3-D FACIES ARCHITECTURE AND STRATIGRAPHIC EVOLUTION OF A TOP-TRUNCATED MIXED-INFLUENCED DELTA FRONT, WALL CREEK SANDSTONE, WYOMING
The GPR interpretation implies two distinct phases of depositional development in the Upper Cretaceous of the Raptor Ridge site. During the first phase, river-borne sediments were deposited in a deltaic setting, forming a fan-shaped delta lobe composed of coalesced mouth bars; river-flood discharge enhanced progradation of the deltaic lobe before the the lobe was abandoned. During the second phase, younger sediments were deposited on the old lobe, forming a new lobe which prograded into the basin in the same direction as the old bar deposits. The younger bedsets prograded further seaward until a regional transgressive ravinement.
An architectural comparison between the barsets in two separate delta lobes (Murphy Creek Reservoir and Raptor Ridge) ~30 km apart in the Wall Creek Member indicates that the bar complexes were deposited on the delta fronts as detached forced regressive deposits during a relative sea-level fall. The older deltaic sequence at Murphy Creek Reservoir prograded south-eastward (124°), whereas the younger bars at Raptor Ridge expanded southward (171°).