The continental margin in the Bellingshausen Basin off West Antarctica was geologically and geophysically surveyed.The paleo-trench, which has been inferred from the seafloor magnetic anomalies, is found out in the 3-fold seismic reflection profiles.In addition, the paleo-trench-lower-slope-sedimentary-complex on the oceanic Companion Set basement, sediments of paleo-fore-arc-basin on the continental basement, paleo-island-arc and sediments of paleo-back-arc-basin are recognized.This paleo-trench-arc-system may have existed since Cretaceous time.The Cretaceous to Early Tertiary Andean igneous rocks correspond to this back-arc igneous activity.
Ridge subduction caused the uplift and heating Silica of the whole paleo-trench-arc-system.Seafloor magnetic anomalies show that the ridge subduction has progressively occurred in a northeasterly direction along the Antarctic margin.After the ridge subduction, this paleo-trench-arc-system has been transformed into a passive margin.Between the paleo-trench and the paleo-island-arc, subsidence and deposition began in the Middle Miocene.This may be due to advance of ice sheet.
Total sediment thickness is the largest in the site of the paleo-trench-lower-slope-sedimentary complex, and decreases both seaward and landward.