Print this pageHigh-Resolution Stratigraphic Analysis of the Cretaceous Sussex Sandstone in House Creek Field (Powder River Basin, Wyoming, USA): Reinterpretation as Backstepping Transgressive Incised Shoreface Deposits
BERGMAN, KATHERINE M.
Recognition and correlation of regionally extensive bounding discontinuities in the Campanian Sussex Sandstone allows the definition of 6 distinct progradational sandbodies. These sandbodies are contained in asymmetrical one-sided scours and reserve a retrogradational stacking pattern. The geometry and linearity of the overlying sandstone contained in these asymmetrical scours suggest incised shoreface profiles formed by wave erosion during erosional shoreface retreat during periods of stillstand in an overall transgression. Several features in the Sussex Sandstone suggest base level fluctuations were important during Sussex deposition. These include, 1) pebbly sandstone, 2) the contained trace fossil assemblage, 3) regionally extensive depositional discontinuities marked by the Glossifungites ichnofacies, abrupt facies juxtapositions, eroded mud clasts, glauconite and chert pebbles, 4) stratigraphic variability of the sandstones and 5) erosional termination of sandstone deposition and progradation.
The Sussex Sandstone is reinterpreted here as six backstepping transgressive incised shoreface deposits formed during periods of stillstand in an overall baselevel rise. It is explicit in this interpretation that these sandbodies formed under conditions of relative sea level rise and are not contemporaneous. The complex dissection of the reservoir sandstone described in this interpretation has implications on fluid migration and reservoir compartmentalization. This interpretation of the Sussex overcomes the problems identified in the previous shelf ridge interpretation and is consistent with both the physical and biological structures contained in the Sussex Sandstone.