Leslie Kanat and Alan Morris
A working stratigraphy for central western Oscar Il Land, Spitsbergen
NORSK POLARINSTITUTT OSLO 1988 Leslie Kanat and Alan Morris
A working stratigraphy for central western Oscar Il Land, Spitsbergen
------�.... _ -_ .... _----
NORSK POLARINSTITUTT OSLO 1988 Cooer page. Deformation in the Chaotic Zone. Two textural oceurrcnccs of veining are common in dolostonc within the Chaotic Zonc. In this drawing, fine grained, rccrystallizcd catadastic quartz (stipp1c) was injcctcd by later quartz vcin (strained) within a massive dolomitic host. The fine graincd texture (stipplc) is typ;cal for quartz in whieh catacl.sis was followcd by rccrystallization accommodated dislocation crcep. Scale bar: 0.5 mm.
ISBN 82-90307-52-7 Norsk Polarinstitutt. Printed December 1988 Rolfstangveien 12, 1330 Oslo Lufthavn, Primcd in Great Bruam by Page Bros (Norwkhi Lld Norway Contents
Abstract " ,.. ,.... , ...... , .. ,."." ..", ... "... '"",.,., ..."".""""""""".,.",." .. " .....",."""",'.'.', .. '"".","' .... ',, ' .. , , ,., " ,,'. 5 Introduction ,.', , ,."" .. , ,., .. ,., " '" ,.. "'."" ,.""."".,.... , .. "."".",.,.,., ..", .. , ..."."",."."""",.".,.""",.""""""""""", 7
Strandtlat strip rocks (CAR)", ...... ".""".""." ...... "", ...... , ...... " ... " ... , ...... ,."... ""., .. ,,, 8 Bullbreen Group ..., ",.""., ,.,.... , , .... , .. ,.,.. ' " ..., , .., ,.,.,., ",.. , ,.. , ,.'.", .." ,.,'... , ,... , , .., , .. , ,.. " .. '".. "., ",.", ."., "'" ,.. ", ,., 9 Holmesletfjella Formation (BHI-6)" ...., ..." ,' .. ,.",., ,.,.. "...... , ...... ,.",... ','.'"", .. ", .., "." .. , .... , ",.,""'" "'"",',' .., .., lO Motalafjella Formation (BMI) ,."."., .., , ... , ,.",., '... " .... ,' .. ,.. " ....." ,.. , ,.,.,.", "'""" ,." ,.' ..... , .., ,... , ,.,.", '.,." "'",."". 13 Sarsøyra Formation (SZI-2) ...... , .. , .. ,., ,., .. """'" ,.. ""., ... , ... , ...... , """ ,' .. ""... ,,, ...... , ...... ,., .. ,."., .. "", .... ,...... , .. " 14 ComfortJessbreen Group",.,.",.".. ",."""",.. "".", .. " .." .." ..", .. , .. "."",.".",.""",.",.. " ... " .. " .. ,., ... "." .. ",.. " "."". 14 Aavatsmarkbreen Formation (CV!-3) ...... " ...... " ...... , ..,...... !4
Annabreen Formation (CA!) . . ,." .. " '., .... , ...... "" .., ... " ,.. ", .. ,,'o '" .. ", ...... ,." " ,.. " , .. ", ., .. '" .. " .. , ...... , ...... , .. , ••' !4 }{aaken Formation (CHI-2) " .., .... , ...... , ...., ...... " ...... ".. " .., ...... , ...... ,.... , .... ,.... , .. , 14 St. Jonsfjorden Group",.", .. ,."."., .. ,... ",.. ",." .. ", .., .... , .."",., ..... ",.",., .... """,.".",.,.,.,."".,... " .. ",."""." , ,., "". , 16 Løvliebreen Formation (SLl·2) .... ",...... , ...... ,.... , ...... , ...... ' , .... ,.. ,..... , .. " "" .., .. ,.. ,,,, .., 16 Alkhorn Formation (SA!·2) .. ".. ,...... "...... , .... , .... ,...... " ...... , , .... ,...... , 16
Miillerneset Formation (MVF) .. ,." . ,." ."""", . ,",." ", ",., ",. , ". " ... " " .,."" " " , " ,'O , . ". " , •• ". ,." " ,," ,." ." " ,'" ,.,., , ••, .", 17 Vestgotabreen Structural Complex" .. ""...... , "", ... ' ,.",.. ""." .... " ... " .., "" ,." '... ' .. ,., .. " ...... , .... , ... ,.'"", ",." ... ".... ,.. 17
Dolostone division (VOD) ...... , ...... , .... , ...... , ,,'...... 18 Micaceous marble division (VM!-2) .. " ...... , ...... , ...... , ...... , .... ", ...... ,...... , .... , ...... , .... "...... 19
Mafic schist division (VSH) ...... " ..., ...., ...... " .." .. " ...... , .. " ...... , ...... , 19 Scrpentinite division (VSP) .""'.".,."."",.,.""""".", ..""""",.,." .. , .. ",... " ... ,.""""."".""", .. "".""",.""""",,, 19 Pelitie sehist division (VPE) ...... , ...... , .... ,...... ,.... , ...... , ...... , .... , .... ,,,"'" ...... ,.. ' 19 Greenstone division (VGT) ", .. ",,., ,.. " ... ", ...... " ... ,, ... "',",., ,' ... ',.. " .." ...... , ,... ", ... ",, .. ', ... ' ..", .., .." , .., ,.. 20 Psammite division (VPS) , ..... , ...... " ...... , " ...... " ...... "...... , ..... " ...... " ...... ,,,.. , " .. ,.. , .... , 20 Garnet glaucophane division (VGG) ...... " ...... , ...... ,...... , ...... , .., .. , 20 Eclogite division (VEC) .., ...... , ...... , ...... ,,...... , .. , .., ...... ,,, ...... , 21
Chaotic Zone " ", .. ", ,., '" ,., ", ,,'o , •• " •••• " .,.,." ., , •• , ,••,'.,. " ". , ,." ,., •• ". , "' .','." ,,, " ' " " ., ,." ,." , ••, , ••• , , .,.' ,., , ••• ", ." ,., ••" , 21 Concluding remarks ", ..", .., ..... """"""" " .. , "'" .. ", ,.".. , ...... , .. "" " .., "." ... , ...... ", ...... ", .. "" .." .. , ...., ....,.. 21 Acknowledgements " """"""." ...., ,., """,'",' ,.. ",... ",.", .".".", " "., ".',.'"'.'.",.,,, .".,."" ",., ., ,.,., , ,... , "."""'" 21 References ,... ,...... , ...... , ...., ...... ,.... ,...... , ... , ...... , ,...... ' ...... 22 Plate"""""",. ", """".,."""".", """"""..", .. "."".,."""",.. ,.""." .." .. """""""""".""",."" .. ",.,.""""".",." 24
Abstract
A modified stratigraphy for the pre-Carboniferous rocks in central Oscar Il Land, Spitsbergen, is needed to rcconcile reccnt mapping with earlier interpretations. Outerop maps and lithological dcscriptions for the Bullbreen, Cnmfortle"brcen and St. Jonsfjorden Groups, the Miillernesel Formalion, and Vestgotabreen Structural Complcx are presented, The contacl at Ihe base of the upper Ordovician Bullbreen Group was originally unoonformable, although it is now thrust at most loealities. A new internal stratigraphy for the Group is prescnted, and a revised sequcnee for the St. Jonsfjorden Group is described based On tbe rccognition of sedimentary oontacts not previously observed, A change in name from Vestgotabreen Formation to Vcstgotabreen Structural Complex is proposed, and severai new rock units within this eomplex are deseribed. Deposilion of the Bullbreen Group rcsulted from uplifl of the Vestgotabreen Complex, Continued orogenesis, rclaled lo mid,Paleozoic plate motion, drove bolh units over the Comfortlessbreen and SL Jonsfjorden Groups.
us/le Kanal, Departmenl of Earlh Sciences, Univer. ity of Cambridge, Downing Street, Cambridge CB2 3EQ. England; Present address: College of Scienæs and Engineering, Division of Earth and Physical Sciences, The University of Texas at San Antonio, SanAntonw, Texas 78285-0663, U.S.A.; Alan Morris, College of Sciences and Engineering, Division of Earlh and Physical Sciences, The University of Texas at San Antonio, San Antonio, Texas 78285-0663, U.S.A.
Introduction forrned nature of the rocks, unit thicknesses are necessarily estimates. The aim of this paper is to erect a working litho Uncertainty exists regarding the nature of the stratigraphic succession for central western Oscar original contacts and age of some lithologic units Il Land, Spitsbergen (Table 1). Three different in Oscar Il Land. However, there is general agree accounts of the stratigraphy and structure of ment on the following points: Oscar Il Land and Prins Karls Forland were pub 1. A significant discontinuity occurs between lished in 1979 (Harland et al. 1979; Hjelle et the Bullbreen Group (Harland et al. 1979; Ohta al. 1979; Krasiltschikov & Kovaleva 1979). The et al. 1983) and the Vestg6tabreen Structural outerop pattern in the study area closely follows Complex. that presented by Harland et al. (1979) and their 2. A late Ordovician depositional age (most nomenclature is largely adopted in this work, likely Caradoc through Liandovery) for the although we propose a name change for the Bullbreen Group (Armstrong et al. 1986; Scrut Vestg6tabreen Formation (formerly the Vest ton et al. 1976) and a mid-Paleozoic metamorphic g6tabreen Suite (Horsfield 1970; Ohta 1979)) to age for the Vestg6tabreen Structural Complex Vestg6tabreen Structural Complex. Waddams (Horsfield 1972). It is also probable that dia (1983) indicated that two diamictites in different mictites which occur in Oscar IT Land are Vendian groups occur in Oscar Il Land, but our field in age (Knoll 1981; Hambrey 1982,1983). observations do not support this interpretation in 3. The rock units represent distinet meta the St. Jonsfjorden area. In the following account, morphie facies: Vestg6tabreen Structural Com the his tory of research is included with the pl ex - blueschists and eclogites; Miillerneset description of each unit in order to preserve name Formation - upper greenschist to amphibolite precedence. facies; St. Jonsfjorden and Comfortlessbreen Pre-Carboniferous rocks in western Spits Groups - lower greenschist facies; Bullbreen bergen have undergone both mid-Paleozoic and Group - extremely low grade metamorphism; Paleogene orogenesis (see for example Harland Carboniferous rocks - unmetamorphosed. 1961; Birkenmajer 1972,1975,1981; Harland & Place names are given in Fig. 1,and the outerop Horsfield 1974). As a result of the highly de pattern of the rocks in the St. Jonsfjorden area is
CENTRAL WESTERN SPITSBERGEN U)r BR GGERHALVØYA
N
MOTALAfjELLA ". t .....r I 'li . +-_ 78· J0RGENFJ iH' 5 KM EIDEMBREEN t '- ; -; .-
Fig. 1. Localities map of Oscar Il Land.
7 Table l. A lithostratigraphic succession, central western Oscar Il Land, Spitshergen.
Litholoqic unit member/description symbol thickness [ (metres)] unit limestone CAR 20
Strandflat strip unit ______bioclastic limestone 10 CAR conglomerate 5 iliceous slate IlH6 20 [ upper sandstone slate BB5 100 ] Holmesletfjella_ upper slate IlH4 30 ] Formation Bulltinden conqlomerate IlH3 60 ] Bullbreen ---- lower slate BH2 10 Group ower sandstone slate BHI 150 Motalafjella rlimestone, slate BM1 100 ] Formation and onglomerate Sarsøyra Formation ______[(not recoqnisedl Aavatsmarkbreen dark pbyllite CV3 5 Formation --cblorite-serpentine phyllite CV2 10 green and cream marble CVl 25+7 Comfortlessbreen Annabreen [quartzite CAI 5+ Group Formation Baaken [green and orange schist CH2 5+ ] Formatl';"" ' o-n-----ldiamictite CRI 100+ I;�:j 7 ] Ll1Ivliebreen [upper: quartzite and pelite SL2 300 ] , ' , . . . Formation Iower: volcanic SL1 20+ ) , ' , " I ] Alkhorn narble SA2 50+ I p St. Jonsfjorden Formatio-n----Lcalcareous psammo-pelite SAl 100+ ] Group Moefjellet (not recognisedl Formation Trondheimfjella (not recognisedl ..... -l Formation
MOllerneset Formation ______garnet-biotite schist MUF 800 o
orange weathering dolostone VOD 20 ] VOD medium grey micaceous marble VM2 50+ ] dark grey micaceous marble VMI 50+ mafic schist VSH c .200 -- Vestqotabreen serpentinite VSP 15 Complex pelitic schist VPE 10 greenstone VGT 50 l psammite VPS ] garnet glaucophanite VGG 5 + eclogite VEC 40+
given in Fig. 2. Lithostratigraphic descriptions kelsenfjella, and north to Brøggerhalvøya (Baker be gin at the top of the succession (Table 1). et al. 1952; Cutbill & Challinor 1965; Challinor 1967). In the field area, south of St. Jonsfjorden, these rocks separate the Miillerneset Formation Strandftat strip rocks (CAR) to the west from the diamictites to the east. Else where, south and north of Eidembukta and in A strongly deformed strip of sedimentary rocks Nordenskiold Land, the Carboniferous rocks rest has been faulted into the pre-Carboniferous unconformably on the Comfortlessbreen Group; sequence in Oscar Il Land from Daudmannsøyra the upper contact of the Carboniferous is faulted (northern Isfjorden), north through Eidembukta, (W. B. Harland 1985, personal communication along the west side of Svartfjella and Thor to LHK).
8 The strandflat strip rocks comprise three dif by its distinct sedimentary nature, extremely low ferent units: metamorphic grade, structural style and limited - An upper buff-coloured limestone member. areal extent. Holtedahl (1913) briefly described A middle bioc1astic limestone member domi one member of the Bullbreen Group, but he was nated by rugose coral fragments and crinoid not able to define its stratigraphic position with ossic1es, which towards the base becomes dolo respect to other rock units in the area. Weiss mitic and poor in fossil con tent. (1953) recognised that bedding was the pro - A basal member cross-bedded, very pale nounced planar fabric in some pre-Carboniferous orange, c1ast-supported conglomerate, con rocks, whereas c1eavage was more apparent in taining dominantly quartzite c1asts. others. He was not able to distinguish the These rocks are equivalent to rocks of middle Bullbreen Group on structural evidence, nor erect Carboniferous age from the Isfjorden, St. Jons a lithologic sequence for the pre-Carboniferous fjorden and Brøggerhalvøya areas as described units. by Cutbill & Challinor (1965). Horsfield (1970) recognised representatives of the Bull breen Group and called them the Bull tinden Formation, a nomenc1ature followed by Bullbreen Group Hjelle et al. (1979). Harland et aL (1979) recog nised a wider association of rock types and restric The Bullbreen Group (Harland et aL 1979) is ted the term Bulltinden to the conglomeratic distinguished from other rocks in Oscar Il Land facies and termed the entire package Bull breen
2km
N
I Sl Jonsflorden
BH4. 5, IS 8H3 eOLLBREEN BHI,2 eM,
CAReONlfEROUS {ElYOONGEfI) ROCKS CAR
t4ULLERNESET Filt o CA1. CVi, 2. CQMFORTLESS9REEN CH1.2 CHAOTIC lONE
Sl. SLl SA> I/ESTGOTABREEN SA' STRUCTURAL
COMPLEX
Fig. 2. Geological map of the St. Jonsfjorden area.
9 Group. The uneonformity at the base of the eognition of large reeumbent folds whieh repeat Bullbreen Group inferred by Harland et al. (1979) the sequenee (most notably the conglomerates) was further doeumented by Ohta et al. (1983). In in the Holmesletfjella and Bulltinden areas. this work we expand the definition of the This formation was referred to as W6 by Wilson Bullbreen Group. but preserve the nomenclature and later named the Holmesletfjella Formation suggested by Harland et al. (1979). by Harland (1960). Harland ineorreetly believed The Bullbreen Group ean be divided into two that this formation was older than the Com forrnations, similar to those deseribed by Hors fortlessbreen Group. In contrast to other workers field (1970). The upper formation eonsists of slate, (Harland et al. 1979; Hjelle et al. 1979), on ly one immature siltstone. sandstone and conglomerate. major eonglomeratic member is distinguished, The lower formation eomprises limestone with the Bulltinden Member. The Holmesletfjella For minor eonglomerates and slates. The two for mation consists predominantly of immature clas mations will be referred to as the Holmesletfjella tie roeks with variable amounts of earbonate. and Motalafjella Forrnations, respeetively, with Winsnes (1965) mapped the Bulltinden Member a total thiekness of 470 m. Hjelle et al. (1979) as a Precambrian tillite. However, no diamictites reeognised a similar sequenee, although in reverse of glacial origin have been recognised in this area. stratigraphie order. Six members are distinguished (five with informal In the st. Jonsfjorden area the Bullbreen names). Group erops out in a band from southeastern Motalafjella and Løvliefjellet northwest through Siliceous slate member (BH6). The silieeous the Skipperbreen-Vestgotabreen ridge, Holme slate member is best exposed in northern sletfjella. Bulltinden, the an te southwest of Holmesletfjella. It is a friable, silieeous slate esti Bulltinden, and Ankerfjella on the north shore mated to be at least 20 m thick; an upper contact of St. Jonsfjorden. has not been reeognised. It commonly exhibits The base of the Bullbreen Group has been dark, elongate, irregularly shaped features with interpreted as an uneonformity (Ohta et al. 1983), elliptical cross sections (approximately a thrust (Horsfield 1970; Harland 1978; Harland 100 x 20 x 4 mm) on fraetured. cleaved or bed et al. 1979), a fault (Hjelle et al. 1979), and a ding surfaees. They have been interpreted as trace eonformable eontaet (Hjelle & Lauritzen 1982). fossils by Scrutton et al. (1976) and Harland et The eontaet between the base of the Bullbreen al. (1979). The lower contact of the silieeous slate Group and the Vestgotabreen Struetural Com member is sharp and conformable. plex has been identified as an unconformity at two loealities at Motalafjella (Ohta et al. 1983). Upper sandstone sla te member (BH5). - Best This same eontaet in Holmesletfjella exhibits exposed in northern Holmesletfjella, this member mylonitie textures and is interpreted as a thrust is also found in central Motalafjella, Bulltinden, (Kanat unpublished). A thrust eontaet is also and the Skipperbreen- Vestgotabreen ridge with observed in Ankerfjella between the Bullbreen minor outcrops on the arete south of Bulltinden and Comfortlessbreen Groups (Morris unpub and western Ankerfjella. The upper contact with lished). Observations have also shown that the siliceous slate member is sharp and the repetition of rock units above the surfaee of conformable. A minimum thiekness of 100 m is the discontinuity is generally a result of folding. estimated from exposures in Holmesletfjella. This No contacts have be en observed between rocks member eonsists of interbedded, slightly cal of known post-Silurian age and the Bullbreen careous sandstone (65%), slates (25%), and Group. The group will be deseribed from top to immature conglomeratic horizons (10%). The bottom. sandstone is medium grained, siliceous, sub mature and well sorted with a slightly ealcareous Holmesletfjella Formation (BHl-6) cement. It is grey weathering to buff in colour, and exhibits weU defined bedding. The slates are The following lithological descriptions of the Hol dark grey and pale grey in colour. mesletfjella Formation are similar to those pre Graded, cross-bedded eonglomerates oeeur in sented by Harland et al. (1979). The thickness association with the sandstone. They are less lat estimates, however, are eonsiderably less than erally persistent than the other horizons and are those given by earlier workers owing to the re only traceable for tens of meters. Angular, non equant quartzose and carbonate iithic fragments, Elsewhere, the proportions are variable, to the usually less than 4 mm in diameter, are typical limit of 20% conglomerate, 70% sandstone and clasts. The lower contact of this member is tran 10% slate, found in north central HolmesletfjeJla. sitional with the underlying member. The bound Coarse-grained conglomerates are character ary is defined by a decrease in abundance of istic of this member. Individual bedded units vary conglomerate and sandstone horizons, and an in thickness from 0.2 m to 5 m with a concomitant increase in the proportion of slate. variation in clast size from granules to large boulders. Thick-bedded units are found on Upper state member (BH4). The upper slate Bulltinden and in Ankerfjella. In these areas this member is best exposed in northem Motalafjella, member is also characterized by a siliceous, fine with minor occurrences on the arete south of to medium-grained sandstone matrix. More thinly Bulltinden, and on the connecting an te between bedded units occur in northern Holmesletfjella southem and northem Holmesletfjella. The slate where the matrix is dominantly calcareous. At is black, slightly calcareous, approximately 30 m Motalafjella both extremes occur. In less defor thick and in sharp contact with the underlying rned areas the clasts have roundness/sphericity Bulltil1den Mem ber. At northem Motalafjella the values of 0.4/0.2 to 0.8/0.8. The low sphericity slate is ferruginous and consists of intercalated values result from the original clast shape and clays (20%) and silts (80%) with minor sandstone from post-depositional deformation (which is towards the contact with the underlying member. always evident to some extent). The conglomerates show variation in clast type Conglomeratic member (BH3). This member in proportion to bed thickness: the thicker the contains one of the most striking lithologies in the bed the greater the variation in clast type. Clast Bullbreen Group and as a result has the most types can be divided in to five categories: complete published description of any member of limestone, schist, dolostone, quartzite, and con the Holmesletfjella Formation (Holtedahl 1913; glomerate (Table 2). At Motalafjella and the Horsfield 1970; Harland et al. 1979; Hjelle et al. Skipperbreen-Vestgotabreen ridge, the Vestgota 1979; Hjelle & Lauritzen 1982). The con breen Structural Complex contains garnet-bear glomeratic member is here informally called the ing schists which are not exposed elsewhere. In Bulltinden conglomerate. The name Bulltinden the same geographical area, the Bulltinden con had previously referred to all units now regarded glomerate contains a small proportion of garnet as the Holmesletfjella Formation (Horsfield1970; bearing clasts which were probably derived from Hjelle et al. 1979), or it had been applied to the the Vestg6tabreen Structural Complex. No such massive conglomerates only (Harland et al. 1979). clasts occur elsewhere in the Bulltinden con In this account the predominantly conglomeratic glomerate (Plate 1). Characteristic high pressure zones, together with subordinate interbedded minerals, or pseudomorphs thereof, have not finer-grained lithologies, are separated from the be en recognised within clasts of the Bulltinden remainder of the Holmesletfjella Formation and conglomerate. At Motalafjella the BuJltinden regarded as the conglomeratic member, formally conglomerate contains fossiliferous Jimestone referred to as the Bulltinden conglomerate (or clasts as early as late Caradodan (Scrutton et al. Member), BH3. 1976; Harland et al. 1979; Armstrong et al. 1986) The Bulltinden conglomerate is best exposed which are rarely found in the conglomerate in in Motalafjella, the Skipperbreen-Vestg6tabreen other parts of the study area. Similarly, it is ridge and northwestern Holmesletfjella with only in this area that fossiliferous zones of the minor occurrences on Bull tinden and in Motalafjella Formation are found. Ankerfjella. It has a sharp upper contact and its In northwestern Motalafjella a slumped block thickness varies from 10 m in the southwest to of presumed Motalafjella limestone (clast volurne 60 m in the northeast. There are three com c. 100 m3) containing a diverse faunal assemblage ponents in this member: conglomerate, is found within the Bulltinden conglomerate sandstone, and slate. An antipathetic relationship (Scrutton et al. 1976). The faunal assemblage is observed between the conglomerate and finer includes Caradoc to Wenlock age fossils (Scrutton grained components. At Motalafjella the Bull et al. 1976; Armstrong et al. 1986). These are the tinden Member consists of 65% conglomerate, youngest pre-Carboniferous fossils known in the 35% sandstone and minor amounts of slate. Western Province (Harland et al. 1979).
11 Table 2. Clast varicly in the Bulllinden conglomerale. Modal structures and ftute casts are found at the inter estimalC of all ciasis wilhin the Bulltinden conglomcratc. Indi faces between slate and sandstone units. Cross vidual lists are arranged in order of decreasing abundancc. bedding and grad ed bedding are common in the Limestone clasl,"" 4()f'{ sandstones and finer-grained conglomerates. dark grcy-eolourcd limestone The lower contact of the Bulltinden Member is medium grcy-colourcd limestone sharp and erosive with the underlying slates. In grcy-colourcd limestone bandcd limestone northwestern Holmesletfjella and in the moraine scrpcntinitc east of Bullbreen there is localized development of an intraformational conglomerate containing Sundstone clust,\': 20% rip-up clasts derived from the underlying slates quartzarcnitc and set in a ferruginous, coarse grained sandstone sublitharcnitc grecn-colourcd sublitharenite matrix. This intraformational conglomerate is red and green bandcd sublitharcnitc considered to form the lowermost horizon of the Bulltinden Member in this area. In Ankerfjella Schistose clasts: 25% and on the Skipperbreen-Vestg6tabreen ridge the chloritc-phcngitc s('hist slate member (BH2) is absent, and the siliccous schist lower garnet-phcngite schist Bulltinden conglomerate rests unconformably on grcy-coloured schist the lower sandstone slate member (BHI). Although two different members occur directly Oolostone c!usts: /Ot7,. below the Bulltinden conglomerate, all evidence brccciatcd dolostonc buff-colourcd dolostonc suggests that this is an erosive sedimentary contact. Conglomeratic clast\': 5°;" me dium grcy-eoloured limestone with dolostonc and crinoid fragments Lower state member (BH2). This member crops medium grained sublitharcnite with maturc quartzarcnitc fragments out on Bulltinden, northwestern Holmesletfjella, large slumpcd blocks of fossiliferous limestone Ankerfjella, and Motalafjella. Hs upper contact with the Bulltinden Member is sharp and IRneous clasts: 12 The sandstone is indurated, commonly cal detrital material (as much as 30%), fossil type careous, medium- to coarse-grained and grey, and abundance, and colour (light medium grey to weathering to buff in colour. The carbonate con dark grey). Owing to the recrystallized nature of tent of the sands tone matrix distinguishes this the rock, bedded units are difficult to distinguish, member from the upper sandstone slate member, and are assumed to be represented by the colour BH5. Grains are well-sorted, well-rounded, and banding. the rock can be described as a grainstone where Carbonaceous fragments, round crinoid stems both grains and matrix are calcareous. Bedded (less than 6 mm in diameter), and coral fragments units vary from 0.1 to 0.75 m in thickness, are recognised within this formation at the type although the variation in adjacent beds is less locality. EIsewhere, fossils are rare, although car than a few percent. Dark grey, slightly calcareous bonaceous fragments do occur. The richest faunal slate, 2-80 mm thick, is interbedded with the horizons occur as clasts, or slump ed blocks, within sandstone. the Bulltinden conglomerate at Motalafjella. A Minor conglomeratic horizons within this mem small proportion of these fossil-bearing clasts con ber are 0.10 to 0.15 m thick. These immature, tain crinoids with pentamerai and round stems polymict conglomerates contain granule-sized (less than 6 mm across), brachiopod fragments quartz, Jimestone, and dolostone clasts. Small 3 and fauna similar to that which is found in the 5 m wide, 0.02-0.06 m thick channeJ structures type section. Other fossil-bearing limestone clasts are common in these rocks. The lower contact of contain portions of the total fossil assemblage as the lower sands tone slate member is sharp and described by Scrutton et al. (1976). The assem conformable with the Motalafjella Formation. blages which have been dated Wenlock to Ludlow in age by Scrutton et al. (1976) occur mainly in the large slumped block in northwestern Motalafjella Formation (BMI) Motalafjella. Armstrong et al. (1986) recognised lower Caradocian conodonts in the clasts. The Motalafjella Formation consists predomi It is inferred that the fossil-bearing limestone nantly of limestone as noted by Maton & Harland clasts within the Bulltinden conglomerate were (1969), and described by Harland et al. (1979). derived from the Motalafjella limestone. Evi This formation is best e (posed at its type locality dence supporting this conclusion is: in Motalafjella where it forms the major peak 1. Similarity of rock type between the clasts of the mountain. In addition, a thin limestone and the Motalafjella Formation. horizon which is found consistently below the 2. Similarity of part of the fossil content within Holmesletfjella Formation in Ankerfjella, on the clasts to that of the complete assemblage Bulltinden, in Holmesletfjella and on the Skipper of the Motalafjella Formation , including the breen-Vestgotabreen ridge, is presumed to be a slumped block. lateral equivalent of the Motalafjella Formation. 3. The fossiliferous limestone clasts lack a tec Minor conglomeratic horizons and a thin, green tonic fabric which predates their incorporation coloured slate are present at the base of the into the Bulltinden conglomerate. This implies Motalafjella Formation. that they could not have been derived from the The upper contact of the Motalafjella For subjacent metamorphic rocks. mation is sharp and conformable with the over 4. No other fossiliferous limestone units have Iying Holmesletfjella Formation. The maximum been recognised in the immediate area. exposed thickness of 100 m is found at the type The lower contact of the Motalafjella For locality. EIsewhere thicknesses are much less, mation is everywhere sharp. This contact was with a minimum of 3 m found in Ankerfjella. In originally unconformable on the Vestgotabreen the Motalafjella area, this formation is a gritty, Structural Compl ex although it is now thrust in fossiliferous, cryptocrystalline grey limestone, most localities. Evidence for an unconformable weathering to buff in colour. Bedding is generally contact includes minor conglomeratic units at the indistinguishable from cleavage, and is petro base of the limestone which truncates the per graphically expressed as elongated carbonate and vasive tectonic fabric of the Complex, and quartz grains in a micritic matrix. Carbonate-filled limestone-filled fractures within the Complex fractures, perpendicular to bedding, are common. greenstones on the an te south of Bulltinden and There is a variation in the amount of siliceous central western Motalafjella. 13 Sarsøyra Formation (SZl-2) previously been ascribed to part of the Sarsøyra Formation. Waddams (1983) described three div The Sarsøyra Formation is best exposed in north isions within this formation. The upper division, CV3, is a dark grey, cal west Oscar Il Land, on Sarsøyra, where it occurs careous phyllite which weathers to a rusty orange as a narrow, elongate unit of marbles and slates (Horsfield 1970; Waddams 1983). The age of colour. Quartz pods, 1-10 cm across, are common these rocks is unclear and could range from Cam and some have iron oxidation stains. Deformed brian to Carboniferous (Harland 1960; Horsfield and boudinaged dolostone and quartzite beds, 1970; Scrutton et al. 1976; Harland et al. 1979; usually less than 25 cm thick, are present, but Waddams 1983). account for less than 10% of the exposure. The We have observed carbonates, dark green unit is fissile, highly deformed, and exhibits two, slates, and minor quartzite conglomerates within well-defined planar fabrics. Both the upper and the Motalafjella Formation at numerous localities lower contacts are sharp and possibly faulted. A south of St. Jonsfjorden, west of Bullbreen (Fig. minimum thickness of 75 mm is estimated for this 2). These may correlate with the Sarsøyra member. Formation. On the an te southwest of Bulltinden, a thin, tightly-folded chlorite-rich schist with minor amounts of a serpentine mineral is recognised. The upper contact is faulted against the Mota Comfortlessbreen Group lafjella limestone, and the lower contact is sharp and possibly conformable with the lower division The Comfortlessbreen Group is characterized by of this formation. A minimum thickness of lO m greenschist facies Vendian glaciomarine sedi is estimated for this member, CV2, which is mentary rocks and was named by Harland (1960) believed to be correlative with the middle division after the glaeier near which they occur. Within as described by Waddams (1983). the study area, this group is best exposed along The lower division, CV1, is represented by the south shore of St. Jonsfjorden between an laminated green and cream coloured marbles. unnarned headland north of Thorkelsenfjella and Individual laminae within this division vary in the western Bullbreen moraine. The structural thickness from l to 10 cm. It is best exposed upper boundary i in fault contact with the Mota in northwest Thorkelsenfjella as a narrow band lafjella Formation approximately 400 m iniand striking NNW and is easily traced from the shore from the shore. The western boundary is defined inland. A minimum thickness of 25 mm is by a sub-vertical fault contact with rocks of pre estimated. sumed Carboniferous age north of Thorkel senfjella. The eastern contact is not exposed. This Annabreen Formation (CAl) group was thought to be 1000 m to 6000 m thick (Hjelle et al. 1979; Hambrey & Waddams 1981; This formation has been referred to as the Irene Waddams 1983). The small exposure, coupled breen Quartzites of Lower Carboniferous age by with intense folding, allows a minimum estimate Cutbill & Challinor (1965), and as W8 by Harland of 300 m for the group thickness in the St. (1960). The formation was named after the Anna Jonsfjorden area. Sofiebreen glaeier on the southern shore of St. In keeping with the nomenclature suggested by Jonsfjorden. Waddams (1983) believed that this Waddams (1983), the Comfortlessbreen Group formation is :.;st exposed in northwest Oscar Il is divided into three forrnations, each of which Land and does not occur south of St. Jonsfjorden. will be diseussed beginning at the top of the Based on descriptions of the unit (Waddams succession. 1983), we recognised this formation in north western Vegardfjella, south of St. Jonsfjorden. Aavatsmarkbreen Formation (CVl-3) The outerop area is small and the contact relation ships are not exposed. This formation consists primarily of dark phyllites, and is best exposed in the St. Jonsfjor Haaken Formation (CHl-2) den area north of Thorkelsenfjella. The name was used by Waddams (1983), although the rocks had Diamictites were first observed in Oscar Il Land 14 by C. B. Wilson (Harland 1960), and sub mlctIte and associated silicie conglomerate and sequently called the Haaken and Engelskbukta quartzite (CH1). Formations by Harland et al. (1979). Hjelle et The dominant unit on the strandflat northwest al. (1979) used the term Tillitic conglomerate to of Bulltinden, east of Thorkelsenfjella and near describe the same rock unit. Horsfield distin the east end of St. Jonsfjorden is the upper guished two diamictite horizons within the st. member, CH2. Green and cream coloured bands Jonsfjorc!en area but included them within one are interlayed on the centimeter scale, and the unit. the Comfortlessbreen Formation. Waddams entire member weathers to a light orange colouT. (1983) divided the diamictites into two distinct The cream colourcd bands are rieher in carbon formations (Haaken and Trondheimfjella For ate, whereas the green laminae have a larger mations) separated by 1.8 km of strata. He used pelitic component. The upper contact is generally two criteria for this distinction: 1) his inter sharp against the overlying Aavatsmarkbreen or pretation of the sequence exposed at Trond Motalafjella Forrnations, and a minimum thiek heimfjella in northwest Oscar Il Land, and 2) ness of 75 m is estimated. a difference in clast compositions between the The clast-bearing member, CH1, is well two horizons. We have been unable to apply his exposed to the north and along the west side of criteria \\1.th confidence to identify two distinct Thorkelsenfjella, the lower slopes of Ankerfjella diamictites locally within the St. Jonsfjorden area. and at the east end of St. Jonsfjorden. This mem M. Hambrey (1983, fieldcommunication to LHK) ber is mapped as the same unit as Horsfield's was also unconvinced that the re are two distinct (1970) massive c1ast-bearing phyllitic semipelites diamictites locally within the St. Jonsfjorden (ComfortIessbreen Formation, HC03), and a por region. tion of the Hjelle et al. (1979) Calc-argillo·vol Diamictites in the St. Jonsfjorden area are canic Formation. associated with rock types that resemble members The c1ast-bearing member is medium grey, of the Comfortlessbreen Group as described by wcathering to brown in colour with a minimum Horsfield (1970). Harland et al. (1979), Hjelle thickness of 100m. It is rhythmically banded on et al. (1979), and Waddams (1983). We have the millimeter scale. Clasts of dolostone, lime therefore retained the name Haaken Formation stone and quartz, usually less than 20 mm across, for these diamictites. Although Waddams (1983) occur sporadically throughout the outcrop area, claims that Trondheimfjella diamictites occur in and never compose more than 5% of the Il cen tral Oscar Land, he does not substantiate exposure. Granitic stones have been described in this with specificlocalities. We have not positively this member by Holtedahl (1913) in a discussion identified any of the informal divisions of the of a limestone conglomerate in Ankerfjella. We Trondheimfjella Formation within the St. have recognised stones with an internal fabric Jonsfjorden area. The existence of diamictites different from that of the matrix, and Wilson & belonging to both the St. Jonsfjorden and Com Harland (1964) recognised grey granite and grey fortlessbreen Groups as described by Harland et granite gneiss clasts within this member. In al. (1979) and Waddams (1983) has not been fully addition, a clast-bearing, grey-coloured, sil substantiated. iceous, matrix-supported conglomeratic bed Finely crystalline diamictites, believed to be occurs within CH1 with clasts of dolostone, glacigenic, are the characteristic rock type of the quartzite and green-coloured schist fragments. A Haaken Formation. This formation has been referred to as the Comfortlessbreen schists (Har light pink massive quartzite horizon, approxi land 1960), Comfortlessbreen Formation (Hors mately 3 m thick, is associated with the field 1970). Tillitic Conglomerate and Ca1c conglomerate. argillo-vo1canic Formation (Hjelle et al. 1979), The presenee of drops tones and rhythmic bed and as the Haaken Formation (Harland et al. ding indicates that CHI is a rock forrned from 1979; Waddams 1983). Here the formation is ice-rafted, glaciomarine sediment. This inter subdivided into two members: an upper stone pretation is in accord with those of Hambrey et free member, con sist ing of calcareous green and al. (1981), Hambrey (1983), and Hambrey & cream-coloured psammitic schist (CH2), and a Waddams (1981). There is variation in cIast con lower member, comprising slightly calcareous, tent within these diamictites, and our obser stone-bearing, finely crystalline schistose dia vations do not precIude the presence of more 15 than one diamictite preserved within the Haaken Alkhorn Formation (Horsfield 1970; Harland et Formation. al. 1979; Hjelle et al. 1979; Waddams 1983). However, exposures in southem Lowzowfjella and east of Copper Camp show a consistent, unbroken and presumed sedimentary sequenee St. Jonsfjorden Group from quartzites down to volcanic green-eoloured phyllites (Løvliebreen Formation), to banded Harland et al. (1979) divided the St. Jonsfjorden marbles, to ealcareous psammo-pelites (Alkhorn Group into four forrnations: Alkhorn, Løvlie Formation) at the base. The relationships breen, Moefjellet, and Trondheimfjella (at the observed at the two loealities neeessitate reversal base). The outerop pattern and Iithologie sue of the relative positions of these forrnations, eession were given by Horsfield (1970) and aJthough the sequence within eaeh formation substantiated by Waddams (1983). Horsfield remains unehanged. (1970) referred to one diamietite horizon in west Harland et al. (1979) divided the Løvliebreen ern Osear n Land (the Haaken Formation), and Formation into two members: J) upper massive Harland et al. (1979) plaeed two diamietite hori quartzites and interealated pelites, and 2) lower zons within the Comfortlessbreen Group (the fine grained volcanic rocks. The up per member Engelskbukta and Haaken Forrnations). Wad eorresponds to the dark quartzites described by dams redefined the Trondheimfjella Formation Holtedahl (1913), the mast>ive quartzite bodies and suggested that a stone-bearing unit dis deseribed by Weiss (1953), and the Quartzite covered on southern Brøggerhalvøya represented shale Formation described by Hjelle et al. (1979). a lower glacigenie horizon within the Western The quartzites. SL2, are dark grey. weathering Province (the upper diamictite still regarded as to black in colour and are approximately 300 m the Haaken Formation of the Com fort less breen thiek. Thin pelitie horizons aceount for less than Group). Hjelle et al. (1979) deseribed the Calc 10% of the exposure. Quartz grains are equant, argillo-volcanie and Quartzite-shale Formations weU sorted, fine sand sized particles and exhibit as their equivalent to the St. Jonsfjorden Group, undulose extinetion. but they did not include any diamietites. The base The lower volcanic member. SU. is best of this group is not exposed, although an angular exposed within the study area in the southeast unconformity with the overlying Comfortless port ion of Hol mesletfjell a, just west of breen Group has be en suggested (Hjelle & Lau Løvliebreen. It corresponds to the Calc-argillo ritzen 1982). There is general consensus that the volcanic Formation of Hjelle et al. (1979). St. Jonsfjorden Group is older than the Com According to Horsfield (1970) and Hjelle et al. fortlessbreen Group (Harland et al. 1979; Hjelle (1979), the main exposure is found in southern et al. 1979; Hjelle & Lauritzen 1982; Waddams Gunnar Knudsenfjella. east of Løvliebreen. The 1983). Ages for the St. Jonsfjorden and Com roeks are typically well foliated, dark greenish fortlessbreen Groups are not known, although the grey lapilli tuffs, estimated to be at least 20 m diamictite horizons are assumed to be Vendian in thiek. They eontain aJbite, ealcite and ehlorite. age. with minor amounts of stilpnomelane, phengite, Within the study area, the St. Jonsfjorden pyrite and rutile. Ohta (1985) ca Ils these rocks Group is exposed along both shores of St, the Trollheimen volcanics. Jonsfjorden from east of Bul/breen to Vegardfjella on the south shore, and from east of Alkhorn Formation (SAl-2) Ankerbreen to Konowbreen on the north shore. Two of the four formations deseribed by Wad This formation derives its name from the eal dams (1983) (Alkhorn and Løvliebreen) have careous roeks exposed on the north shore of been reeognised in the St. Jonsfjorden area. The Isfjorden at Alkhornet, and was deseribed by formations will be deseribed from top to bottom. Holtedahl (1913) and reeorded by Major et al. (1956). Horsfield (1970) defined the Dahlbreen Løvliebreen Formation (SU-2) Formation and divided it into two members: the upper comprising mainly marble and the lower All previous workers have placed the Løvliebreen consisting of semipelite. Harland et al. (1979) Formation, or its direet eorrelative, below the renamed the Dahlbreen limestone the Alkhorn 16 Formation, acknowledging Holtedahl's earlicr correspond weU with those presented by Hjelle work, and apparently disregarded the lower mem et al. (1979), and are consistent with the sequence ber (HD2), as did Waddams (1983). Hjelle et al. observed by the present authors. The lithologic (1979) included the Alkhorn Formation and the descriptions more closely follow those by Harland Løvliebreen Formation as separate members of et al. (1979) than those of other workers. Pelites, the Calc-argillo-voIcanic Formation. semipelites, and psammites are the predominant It is suggested here that the Alkhorn Formation lithologies in this formation on MiiIlerneset, be divided into two members similar to those although lesser amounts of intercalated carbonate described by Horsfield (1970). The original name, rocks do occur. Alkhorn, as defined by Holtedahl (1913), instead The formation is exposed as a l km-thick folded of Dahlbreen (Horsfield 1970) will be used in this unit in vertical fault contact with presumed Carb work. The upper member will be referred to as oniferous-age rocks to the east and the Com the marble member and the lower referred to as fortlessbreen Group to the west. The exposure the semipelite member. can be traced for a distance of approximately The upper member, SA2, is best exposed along 13 km south from St. Jonsfjorden. the shore approximately 1500 m east of Copper Camp. This fine-grained, recrystallized marble is dominantly grey in colour with interlayered cream and black horizons, 3 mm to 1 mm thick. Car bonaceous fragments and pisolitic structures are Vestgotabreen Structural Complex recognised. Quartz pods, which exhibit bou dinage structures parallei to the lamination, are The description of the se rocks is presented last, present, although rare. Tight asymmetric folds, although they do not necessarily represent the defined by bedding, are characteristic of this oldest unit in the study area. The Vestgotabreen member. A minimum thickness of 50 m is Structural Complex is easily distinguished in the estimated. field from other rocks in the study area by its The semipelites, SAl, are dark grey in colour, physical characteristics (i.e. massive greenstones pyritic and variably caIcareous. The psammitic and coarsely crystalline schists) which are a result layers consist of mature, medium-grained quartz of a high pressure, low tempera ture metamorphic grains cemented by siliceous and/or calcareous event (Ohta 1979; Kanat 1984; Hirajima et al. cement. Graded bedding is present, although 1984; Ohta 1986). The unit occurs as a deformed, younging directions are ambiguous (observed in narrow thrust slice, approximately l km thick, various orientations). A minimum thickness of which can be traced over a distance of approxi 100 m is estimated. mately 15 km subparallel to the regional fabric. The complex is best exposed in the southwest portion of Motalafjella, although it also occurs on southern Bulltinden, in southern Holmesletfjella, Miillerneset Formation (MUF) and on the Skipperbreen-Vestgotabreen ridge. The type locality is located on the central western The Miillerneset Formation crops out on MiiI side of Motalafjella. The upper contact is usually lerneset, southwest of St. Jonsfjorden, and occu adjacent to the Motalafjella Formation. A lower pies most of the Svartfjella coastal plain. Harland contact has not been observed. et al. (1979) described it as '2000 mm of schistose According to Horsfield (1970), glaucophane pelites and semipelites with psammites and white schists and eclogite rock fragments were first quartzite layers' Hjelle et al. (1979) described found in 1957 by C. B. Wilson within the moraines the Miillerneset Formation as garnet-biotite sch of Eidembreen and Vestg6tabreen. Sub ists and quartzite-shale alternations with a thick sequently, D. Gee, as a member of the 1962 ness of 800 m. Harland et al. (1979) and Horsfield Cambridge Spitsbergen Expedition, located the (1970) described three formations within the source area of these rocks in Motalafjella. The Kongsvegen Group (Orvin 1934; Harland et al. suite was first mapped by Horsfield (1970, 1972) 1966) and correlated the upper Nielsenfjellet For during the 1968 and 1969 field seasons. mation with the Miillerneset Formation. The Horsfield (1972) distinguished the following thickness estimates by Ague & Morris (1985) rock groups on his geologic map of the area: 1) 17 gIaucophane-bearing rocks, 2) epidote-actinolite apparent structural succession: greenstones, 3) mi ca schists, mylonites and brec 1) dolostone division cias, 4) Bulltinden Formation, and 5) marbles. 2) micaceous marble division Horsfield (1972) defined group 1 and group 3 as 3) mafic schist division the Vestg6tabreen suite. The name derives from 4) serpentinite divisjon the glacier near which the rocks occur. 5) pelitic schist division During the summers of 1973 and 1975, Ohta 6) greenstone division (1979) mapped the occurrence of this suite 7) psammite division and the Bullbreen Group in more detail and 8) garnet glaucophane division added Horsfield's group 2, epidote-actinolite 9) ec\ogite division greenstones, to the Vestgotabreen suite and sug gested that all the se rocks be tentatively named Dolostone division (VOD) the Vestg6tabreen Formation. Ohta (1979) argued for a min or thrust which he used to divide This unit is characterized by an orange-weath this complex into two units: a) the glaucophane ering dolostone. The dolostone is consistently bearing rocks, edogitic rocks, calcareous schists found below the Motalafjella Formation, and ils and dolostones in the upper part, and b) epidote chemistry and structural and metamorphic styl es actinolite greenstones, dolomites and serpen indicate that it is related to the Vestg6tabreen tinites of the lo'.ver part. Structural Complex. The two member distinction used by Ohta Exposure throughout the study area is patchy (1979), Hirajima et al. (1984) and Ohta (1986) is and unit thickness is variable, ranging from O to toa simple because of the common dose juxta 20 m. The best exposure is on southern Bulltin position of greenstones, garnet glaucophanites, den where it attains maximurn thickness. EIse and schistose horizons. Furthermore. the pro where it is less than 20 m thick and is absent in posed thrust betwecn the se two units has not been western Motalafjella. The upper contact is adjac substantiated by the present authors. I nconsistent ent to the Motalafjella Formation. The lower stratigraphic relationships and numerous minor contact is most commonly associated with the thrusts prec!ude an establishment of a lithologic Vestgotabreen Structural Complex, although at succession within the Vestg6tabreen Structural Ankerfjella and northem Bulltinden it is adjacent Complex. to the Comfortlessbreen Group. Minor occur We propose that the words Structural Complex rences of this division are also found as boudins be substituted for Formation in the formal name within the micaceous marble division on the because of the presence of highly complicated Skipperbreen-Vestgotabreen ridge. structures and a diverse range of rock types and Common to all exposures is a coarsely crys metamorphic facies (North American Strati talline siliceous dolostone which contains approxi graphic Code. 1983. American Association of mately 5% mariposite (chromian phengite). Petroleum Geologists Bulletin. Vol. 67, Artic!e However, the abundance of rnariposite varies 37, point C). sporadically and in places it makes up as much as Manby (1978) presented chemical data from 10% of the total rock. This unit is light grey and selected minerals of the Vestgotabreen Structural weathers to a distinctive and characteristic orange Complex. During the 1983 fie\d season, Ohta et colour. Internal sedimentary structures are absent al. (1983) began a renewed investigation of these and tectonic fabrics are well developed. In some rocks. Hirajima et al. (1984) recognised the pres areas, distinctive boxwork quartz-ca\cite veins are ence of lawsonite and pumpellyite in Vestg6ta present. breen Structural greenstones. Rock and mineral The dolostone is commonly brecciated and the chemical data for jadeite bearing psammites interstices are filled with a light grey limestone within the Vestg6tabreen Structural Complex derived from the Motalafjella Formation and were presented by Kanat (1984) along with a associated with its emplacement. Quartz grains preliminary pressure-temperature estimate for exhibit strong deformation features (deformation the development of this assemblage. A review of bands. deformation lamellae. undulose extinction these rocks was presented by Ohta (1986). and a shape fabric), and the carbonate minerals Nine informal divisions of the Vestgotabreen exhibit two distinct crystal sizes. The dolostone is Structural Complex are described in order of their host to various highly deformed, locally derived, 18 tectonically included exotic clasts, usually rep The division is tabular in form, individual hori resentative of the Vestgatabreen Structural zons are approximately 50 m thick and bounded Complex. The size of individual clasts ranges from by sharp contacts, presurnably thrusts. The lower pebbles to cobbles. surface is thrust against the mafic schists, and The lower contact is poorly exposed; at certain the upper surface commonly occurs beneath the localities in Motalafjella it is interpreted as an dolostone division with tectonie eontact. The unconformity on top of the Vestgatabreen Strue observed lateral extent of this unit is well defined tural Complex, but elsewhere it is il teetonie near the moraine, although it pinches out near eontaet. Supporting evidenee for this inter the 400 m eontour where it is enveloped by the pretation is the presenee of mylonitie textures mafic schists. and juxtaposition of the dolostone with various members of the Comfortlessbreen and St. Majic schist division (VSH) Jonsfjorden Groups and the Vestgatabreen Struetural Complex. Furthermore, the Rocks from this division are green ehlorite-rich Comfortlessbreen and St. Jonsfjorden Groups sehists. It is volumetrically the most abundant display compIex folding and refolding which are and mineralogically heterogeneous division of the not recognised in the orange weathering Vestgatabreen Structural Complex. Common to dolostone. The breeeiated charaeter, lack of sedi all specimens from this division are minerals typi mentary structures, association with tectonic cal of the greensehist facies: ehlorite (as alteration boundaries and the presenee of exotics indicate produets of white mica and garnet), quartz, that this unit is not simply a sedimentary horizon. calcite, phengite, and albite. However, chloritoid, The high MgO, chromium and nickel content of epidote, garnet, jadeite and glaucophane are the unit, and its association with the Vestgata reeognised in association with the more massive breen Structural Complex, suggest that it may representations of this division. The mafic schist represent a carbonated and metasomatised ultra division is in contact with all other divisions of basic rock unit. The orange-weathering dolostone the Vestgatabreen Structural Complex and oceurs represents an unconformity and a decollement throughout the exposed area of these rocks. The zone which is best developed on overturned limbs thickness of this division is difficult to estimate, of major folds where the Bullbreen Group is and a minimum of 200 m is suggested. This div separated from the Vestgatabreen Structural ision appears to have been produced by tectonie Complex (for exampIe, on southem Bulltinden, reworking of other divisions within this complex. in southem Holmesletfjella and Motalafjella). Serpentinite division (VSP) Micaceous marble division (VMl-2) Serpentinites are best exposed in the valley in The micaceous marble division is found just east central Motalafjella. The occurrence of this rock of the Vestgatabreen lateral moraine on the cen type is very patchy throughout the valley, and the tral western side of Motalafjella and on the exposures can be traeed over distanees of less southem portion of the Skipperbreen-Vestgata than 20 m. The serpentinites are black in colour, breen ridge. The division contains two distinct finely crystalline and consist of individual pods units: one is dark grey (VMt) and is interbanded ranging from 0.8 to 1.5 m in diameter. The pods with a medium grey lithology (VM2). Both units are ftattened parallei to the pervasive cleavage eontain characteristic micaceous partings and a and have an aspeet ratio of approximately 2: 1. gritty texture whieh results from the presenee of The serpentine mineral is chrysotile and associ quartz grains and pods usually less than 4 cm ated phases include magnesite, dolomite, and long. Quartz-filledtension gashes and asymmetric ehromite. Chrysotile is twinned, and dissected by isoclinal folds are common in this division. Late ealcite and/or dolornite veins. stage ealcite and quartz veins are parallei and oblique to the foliation. Calcite, phengite and Pelitic schist division (VPE) quartz are common with minor oeeurrenees of albite, opaques, pyrite, and ehlorite. Garnets, This division occurs in central western Motala approximateIy 3-7 mm aeross, and completely fjella and the Skipperbreen-Vestgotabreen replaeed by chlorite, have been found. ridge. Easily distinguished from other units of the 19 complex, it is well foliated and light grey in colour, Bullbreen Group and the Vestgatabreen Struc with porphyroblasts of garnet and staurolite in a tural Complex). dominantly phengitic matrix. The garnet dia This division crops out south of Bulltinden meters range from approximately 2 mm in some where it is presented a a nunatak. A contact zones to 15 mm in others. No systematic relation between the Motalafjella limestone and the ship between garnet diameter and structural posi greenstone division has not been recognised at tion has be en recognised. Other minerals in this locality. Elsewhere. the contact relationships association with those listed above include quartz, of the greenstone unit are sharp against the chloritoid, chlorite, hematite, and pressure-insol micaceous marble, mafic schist, eclogite and gar uble, fine-grained opaque material concentrated net glaucophane divisions. along cleavage planes. Late-stage calcite veins are present. Tourmaline, epidote, pyrite and zircon also occur as accessory phases within this division. Psammite diuision (VPS) At central western Motalafjella the division is poorly exposed, and on ly occurs as scree frag The psammite division is best exposed east of the ments below an elevation of c. 350 m. The only Vestgatabreen lateral moraine on the western lithologic contact in Motalafjella is found towards face of Motalafjella at elevations of approxi the southwest of the mountain where the division mately 30U m. The division is characteristically is in contact with eclogite, and garnets have grown composed of very dusky purple, coarsely crys across the interface. The best exposure of this talline silicic schist, usually 1 4 cm thick, inter division (staurolite absent) is found along the banded with thin layers « 1 cm) of grey olive crest of the Skipperbreen-Vestgotabreen ridge green pelitic horizons and quartz and/or feidspar where it is thrust bounded by units of the pods. Calcite veins, approximately 1 2 mm thick, micaceous marble division. occur at a high angle to the banding. Jadeite, the characteristic mineral of this division (Kanat 1984). occurs with quartz, albite, phengite, hem Greenstone diuision (VGT) atite, sericite, chlorite, mangnesioriebeckite, cal cite, rutile rimmed by sphene, pyrite, and apatite. Best exposed in Motalafjella, this division also The interbanded psammitic and pelitic horizons crops out at all occurrences of the Vestgatabreen are commonly less than 25 cm thick and bounded Structural Complex. It is distinguished by its on either side by the garnet glaucophane division. massive nature and mineral associations. Indi The cumulative thickness of this division is vidual exposures are never greater than 50 m approximately 4 m. Contacts are concordant, and thick. The com mon mineralogy is typical of the individual horizons can be traced over a distance greenschist facies and includes epidote, actinolite of a few meters before pinching out. and albite, with barroisite, retrograde chlorite, hematite and garnet, with minor amounts of vein carbonate, quartz, phengite, rutile rimmed by Garnet glaucophane diuision (VGG) sphene, pressure insoluble opaque material and apatite. The rocks within this division have trace The garnet glaucophane division is best exposed element ratios which suggest that they represent in central western Motalafjella at an elevation of metamorphosed ocean floor tholeiitic basaits 3UU m. Almandine rich garnets, 2 1O mm across. (Morris et al. 1983; Kanat 1984; Ohta 1986). are contained within a dusky blue matrix of glau On the arNe south of Bulltinden and in central cophane with lesser amounts of phengite and western Motalafjella, 'stringers' of grey lime chlorite, and occasional calcite, paragonite, sodic stone, less than 15 cm thick, are recognised clinopyroxene, hematite, quartz, and rutile rim within this division. The limestones could have med by hematite, with minor amounts of actino been incorporated by deformation, or they may lite and epidote. The mineral assemblages are be veins or fracture fillings. The limestones cut typical of blueschist facies metamorphism. Foli across an early fabric of the Vestgatabreen Struc ation is defined by the alignment of both phengite tural Complex and may therefore represent the and glaucophane as well as by a mineralogical initial stages of precipitation of the Motalafjella banding. Psammitic layers are also present, but limestone (i.e. the unconformity between the rare. 20 Exposures appear as weather-resistant blocks Concluding remarks (c. 150 x 80 m exposed) approximately 50 m high. These blocks are isolated from the rest of the Based on sedimentary contacts not previously Vestg6tabreen Structural Compiex and sur deseribed, we present a revised lithostratigraphic rounded by scree and/or ice patches. Horstieid succession for central Oscar Il Land, Spitsbergen: (1972) determined a whole rock K-Ar apparent 1) the base of the Bullbreen Group has been cooling age for this division of 402 ± 14 Ma. redetined by incorporating slates and conglom erates, not previously described, at the base of Eclogite division (VEC) the Motalafjella Formation; 2) the relative posi tions of the Alkhorn and Løvliebreen Formations EcIogites are best exposed in southwest Motala have been reversed; 3) the presence of two distinct fjella at an elevation of 200 m. Hypidioblastic glacigenic diamictite horizons, described in north pink almandine rich garnets, 3-7 mm across, are west Oscar Il Land by Waddams (1983), cannot contained within a dark greenish grey, medium be substantiated in the St. Jonsfjorden region. We crystalline granoblastic omphacitic matrix which suggest that a name change to the Vestg6tabreen gives the rock a distinet porphyroblastic texture. Struetural Complex is proposed and a detailed The following minerals occur within this unit: lithological deseription of these rocks is primary omphacite and almandine, with secon presented. dary glaucophane and occasionally chlorite, One of the most remarkable geological features quartz, epidote, phengite, calcite, hematite, of southwcst Oscar Il Land is the relationship albite, chloritoid, actinolite, and rutile rimmed by between the Bullbreen Group and the Vestg6ta sphene. Following the nomenclature suggested by breen Structural Complex. Mineral parageneses Coleman et al. (1965), this division is a Group C within the Vestg6tabreen Structural Complex eclogite. The exposure is dissected by idiomorphic indicate depths of burial on the order of 50 km glaucophane-quartz-albite veins which are usually (Kanat unpublished; Ohta 1986). Preservation of less than 6 cm wide. these assemblages requires rapid uplift rates in an The major outcrop appears as a weather-resist unstable tectonic regime. The rise of the Vest ant block, approximately 70 x 80 m, with a con gotabreen Structural Complex appears to have cordant pelitic band in contact with the top of the initiated deposition of the Bullbreen Group in a exposure. The block is surrounded by scree from fault-bounded basin. The metamorphic contrast the matic schists, thus making correlation with between the Bullbreen Group and Vestg6tabreen other blocks difticult. This division also crops out Structural Complex, and inclusion of Vestg6ta at the base of the Skipperbreen-Vestg6tabreen breen clasts within the Bulltinden conglomerate, ridge near the micaceous marble division. attest to this relationship. Continued orogenesis drove the Vestg6tabreen Structural Complex over the Bullbreen Group, and both are allochthonous with respect to the Comfortlessbreen and St. Chaotic Zone Jonsfjorden Groups. A zone of tectonically mixed, intensely deformed rocks trends NNW in Thorkelsenfjella and sep Acknowledgements arates Carboniferous rocks to the west from the Bullbreen, Comfortlessbreen and St. Jonsfjorden LHK gratefully acknowledges W. B. Harland for Groups, and VestgOtabreen Structural Complex his time, thought-provoking disellssions, and to the east. Rocks from the Comfortlessbreen and logistical support (1983). We thank M. J. Ham St. Jonsfjorden Groups are represented in this brey and R. Ratliff for valllable discussions and zone. Individual units are lenticular and difficult comments. Y. Ohta made substantial improve to distinguish, and no eoherent strueture has been ments to an early draft of this manuscript. This observed. It is an important observation that the work was part of a Ph.D. research programme rock types which occur east of this zone are not conducted by LHK (1982-1985) at the University represented to the west, and therefore this bound of Cambridge, England, and tinanced by a Ful ary has regional significance. bright Scholarship (USA) and an Overseas 21 Research Students Award (UK). The National oroget/ie studies. Geologieal Society of London Speeial Pub lieation 4. Science Foundation (grant number DPP8107663, Harland, W. B., WaHi" R. H. & Gaycr, R. A. 1966: Arevision awarded to APM) financed the 1982 field season of the Lowcr Hecla Hock suceession in cenlral north Spits for LHK and APM. bergen and corrclation el>ewhere. Geological Magazine J03 ( 1), 70-97. Harland, W. B., Horsficld, W. T .. Manby, G. M. & Morris, References A. P. 1979: An outline prc-Carboniferous Stratigraphy of central western Spitsbergen. Norsk PolarinslituJl Skrifter 167, 119-144. Ague, J. J. & Morris, A. P. 1985: Metamorphism of the Hirajima, T., Hiroi. Y. & Ohta. Y. 1984: Lawsonite and pum Miillerneset Formation, St. Jonsfjorden, Svalbard. pellyitc from the Vcstgotabreen Complcx in Spitsbergen. Polar Research 3 n.s .• 93-106. Norsk Geologisk Tidsskrift 64, 267-274. Armstrong. H. A.. Nakrem. H. A. & Ohta. Y. 1986: Ordovieian Hjelle, A. & Lauritzen, ø. 1982: Geological Map of Svalbard conodonts from the Bulltinden Formation, MOIalafjella. cen l : 500,000. Sheet 3G Spitsbergen northern part Norsk Polar. tral-western Spitsbergen. Polar Research 4 n.s., 17-23. institutt Skrifter 154C. 15 pp. Baker. R IL Forbes. C L & Holland. M. F. W. 1952: Hjelle, A .. Ohta, Y. & Winsnes. T. S. 1979: Heela Boek rocks Fossiliferous slrata at Kapp Seania, Daudmannsøyra. Vest of Oscar Il Land and Prins Karls Forland, Svalbard. Norsk Spitsbergen. Geological Magazine 89, 303-304. Polarinstitutt Skrifter 16 7, 145--169. Birkenmajer. K. 1972: Alpine fold belt of Spitsbergen. 24 th Holtedahl, O. 1913: Zur Kenntnis dcr Karbonablagerungen des International Geological Conference (Canada), section 3.282- Westlichen Spitzbergens. Il. Allgemeine stratigraphisehe und 292. tektonisehe Bcobachtungen. Skrifter Norske Videnskapssel Birkenmajer, K. 1975: Caledonides of Svalbard and Plate skabet Christiania I. Math. Naturv. Kl. 23. 1-9L tectonics. Bulletin of the Geological Society of Denmark 24. Horsf1cld, W. T. 1970: The geology of Oscar 11 Land, 1-19. Spitsbergen. Ph.D. dissertation. University of Cambridge, Birkenmajer, K. 1981: The geology of Svalbard, the western England. 191 pp. part of the Barents Sea and the continental margin of Horsfield. W. T. 1972: Glaueophanc schists of Calcdonian age Scandinavia. Pp. 265--329 in Nairn, A. E. M., Churkin. M. from Spitsbergen. Geologieal Magazine 109. 29-36. & Stehli, F. G. (eds.): The ocean basins and margins. Vol. 5: Kanat. L. H. 1984: Jadeite from southern Oscar Il Land, The Arctic Ocean. Svalbard. Mineralogical Magazine 48, 301-303. Challinor, A. 1967: The structure of BrøggerhalvØya. Knoll. A. FL 1981: Appendix: Chronostratigraphie age of late Spitsbergen. Geological Magazine 104,322-336. Precambrian tillites in Svalbard. P. 601 in Hambrey. M. J. & Colcman. R. G., Lee, D. E., Beatty. L. B. & Brannoek, Harland, W. B. (cds.): Earth's pre-Plei,roæne glacial record. W. W. 1965: Ec10gites and cdogitcs: The;r diffcrences and Krasiltschikov. A. A. & Kova1cva, G, A. 1979: Precambrian similarities. Bulletin of the Geological Society of Ameriea 76. rock-stratigraphic units of the west coast of Spitsbergen. 483-508. Norsk Polarinstitutt Skrifter 167, 81-88. Cutbill, J. L. & Challinor, A. 1965: Revision of the strati· Major, H., Harland, W. B. & Strand, T. 1956: Lexique Strati grapbical sehemc for the Carboniferous and Permian rocks graphique International I, Fascicule Id Svalbard, 21-101. of Spitsbergen and Bjørnøya. Geological Magazine /02.418- Manby. G. M. 1978: Aspcets of Caledonian metamorphism in 439. central western Svalbard with particular reference to the Hambrey, M. J .1982: Late Precambrian diamietites of north glaucophane schists of Oscar Il Land. Polarforschung 48(1/ east Svalbard. Geological Magazine 1/9(6). 527-551. 2),92-102. Hambrey, M. J. 1983: Correlation of Late Proterozoic tillites in Maton, P. L & Harland, W. B. 1969: Cambridge Spitsbergen the North Atlantic region and Europc. Geological Magazine Expedition. 1968. Polar Record 14(91), 492·494. /20(3), 209-232 Morris, A. P., Ague, J. J., Kanal, L H. & Manby, G. M. Hambrey, M. J. & Waddams, P. 1981: Deformed sto nes of 1983: Caledonian orogcncsis in central western Spitsbergen. varied lithology in late Precambrian tillites, western Gealogieal Sociery of Ameriea Abstracts with Programs 15, Spitsbergen. Journal of the Geological Society, London 138, 647. 445-453. Ohta, Y. 1979: Blue schists from Motalafjella, wcstern Hambrey, M. J., Harland. W. B. & Waddams, P. 1981: Late Spitsbergen. Norsk Polarinstitutt Skrifter 167, 171-218. Precambrian tillites of Svalbard in Earth's pre·Ple;stoccne Ohta, Y. 1985: Geochemistry of Precambrian basic igncous gladal record. Internmional Geological Correlation Pro rocks betwcen St. Jonsfjorden and Isfjorden. central western gramme 38, 592-601 . Spitsbergen, Svalbard. Polar Research 3 n.s., 49-67. Harland. W. B. 1960: The deve10pment of Hecla Hoek rocks Ohta, Y. 1986: Caledonian high-pressure metamorphism in in Spitsbergen. 2151 International Geological Conference central western Spitsbergen. Geological Society of Ameriea (Norden). section 19,7-16. Memoir 164. Harland. W. B. 1961: An outline structural bistory of Ohta, Y., Hiroi, Y. & Hirajima, T. 1983: Additional evidence of Spitsbergen. Pp. 68-132 in Geology of the Arctic. University pre-Silurian high-pressure metamorphic rocks in Spitsbergen. of Toronto Press. Polar Research l /l.S., 215-218. Harland, W. B. 1978: The Caledonides of Svalbard in Cale Orvin, A. K. 1934: Geology of the Kings Bay region, Spits donian Appalaehian Orogen of the North Atlantic Region. bergen, with spedal reference to the coal dcposits. Skrifter International Geological Correlation Programme 27, Geo· om Svalbard og Ishavet 57. 195 pp. logical Survey of Canada, paper 78--1, 3-11. Scru1ton, C T, Horsfield. W, T. & Harland, W. B. 1976: Harland, W. B. & Horsfield, W. T. 1974: West Spitsbergen Silurian fossiIs from Western Spitsbergen. Geological Maga Orogen. Pp. 747-755 in Speneer. A. M. (ed.): Data for zine 1/3(6), 519-523. 22 Waddams, P. 1983: The Late Precambrian succession in north and other evidences of late Precambrian ice ages in west Oscar II Land, Spitsbergen. Geological Magazille Spitsbergen. Geological Magazine 101, 198--219. 120(3), 233-252. Winsnes, T. S. 1965: The Precambrian of Spitsbergen and We;ss, L E. 1953: Tectonic features of the Beda Bock to Bjørnøya. Pp. 1-24 in Rankrna, K. (ed.): The geologic the south of St. Jonsfjorden, Vestspitsbergen. Geological systems. The Precambriall2. Tnterscience Publishers, Wiley, Magazille 90, 273-286. London. Wilson, C. B. & Barland, W. B. 1964: The Polarisbreen Series 23 Plate 1 Comparativc photomicrographs. a: Photomicrograph of retrogrcsscd garnetiferous c1ast from the Bulltinden conglomeratc at Motalafjella under eros>cd nicols (spedmen numbcr 10116). b: Photomicrograph of retrogressed garnet from the malic schis! division of the Vestgotabrcen Structural Complcx at Motalafjella under crossed nicols (spedmen number K3231). c: Photomicrograph of chloritoid rosettes from a clast within the Bulltinden conglomcrate at Motalafjella in planc polarizcd light (speeimen numher K32?8). d: Photomicrograph of chloritoid rosettcs from the malic sehist division of the Vcstgotahreen Structural Complcx at Motalafjella in plane polarized light (spedmen number K3314). Seale bars 0.5 mm for all phntomicrographs . • An uncoded ASCII MS-DOS file cntitJcd LHKRKCAT.CUP (221Kb) which catalogues locations. mineral assemblagcs, and other collection data for all specimens descrihed in the text is availablc from LHK.