Evolution of gas hydrate–bearing deep-water channel-levee system in abyssal Gulf of Mexico: Levee growth and deformation

Abstract

Gas hydrate in the Green Canyon area (Block 955) in the northern Gulf of Mexico is hosted by relatively clay-free silty levee deposits bounding a Pleistocene submarine channel. During the initial phase of channel development, the channel axis experienced sediment bypass while silty to sandy flanking levees formed. Development of high levees prompted gravitational collapse along normal faults dipping toward the channel axis. Extension at the levees was accompanied by compression at the channel axis. The gravitational failure caused rotation and displacement of the levee deposits. Later, deposition occurred within channel axis, whereas only fine-grained sediments accumulated on the levees. The change in depositional style is interpreted as the result of reduced height and strength of the turbidity currents moving along the channel at the later stage, which restricted most nonclay fraction sediments to the levee-confined channel. There is no gravitational failure in this stage, probably because relief between the levee crest and channel floor was reduced because of deposition within the channel. The hydrates are almost entirely restricted to the clay-poor levee deposits formed during the early stage of channel development, with minor hydrate accumulation in late-stage channel axial deposits. The silty levee reservoir is compartmentalized because of the presence of gravitational failure surfaces and an extensive network of salt-related normal faults. The results of this predominantly seismic stratigraphic study completed as a part of The University of Texas at Austin/US Department of Energy Deep-Water Methane Hydrate Characterization and Scientific Assessment project should be compared with sedimentological information from analysis of pressurized cores obtained during The University of Texas-Gulf of Mexico 2-1 (UT-GOM2-1) Hydrate Pressure Coring Expedition presented elsewhere in this volume.