--> Abstract: Oceanic Flood Deposits in the Cretaceous Western Interior of North America, by Simon A. Pattison; #90078 (2008)
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Oceanic Previous HitFloodNext Hit Deposits in the Cretaceous Western Interior of North America

Simon A. Pattison
Department of Geology, Brandon University, Brandon, MB, Canada

The apparent paucity of storm wave-induced underflow deposits in ancient shelf settings is puzzling given the ubiquity of storm deposits in many shallow marine sections worldwide. The western margin of the Cretaceous Western Interior Seaway was characterized by small-to-moderate-sized rivers and was storm-dominated, which are near perfect conditions for the generation of storm wave-induced underflows or oceanic floods. In these settings, storm waves are coupled with an increased delivery of river-derived fresh water and fine-grained sediments, creating high density underflows which transport sediments from the shoreface to the shelf. Even though oceanic floods occur over a shorter time period (i.e. days) compared to sustained river Previous HitfloodNext Hit-induced underflows (i.e. weeks), they have the capacity to transfer a much greater volume of fine-grained sediments onto the shelf.

Early results from the Upper Cretaceous strata of the Book Cliffs region, eastern Utah and western Colorado have revealed the presence of oceanic Previous HitfloodNext Hit deposits in a variety of stratigraphic intervals. The oceanic Previous HitfloodNext Hit deposits occur as channelized or lobate, isolated shelf bodies that are dominated by organic-rich siltstones and mudstones; very fine- to fine-grained Bouma-like sandstone beds, including wave-modified turbidites, hyperpycnites and classical turbidites; and hummocky-cross-stratified sandstones. Paleocurrent data reveals a dominant across-shelf, offshore-directed transport trend. Wave-modification is prevalent and includes combined flow ripples, quasi-planar laminations, and low-amplitude HCS, indicating deposition above storm wave base. Storm wave-induced underflows or oceanic Previous HitfloodTop deposits require further investigation before a genetic facies model for hyperpycnites can be constructed.

 

AAPG Search and Discovery Article #90078©2008 AAPG Annual Convention, San Antonio, Texas