Tag Archives: Tectonics

Let’s dry up a remnant ocean


Garcia-Castellanos, D. & Villasenor, A., 2011: Messinian salinity crisis
regulated by competing tectonics and erosion at the Gibraltar arc.
–Nature: Vol. 480, #7377, pp. 359-363 [doi: 10.1038/nature10651]

The Messinian salinity crisis1, 2 (5.96 to 5.33 million years ago) was
caused by reduced water inflow from the Atlantic Ocean to the Mediterranean
Sea resulting in widespread salt precipitation and a decrease in
Mediterranean sea level of about 1.5 kilometres due to evaporation3. The
reduced connectivity between the Atlantic and the Mediterranean at the time
of the salinity crisis is thought to have resulted from tectonic uplift of
the Gibraltar arc seaway and global sea-level changes, both of which control
the inflow of water required to compensate for the hydrological deficit of
the Mediterranean1, 4. However, the different timescales on which tectonic
uplift and changes in sea level occur are difficult to reconcile with the
long duration of the shallow connection between the Mediterranean and the
Atlantic5 needed to explain the large amount of salt precipitated. Here we
use numerical modelling to show that seaway erosion caused by the Atlantic
inflow could sustain such a shallow connection between the Atlantic and the
Mediterranean by counteracting tectonic uplift. The erosion and uplift rates
required are consistent with previous mountain erosion studies, with the
present altitude of marine sediments in the Gibraltar arc6, 7 and with
geodynamic models suggesting a lithospheric slab tear underneath the
region8, 9, 10. The moderate Mediterranean sea-level drawdown during the
early stages of the Messinian salinity crisis3, 5 can be explained by an
uplift of a few millimetres per year counteracted by similar rates of
erosion due to Atlantic inflow. Our findings suggest that the competition
between uplift and erosion can result in harmonic coupling between erosion
and the Mediterranean sea level, providing an alternative mechanism for the
cyclicity observed in early salt precipitation deposits and calling into
question previous ideas regarding the timing of the events that occurred
during the Messinian salinity crisis1.

– Mikko