Abstract
Abstract The Upper Cretaceous Wyandot Formation is a 400 m thick succession of fine-grained calcareous mudstone deposited in an outer shelf to upper bathyal setting. The formation is divided into two lithofacies, a pure chalk and an interbedded kaolinite-bearing, argillaceous and calcareous claystone. Components of both lithofacies are derived from primary production in the photic zone, being rich in foraminifers and coccoliths. The Wyandot Formation is bioturbated, showing classic tiering and continual overprinting of trace fossils related to low pelagic sediment accumulation rates. Ichnological analysis reveals trends of environmental deterioration and amelioration. Changes in trace fossil assemblages are linked to fluctuations of organic matter input leading to rising of the redox front and low porewater/sediment oxygenation which excluded many endobenthic organisms. Mineralogical differences between burrow fill and host sediment demonstrate that bioturbation affects sediment texture by altering authigenic clay mineral assemblages. The clay mineral assemblage within burrows was found to be more diverse than in the surrounding sediment. This is probably the result of low temperature authigenesis in the digestive system of deposit feeding endobenthos, ingesting sedimentary particles and egesting material of a different mineralogical composition.
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