High-Frequency Sequence Stratigraphy and Paleogeography of the Kenilworth Member, Blackhawk Formation, Book Cliffs, Utah, U.S.A.

Abstract

Shallow-marine strata within the Campanian Kenilworth Member of the Blackhawk Formation that crop out in the Book Cliffs of east-central Utah were examined from their updip to downdip depositional limits. Outcrop sections of 31 localities were measured, recording facies, stratal surfaces, and paleoflow indicators. The geometry of stratal surfaces and the continuity of sandstones were traced between measured sections using binoculars and photographic panoramas of cliff exposures, and these data were used to interpret the chronostratigraphic framework and define the limits of depositional environments within the Kenilworth Member. Sandstones of the Kenilworth Member are interpreted to comprise parts of two high-frequency sequences. A sequence boundary occurs within the Kenilworth and separates the highstand systems tract of an older sequence from the lowstand and transgressive systems tracts of a younger sequence. The sequence boundary can be recognized by the presence of a regionally extensive erosional surface, an abrupt basinward shift of the shoreline, and a change in parasequence stacking pattern. The magnitude of the relative sea level fall that occurred within the Kenilworth is estimated to be about 20 m, based on the amount of fluvial channel incision observed at the sequence boundary. This magnitude of relative sea level fall resulted in a basinward shift in the shoreline of 16 km. The resultant paleoslope is calculated to be 0.07š, comparable to depositional slopes on the present-day Gulf of Mexico shelf. Five wave-dominated shoreline parasequences were recognized, each with a north-south to northwest-southeast paleoshoreline orientation. The oldest four parasequences are part of the highstand systems tract. Above the