PALEOSOL DIAGENESIS AND ITS DEEP-TIME PALEOENVIRONMENTAL IMPLICATIONS, PENNSYLVANIAN-PERMIAN LODEVE BASIN, FRANCE

摘要

Sedimentological, petrographic, and geochemical investigations of the Permo-Carboniferous Lodeve Basin, France show complete diagenetic resetting of soil-formed minerals. Carbonate cements include diagenetic end-member phreatic-zone and burial cements in nodules and veins. Cement stratigraphy reveals multiple generations, including low-Mg calcite, ferroan calcite, dolomite, barite, and silica cements that record the burial and exhumation history of the basin. Stable-isotope analysis of calcite nodules yields uncorrected delta C-13 values of -5.0 parts per thousand and -0.7 parts per thousand, and between 0.4 parts per thousand and -3.8 parts per thousand for calcite veins; corresponding delta O-18 values of the calcite nodules are -3.6 parts per thousand and 0.2 parts per thousand, while veins are between -3.1 parts per thousand and -11.0 parts per thousand. Dolomite cements have uncorrected delta C-13 values of -0.2 parts per thousand to -6.7 parts per thousand and delta O-18 values of 2.0 parts per thousand to -6.1 parts per thousand. These values represent micritic calcite as well as mimetic dolomite, dolomite rhombs, microspar calcite, sparry calcite, and ferroan calcite. Isotopic values record multiple fluids of increasing temperature that flowed through the basin from the Triassic through Cenozoic, and are affiliated with the burial of the basin as well as lithospheric thinning during Pangean breakup. Following careful screening of groundwater nodules, veins and paleosols (n = 46), no carbonate retains its primary pedogenic signal or utility for use in quantitative paleoclimate reconstructions. These data document the importance of careful petrographic and geochemical screening for diagenetic alteration of paleosol carbonates before quantitative paleoclimate proxies are applied.