Upper Triassic-Lower Jurassic tidal deposits of the Gassum Formation on Sjælland, Denmark

Abstract

Three deep wells on the Danish island of Sjælland penetrate the Upper Triassic - Lower Jurassic Gassum Formation. The formation has been the subject of a facies analysis of cored sediments and interpretation of petrophysical logs. The principal part of the work presented is based on data from the Stenlille-1 well. The sediments were deposited in a NW-SE trending, microto mesotidal, prograding coastal zone and the adjacent fluvial hinterland. In the Stenlille-1 well, the coastal progradation is recorded as a thick, coarse-grained sandstone unit deposited within a barrier island complex. This basal part of the formation is overlain by four stacked regressive sequences consisting of finegrained sandstones and mudstones deposited on tidal flats. A thin transgressive sandstone sheet terminates the formation and marks the boundary to marine claystones of the Fjerritslev Formation.