Tectonic and sedimentary evolution of the Bransfield Basin, Antarctica
Jeffers, John Douglas
Anderson, John B.
Master of Arts
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.