Deep-water changes: the near-synchronous disappearance of a group of benthic foraminifera from the Late Miocene Mediterranean

Benthic foraminiferal and geochemical data from the Monte del Casino sectio n in northern Italy are employed to reconstruct the sequence of events prec eding the Late Miocene Mediterranean salinity crisis. We evaluate the effec ts of eustatic sea-level changes and tectonic events, affecting the Atlanti c-Mediterranean connections. Changing benthic foraminiferal assemblages rec ord changes in the deep-water environment, that can be explained by progres sive isolation of the Mediterranean basin. The results of the analyses of s table oxygen- and carbon isotopes and redox-sensitive elements are in line with the benthic faunal trends. At 7.16 Ma, a first major step in isolation of the basin is indicated by the nearly simultaneous disappearance of a gr oup of deeper-water benthic species usually found in middle to lower slope environments. At the same time, stable isotopes and redox-sensitive element s indicate cooling and decreasing bottom water oxygenation. After 6.8 Ma gr adual development of water-mass stratification, probably accompanied by inc reasing bottom-water salinity, is indicated by all proxies. The cyclic patt ern of homogeneous and sapropelitic sediments in the section is related to astronomical parameters, and allows a detailed correlation with Mediterrane an sections at considerable geographic distances. We compared the benthic f oraminiferal faunas with those from the Metochia section (Gavdos, Greece), deposited at a similar water depth (similar to 1000 m), to find that the be nthic foraminifera at both sites indicate a similar, synchronous paleoenvir onmental development. All proxies indicate that the onset of the Late Mioce ne Mediterranean salinity crisis dates back to the earliest Messinian. The development of the Mediterranean basin toward an evaporite trap is a result of interactions between a 400-kyr eccentricity related climatic effect sup erimposed upon gateway dynamics at the Atlantic-Mediteranean connections. B enthic foraminifera accurately record the steps in increasing isolation of the Mediterranean basin. (C) 1999 Elsevier Science B.V. All rights reserved .