A History of Sediment Lithofacies in the South Atlantic Ocean

Abstract

Changes in sediment types (lithofacies) and sediment components (carbonate, foraminifers, calcareous nannoplankton) in the South Atlantic Ocean from Early Cretaceous through Pliocene are portrayed on a series of palinspastic maps which graphically document the sedimentological succession as this ocean basin evolves. Determination of paleolithofacies is based upon smear slide analyses of dated sediment from the base of over 300 piston cores and dredges which provides a broad regional coverage and supplements DSDP drilling data (with Leg 39 results as the primary data base). These maps graphically illustrate the development of oceanic circulation, CCD levels, terrigenous sediment influx, and biological productivity concomitant with changing sea-floor physiography, cycles of transgression and regression, and the Tertiary climatic deterioration.

Oxygen and Carbon Isotope Record through the Oligocene, DSDP Site 366, Equatorial Atlantic

“…Evidently, relatively cold water that entered the Pacific was not able to penetrate into the Atlantic. This is consistent with circulation patterns in the Oligocene of the South Atlantic inferred by McCoy and Zimmerman (1977).…”

Geochemical Investigation of Sediments from the Brazil Basin and the Rio Grande Rise

“…For instance, perhaps a cold spell in South America during the Miocene (Kennett and Brunner, 1973;Barker et al, 1976) or a shift northwards of the hydrofront (Antarctic divergence) toward the southern part of the Brazil Basin (Barker et al, 1976;McCoy and Zimmerman, 1977) resulted in increased accumulation of amorphous SiO 2 . Enhanced Mn quantities in the lower portion of Hole 515A may be evidence of decreased sedimentation rates, as is the appearance of sharply oxidizing conditions in the upper portion of sediments.…”

Angola Continental Margin—Sites 364 and 365

“…This would have limited productivity, and thus the potential for an oxygen minimum. Instead a circulation system analogous to paired linked basins separated by high sills (such as the Balearic and Ionian basins in the Mediterranean, or the Mediterranean-Black Sea basins) seems more likely (Natland, this volume; McCoy and Zimmerman, 1977). 7) Sapropelic sediments at Site 364 contain evidence for mineral precipitation or diagenesis in waters of high salinities.…”