Isotopic Composition of Early Diagenetic Carbonate from the Ordovician: Implications for Greenhouse Paleoceanography & Paleoclimate & Pre-Vascular Plant Meteoric Diagenesi

早期成岩碳酸盐胶结物（海相和大气）的同位素组成将为确定奥陶纪古海洋学和古气候以及与陆前植物、碳酸盐大气系统相关的同位素变化提供证据。仔细的岩石学、阴极发光和微量元素研究将有助于圈定变化最小的海相胶结相。来自Llanvirn时代古地理差异地区的两个热带台地边缘构造的变化最小的海洋胶结物将与奥陶纪后期的数据进行比较，以确定奥陶纪纤维方解石818O成分的变化是否反映了海水温度的局部变化或海水818O成分的长期变化。本部分研究的目的是确定两个古地理分化区温带至极地古高纬度地区大气胶结物的818O组成，并将其用于评价奥陶纪气候的平稳性。二氧化碳分压升高的时期，如奥陶纪，是否与先前假设的气候稳定时期相对应？来自热带和温带台地碳酸盐沉积物（四个地区）的早期大气胶结物将提供与缺乏维管植物的景观暴露表面相关的稳定同位素组成（813C和818O）变化的信息。本部分研究的最终目标是全面建立奥陶系前维管植物大气碳酸盐稳定同位素组成模型，该模型可广泛应用于早古生代及更古老的岩石。

9315651 Walker The isotopic compositions of early diagenetic carbonate cements (marine and meteoric) will provide evidence to determine Ordovician paleoceanography and paleoclimate and the isotopic variation associated with pre-land plant, carbonate meteoric systems. Careful petrographic, cathodolumenescence, and trace element studies will allow delineation of the least altered marine cement phases. Least altered marine cements from two tropical, platform- marginal buildups located in paleogeographically divergent localities from the Llanvirn epoch will be compared with data from later epochs in the Ordovician to determine whether the variation in the 818O composition of Ordovician fibrous calcite reflects either local variations in sea water temperature or secular variation in the 818O composition of sea water. The goal of this part of the research is to determine the 818O composition of meteoric cement from temperate to polar paleolatitudes, in two paleogeographic divergent regions, which will be used to assess Ordovician climatic equability. Do periods of elevated pCO2, such as the Ordovician, correspond with periods of climatic equability as previously hypothesized? Early meteoric cements from both tropical and temperate platform carbonate deposits (four regions) will provide information with regard to the variation of stable isotopic composition (813C and 818O) associated with exposure surfaces on a landscape lacking vascular plants. The ultimate goal of this part of the research is to fully develop a model for the stable isotopic composition of pre-vascular plant meteoric carbonate from the Ordovician that can be broadly applied to early Paleozoic and older rocks.