Conference:
International Meeting of Sedimentology, Toulouse, 10-12 October 2017, Page 212.
https://ims2017.sciencesconf.org
Authors:
Speranta-Maria Popescu, Jean-Pierre Suc, Nadia Barhoun, Mihaela Carmen Melinte-Dobrinescu, Maria Angela Bassetti, Martin J. Head, Christian Gorini, Jean-Loup Rubino.
Abstract:
The Messinian uppermost sediments and the Zanclean lowermost ones from nine DSDP-ODP sites in the Western Mediterranean (from the Alboran Sea to the Tyrrhenian Sea) have been analysed at high sampling resolution for calcareous nannofossils, planktonic foraminifers, ostracods, dinoflagellate cysts and pollen grains. Biostratigraphy is specified by the occurrence of microplankton markers, especially by the first occurrence of Ceratolithus acutus (5.35 Ma) and foraminifers indicating the base of the Zanclean (Sphaeroidinellopsis acme at 5.33 Ma). This study provides detailed information on the paleoenvironmental conditions of deposition of the Upper Evaporites (i.e. the Upper Unit, UU), which include some halite layers.
UU deposited in a continuous marine setting but in a relatively shallow context according to the poor assemblage of calcareous microfossils (foraminifers and nannofossils) and relatively near to the coastline according to the dinoflagellate cyst assemblage. Pollen flora, rich in herbs and particularly halophytes, also supports a coastal paleoenvironment. It is clear that the Western Mediterranean Basin received a continuous influx of oceanic waters during the UU deposition. A similar process may be considered for the deposition of the thick underlying Mobile Unit.
Several samples are rich in Paratethyan dinoflagellate cysts, displaying successive intrusions of brackish waters from the Paratethys, known as Lago Mare episodes. Such episodes are also characterized by dry climatic conditions, that discards the hypothesis of humid phases often proposed to explain a Lago Mare event. In fact, there were three Lago Mare events: the oldest one at the end of the first step of the Messinian Salinity Crisis (evaporites in the peripheral basins) just before 5.6 Ma, the second one at the end of the second step of the crisis (evaporites in the central basins) just before 5.46 Ma, the last one just after the complete marine reflooding of the Mediterranean Basin just after 5.46 Ma. The first and third Lago Mare episodes are shown to result from high sea-level exchanges between the Paratethys and the Mediterranean. The second Lago Mare episode may have been caused by the collapse (by erosion) of a segment of the Hellenic Arc, which could have released Paratethyan waters probably stored within the isolated Aegean Basin during the peak of the crisis.