Seismic signature of gas hydrate and mud volcanoes of the South African continental margin

Widespread occurrence of bottom-simulating reflectors (BSRs) has been detected in multichannel seismic profiles on the upper continental slope in the southern periphery of the Orange River delta, Another remarkable feature in the area is the occurrence of a large number of mud volcanoes. The gas hydrate in this region may consist of a mixture of microbial and thermogenic gas, whereas much of the gas flowing through the mud volcanoes probably originated from deep-seated Aptian source shales. The mud volcanoes form a distinct lineament subparallel to the bathymetric contours in this area. They are of different sizes and different stages of development. In several locations, the volcanoes penetrate the seafloor while in others they are buried. The exposed size of these volcanoes is typically few hundred meters in diameter with a height of 10-40 m. Faults play a key role in the formation of mud volcanoes on this part of the southwest African continental margin.