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Characterization and Modeling of Tidal Influence in a Fluvial to Marine Transition Zone: Cretaceous John Henry Member (Straight Cliffs Formation), Southern Utah

Abstract

Development of predictive and detailed reservoir scale facies models is important for petroleum exploration in tidally influenced fluvial systems, due to the heterolithic nature of such strata. The three dimensional canyon exposures of the John Henry Member, located in the Kelly Grade and Tibbet Canyon areas of the Kaiparowits Plateau, offer an excellent opportunity to study fluvial architecture of such a system. Facies models for this fluvial-tidal stratigraphy may serve as outcrop analogs for other systems, such as the McMurray Formation of Canada, and can be used to more accurately predict reservoir potential and connectivity in transitional fluvial-tidal systems. The main focus of this study is to capture the fluvial architecture of the lower section of the John Henry Member in order to understand the nature of tidal influence within the fluvial to marine transition of the Late Cretaceous (Coniacian-Santonian) Western Interior Seaway and to present modeling approaches capturing such architecture. Detailed, centimeter-scale stratigraphic sections illustrate facies, facies associations, and architectural elements. Fluvial facies include very fine- to coarse-grained trough cross-stratified, ripple laminated, climbing ripple laminated, planar laminated, and planar cross-stratified sandstones which also contain wood fragments, load casts, and convolute bedding. Fine-grained facies include coal, mudstone, and siltstone. These facies comprise the fluvial/coastal plain facies association which contains such architectural elements as fluvial channels, floodplain fines, crevasse splays, and coal. Tidal facies identified include Teredolites borings and Thalassinoides traces, inclined heterolithic bedforms, bidirectional flow, mud-draped ripple laminations, flaser and wavy bedding, and centimeter-scale interbeds of mudstone and siltstone. Differential GPS and a laser rangefinder were used to map the distribution of these elements in three dimensions with the aid of interpreted outcrop photomosaic images. Based on facies associations, the degree of tidal influence increases up section in coordination with the “A” interval of the Straight Cliffs Formation described farther east in Kaiparowits Plateau. A literature review of existing workflows and modeling algorithms informs best-practices and approaches for predictive and deterministic modeling of these systems. A comparison of preliminary modeling results utilizing Tibbet Canyon outcrop data is presented here.