KRZYSZTOF BIRKENMAJER , HALINA PUGACZEWSKA and ANDRZEJ WIERZBOWSKI THE JANUSFJELLET FORMATION (JURASSIC-LOWER CRETACEOUS) AT MYKLEGARDFJELLET, EAST SPITSBERGEN BIRKENMAJER, K; PUGACZEWSKA, H. and WIERZBOWSKI, A.,: The Janusfjellet Formation (Jurassic-Lower Cretaceous) at Myklegardfjellet, cast Spitsbergen.Palaeont. Polonica, 43, 107-140. \ Fossiliferous marine strata of the Janusfjellet Formation (Jurassic-Lower Cretaceous) are describ­ ed from Myklcgardfjellet, Agardhbukta area , east Spitsbergen. The invertebrate fauna collected by the first author from these beds in 1977 has been determin ed by the second author (serpulids, bivalves, belemnites) and by the third author (ammonit es). This assemblage allows to distinguish the Upper Callovian, the Kimmeridgian (Lower and Upper) and the Lower Volgian stages in the lower part of the Janusfjellet Formation (Agardhfjellet Member) . The upper part of the Janusfjellet Formation (Rurikfjellet Member) yielded poorly preserved fossils of litt le stratigraphic value . Key words: Mesozoic, stratigraphy, ammonites, bivalves, belemni tes, serpulids, Spitsbergen, K. Birkenmajer, Ins tytut Nauk Geologicznych,Po/ska Akademia Nauk, 31-002 Krakow, Senacka 3 ; H. Pugaczewska, Zakiad Paleobiologii,Po/ska Akademia Nauk, 02-089 Warszawa, Z lI'irki i Wigury 93; A. Wierzbowski, Instytut Geologii Podsta wowej, Unlwersytet Warszawskl, 02-089 Warszawa, Z wirki i Wigury 93, Po/and. Received: June 1979. FORMACJA JANUSFJELLET (JU RA - DOLNA KR EDA) MYKLEGARDFJELLET. WSCHODNI SPITSBERGEN Streszczenie. - W pracy przedstawion o wyniki bada ri nad stra tygrafia formacji Janusfjellet (jura-d olna kreda) na Mykle­ gardfj ellet (obszar Agardhbukta) na wschodnim Spitsbergenie. Fauna bezkregowco w pochodzaca z tych warstw zostala zebrana przez pierwszcgo autora podczas kierowanej przez niego polsko-amerykanskiej ekspedycji dzialajqcej w 1977 r. na wschodnim Spitsbergcnie, Zesp61 skamienialoSci zawierajacy og61em 33 gatunki rnalzow, belemni t6w, serpulid (opi­ sanych przez H. PUGACZEWSKJ\) oraz amonit6w (opisanych przez A.WIERZBOWSK IEGO)pozwolil na wyroznienie 20 pozio­ m6w fauni stycznych. Na ich pod stawie w dolnej czesci formacji (ogniwo Agardhfjellet) stwierdzono g6rny kelowej, dolny i gorny kimeryd oraz do lny wolg. G6rn a czc;st formacji Janusfjellet (ogniwo Rurikfjellet) zawiera He zachowana faune o malej przydat nosci stra tygraficznej. INTRODUCTION The faunas investigated have been collected by the first author from marine Jurassic­ Lower Cretaceous strata of the Janusfj ellet Formation at Myklegardfjellet, Agardhbukta area (figs. 1, 2) during a Polish-American expedition led by him to east Spitsbergen in 1977. 108 K. BIRKENMAJER, H. PUGACZEWSKA AND A. WIERZBOWSKI The serpulids, bivalves and belemnites have been determined by the second author and the ammonites by the th ird author. The specimens here described are housed in the Institute of Paleobiology, Polish Academy of Sciences, Warsaw (abbreviated as ZPAL). STRATlGRApHIC rosrrto» OF THE JANUSFJELLET FORMATION by KRZYSzrOF BIRKENMAJER The Janusfjellet Formation (MAJOR 1964: map - in MAJOR and NAGY 1972; Janusfjel­ let Subgroup of PARKER ' 1967) consists of marine strata contained between two continental complexes - a basal one represented by the De Geerdalen Formation (Upper Triassic - ?Het­ tangian), and a top one - represented by the Helvetiafjellet Formation (BUCHAN et al. 1965, PARKER 1967, BIRKENMAJER 1972, 1975, 1977). In central and eastern Spitsbergen the formation is' usually subdivided into two units: the lower Agardhfjellet Member (Formation of Parker 1967) and the upper Rurikfjellet Member (Formation of PARKER 1967), separated by a non­ sequence about the Jurassic/Cretaceous boundary. A characteristic yellow clay horizon at the base ofthe Rurikfjellet Formation (PARKER 1967, BJAERKE et ai, 1976) has been distinguished as the Myklegardfjellet Bed (BIRKENMAJER 1980). In southern Spitsbergen, mainly in Torell Land, a tripartite subdivision of the Janusfjellet Formation was found useful (R6zYCKI 1959, BIRKENMAJER 1972, 1975). The Janusfjellet For­ mation is there subdivided into the lower Ingebrigtsenbukta Member, the middle Tirolarpasset Member and the upper Ullaberget Member (Table 1). In Torell Land there is either a conti­ nuous sedimentation throughout the Janusfjellet Formation, or - in some areas - a break in deposition and intraformational erosion appears at the base of the Tirolarpasset Member. In the latter case, it is marked by arenaceous-conglomeratic rocks of the Polakkfjellet Bed. A hiatus which covers most of the Lower and Middle Jurassic separates the De Geerdalen Formation from the Janusfjellet Formation. The latter begins as a rule with the Brentskard­ haugen Bed (phosphorite conglomerate) which is a very characteristic thin phosphorite-quartz conglomerate or pebbly clay containing reworked marine fauna of several Liassic through Dogger zones, as well as some still older material (see BIRKENMAJER 1975, BIRKENMAJER and PuGACZEWSKA 1975). The conglomeratic bed itself is believed to represent the Lower Callovian or uppermost Bathonian - Lower Callovian. Lithostratigraphic sections investigated at Myklegardfjellet, which include the De Ge­ erdalen Formation, the Janusfjellet Formation and the Helvetiafjellet Formation, are shown in figs. 3 and 4. A detailed description ofstrata in these sections is presented elsewhere (BIRKEN­ MAJER 1980). AgardhfjeUet Member Loose fragments of quartz-phosphatic conglomerate arid pebbles of grey fossiliferous phosphorite and white quartz which occur at the foot of Myklegardfjellet scattered over the morphologic ledge formed by the De Geerdalen Formation, indicate the presence of the Brent­ skardhaugen Bed at the base of the discussed sequence of the Janusfjellet Formation (fig. 4). The basal part of Agardhfjellet Member, some 40 m thick, is very poorly exposed. This part of the member is represented by black shales, possibly with some clay-ironstone and/or siltstone intercalations. Higher up come black to dark-grey, rather hard shales and papery-shales which in the lower part of the member, up to about 135 m above the bottom of the unit (see fig. 4), contain THE JANUSFJELLET FORMATION AT MYKLEGARDFJELLET 109 010 30 SOkm II,I II EDGE~YA :z tu Q Q:­ o c Q:­ o ..--- selected faults "- V) f-\ :'-: .::. ;~}>d Tertiary strata I~~I dolerites ~ Mesozoic strata ~ Permian and ~ Carboniferous strata o pr e-Ccrboniferous rocks 0 21 0 24 Fig. I Position of Agardhbukta against simplified geological map of Svalbard , thin intercalations of often iron-rich siltstone, fine-grained sandstone and black bituminous shale, subordinately also clay-ironstone layers. In the upper part of the Agardhfjellet Member, the sandstone and siltstone intercalations disappear, bituminous shales become infrequent, while clay-ironstones (siderites) become a typical feature. The latt er form thin intercalations or lenses in a lower portion of the upper part of the Agardhfjellet Member, and zones of discoidal concretions or balls in the upper­ most portion of the member. 110 K. BlRKENMAJ ER,H. PUGACZEWSKA AND A. WI ERZBOWSKI iZ UJ Q Q:; ...,o I.L. Q:­ o s-; A A GARDHBUKTA o 2 3 , " 5 I I I I I Ki l o m et r es 'af 20' 7BoN L..-_-l... .L- L-_-----1...71 5 i t e I@ @l Rocks l ides 1=====1 Janusfjellet ~ Formation Glac ie r If!.,J IDo lerite F'i77/] De Geerdalen tLL::LL;;l Formation DCOV Qred ItI\fCWIHelvetiafj ell et Formation Fig. 2 Geological sketch-map of the Agardhbukta area, with position of stratigraphical sections: A (fig. 3) and B (fig. 4). About 20 fossiliferous horizons have been recognized in the section of SW Myklegardfjellet (BIRKENMAJER 1980). Eight of these (Faunules 1-8, see below) yielded determinable invertebrate fossils, here listed with age ranges (after determinations by H. PUGACZEWSKA and A. WlERZ­ BOWSKI) and stratigraphical comments. Faunule 1 (80-81 m) ?Longaeviceras sp. This ammonite genus is characteristic of the Upper Callovian. Faunule 2 (110 m) Buchia bronni (LAHUSEN): Oxfordian - Upper Kimmeridgian; Rasenia (Zonovia) evoluta SPATH: Lower Kirnmerir'gian (higher part of cymodoce Zone); Amoeboceras (Amoebites) cf. kitchini (Salfcld) : Lower K immeridgian to Upper Kimmerid- gian (mutabilis Zone); THE JANUSFJELLET FORMATION ATMYKLEGARDFJELLET III Table 1 Lithostrat igraphic stand ard for the Jurassic - Lower Cretaceous of Spitsbergen: M-Myklegard fjellet Bed ; P-Po­ lakkfjellet Bed. ~lI'l UJUJ lno::: STAGE CENTRAL SPITSBERGEN SOUTH SP ITSBERGEN >-UJ lI'l ll'l ffi MAASTRICl-jTIAN I a.. to ~ CENDMANIAN en ALBIAN ::J ~ 0::: APTlAN· . Car 0 I in e f j e l l et For m at ion 270-850 m UUJ ~ BARREMIAN Helvetiafjellet rormation SO-lOOm UJ~t-------+--::-----------.,.-------------1 ~ 0 HAUTER IVIAN Rurik f jellet Mb. Ullaberget Mb. 10-lSOm ...J c: c: VALANGINIAN o 'M o t-------l .;: E o d o - BERRIASIAN Eo Tirolarpasset '-["0­ ~E o. Mb· 28 -!.OO m )~~ U.o VOLG IAN o ["0­ 0::: 1------ --1 Q;Ll1 n TI Tll r - - ~ _ I UJ CIIo Qi a.. KIMMERIDGIAN =coCII~ ~ Ingebri gt s en - ...... a.. Ag,\rdhfje llet Mb. ::J :J III -:J U OXFORD IAN c: bukta Mb. l.0-2l.5m c: -1---1f--------l d e en~ ...... ...... CALLOV IAN en°I-;::-":"-=:-:-::-,:",,:,,:,,":-:-:,-trn'TT'TTT~;TTT7'T"'::;-'rTTrnn=rrnrni'Tr...-rT":;::':'rTrrn"TT'TTO'TT'"mTT1'"7T"TTT'T'i <to BATHON IAN o:::~ BA JOC IAN ::J TOARC IAN ...... 0::: UJ P1I ENSBACH. ~ !-=-'c.:..=:.:....:..=c:.=...:.:...:..+"-SINEMUR IAN L...u o ...J HETTANGIAN De Gee rda len For mation Amoeboceras (Amoebites) sp. Th is fauna is clearly of a Lower K immeridgian age, as indicated by the presence of