Astronomical tuning as the basis for high resolution chronostratigraphy: the intricate history of the Messinian Salinity Crisis

Abstract

The Messinian Salinity Crisis (MSC) in the Mediterranean resulted from a complex interplay between tectonic gateway closure and climate evolution. The climate factor, in turn, can be separated into two components, one associated with dominantly precession controlled regional climate change and the other with dominantly obliquity related glacial cyclicity. The influence of these climate changes occurred superimposed on a long(er)-term tectonic trend. Discrimination into the various forcing factors only recently came within reach due to the development of an integrated high-resolution stratigraphy and astronomically tuned age models, both for the Messinian (pre-)evaporite successions in the Mediterranean and for benthic oxygen isotope records from the open ocean. The application of these time scales in combination with a high-resolution integrated stratigraphic approach showed that 1) the onset of the MSC proper at 5.96 Ma is not related to glacio-eustatic sealevel lowering but its timing can best be attributed to the influence of the 400-kyr eccentricity cycle on regional climate superimposed on a tectonic trend, 2) the main desiccation phase between the Lower and Upper Evaporites coincides with the twin peak glacials TG12-14 suggesting a glacio-eustatic control, 3) the beginning of the Upper Evaporites and Lago Mare phase coincides with the onset of the major deglaciation following peak glacial TG 12, indicating that glacio-eustatic sealevel rise played a role, 4) the Pliocene flooding of the Mediterranean is not related to a glacioeustatic sealevel rise, and 5) the evaporite cycles are controlled by precession induced regional climate changes rather than by obliquity forced glacio-eustatic sealevel change. Our astronomical age model for the Mediterranean Messinian is consistent with 40Ar/39Ar ages of ash layers intercalated in Messinian successions in the Mediterranean. However, the intercalibration between astronomical and 40Ar/39Ar dating has to be taken into account for a direct comparison of these ages.