Late quaternary sedimentation rate variations on the Mediterranean Ridge, as results from the 230Th excess method

Abstract

Average sedimentation rates of about 2 cm/1000 y were determined in four deep-sea cores from the Mediterranean Ridge, by means of the Io excess method. Detailed analysis of the results from cores 17 M 17 and 22 M 48 from the Ionian Sea indicates that the deposition rate during the last cold period (∼6 cm/1000 y) was by a factor of 3 higher than during preceding climate cycles. Consequently, the hitherto discrepancy between the sedimentation rate estimations derived from extrapolation of 14C-ages and those established with magnetic reserval is explained. Although climatically controlled changes of the sedimentation rate make the exact age determination of individual sapropel layers difficult, a correlation of the climatic δ 18O curves from the Mediterranean and the generalized climatic curve is possible, at least up to about 250,000 B.P. (warm stage 7). The correlation proves, the correctness of Emiliani's (1955), Ryan's (1972) and Cita et al.'s (1977) interpretations of the Late Quaternary climatic sequences in the Eastern Mediterranean sediments. A comparison to the Nile Cone area suggests the basin-wide range of the climatically induced time synchronous variations of the sedimentation rate. Sea-level oscillations are proposed as one of the most important factors controlling the deposition rate.