Sedimentation Rates in Neogene Deep-Sea Sediments from the Mediterranean and Geodynamic Implications of Their Changes

Abstract

Sedimentation rates calculated for Mediterranean deep-sea sediments predating the onset of the salinity crisis range from 2.5 to 9 cm/1000 years. Accumulation rates for the Messinian age evaporites are highly variable and likely to be excessive by more than one order of magnitude (i.e., more than 1 km/m.y.). Sedimentation rates calculated for the Pliocene/Pleistocene range from more than 30 cm/1000 years (Pleistocene of the Nile Cone area) to less than 0.1 cm/1000 years (early Pliocene of the Antalya Basin), the average value (including minor hiatuses) being 5.9 cm/1000 years.The anomalously low rate of sediment supply in Pliocene times to locations which at the present day are basinal settings is interpreted as a consequence of a rapid eustatic sealevel rise, which accompanied the marine flooding of a depressed water body at the close of the late Miocene salinity crisis. The subsequent increase in the Quaternary to values equivalent to those attained prior to the salinity crisis is an indication that the modern surfaces of deposition are now in equilibrium.Tectonically controlled facies changes are consistently accompanied by detectable changes in rates of sediment accumulation, as recorded in the Pleistocene of the Levantine and Antalya basins.

Transient erosion in the Valencia Trough turbidite systems, NW Mediterranean Basin

“…Incision in the Valencia Trough may have originated under subaerial conditions during the Messinian salinity crisis (Cita et al, 1978;Alonso et al, 1995;Maillard et al, 2006). Some of the submarine valleys draining into the Valencia Channel are also of Messinian origin, though there is not a one to one relationship between Messinian canyons and present-day canyons (e.g.…”

Changing perspectives in the concept of “Lago-Mare” in Mediterranean Late Miocene evolution

“…The similarities between the Paratethys and the Mediterranean faunas during this period led to the terms "Paratethyan" or "Caspi-brackish" and this leads authors (Hsü et al, 1977;Hsü, 1978;Cita et al, 1978b), to propose these faunas emigrated from the Paratethys into the Mediterranean via aquatic ways. These assemblages indicate very shallow brackish to fresh water environments as shown by many authors: molluscs such as Congeria, Melanopsis, Melanoides or Limnocardium, live around a depth of 0 to 10 m, and tolerate only a very slight salinity.…”

Heat flow and tectonics of the Ligurian Sea basin and margins

“…Due to the steep basement interface, the total sediment thickness is much thinner on the margins than in the deep basin. The reduced thickness is also due to the displacement of up to a kilometer of drift Miocene sediment during the Messinian salinity crisis (Ryan, 1976;Ryan and Cita, 1978;Cita et al, 1978;Steckler and Watts, 1980;Bessis, 1986). The post-Messinian subsidence rates are probably of the same order as the pre-Messinian rates (Steckler and Watts, 1980;Bessis, 1986;Ryan, 1976).…”

“…Erosional products of the Messinian Event are found on some margins and appear as a sediment wedge beneath some margins Cita et al, 1978). The early Pliocene is condensed throughout most of the basin for the following reasons : 1) the Pliocene flooding of the basin trapped sediment on the sediment-deficient helves, 2) the sediment supply decreased as a result of high erosion rates during the Messinian, and 3) contour currents removed sediment and caused occasional hardground deposits.…”