Home – Home – Jornals – Russian Geology and Geophysics 2015 number 7

On the basis of the author’s data on the composition of sediments and seismic cross sections, together with literature data, the bottom topography was described and the main structural features of the top 10-100 m thick sedimentary sequence in the Southwestern Atlantic (Brazil Basin) were identified. The presence of a heavy northward flow of Antarctic bottom water (AABW) and its active erosive activity were confirmed. The AABW caused the erosion or redeposition of red pelagic clays and hemipelagic clays, which accumulated in the Brazil Basin in the Holocene and Pleistocene; the clays contain abundant redeposited Pleistocene diatoms and Neogene and Paleogene discoasters. In most of the sediment columns of the Brazil Basin, the red pelagic clays are of Pleistocene age. Contourites and sandy microbeds have been found in the sediments at the foot of the continental slope of South America; this is the effect of the Deep Western Boundary Current on the ocean floor. The AABW transfers Antarctic diatom species along the continental slope of South America to 10º-5º S. The presence of the Equatorial Midocean Channel with a relative depth of 149 m in the western pelagic equatorial part of the Atlantic was confirmed, and new channels, such as Vavilov and Akademik Ioffe, have been found. The AABW flows northward along the Equatorial Mid-Ocean Channel. Apparently, the Akademik Ioffe Channel is not a proper mid-ocean channel. At 20º S (at a depth of 5000 m), Pleistocene diatomaceous ( Ethmodiscus rex ) ooze containing up to 74% amorphous SiO ₂ was detected. On the Amazon-Mid-Atlantic Ridge profile, the AABW flows into the Guyana Basin through only one valley of the Nara Plain, with a depth of 4620 m. Near the Ceara Rise and on the Amazon Fan, no geologic traces of the AABW flow into the Guyana Basin were found. Near the Rio Grande Rise, the AABW might have appeared in the Eocene. The formation of the Vema Channel, which separates the Rio Grande Rise from South America, also began at that time. The AABW flows were the heaviest before the largest glaciations (particularly at isotopic stages 7/6 and 3/2).