Tectonic and sedimentary evolution of the Bransfield Basin, Antarctica

Abstract

Application of sequence stratigraphy to seismic reflection profiles from the Bransfield Basin indicates that this modern back-arc basin formed in response to cessation of subduction at the South Shetland trench at 4 Ma. Two distinct systems tracts stack to form depositional sequences; hemipelagic sediments drape the basin during highstand/interglacial periods, whereas glacially-eroded sediments prograde into the basin during lowstand/glacial maxima. Relative ages of back-arc and forearc sequences suggest that forearc subsidence due to subduction cessation predated back-arc rifting. Since glacial fluctuations in the region are controlled primarily by sea level, the Bransfield Basin sequences may correlate with global eustatic cycles; subsidence rates and sediment thicknesses suggest that they are of $\sim$0.8 Ma duration. If so, the forearc started subsiding by 3.1 Ma, a rifted back-arc margin existed by 2.4 Ma, and basin floor volcanism began before 1.6 Ma. Tectonic segmentation of the back-arc reflects the continuing influence of the formerly active South Shetland subduction zone.