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1 Bulletin of the Polish Academy of Sciences. Earth Sciences

1 1998

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Clay-mineralogy of Jurrasic marine black shales in Spitsbergen: a possible evidence for climate cooling during oxfordian

Bausz W., Birkenmajer K., Grunenberg T., Krajewski K., Kutyba J.

Bulletin of the Polish Academy of Sciences. Earth Sciences

1998

Vol. 46, nr 3-4

211-221

Clay -mineral investigations were carries out on Jurassic marine black shale samples of the Janusfjellet Subgroup (Upper Bathonian-Hauterivian) collected from four field sections at Van Keulenfjordrn and Isfjorden, Spitsbergen. Based on the presence or absence of kaolonite in the Jurassic parts of the stratigraphic columns studied, three subunits have been distinguished: (i) the kaolinite- bearing basal subunit; (ii) the kaolinite-free middle subunit; (iii) the kaolinite-bearing upper subunit. These subunits are unrelated to any observable change in the monotonous black shalelithology. Taking into account stable paleolatitundial position of epicontiental seans, and lack of activeterrestrial sources of clastics in and around Spitsbergen during the Upper Bathonian-Volgian times, it is suggested that the clay-mineralogical history of marine black shales in the Jurassic part of the Janusfjellet Subgroup reflects predominantly a global or regional climate change. We suppose that the climate, warm and favourable to kaolinite formation on borderlands of the Spitsbergen sea at theonset (lower subunit: Upper Bathonian-Callovian), subsequenlty condisered cooled as na kaolinite was supplied from the lanf to sea (miffle subunit: Oxfordian), then warmed again as the kaolinite supply was re-established (upper subunit: Kimmeridgan-Volgian)