Hiatuses and Core Correlations

The study of six sediments cores from the Ioffe Drift area documented the reduced thickness and/or absence of biostratigraphic zones and the occurrence of several hiatuses. The multi-proxy biostratigraphic, magnetic susceptibility (MS), color reflectance and X-ray fluorescence (XRF) data from five of the six cores reported numerous long- and short-term stratigraphic gaps over the last ~3–4 Ma. The correlation of sediment records from the drift suggests that the most pronounced series of hiatuses, associated with enhanced Lower Circumpolar Deep Water (LCDW) flow intensity, occurred from 2.51/2.59 to ~1.9 Ma (i.e., the onset of the modern-type deep-water circulation in the South Atlantic). This interval of specific high-amplitude peaks representing abrupt changes in volume MS and chemical composition variation may well serve as a regional stratigraphic benchmark in future studies of deep-sea contourites. A temporary intensification of the LCDW flow, probably due to its increased production in the Antarctic, led to deep erosion, ultimately resulting in long-term hiatuses and hence contributing to the enormously compressed Upper Pliocene–Middle Pleistocene section of the drift. The interval from 1.47/1.6 to 0.81 Ma, embracing the Mid-Pleistocene Transition, contains the longest stratigraphic gaps, up to ~1 Ma in some cores. Comparison of the studied sediment records to DSDP Site 516 reveals the reduced thickness of all the recovered biostratigraphic zones and evidence of more frequent hiatuses in the Ioffe Drift than on the neighboring Rio Grande Rise, suggesting more vigorous contour currents in the former.