Insights into mudstone sedimentology, organic richness, and anoxia at the opening of the Cretaceous Interior Seaway: Colorado's Skull Creek Formation

• Main Author: Sullivan, Patrick M.
• Other Authors: Sonnenberg, Stephen A., Anderson, Donna S., Hagadorn, James W.
• Format: Text
• Language: English
• Published: Colorado School of Mines. Arthur Lakes Library 2021
• Subjects: mudstone sedimentology; source rock; Western Cretaceous Interior Seaway; Skull Creek; Dakota; Wattenberg field; Arctic
• Online Access: https://hdl.handle.net/11124/176414

Includes bibliographical references. 2021 Spring. The Skull Creek Formation is a suite of shallow marine mudstones and fine sandstones within the Lower Cretaceous Dakota Group. The formation signals the onset of marine deposition in the Western Interior Seaway (WIS) and is a potential source rock to the Dakota-Mowry petroleum system in the Denver Basin of northeastern Colorado, yet its depositional environments, stratigraphic correlations, and source rock contributions remain poorly understood. This study aims to remove those uncertainties and presents new sedimentological and geochemical data from four cores and 38 well logs in the subsurface of the central Denver Basin, integrating it into previous outcrop-based analyses of the Skull Creek Formation.Four major flooding surfaces divide the Skull Creek Formation into geochemically distinct informal lower, middle, and upper units. The Lower Skull Creek contains a silica-rich basinal to lower slope facies succession and displays poor TOC (avg. 0.9 wt. %). The Middle Skull Creek documents a transition from silica-rich to calcareous basin to slope facies and displays good TOC (avg. 2.3 wt. %). This notable unit represents the maximum flooding surface and documents the earliest connection between the Arctic and Tethyan lobes of the WIS. The Upper Skull Creek displays good TOC values (avg. 2.3 wt. %) which decrease upward. There is a strong correlation between TOC and anoxic proxies - high Molybdenum (ppm) and low bioturbation intensity. Considering the thickness and TOC trends in the Wattenberg, the Skull Creek Formation is a promising, historically underestimated source rock to the Dakota-Mowry petroleum system.