Oxygen Isotope Compositions of Fossil Biogenic Phosphates: Climate Reconstruction in East Africa

在美国国家科学基金会的支持下，玛格丽特·舍宁格博士和她的同事将启动一项长期项目，根据对牙釉质中含磷氧的分析，重建东非上新世至更新世的气候变化。研究的第一阶段将直接研究珐琅质，以确定沉积后蚀变或成岩作用的程度。该小组将开发测试，以确定是否发生了成岩作用，以便相应地选择样品。为了实现这一目标，他们将收集珐琅和相关的地质样本，并确定寄主岩石的石化程度。这就比较了牙釉质化学蚀变的程度。红外光谱将得到，因为初步信息表明，再结晶磷灰石是可识别的不同于未改变的磷酸盐。还将测量随着成岩变化而增加的氟含量，并检查若干其他变化指标。有了这些数据，应该可以确定是否存在未改变的样本，并确定选择它们的标准。如果项目成功，它将为许多地球化学家、生物化学家和相关科学家提供有价值的方法论工具。这也将为下一步的研究奠定基础。根据饮食和体温调节的不同，不同动物物种的氧同位素比率反映了不同的气候变量，通过对精心控制的地层环境中样品的分析，可以监测温度、湿度和降雨随时间的变化。研究人员希望建立肯尼亚北部图尔卡纳地区从大约50万年前到近代的气候记录。根据这些数据，将有可能研究包括原始人在内的哺乳动物物种的进化。这个地区特别重要，因为它含有丰富的化石材料。许多科学家推测物种变化和气候之间的关系，这项研究将为解决这一问题提供重要的数据。

With National Science Foundation support Dr. Margaret Schoeninger and her colleagues will initiate a long term project to reconstruct East African Plio-pleistocene climatic variation based on the analysis of phosphate oxygen incorporated into tooth enamel. This first stage of the research will be directed to the study of enamel to determine the extent of post depositional alteration or diagenesis. The group will develop tests which determine whether or not diagenesis has occurred so that samples can be selected accordingly. To accomplish this goal they will collect both enamel and associated geological samples and determine the degree to which host rocks are lithified. This will be compared to the degree of enamel chemical alteration. Infrared spectra will be obtained since preliminary information indicates that recrystallized apatites are identifiably different from unaltered phosphates. Fluorine content, which increases with diagenetic alteration, will also be measured and several other indicators of change examined as well. With such data it should be possible to determine if unaltered samples exist and determine criteria to select them. If the project is successful it will provide a methodological tool of value to many geochemists, biochemists and related scientists. It will also set the stage for the next step of this research. Depending on diet and thermoregulation the oxygen isotope ratios in different species of animal reflect different climatic variables and through analysis of samples from carefully controlled stratigraphic contexts it is possible to monitor changes in temperature humidity and rainfall over time. The researchers hope to establish a climatic record for the Northern Turkana area of Kenya over the period from ca. 5 million years ago to recent times. Against these data it will then be possible to examine the evolution of mammalian species including hominids. This region is particularly important because of the rich fossil materials it contains. Many scientists have speculated on the relationship between species change and climate and this research will provide important data to address the issue.