The BGR Antarctic cruise 1996 from 29th December 1995 to 6th February 1996 with M.S. AKADEMIK NEMCHINOV was designed to acquire new marine geophysical data for a better understanding of the geological processes, timing, occurrence and location of rifts of the initial break-up of southern Gondwanaland. A total of 3,836 km of multichannel seismic reflection data have been collected in the areas of the Cosmonaut Sea, the Astrid Ridge, the Lazarev Sea and the southern Agulhas Plateau in parallel with magnetic and gravity measurements. In addition magnetic and gravity measurements were carried out on transit. Major new observations of the collected MCS data include: (1) Volcanic rocks play a major part in the construction of the Astrid Ridge and also of the Agulhas Plateau. (2) The early opening of the Lazarev Sea was associated with excessive volcanism resulting in the emplacement of a voluminous volcanic body characterized by an internally divergent pattern of seaward-dipping reflectors. (3) The Astrid Fracture Zone continues in form of a sediment-filled basement depression flanked by distinct basement highs into the Lazarev Sea, and apparently swings to the west parallel to the coast of Queen Maud Land. (4) The thickness of sediments in the Cosmonaut Sea overlying oceanic crust of inferred Early Cretaceous age is in excess of 4s (twt), i.e. about 6,000 m. Three regional seismic markers of inferred Cretaceous, Late Eocene-Oligocene and Middle Miocene ages subdivide the sedimentary column.
The preceding results of the Deep Sea Drilling Project/International Program of Ocean Drilling (DSDP/IPOD) have shown that inspection of borehole cores in the Southern Ocean and around Antarctica are necessary for reconstruction of the development of the Atlantic Ocean and for the understanding of the sedimentary deposition which is strongly affected by the palaeo-oceanographic processes. As the geological development of the Weddell Sea plays a key role for the reconstruction of the south-american and african part of the former supercontinent Gondwana, the Federal Institute for Geosciences and Natural Resources (BGR) has decided to conduct a synoptic geophysical survey in the eastern Weddell Sea and in front of the eastern Antarctic continental margin. This survey has been designed as a prearrangement for a larger "presite" program for preparation of future DSDP/IPOD sites. The main focus of the geophysical survey during the first leg of cruise BGR78 from 5th of January to 13th of February 1978 with M.S. EXPLORA has been put on the continental margin of the south-eastern Weddell Sea and eastern Antarctica between 20°E and 30°W and south of 67°S. Especially the lines BGR78-03 to BGR78-23 of seismic reflection measurements have been carried out in this region which were affected by heavy ice conditions at this time. Additionally, on 43 stations sonobuoy refraction measurements have been conducted.