Howell, Charles D.¹, Janok P. Bhattacharya¹ 
(1) University of Texas at Dallas, Richardson, TX

ABSTRACT: Geology and Stratigraphic Architecture of the Upper-Cretaceous Wall Creek Member, Frontier Formation, Powder River Basin, Wyoming: An Outcrop Analog for Top-Truncated Mixed-Influence Lowstand Deltas

Marine mudstones encasing top-truncated lowstand delta lobes are exposed in laterally continuous outcrops of the Turonian Wall Creek Member on the southwestern flanks of the Powder River Basin. Paralic and non-marine facies are absent, reflecting high degrees of top-truncation, likely caused by the generally low accommodation and basin-distal setting. 98 measured sections were collected and correlated over a 1900 km² area. The Wall Creek was deposited into a tectonically active foreland basin along the western flanks of the Cretaceous epicontinental seaway. 5 offlapping parasequences have been identified and correlated, some of which are bound above and below by marine erosional surfaces. Not all are present locally, most likely due to syntectonic movements of the basin floor. From north to south the Wall Creek expands from a single sharp-based parasequence floored by a pebble lag into several upward coarsening distinct parasequences interpreted as different delta lobes. Pebble lags at the base of sharp-based sand bodies indicate a marine erosional surface possibly associated with a forced regression. Paleocurrents indicate a north-northwest to south-southeast progradation. Sand bodies with length scales of several kilometers to tens of kilometers represent large-scale reservoir compartments.

AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.