The occurrence of vertebrate and invertebrate fossils in a sequence stratigraphic context: the Jurassic Sundance Formation, Bighorn Basin, Wyoming, USA

Fourteen outcrops and six supplemental partial outcrops of the Middle to Upper Jurassic Sundance Formation were measured and described along the eastern flank of the Bighorn Basin, Wyoming to develop a sequence stratigraphic interpretation and to evaluate the occurrence of marine fossils. The Sundance Formation contains four depositional sequences with three distinct facies associations. The lowest two sequences preserve a carbonate ramp, the third sequence preserves a siliciclastic low-energy wave- dominated margin, and the final sequence preserves an estuarine incised-valley fill. Preservation of marine vertebrates and invertebrates in the Sundance is governed by both facies and sequence stratigraphic architecture. Invertebrates in the lower Sundance are distinct from invertebrates in the upper Sundance. Vertebrates occur only in the upper Sundance and can be found on flooding surfaces, within mudstone, or in a channel lag. Vertebrate preservation is best along a maximum flooding surface that preserves partially articulated specimens within fine-grained concretions.