GEUS Report file no. A stratigraphic section through the Silurian 22488 turbidite sequence (Peary Land Group) in northern Nyeboe Land, North Greenland
Poul-Henrik Larsen and Jan C. Escher
GRØNLANDS GEOLOGISKE UNDERSØGELSE
1991 GRØNLANDS GEOLOGISKE UNDERSØGELSE RAPPORT 151
_ t\ A stratigraphic section through the Silurian turbidite sequence (Peary Land Group) in northern Nyeboe Land, North Greenland
Poul-Henrik Larsen and Jan C. Escher
1991 Larsen, P.-H. L. and Escher, J. C. 1991: A stratigraphic of the Merqujoq, Lauge Koch Land, Wulff Land and section through the Silurian turbidite sequence (Pe Nyeboe Land Formations, the Castle ø Member of ary Land Group) in northern Nyeboe Land, North Nordkronen Formation and the Chester Bjerg Forma Greenland. Rapp. Grønlands geol. Unders. 151, 21 tion are described. pp. Authors' address: A stratigraphic section is presented through the 6330 Geological Survey of Greenland, øster Voldgade 10, m thick Silurian turbidite sequence of the Peary Land DK-l3S0 Copenhagen K, Denmark. Group at Hand Bugt in northern Nyeboe Land, North P.-H. L. present address: Statoil, Løkkemyra, Postboks Greenland. Thickness, age and sediment characteristics 2123, N-6S01 Kristiansund N, Norway.
Grønlands Geologiske Undersøgelse Kalaallit Nunaanni Ujarassiortut Misissuisoqarfiat Geological Survey of Greenland
The Geological Survey of Greenland (GGU) is a research institute affiliated to the Mineral Resources Administration for Greenland (MRA) within the Danish Ministry of Energy. As with all other activities involving the non-living resources in Greenland, GGU's investigations are carried out within the frarnework of the policies decided jointly by the Greenland Home Rule Authority and the Danish State.
© GGU, Copenhagen, 1991 ISSN 0418-6559 Contents
Dansk sammendrag - Imaqarnersiuineq ...... 4 Wulff Land Formation ...... 15 Introduction ...... 5 Nyeboe Land Formation ...... 18 Sedimentary logs and beds thickness diagrams. . . 5 Castle ø Member (Nordkronen Formation) ... 18 Merquj6q Formation 6 Chester Bjerg Formation...... 20 Section 14a ...... 7 Summary and discussion ...... 20 Section 14b...... 11 Acknowledgements ...... 21 Thors Fjord Member ...... 13 References ...... 21 Lauge Koch Land Formation ...... 13 Dansk sammendrag
Artiklen præsenterer en stratigrafisk profil gennem der og sedimentære karakteristika for Merqujoq, Lauge de 6330 m tykke, sandede, silure dybhavssedimenter i Koch Land, Wulff Land og Nyeboe Land Formatio Peary Land Gruppen i Hand Bugt, det nordlige Nyeboe nerne, Castle ø Member i Nordkronen Formationen Land, Nordgrønland. Desuden beskrives tykkelse, al- samt Chester Bjerg Formationen.
Imaqarnersiuineq
Allaaserisami Kalaallit Nunaata avannaani, Nyboe tassa kinnganerit immikkoortinneqarsinnaasut issussu Landip avannaa tungaani, Hand Bugtimi sioqqat imar saat, pisoqaassusaat isikkuilu allaaserineqarput. Taak pissuup naqqata kinnganeri qaleriissitaartut 6330 mete kulu saniatigut Nordkronen Formationip iluani immik rinik issussuseqartut, silurip naiaani kiviorarsimasut il koortut Castle ø Member-imik taaguutillit kiisalu Ches isaritinneqarput. Kiisalu Merqujome, Lauge Koch Lan ter Bjerg Formation allaaserineqarput. dimi, Wulff Landimi Nyboe Landimilu Formationit, Introductian
During the regional rnapping programme by the ~orth Greenland, documenting the thicknesses, ages Geological Survey af Greenland in western North and sedimentalogical eharacteristies af the formations Greenland in 1984-85 (Henriksen, 1985, 1987), two Sedimentary lags and beds thickness diagrams The stratigraphie seetlon rncasurcd through thc Silur graphie faeies scbeme shown in Pig. 4, whieh was ian turbidite sequcncc in thc Hand Bugt mea is pre erected by llurst & Surlyk (19.s2). with some additions sented in PJate 1 and a generalised section log is shawn by Larsen & Escher (1985, 1987), in Fig. 2. The measured section has been divided into B<:d thiekncss diagrams are used to illustratc system two parts as sho~.'n in Plate l and in thc oblique aerial atie variations in the thiekness af sandstone turbidites photo of thc locality (Fig. 3). The lowcr part (scction and the relations of sandstone turbiditc sequenecs ver 14a in Fig. ~) covers the basal 259 m af the Peary Land sus mudstone intervals (Figs 9-10, 12, 15). Group turbidites which outerop in tbe northern part of To eOl1struct a bcd thickness diagram eaeh ROllrna thc I-land Bugt region. The uppcr part (sectioll 14b in division (Bouma. 1962) of a single Lurbidite bed is plot Fig. ~) covers approximately ~300 m of the Silurian tcd horizontal1y showing the sand/silt divisions (Tabcd) turbidites locatecl to the soutb. A stratigraphic sequence to the rigbt and thc mudstonc division (Te) to tbc lefl. of approximately 2000 m separating thc two scctions has Sequences af a1ternating Te and Te divisions are also not been investigated. ploned to tbe lefl. Non-graded. struetureless fine sand Sejeeted parts of seetians 14a and 14h have been stone turbidites, which cannot be described by BOUOla logged in detail and standardised aecording to the lithol divisions, are plottcd to tbc right in tbc diagrams with ogy and structure legend shown in Fig. 4. Other parts the same ornamentation as the Ta-divisolls. This way of hciVe been logged in general applying tbe lithostrati- plotting the thiekness of each wrhidite hed gives a visual 6 Fig. 2. Generalisd :-ectioll log of the 6330 III t!lick succession m af Siluri,m lurbidites of lhe PeMY Land Group rncasured in 6000 Chester Bjerg Fm Hand Bugt. J10rlhern Nyebnc Land. - ?- 5000 Nyeboe Land Fm impressioll af the bed thickness variations and lhe sand (silt)/mud ratio. It also provides an easy way to delin O• Castle ø Mb O eate S -....-,- WULFF LAND HENDRIK ø NYEBOE LAND i L ..J'_~ ~ .. Fig. 3. View to the east across northcrn Nyeboe Land of the steeply dipping Silurian turbidites of the Nyeboe Land linear belt. C-S: Cambrian- Lower Silurian clastic sediment. M: Merquj6q Formation, TF: Thors Fjord Mcmber (\Vulff Land Formation). LKL: LlUgC Koch Land Formation. WL: Wulff Land Formation, NL, Nyeboe Land Formation, C0: Cas)le ø Mcmber (Nordkronen I'ormalion). CG: Chester Gjerg formation. Aeriai photograph 546 E~Ø, no. 11575; copyright Kon- og Malrikelsty rcl~cn, Denmark. 7 lithology Slruclure Facies F"Ol Mass"c DiSO'08 nlS"O ~ Conglomeratc ~ D conglome,atC A Pebbly saMstone ~ Parallel lamlnallOo Q j"A, O'1I3,,,aea poebble con9'ome,ale Saodstolle ~ 10d,.I,oct par~II..1 IKm",ahoo D Noo.0'3'''''' m..d,um 5mall scale eross lamlnat,on O! f,n" saOOSlo"" o E8 8 Non_g'30eO S.I1SIOO" 00 l3'SJ w .. "~ 1.. ",,,,aTlot> 1"'.", or lone ~M"ls!one ~ S,II,'on" F,a .." 'am.03"oo (lo"m3 ~r ..s."'1 ~ II C, '3 Imedium O' line san sectioll 14b (0-597 m) represents the rop of the forrna A statistieal representation ofbed thieknesses and the tion. The stratigraphic thickncss het\veen the top of sand/mud nltio in seclion 14a is shown in Fig. SA. The scetioll 14 (Plate I. a·b) of lhe Mcrquj6q Formation. 23< d ~ -~ Legend gi\'cn in Fig. 4. ==-~~, 233 ~ ..=-~--~~ '32 __~ d ~',," ~, '" - -~ -e-~ 230 -~--:::==~ "~-l 229 ~ 92 22. -'-~"\ - ~- ,,~~CJC -~- ~~~-~ - I 227 J ~ ". ~ ~ - ~--§ .01=_...... 0:: 226 - = 225 '2' 223 Q o 2 E 222 " C) "- .:1~ =- _'"t U c o- '.2. 221 ro o -' o- O>. " 220 'O. $ " -~= .=.} ."- - -~ 219' 107= , \ ". --.-=--:--- ~'\. :;3' '06- I~,~~~ " ~ "1 ,o, '" I _J 80 ". I, ~ 7' j 'O, n 'O, 100 - i J a "J:4i$=-:t CiS;fmc' " Fig. 6. DClailcd log uf part of scction 14a c (Pinte l. c-d) of thc Mcrquj6q Formalion. Legend given in Fig. 4. Merqujoq Fm Merqujoq Fm Lauge Koch Land Fm a c d Fig. 7. GroupeJ palaeocurrent data for thc Silurian turbidites at Hand Bugt. Stipplcd rose diagrams are dirl'ctional mcasurcmcnts aIld (c.g. flutes); apen rose diagrams are trend measurements (c.g. grooves). a. Scction 14a (Platc l, (1.-259 m) b. Scction 14b (Platc l, 0--597 m) c. Section 14b (Plate l, 680-1532 m) d. Sum af a,b and c abave. ® ® © @ Section 14 Cumulatille b thickness of facies c c Ta -c{dI/T 1.7 fo.; 0,7 1-}4' Facles ratios I c/e Ta - C(dl,/re. TcJe 1.4 d 46 d 05 d 11 d Fig. 8. Statisticai rcpresl'ntation af bcd thicknesses and sand/mud ratios. a. Frequency ol" sandstone turbidites (Ta-c(d» in cach bed thiekness interval. Non-graded !:itructurclcss, sandstone beds are included. b. Cumulative thickness of bed!:i within cach bcd thickness interval as percentage af total thickness in the int1ivit1ua! scctions. c. Cumuiativc thieklless af facies as percenlage oftotal thickncss in thl' individual sections. Non-graded strudureless sillHls!one heds are calculatcd in the Ta-e(d) facies. d. Sand/mud ratios ealculated in tilTec different ways based on data from c. IO 535cm Tele c===:; 200 100 6 200cm Fig Te Ta mud sand/silt Te le C=====i:;:"" Te/e C======~"-'-~="""" 260 100 o 200 cm Fig. 10. Bcd lhickness diagram silOwing thining-upward cydes af sandstone turbidites separated by Telc facies. The rninor cydes rnakc up ti major composite cyde sbowing il general thining-upward scqucncc (Plate L scction 14a, 209-234 m). Thc diagram rcpresents the section in Fig. 6. Il ations ean be demollstrated between {be [hickening up (76--597 m) which has heen loggcd using the facies ward cycles and thinning up\vard cycles; in both cases schcl11e in Fig. 4. The sandstone dominated units tend lhe sand/mucl ratio is > [ (Figs 9. IO). to occur isolated and are sep Hand Bugt (Higgins & Sopcr. 19H5; personal eommuni 20---~~~ cation. 1986). and Latc L1andovcry graptolites art' also present in scction 14b (see helow). 'I m c--- b I 42 --j--~, --- , SeClioll /4b I 17 Tile basal part af scction l4b (Plate I) rcprcscnts thc I topmost 597 111 of the Merqujoq Formation at Hand Bugt. The lowermost 76 m has been measured in detail while the rcmainder was [ogged folIowing the facies 39 sehclne III Fig. 4. The lowermost 76 m are eharacterised by bull-yellow to brown wcathering, medium to fine 38 grainecl sanclstone turbidites. The turbidites shmv abun " dant Tahe. Tale and Tbe Bourna sequenees, hUl non '3 37 graded structurdess medium or fine grained sandstones <.l[sa occur (Fig. Il). Thc sandstone turbidites have char 36 acteristically loadcd and f1lJtcd soles. - A statisticai representation of bcd thicknesscs and 35 sand/mud ratios in seetion 14 (0--76 m) is shown in Fig. 8B. The sandstone turbidites oecur in beds frorn a fe\\' eentirnetres to 6.5 ITl in thickness. However, [he me dium and thick-beclcled turbidites me [hc most abun 9 danI types comprising approxirnateJy 70"Yo af tile beds 32 ~--"- - - ... ~--- (Fig, 88a), Although ve ry thick-hcJJcJ lurbiJitcs (1-3 m) are few in Ilumber. they aceount for more lhan 40% af tile total cUJllulatlve thickness of the sandstones (Fig. ~ 8Bb). Whcn takcn togelhcr the sandstone turbiditcs rnake up more thim 80% of the rneasured section (Fig. 6~~==~~~' '. ~\ BBe). giving a sandstone/mudstone ratio » I (Fig. 5 88d), Systematic variations in bcd thickness in the seetion '~l!! (0--76 m) eannot hc dcmonstratcd. [nstcad adistinet .. _-~-~ medium to fine grained sandSlOne [urbjdite sequence 3 1 _- ~~ \vith a sand/mud ratio approaching infinity ean bc dcrn onstratcd in thc lowcr part and is hcrc reprcsentco by 2 the log in Fig. Il and the hed thickness diagram in Fig. ~a 12. Thc scquence is boundcd below and above by pack crsd..!!lf- b'sl!..!%..' ages (1.5-2.5 m) af lTIudstone turbidites 01' Te/e facies. ss ss Such sanJstone Jominatcd units, 5~[O m thick, are Fig. ll. Dctailcd log of part of scction [4h (Plalt: [. a-b) ()f [ile frequently found in the rest of the Mcrquj6q Formation Merquj6q Formation. Legend given in Fig. 4. 12 Te Ta mud sand / silt "·1 670cm , , , 200 '00 O 100 200cm Fig. 12. Hed thickncss diagram rcprcscflling the sediment log (Jf Fig. 11 (Plalc I, seclion 14b. 1--42 In) showing a scqucnce of very Ihick beds (0.50-6.70 m) (Irranged in a symmctric Ihinning Fig. 13. Thinnillg-upw Tale L30urna sequcnces, but non-grilcled structureless m fine graincd sandstones also occur (Fig. 14). A statistica[ representation of bed thickncsses and sand/mud ratios uf the uppcrmost c. 95 III uf the forma tion is shawn in Fig. Se. Thc sandstone turbidites ap peal' in beds from a few ccntimetres to 2 m in thickness. Tlle medium-bedded lurbidites are the Illosl ahunclant type cornprising almost 50'}~ af thc beds (Fig. 8Ca). while the thick-bcddcd turbiditcs makc up more lhan 5lVXl of the cutnulativc thickncss of thc sandstone turbi dites (Fig.. XCb). ThI..' fille graincJ sandstone turbiditcs takcn together only account for 30% of the measufcd " scction (Fig. .RCc). giving a sandstollc/mudsrone ratio < l (Fig 8Cd). " R,,"~ Systematic variation in bcd thickn~sscs within th~ 12 sandy turbidite pac kages in the scction has been ob ~ ~~ serv~d. with thickcning upward cydes bcing separated by 2.5-3.5 m thick mudstonc units (Te/c Licies) (Figs 14. " 15). Within each cyde the sand/mud ratio is > I. 1510 Channcls have not becn observecl in this uppermost part af tlle formation. Thc bcd shapc is Ilormally planar. 00 but some !::lteral wedging out af scvcral af the medium co.. ~- 08 c!O(;S O- o beclclecl turbidit(;s occur. Dir(;ctioll,-ll palacocurrcnt o ~ ~ ~ ~ r- o ~ lhlta from the Laugc Koch Land Formation in Hancl .~ cO ~ o, --- Bugt show a wcstward sediment transport whieh is par ~• ~ ~ c ~ allel to the trend af the obsen'ed minor channel in the "æ u --' o 06 lowl'r part of the formation (Fig. 7c). ~ Monograplus priadan (GGU 315475) has bcen reco verccl from till' section about 100 m abov(; the base (s(;ction 14b. 790 m). This species has a lang r Te T a mud sand / sitt Tele / TC/e=~ 300 200 100 o 100cm Fig. 15. lkd thickncss diagram showing thickl1ing~upwardcydes of sands\ol1c turbidile.s separated by Te/c faeies (Plalc l. seclioll 14b, 14':)4-1520111). Thc diagram represents the seclioll in Fig. [4. Wulff Lancl formation ised by units of thin-bedded silty mudstone turbidites (50--400 cm Ihiek) intcrbcddcd with mediulll to thick Thc Wulff Land Formation was erected ny HUfst & bcdded, caJcareous. silty sandstone turbiditcs. Tlle silty Surlyk (1982) for Cl sequcnce af bl m -" Fig. 16. Dctailcd log of part of scclion 14b (Plate I. c-f) ol' the intcrfingcring Lauge I "' ~.;..... ~ Koch Land Fonnatioll and Wlllff Land For mation. Legend given in Fig. ~. , 79 \ 78 ~-~/' - --- - :- m 1601 160oF~~!'! 99 •E o 97 3 ~ g~ - ---::-~ ~ E E 95~ "'.u~ ~ c • ro " ~t ~ 94 _-_- ~ o ;lj----i " ~ ~ . g o.~• 93 o. 3 o • , ~ E "'~ u~ j C • " ._- ~- ~g. ~• 91 66 ;:-. 9'1-" ~ ~ eJ@ 0. ::; -- 3 1::;90 ~:I~:: .t!. -~ & 99 ~;f'~-~:~~1'4=:~Jl;;1 J'~ ":;• (J@ 68 ~=::'~'.A~l ::1--= 85 >:':./':l." J).. ~-- ~ ~--~--"",! 59i:;:=--=::-~~ 9' o BR~CHIOPODS ~ CR1NOOS 1557 e btsi'lm2 " ,lild thick-beddcd lurbiditcs are the must abundant 60% of tlle cumul,uivc thickncss uf tlle vcry fine grained types comprising morc lhan 80°,.{1 uf the heds (Fig. 8Da). SandsLOlle turbidites (Fig. 80b). while tile sandstone Tlle thick·bcddcd turbidites make up approximatcJy lurbiditcs takcn together account for approximatcly half 17 af the rncasurcd scelion (Pig. 80e). Mudstonc turbi m elites (Te divisions) together with the T c1c-faeies aecount 6. I~ -ct=.===t: for the olher hall'. The sanJstone mudstonc ratio is > J 1860~-~\ (Fig WeI). Sandstone beds (2-10 cm thick) \Vith a high content af 5geb~ crinoid and brachiopod debris often aeeur within indi vidu,,! lurbiditcs (Fig. 16). Somclimes these beds are 58'~ foune! at the base af the Ta di .... ision but normally thcy arc associatccl witb tlle basc af Tb divisions. Trace fos 57~ sils are flbund,)Ilt at the base af lhe silty fine grained sanclstone bt'lb throllghollt the sequence. Ncither ehan 561--1-__ - nelling nor ckar systematic variation ill bcd thickness lwve been obscrvcd. The few palacoeurrclH measurc ments inciicate a llorlhward sediment transport. The remaining part af the Wulff Land Formation at Hand Bugt (section 14b, 1625-2J97 111) is dominflted of 53 ' thick units (1-100 m) af lhin-bedcleJ muclstone and siltstollc turbiditcs (Tele alld Tdc) set against a ba<:k ground af silty mlldstone. The siltl' lll11dstones are mainly clark green but lighter colours such as light green, grcyish green and grel' may oecur. The eolour changes gradualll' up the sequence and greyish tones are musl conspiCLloUS near the top, where alsa several in tervals of ptlper shales oeeur. Throughout thc sequcnce tlle sil1y rnudstones and shales are aften bioturbated and eonti.lin abllndant starved rippies and pl'ritc eanere tions. In two 80 m intervals (1717-1796 m and 1892 1968 m) the grade is gcneralll' uniform fine grainecl si\(. and layering is only indieated by [he eolour banding in variaus shades of grecn to brownish red. Thc thiJl bedded silty mudstonc units are interbedJeu by thickcr hedded (IO-50 cm) silty s 35~ Fig. 17. Dctailcd log af part ol' scction 14b (Platc l, g-h) of an 1834]~-1~ g interfingering sandstone p From studies of aerial photographs the sandstone of Larsen & Escher (1987). The sequence has been packages between levels 1834 m and 2050 m in section examined only briefly at Hand Bugt, and its thickness is 14b can be traced into the conglomerate dominated estimated to approximately 950 m. It is the southern sequence occurring east of Frankfield Bugt; they might most very steeply dipping unit within the Nyeboe Land therefore be interpreted as distal sandstone lobes of the linear belt and interdigitates with the overlying Chester Hendrik ø Member of the Nordkronen Formation. The Bjerg Formation (Figs 2, 3). sandstone turbidites or sandstone packages occurring No graptolites were recovered from the formation at above level 2050 m are interpreted as interdigitations of Hand Bugt. However, as Early to Middle Ludlow grap the overlying Nyeboe Land Formation into the Wulff tolites were recovered from the underlying Wulff Land Land Formation. Formation (see above) and as the base of the overlying Bohemograptus bohemicus (GGU 319269), Mono Chester Bjerg Formation might be older than Pridoli graptus uncinatus (GGU 3]9269) and Pristiograptus sp. (see later), the age of the Nyeboe Land Formation (GGU 319269-270) collected within the 665 m thick seems to be Ludlow, possibly Late Ludlow (Larsen & Wulff Land Formation at Hand Bugt indicate an Early Escher, 1987). to Middle Ludlow age. This is in accordance with grap tolite assemblages collected within the Hand Bugt and Castle ø Member (Nordkronen Repulse Havn Members to the east of Hand Bugt Formation) (Hurst & Surlyk, 1982; Larsen & Escher, 1985, 1987). Bohemograptus bohemicus (GGU 319246, 319249, The Castle ø Member of the Nordkronen Formation 319252), Monograptus ?micropoma (GGU 319252) and (Larsen & Escher, 1987) at Hand Bugt comprises a 36 m Pristiograptus dubius (GGU 319249) collected from the thick sequence characterised by chert pebble conglom Wulff Land Formation in Hall Land also indicate an erates (section 14b, 2310-2346 m). A basal megabed Early to Middle Ludlow age for the Formation. (5.5 m thick) of coarse chert pebble conglomerates is overlain by medium to thick-bedded generally coarse pebble conglomerates interbedded with fine grained Nyeboe Land Formation sandstone turbidites and few thin mudstone intervals (Fig. 18). The conglomerate beds are structureless and Outcrops of the Nyeboe Land Formation in section sometimes graded. Sub-horizontal clast orientation may 14b are separated into a basal sequence (2197-2310 m) occur and rare weakly imbricated horizons have been and an upper sequence (2346-3296 m) by the interven observed. ing Castle ø Member of the Nordkronen Formation. The conglomerates are clast supported, well sorted and generally the clasts are sub to well rounded. The Basal sequence. This 113 m thick sequence (section clasts are predominantly black, green and grey cherts 14b, 2197-2310 m), corresponding to the basal part of (c. 90%), the remainder consisting of quartzites, car the Nyeboe Land Formation of Larsen & Escher (1987), bonates and intraformational turbidite sandstones. The is characterised by buff-yellow weathering fine grained matrix of the conglomerates is well sorted, fine grained sandstone turbidites interbedded with finer grained silt sand corresponding to the lithology of the interbedded stone and mudstone intervals. The sand/mud ratio is > fine grained sandstone turbidites. 1. The fine grained sandstone turbidites are normally The sequence was not logged in detail and no faunal thick to very thick, structureless and non-graded beds; assemblages were recovered. However, graptolites de they are closely associated with the conglomerates. scribed from the underlying Wulff Land Formation (see No palaeocurrent indicators or faunal assemblages above) indicate that the base of the Nyeboe Land For were found. Age constraints imposed by the underlying mation cannot be older than Early Ludlow. and overlying turbidite sequence of the Nyeboe Land Upper sequence. This fine grained sandstone turbidite Formation, discussed elsewhere, indicate that the Castle dominated sequence (section 14b, 2346-3296 m) corre ø Member of the Nordkronen Formation can be no sponds to the main part of the Nyeboe Land Formation older than Early Ludlow, possibly Middle Ludlow. Fig. JS. t~ Lktalkd 10 0 at 1\' laIt.: l),1~J of the '"C t partlA of seC[lon 14b (P ord kronen Forrn'ltloll._ . ,1stLeC '>U_ M'em bcr of lhe gcnd given in F·~Ig. 4. 23 21 m 2346~-~ 2320 44 42 2340 39 38 37 36 \ L clsi'.!b~Vfljm'cR ss~ 20 Chester Bjerg Formation The formation was only briefly examined at Hand Bugt. The graptolite Pristiograptus dubius (GGU The Chester Bjerg Formation defined from western 315484) was collected within the formation 7 km south North Greenland by Hurst & Surlyk (1982) is the up of Hand Bugt, indicating that the base of the Chester permost lithostratigraphic unit of the Peary Land Bjerg Formation might be older than Pridoli, i.e. Lud Group. It interfingers with and overlies the Nyeboe low. The occurrence of Pristiograptus separabilis (GGU Land Formation (Larsen & Escher, 1987) and is ex 319223) in Hall Land confirms the Pridoli age for the posed in section 14b between 3296 and c. 4096 m. formation suggested by earlier finds (Hurst & Surlyk, The formation is characterised by laminated light 1982; Dawes & Peel, 1984). No unequivocal faunal green weathering mudstones or siltstones. Its stratigra evidence for the presence of Devonian strata within the phic thickness has not been measured, but may be esti formation has been found. mated to 500-800 m (Dawes, 1976; Hurst & Surlyk, 1982; Larsen & Escher, 1985). Summary and discussion Two stratigraphic sections 14a and 14b covering the which is dominated by mudstone and siltstone turbi base and upper part of the Silurian Peary Land Group dites. The base of the Chester Bjerg Formation might have been logged at Hand Bugt (Plate 1 and Figs 1-3). be older than Pridoli and the formation may extend The work documents thickness, age and sediment char through to the end of the Silurian, or even beyond. acteristics of the various lithostratigraphic units of the The palaeocurrent directional measurements from group plus an estimate of the total thickness of approxi the logged turbidite column show a unimodal westward mately 6300 m for the Silurian turbidite succession in sediment transport (Fig. 7d). This is in agreement with western North Greenland (Fig. 2). data obtained by Hurst & Surlyk (1982) who suggested Faunal evidence points to a Late Llandovery age for an eastern Caledonian source for the deep-water sedi the basal 2800 m of turbidites referred to the Merqujoq ments. However, the high lime mud content of the Formation. The Merqujoq Formation is overlain by an shales and the calcareous turbidites occurring in the 83 m thick mudstone unit, the Thors Fjord Member of Thors Fjord Member, the few northward directed pa the Wulff Land Formation. Graptolite assemblages sug laeocurrent measurements obtained in the sandy turbi gest that the Thors Fjord Member in the Hand Bugt dites interfingering the Wulff Land Formation higher in area marks the Llandovery - Lower Wenlock transition. the succession and the crinoid and brachiopod detritus The Thors Fjord Member is succeeded by 852 m of frequently found in these often calcareous turbidites mainly sandstone turbidites belonging to the Lauge suggest that some material was derived from the south Koch Land Formation which contain sparse graptolite where the deep-water basin was fringed by large, de material indicating a Wenlock age. The Lauge Koch grading carbonate mound complexes on the slopes of a Land Formation is succeeded by 665 m of mainly mud drowning carbonate platform (Sønderholm et al., 1987; stone and siltstone turbidites, with few interdigitations Sønderholm & Harland, 1989; Higgins et al., in press). of sandy turbidites, referred to the Wulff Land Forma The general evolution of the Silurian deep-water ba tion; graptolite assemblages suggest an Early to Middle sin in North Greenland was described by Hurst & Sur Ludlow age. The Wulff Land Formation is overlain by a lyk (1982) and Surlyk & Hurst (1983, 1984). These succession of 1100 m of mainly sandstone turbidites of authors regarded the Peary Land Group as representing the Nyeboe Land Formation. Approximately 110 m a longitudinal E-W trending deep-water fan system fed above the base of this formation, a 35 m thick sequence from the east as mentioned above. In their model the of chert pebble conglomerates occurs, which is referred sandstone turbidite sequences in northern Nyeboe Land to the Castle ø Member of the Nordkronen Formation. are distal in respect to the source and were thus in The Nyeboe Land Formation and Castle ø Member terpreted as representing outer fan or fan fringe deposi have not yielded faunal assemblages but age constraints tional environments, while the mudstone sequences imposed by underlying and overlying sequences suggest were regarded as basin plain or lower slope deposits. Middle to Late Ludlow. The measured sequence is Our data presented here are in good agreement with topped by the Chester Bjerg Formation (at least 800 m), these interpretations. 21 In the most distal western parts of the turbidite basin sition either as deep-sea channel deposits or as sand in Hall Land Hurst & Surlyk (1982) noted character stone lobes in an outer fan or fan fringe environment. istically alternating turbidite units and mudstone se The mudstone units may reflect periods of non-deposi quences. They tentatively suggested that the mudstones tion directly from turbidity currents and thus represent were reminiscent of levee deposits bordering wide E-W temporary interchannel or interlobe deposits consisting trending deep-sea channels which were thought to have of pelagic and hemipelagic material, and occasionally migrated laterally across the basin plain. The coarse diluted suspension deposits derived from bypassing tur units thus corresponded to channel deposits. bidity currents plus resedimented material from the The isolated sandstone packages occurring in the deep-water circulation. mudstone dominated Wulff Land Formation reported here from the section at Hand Bugt may be interpreted Acknowledgements. We thank N. Henriksen, A. K. Higgins, J. in the same way. The alternating sequences of sand S. Peel, F. Surlyk and M. Sønderholm for critically reviewing stone packages and mudstone units described from the earlier drafts of the manuscript. M. Bjerreskov is gratefully top of the Merqujoq and Lauge Koch Land Formations acknowledged for identification of the graptolite faunas. Fi-' at Hand Bugt may be more proximal in character. The nally, we thank B. Thomas for drawing the many figures and coarse units may reflect periods of active turbidite depo- V. Hermansen and J. Lautrup for technical assistance. References Bjerreskov, M. 1981: Silurian graptolites from Washington ogy ofNorth Arnerica, vo!. E. Ottawa, Ontario: Geo!. Surv. Land, western North Grønland. Bull. Grønlands geol. Un Canada. ders. 142, 58 pp. Hurst, J. M. & Surlyk. F. 1982: Stratigraphy of the Silurian Bjerreskov, M. 1986: Silurian graptolites from N Greenland. turbidite sequence of North Greenland. Bull. Grønlands In Hughes, C. P. & Rickards, R. B. (ed.) Palaeoecology and geol. Unders. 145, 121 pp. biostratigraphy of graptolites. Geol. Soc.Spec. Publ. 20, Larsen, P.-H. 1986: Soft sediment deformation structures in 181-189. Silurian turbidites from North Greenland. Bull. geol. Soc. Bouma, A. M. 1962: Sedirnentology of sorne flysch deposits, Denmark 35, 19-23. 168 pp. Amsterdam: Elsevier. Larsen, P.-H. & Escher, J. C. 1985: The Silurian turbidite Dawes, P. R. 1976: Precambrian to Tertiary of northern Green sequence of the Peary Land Group between Newman Bugt land. In Escher, A. & Watt, W. S. (ed.) Geology ofGreen and Victoria Fjord, western North Greenland. Rapp. Grøn land, 248-303. Copenhagen: Geo!. Surv. Greenland. lands geol. Unders. 126,47-67. Dawes, P. R. 1982: The Nyeboe Land fault zone: a major Larsen, P.-H. & Escher, J. C. 1987: Additions to the litho dislocation on the Greenland coast along northern Nares stratigraphy of the Peary Land Group (Silurian) in western Strait. In Dawes, P. R. & Kerr, J. W. (ed.) Nares Strait and and central North Greenland. Rapp. Grønlands geol. Un the drift of Greenland: a conflict in plate tectonics. Meddr ders. 133, 65-80. Grønland Geosci. 8, 117-192. Sønderho1m, M. & Harland, T. L. 1989: Franklinian reef belt, Dawes, P. R. & Peel, J. S. 1984: Biostratigraphic studies in Silurian, North Greenland. In Geldsetzer, H. H. J., James, western North Greenland; Operation Grant Land 1965 N. P. & Tebbutt, G. E. (ed.) Reefs, Canada and adjacent 1966. Rapp. Grønlands geol. Unders. 121, 19-51. area. Mern. Can. Soc. petrol. Geol. 13, 356--366. Henriksen, N. 1985: Systematic geological mapping in 1984 in Sønderho1m, M., Harland, T. L., Due, P. H., Jørgensen, L. N. central and western north Greenland. Rapp. Grønlands & Peel, J. S. 1987: Lithostratigraphy and depositional his geo!. Unders. 126, 5-10. tory of Upper Ordovician - Silurian shelf carbonates in Henriksen, N. 1987: Systematic geological mapping in 1985 in central and western North Greenland. Rapp. Grønlands central and western North Greenland Rapp. Grønlands geol. geol. Unders. 133, 27-40. Unders. 133,5-12. Surlyk, F. & Hurst, J. M. 1983: Evolution of the early Paleo Higgins, A. K. & Soper, N. J. 1985: Cambrian - Lower Silur zoic deep-water basin of North Greenland - aulacogen or ian slope and basin stratigraphy between northern Nyeboe narrow ocean. Geology 11, 77-86. Land and western Amundsen Land, North Greenland, Surlyk, F. & Hurst, J. M. 1984: The evolution of the early Rapp. Grønlands geol. Unders. 126, 79-86. Palaeozoic deep-water basin of North Greenland. Bull. geol. Higgins, A. K., Ineson, J. R., Peel, J. S., Surlyk, F. & Sønder Soc. Arn. 95, 131-154. ho1m, M. in press: The Franklinian Basin in North Green Trettin, H. P. & Balkwill, H. R. 1979: Contributions to the land. In Trettin, H. P. (ed.) The Innuitian region. The geol- tectonic history of the Innuitian Province, Arctic Canada. Can. J. Earth Sd. 16, 748-769. Plate 1 Section 14 measured in 1984-85 at Hand Bugt, northern Nye boe Land. The section shows the basal part (section 14a) and the upper part (section 14b) of the 6330 m thick Silurian turbidite sequence of the Peary Land Group. Lines a-b, c-d, etc. indicate those parts of the sections which have been ex· panded and incorporated in the text under the appropriate figures. GGU sample numbers indicate graptolite assemblages.