Morpho-Mineralogical and Bio-Geochemical Description of Cave Manganese Stromatolite-Like Patinas (Grotta del Cervo, Central Italy) and Hints on Their Paleohydrological-Driven Genesis

Caves are dark subsurface environments with relatively constant temperatures that allow studying bio-mineralization processes and paleoenvironmental or climate changes in optimal conditions. In the extreme oligotrophic cave environment, manganese patinas having stromatolite-like features uncommon. Here we provide first detailed mineralogical, geochemical, microbiological investigation of fine-grained poorly crystalline MnFe wall formed a deep-cave environment Italy. These mineralizations, about 3 mm thick, consist an alternation Mn-layers Fe-lenses. We show microbial communities' composition is dominated by Mn-oxidizing bacteria, such as Bacillus , Flavobacterium Pseudomonas . Our multidisciplinary investigation, integrating data from different analytical techniques ( i.e., optical microscopy, SEM-EDS, ?XRF, XRPD, FT-IR, Raman spectroscopy, DNA sequencing), revealed peculiar chemical, biological features: 1) A cyclical oscillation Mn Fe along growth patinas. propose this represents shift between oxic suboxic conditions related to phases occurring during paleo-flood events; 2) typical spatial distribution mineralogy oxidation state Mn, bacterial imprints, detrital content, morphologies Mn-layers. controlled local hydraulic regime paleo-floods, which, turn, directly morphology surface. Under less turbulent conditions, combination clay mineral catalysis produced vernadite, poor-crystalline phyllomanganate low average branched columnar morphologies. On other hand, under more sedimentation minerals development both inhibited. lower rate 2+ favored formation todorokite and/or ranciéite, two compounds high flat-laminated