The nature and distribution of Messinian erosional surfaces — Indicators of a several-kilometer-deep Mediterranean in the Miocene

Abstract

The deep-basin desiccation model for the origin of Messinian-age Mediterranean evaporites implies two basic assumptions: 1. (1) The evaporites were in part laid down under shallow-water conditions, with intermittent subaerial episodes brought about by evaporitic drawdown. 2. (2) Some of the depressions in which the evaporites were deposited were already several kilometers deep during Messinian time, and hence, the general configuration of these basins predated, and was essentially independent of the salinity crisis. The first assumption has been more or less accepted by the scientific community as a consequence of the discovery of supratidal to intertidal features in the evaporites, whereas there has been less acceptance of the second assumption. The arguments on which the second assumption was first formulated, were multiple and included: (a) the presence in seismic reflection profiles of large pre-salinity-crisis depocenters with sediment-distribution patterns not substantially different from those of the post-salinity-crisis strata; (b) systematic changes in the evaporitic facies along basin-slope transects indicative of existing paleorelief; and (c) the occurrence of continental-rise and abyssal-plain-type deposits in both pre- and post-salinity-crisis successions. New attention is herein focused on Messinian-age erosional surfaces created by evaporitic drawdown of an isolated Mediterranean Sea. These erosional surfaces are detected as discordances in seismic reflection profiles. The discordances can be traced from the subsurface of the present coastal plains and continental shelves to the subsurface of the modern abyssal plains and show entrenchment into the underlying strata. On the passive-type continental margins, like those of the Balearic Sea and those in the southeastern corner of the Levantine Sea, the seaward gradients of the erosion surfaces, corrected for post-Messinian isostatic sediment loading and compaction and adjusted for regional subsidence, permit the calculation of a former relief between the pre-salinity-crisis shore-line and basin center of more than 2.5 km for the western Mediterranean and more than 3.0 km for the eastern Mediterranean.