Towards a Mechanistic Model for the Messinian Salinity Crisis: Tectonic Uplift Competing with Erosion along the Betic-Rifean Corridors
Both the timing and the processes involved in the Messinian Salinity Crisis (MSC) remain controversial. There is an agreement that the interplay between global sea level changes and the tectonic uplift of the connecting corridors in the Gibraltar Arc were the main control on the salinity crisis. But there is no full consensus, for example, on whether a kilometric drawdown ever took place, or when during the MSC would it have happened, or whether it may have occurred in multiple occasions intercalated by an equal number of floods refilling the Mediterranean. Two of the reasons behind these uncertainties are the absence of drillings that cross the entire evaporitic sequence in the deep basins and the lack of direct correlation between marginal and deep stratigraphy. I will focus on a third reason: the shortage for quantitative, process-based, mechanistic models that aim to account for the vast amount of multidisciplinary observations available on the MSC.
In this line, I will show forward models based on mathematical approaches to water-flow, erosion, salt precipitation, and climatic processes, in combination with an uplifting interoceanic seaway. The results show that seaway erosion by the Atlantic inflowing water allows a long-term connection of a few tens of meters between the Ocean and the Mediterranean by reaching a dynamic equilibrium with tectonic uplift. This imposes constraints on the timing and amount of drawdown expected for the first MSC stage. Furthermore, they suggest that the cyclicity observed in gypsum outcrops of that stage may be the result from harmonic coupling between Mediterranean evaporation, Atlantic inflow, and seaway erosion, predicting oscillations of the Mediterranean level of up to 500 m, and cycles of salt precipitation of 2-10 kyr, although this possibility calls for future independent assessment. More significant is the result that the predicted uplift rates required to block the inflow of Atlantic water are consistent with the present altitude of uplifted marine sediments (Iribarren et al., 2009; Babault et al., 2008) and with geodynamic models of a proposed lithospheric slab detachment under the Gibraltar Arc (Duggen et al., 2003; Wortel et al., 2004; Garcia-Castellanos & Villaseñor, 2011; Vergés & Fernàndez, 2012).
AAPG Search and Discovery Article #90161©2013 AAPG European Regional Conference, Barcelona, Spain, 8-10 April 2013