Evidence of Fine-Grained Sediment Transport by Turbidity Currents, Hyperpycnal Flows and Storm Waves: Inner Shelf Prodelta Turbidite Complex, Hatch Mesa Succession, Book Cliffs, Utah

Simon A.J. Pattison¹ and Trevor A. Hoffman^2
1 Brandon University, Brandon, MB
² University of Alberta, Edmonton, AB

The marine mudstone-encased, Hatch Mesa succession (lower Kenilworth Member, Campanian) is exposed in a 7 km long outcrop belt along the southern edge of the Book Cliffs in eastern Utah. In comparison to the majority of isolated shelf bodies in the Cretaceous Western Interior of North America, the Hatch Mesa succession has a greater proportion of mudstone and siltstone (50-70 %), is thinner (6-20 m), and is weakly coarsening-upward. The background deposits consist of non- to mildly-bioturbated, pin-striped mudstones and sandy siltstones, with a paucity of wave ripples, suggesting deposition below fair weather wave base. In contrast, the sandstone beds represent high energy event beds that punctuate the quiet water, background conditions. The sandstones have a great diversity of vertical stratification styles and sedimentary structures, and are dominated by turbidite beds, with lesser amounts of storm-generated beds. Classical turbidites, hyperpycnal flow-derived turbidites, storm-modified turbidites and HCS sandstones are all observed within the Hatch Mesa succession. These attributes, in combination with locally abundant carbonaceous matter, convolute bedding, pinch and swell geometries, a lack of clinoforms, and a low diversity/abundance trace fossil suite, suggest deposition in a prodelta environment, between fair weather and storm wave base. A variety of mechanisms are capable of generating instability in the delta front and triggering the turbid flow of sediments into deeper water, including high rates of sedimentation, river flooding, storm events or earthquakes. Sediments would be transported into the prodelta region through subaqueous channels or gullies. Shallow marine facies models should be revised to include isolated prodelta turbidite complexes down-dip of river-dominated deltas.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005