Abstract
During the Messinian salinity crisis (MSC, 5.96-5.33 million years ago (Ma)), Atlantic–Mediterranean connections became stepwise restricted and interrupted. Massive evaporites were deposited in the Mediterranean Basin, which - after water levels dropped ~1km (5.59-5.5 Ma) - was partially refilled with non-marine waters. The MSC deposits are subdivided into Lower Evaporites
... read more
of the marine phase (5.96-5.59 Ma) and Upper Evaporites of the shallow water environment (5.5-5.33 Ma), which is especially characterized by non-marine (Lago Mare) beds. Inflow of oceanic water through the Gibraltar gateway at the onset of the Pliocene restored marine conditions. This Ph.D. study focussed on the paleoceanographic and environmental response of the circum-Mediterranean to deteriorating Atlantic–Mediterranean and intra-Mediterranean connections and to possible opening of a Mediterranean–Paratethys gateway in the MSC interval. To constrain the timing of the latter, correlation between Mediterranean and Paratethys was achieved through establishing reliable age models on both sides of the gateway. Magnetostratigraphic and biostratigraphic data from the Dacic Basin (Romania) show that the upper half of the Messinian corresponds to the Pontian of the Paratethys. Data from the Strimon Basin (Greece) indicate that a shallow marine to brackish-lacustrine transition occurred at 6.3 Ma. Along the adjacent Orphanic Gulf, shallow marine clastics and gypsum beds (correlated to the Lower Evaporites) are followed by a brackish/fresh water unit that may reflect the desiccation event and Upper Evaporites. The Miocene–Pliocene boundary is locally marked by a transition to marine conditions in a relatively deep basin; in the Strimon Basin a shallow marine interval interrupted fluvio-lacustrine conditions. Reconstruction of the early Pliocene paleobathymetry of Milos and Aegina (Greece) shows that rapid subsidence occurred associated with late-orogenic extension in the Southern Aegean, 1-1.5 million years before the onset of volcanism that formed these islands. The relative sea level rise post-dated the MSC by 0.3 million years. Upper Miocene and lowermost Pliocene sediments on Milos and Aegina possibly represent the paleoenvironment of a Mediterranean–Agean threshold region, which possibly was too shallow to record the MSC events. An integrated, high-resolution stratigraphy study of the Loulja sections (Atlantic coast, Morocco) results in a tuned open ocean benthic isotope record that permits comparison of the glacial history to Mediterranean paleoenvironmental events of the MSC. Analyses of nannofossils and dinoflagellates from the Lower and Upper Evaporites and from the Orphanic Gulf, Strimon, and Dacic basins reveal that Atlantic water entered the Mediterranean during the Lower Evaporite interval, but that the Mediterranean and tributary Paratethys remained isolated throughout the desiccation and Upper Evaporite interval. The MSC onset had no direct glacio-eustatic origin, but resulted from the climatic effect of the eccentricity cycle superimposed on the regional tectonic trend of restriction of the Atlantic gateway; two successive glacials controlled the isolation and desiccation phase. Subsequent deglaciation corresponded to the onset of the Upper Evaporites. The Miocene–Pliocene boundary concurred with a minor precession-related shift to lighter benthic isotope values; the Mediterranean flooding was therefore related to tectonics or headward fluvial erosion rather than to a major glacio-eustatic sea level rise.
show less
