Origin of the Myklegardfjellet Bed, a basal Cretaceous marker on Spitsbergen

The Ryazanian Myklegardfjellet Bed, composed of yellow to greenish plastic clays, is a regional marker horizon in central and eastern Spitsbergen, where it occurs just above the boundary between the Agardhfjellet and Rurikfjellet formations. Through a combined mineralogical, sedimentological and micropaleontological approach, it is demonstrated that the bed was deposited by marine shelf processes and subsequently altered by decomposition of the unstable glauconite bearing components. These sediments were deposited at the culmination of a shallowing episode in the depositional area. This event marks a shift in depositional mode, from predominantly shelf sedimentation controlled by global eustatic sea level changes (Late Bathonian-Ryazanian), to a locally regulated, deep sea to shallow shelf-prodeltaic to deltaic pattern of deposition (Ryazanian-Hauterivian).