Sedimentology and stratigraphy of a deep-water gas hydrate reservoir in the northern Gulf of Mexico

We interpret the sedimentologic evolution of a deep-water channel levee deposit in Green Canyon Block 955 (deep-water Gulf of Mexico) by analyzing hydrate-bearing pressure cores and nonpressure cores collected during The University of Texas-Gulf of Mexico 2-1 (UT-GOM2-1) Hydrate Pressure Coring Expedition that preserve remarkable sedimentary structures. The levee is composed of alternating beds of sandy silt and clayey silt that range from millimeters to meters in thickness. We interpret that each couplet of sandy silt and clayey silt records a single turbidity current flow in which the upper part of the flow overtops the levee and is deposited along its flank. The sandy silt is coarser, its beds are thicker, and the fraction of sandy silt to clayey silt (netto-gross) is greater near the base of the levee. We interpret that as the levee grew, the channel depth increased and a smaller fraction of the flow overtopped the levee. An increase in net-togross, both at the base and near the top of the cored section, may record an increase in the size of turbidity current flows or a decrease in the relative height of the levee. Based on the limited core recovery, we infer that the lithology of the bounding unit immediately above the hydrate-bearing unit is thinner bedded and has lower net-to-gross than the hydrate reservoir. The bounding unit below the hydrate-bearing interval is similarly thinner bedded, yet contains high saturations of hydrate. This study illuminates the lithologic architecture of leveed-channel turbidite reservoirs at core scale and provides insight into how lithology controls hydrate distribution and concentration.