STRATAL PATTERNS OF THE WILLIAMS FORK (HUNTER CANYON) FORMATION, PICEANCE BASIN, COLORADO

The Cretaceous Williams Fork Formation contains stratal packages that represent the final stage of deposition within the Cretaceous Western Interior foreland basin (Colorado). These stratal packages record changes in accommodation through time and are interpreted using a sequence-stratigraphic approach. The formation is divided into three units based on changes in stratal packaging and accommodation style. Unit 1 contains aggradationally stacked parasequences interpreted to represent deposition during highstand systems tracts. Units 2 and 3 both contain stacked, repetitive stratal packages interpreted as depositional sequences. Depositional sequences contain lowstand, transgressive and highstand systems tracts. A complicated interplay between eustatic oscillations and tectonic subsidence controls deposition of the stratal packages and depositional sequences. Eustatic oscillations control deposition of depositional sequences while tectonic subsidence forms the accommodation necessary to preserve multiple stacked stratal packages. The overall change in accommodation style from Units 1- 3 records a decrease in accommodation through time interpreted to represent a decrease in the rate of tectonic subsidence