Variability of lowstand wedges and their distinction from forced-regressive wedges in the Mesaverde Group, southeast Wyoming

Abstract

The debate on the geometry and origin of shelf sandbodies has evolved from a discussion of how sands and gravels managed to move from shorelines far out onto muddy shelves to an acceptance that many of these sandbodies did not originate on the shelf but were simply resident there after a fall and subsequent rise of sea level. In the efforts to reinterpret these sandstones there has been some tendency to underestimate how varied they can be. Data from eight such shelf sandstone tongues (Campanian) in southeast Wyoming are used to illustrate how variable lowstand prograding wedges can be and how these should, in addition, be distinguished from forced-regressive wedges. The depositional environments encountered in these two types of wedges are surprisingly different, and the lowstand wedges, which are frequently tidally influenced, show a greater affinity with the overlying transgressive tract than with the preceding wave-dominated, forced-regressive shoreface deposits.