Petrographic evidence of the past occurrence of gas hydrates in the Tertiary Piedmont Basin (NW Italy)     

Luca Martire  Marcello Natalicchio  Catalin Costel Petrea  Simona Cavagna  Pierangelo Clari  Francesco Dela Pierre 《Geo-Marine Letters》2010,30(3-4):461-476

Methane-derived rocks in Monferrato and the Tertiary Piedmont Basin (NW Italy) consist of seep carbonates, formed by gas seepage at the seafloor, and macroconcretions resulting from the cementation of buried sediments crossed by gas-rich fluids. These rocks are characterized by both negative δ¹³C values and a marked enrichment in δ¹⁸O. Petrographic features not commonly described and that point to enigmatic depositional and diagenetic conditions have been observed in both types of rocks: inhomogeneous distribution of cements within cavities; dolomite crystals floating within cavity-filling calcite spar; non-gravitational fabrics of internal sediments plastering cavity walls; open framework within microbial crusts. These features suggest the former presence of gas hydrates in sediments. During their dissociation, new space was formed and filled with authigenic carbonates or injected sediments. Analogous mechanisms of clathrate freeze-and-thaw processes have been inferred for the genesis of zebra and stromatactis structures and particular kinds of carbonate breccias. The term melt-seal structure is proposed for this kind of diagenetic structure. The fabrics of gas hydrates and the geochemical conditions of sediments, in turn depending on the relative rates of supply of methane-rich fluids and normal seawater, conditioned the final aspect of the rocks.  相似文献   

Estimation of hydraulic parameters in a heterogeneous low-lying farmland near Venice     

Ester Zancanaro  Claudia Zoccarato  Francesco Morari  Pietro Teatini 《水文研究》2023,37(1):e14791

  相似文献