Date of Award

12-15-2014

Document Type

Open Access Thesis

Department

Earth and Ocean Sciences

First Advisor

James H. Knapp

Abstract

Woolsey Mound is a thermogenic gas hydrate and cold seep system in the deepwater (900m) Gulf of Mexico. A set of sub-bottom seismic profiles acquired at MC-118 Woolsey Mound provide decimeter-scale vertical resolution of the upper ~50m of the subsurface throughout the lease block. Integration of these data with radiocarbon, lithostratigraphic, and biostratigraphic data from shallow gravity cores provides the basis for detailed interpretation of the mound evolution within the last 12,000 years. Uniform sedimentation during the Last Glacial Maximum and following changes in sediment distribution over MC-118 suggests modern mound activity did not begin until at least ~12ka. Development of the mound system appears to be related to salt tectonism, and was characterized in sequence by (1) formation of NNE-trending folds (~10 m structural relief), (2) shallow normal faulting (1-2 m apparent offsets), (3) subsea erosion of the mound superstructure, and (4) deposition of a sedimentary drape across the entire modern mound edifice. The base of the sedimentary drape sits in angular unconformity with the underlying folded, faulted, and eroded strata, and is dated to be no younger than 4 ka, suggesting the modern mound developed within a period of <8ka, and had assumed its current configuration by 4 ka. If correct, the mound, and by analogy, the cold seep and hydrate system, was entirely inactive until after the Last Glacial Maximum. These data place the first quantitative temporal constraints on the development of an episodic hydrate mound and associated cold seep system.

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