Sedimentology, Architecture, and Origin of Shelf Turbidite Bodies in the Upper Cretaceous Kenilworth Member, Book Cliffs, Utah, U.S.A.
Simon A.J. Pattison, Trevor A. Hoffman, 2008. "Sedimentology, Architecture, and Origin of Shelf Turbidite Bodies in the Upper Cretaceous Kenilworth Member, Book Cliffs, Utah, U.S.A.", Recent Advances in Models of Siliciclastic Shallow-Marine Stratigraphy, Gray J. Hampson, Ronald J. Steel, Peter M. Burgess, Robert W. Dalrymple
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Shelf turbidite bodies have long been recognized in ancient rock successions, but most examples are poorly constrained both by the limited outcrop exposures and by the lack of modern analogues or data. Uncertainties include the mechanism or mechanisms responsible for generating the turbidites, the mode of transport onto and across shelf, the relationship to time-equivalent shoreface deposits, and the resulting three-dimensional sand-body geometry or sedimentary architecture. This study takes advantage of the exceptional outcrop exposures in the Book Cliffs of eastern Utah to answer some fundamental questions regarding the origin and distribution of shelf turbidite bodies. The lower Kenilworth Member (Campanian, Blackhawk Formation) is an extremely well constrained stratigraphic interval and is characterized by turbidite-rich shelf deposits at a number of localities. The outcrop exposure is excellent, with some areas offering unparalleled three-dimensional transects across the shelf, along both depositional dip and depositional strike.
A sedimentological analysis of the lower Kenilworth Member shelf deposits in the Price River Canyon to Hatch Mesa area has revealed a mixture of high-energy event beds, including wave-modified turbidites, hummocky cross-stratified sandstones, hyperpycnites, and classical turbidites, that are interbedded with quiet-water mudstones and siltstones. The paucity of wave-generated fair-weather deposits, combined with an abundance of wave-modified event beds, suggests deposition between fair-weather and storm wave base. Fresh-water input is indicated by the presence of carbonaceous matter, and the low-diversity and low-abundance trace-fossil suite in all facies. These shelf turbidite bodies are detached from their time-equivalent Kenilworth parasequence 2 (KPS2) shoreface deposits. The Middle Mountain to Gunnison Butte lenticular body was deposited at least 10 km basinward of the KPS2 shoreline in approximately 25-30 m water depth, and the Hatch Mesa succession was deposited 16 km basinward of the KPS2 shoreface in approximately 35-45 m water depth. Sediments bypassed the shoreface through a network of subaqueous channels which were cut by the turbid underflow of sediment and water generated by storm and/or river flood events. The results of this study indicate that shallow marine facies models should be revised to include isolated or shoreface-detached turbidite complexes in some shelf settings. Preliminary work suggests that the generation and preservation of these isolated sandstone bodies is linked to a short-term period of tectonic uplift and subsidence in the Sevier thrust front, northwest of the Book Cliffs. Further work is required to test the validity of this tectonic hypothesis.