitutfinaflfow lhrough('r:ntrll Arrcriclr(l)r. W.v|.| t,t tl ltt|,6l. l.hisnew corl Mostradiolaritcs lionr Tcthyanregions, as well asfurther to theeast, probably municationtlrastically changcd tlrc c ftcnt lnr ctrl lr ! rt!Ur. lrr thc Mediterrancarr dcpositcdin relativelyshallow environments (Ijima et qL. , l9'78,l98l, 1985), Tcthyancolncl (andils assl)citc(l rrIwcllirrgs ) l(, I lltt rllIrtl tl rtlcrcurrent ano cal, thc cstimateddepth for radiolaritesat 1500to 2000m. therclblc,cxplain thc dislpPcarlnccol rrrrliolrrrrtr.rfrllll,lt{tIrl (l)c Wevere/.r/ , Sonlc presentlocalities are comparablegeographically with ancient sites that 1986).The currcntcould, t lcitstlocirlly. t.u lt0 t f rl tt| |lr\1. as suggestedby radiolarites,such as the Gulf of BajaCalifomia, I 100km long, 100km Thiébault// a/. (l9ll(r). I'his hypothcsisir co st\tf||t rï[lt tlx. long duration0l 23-31'N; Owen Basin(NW of lndianOcean, offof Arabia),1000 km long, radiolariticsedimcntation on thc cilstcf A|llhilt tnttl|| rrt llrr,.li:thys(Oman; I)r, kru wide. l5 23'N (Fig. l0): and the SomaliaBasin, 1000km long, 100 km t eyeret al,, 1987);thc cuncnts thcrc r.crrlrilr.rl crrr.rrllllly lhp rrrrnc,and upwellinl , 5"S-10'N. By comparison, the Jurassic paleo-basins of the Oman- persisted,supporting radiolaritcs Lrp to tltc tj||lx.r (,tr!lrtrFl|{r(l)c Weverer c/., KermanshahTroush measures2400 km lone. 100 km wide and extends 1990).At the exacttinrc whcn thc cut.rcnll]l| (. t lx,r.nnxllH ltt(linal,lnstead ol it l5'S to 5'N; the Pindos-Olonos trough was 800 to 1200 km long, with a gyre, a sudden"deepcning" occurrcrl lhc'c. wlrir'lrrr rrt rrtrlprlrrr the sediments.l width. near lO'N: and the LigurianTrough s.l. measures1000 km, near ,'llush" the AutochthonousUnit (Onl n). 'l'his co hl r$rrrlt lrol { effecÎ at th( beginningof the 'l'ltc 'l'he latitudinalcurrcrt. sc(li t(, t tirxtI !la tvcly changedbacli comparable basins. present and fossil, are not completely open to the to shallowerduring the Ncoconliiu. In.lu|)rrrr.lrr.irrg l tlhËtr{rl whcreradiolaritcs , becausethey are protectedby a platform: the Owen Ridge for the Presentand arenot dilutedby detritalscdinrcntrlion, tltis ||||xllllr[ll [ llt *Itcr currentshad 0rl PclagonianRidge for Mesozoic. A comparisonof thesebasins indicates several effect, and radiolariteproduclion pcrsislc(l u til tltr NFrx,ttlnlun.In concluslon, tèatures.They are subjectto bottom-watercurrents, are located in similar \À/ater-currentregimes contlol thc cslll]lislt'u'l ,l InrllrldtllËri'the Tèthyand. (Fig. l0), and occur on the ûorthwesternmargins of the ocean;by contrast, main. This sedimentationhas bccn inllucrrttrl(litr{ tlV ht llF gFr(lynamicconfigrt on the easternside of a continent is not the most common for zones ol ration of the TèthyanOccan with its wcstctly,r,lrr,crl V rltcpe llacliolariteswclr, Nevertheless,monsoon activity allows these regions to benefit from depositedin this cul-dc-sacli.onl thc l)cf ril t t I ntFrl llt$riic. until the N S upwelling.Attributing the presence or absenceof radiolaritesto monsoonal openingof the Caribbeandonrrin nralkctlthc r.rrrlrrl thtr gÊnglrtrhy.This changc lingsintegrates several proposals previously used as explanations: (l) connec- influenced cunentregimcs; culscq cntly,plurrltorrlr' lnrxhtr llvlty irndas a seconrl with the sea level (Steinberg, 1981), (2) connection wilh water cunents ary effectlead to a dccpcningol thc ('('l), yns andWinterer, 1982), (3) connectionwith hot versuscold climates(Hal- lqlJ4, 1986)and (4) connectionwith climaticcycles (De Wevel 1987).To B. Sites of Tethyan Radiolsr.itc l)rposllk||l lhc monsoonalphenomenon as a possibility during the Jurassicdespite the thut thc Himalayas were not yet a mountain range (India collided only later, A prercquisitclirr scdinrcntslhat will corrtrrirrrrlIrln111r, ,, high procluctivity l,utctian time), it is only necessaryto point out that high mountainsdo not of siliceousorganisnts (Mrliva d. ,,lt)t)lll, Ilt(.ltl|r l rl $lhll rlr tlx)ncnts(ctity\. nronsoons,but only amplify their effects, and mainly in regions proximal to detritus,carbonatcs) nrry viu.y.'l'hc'c'rr,rr rrrrrrrlrr,trrl lhÈ'tlfs (,' (hc sitc.l lantls. Monsoons result from the relative distribution in latitude of seas dcpositionol radiolaritcsin'l.f,thy,rr Îcgi,.s lrrr rrIl'p IoF, ll |'ru l)(:cnknown rl'rr Iundsand also exist in Africa (from Nigeriato SienaLeone) and Australia. siliccousscdirncnts accutnulilte irr l,l,gc. tltcI lr'rlrrr (th,r,lldtlhÉl l0()()nr)cnr.ichr.rl iircs ol lands and seas involved during the Jurassicwere greater than those in silica by volcanisnrol sprclrlilg lirlpt.s,A lr.w Vr.ntritÉ1, ll wll| l)rolx)sc(ltlltl i lhcrcli)rc,thcir cllccts nay havebeen greater. scdirncntsth.t c(nlt in ;rrcscnr

ft NORIAN E"- ffi e'æ.cr."a rclrr. tot..dlic,ldc. 1,4 t-----{ h..Iv. rDE.dri, ,rdr. > oc..irô llbduc oi

',\,. !|nn. d oc..Dlc c@t

DTAIA

Fi!, tO- I-@tioo of tnown radiolarite depositsor the Triassic(Norian) T€thyspaleogeographic map (aftet Marcoux etal., 1993, modified): (Da) Damo (Huûgary): rtlr r Ilrrrr rtunt ûtu8) X!ç.ti B:si! (Tu*ey). (Kt) K"q.""b"h- (I'."), (H) rt€"*s',r:reBÀ (Idv)t (

LrrE snclr.nlÂ'l EI EI

Èd rb

È.-L -..- - I'rlrk,k l)(, Wûvrr /l x,

Cc|ltrdl lblhys. whcrr thcy ovcrlic orcit i. lrrrslts ol llrc l)urno scrics(lh; l)(. -.i .'! à ! Wevcr, l9ti4) in thc Pclrgonianzonc (l)c Wcvfr', l()8.Ih).lhcy rc prcscr(l rgcl! 4ô4"- on the edgeof the ArabianPlatlbrm in Kcrr|larrslrh (Kr; llraud, l9fl9), Pichrkrrrr tËczE c g (Pic:Ricou and Marcoux, 1980)andHawasinr(llw:l)cWcvcrrta1., 1990),aswcll -;ÂEi É as in the small Umar Basin (UB; De Weverct ul., 19901.During this period,tlx. - Atlantic Tèthys (which will develop later into the Atlantic Ocean) was a nanow, evaporitic basin deposit (Marcoux et al., 1993) passing to the east into the citl careousdomain of the Central -tethys. Still farther to the east, the Tethyswidenc(l YE^É, ÈvS-! progressivelyinto the vast Panthalassaoceanic domain. 3qÉÉ During the Early Jurassic,as early as the Sinemurianperiod (Fig. 12), and latcr 1ÂE .q during the Toarcian(Fig. l3), the Atlantic Tethyswas a trough in which lacustrinf and marginoJittoral sedimentswere deposited(Bassoullet et al., 1993).The Medi ql., terraneanSeuil (Derco|urtet 1993, 1994) was a domain of complex topography ÈË^t with platforms and basins above the CCD, connectedby slopeswhere calcareour é\ = ;,-", .]5Y,E deposits, nodular limestones(ammonitico-rosso, particularly during the Toarcian) and pelagic limestonesaccumulated with clastic deposits.In this relatively shallow ai c6 setting, some rare basinswere locally below the CCD, forming radiolarites.On th( Ë?FJ.: u) !:u) southem margin of the MediterraneanSeuil, they accumulatedin several places, dàÊ, such as Lagonegro(LnT; De Wever and Miconnet, 1985), Budva (BuT; Obradovic ;:9in and Gorican, 1989; Gorican, 1993), Pindos-Olonos (PO; De Wever and Origlia ii sHFl /1 i,ti2É Devos, 1982),Mamonia (MB; Lapierre, 19?2),Koçali (KoB; Fourcadeet al., 199| ) e* ; in tbe north of the emergentMardin mole, and Hawasina (Hw; De Wever er a/., É:r Ë"i lr g'' Ë r, 1990) in the northeastempart of the Arabian Shield. During the Toarcian, radio- !!E < ^ larites appearedon the northem margin of the Central Tèthysin the Trekljano (Trk), Strandja Basin (Str; Tikhomirova et al., 1988), off of the detrital cettic platfomr; g,:,H 3 and further to the east in the Lesser CaucasusBasin (LCB; Lordkipanidze er a/., '- 1984;Vishnevskaya, 1993). 3 = "' In the Mediteranean Seuil, the complex topographypromoted water stratificil â È1E tion, sometimesreinforced by the influx of salinewater ftom surrounding,shallow e": â ê water, evaporitic platforms. ThesefactoN, associatedwith phytoplanktonicprodu( o I io tivity, contributedto the developmentof oxygen-depleted,deep waters and, hencc. to the preservation and accumulation of marine, organic matter. Organic- arul carbon-rich black shalesand iimestonesespecially are well developedirr northclr e eY.1 Italy within the Lombardian(L; Jenkyns, 1988;Farrimond er al., 1989)and Belluno EF.=E ;; B,-i basins(Bel; Bitterli, 1963;Jenkyns, 1988; Farrimond et al., 1989tBaudin er a/., FEbF 1990), as well as in the Ionian Trough of western Greece (I; Baudin er a/., l9ltl{t nË Jenkyns,1988; Baudin and Lachkar,1990), Hungary (Bk and Mck; Polgaricr rrl., s:, 3 1989;Jenkyns, 1991), and northernTunisia (T; Soussiet al., 1988, I9119).ln tlx. rll! ft .: .e É9:. radiolarianbasins such as the Lagonegro(LN) or the Pin(los Olonos (PO). thc lar'f| F: e,e size of the basinsprobably permitted bettcr oxygcl lion, s||l)ptctisi|lglltc witt(.r t.fl! i I ,i'x stratificationand the relatedpreserv.rlion ol olp rrir'Irxll('r' 'lixttci n or1.lrrrrir..rir'lr :rq â !! depositsare dcvclopcd ln inly on thc cl)i(oItirfrlnl, lf||ltlr! rxtr l!lnllil l cxlctnli ll |t'il 1\ )r tizÉ,!

!-F 298 Ihlrl(k lh W1vrr dl ar, fudk,hrhrns |ul(|'l0lhynn Rrrdkrlrrrlir,i

I Ê9 thc North Sca(NSIJ) k) thc ParisBasin (Parll). Thcy includcthc Jct-l{ockin Â=- Britain, PosidoniaShales in the southernNorth Sea,Schistcs Cartons in (hc Basin,and Posidonienschieferin Germany and Switzerland. Such lcvcls also ] I known along the Ardèche margin (Dromart et aL., 1989\ and in the Caussc g Àâ; , 1983). On the northern margin of the Tèthys, the large, deltaic onviron- 2 that extendedfrom Rhodope to the Pamirs was suitable for coal tbrmation. =Y à (Baudin 46= is no preservedorganic matter all around the Arabian Block cl a/.,

In the late Mid-Jurassic, during the Callovian (Fig. l4), thc Atlantic Tcthys clearly distinguishableand correspondedto an elongatedbasin abovc thc CCI) ë 1c (t:nuy E?,: by calcareousor sometimesterrigenous platlonns rt ul,, lt)\)31, Meditenanean Seuil becamea more homogenouscnvirontttcnl hy tl)c Sctcrltl Sà; of the previously insular platforms (Trcnto, 'l irolikuttt, 'litttn ), A t utlio- faciesis widely distributedand is found in nrostol lhc Mcrdilctrttttt'ttnl{itlpc, Lagonegro(LnT; De Wever and Miconncl, l9li5) ln(l liolrr lllc Kllhyl(l Trench(KRD: Raoult, 1974; De wevcr('t a/,, l9lt5;Mftrt(rr.rl,, lrlrll ltl !cF southto theMecsek region (Mck; Galacz, l9tt4) lnd uslitr un lltc itttlll S$volhl êef (Se;Sândulescu, 1984) to the north via lhc lliikk (ll(li Kozttt, lt)l'14)ttlttl lltR (Si: Dumitricaand Mello, 1982). !,ii * È- ii To the east,the CentralTèthys shows a noticcublcdissyttttttctt'y l)clwccll ili ; 3.< margin,almost void of radiolarites(exccpt li)r thc l,csscl('tntcnrtttt llttttl',, a: z ; Lordkipanidze et al., 1984) and its southcrn cdgc, whctc this litcics "cx" ", as on the MediterraneanRidge. Radiolaritesarc known Iront lhc l)ind(ts 9"2 Trench (PO; De'ly'everand Cordey, 1986)in the west to thc Hawasinullusin 9.rÉ iDeWevereta/., 1990)in the eastvia the Kermanshah(Kr; Braud, 1989)and trenches (Pic: Ricou and Marcoux, 1980). If we consider these basins .s'Eë céE of eachother, the total length is around4000 km, with a width ol'200 300 km. The basinjoins the basinsfrom the MediterraneanSeuil, througha :s: locatedeast of the Serbo-PelagonianPlatform. It correspondsto the Koçali ô-: (BaB; Delaune-Mayra at al c:;. ; Fourcadeet al., l99l) and Baër-Bassitbasins ' ; Delaune-Mayre and SainrMarc, 1980). Duringthe Oxfordian,the general picture is the sameas during the Callovian. , during thc Kimmeridgianand Tithonian,the developmentof the Atlantic z und thc Caribbeândomain continued. Radiolaritesare still absent.Thcrc was 6 rerxgunizationof the MediterrancanSeuil; the wide radiolariticdomain IE lotul irhcdduring thc Cullovian was liagmcntcd. tn thcEarly Kimmcridgiun (liig. €; nuntcfr)ulrpchrgic rircs rcuppctrcdin thc Mcditcrrancunscuil, uponwhich lco-rorllrwun l(nlrc(l $k)ng with srnnll,insulttt pltttltrrrns surroundcd by lgË hluilnr(('r('rs r,tal,, lt)0,1),llslwëBn thcfic clcnlctll$, ru(lk)lttritic trcnchcs, " e- 3 ;Ès ttn(lhrrhi lrntttu r,rttttplelttetw(n'k wlth lhr Srtbhcticllrtln (Sull:Azénru 1l !l{ 11I (Kl(l)r llnuttlt,lq?ili lh Wevctdl (l/', !mIi ilfr ,, lt-t7utflnrl tlrp Xahylrr Rlftlân'llellrh il. ,!,.fI sl'È I M$!tdrr rrl, lgtlll in th *$lhwtrl, ft||tnl,uguttertu (l'tt'l'l llc Wsvelrrrtl ='''-- ÊABLYK II/MERIDG IAN E m

'rar4

LÂ-lE trllrxrlra

.tJ,",u,,u"'' /t ,."

: t"ii -*s

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=) 't_ -_/:- "-/

Fir.l5'Lû..arionofbo.ÀnRii!.Irnl.iteF\iIionthe1ithoniarrTeù1sp,cle.'gel1rî=-Efjd...ij:.:lej:.;-l'.l99.j.rnodifed):(A}Apulia|llal}|:|B:.B! ,t:="-r : rr ero-r r"ro=-. 1;l.) r: ,H$ | Hâ$asina(omanl: rKoBr K\-ali Ba*- b.a-*.,3r: (BaB, Bæ! &:rsii .slr.r : ,oi, or* rKashm'r: rEr Etli; ^r. vB urm:',i 3o;: C];o',: r:{ Pi. r Pichaliunrça'l: I s \B t Sd13n.\liei-.r Bë: .Tsl.] ,:,hr,L:fûrL.hab l,-æ r--s. Ls_; B-.J rlratl.r:r\lar tlarcin,Tr::t+ : - (TtS' SoÙrhê'flTib't: rfTr fmrr Be'= &5itr À-tÈii.', S"h>'Peh5.]a;ft: G::: i; :m:r B:s- L'}ÛÈ-'i3r: -t--.j;- .{z:ràoi,'"rÈ: SÉB SË:= 'ip' OEic , t s_Ëlài Lie JùlL Iai:Ûàil : Ê Zaù ' P3til'tân'' Mir'ottttcl,l()l(5) to lltc l\riiurrrlirtist.i llrrsrrr(l'll: Sllrrrlrrlcsr,rr,l()fl4) ul(l to )c Itttsinsiuc' llrvolitl)lc lil llrerh.Ûrsitiorr ol sorrrccnrclt. lhcy collcslxrttdrlainly kl a llcllurx)(llcr) untlthu llakony(llk; (irrlrrr,z,lr)g{)}. lIlrs. r.rrrli,luritcs[c al)und.'l ;ilfcd b si|l iI southcrr littkcy (lluutlirrI tl., l\)\)4)or (o an isolutcdlonian trough In lhc silî)ç placcsas c'r1icr, but tlrciI cxrcusirnris lrxnc fcslficlcd.on thc northcr' Itt wcstcrn(ircccc (l)ancliurrand llaudirr,1990). Wcll datr on thc substntumofthe bordcrol thc Ccntral'lcthys, thc Lcsscf(, Ltcllsrrs(r.adiolaritic) Basin(LtBi Lor(|, Auslrian Mohssc llasin indicatcthat Uppcr Jurassicbasinal shales are the main kipanidzccl ul.' 1984)persists, as doesthe rong and narrowbasin on the southe.r iourcc lbr thc hydrocarbonsin the Vienna Basin (Ladwein, 1988).The north- border that appeareddu ng the Callovian between the Budva cul-de_sac(tsuT). thc wcstcrn, argillaceousEuropean Platform, which prevailedduring the Toarcian,was Pindos-Olonos Basin (PO; De Wever and Dercourt, l9g5) in the wesr, ro rhc Invadedby the developmentof a carbonateplatform on its southernborder. Organ- Hawasina Basin (Hw; De Wever et al., 1990) in the east. The small, westem lc-rich, sapropelic, black shalesof Kimmeridgian and Tithonian (Volgian) age are appendage-the Mamonia (MB; Lapiene, 1972), Baër_Bassit (BaB; Delaune wcll developed to the north (North Sea, Spitzbergen, westem Siberia, northern Mayreet al., 1977)and Koçali (KoB;Fourcade et al.,l99l)_Basins alsocontinuc illope of Alaska). Marine source rocks also are present in offshore Canada in the and are connectedwith the MediterraneanSeuil east pelagonian of the Serbo plat PorcupineTrough (Croker and Shannon,1987), Jeanne d'Arc Basin (Powell, 1985; form. A new feature is the appearanceof radiolarites .lb in the eastemïèthys. thc Von der Dick, 1989t crarrt et aL., 1988),and along the Scotianshelf (Purcell et al., north, these facies are known only in the Dras (insular) Arc (DA; Frank e, lz/.. 1980; Mukhopadhyay and Wade, 1990). ln the Gulf of Mexico province, Kim- 1977). They also are known north and northwest of present the India in the Zhob meridgian to Tithonian organic-rich shalescontaining dominant, marine, organic Basin (Zh; Japanese-PakistanResearch Group, l9g9) and in southern.flbet (TtS: matter are depositedin the Tàmpico Tlrxpan Basin (TamB; Guzman-Vcga. l99l) Bally et al., 1980); and especially in the east, ,,Indonesian,, in the Basrn, which and SabinasBasin (Sab; Longoria, 1984) in Mexico. Thesesourcc nrcks arc rlcpos- extends from Timor (TiB; Audley-Charles, 1988) pigram to Waigeo (W; and Ited on a newly createdmargin in deep, isolatedlroughs whcrc citculttton wils Davies, 1987) via Babar (Ba) and Seram (SeB; Audley_Charleset at., t9j9) in restricted.In general,the radiolaritic facies depositsarc closor to thc opcn, occiulte northem Australia. The earlier basins are, therefore, fragmented;but the facies is domain than those with preserved,organic matter. This is truc, li)r cxarrrplc, lirr' more widespread,because the radiolariteshave never been found so far to tne east. radiolarites of the Pindos-Olonos Basin, whereas organic nlattcr occurs In tlro This faciesoccurred over a latitudinal rangeof70., from 45"S (TiB, Ba, SeB, W) to Ionian Basin. In the westem part of the MediterraneanSeuil, the radiolaritic lacics 25"N (tCB). ls absent,but organic matter is preserved.This probably is the result of upwelling The distribution of theseradiolaritic facies and the preserved,manne, organrc not active enough to produce sufficient biogenic silica to be above the thresholdat lnirttcr (Baudin et al., 1992) are similar, but the organic matt€r lies closer io the which the silica is preserved.The organic matter there is preservedbecause of the continent. lûck of oxygenation. The rifting on the northem shelf of Australia creatednumerous small, lsolated During the Late Tithonian (Fig. 16), the MediterraneanSeuil extended(Four- basins suitable for deposition of marine, organic matter mixed with terrestrial. çndeet al., 1993). To the east, it is marked by the overthrust and merging of the organic components; several of these small basins, such as the Browse (BrB; Scrbo-Pelagonian domain; only the small, radiolaritic Ligurian Basin persisted Thomas,1982; Volkman €ral., 1983),Camarvon (CarB; Thomas,l9g2), Dampier (LiB). Northward, in Central Tethys,the LesserCaucasus (radiolaritic) Basin (t,cB) or Barrow (Osbome and Howell, 198?), and southTimor (TiB; Whibley and Jacob disappeared,but the SevanAkera Basin appeared(SAB; Knipper er a/., 1986). Its $on, 1990;Botten and Wulff, 1990),contain thick, organic_rich,argillaceous facies. Éituationstill has to be determined. On the southernmargin, the giant basin that On the northem shelf of India, thick, black-shale formations (e.g., Spiti Shalesand cxisted during the Early Kimmeridgian from Budva (BuT) to Hawasina (Hw; Bé- Nupra Formation) are widely distributed (Gradstein et ol., lggg, t9ôt,). nifting in chennecet ol., 1990) was reduceddrastically: westward, the only radiolarite depos- Gondwanaresulted in the opening of an oceanic basin betweenEast Africa and the its known are those from the extreme south of the Pindos-Olonos Zone (PO:' India-Madagascar block. This new channel promoted the deposition of a black_ 'l'hiébault el al., l98l) and in Cretia (E; Bonneau, 1991). North of the emerged shalc facieson the Hom of Africa {e.g.. Agula Shales,Uarandab and Gehodleh Murdin Ridge and the Arabian Platform, this basin remains well developed. In lirrmations) that are especiallywell developedin (Beydoun, Somalia 1989) as well e$stcrnTethys, the same distribution observed during the early Kimmeridgiân is as in Ethiopia (Carey and Cayce, 1979; Savoyat e/ at., l9g9). Restncted_shcll continucd,with radiol ritcsin the DrasArc to thenorth (DA; Franketal.,1977),in cnvrronnrcntson the Arabian peninsula(Ap) are suitablefor the depositionol. Zhob (Zh; Japancscl)rrkistun Rcscarch Group, 1989),southern Tibet (TtS;Bally e, rt|luinc,organic mattcr. The Hanifa Formation(and its cquivalents)is a prolil.ic. (,/,, l9fl0), sutrourrdirrglrrrlirr, irr llrc IndoncsianBasin (TiB, Ba, SeB, W), and on ù soulcclock in thc Middle (Bcytkrun, l)cllltcl East l()li6;l)ro$tc, 1990).ln (.cn_ lhc Aus(nllilr)nlitrllin lo llx'Br|||llr, lfrl 'lL:thys,thc gcncralorganization in troughsirnrl tlil.ttti ;rl llts not chantctl.I:cw l{ tliol ritcs ure \lill l|lr\frtl rhIiIg llrr ('tciuccousin lhc AtlanticTethys, and As (lltritllltltl' 'lillx)llixll' ç2; rtccitl ( i'lllllrl rlll(l('nhl('lll li'tlryr'+ tlt'clirrt'rl t: =,^ ) tlrtrilrlttttul itt srllllel]lll{s ol tltc l}ttllvtt flt(li1)litrilicsr(litlx. tIlt wIs vr'ty llttrtl,ttccttttittg < 3il - ((;(niellll'l(X)l) illl(lcxllctllcly s(xlth llll$irt(liu) lj1)lllllrr lllllltrtlvllllllo S('rxrllillll sclir:sirr ('rcti (lil l}on.ncu' l99l)' -ie: ,,1,h" l'in,1,,,Olrrttor llitsitt {l'O)llrl(l lllc lithirr ('cnottlilrl (l;ig l6) is ilncxccPti(n (l)hilil) 1n .'aa thi. g"n"rutcvolulilnl, lhc iilt)PcIiod 'l 1,, ttr '4 locallybyabricllcncwal ol lhc ic lircics ,,i.,t,rô,l,n..uur"itisntarkctl -rldiolarit platlirr.rn(Kr, Braucl,lgltg; pic, I{icou anrl Murc.rrx ii.," turin ott of thc Arabian < 9.. ' 1990) At thc samc pcriod iu thc prcscrrl l9ttOl Hw and UB' Dc Wevcr cl a/ ' illl(rchlll(nrolls the first siliceousscdiments are lbund in sotno C ribbeanrcgion, (Si (Sienade SantaCruz' SiCr; Rosentcld'lglll)' Vcnczuclir unit, in Cuoè.uto (tltl ()nt j the Dominicanl{cpuhlic é"6 Tocuyorunit, Sq; Stephan'1982)' u"irio""-*t" ()115 l\r('tl(l interlayeredwith volcanites;.Bourdon '..1 )' I, AjYm ilnr.otion-Coniu"ian cherts Hispaniola. (S iclc ('rrl)('rllri = cherts;Mattson and Pessagno'1979)' -'? Rico (Mariquita t)lt Formation;Mercior dc Lcpirruy' I / l' :t ? Iiormation, Upper Cretaceous,and Peravillo !Ëç] .9;Éi Jumaica(Bath_DunrobinFormation'Campanian;Mercierdc|-cpinily.It)l{,/).(.|||n| 1982)and in La Désirûclo(Morllllrrrr( Iy |,' (Albiun-toroniun;Vishnevskaya et at ' l û1., 1992). shalcswctc tccttvcrctlrttt lltt' On the southemborder of'lèthys' organic-rich margin)at ODP sitc76J ('ll)trrowr'' trl Exm;th plateau(northwestern Austialian ' .92d. - 't'ô. northcrn shclvctittl .urbonate platforms occupiedthe easternand +.Èco! sttlt correspondingto protectedcnvirontttcltls 9.>-lj niri"u "*,"nr*"una Arabia. some locations matter' such as thc trascol lltr' ponit.,. pr"a"-u,ion of black shalesor type ll organic 'Balhoul A Forlration in cirslcltl F 3 iù Formation from TirnisianAtlas (T) or the Karababa 1-Y; In lsrael and Lebanon' the Cenolnaniun l)lliyyll F.i+i Taurus (Et; Cros et al , 1991) È; Ë- marls enriched in marinc' lttgitttic Formation or its equivalent rnclude bituminous (rl" In the Arabianpeninsula (lraq' tJAli' rrtxl inatte.1t-ipson-nen \1ah et 1990) of the organic-rich Mislrrit liorrrtlttioll' ôman), ttre shelf areais dominatedby beds Ë !:/ the Rif Mount irs corrsists()l ,a,a?t in" nyr.tt zone of the Gibraliar Arch and shales'often siliceous'wilh hilh l'o(' Ë-:Ê scdirnentsieposited below CCD Black and Mauretanianseries (Thurow tttl Kttltltl' .9. art,"n, ur" recordedin Massylian ! ! I ! aÊ ^F "Livello Bonarelli"in thc [Jrrrbfirrlvlrll( ll(' lCtfO;HerUin et al.' 1986)The lamous â: È:i: +: - - ç (Arthur and PrcrtroliSilvrt lr)t'lll " -3. : llasin (UMB) is fich rn marlne,organic matter !;Fil -'i of the North Atlantic-c()ns isl Irl l)llr('h I lcrbin cl a/. , 1986).The deep,uasin deposits L in numcrousl)Sl)l'rrrrrl ol)ll !Eniill !I = I: to gray-grecn shalesthat have been investigated Y _:; r lcvcls trttrlrttr' z and carbon-richlayers appearat all bathynctric t z;; 1 *.i*.'ui**" 2 9,iî*rrr herc Highly siliccorlrltr('rr'r rll('lrnr$rl o .Wc lhc truc. radiolaritlcfacies s s-' as defined ùtonli(ùiorlly llrllf z thcy are named"phtânilcs' in Motoccl)'-llonrlclllltl lîonl thc (ctlonrrrnianin Ccnlral lèthys; 'r r.t(,.,orîr.crissr)(iirtcdwithurgnnrcnrurt"rsuchasthcscllilcvclinthcApcDllincrlnnrll|(lilrlv^||tlnl((nlr'll H,qÉ; Thcsc trcics rll sonlcwhlltpetrrlint Mlr|nct| lircoi(lii( (rLl(nli 1987) 'rr'c -ô,1,.r (llrs( t'l th0 'rl willl ltlrr'trlrllrl ..9> a: r, 'r oùÈis 'thcir only conrrùrrrpr)itrt otprrrti(tich. llnolhcris cLryri(h lrrrolll('l Dowdcry) (('rrl(.rrl .u E:,'r lrfil( |, ii tln'if hifh siliu' "rnrc"rrr(lioIrrircs !i : di ,/; ,ilt;;;i;,"i;r ,,rcrrr1u,",1.*6,,'1. rh('ylrr rrtrr ',," .1116 lhtrl(h th Wevcr/,,rl. tt||dk)lnrhrn'irrtd'ltlh]rrl llfilhrltlrllfr

charactsrizedlicquontly by typicatal(crn.ri(nrs.l tk.r,.irrrctric,bl.ck antrgrcc'cray- .1. 'l'hcy lrc tlcvcklx'tl (ltlilc cxlcnsivclyott lltc MctliterrltttcrtttScttil tltttittg stones.Such black shaleswere recovercd in l)SI)t, tiitcs 5, l0l, l(,5, li-5, ()xlindi tl tilllcs 36'7, 137, Crlkrvian nrl(l 370, 386, 38'7,391, 398, 4ts, 417,534, r)rirrgitl -54.5,S+i. s+9. ;0, 55l, an

i,i€ne"-". ricvcrxlcollcngucl lirr thcir'hclplirl vurhln lclsorrs,clpccillly to .lcunl)crcou |(t|th.|l||c((l(\(f}|ir{tll||l({|'||t|||d(|ll|r|||l|||(|I|['l[l(d(I[|I|c (Ul'MC), who cunicdout llrc'l'cthysprrrgrlrl lnrl cliticizcdund pflinstukingly Snt. (iu,l Iin,r,r tl|l2.1 l.t) helpedus to improvcthc nr nuscfipt. , lj. Mrr||rrrl,O., lléBrnrr'I.V, l. lt!'nÙt-l)clllrlc, Ii., trndItcrso[, 1994,Cûrâctérisation ct dirrttcuù$ùdc lu ||nrtiùr'cor8r i(lucrlu .10ftssi(luosopéricur du'Iuurus ^.,occidcntal ('furquie Méridi- o|lûlc).Rccofrslituti(nr pifléocnvit1rl,rcnrcnrûlc cr conséqucnccs lccloniques, Bull. Soc.Géol. Frcnce 165{2):135-145. REFERENCES Bâunrg,rrtn"r.P. O.. l9ti4. A MiddlcJù'assic-Early Crelâceous lowlalitude râdioldian zonation based on UnilàryAssocialioN and agc of Tcthyânradiolarites, Eclogae Geot. Helv. 77:129-837. lochcnncc,F., tÆMctour, J.. Rabu,D., BourdillonJeudy De Grissac,C., De Wevet P., Beutfier,M., Anderson,R. 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Ëranrlrr||htr r,,rrr,,r,r,Kry\ryr,|,M'rr,rrr,r.,,rrrr delinl,l{, thlh | 1,, fi[tr trt li ^ lrr,r,.rrlrr iùù1,'iii!,iilii.,irr'rrr,,tlMar tâJ rn M , Mahù,lrd l, l9lg, Il{ltltl$llr{r rrl lhÉùrtr$rr llrr hénlr l rt|rly r'l ll[' e RtrrlhrlrrrltrttrrIul'li'lh!||ll ll l|ollllllt'r |rlrrt'|.s|rlrli'Mrr(l|||l(|||l||fs(ll|k.l|{1.ll||||t(||||||l'l||t|l||l||{l||lll|l|li$|ll|('t|lt.l\4|lfl|l|'!|i||{\| rl(krtr(srrrllrtnirl0Mt11.tlj.Slovirlr|) !ltcilt'(.'l,'.l|'l{|lt'll.|l]ll||(|..|||''|ll/l|'|i\ll||llll(||lI|||){lt'|||l|tlilf|C(ly\ll|lliZl|lll N,lrl,tItliul tlt(,trr,frr\lrvIliIl worli l,l(.(i.)5.1 t tr,0l, Jf./ /t1l'lr']qf 4(ri'll{) 'l\'l(lrrllilerorrsbltlet s[rrlcs. .].t li(n)irn{l 8lt)r'tlh rllr,(l(l / '115' ,, . -15 Irr l(rN,, irl\r|lri.t\,lllll t , llt l)t). silicr budgcl flÙctuations' lr)l{1,ltir)\ilitct'rr\ scdinrcrrltrli(nr.ri|diolirfilc Icfi(xls Lrnd ''()P(,vll.|'M'.|l)l((l.'lïl|t|s|xn1nti(n|('||i|(|(||u|ll|ls|K.l|!hytl|||l.\l(||l!l||l|i(l|sbl\0di $tcinbcrg, M, (,1Kul1)shio), ill: (1,.t)c Wcvu., Ocornol(l8icxAcla. sp. 119 154 cd ). |t). t()7 t0.t ti|orir(l lV lVrt.hk,I,littr$ul(rntt. Spcc. tssur. to th€ understanding I l: M., Su*uu-Courrois. C . and Tlig, S l9ll3' GcochcmicalC^ontribution t-.1. St.infr"À,- l1'$!ll. - an{l R Sievcr') pp 193-210' Siliceous depositsin the f. (; . r')x5 r'rr(,'ru,rsrrphi( uiËOa",l Cft"n. in: (A Ijinta. J R. H;ifl, irnphcirr..,rsIn lrrcdisrrib.'rr(nr or uppcr JuLrssicsoufcc bc(r\ I'rrslk,I( ( p,!.Gû,l Pacificregion. Dev- Scdimentol 36, Elsevier,Amsterdâm' .. {r\t n rnrJr. tult. C,ut. 3.r:t. U(,_ ,,. caraibesur la rLrfi:ell. 1982,Evolution géodynamique du domaineCâmibe Andes et chaine L |., Unrf(hy D.C.,ancl wJtje,J.A., I9t0, Rcgionalgcologyand hydrocarbon Sf"pi*-i.-' n.i occurcnccs - Thésed'Etât Univ P et M Curie' Parisvl' 512 pp' rff rhc cu\l (i,usr,,t CrnJdJ. in principles petrole tr*.u"rrui" d" uo.quisirnitoavénézuéla) F.cts and o] the World.s um Occurcncc ( a. t) of dilïcrentsilica modification Adv' !rrrll. pelrot. W iqOl e".tition of silicic aci