Stratigraphic Hiatuses in the Sedimentary Cover of the Ninetyeast Ridge

Abstract

The Ninetyeast Ridge is one of the longest structures in the World Ocean. Owing to the seismostratigraphic analysis, three seismic complexes are distinguished in the sedimentary cover of this ridge, lower subaerial—shallow-water (SC3), transition (SC2), and upper deep-water (SC1), and nine reflectors: 0, 0a, 1, 1a, 2, 3, 4, 5, and F. On the basis of the results of correlation of seismic sections with those of deepwater sites recording the entire period of formation of the sedimentary cover of the Ninetyeast Ridge (Late Cretaceous—Quaternary), several nondepositional hiatuses are distinguished. The following reasons for these hiatuses are proposed. The hiatus in the beginning of the Early Paleocene coincides in time with the general decrease in the World Ocean level and is recorded only within the northern part of the ridge. The first “soft” collision of the Indian and Eurasian plates, as well as Paleocene—Eocene Thermal Maximum (PETM), could have been a reason for the most long-lasting hiatus in the Early—Middle Eocene in the northern and central parts of the Ninetyeast Ridge. The hiatus in the Early Oligocene is also distinguished in these parts of the ridge and is likely associated with underwater erosion. The formation of the Antarctic Circumpolar Current (ACC) and the change in the hydrodynamic regime of the Indian Ocean could have been reasons for the hiatus in the Middle Miocene, which is traced in the sedimentary cover throughout the entire Ninetyeast Ridge.