High-resolution seismic investigation of the evolution (stratigraphy and structure) of the continental margins of the eastern Weddell Sea and of the Antarctic peninsula

During the ANTARKTIS VIII/5 cruise (December 1989 -March 1990), which was jointly carried out by AWI and RCMG, the seismic grid already available in the Weddell Sea could be expanded with up to 4100 km of high-resolution reflection seismic profiles. The Meso-Cenozoic seismostratigraphic model, originally defined on ODP Site 693 (Leg 113), was extended throughout the existing seismic database along the entire eastern Weddell Sea continental margin. This correlation effort provides some closer time constraints on different stratigraphic units elsewhere in the Weddell Sea, a.o. within the Crary Fan depositional system. A major unconformity (WO4) reflects important erosive and tectonic events at the Meso-Cenozoic boundary, which could be attributed to the existence of a structurally controlled Late Mesozoic Transantarctic seaway. Such implies a paleoceanographic control on the development of at least some of the Mesozoic Weddell Sea unconformities. The Cenozoic unconformities are weIl controlled by paleoclimatic factors. A structural ana!ysis of the seismic data provides new insights in the possible origin of the Explora Escarpment and the associated Outer High, as weIl as in the development of the Wegener Canyon. The "Polarstern Bank" is a major structural feature that has been discovered during the ANTARKTIS VIII/5 cruise. Its presence is evaluated in view of the prevailing models for the initial break-up of Gondwana, which assume a major structural lineament throughout the Weddell Sea, connecting the Explora Escarpment and the Andenes Chain. The high-resolution seismic database in the southeastern Weddell Sea yields new insights in the detailed and fine-scale sequence stratigraphic structure and build-up of the entire Crary Fan depositional system, from the proximal parts on the continental slope to the more distal parts in the Polarstern Bank area. Sedimentary processes, such as channel-levee deposition and depocentre migration, are discussed, as well as the fan system's development through time and as a response to eustatic sealevel fluctuations. On base of a good-quality seismic profile, connecting the shelf deposits (off Halley Bay) with the fan area, a climatic-eustatic controlled sedimentation model is advanced, explaining the development of the entire southeastern Weddell Sea continental margin since mid-Oligocene times. Further interpretation has also been carried out of the seismic data of the northwestern Antarctic Peninsula. which are covering the rift basin of Bransfield Strait. an elongated sediment-filled trough interpreted as a fore-arc basin. accretional and progradational slopes, recent and ancient trench environments and the facing oceanic domain. In this oceanic domain, different fracture zones have highly contrasting morphological and geophysical expressions. The subduction of a fracture zone like Hero F.Z., characterized by a significant relief possibly related to the presence of buoyant (serpentinite) ridges, may have been a factor of subductio