A reconstruction of late Miocene Mediterranean circulation patterns using benthic foraminifera

Abstract

Extensive research on the late Miocene Mediterranean has solved a number of questions concerning the development of the area, but questions remain on, for instance, the Mediterranean water circulation patterns. Knowledge of, preferably quantitative, oxygen contents of water masses could be of help to reconstruct paleo-circulation, and understand how this contributed to the development of the Mediterranean Messinian salinity crisis (MSC). Bottom-water oxygenation is usually estimated qualitatively, or semi-quantitatively at best, from abundances of infaunal benthic foraminifera, from stable carbon isotope data, or redox-sensitive elements. We present data from six Mediterranean land sections and one section located at the Atlantic side of the Rifian corridor, as an Atlantic reference location. We introduce a semi-quantitative reconstruction of oxygen levels at the sediment–water interface employing a simple index that operates on a scale from 1 (low oxygen) to 5 (normal to high oxygen). Using this method, we present a tentative reconstruction of the Mediterranean water circulation in the period preceding the continuous development towards the MSC, which started at 7.17 Ma. We found that during the late Miocene an anti-estuarine circulation was likely, quite comparable to the modern pattern. Deep-water formation appears to have existed in the central northeastern part of the basin. Around 7.2 Ma constriction of the Rif Corridor (Morocco) led to restricted exchange of Mediterranean and Atlantic water masses, a reduction of the deep circulation, and decreasing bottom water ventilation. Deep-water formation weakened and the Mediterranean hydrography changed thoroughly, eventually contributing to the development of the MSC.