EGU2020-4533
https://doi.org/10.5194/egusphere-egu2020-4533
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

The geochemical riddle of Mediterranean low-salinity gypsum deposits

Giovanni Aloisi1, Marcello Natalicchio2, Laetitia Guibourdenche1, Antonio Caruso3, and Francesco Dela Pierre2
Giovanni Aloisi et al.
  • 1Institut de Physique du Globe de Paris, Paris, France (aloisi@ipgp.fr)
  • 2Dipartimento di Scienze della Terra, Università di Torino, 10125 Turin, Italy
  • 3Dipartimento di Scienze della Terra e del Mare, Università degli Studi di Palermo, 90123 Palermo,Italy

Large deposits of gypsum accumulated in the marginal basins of the Mediterranean Sea during the Messinian Salinity Crisis. These form the marginal portions of the Mediterranean Salt Giant (MSG) that also occupies the deep, central Mediterranean basins. Although the marine, evaporitic origin of the MSG is undisputed, the analysis of gypsum fluid inclusions and of gypsum-bound water (d18OH2O and dDH2O) suggest that marginal basin gypsum formed from low- to moderate-salinity water masses (5 - 60 ‰), rather than from high-salinity brines (130 - 320 ‰), as expected during the evaporation of seawater.  The formation of low-salinity gypsum poses a fundamental geochemical problem: how can gypsum saturation conditions be met in marginal basins if evaporation does not concentrate marine water to high salinity? In other words, can gypsum saturation be attained by adding Ca2+ and/or SO42- ions rather than by extracting water? We are exploring two geochemical scenarios to explain this phenomenon: (1) the addition of Ca2+ and SO42- to marginal basins by continental runoff, and (2) the non-steady state addition of SO42- to marginal basins via the biogeochemical oxidation of reduced sulfur. Both scenarios may lead - at least theoretically - to the decoupling of saturation state from salinity that is suggested by gypsum geochemical signatures.

How to cite: Aloisi, G., Natalicchio, M., Guibourdenche, L., Caruso, A., and Dela Pierre, F.: The geochemical riddle of Mediterranean low-salinity gypsum deposits, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4533, https://doi.org/10.5194/egusphere-egu2020-4533, 2020

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