|mhorn||Дата: Tuesday, 03.11.2015, 17:11 | Сообщение # 1|
|Kenny R. (2015) A cool time in the Early Jurassic: first continental palaeoclimate estimates from oxygen and hydrogen isotope ratios in chert from Navajo Sandstone carbonate lenses, Utah (USA) // Carbonates Evaporites, DOI 10.1007/s13146-015-0276-z|
Cool continental palaeoclimate estimates ranging from *9 to 18 C were inferred from oxygen and hydrogen isotope composition of chert precipitated contemporaneously with algal carbonate in interdune, freshwater lakes of the Early Jurassic Navajo Sandstone (USA). The oxygen and hydrogen isotope composition also indicate that meteoric waters were involved in the crystallization history of the chert. These results are consistent with previous studies that suggest that the interdune carbonate lenses in the Navajo Sandstone are freshwater carbonates precipitated in a wet-climate, pluvial episode. Approximate palaeotemperature estimates from oxygen and hydrogen isotope composition of silicified wood samples adjacent to a carbonate lens yield palaeotemperature estimates of *33 to 43 C. These data are consistent with burial diagenetic temperatures and support the interpretation that the algal chert precipitated contemporaneously with the algal carbonate. The results of this study demonstrate that the potential for obtaining quantitative, continental palaeoclimate estimates from freshwater chert found throughout the geologic record.
Middle Jurassic - Lower Cretaceous ammonites & aptychi