Shannon Sandstone in Wyoming: A shelf-ridge complex reinterpreted as lowstand shoreface deposits
- McMaster Univ., Hamilton, Ontario (Canada). Dept. of Geology
The Shannon Sandstone (Campanian) of Wyoming was formerly interpreted as two stacked shelf-ridge complexes. Sand was believed to have been transported from a time-equivalent shoreline 110-150 km to the west and reworked or molded into ridges at the depositional site. The authors show that this time-equivalent shoreline section at Lucerne, Wyoming, consists of not one shoreface sandbody, but two superimposed. They are both storm-dominated, and the lower one terminates in beach facies capped by root traces. There must have been a rise in relative sea level of at least 14m to make accommodation space for the second shoreface sandbody. In the Slat Creek area and the adjacent subsurface Teapot Dome, there are two sandier-upward facies successions. In the lower succession there are abrupt vertical facies contacts between offshore bioturbated sandstones, thicker hummocky cross-stratified sandstones, and coarser cross-bedded sandstones. There is also evidence that the cross-bedded sandstones rest erosively on underlying facies. The trace fauna in the sandstones includes Macaronichnum segregatis, Rosselia socialis, and Ophiomorpha. The M. segregatis suggests a foreshore or upper-shoreface depositional environment, and R. socialis indicates a lower to middle shoreface; neither are characteristic of a shelf-ridge complex. The abrupt and probably erosive facies contacts, along with the trace fauna, suggest that the cross-bedded sandstones in this succession represent a shoreface deposit that formed during a stage of actively falling relative sea level. Overlying muddy bioturbated sandstones indicate that shoreface deposition was terminated by a transgression. The upper sandier-upward succession contains facies and trace fauna similar to those of the lower succession, and is also interpreted as a prograding shoreface.
- OSTI ID:
- 5950260
- Journal Information:
- Journal of Sedimentary Petrology; (United States), Vol. 63:5; ISSN 0022-4472
- Country of Publication:
- United States
- Language:
- English
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