Marilyn C. Huff¹
(1) N/A, Las Cruces, NM

Abstract: Sequence stratigraphy of the Wall Creek Member of the Frontier Formation, Powder River Basin, Wyoming

The Cretaceous (Turonian) Wall Creek Member of the Frontier Formation has long been an enigma. Present throughout much of Wyoming, it, and the correlative Turner Sandstone of the Carlile Shale, is a complex unit of interbedded sandstone, siltstone, shale and bentonite deposited in and along the western margin of the Cretaceous Western Interior Seaway. The focus of this study of the Wall Creek Member is the southwestern margin of the Powder River Basin where sequence stratigraphic principles were applied to interpret the depositional history using data from detailed measured sections, subsurface core and geophysical well logs.

The Wall Creek forms most of the transgressive systems tract of its third-order depositional sequence. The lower sequence boundary is a regional unconformity with a hiatus of several million years. The marine Cody Shale which overlies the Wall Creek occupies the upper portion of the transgressive systems tract.

Five fifth-order sequences comprise the Wall Creek. Transgression was not a simple water-deepening process, but rather occurred as multiple discrete events. Sedimentation rates on the whole kept pace with transgression rates yielding multiple transgressive-regressive couplets recorded as stacked shorefaces. The transgressive portion of the sequence typically is recorded only by a lag and the sequence boundary and maximum flooding surface are merged. In the upper part of the Wall Creek, transgressive sedimentation is preserved in a few places. Wall Creek sedimentation is primarily storm-dominated. Evidence of tide-dominated sedimentation can be found in a limited number of outcrops and in subsurface data from Salt Creek Field.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana