Abstract:
High resolution seismic data collected on four profiles located on the Bengal Fan at 8 degrees N, 11 degrees N, 14 degrees N, and 17 degrees N were analyzed. Numerous channel-levee systems were identified as main architectural elements, all characterized by erosional incision into underlying sediments. On the upper middle fan (17 degrees N), the channel-levee systems are grouped into four complexes. They are separated by regional unconformities, which were partly caused by generation of nonchannelized turbidity currents or switching of the feeding canyon. Succession of the systems and dating of two surface channels (Weber et al., 1997; Weber et al., 2003) indicate activity of the Bengal Fan even during sea-level rises and highstands. In all three profiles from the lower fan, two regional unconformities were found. At 8 degrees N, the unconformities could be dated at DSDP Site 218 to have Pliocene and Pleistocene ages, and were interpreted to be the equivalents of unconformities found in the central Indian Ocean, which are caused by deformation events of the oceanic crust (Krishna et al., 2001a). Faults terminating within Pleistocene sediments suggest tectonic activity at least within the Pleistocene at 8 degrees N. The unconformities identified at 11 degrees N and 14 degrees N may also result from tectonic events. Besides these unconformities, variations of sedimentation rates in time and space determined at 8 degrees N and the onset of channel-levee systems simultaneously with lithological changes at ODP Leg 116 sites suggest that tectonic events at the Bengal Fan as well as changes of sediment supply and transport occurred partly concurrently. The sediment supply in turn depends on the erosional regime in the Himalayas, which is controlled by tectonic or climate or an interaction of both. Therefore we propose that a tectonic link may exist between source and sink areas of Bengal Fan turbidites, i.e., between uplift of the Himalayas and deformation events of the Indian Ocean lithosphere.