Sadeque, Junaid1, Janok P. Bhattacharya1
(1) University of Texas at Dallas, Richardson, TX
ABSTRACT: Integrated Stratigraphic Study of The Turonian Wall Creek Member, Frontier Formation, Powder River Basin, Wyoming
Recent outcrop investigations suggest the upper Turonian Wall Creek Member of the Frontier Formation to be a top truncated lowstand delta system influenced by waves and tides. The present study incorporates subsurface data from 2000 well logs and core data from 40 borehole cores to further examine the viability of this outcrop-based model and establish a sequence stratigraphic framework for the Wall Creek.
Well log correlations, calibrated by core data and closely associated outcrops, show several parasequences that are laterally traceable in the outcrop. These parasequences, interspersed with thin mudstones and mud-dominated heterolithic deposits, offlap south-southeast reflecting increasing accommodation and representing the progradation of individual delta lobes. Internal sedimentological and ichnological features of the delta front deposits indicate variable influence by waves and tides, both in upper- and lower-shoreface environments. In a number of wells, the Wall Creek sandstones have a sharp lower contact displaying thin pebble lags and/or Glossifungites ichnofacies. This signifies a forced regressive surface of erosion, probably associated with local syntectonic movements.
The uppermost Wall Creek parasequence is truncated by a marine ravinement surface separating the Frontier Formation from the overlying Cody Shale. Absence of paralic and nonmarine deposits in the Wall Creek is probably due to this top-truncation as locally indicated by pebble lags and Glossifungites, as well as palimpsest softground ichnogenera. The Wall Creek is bounded below by a regional unconformity associated with the Emigrant Gap Member, demarcated in the outcrop by a regionally traceable conglomerate lag that also shows distinct well log signatures.
AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.