Chronology of late Brunhes biostratigraphy and late Cenozoic disconformities in the Vema Channel (South Atlantic)

Abstract

The stratigraphic ranges of two planktonic foraminiferal species provide a useful biostratigraphic zonation for late Brunhes sediments of the subtropical South Atlantic (30°S). By comparison with oxygen isotopic stratigraphy in two cores and calcium carbonate stratigraphy in nine cores, the range of G. hirsuta extends from isotope stage 7 to the Recent ( t = 240,000 years B.P. to Present Day) and that of G. crassaformis from the late Pliocene to isotope stage 5 (120,000 years B.P.). This biostratigraphic zonation was utilized to demonstrate that for the last 130,000 years sediment accumulation changes between water depths of 2,940–4,235 m reflect the transition between Antarctic Bottom Water (AABW) and North Atlantic Deep Water (NADW) in the Vema Channel. The combination of the paleomagnetic stratigraphy and planktonic foraminiferal biostratigraphy in two other cores enabled the detection of two late Cenozoic disconformities in the Vema Channel. The late Pliocene disconformity is marked by a buried manganese oxide crust and associated winnowing of slope sediments. The intensification of bottom currents which produced the Mn-crust ceased in the middle of the Gauss Epoch (2.90 m.y. B.P.). The late Pliocene disconformity may be related to the initial build-up of Northern Hemispheric ice sheets and/or Southern Hemispheric cooling. The second disconformity extends from the late Miocene to the middle of the Gilbert Epoch (3.8 m.y. B.P.).