Global Change: A Record of Late Eocene to Miocene Continental Paleoclimate: Stable Isotope Geochemistry of Equid Enamel-Phosphate

我们将根据化石的氧同位素组成重建晚始新世至中新世的大陆气候。这是一个重要的全球气候恶化时期，根据古海洋资料推断，缺乏定量的大陆地球化学信息。18O哺乳动物磷灰石沉淀与体内水分平衡，反映了摄入的水分。哺乳动物的体温是恒定的，因此18OPO4记录了受全球水文循环支配的当地水源的18O。化石珐琅质的18OPO4可能记录了大陆古气候。马科动物化石是理想的，因为它们在地理上分布广泛，从始新世到晚更新世都很常见，并且有现代的类似物。我们将测定现代马科动物牙齿、身体水和饮水之间的同位素分馏，定量重建化石马科动物饮水的18O。我们将确定牙釉质化石中是否保留了大陆气候信号；如果大陆气候在大小、方向和时间上反映了海洋记录；如果动物进化变化与大陆气候变化同时发生。我们将分析来自怀俄明州、南达科他州和内布拉斯加州的化石，这些地方有化石样本，区域地层学和年代学都很有名，而且靠近大陆中心的位置有利于气候研究。我们的初步数据表明，大多数牙釉质样品保留了主要信号，并且可以检测到成岩作用。我们将进一步开发利用红外、XRD和元素分析评价成岩作用的标准。如果成岩作用可以忽略不计，我们将从18O年的古降水中建立晚始新世至中新世的古气候定量记录。

We will reconstruct late eocene to Miocene continental climate from the oxygen isotopic composition of fossel equid enamel phosphate. This interval is an important period of global climatic deterioration inferred from paleoceanographic data with scant quantitative geochemical information from continents. The 18O mammalian apatite precipitates in equilibrium with body water, whcih reflects ingested water. Body temperature of mammals is constant and known so 18OPO4 records the 18O of local water sources which are dominated by the global hydrologic cycle. The 18OPO4 of fossil enamel may record continetal paleoclimate. Fossil equids are ideal because they are geographically widespread, common from the Eocene to late Pleistocne, and have modern analogues. We will determine the isotopic fractionation between teeth, body water, and ingested water in modern equids to quantitatively reconstruct 18O of ingested water for fossil equids. We will determine if a continental climatic signal is preserved in fossil tooth enamal; if continental climate reflects the marine record in magnitude, direction, and timing; and if equid evolutionary change occurred concurrently with continetal climatic change. We will analyze fossils from Wyoming, South Dakota, and Nebraska, where fossil samples are available, regional stratigraphy and chronology are well known, and location near the center of the continent is advantageous for climate studies. Our preliminary data indicate a primary signal is retained by most enamel samples and diagenesis can be detected. We will further develop criteria for evaluating diagenesis with infrared, XRD, and elemental analyses. If diagenesis is negligible, we will develop a quantitative record of late Eocene to Miocene paleoclimate from 18O of ancient precipitation.