MIDDLE THOMPSON CREEK ISOLATED SAND BODY: A TIDE-DOMINATED DELTA’S IMPLICATIONS ON THE STRATIGRAPHY OF THE PICEANCE BASIN’S EASTERN EDGE

The Middle Thompson Creek (MTC) outcrop is part of an unnamed and unresearched middle Campanian isolated sand body encased within the Mancos Shale, on the eastern edge of the Piceance Basin (Near Carbondale, Colorado, USA). Outcrop measured sections, ammonite dating, GPS geological mapping surveys, detail photos and photo mosaics are integrated to understand the MTC outcrops’ relevant facies, depositional environment, and relationship to the Piceance Basin stratigraphy. Field data revealed that the MTC outcrop consists of two isolated sandstone sections separated by roughly 100 m of dark marine shale. Each section contains repeated cycles of increasing and decreasing sand percentage, transitioning from siltstone to mud draped very fine sandstone. Bioturbation is abundant, and where sedimentary structures are preserved FWL bedding and ripple cross lamination predominate. These observations along with an overall increase in grain size and immature sediment suggest a tide-dominated deltaic environment.

Local stratigraphic correlations of the Piceance Basin by Hettinger and Kirschbaum (2002), end after the late Campanian Cozzette Member of the Iles Formation. With this research, we can extend our understanding of this portion of the Piceance Basin deeper in time. Isolated sand bodies have been drilled as reservoirs within the Piceance by the petroleum industry, however their origin and deposition is still a contested subject. This study can contribute to this discussion and more accurate modeling of these reservoirs.