Tectonic Control of Nested Sequence Architecture in the Castlegate Sandstone (Upper Cretaceous), Utah

S. Yoshida, A. Willis, and A. D. Miall

The braided-fluvial Castlegate Sandstone at Price Canyon, Utah, consists of a single stratigraphic sequence spanning approximately 5 m.y.. From near Trail Canyon eastward this sequence passes laterally into a succession of at least six higher frequency sequences of fluvial-estuarine origin.

We suggest that the origin of sequences is related to flexural loading and intraplate stress on two time scales. The main 5 m.y. sequence reflects regional tectonism, with sandstone sheets of the lower part of the sequence developing at a time of slow subsidence, and the upper part of the sequence with abundant shale and some tidal influence reflecting a high subsidence rate. The higher order sequences are interpreted as a basinal response to episodes of crustal shortening on a 10⁵-year time scale. This study amplifies Posamentier and Allen's (1993) model, in which foreland basins are divided into areas of rapid and slow subsidence (Zone A and B). We postulate that these zones migrated laterally in response to variations in long-term subsidence rate, and can be mapped by re erence to the distribution of type-1 sequence boundaries.

The zone A/zone B differentiation of the basin was probably amplified by the differences in crustal rheology. The higher frequency sequences occurs within the area of the Paleozoic Paradox Basin, which may have been more prone to vertical structural movements in response to intraplate stress.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California