Late Messinian to Early Pliocene paleoenvironmental changes in the Melilla Basin (NE Morocco) and their relation to Mediterranean evolution

Abstract

Three major paleoenvironmental changes have been recognized during the late Miocene to Early Pliocene in the Melilla Basin (Northeastern Morocco) and compared with the regional events that affected the Mediterranean hydrology during this crucial period. The first change was the definitive conversion of the restricted marine conditions that prevailed since the end of the reef carbonate complex into lacustrine environments; this occurred around 5.8 Ma which is earlier than in the rest of the Mediterranean where the Lower Evaporites were still forming. These lacustrine settings display great similarities with the Lago-Mare environments that started in the Mediterranean during the deposition of the Upper Evaporites and climaxed during the latest Messinian. The second change corresponds to a long period of subaerial exposure that caused a widespread erosional surface; this resulted in a deep paleovalley, which truncates the Messinian sedimentary succession of the deeper southwestern part of the basin. This event postdates a lava flow dated at 5.77 Ma and confirms the importance of the latest Messinian erosional event. The third change was the infilling of this topography by marine sediments when the basin was rapidly reflooded in Early Pliocene. The lack of evaporites indicates that the Melilla Basin did not experience the Messinian Salinity Crisis. This could be explained either by the drainage of the brines towards the deeper South Alboran Basin or rather by an early dilution of the basin due to local excess of continental water inputs while most of the other Mediterranean basins evolved at the same time into evaporitic settings. These data confirm that the Rifian gateway was completely closed, thus, preventing Atlantic water inputs in the Mediterranean during the whole evaporitic deposition and the Lago-Mare episode. Such an evolution fits well with the history of depositional environments in the Alboran domain where evaporites are poorly developed and the Messinian is mainly represented by an erosional surface.