Potential Fossilized Sulfide-Oxidizing Bacteria in the Upper Miocene Sulfur-Bearing Limestones From the Lorca Basin (SE Spain): Paleoenvironmental Implications

Abstract

The sulfur-bearing limestones interbedded in the upper Miocene diatomaceous sediments (Tripoli Formation) of the Lorca Basin (SE Spain) are typified, as other Mediterranean coeval carbonate and gypsum deposits, by filamentous, circular and rod-shaped microstructures of controversial origin. These features have been interpreted both as fecal pellets of brine shrimps and/or of copepods, remains of algae or cyanobacteria and fossilized sulfide-oxidizing bacteria. To shed light on their origin, a multidisciplinary study including optical, UV and scanning electron microscopy, Raman microspectroscopy, and geochemical (carbon and oxygen stable isotopes) analyses has been carried out on three carbonate beds exposed along the La Serrata ridge. The different composition of the filamentous and circular objects with respect to the rod-shaped microstructures suggest that the former represent remains of bacteria, while the latter fecal pellets of deposit- or suspension-feeder organisms. Size and shape of the filamentous and circular microfossils are consistent with their assignment to colorless sulfide-oxidizing bacteria like Beggiatoa (or Thioploca) and Thiomargarita , which is further supported by the presence, only within the microfossil body, of tiny pyrite grains. These grains possibly result from early diagenetic transformation of original sulfur globules stored by the bacteria, which are a diagnostic feature of this group of prokaryotes. The development of microbial communities dominated by putative sulfide-oxidizing bacteria at Lorca was favored by hydrogen sulfide flows generated through degradation of organic matter by sulfate-reducing bacteria thriving in underlying organic-rich sediments.

Paratethys pacing of the Messinian Salinity Crisis: Low salinity waters contributing to gypsum precipitation?

“…Lin et al, 2016) or biologic (e.g. Bailey et al, 2009) oxidation of reduced sulfur compounds. The MSC gypsum and shale deposits contain ubiquitous large filamentous microfossils, interpreted initially as remains of algae (Vai and Ricci Lucchi, 1977), faecal pellets (Guido et al, 2007) or cyanobacteria (Panieri et al, 2010).…”

“…The MSC gypsum and shale deposits contain ubiquitous large filamentous microfossils, interpreted initially as remains of algae (Vai and Ricci Lucchi, 1977), faecal pellets (Guido et al, 2007) or cyanobacteria (Panieri et al, 2010). More recently they have been interpreted as remains of sulfide-oxidizing bacteria (SOB), based on the identification of sulfur-containing minerals possibly derived from the diagenetic transformation of elemental sulfur stored within cytoplasm (Dela Pierre et al, , 2015Andreetto et al, 2019). SOBs do not provide useful paleobathymetrical and salinity information, but they play a key role in the biogeochemical sulfur cycle by producing SO 2− 4 from the oxidation of reduced sulfur species [e.g.…”

“…H 2 S, S 2− ] (e.g. Bailey et al, 2009). The exact role of microbes in gypsum precipitation is still poorly understood, but potential additional sulfate input from SOB would result in super saturation being reached at lower levels of evaporation than shown in Fig.…”

Integrated isotopic and organic geochemical constraints on the depositional controls and source rock quality of the Neogene Kalamaki sedimentary successions (Zakynthos Island, Ionian Sea)

“…Moreover, the temperature drop in water column during that period can also favor the CaCO 3 dissolution. The change in seawater chemistry favored the predominance of specific eukaryotes and mostly prokaryotes (especially the versatile archaeal domain), which are tolerant to such environmental conditions (Natalicchio et al 2017(Natalicchio et al , 2019Dela Pierre et al 2014Perri et al 2017;Isaji et al 2019b;Andreetto et al 2019). Overall, the combination of such marked temperature changes, pressure drop due to water unloading, rapid burial by salt deposition, pressure increase during the subsequent water loading, and relative sea-level fluctuations (Fig.…”

Late Miocene evaporite geochemistry of Lorca and Fortuna basins (Eastern Betics, SE Spain): Evidence of restriction and continentalization

“…The Varied Mb (Tripoli Unit of Rouchy et al, ) up to 140 m thick, is mainly composed of marls with abundant diatomites, organic‐rich shales, and 7–8 nodular gypsum beds, up to 1 m thick, partly replaced in the centre of the basin by sulphur‐bearing carbonates (Andreetto, Dela Pierre, Gibert, Natalicchio, & Ferrando, ; Rouchy et al, ).…”