Outcrop Gamma Ray spectrometry of the Sunnyside Member, Book Cliffs, East Central Utah

Keith Adamson, John A. Howell, Stephen S. Flint, and Diane L. Kamola

The Book Cliffs of East Central Utah provide excellent exposure in which to test and further the concepts of sequence stratigraphy within both marine and marginal marine depositional systems. Within a study of the Sunnyside Member of the Blackhawk Formation spectral gamma ray profiles were run through 12 of the measured sections. The Sunnyside Member represents three shallow marine parasequences truncated by at least one high frequency sequence boundary which is overlain by incised valley fill deposits. The gamma ray studies were undertaken with the following aims:

To quantify gamma ray profiles and spectral gamma responses to known and well understood stratal geometries, including marine shoreface parasequences, incised valley fills and coastal plain succession.

To quantify changes which occur across stratal surfaces, parasequence and sequence boundaries

To assist in the understanding of certain stratal elements which are less well understood, such as the recognition of interfluves in marine shales

To assist in the accurate tying of well gamma ray logs from 80 coal bed methane wells drilled behind the outcrops.

The results have this study have important implications for the application of spectral gamma ray studies within sub-surface reservoir intervals. Architectural elements can be categorized and significant changes in mineralogy can be observed across key stratal surfaces.

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