Reconnaissance stratigraphy of the Red Glacier Formation (Middle Jurassic) near Hungryman Creek, Cook Inlet basin, Alaska

Geochemical data suggest the source of oil in upper Cook Inlet fields is Middle Jurassic organic-rich shales in the Tuxedni Group (Magoon and Anders, 1992; Lillis and Stanley, 2011; LePain and others, 2012, 2013). Of the six formations in the group (Detterman, 1963), the basal Red Glacier Formation is the only unit that includes fine-grained rocks in outcrop that appear to be organic-rich (fig. 3-1). In an effort to better understand the stratigraphy and source-rock potential of the Red Glacier Formation, the Alaska Division of Geological & Geophysical Surveys, in collaboration with the Alaska Division of Oil and Gas and the U.S. Geological Survey, has been investigating the unit in outcrop between Tuxedni Bay and the type section at Lateral and Red glaciers (Stanley and others, 2013; LePain and Stanley, 2015; Helmold and others, 2016 [this volume]). Fieldwork in 2015 focused on a southeast-trending ridge south of Hungryman Creek, where the lower 60–70 percent of the formation (400–500 m) is exposed and accessible, except for the near-vertical faces of three segments near the southeast end of the ridge (figs. 3-2 and 3-3). Three stratigraphic sections were measured along the ridge to document facies and depositional environments (figs. 3-3 and 3-4). Steep terrain precluded study of the upper part of the formation exposed east of the ridge. This report includes a preliminary summary of findings from the 2015 field season.