碳酸盐岩氧、碳稳定同位素地球化学研究目前面临的几个问题

PROBLEMS IN STUDIES ON CARBON AND OXYGEN STABLE ISOTOPES IN CARBONATES

碳酸盐岩氧、碳同位素的研究是地球化学重要的示踪手段之一。它可以为认识地质历史时期的地质过程、地球表面的气候过程和海洋环境过程等提供定量依据。４０多年的研究结果，尤其是进入８０年代方解石质的腕足化石壳体和早期成岩胶结物等特殊样品的应用，取得了若干重大研究进展，但同时也发现了一些新的问题。他们包括：碳酸盐岩氧、碳同位素分析结果的解释问题；反映原始氧、碳同位素组成样品的保存程度识别方法问题；腕足化石壳体是否具有氧、碳同位素生命效应问题；原始生活环境差异对腕足化石壳体同位素组成的影响强度问题和碳酸盐岩早期成岩胶结物的应用问题等。该文在讨论这些问题的同时。

Carbon and Oxygen stable isotopes in carbonates have long been the important geochemical tracers. Studies on the isotopic compositions can provide insights into the paleoclimatic processes, the paleoceanic environmental processes and the geological processes as well. Researches of more than four decades in the field, especially from the early 1980s on, during which the analysis of the isotopes in fossil brachiopods and early diagenetic cements has contributed much to the knowledge, achieved appreciable progress. However, problems still remained with how to explain the data that already existed on the isotopic compositions of carbonates, on which there is a dichotomy between those who advocate that the data represent the original characteristics of the isotopes and those who argue that the data have been altered diagenetically; with how to select the samples of carbonate for analysis of the isotopic ratios, which has a set of criteria, namely, the microstructure, the Cathodoluminescence and trace elements, for tests of the sample preservations; with whether the fossil brachiopods′ shells have vital effects on the isotopic compositions, on which there is a tendency toward the existence in recent years; with to what extent the living environment variations of the fossil affect their carbon and oxygen isotopic ratios and with the utilization of early diagenetic cement as analyzing samples. Along with the problem raising, this paper reviewed the methods on, and new developing trends toward, the problem solvings, as well as the up to date advances of studies on each problem.