Seafloor Slumping in the South Caspian Sea Evidence

Seafloor Slumping in the South Caspian Sea: Evidence for Massive Gas Hydrate Dissociation During the late Pleistocene Camelia C. Knapp, Christopher C. Amos, James H. Knapp, Department of Earth and Ocean Sciences, University of South Carolina A large (>2, 500 km 2) late-Pleistocene zone of seafloor deformation and slumping, called the Absheron Allochthon (AA), has been imaged in the South Caspian Basin (SCB) using 2 D and 3 D seismic datasets. Since the history of sea level changes in the Caspian Sea in the past ~700 ka emphasizes a major ~100 m rise (Khvalyn transgression) and ~100 m drop (Yenotavian regression) in sea level during the late Pleistocene which would cause the expansion and subsequent dissociation of a massive gas hydrate reservoir, the emplacement of the AA may be related to the dissociation of gas hydrates. Such a sea level rise would increase seafloor pressure over a larger portion of the SCB, allowing gas hydrates to form further inland within the marine sediments. A ~100 m sea level drop following this hydrate reservoir expansion would result in a ~1 MPa pressure reduction on the seafloor, and due to the quasi-stable nature of gas hydrates this drop in pressure could provide a mechanism for gas hydrate dissociation. This research utilizes 2 D and 3 D seismic data in conjunction with well data to place temporal constraints on the emplacement of the AA to evaluate whether this large-scale submarine slump could be related to the dissociation of gas hydrates. These data are uniquely set to evaluate proposed mechanisms for late-Pleistocene largescale submarine slope failure, and favor a relationship with the dissociation of underlying gas hydrates. North to South seismic profile showing the extensional and compressional features observed within the continuous facies component of the AA. HORIZONS (top to bottom): seafloor (red), top of AA (blue), base of AA (yellow), Absheron series (red). Faults are shown in red. Note the extensional features within the northern portion of the profile and the compressional features in close proximity to the northern buttress of the mud volcano where a sharp topography change is observed on the base of the AA. Seismic profile location shown atop a depth map of the base of the AA.