The type section of the Vikinghggda Formation: a new Lower Triassic unit in central and eastern Svalbard ATLE MGRK, GEIR ELVEBAKK, ARNE W. FORSBERG, MARK W. HOUNSLOW. HANS ARNE NAKREM. JORUNN 0s VIGRAN and WOLFGANG WEITSCHAT L Mcnrk, A,, Ehehakk, G., Forsberg, A. W., Hounslow, M. W., Nakrem, H. A,. Vigran, J. 0. & Weitschat. W. 1999: The type section of the Vikinghogda Formation: a new Lower Triassic unit in central and eastern Svalbard. Polirr Resi~orchI&lJ, 51-XI. The Vikinghogda Formation (250 in) is defined with a stratotype in Deltadalen-Vikinghcngda in central Spitsbergen. The Vikinghogda Formation replaces the Vardebukta and Sticky Keep Formations of Buchan -U+P~~~~~NS''et al. (1965) and the lower part of the Barentscnya Formation of Lock et al. (1978) a!, extended geographically by Mvcrk, Knarud et al. (1982) in central Spitsbergen, Barentscnya and Edgecnya. The formation consists of three member\: the Deltadalen Member (cornposed of mudstones with sandstones and siltstones), the Lusitaniadalen Meinher (dominated by mudstones with thin siltstone beds and some limestone concretions) and the Vendorndalen Member (composed of dark shales with dolomite interbeds and nodules). The Lu,itaniadalen and Vendomdalen members replace the former Sticky Keep Formation/ Member in the siirne areu. The Vikinghogda Formation can be followed through central and eastern Spitsbergen to Barentseya and Edgecrya and includes all sediments between the chert-rich Kapp Starostin Formation (Permian) and the organic-rich shales of the Botneheia Formation (Middle Tri subdivision into three members is :itso reflected in the organic carbon content and palynofacies. Upwards. each succeeding member becomes inure distal, organic-rich and oil-prone than the one helow. The Vikinghegda Formation is well-dated by six ammonoid zones. although the transitional beds between the Deltadalen and Lusironiadalen members lack age diagnostic macrofossils. Corresponding palynozonation and magnetustratigraphy have also been determined. The overall stratigraphical development correlates well with other key Triassic mas in the Arctic, although intervals in the late Dienerian and early Smithian may bt. condensed or missing. Ar/e Mgrk, IKti/SINTEF Pi,rri)/ivtni R<,.WU~C/?.N- 7465 Trundheini. Nor?wy: Geir Elcehnkk. Saga Pefro/eirm ASA, P.O. B(1.r 113-1, N-9401 H~irsrizd,Norwny; Anw W. Forsberg, Norsk Hydro ASA. P.O. BOA -700 N- 132/ Smhekk, Nunvuy: Mark W.Horindi~w. .khiio/ of Eiwironnwnrnl Sciences, UniwrAiry cf Eosf Atigliu, Nonvich, NR4 7TJ. UK; Hi7n.c Arne Ntrkrcni. Pu/eiiritologicu/ Mirsrunt. tiniwrsity if Odo, Sursgr. I, N- 0502 Os/iJ5, Ni)nr.n,v; Jorrrnn OS l'iqrcni. Hans H~gerripsgt.10. N-7012 Trondheirn, Norway: WolfKntig Wrifschur.G'ri~lo~ic~ul-P~r/nci~nti~/i~,~i~~o/ Instirrife inid Musewn. Uniivrtity o$ Hanhirg, Bundessrr. 55. D- 20146 Hunfhr~.Genncrn,v. Introduction unit on the map series of the Norwegian Polar Institute (Major et al. 1992; Miloslavskij, Birju- The Lower and Middle Triassic succession of kov. Slenskij. Hansen et al. 1993; Miloslavskij. Svalbard consists of fine-grained clastics. The Birjukov, Slenskij & Dallmann 1998). The dominant sediment supply from the west resulted lithological and sedimentological description of in extensive deposits of coastal and shallow the Vikinghogda Formation type section is sup- marine sandstones and shales in western Spitsber- plemented with biostratigraphical dating (macro- gen, whereas shales with minor siltstones and fossils and palynology), magnetostratigraphy, and sandstones were deposited in a basinal setting in organic geochemical screening analyses. central and eastern Spitsbergen, Barentsoya and Edgeoya (Fig. 1). This sedimentary pattern con- Lithostratigrciphical review: The Lower and tinues southwards under the Barents Sea, with Middle Triassic succession of Svalbard, the deposition of shales in basins and coarser grained Sassendalen Group, was originally subdivided clastics along the basin margins and on local highb. into the Vardebukta (Induan), Sticky Keep The Viliinghmgda Formation. formally defined (Olenekian) and Botneheia (Anisian and Ladi- here. comprises Lower Triassic sediments in nian) formations by Buchan et al. (1965; Fig. 2). It central and eastern Spitsbergen, Barentsoya and was based on coastal and mountain exposures Edgeoya and has served as a practical mapping around Isfjorden. This nomenclature was followed 52 A. M@rk et al. nomenclature for the whole Triassic succession of Barents@yaand Edgeoya. These authors postu- lated that no subdivision was practical in these islands, and grouped all the sediments of the Sassendalen Group into the Barentsoya Formation, although they recognized the upper dark shales (the “oil shales member” of Falcon 1928), as forming a separate member. The shale-dominated Sassendalen Group sediments on eastern Spitsber- gen, Barentsoya and Edgeoya show close simila- rities, that can be followed to central Spitsbergen and to the south-western part of Nordaustlandet, as shown by M@rk& Worsley (figure 7 in M~rk& Worsley 1979) and PEelina (1983). Against this background, M@rk,Knarud et al. (1982) extended the Barentsoya Formation, as defined by Lock et 779 al. (1978), to central and eastern Spitsbergen. In addition, they retained the units as defined by Buchan et al. (1965) as members, and they had to rename the lower unit the Deltadalen member as the Vardebukta Formation was retained for its type Fig. I. Triassic exposures in Svalbard (black). Square indicates area in western Spitsbergen. the detailed map of Fig. 3. However, PEelina (1983) retained the Varde- bukta Formation for the central and eastern areas, but assigned the equivalent of the Sticky Keep on the map sheets, although the Sticky Keep and FormatiodMember to the Wichebukta Formation Botneheia formations were grouped together as with a type section at Teistberget on eastern the Kongressfjellet Subgroup (Flood et al. 1971a; Spitsbergen. PEelina also retained the Botneheia Major & Nagy 1972). Buchan et al. (1965) Formation with formational status in the same defined the Vardebukta Formation with a type areas, although she followed Mork, Knarud et al. section at Festningen in western Spitsbergen and (1982) and kept the Bravaisberget Formation for the Sticky Keep Formation with a type section at the equivalent beds in western Spitsbergen (Fig. 2). Vikinghogda in central Spitsbergen. The Committee on the Stratigraphy of Svalbard In the Hornsund area the local lithostratigraphy (Mork. Dallmann et al. in press) suggests that the defined by Birkenmajer (1977) was later modified organic-rich phosphate-bearing shales defined as and incorporated into the general scheme erected the Botneheia Formation by Buchan et al. (1965) for central Spitsbergen during the reappraisal of should retain formational status, as suggested by southern Spitsbergen by Worsley & Mork (1978). PEelina (1983). It will consequently replace the Mork & Worsley (1979) subsequently applied the upper part of the Barentsoya Formation of Lock et stratigraphical scheme of Buchan et al. (1965) to al. (1978) and Mork, Knarud et al. (1982), and the entire Svalbard archipelago. prompt the need for a new formational unit for the In the eastern islands, Barentsoya and Edgeoya, underlying part of the Sassendalen Group. extensive fieldwork by CASP (Cambridge Arctic The boundary between the two lower units of Shelf Programme) and Norwegian Polar Institute the Sassendalen Group has traditionally been geologists resulted in the preliminary map and regarded as corresponding to the InduadOlene- stratigraphy of Flood et al. (1971b), adapting the kian boundary. According to traditional western principles used for Spitsbergen, although with boreal terminology, this boundary corresponds to lowered rank (i.e. Kongressfjellet Formation and the DieneriadSmithian transition (Lower and Sticky Keep and Botneheia members). This Upper Scythian: Buchan et al. 1965; Induan to nomenclature was followed on the published Olenekian: PEelina 1965, 1967, 1977, 1983; 1 :500 000 map (Winsnes 1981). A more compre- KorEinskaja 1982; Dienerian to Smithian: Tozer hensive description was given by the CASP group, & Parker 1968; M@rk,Knarud et al. 1982; Mork, with Lock et al. (1978) introducing a local Embry et al. 1989; Mark, Vigran et al. 1993; Early Triassic lithostratigraphical units of Svalbard and the Barents Shelf I ~ Central-East Central-East Central-East Svalbard Hornsund Barentseya Western Spitsbergen Spitsbergen Spitsbergen lamrnerfest Svalis Western Spitsbergen a Area Edgeeya Spitsbergen BEyg$a West - South BarentsBYa Basin Dome Spitsbergen @?,",$'a -J Edge0ya Me* and Buchan et al. Birk;wTjer Locket al. Melk st al. 1971a 1971b I PEeline vorsley et a!. Elvebakk This work 1978 1982 1983 1988 8 I I 1999 Van Keulen- a 1-fjorden Fm. I 3 0 c L ,,, ,,, Botne- Botne- Botneheia n heia m heia Fm. c s Fm. E Mb. 1 1 L v) 0 U. t Vendorn- C Ka .-m Mb Sticky Keep - Q) Fm. IS. 0 dalen B Mb t t Varde- Varde- Varde- Delta- Vardebukta 3 bukta dalen - Fin. Is. = lskletten Member Ka. = Kaosfjellet Member Fig. 2. Lithostratigraphical units used in the Lower and Middle Triassic succession. 54 A. MGrk et al. Hochuli et al. 1989; and on numerous maps). The shore exposure as belonging to their Vardebukta general description of these lower and upper units Formation, and Xenoceltites sp. was reported from by all authors, has followed the same general this exposure. We have also found numerous principles, however the application of these examples of Arctocerus sp. in limestone nodules in definitions has not been straightforward, and this sea cliff, which shows that the exposure should misinterpretations have been inherited from paper be included in the Lusitaniadalen Member as to paper. Mark, Embry et al. (1989), Mark, Egorov defined herein. However, at Tschermakfjellet, the et al. (1994) and Mark (1994) interpreted a major situation is the reverse. Here the base of a cliff circum-Arctic transgression as early Olenekian in 60 m above the top of the Permian was regarded as age, and Vigran et al. (1998) and Van Veen et al. the base of the former Sticky Keep Formation, an ( 1993) reported a pronounced transgression early interpretation also followed by Mark, Knarud et al.