Wave- and River Influenced Deltaic Clinoforms of the Chimney Rock Sandstone, Flaming Gorge Reservoir, Utah

Skinner, Jay P.¹ and Piret Plink-Bjorklund^2
1Colorado School of Mines, Denver, CO
²Colorado School of Mines, Golden, CO

     The Chimney Rock Sandstone is an Upper Cretaceous sandstone deposited in near shore deltaic, and estuarine environments in the Western Interior Basin. The Chimney Rock Sandstone outcrops in a 15 km long, near continuous exposure near Flaming Gorge Reservoir, Utah. Previous work has shown that the wave-dominated highstand, falling stage or forced regression, and lowstand deltas can be distinguished based on the stacking patterns and shoreline trajectory. The deltaic clinoforms consist of shoreface deposits, fluviallydominated mouth bars, delta front deposits and distributary channel deposits. One of the objectives of this study is to study in detail the deltaic clinoforms, to develop sedimentologic and early diagenetic criteria for recognition of the HST, FRST and the LST clinoforms, as well as to distinguish the fluvial-dominated mouth bar deposits and upper-shoreface deposits. The detail study will compare the lithology changes, clinoform steepness, sandbody geometry, degree of amalgamation, net to gross ratios, and local permeability barriers. The study suggests that there are more mud-rich intervals in parts of the delta that have more fluvial domination, and more clean sand-rich intervals in the wave dominated areas of the delta. The degree of amalgamation is also expected to change with the systems tract. The tops of the clinoforms show significant cementation that could be preferentially related to a specific systems tract. The second aim of the project is to apply the criteria developed in outcrops to subsurface data, and determine if the delta system exposed in outcrops has equivalent attached or detached lowstand deposits further seaward.

AAPG Search and Discovery Article #90071 © 2007 AAPG Rocky Mountain Meeting, Snowbird, Utah