Precise ~(40)Ar/~(39)Ar dating of volcanic tuffs within the upper Messinian sequences in the Melilla carbonate complex (NE Morocco): implications for the Messinian Salinity Crisis

摘要

The Melilla carbonate complex (NE Morocco) is the only area of the Paleo-Mediterranean Sea where volcanic activity was present throughout most of the Messinian. ~(40)Ar/~(39)Ar dating of volcanic tuffs interbed-ded within the upper Messinian sedimentary deposits, known as the Terminal Carbonate Complex (TCC), yields accurate ages of paleoenvironmental and sea-level changes related to the Messinian Salinity Crisis. The new chronologic data (1) provide an average of 5.95-5.99 Ma for the base of the TCC, thus being synchronous with the onset of the Messinian Salinity Crisis, (2) demonstrate for the first time that the basal unconformity of the TCC does not represent a hiatus of long duration, (3) define a precise time line at 5.87 ± 0.02 Ma (2σ) corresponding to sedimentary rocks exhibiting a lateral transition between continental and marine deposits typical of the TCC and (4) yield evidence that emersion of the Melilla platform during deposition of the TCC is partly related to tectono-magmatic activity. An erosional surface, capping the TCC deposits in the Melilla basin, is related to the major Messinian Mediterranean drawdown. The duration of the hiatus, associated with this surface, is estimated to be at most 450 kyr, but is probably shorter.