Incised valleys in the Parkman sandstone at Teapot Dome, Wyoming: a comprehensive outcrop analysis

Abstract

The Upper Cretaceous (lower Mesaverde) Parkman Sandstone (PS) is a deltaic succession that displays overall progradational parasequence set stacking, with depositional environments ranging from offshore marine to coastal plain deposits. Shoreface facies of the PS that show strong wave and some tidal influence and are excellent reservoirs. The PS crops out all along the western margin of the Powder River Basin. Nine sections were measured at Teapot Dome and integrated with observations of previous outcrop work to create a new proximal framework for the PS that suggests the occurrence of a previously unrecognized, major sequence boundary and associated incised valley system near the top of the lower PS in outcrop. Above the sequence boundary, the base of the valley fill system consists of estuarine deposits. Above the estuarine deposits are multi-story fluvial deposits. Relief on the valley incision is on the order of 60 ft. – 70 ft., individual fluvial channels display relief on the order of 10 ft. – 20 ft., with multiple channels stacking upwards of 40 ft. - 50 ft. The recognition of an incised valley and sequence bounding unconformity has important implications in terms of subsurface exploration and production of PS reservoirs. Namely, the possibility of a new play type (incised valleys) in the PS as well as a better understanding of distal PS deposition in terms of lowstand sediment transport and lowstand reservoirs.