AN INTEGRATED STRUCTURAL ANALYSIS ON CHIRP DATA OF AN INTERPRETED PALEO ‘CARBONATE’ MOUND DEVELOPMENT, MC – 118, NORTHERN GULF OF MEXICO

Woolsey Mound is a ~1 km diameter thermogenic gas hydrate and cold seep (GHCS) complex system. It is located ~ 900m water depth in the Mississippi Canyon Lease Block 118 (MC-118) on the upper continental slope of the northern Gulf of Mexico (GOM). Due to its complex geology, widespread hydrate seepage and presence of benthic fauna, the mound serves as a permanent research site for a multidisciplinary seafloor observatory, thus providing insights into the dynamics of shallow fluid expulsion, their spatial and time variations and possible geological forcing mechanisms.

This study utilizes a set of high resolution 2D autonomous underwater vehicle (AUV) borne chirp seismic profile data acquired at MC-118, and provides a unique basis for a twofold detailed structural characterization of an interpreted paleo mound development (PMD). The profiler gives ~70 m of subbottom penetration with ~0.1 m of vertical resolution. First, isochore analysis of deeper stratigraphy suggests 1) uniform sedimentation prior to and post PMD with strata variance of ~0.5-1 m, 2) uneven sediment distribution during PMD activity, showing a localized growth strata or differential subsidence of ~5-6 m, as well as truncation and onlapping synkinematic geometry. Integration with modern chronostratigraphic results further indicates that PMD is correlative to a relative sea level lowstands, of mid-Late Pleistocene. Second, PMD appears to have occurred during a quiescent tectonic environment as evidenced by a constant offset of ~1-2.5 m throughout stratigraphy, along major faults. These data may substantiate that Woolsey Mound cold seeps are ‘episodic’, and that sea level fluctuation or tectonic governance ‘alone’ may not be critical geological triggers of seepage development.