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Geological Society, London, Special Publications; 2007; v. 285; p. 179-190;
DOI: 10.1144/SP285.11
© 2007 Geological Society of London

Ancient basins

The Messinian ‘Vena del Gesso’ evaporites revisited: characterization of isotopic composition and organic matter

S. Lugli1, M. A. Bassetti2,*, V. Manzi3, M. Barbieri4, A. Longinelli3 & M. Roveri3

1 Dipartimento di Scienze della Terra, Università degli Studi di Modena e Reggio Emilia, Largo S. Eufemia 19, 41100 Modena, Italy (e-mail: lugli.stefano{at}unimore.it)
2 IUEM0-UMR, 6538 Place Copernic, 29280 Plouzanè, France
3 Dipartimento di Scienze Geologiche, Università di Parma, Parco Area delle Scienze 157/A, 43100, Parma, Italy
4 Dipartimento di Scienze della Terra, Università ‘La Sapienza’, Piazzale Aldo Moro, 00185 Roma, Italy
* Present Address: LEGEM, Université de Perpignan, 52 Avenue Paul Alduy, 66860 Perpignan, France

The ‘Vena del Gesso’ (Gessoso-Solfifera Fm, Messinian) is a 227 m-thick ridge along the western Romagna Apennines (Italy) consisting of up to 16 selenite cycles separated by shales and minor carbonate. The total organic carbon values of these deposits range between 0.087–0.016% (gypsum) and 3% (shales). Organic matter is dominated by black debris associated with continental debris. Algae and dynocysts are rare (<1%). The amount of amorphous organic matter is low but it may reach up to c. 40%. The 87Sr/86Sr of gypsum and carbonate vary from 0.708890 to 0.709024, yielding non-oceanic values with several exceptions that plot within error of coeval oceanic values only in the upper part of the section (from the 6° bed). The sulphur isotope composition of gypsum range between {delta}34S =+21.8 and +23.7{per thousand} and may represent precipitation of {delta}34S-enriched gypsum due to the fractionation effect or recycling of coeval gypsum with contributions of brine-sediment redox variations. The isotope values of carbonates show a large variability (–6.4<{delta}18O<+6.05{per thousand}; –14.68<{delta}13C<+2.5{per thousand}), suggesting a complex origin by mixing of marine and non-marine waters with a significant contribution of reduced organic matter. These data point to an evaporite basin dominated by continental waters which received significant phases of marine recharge in the upper part together with a marked facies change. Because seawater recharges and a similar facies change are present in other Messinian sections, it follows that we have new possible geochemical and facies markers to correlate the Lower Evaporites across the Mediterranean.