DEEP-WATER CONTOURITES OF THE SOUTHWESTERN ATLANTIC AS ARCHIVES OF PALEOCEANOGRAPHIC AND PALEOCLIMATIC INFORMATION
E.V. Ivanova, D.G. Borisov, I.O. Murdmaa, E.A. Ovsepyan
Shirshov Institute of Oceanology, Russian Academy of Sciences, Moscow, Russia
Keywords: Contourite system, hiatus, bottom current, Pliocene, Pleistocene, erosion, accumulation, drift, sortable silt, Antarctic Bottom Water
Abstract
This article presents a review of the results from a comprehensive study and dating of contourite deposits in the southwestern Atlantic. It focuses on identifying the sources and transport processes of sedimentary material in the context of Pliocene-Quaternary environmental and climatic changes. The primary emphasis is on research conducted by the Laboratory of Paleoceanography at the Shirshov Institute of Oceanology RAS in collaboration with colleagues over the past decade. The contourite systems examined include those on the continental slope of Argentinian Patagonia, the Santa Catarina and São Paulo plateaus, the Ioffe Drift, and the gravitite-contourite system at the base of São Tomé Seamount. The identification of these systems is based on a comprehensive set of seismoacoustic, lithological, and geochemical data, including variations in magnetic susceptibility. Diagnostic features that distinguish contourites from other types of bottom sediments are discussed. The age of the sediments is determined using biostratigraphy or oxygen isotope stratigraphy and corroborated by accelerator mass spectrometry radiocarbon dating for the last 50,000 years. It is demonstrated that the primary agent in the formation of these contourite systems is the erosional and depositional activity of bottom (along-slope) currents of Antarctic origin, which are a key component of the Atlantic meridional circulation and the global ocean conveyor belt. Consequently, contourite systems preserve a record of the geological and climatic history of the region. Among all the systems considered in this study, the Ioffe Drift contains the oldest sediments, which have accumulated over the last 3.2 Ma. This interval corresponds to the period of modern-type paleoceanographic variability that followed the closure of the Panama Seaway. For the other systems, the sediment cores characterize the glacial-interglacial stages of the Late Quaternary and the associated changes in sea level, climate, and bottom-water circulation.
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