ABSTRACT: The Cretaceous Section at Coalville, Utah

Thomas A. Ryer

The Cretaceous section exposed near Coalville, Utah, is among the thickest in the Western Interior, totaling approximately 16,600 ft. The recognized formations, in ascending order, and their thickness reported from surface sections are: Kelvin Formation, 3200 ft; Aspen Shale, 60 ft; Frontier Formation, 7750 ft; Henefer Formation, 2500 ft; and Echo Canyon Conglomerate, 3100 ft.

The section consists predominantly of rocks deposited in fluvial environments. Because of very rapid subsidence, rivers that flowed eastward from the Sevier orogenic belt across this area aggraded rapidly, depositing large quantities of fine-grained, overbank deposits. These deposits contain numerous, thick, ash-fall layers. Braided-stream to alluvial-fan, coarse-grained deposits occur at three levels in the section. A conglomeratic interval in the basal part of the Kelvin, an equivalent of the widespread Cloverly conglomerate, records initial slow subsidence and regional bypassing of sediment; the Coalville conglomerate of the Frontier and the Echo Canyon Conglomerate record thrusting events and eastward migration of alluvial fans.

Coastal to offshore marine strata record marine invasions of northcentral Utah during late Albian, early-middle Turonian, and Coniacian time. These are represented, respectively, by: (1) the uppermost Kelvin Formation, the Aspen Shale, and the Longwall Sandstone Member of the Frontier; the Aspen Shale, and the Longwall Sandstone Member of the Frontier; (2) the Coalville, Allen Hollow Shale, and Oyster Ridge Members of the Frontier; and (3) the Dry Hollow, Grass Creek, Judd Shale, and Upton Sandstone Members of the Frontier.

The composite stratigraphic section prepared for this study relies primarily on subsurface data from wells drilled on and near the Coalville anticline; stratigraphic, lithologic, and faunal information from outcrops are integrated to the extent possible.

AAPG Search and Discovery Article #91002©1990 AAPG Rocky Mountain Section Meeting, Denver, Colorado, September 16-19, 1990