The precessional phase lag of Messinian gypsum deposition in Mediterranean marginal basins

The uncertainty of the phase relation between the forcing and sedimentary expression is yet unquantified, introducing a bias in tuning recurrent facies variations in the sedimentary record to the astronomical forcing. The identification of a phase lag between precession and the most recent sapropel in the Mediterranean demonstrates that astronomical forcing and its sedimentary expression are not always in phase. Gypsum deposition in Mediterranean marginal basins during the Messinian Salinity Crisis is also forced by precession-driven climate changes. In contrast to sapropel formation, which involves complex interactions of circulation and biogeochemistry, gypsum formation in such basins is primarily controlled by salinity. Using a simple box model to represent the Late Miocene Mediterranean, we examine the phase relation between gypsum deposition and precessional forcing. For a large range of settings model results show a consistent phase lag between the precessional forcing and salinity in the marginal and deep basins of the Mediterranean. On the basis of our quantitative modelling results we propose that in the astronomical tuning of the Messinian gypsum deposits, a phase lag of 3.3 kyr ± 2.6 kyr should be taken into account for cycles with a duration of 20 kyr. Accordingly, the astronomically tuned ages of the gypsum deposits become, on average, 3.3 kyr younger. In the anomalously short 14 kyr cycle that follows the onset of the Messinian Salinity Crisis the phase lag is smaller and within range of the other uncertainties of astronomical tuning.