The Janusfjellet Subgroup (Bathonian to Hauterivian) on central : a revised lithostratigraphy

H. DYPVIK, J. NAGY, T. A. EIKELAND, K. BACKER-OWE, A. ANDRESEN, P. HAREMO, T. BJAZRKE, H. JOHANSEN, and A. ELVERHBI

Dypvik, H.,Nagy, J., Eikeland, T. A., Backer-Owe, K., Andresen, A,, Haremo, P., Bjrerke, T.,Johansen, H. & Elverhl, A.: The Janusfjellet Subgroup (Bathonian to Hauterivian) on central Spitsbergen: a revised lithostratigraphy. Polar Research 9(1), 21-43. The Janusfjellet Subgroup is a marine shelf to prodeltaic succession dominated by shales with subordinate siltstones and sandstones. The subgroup comprises a lower Agardhfjellet (Upper Bathonian - ) and an upper Rurikfjellet (Berriasian - Hauterivian) formation. Based on field work in central Spitsbergen the following subdivisions of the formations are proposed (units listed in ascending order). The Agardhfjellet Formation (up to 290 m thick) contains four members: Oppdalen - a fining upwards succession from conglomerates to shales; Lardyfjellet - black paper shales; Oppdalsita - grey shales with siltstones and sandstones; and SlottsmQya - grey shales and black paper shales. Within the Oppdalen Member three beds are recognised: Brentskardhaugen - phosphoritic conglomerate; Marhogda - glauconitic sandstones; and Dronbreen - siltstones and shales. The Rurikfjellet Formation (thickness up to 226 m) is composed of two members: Wimanfjellet - grey and partly silty shale sequence, containing the Myklegardfjellet Bed (of plastic clays) at its base; and Ullaberget - silty and sandy shales with siltstones and sandstones. H. Dypvik, J. Nagy, T.A. Eikeland, K. Backer-Owe, A. Andresen, and A. Elverh@i, Department of Geology, University of Oslo, P.O. Box 1047 Blindern, N-0316 Oslo 3, ; P. Haremo, Norsk Hydro AIS, P.O. Box 200, N-1321 Stabekk, Norway; T. Bjerke, Storgata 47, 3290 Stauern; H. Johansen, Norsk Polarinstitutt, Rolfstangveien 12. Snar@ya, P.O. Box 158, N-1330 Oslo lufthavn, Norway.

In light of the latest stratigraphical information graphical correlation, to increase the resolution generated by recent structural, sedimentological potential of the structural geology and to act as an and paleontological investigations (Andresen et improved framework in ongoing sedimentological al. unpubl.; Dypvik et al. 1988; Nagy et al. discussions (Figs. 1 and 2). The study is con- 1990; Dypvik et al. in press), a revision of the centrated around the region between Sassen- / stratigraphy of central Spits- fjorden, Kjellstr0mdalen and Agardhbukta. bergen appears to be required. The revised strati- designated here as central Spitsbergen. graphical subdivision proposed below aims to The Bathonian to Hauterivian time-span in facilitate detailed geological mapping and strati- Spitsbergen is represented by an approximately 400 m thick sedimentary succession composed New or revised definitions of stratigraphic units in Norway mainly of shales with subordinate siltstones and (including the Norwegian polar areas) are to be registered sandstones deposited in shelf environments and confirmed by the ‘Norwegian Committee on Stratigraphy’ (Dypvik 1985). This succession is the Janusfjellet (NSK). A subcommission, the ‘Committee on the Stratigraphy of ’ (SKS), has recently (1990) been established to unit (Fig. l), which was ranked originally as sub- develop a formal stratigraphic nomenclature for the bedrock group (Parker 1967) but changed subsequently to stratigraphy of the mainland of Svalbard. Until this work has formation. The present contribution revises the been completed, SKS will not accept individual applications. stratigraphy of the Janusfjellet unit, and the main Authors are requrested not to submit formal definitions of stratigraphic units in Svalbard during this time without first items of this revision are: redefining the Janusfjel- consulting SKS (c/o Norwegian Polar Research Institute, P.O. let unit as subgroup; elevating the rank of its two Box 158, N-1330 Oslo Lufthavn). subunits (the Agardhfjellet and Rurikfjellet) from The present article was submitted prior to the establishment member to formation; providing a new and of SKS and has therefore been treated as an exception. The detailed subdivision of these formations. stratigraphy presented has not yet been confirmed by NSK and will be considered along with other proposed stratigraphic The basis of the present stratigraphical study is subdivisions. extensive field work carried out at Bohemanflya, 22 H.Dypvik et al.

Fig. I. The Janusfjellet Subgroup at Wimanfjellet, seen from Isfjorden (WI-Wilhelm~yaFormation, JA-Janusfjellet Subgroup).

Festningen, Janusfjellet, Wimanfjellet, Knor- FJELLE? ringfjellet, numerous sections in the Advent- FM. FESTNINGEN MEMBER dalen-Reindalen area, Lardyfjellet in Kjell-

ULLABERGET strcbmdalen and sections at Agardhbukta (Figs. 3 and 4). The preliminary results of these in- vestigations have partially been published else- where (Dypvik et al. 1988; Nagy et al. 1990), and the present paper is devoted to the more general features of stratigraphical relevance. A proposed sedimentological model based on the new data from the subgroup will be presented in a separate 1 SLOTTSMBYA MEMBER paper (Dypvik et al. in press). z P tia General stratigraphy of the P Janusfjellet Subgroup c W The Middle Jurassic to Lower Cretaceous suc- d LARDYFJE~LET MEMBER d cession in Spitsbergen forms a single major strati- W v 3 graphic unit, the Group originally 0 OPPDALEN proposed by Parker (1967), which contains a L MARHBGDA BED fluviodeltaic and three marine formations. The MEMBER : BRENTSKARDHAUGEN BED Fig. 3. Geological map of Spitsbergen showing position of Fig. 2. Revised stratigraphical scheme of the Janusfjellet Suh- localities discussed in text. Central Spitsbergen, hoxcd in. is group for central and eastern Spitsbergen. enlarged in Fig. 4. The Janusfellet Subgroup (Bathonian to Hauterivian) on central Spitsbergen 23

@ Syltoppen @ Bohemanflya @ Billefjorden @ Sassenfjorden @ lsfjorden @ Festningen @ Van Keulenfjorden @ Ullaberget @ Kvalvagen @ Jurakammen @ Wedel Jarlsberg L.= @ Torell Land @ Hornsund @ Serrkapp Land @ Keilhaufjellet

/19O 11 5O I180 24 H. Dypuik et al.

Janusfjellet @) Aasgaardfjellet I 1 GLACIERS 0 @ Marhragda @ Bergmraya @ Oppdalen @ Knorringfjellet @ OppdalsAta I_=] JURASSIC @ Marmierfjellet @ VrAbreen - CRETACEOUS Roulettegga Lardyfjellet - @ @- l;T,?j @ Arctowskifjellet @ Glitrefjellet @ Juvdalskampen @ ~~ottsmraya II I Ll @ Brentskardhaugen @ Lundstrramdalen @ Drranbreen @ Agardhfjellet \ FAULTS @ Fleksurfjellet @ Myklegardfjellet @ Fonnhetta @ Klementievfjellet @ Tronfjellet @ Rurikfjellet

Fig. 4. Geological map of Central Spitsbergen. Position of localities discussed in text indicated.

group unconformably overlies the large hiatus 1940). The unit was formally termed the Janus- which comprises much of the Middle Jurassic, fjellet Subgroup by Parker (1967), and this usage while the top of the group corresponds to an was shared by Flood et al. (1971). Later on the extensive Late Cretaceous hiatus. The lower, unit was currently ranked as formation. The sub- shaley part of this succession has long been recog- group rests on shallow shelf to marginal marine nized as a major single unit variously designated sandstones and shales of the Wilhelmoya Forma- as Aucellensichten (Nathorst 1897; Hoe1 & Orvin tion. It is overlaid by fluviodeltaic sandstones of 1937) or Aucellen shale (Hagerman 1925; Orvin the Helvetiafjellet Formation. The Janusfjellet Subgroup (Bathonian to Hauteriuian) on central Spitsbergen 25

The Janusfjellet Subgroup is composed of the Maher (1989) discusses a storm-related origin for Agardhfjellet Formation of Late Bathonian to the Brentskardhaugen Bed. Directly on top of Berriasian age, and the Rurikfjellet Formation of this conglomerate, the oolitic sediments of the Berriasian to Hauterivian age. These two units Marh~gdaBed follow in an upward fining de- are separated by a thin interval (usually <2 m) of velopment. yellowish weathering clays. The lower part of the Agardhfjellet Formation is dominated by somewhat silty and sandy sedi- ments, grading upwards into black (often papery) Agardhfjellet Formation and grey shales forming the main part of the unit. This unit was originally defined as formation (Par- The age of this formation is Late Bathonian to ker 1967), but became changed in rank to member Berriasian as deduced from the literature includ- in several papers (Major & Nagy 1972; Bir- ing Pchelina (1965a, b); L~faldli& Nagy (1983); kenmajer et al. 1982; LGfaldli & Nagy 1983). Parker (1967); Erschova (1983); Kopik & Wierz- Detailed studies in central Spitsbergen demon- bowski (1988) Wierzbowski (1989); Nagy et al. strated that the unit has a varied lithology, which (1990). The thickness of the Agardhfjellet For- together with its large thickness warrants its rank- mation varies between 165 m at Keilhaufjellet to ing as formation. 255-290 m in the Van Keulenfjorden and Festnin- The lower part of the Janusfjellet Subgroup is gen areas. The dark shales of the Agardhfjellet made up of the few decimeter to some meter thick Formation contain some siltstone and sandstone Brentskardhaugen Bed, containing pebbles of beds, but generally represent deposition in oxy- phosphate, chert, rock fragments, etc. (Back- gen-deficient shelf environments characterized by strom & Nagy 1985). The position of the Brent- sedimentation of fine-grained material such as skardhaugen Bed with regard to higher category clay and organic matter (Dypvik 1985). The dark is not well established. The bed was first claimed coloured siltstones and sandstones of Callovian to be part of the Janusfjellet Subgroup (Parker age, commonly observed in Central Spitsbergen, 1966, Pchelina 1965a, b; Buchan et al. 1965). have also been noted by Pchelina (1965a, b) in the Parker (1967), however, preferred to place the Festningen and Van Keulenfjorden areas (Fig. 3). Brentskardhaugen Bed at the top of the Kapp The and Kimmeridgian parts of the Toscana Group, due to lithological similarities sequences are dominated by bituminous intervals between the matrix of the conglomerate and the of black paper shales (Pchelina 1965a, b; Nagy sandstones forming the uppermost part of the & L0faldli (1981). Based on a combination of group. These sandstones belong to the Wilhelm- lithological and faunal evidence, Nagy et al. 0ya Formation introduced by Worsley (1973) (1988) argue that the shales mainly represent and subsequently discussed by M0rk et al. (1982). dysaerobic depositional conditions in a shelf In more recent literature the Brentskardhaugen environment. Bed is regarded by some authors as the uppermost The Polakkfjellet Bed is a coarse-grained sub- unit within Wilhelm~ya Formation (Worsley unit of the formation. In 1973; Harland et al. 1974; Bjarke & Dypvik the bed is developed as a 5 m thick sandstone unit 1977). On the other hand, Flood et al. (1971), in the lower part of the Tirolarpasset Member Major & Nagy (1972), Birkenmajer (1975), Back- (Rozycki 1959; Birkenmajer 1975). Comparable strom & Nagy (1985), and Birkenmajer et al. sandstone beds in the middle part of the formation (1982) claim the Brentskardhaugen Bed to be a (the OppdalsPta Member discussed below) occur part of the Janusfjellet Subgroup. at several localities and are assumed to have been The Brentskardhaugen Bed is a remaniC unit deposited as shelf sand ridges. containing bivalves and ammonites representing The palynological assemblages of the the Toarcian. In addition its content of younger Agardhfjellet Formation are characterized by suggests that partial presence of the Aalen- dinoflagellates with minor amounts of bisaccate ian to Bathonian interval is not unlikely. After a pollen and spores (Bjarke et al. 1976). The fora- regressive/transgressive event in Middle Jurassic miniferal fauna of the formation consists almost time the bed was finally deposited under littoral exclusively of arenaceous species. Intervals with condition in its present state in the uppermost high organic carbon content show low species Bathonian or at the transition between this stage diversities or are barren of foraminifera (Nagy et and the Callovian (Backstrom & Nagy 1985). al. 1988). 26 H. Dypuik et al.

Rurikfjellet Formation sandstones, and these coarser-grained intervals were named the Ullaberget Series in the western The Rurikfjellet unit was originally proposed by part of Spitsbergen by Rozycki (1959). The name Parker (1967) as formation, but in later current was later formalised to Ullaberget Member by usage it became lowered to member rank (Bir- Birkenmajer (1975). The distribution of this unit kenmajer 1980; Steel & Worsley 1984; Nagy et is also discussed by Parker (1967), who claimed al. 1988). The dominant lithologies of the that it was only locally developed and confined to Rurikfjellet Formation are shales, siltstones and western areas. The sandstones within the Ulla- sandstones composing several coarsening-upward berget Member were shown by Edwards (1976) sequences deposited in marine shelf to prodeltaic to occur in coarsening-upward sequences, inter- environments. preted as shallow marine and prodeltaic deposits The formation varies in thickness from 123 m in S~rkappland.A similar explanation is applied at Keilhaufjellet (L~faldli& Nagy 1983) to 225 also on the Ullaberget sandstones in Hornsund and 290m in the Festningen and Van Keu- by Mark (1978). This opinion was shared by lenfjorden areas. The age of the Rurikfjellet Bxnevad (1986) and may also be applicable to Formation is Berriasian to Hauterivian (Parker central Spitsbergen (Dypvik et al. in press). The 1967; Pchelina 1967). Harland (1972) claimed, upward-coarsening units show depositional direc- however, the Berriasian Stage not to be present in tion towards the S-SE and represent upward- Spitsbergen, arguing that the formation contains increasing current and wave activity, a response only Valanginian to Upper Hauterivian deposits. to a generally prograding deltaic development. Pchelina (1965) demonstrated the presence of Bxnevad (1986) shows both fluviodeltaic pro- beds from Valanginian and Hauterivian, based cesses and geostrophic storm currents with trans- on macrofossil evidence. port direction towards S-SW to have distributed An important stratigraphical marker horizon in and deposited the sandy sediments in the upper- central and eastern Spitsbergen is formed by the most part of the Rurikfjellet Formation. yellow weathering clays in the middle of the The time equivalent deposits of the Janusfjellet Janusfjellet Subgroup at the boundary between Subgroup on were assigned to the Agardhfjellet and Rurikfjellet formations. the Kongs~yaFormation by Smith et al. (1976). The origin of these beds is not clearly understood, This unit consists mainly of grey to black shales but explanations such as bentonites, glauconitic and clays with some siltstones - lithologies essen- beds. weathering products of carbonate beds and tially similar to those of Spitsbergen. weathered dolerites may be suggested. It should The Festningen Member of the Helvetiafjellet be noted that Pchelina (196Sb) found no sharp Formation (Barremian) consists of fluviodeltaic, boundary between the Agardhfjellet and the coarse-grained, light-coloured sandstones de- Rurikfjellet formations in the Van Keulenfjorden posited, with erosion at base, directly on the area. Rurikfjellet Formation. The Festningen Member In previous studies sediments from the Berria- represents the delta-dominated coastline which sian had not been recognized, and deposits of this succeeded the prodeltaic sediments seen in the time interval were supposed to be absent from Rurikfjellet Formation (Nemec et al. 1988; Steel the succession (Harland 1972). Parker (1967) sug- 1977). The regional regression is first reflected gested that the boundary between the two for- by the coarsening-upward developments of the mations actually is a Late Volgian non sequence. Rurikfjellet Formation, which were connected to Birkenmajer (1975) claimed, however, that sedi- deltas prograding from northern to westerly mentation was continuous across the Jurassic- areas. The Helvetiafjellet Formation is dom- Cretaceous transition in Torell Land. In accord- inated by the deltafront and floodplain deposits ance with this the presence of the Berriasian is of these deltas. demonstrated by Pchelina (1967) in Sorkappland. The Festningen Member consists of multistorey In central Spitsbergen the Myklegardfjellet hori- sandbodies. with southerly transport directions in zon is referred to as the Ryazanian (Late Berria- its lower part (Steel 1977). In the middle part of sian) by Nagy et al. (1990), based on foraminifera1 the member some eastern transport directions are evidence. observed. The lithological development of the The upper part of the Rurikfjellet Formation member is quite uniform throughout Spitsbergen in several areas is dominated by siltstones and (Edwards 1976; Steel 1977; Steel & Worsley The Janusfjellet Subgroup (Bathonian to Hauteriuian) on central Spitsbergen 27

1984). The latter two authors claim the Festningen of dolerites, which were distinguished mainly by Member to be more deltaic than fluvial in origin. their quartz content. The influence of magmatism Nemec et al. (1988) note the presence of rotated on the sediments of the Agardhfjellet Formation faultblocks, slides, and mudflows within the delta at Agardhfjellet is probably reflected by the some- front deposits of the Kvalvlgen area. what higher vitrinite reflectance values found in this unit, compared to the overlying Rurikfjellet Tectonic and magmatic activity Formation (Bjcerke et al. 1976). Parker (1966) claimed that three major epi- The Janusfjellet Subgroup shows marked regional sodes of tectonic activity took place in Svalbard thickness variations on Spitsbergen. These in post-Paleozoic times: in the mid-Triassic, at changes have previously to a large extent been the Jurassic-Cretaceous transition and in the post explained either as several episodes of syn- Eocene period. He assumed that the structures depositional movement or as differences in sedi- of the Billefjorden Lineament die out south of ment accumulation. Birkenmajer (1975) claims Kjellstr0mdalen, which is, however, not the case, that the increased thickness of the subgroup in as demonstrated by Haremo et al. (1990). Accord- western areas mainly reflects the depositional axis ing to Parker (1966), when the effects of Tertiary of the basin. The thickness changes are also dis- tectonism are removed, a pre-Cretaceous anti- cussed by Steel & Worsley (1984), who favored clinal structure is left in the middle and eastern Mesozoic normal faulting to be a major con- parts of Spitsbergen. He suggests that the trolling factor. In Central Spitsbergen, along the Janusfjellet Subgroup in the west acted as a dec- Billefjorden Fault Zone, Parker (1966) and Har- ollement zone during the Tertiary tectonic move- land et al. (1974) claimed that tectonic events had ments. taken place, resulting in extensive erosion at the According to Parker (1966) and Harland et al. Jurassic/Cretaceous transition. The absence of (1974) the tectonic highs formed at Marmierfjellet the Agardhfjellet Formation in some areas along and Fleksurfjellet along the Billefjorden Fault the fault zone is by these authors explained by Zone, also controlled sedimentation of the the same tectonic events. Recent investigations, Rurikfjellet Formation. The products of erosion however, have shown that this is not the case, of the Agardhfjellet Formation in connection with and Haremo et al. (1990) have demonstrated that the tectonic activity at the Jurassic-Cretaceous most of the thickness variations found within the boundary should, then, be the main reason for Janusfjellet Subgroup can be explained by Ter- the thickness variations observed. Harland (1972) tiary compressional tectonics including thrusting. claims that movements have taken place along Mesozoic magmatic activity is documented by two fault zones. Recent investigations reduce the the presence of dolerite sills and dykes in large importance of these tectonic movements, but sug- parts of Spitsbergen and on Kong Karls Land gest that the Marmierfjellet-Fleksurfjellet areas (Burov & Livsic 1970; Smith et al. 1976; Tyrell & may have appeared as shallow banks in the Jur- Sandford 1933). The dolerites have been dated assic shelf area. (K-Ar) by Gayer et al. (1966) and by Firsov & Livsic (1967) and given ages of about 110 to 143 my. In Agardhbukta, dolerites have been Subdivision of the Agardhfjellet found to pass through the Agardhfjellet For- Formation mation but not the Rurikfjellet Formation (Par- ker 1967); consequently they are attributed to The Oppdalen Member magmatic events at the transition between the The Oppdalen Member forms an upward-fining Jurassic and Cretaceous systems (Burov & Livsic sequence, from conglomerates through sandy and 1970; Tyrell & Sandford 1933). On Kong Karls silty beds to shales, making up the lower part of Land, however, the volcanics are of Kim- the Agardhfjellet Formation (Figs. 2,5, and 6). meridgian to Barremian age, with peaks in the The member consists of three subunits with tran- Volgian and Valanginian (Smith et al. 1976). The sitional boundaries (from base upwards): the bulk of the Spitsbergen dolerites are sills (Tyrell Brentskardhaugen, Marhogda and Drmbreen & Sandfjord 1933) with a uniform tholeiitic com- beds. The type section of the member is located position, characterized by plagioclase with An 45 to the lowermost part of Oppdalslta. in the inner- to 65. Burov & Livsic (1965) described four types most part of Oppdalen (Figs. 3 and 4). 28 H. Dypuik ef al.

THE AGARDHFJELLET FORMATION East 250 . m

200

150

100

50

0

A Bohernanflya F Glitrefjellel Sand B Janusllellet G Oppdalsata C Wimanl~ellel/Knorringl~ellel ti Lardyfjellel Sandy shales D Juvdalskarnpm I Agardhbukla S Paper shales E Fleksurflellet - Clay Fig. 5. The regional stratigraphlcal developrncnt of the Agardhfjellet Formation in Central Spitsbergen

The Brentskardhaugen Bed. - The name Brent- (1985). The conglomerate is found to be only skardhaugen Bed was proposed by Parker (1967) 20 cm thick at Vribreen (inner part of Kjellstr0m- for the 'phosphatic conglomerate' or 'Liassic con- dalen, Fig. 3) where it is dominated by minor glomerate' of earlier workers. The type locality is phosphatic pebbles. At Oppdalsssta (inner part Brentskardet. at the head of Adventdalen, where of Reindalen) the bed is poorly cemented and the unit is 1.3m thick. The fauna of the Brent- only 30 cm thick. skardhaugen Bed at Sassenfjorden has been rec- orded by Wierzbowski et al. (1981). Backstrom The Marhagda Bed. - Resting on the Brent- and Nagy (1985) discuss in detail the lithology skardhaugen Bed an oolitic, glauconitic to cha- and fauna of the unit. covering several regions of mositic sand/siltstone is commonly found on Spitsbergen. Spitsbergen (Fig. 8). This 0.3 to 1.5 m thick unit The bed is from 0.2 to 4 m thick and consists was named the Marh~gdaBed by Backstrom & of phosphorite, quartzite, and chert clasts in a Nagy (1985). The type section of the unit is matrix-supported texture, dominated by well- located at Marh~gda,at the southern shore of cemented sandy material (Fig. 7). The pebbles Sassenfjorden, where it is from 1.2 to 1.S m thick. contain several marine groups and pieces of This glauconitic/chamositic marker bed is also wood. Ammonites and bivalves indicate clast ages found at Fonnhetta, Dronbreen and Fleksurfjel- of Toarcian to probably Bajocian, while the let. In these areas the grey to greenish bed is matrix age and consequently the age of the con- characterized by dispersed oolitic glauconite/ glomerate bed as a lithological unit is regarded as chamositic grains and some similar sized phos- probably Upper Bathonian (Backstrom & Nagy phate pebbles in a sandy matrix. The composition 1985). The Brentskardhaugen Bed has been of the oolites varies to some extent, however, observed in the study area in somewhat varying with chamosite found in siderite cemented beds developments as discussed by Backstrom & Nagy and with glauconite associated with dolomite The Janusfiellet Subgroup (Bathonian to Hauteriuian) on central Spitsbergen 29

LARDYFJELLET

LEGEND

CLAY PAPER SHALE CARBONATE NODULES THIN SILTSTONE BEDS SIDERITE LENSES

SHALE /SILT

SANDSTONE CROSS BEDDING SIDERITE CONCRETIONS CONGLOMERATE LIMESTONE SIDERITE EROSIONAL SURFACE DOLOMITE COVERED H

[3 CALCITE CEMENT SIDERITE CEMENT a DOLOMITE CEMENT %f BIOTURBATION UHHORIZONTAL TRACES OVVERTICAL TRACES 9 SKOLITHOS 8 MOLLUSKS 6 AMMONITE !' BELEMNITE 6; WOOD FRAGMENTS + COAL FRAGMENTS W BONES VERTEBRATES G GLAUCONITE m PHOSPHATE BED 0 OOIDS /h RIPPLES - PLANAR LAMINATION HCS HUMMOCKY CROSS STRATIFICATION 9 PLANT FRAGMENTS

WI = Wilhelmoya Formation Op. = Oppdalen Member Be Brentskardhaugen Bed Dr = Dronbreen Bed

Fig. 6. Columnar section showing the Agardhfjellet Formation and lower pan of the Rurikfjellet Formation at Lardyfjellet. S Kjellstromdalen (78" 3.8'N, 17" 48.8'E). 30 H. Dypvik et al.

Fig. 7. The Brentskardhaugen Bed at the front of Dronbreen. the inner part of Adventdalen. Outcrop surface formed by well- developed bedding plane is seen.

Fig. 8. The Marh0gda Bed at the front of Dr~nbreen.inner Adventdalen (BE-Breentskardhaugen Bed, MA-Marhbgda Bed. DR- Dronbreen Bed). The Janusjjellet Subgroup (Bathonian to Hauteriuian) on central Spitsbergen 3 1 cemented units. A similar oolitic sandstone is papery shales of the overlying Lardyfjellet also developed at Juvdalskampen. Rozycki (1959) Member. The type section of this bed is situated mentions an iron-rich oolite bed directly overlying at the head of Adventdalen, about 1 km northeast the phosphate conglomerate in the Ingebrigtsen- of the front of Dr~nbreen. bukta area, southern side of Van Keulenfjorden. The bed is generally structureless, probably due In the inner part of Reindalen, at Oppdalsita, to a high degree of bioturbation. In the lower part the Marhcigda Bed is recognized as a 30 cm thick of the unit, at Janusfjellet, it is possible that carbonate cemented glauconitic sandstone bed. hummocky cross-stratification was observed. The In the inner part of KjellstrBmdalen, at Vribreen, unit shows a gradually upward-fining devel- the unit is 0.8m thick, and consists of loose, opment from the glauconitic sandstones of the partly carbonate-cemented, glauconitic/chamosi- Marh~gdaBed to the black shales of the Lar- tic sand. The loose sandy appearance may be a dyfjellet Member. result of weathering and suggests the sediment to The Dr0nbreen Bed thins to some extent from be more firmly cemented deeper in the section. the northwestern margin of the basin and east- wards. This thickness reduction matches the The Dranbreen Bed. - The Marh~gdaBed is sedimentary transport directions measured in overlaid by an upward-fining unit of poorly Reindalen, where the main transport directions sorted, clay-rich fine sand and silt with up to 30 cm are towards S-SE, with a minor component thick beds of siderite (Fig. 9). Due to its extensive towards E-NE and W-NW. The thickness of the exposures west of Drmbreen we have named bed at seven localities is as follows: the unit after this glacier. The unit represents a Bathonian to Callovian transgressive phase. It Janusfjellet 25 rn comprises a 10 to 60 m thick sequence of loosely Syltoppen, Bohemanflya 60 m cemented sediments which separate the Mar- Myklegardfjellet 40 m hagda Bed from the typically black, commonly Fleksurfjellet area 3C-35 m

Fig. 9. The Dronbreen Bed consisting of siltstones and shales. and containing a well-developed carbonate bed displaced by a small fault. Exposure at the front of Dronbreen. Adventdalen. 32 H. Dypvik el al.

Fig. 10. The black, finely laminated paper shales of the Agardhfjellet Formation, Oppdalsita

Oppdalsita/Slottsm~yaarea 45-50 m most probably reflects the degree of bioturbation, Lardyfjelle t/Vribreen 15 m the amount of organic material and the changing Knorringfjellet area 10-20 m contents of coarse-grained (silty-sandy) com- ponents. The paper shales are characterized by a The Dr~nbreenBed is relatively rich in fossils, low silt and sand content. The observable degree mainly ammonites, belemnites and bivalves of bioturbation is still generally low in the coarse (Buchia). Its foraminifera1 faunas consist of intervals of the Agardhfjellet Formation, and no agglutinated assemblages with relatively high bioturbation has been seen in the paper shales. species diversity. The paper shale sequences are developed in the Callovian, Kimmeridgian and Volgian parts of The Lardyfjellet and Slottsm0ya Members the succession. The intervals consisting of grey shale are mod- The main part of the Agardhfjellet Formation erately rich in fossils such as bivalves (Buchia), consists of dark-grey to black shales and paper ammonites and belemnites, while the paper shale shales, with common carbonate concretionary beds normally are more or less depleted in com- beds (Fig. 10). This shale sequence comprises a parison to the more blocky fracturing, siltier lower Lardyfjellet Member and an upper Slotts- parts. The shales also contain well-preserved ple- m~yaMember, separated by the silty to sandy siosaur remains. development of the OppdalsAta Member (Figs. 2 The Lardyfjellet Member consists almost and 11). exclusively of black paper shales, and the highest The paper shales of the Agardhfjellet For- concentrations of organic carbon are found in mation are dark, rich in organic material and have a fine papery fissility, most probably following Fig. 11. Columnar sections showing the Agardhfjellet For- the well-developed lamination of the sediment. mation at Oppdalsita (78" 4.6'N, 17"23.7'E) and Slottsmdya, However, shales with more blocky to prismatic Reindalen (78O3.5". 1721.2'E). Legend for symbols is given fracture also occur. The varying degree of fissility in Figure 6. The Janusfjellet Subgroup (Bathonian to Hauteriuian) on central Spitsbergen 33

OPPDALSATAL biI WI = Wilhelm0ya Formation Be = Brentskardhaugen Bed RU = Rurikfjellet Formation Ma = Marhogda Bed G WI = Wimanfjellet Member Dr = Dronbreen Bed = A,- A,- My Myklegardfjellet Bf?d

-= .. SLOTTSMPIYA

OH

+V OVE I I1

=- =-

IIIIII, I, sivffmcvc sivffrncvc sandstone- - sandstone 34 H. Dypvik el al. this unit. The type section of the member is the the thickness of the shales in the Agardhfjellet northwestern corner of Lardyfjellet on the sou- Formation to increase relatively to the sandstones thern side of Kjellstr~mdalenwhere the thickness towards the east. The dominance of paper shales of the member is 35 m. The member shows higher is also shown to increase in the same direction natural gamma activity and uranium enrichments (Fig. 5). These shales are suggested to have acted compared to the Slottsm~yaMember. The con- as decollement zones for Tertiary movements cretions found in the Lardyfjellet Member are (Harem0 et al. 1990), indicating that some of made up of dolomite, while those in Slottsm@ya the thickness variations are results of tectonic Member are sideritic. thickening. The SlottsmGya Member consists mainly of grey shales commonly found with locally-developed The OppdalsHta Member occurrences of black. paper shales. In the upper part 3f this member coarsening-upward shale-silt- The Oppdalsiita Member (Figs. 2 and 11) is sand sequences are commonly developed at the characterized by the appearance of more silty and Don~planireshorizons. The type locality of this sandy developments than the beds above and mem3er is the northern slope of Slottsmoya. at below. At SlottsmBya (Figs. 3 and 4) fine sand the junction between Reindalen and Lund- dominates. but in the region as a whole the grain stromdalen. where the thickness of the member size is somewhat finer. At Sassenfjorden and is 90 m. Agardhfjellet sandy developments of the Th: concretions occurring in the shales of the Agardhfjellet Formation are referred to this Agardhfjellet Formations are normally red to yel- member (Nagy et al. 1990). It should be noted, lowish in colour. Close to the boundary towards however. that lack of detailed observations pro- the Rurikfjellet Formation, light-yellow 10-30 cm vides only sparse information concerning the de- thick concretionary beds dominate. velopment of the Oppdalsiita Member. In the A transect across central Spitsbergen shows western outcrop belt at Jurakammen and Keil-

Fig. 12. The uppermost coarse-grained part of the Oppdalshta Member at Gtitrefjellet. Reindalen (OP-Oppdalsita Member, SL- Slottsm6ya Member). The Janusfjellet Subgroup (Bathonian to Hauteriuian) on central Spitsbergen 35

haufjellet (Figs. 3 and 4), for example, only shales sening units, with 4 to 10m thick heavily bio- have been noted at this stratigraphical level. The turbated siltstones at the top. At Glitrefjellet and possibility for presence of some sandier beds Slottsm~yatwo upward-fining sequences are also equivalent to this member should nevertheless observed which are 5m in thickness each and not be completely excluded. At Keilhaufjellet display some modest degree of bioturbation. only a 2 m thick sand bed is thought to represent The silt and sand beds of the Oppdalsdta Mem- a probable correlative unit. The type locality of ber are generally rich in fossils. The most common the member is the western slope of Oppdalsdta groups are bivalves, ammonites and belemnites. in Oppdalen, where the thickness of the member is 41 m. The silty to sandy (very fine sand) sediments of the Oppdalsdta Member compose several Subdivision of the Rurikfjellet upward-coarsening units (Fig. 12). In the Sas- Formation senfjorden area (Janusfjellet, Wimanfjellet, The Myklegardfjellet Bed Knorringfjellet), three sequences show coars- ening-upward developments into siltstone (Fig. This distinct clay unit is an important marker 5). The beds in that area are heavily bioturbated horizon, easily observable at the boundary and rich in fossils. Two sequences are each 20 m between the Agardhfjellet and Rurikfjellet for- thick and one is 60 m thick. mations. It was originally defined by Birkenmajer In the western outcrop belt, at Festningen and (1980) with type locality at Myklegardfjellet near Ahlstrandodden (Van Keulenfjorden) (Figs. 2, 3 Agardhbukta, where the bed is from 0.5 to 10 m and 4), two upward-fining sequences are assigned thick. to the Oppdalsdta Member; these are from 10 to Although the Myklegardfjellet Bed shows vari- 20 m thick. At Bohemanflya/Syltoppen an able thickness, it has been found at all localities approximately 30 m thick highly bioturbated, where the formation boundary was studied by poorly sorted organic rich sandstone unit is our field parties on the eastern-central part of observed. The section at Bohemanflya contains Spitsbergen (Fig. 5). The observed thickness vari- in addition several coarsening-upward sequences ation of the unit might partially be influenced by throughout the Agardhfjellet Formation, soil creep along the hillsides. On the northern reflecting a possibly more marginal position in the slope of Arctowskifjellet (Fig. 14), the Myk- depositional basin than the more south-easterly legardfjellet Bed forms a thick horizon totalling localities. 2m. It contains two clay-rich zones, the lower In central parts of Spitsbergen some distinct 15cm and the upper 30cm thick separated by sedimentological variations are seen in the grey shales. The two zones are made up of from Oppdalsita Member. At Juvdalskampen, Flek- 5 to 10 cm plastic clay beds with yellow, reddish surfjellet E, and Lardyfjellet (Figs. 3 and 4) silty, to grey colours, and they are separated by grey heavily bioturbated sediments dominate a 30 m cla ystones/shales. thick interval, while at Fleksurfjellet W and At Lardyfjellet the bed is found as a 40cm Arctowskifjellet one or two coarsening-upward thick, white-yellow and green clay unit reflecting sequences are found. Some possible hummocky various oxidation stages of iron. The reddish cross-stratification, appearance of glauconite, and brown colours are seen along the bounding sur- various degrees of bioturbation characterize these faces of the clay bed, probably indicating oxi- beds. At Arctowskifjellet some coarsening- dation along these contact horizons. upward sequences are observed terminating in 1 At Glitrefjellet (Fig. 4) the Myklegardfjellet to 2 m thick beds of siltstone and very fine sand- Bed is developed as a 0.5 m thick zone with partly stone at some horizons showing parallel bedding. plastic-yellow to light-grey clays. Glauconite Although the development of the Oppdalsdta occurs in varying amounts. Enrichments of glau- Member in central Spitsbergen is variable, it is conite are also observed in the clay beds at always recognizable by the presence of sediments Tronfjellet, where 70 cm of glauconitic, silty clays coarser than the shales above and below. At and siltstones with two 10cm thick plastic clay Slottsmcbya, Oppdalsdta, Fonnhetta and Gli- layers are developed. Both at Oppdalsita and trefjellet NW, the development of the Oppdalsita Slottsmcbya, grey to yellow and green plastic clays Member is characterized by three upward-coar- make up the Myklegardfjellet Bed. 36 H. Dypvik et al.

THE ULLABERGET MEMBER OF THE RURIKFJELLET FORMATION West East Festningen 0 m

50 "1 H I .- E

A Bohemanflya 6 Janusfjellet 100 C WimanflelletiKnorrtngf~ellet D Juvdalskampen E FleksurfjelletiFonhetta F GlitrefleIletiAasgaardfjellet G Oppdalsata H Lardyflellet I Agardhbukta S J Agardhfjellet

150 Mainly sandstones Mainly shales B

Fig. 13 The regional stratigraphical development of the Ullabcrgct Mcmbcr ot' thc Rurrkfjcllct Formation

A few belemnites have been found in this clay teristically made up of mostly reddish, sideritic unit at Arctowskifjellet and Glitrefjellet. Samples lenticular concretions up to a meter in diameter. analysed for foraminifera from the plastic clays The upper part of the member contains cannon of Arctowskifjellet contained agglutinated speci- ball-shaped and ovoidal nodules of siderite and mens, but in considerably smaller amounts than calcite (Dypvik 1978). Together with these con- the adjacent grey shales. On the contrary, the cretions, thin cigar-like nodules are also com- plastic clays at Janusfjellet where somewhat monly seen. enriched in foraminifera compared to the adjac- The Wimanfjellet Member contains rather ent shales. moderate amounts of fossils: bivalves, belemnites and more rarely, ammonites. The fossil content here is clearly lower than in the shales of the The Wimanfjeller Member Agardhfjellet Formation, where the highest In central and eastern Spitsbergen the Myk- amounts were found just below the Rurikfjellet legardfjellet Bed defines the base of the Rurikfjel- Formation boundary. let Formation. Above this thin clay unit, the formation is made up of grey shales and partly The Ullaberget Member silty shales composing the Wimanfjellet Member (Figs. 15 and 16). The shales show prismatic frac- The sandstone-siltstone-shale sequence devel- ture and varying degrees of bioturbation. The oped in the upper part of the Rurikfjellet For- lowermost, least silty beds are only moderately mation has been defined as the Ullaberget Series bioturbated in comparison to the more silty and by Rozycki (1959) in western outcrop areas (outer sandy beds higher up in the member. The car- Van Keulenfjorden and Torell Land), and the bonates of the Wimanfjellet Member are charac- unit was redefined as the Ullaberget Member by The Janusfiellet Subgroup (Bathonian to Hauteriuian) on central Spitsbergen 37

Fig. 14. The upper clay units of the Myklegardfjellet Bed at Arctowskifjellet. Adventdalen.

Birkenmajer (1975). In addition to the type area with some minor fining-upward horizons. The (Ullaberget in Van Keulenfjorden), the member member contains well-developed hummocky is also recognized in S~rkappLand and in central cross-stratification, cross-bedding and some bio- and eastern Spitsbergen, although it shows large turbation. At Bohemanflya some of the sand- variability in thickness and lithological devel- stones in the upper part of the section are coarse opment compared with its type locality. grained. The hummocky cross-stratified beds In the areas investigated by us the Ullaberget at Bohemanflya are succeeded by parallel Member consists generally of very fine sands, laminated, in part heavily bioturbated sand- with some interbedded fine sands, silts and shales stones. At Jurakammen, north of Hornsund (Fig. (Figs. 15 and 17). Fine sands dominate in the 3) one upward-coarsening sequence is indicated Keilhaufjellet, Glitrefjellet and Aasgaardfjellet (Rozycki 1959). sections (Figs. 3 and 4), but the overall variations In the Isfjorden area the Ullaberget Member in grain size are minor. Regionally, the thickness has been studied at Festningen, Bohemanflya, and the sand content of the Ullaberget Member Janusfjellet, Wimanfjellet and Knorringfjellet. In decreases towards the east (Fig. 13). The sections this region the member is commonly made up at Keilhaufjellet and in Hornsund are made up of 4 coarsening upward sequences, varying in of four coarsening-upward sequences (Edwards thickness from 10 to 30m. The total member 1976; M0rk 1978) with thicknesses varying thickness is 85 m and the unit shows a gradually between 15 and 35 m, totalling 85 m. Similar up- upward-increasing sand content. The lower three ward-coarsening sequences are reported from coarsening-upward sequences are characterized Bohemanflya (Hvoslef 1984; (dxnevad 1986) and by bioturbation, ripple lamination, and parallel Festningen near the west coast. These sections lamination, while the uppermost sequence con- generally contain from 50 to 60 m thick upward- tains hummocky cross-stratification and shows a coarsening developments, including several reduced degree of bioturbation. minor coarsening-upward intervals, interbedded In the Adventdalen area, sections have been 38 H. Dypvik et al.

WIMANFJELLET GLITREFJELLET

$4 f 4+ 4 f 4 t 4 +n

+V% $4 $4 K 4 Ia

4 4

rn f mcvc dstone

AG = Agardhfjellet Formation HE = Helvetiafjellet Formation SI = Slottsmeya Member Fe = Festningen Member My = Myklegardfjellet Bed

Fig. 15. Columnar sections showing the Rurikfjellet Forma- siv1 f mcvc tion at Wimanfjellet (78’20.3”. 16’5.8’E) and Glitrefjellet - 78O3.4”. 17”4.9’E).Legend for symbols is given in Fig. 6. sandstone The Janusfiellet Subgroup (Bathonian to Hauteriuian) on central Spitsbergen 39

Fig. 16. The Wimanfjellet Member of dark silty shales with ‘cannonball’-like carbonate concretions, Reindalen

Fig. 17. The UUaberget Member at Oppdalsata, Reindalen. In the background the sandstones of the Festningen Member, Helvetiafjellet Formation, can be seen. 40 H. Dypvik et al. studied at Juvdalskampen, Roulettegga and gastropods, Buchia and plant remains have been Drcbnbreen (Fig. 4). In this area. the member seen. is approximately 30m thick and forms a single upward-coarsening sequence. Further south at Fleksurfjellet and Tronfjellet the upward-coar- sening member consists internally of three 5 to Summary and conclusions 10 m thick sandstone dominated intervals. In the The stratigraphical revision of the Janusfjellet uppermost beds hummocky cross-lamination is Subgroup presented here is generally based on well-developed. In addition black-coloured feed- new field information obtained during the last ing tunnels (Muensreria) are found. Bioturbated few years. The demand for a more elaborate units dominate below the hummocky stratified stratigraphy became clear during increased field beds. activity which has taken place in Spitsbergen in Around the inner part of Reindalen, the Ulla- the last decade. The stratigraphical subdivision berget Member was studied at Slottsmoya, proposed by Parker (1967) provided an adequate OppdalsHta. Glitrefjellet, Aasgaardfjellet and basis for this study. Bergmcbya (Fig. 4). At these localities the member The emended stratigraphical scheme presented comprises from two to three coarsening-upward here (Fig. 2) is primarily based on observations sequences, varying in thickness from 10 to 20 m made in central and eastern Spitsbergen. Based with a high degree of bioturbation and Muensreria on reconnaissance work in other parts of Spits- tunnels in the upper part. The upward-coarsening bergen, we expect that it will be applicable with units terminate in 2 to4 m thick sandstones, which some modifications also to the western outcrop also in this area contain well-developed hum- belt and the northeastern areas of Spitsbergen. mocky cross-stratification. Below the hummocky An updated correlation with these areas requires, cross-stratified sandstone, zones of alternating silt however, new and detailed field information. and sand with abundant bioturbation are found. Important items of the revised scheme are the Further towards the east the Lardyfjellet sec- inclusion of the Brentskardhaugen Bed in the tion was studied. This section, however, shows Oppdalen Member composing the lower part of only 30m of silty shales. A high degree of bio- the Agardhfjellet Formation, and the definition turbation is characteristic in the topmost part of of the OppdalsHta and Ullaberget members. The these beds, although parallel lamination occurs in Brentskardhaugen Bed marks the onset of the parts of the sequence. Along the eastern coast of Middle Jurassic transgression, continuing directly Spitsbergen the sections at Agardhfjellet, into the Marh~gdaBed, Drcbnbreen Bed and Lar- Rurikfjellet, Klementievfjellet and Myklegard- dyfjellet Member. This solution ties together fjellet were studied (Fig. 4), and coarsening- related depositional units formed during a major upward sequences are also found at all these transgressive event in the lower part of the localities. The uppermost 20 m of the Rurikfjellet Agardhfjellet Formation, with the directly suc- Formation shows a weak upward-increasing sand- ceeding organic-rich shales above. silt content in a rather shale-like sequence. Three The OppdalsHta and the Ullaberget Members such upward-coarsening units appear to be are characterized by increased sand and silt con- present as indicated by means of mineralogical tent in the Janusfjellet Subgroup. As described and geochemical analyses (Dypvik 1980). earlier in this presentation the lithology of these The sediments forming the Ullaberget Member formations varies from sandstone to silty-shale, display a general transport direction towards S- but they reveal marked differences with regard to SE, a feature also found at Bohemanflya (Hvoslef sedimentary structures. The OppdalsHta sands are 1984) and in Reindalen. Bxnevad (1986) pre- interpreted as shelf sand ridges. The deposition sented multiple transport directions in the Ulla- of the Ullaberget sands is attributed to the pro- berget Member at Bohemanflya, showing gradation of the Festningen delta system. transport towards S, SW and S-E. We prefer to retain the Janusfjellet Subgroup The Ullaberget Member is poor in fossils com- (Upper Bathonian-Hauterivian) as a single major pared to the beds below, but it contains a high stratigraphical unit, as proposed by Parker (1967). degree of bioturbation. In several sections saurian It makes room for a more elaborate strati- bone fragments have been observed, while also graphical framework applicable in future studies other fossils including ammonites, belemnites, involving detailed field work. Main features of The Janusfjellet Subgroup (Bathonian to Hauteriuian) on central Spitsbergen 41 the two formations composing the subgroup are legardfjellet Bed. The rest of the member is made given below. up of grey, silty shales to dark-grey shales. The first appearing sand bed marks the boundary to the overlying Ullaberget Member, which in The Agardhfjellet Formation addition to silty/sandy shales contains several The thickness of this unit varies from 65m at sandstone beds commonly with cross-bedding and Juvdalskampen (less than 40 m at Roulettegga) bioturbation. The boundary between the two to 290m in Van Keulenfjorden area (Rozycki members is commonly found near the uppermost 1959). The Brentskardhaugen Bed, a phosphorite ‘cannon ball’ concretionary beds. conglomerate, forms the base of the unit, towards Acknowledgements. - The project was financed by BP Pet- the light coloured sandstones of the underlying roleum Development (Norway) Ltd. (R&D 1068). We are Wilhelmoya Formation. The upper part of the grateful for the valuable cooperation of the Norwegian Polar formation terminates at the lower boundary of the Research Institute (Oslo) and the Sysselmannskontoret (Lon- gyearbyen). Special thanks are given to A. Stensrud (Store light-grey to yellow clays of the Myklegardfjellet Norske Spitsbergen Kulkompani A/S) for his help in solving Bed. The Agardhfjellet Formation is divided into some of the logistic problems connected with the field work. four members: the Oppdalen, Lardyfjellet, Comments on the manuscript from D. Worsley and A. Mdrk Oppdalsita and Slottsmoya. are also highly appreciated. The Oppdalen Member, a sandy and silty unit, consists of the Brentskardhaugen Bed, the glau- conitic sandstones of the Marhogda Bed, which References are succeeded by the upward fining sandy silt- Andresen, A,, Dypvik, H.. Elverhoi, A,, Nagy, J., Eikeland, stones of the Dronbreen Bed. T. A., Haremo. P., Johansen, A. & Strand, K. 1987: Study The Lardyfjellet Member, consisting of black of the sedimentological and structural evolution of the area paper shales with scattered carbonate con- between Kjellstrandalen and Adventdalen/Sassendalen, cretions, overlies the Oppdalen Member. The top Central Spitsbergen. Unpubl. report. of the Lardyfjellet Member is drawn at the first Birkenmajer, K. 1975: Jurassic and Lower Cretaceous sedi- mentary formations of SW Torell Land, Spitsbergen. Studia. appearance of silt-sand beds and disappearance Geol. Polon. 44, 7-42. of black shales. Birkenmajer, K. 1980: Jurassic-Lower Cretaceous succession at The Oppdalsita Member found on top of the Agardhbukta, East Spitsbergen. Studio Geol. Polon. 66, 35- Lardyfjellet Member commonly consists of sev- 52. Birkenmajer. K., Pugaczewska, H. & Wierzbowski, A. 1982: eral upward-coarsening sands and sandy shale The Janusfjellet Formation (Jurassic-Lower Cretaceous) at units. The last sand bed marks the top of this Myklegardfjellet, East Spitsbergen. Paleont. Polon. 43, 107- member. 140. The Slottsmoya Member, resting on the Bjzrke, T. & Dypvik, H. 1977: Sedimentological and paly- Oppdalsita Member, consists of black paper nological studies of Upper Triassic- Lower Jurassic sediments in Sassenfjorden, Spitsbergen. Norsk Polarinst. Arbok 1976, shales sometimes with faint developments of 131-150. coarsening-upward sequences in the upper part. Bjzrke, T., Edwards, M. B. & Thusu, B. 1976: Microplankton The unit terminates in the Myklegardfjellet Bed. from the Janusfjellet Subgroup (Jurassic- Lower Cretaceous) at Agardhfjellet, Spitsbergen. A preliminary report. Norsk Polarinst. Arbok 1974. 63-68. Backstrom, S. A. & Nagy, J. 1985. Depositional history and The Rurikfjellet Formation fauna of a Jurassic phosphorite conglomerate (the Brent- skardhaugen Bed) in Spitsbergen. Norsk Polarinst. Skr. 183. The thickness of the Rurikfjellet Formation varies 61 PP. from 40 m at Juvdalskampen to 290 m in the Van Buchan. S. H., Challinor, A,, Harland, W. B. & Parker. J. R. Keulenfjorden area (Rozycki 1959). The lower 1965: The Triassic stratigraphy of Svalbard. Norsk Polarinst. boundary of the formation is marked by the clays Skr. 135. 72 pp. Burov, Yu. P. & Livsic. Yu. Ya. 1965: Poorly differentiated of the Myklegardfjellet Bed, while the uppermost dolerite intrusions in Spitsbergen. Pp. 255-266 in Sokolov, beds are found below the cross-bedded sand- V. N. (ed.): Geology of Spifsbergen (English translation stones of the Festningen Member. The Rurikfjel- 1970). National Lending Lib. Sci. Tech., Boston Spa, let Formation is divided into the Wimanfjellet England. Dypvik, H. 1978: Origin of carbonate in marine shales of the and the Ullaberget Members. Janusfjellet Formation, Svalbard. Norsk Polarinst. Arbok The Wimanfjellet Member contains at its base 1977, 101-109. the light-grey to yellow soft clays of the Myk- Dypvik, H. 1980: The sedimentology of the Janusfjellet For- 42 H. Dypvik et al.

mation, Central Spitsbergen (Sassenfjorden and Agardhfjel- Maher. H. D. 1989: A storm-related origin for the Jurassic let areas). Norsk Polarinst. Skr. 117, 97-134. Brentskardhaugen Bed of Spitsbergen, Norway. Polar Dypvik. H. 1985: Jurassic and Cretaceous black shales of the Research 7. 67-77. Janusfjellet Formation. Svalbdrd. Norway. Sed. Geol. 41. Major, H. & Nagy, J. 1972: Geology of the Adventdalen map 23>?48. area. Norsk Polarinsf. Skr. 138. 58 pp. Dypvik. H , Andresen. A., Haremo. P., Nagy. J., Elverhei. Msrk. A. 1978: Observations on the stratigraphy and structure A,, Eikeland, T. A.. Johansen, H. & Strand, K. 1988: Sedi- of the inner Hornsund area. Norsk Polarinst. Arbok 1977, mentation and tectonics in the Jurassic/Cretaceous sequences 61-70. of central Spitsbergen. Proceed, Arcf.Res. Conf., Leningrad Mark, A., Knarud. R. & Worsley, D. 1982: Depositional and 1988.348-359. diagenetic environments of the Triassic and Lower Jurassic Dypvik. H.. Nagy. J.. Eikeland. T. A,, Backer-Owe, K. & succession of Svalbard. Pp. 371-398 in Embry, A. F. & Johansen. H. in press: Depositional conditions of the Bathon- Balkwill. H. R. (eds.): Arcfic Geology and Geophysics. Can. ian to Hauterivian. Janusfjellet Subgroup. Spitsbergen. Nor- SOC. Perrol. Geol. Mem. 8. way. Sed. Geol. Nagy. J. & Lsfaldi. M. 1981: Agglutinated Foraminifera in Edwards. M. B. 1976: Depositional environments in Lower Jurassic dark shale faeies in Svalbard. Pp. 113-121 in Neale, Cretaceous regressive sediments. Kikutodden. S~rkapp J. W. & Brasier. M. D. (eds.): Microfossils from Recent and Land, Svalbard. Norsk Polarittsr. Arbok 1974. 3SW. Fossil Shelf Seas. Ellis Horwood Ltd., Chichester. Ershova. E S. 1983: Explanatory notes to the biostratigraphical Nagy, J., Lafaldi, M. & Backstrom. S. A. 1988: Aspects of scheme of Jurassic and Lower Cretaceous deposits of the foraminifera1 distributions and depositional conditions in Spitsbergen Archipelago. Min. Geol. 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