Abstract
AbstractRecent studies on the genesis of sedimentary native sulfur deposits indicate diagenetic mid‐low temperature Bacterial Sulfate Reduction (BSR) as the main process, involving organic compounds (kerogen/hydrocarbons), bacterial colonies and gypsiferous rocks. In the peri‐Mediterranean area (Southern Spain, Sicily, Northern Apennines, Israel), the main sulfur accumulations are always associated with late Miocene sulfates and organic‐rich successions encompassing the Messinian salinity crisis (MSC). In particular, the Messinian successions of the Apennine‐Adriatic foreland basin system, due to a large amount of high‐resolution stratigraphic data, represent a perfect case study for understanding the diagenetic conditions controlling the development of the BSR process during sedimentary basin evolution. In this work, thermal models performed in three sub‐basins in a sector of the Northern Apennines comprised of the Sillaro and Marecchia rivers (Italy), calibrated by means of organic and inorganic geothermometers, indicate a general thermal immaturity of the studied successions attained as a result of a constant heat flow similar to the present day one (ca. 40 mW/m2) since Late Tortonian and lithostatic loads between 615 and 1,710 m depending on different sub‐basins. These results suggest that the MSC deposits experienced maximum temperatures between about 39°C and 65°C. Temperatures derived from thermal models have been used to constraint occurrence of the diagenetic BSR associated with evaporitic deposits providing thermal constraints in sulfur genesis as well as new useful thermal‐constraints for basin analysis studies.
Highlights
Worldwide economically exploited sedimentary native sulfur is mainly associated with large evaporitic deposits
Paleo-thermal data obtained from the thermal modelling of threebasins of the Northern Apennines provided qualitative and quantitative information on the triggering conditions needed to form native sulfur from evaporites through Bacterial Sulfate Reduction (BSR) in both local and regional contexts
Considering the minimum paleo-temperature (55°C) reached by the organic-rich shale (ORS)/Foraminifera Barren Interval unit (FBI) interface, where native sulfur developed (Giaggiolo-C ella, Sapigno and westernmost portion of Vena del Gesso sub-basins), these conditions are enough for organic matter degradation and generation of organic compounds necessary for BSR
Summary
Worldwide economically exploited sedimentary native sulfur is mainly associated with large evaporitic deposits. Many authors consider the diagenetic Bacterial Sulfate Reduction (BSR; Figure 1) as the main process for the generation of sedimentary sulfur from evaporites in foredeep-foreland geological settings (Davis & Kirkland, 1970; Feely & Kulp, 1957; Manzi et al, 2011; Peckmann et al, 1999; Rouchy et al, 1998; a detailed description of this process is reported in the supplementary information). Decima et al, 1988; Dessau et al, 1962; Ziegenbalg et al, 2010), the geological conditions necessary to generate BSR-related native sulfur deposits have never been defined in detail. Paleotemperature conditions have been defined only experimentally with no further constraint that can be applied to natural cases (Machel, 2001 and references therein)
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