Environmental reconstruction of Ain el Beida (Atlantic site of the Rifian Corridor, Morocco) during the first stages of the Messinian Salinity Crisis using benthic foraminifera

Abstract

Studies show that water exchange between the Mediterranean Sea and Atlantic Ocean must have occurred during the first stage of the Messinian Salinity Crisis (MSC). However, the scale and location of this exchange is poorly understood. Benthic foraminiferal assemblages of the Ain el Beida section are therefore studied to expose the bathymetric history and environmental conditions on the Atlantic side of the Rifian Corridor during the first stages of the MSC. In addition, studies suggest that the cyclic alternations of red and light beige marls of the Ain el Beida section are related to the alternations of sapropels and marls of Mediterranean sections. The benthic foraminiferal assemblages of this study are used to evaluate this relation. Benthic foraminifera are used as proxy because they accurately record changes in the environment. The benthic assemblages show a clear astronomical signal related to the cyclic alternations of red and light beige marls. They indicate lowered oxygen levels and enhanced organic flux during red marl formation. The light beige marls are associated with reoxygenation. The red marls are linked to Mediterranean sapropels, but the reduction in oxygen levels was not as extreme as during sapropel formation. The distribution of the species U. pigmea indicates coastal upwelling during red marl formation. The study demonstrates that the perceived reduction in vertical circulation during red marl formation is best explained by increased fluvial run-off and precipitation instead of Mediterranean outflow. The paleodepth reconstruction demonstrates a relatively deep and stable interval during the first stage of the MSC. A shallowing of 200-300 m occurred during the extreme second stage of the MSC. The benthic assemblages of the Ain el Beida do not show evidence for Mediterranean outflow during the first stages of the MSC. However, Mediterranean outflow to the Rifian Corridor during the first stage of the MSC cannot be excluded.