Luncheon – October 2, 2009

Title: Anatomy and Development of a Low-accommodation Clastic Wedge: Cordilleran
Foreland Basin, Utah and Colorado, USA

Speaker: Jennifer L. Aschoff, Assistant Professor, Stratigraphy, Department of Geology and Geological Engineering, Colorado School of Mines, Golden, Colorado

Date: October 2, 2009

Publication: The Outcrop, October 2009, p. 24

Distinguishing sequence architecture within a regional stratigraphic framework provides insight into long-, and short-term processes of foreland basin development. Two main types of elastic wedges are identified in Cretaceous Cordilleran Foreland basin fill based on their sequence architecture: (1) thick, vertically stacked, high aspect ratio wedges and (2) thinner, more extensive, low aspect ratio wedges. Low­aspect-ratio wedges are relatively rare in the Cordilleran foreland basin, and record a complex interplay of tectonic styles, climatic conditions and eustatic processes. Low aspect-ratio wedges typically consist of numerous incomplete, amalgamated and offlapping sequences with longer shoreline tongues that stack in a flat to falling pattern; these characteristics are the hallmarks of a low-accommodation setting. This elastic wedge consists of twenty-five facies assemblages and six key parasequence types that stack into 3rd-, 4th- and 5th-order depositional sequences and sequence sets. High-order sequences stack in a striking offlapping pattern and contain a high proportion of tidally influenced facies with numerous incisions. Sequence­stratigraphic and biostratigraphic correlation, coupled with thinning trends indicate that the wedge developed coeval with Sevier- and Laramide-style deformation. The unique, low aspect ratio elastic wedge records an overlap in deformation style that may have interfered with the thrust-belt-controlled flexural wavelength of the foreland basin and changed accommodation patterns. Such elastic wedges are observed in other parts of the Cordilleran Foreland basin and may have formed under similar conditions. Classification of elastic wedges and careful description of the internal architecture of them can provide a unique predictive tool for exploration. This study describes one of these unique, low-aspect-ratio (i.e., low accommodation) elastic wedges and proposes their utility as an indicator of change in tectonic style and as a predictive tool for internal facies types and connectivity.