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Facies Analysis and Interpretation of Argillaceous Sandstone Beds in the Paleogene Wilcox Formation, Deep Water Gulf of Mexico

Bruce Power, Brooke Carson, Julian Clark, Jacob Covault, Andrea Fildani, Morgan Sullivan, and Larry Zarra
[email protected]

The Wilcox Formation in the deep water Gulf of Mexico comprises a thick (2000-6000 feet) sandstone-rich succession of deep water sedimentary rocks interpreted to have been deposited in channelized and unconfined lobe/sheet systems in slope and basin floor environments. Argillaceous sandstone beds are a common occurrence in the deep water Wilcox Formation. They are interpreted to be deposited by gravity driven flows that are transitional between laminar and turbulent flow, and are classified as hybrid event beds. In the Wilcox Formation, these hybrid event beds are interpreted to occur in two distinct facies associations. They are most commonly interpreted to have been deposited in medial to distal unconfined lobe/sheet environments, an interpretation that is consistent with their observed presence in many other deep water systems. The argillaceous character of these beds is interpreted to reflect longitudinal flow evolution of the turbidity current, in which the ratio of silt and clay to sand increases along the runout length. The Wilcox Formation also contains intervals with abundant hybrid event beds that are interstratified with strata interpreted to have been deposited in channel and overbank environments. Interpretation of these hybrid event–dominated intervals as distal lobe/sheet sediments is challenging, as it requires repeated large magnitude shifts of depositional environment from proximal to distal. These argillaceous intervals with abundant hybrid event beds are interpreted to represent the initial deposits of channel avulsion. The mixture of hybrid event beds, debrites, and turbidite sands and mud is interpreted to have been deposited by the initial flows of an incipient channel that has broken through its confining levee, and is forming an avulsion splay in what was previously an unconfined environment. A distinctive aspect of the interpreted avulsion splay intervals is that they commonly underlie confined channel or levee/overbank intervals, and are interpreted to have a genetic relationship to these overlying channelized strata.

AAPG Search and Discovery Article #90167©2013 GCAGS and GCSSEPM 63rd Annual Convention, New Orleans, Louisiana, October 6-8, 2013