Two modes of gypsum replacement by carbonate and native sulfur in the Lorca Basin, SE Spain

Organoclastic sulfate reduction and bacterial sulfide oxidation have been suggested to explain the formation of authigenic carbonate native sulfur replacing gypsum in Lorca Basin, Spain. To gain more insight into nature this replacement, two types sulfur-bearing (laminated brecciated) from late Miocene Basin were studied. Petrographic observations revealed that a laminated consists clay-rich dolomite-rich laminae with pseudomorphs after gypsum. Positive δ 18 O values (δ = 2.6‰) lipid biomarkers halophilic archaea (e.g., extended archaeol) suggest under hypersaline conditions. Bacterial reduction, evidenced by such as iso -C 15 , 16 17 fatty acids, produced hydrogen inducing abiotic organic compounds. Gypsum likely dissolved due undersaturation low content carbonate-associated (3,668 ppm) 34 S-enriched S 22.4‰), reflecting limitation. Such S-enrichment implies limited fluid flow, which probably restricted supply molecular oxygen required for through sulfide. Alternatively, sulfate-reducing bacteria may mediated directly stress response environmental The calcite brecciated carbonates is post-depositional alteration. Negative −1.5‰) tenfold decrease (752 dissolution subsequent precipitation meteoric water. Relatively S-depleted 13.1‰) leaves it ambiguous whether water influx could supplied sufficient In case carbonate, methanogenesis, anaerobic methane, apparently secondary minerals indicated 13 C-depleted representative respective metabolisms. This study reveals conditions timing replacement are variable–taking place 1) during or shortly deposition 2) significantly sedimentation–and suggests methanogens addition methanotrophic be involved mineral-forming processes sedimentary subsurface.