Biomineralization is an important process by which living forms induce precipitation of minerals that, in normal physico-chemical conditions and absence of any biological contribution, tend to form slowly due to low kinetics of reaction. The aim of this work is the study of biomineralization events under two different environmental settings: i) a hydrothermal area ("Specchio di Venere" lake) at the volcanic island of Pantelleria and ii) an area in the Strait of Sicily, adjacent to faults of the Scicli fracture zone, characterized by the presence of mud volcanoes. From the ecological point of view, both settings represent extreme environments. In the Specchio di Venere lake CO2 emissions are permanent, while the mud volcano area is influenced by continuous CH4 overflow. Thus, biomineralization could represent an important tool for limiting greenhouse gas emissions.
This research has been focused on siliceous stromatolites, that are forming near thermal pools in the Specchio di Venere lake, and on carbonate crusts sampled during two MESC (Mud Volcanoes Ecosystem Sicily Channel) Oceanographic Cruises. Detailed observations under the SEM and petrographic microscope highlight the presence of biofilm, microbial filaments and silica spheres in alveolar structures from the stromatolites of Pantelleria. The REE patterns of these samples identify a typical enrichment in HREE, in the region Tm-Yb-Lu, probably due to bacterial activity. In carbonate authigenic crusts from the Strait of Sicily, textural features such as carbonate bridges (biofilm) cross linking crystals within pores, epibiotic structures and aggregates of micritic aragonite and Mg-calcite with dumbbell and spherular shapes strongly resemble biologically formed carbonates. Consistently with petrographic characteristics, carbon and oxygen compositions of carbonate crusts show δ13C and δ18O values in the range -31.0‰ to 2.8‰ and 2‰to 7.0‰, respectively, supporting a bacterially mediated formation under conditions of methane anaerobic oxidation.