History of the Ioffe Drift

The comprehensive analysis of a large dataset of seismic, lithological, geochemical and micropaleontological data has shed light on the Ioffe Drift’s origin and evolution. Although the drift’s prehistory still has blank spots, it is suggested that oceanographic processes may have affected the formation of this depositional body since its earliest stage. The drift’s formation probably began over the volcanic ridge in the Florianopolis Fracture Zone just after the ridge’s formation approximately 95–80 Ma ago. Variations in bottom-current intensity in response to regional and global paleoceanographic and paleoclimatic changes are most clearly imprinted in the seismic structure of the upper 80 m of drift deposits and in sediment records recovered by cores (down to 7 m below sea floor (mbsf)). The drift’s contourite formation underwent alternating phases of erosion caused by the intensification of bottom currents, probably followed by prevailing pelagic settling upon weakening of the bottom currents. The most thoroughly studied history of the Ioffe contourite drift, the Late Pliocene to Recent, was interrupted by multiple erosional hiatuses resulting from the activity of the Lower Circumpolar Deep Water (LCDW) bottom current during the intervals from 2.51/2.59 to 1.9 Ma and from 1.47/1.6 to 0.81 Ma. The numerous hiatuses that detached layers of calcareous contourites are an essential characteristic of the Ioffe Drift deposits, as well as layered sedimentary structures expressing effects of different bottom-currents velocities on the contourite deposition.