PRELIMINARY STUDY OF PARASEQUENCES IN THE LOWER CRETACEOUS ASPEN SHALE, WANSHIP AREA, UTAH

Global sea level rise and the actively subsiding foreland basin east of the Sevier Orogenic Belt during the Early Cretaceous resulted in the marine invasion of the Western Interior basin. In north-central Utah, the Aspen Shale represents the first Cretaceous transgression of the sea. In this area, approximately 40 km (25 miles) east of Salt Lake City, the Aspen Shale is between 105-120 m thick. It is conformably bounded below by the Kelvin Formation, and above by the Longwall Sandstone Member of the Frontier Formation. Parasequences observed within the Aspen Shale display a definite shallowing upwards sequence recorded by ichnofossils as well as bedforms. Each parasequence is 10 to 20 m thick and each is capped by an erosional flooding surface. Because the orogenic belt was proximal to the depositional basin, local subsidence and sedimentary rates were high resulting in progradation of the shoreline within each parasequence. It is less certain whether the parasequences represent eustatic or tectonic controls, but proximity to the Sevier orogenic belt suggests the later.