Mesozoic mudstone compositions and the role of kaolinite weathering – a view from shallow cores in the Norwegian Sea (Møre to Troms)
pp. 61-78

Mineralogical data from Mesozoic fine clastic sediments in shallow cores offshore Møre to Troms are compiled. The purpose is to examine stratigraphic and geographic variations in rock composition as a basis for regional comparative studies and the prediction of rock properties in offshore petroleum exploration areas. The studied successions include different depositional environments, varying from continental, paralic and shallow marine in the Triassic – Lower Jurassic, and shallow to open marine in the Middle Jurassic to Lower Cretaceous. Stratigraphic and regional variation in mineralogical distributions reflect combinations of depositional environment, climate and provenance and we also infer variable influences from Late Jurassic volcanism.

Some of the most distinct stratigraphic mineralogical variations are: 1) change from mica/illite + chlorite + feldspar + mixed-layer clay rich compositions in the Lower Triassic to kaolinite-dominated and feldspar-poor compositions in the Upper Triassic-lowermost Jurassic deposits. This coincides with changes from arid continental to humid continental and paralic environments. Kaolinite is the dominant clay mineral also in upper Lower to Middle Jurassic transgressive beds, that overlie kaolin-weathered basement. 2) The amounts of kaolinite decrease while the smectite/mixed-layer clay mineral concentrations increase in the Upper Jurassic deposits and with notable mineralogical differences between the Spekk and Hekkingen formations. This records transgression and sediment mixing in response to increasing marine influences. 3) The amounts of feldspar increase (plagioclase reappearance) in the Lower Cretaceous Kolje Formation. This change is of regional significance in the Western Barents Sea, possibly related to Early Cretaceous rifting.