Geochemical Investigations of Major Environmental and Tectonic Changes in the Permian and Triassic

随着时间的推移，海水的化学和同位素组成的记录包含了关于气候、构造、海底热液活动的丰富信息，甚至可能包含关于海平面变化、海洋环流和大气组成的细节。问题是要解开这些过程中记录在沉积物中的各种信号。在这里，我们将研究跨越二叠纪和早三叠世的时间段，这是一个全球环境变化的时间段。我们的研究将集中在锶和钕的同位素记录，但也将包括各种其他的，可能相关的地球化学指标。通过合作者，我们从地理上广泛分布的、地层控制的、重叠的剖面中获得了这项工作的一套样本。我们的大部分工作将在牙形刺上完成，它提供了地层信息，而且大多数感兴趣的元素都有很高的密度，因此在大多数情况下可以对单个个体或碎片进行分析。我们将仔细研究可能的成岩作用，并试图比以前更准确地描绘出在这段时间内观察到的海水中锶和钕同位素比率大幅变化的时间和幅度。这些数据将根据目前对古构造、古气候和古地理的知识进行审查。此外，我们还将探索在这个时间间隔内进行牙形刺U-Th测年的可行性，以完善我们的同位素研究的时间框架，并帮助进行剖面对比。

The record the chemical and isotopic composition of seawater through time contains a wealth of information about climate, tectonics, hydrothermal activity on the sea floor, and perhaps even about the details of sea level change, ocean circulation and atmospheric composition. The problem is to unravel the various signals recorded in sediments in terms of these processes. Here we will examine the time period spanning the Permian and early Triassic, a time of global environmental change. Our study will concentrate on the SR and Nd isotopic record, but will also include various other, probably related, geochemical indicators. Through collaborators, we have acquired a suite of samples for this work from geographically widespread, stratigraphically controlled, overlapping sections. Much of our work will be done on conodonts, which provide stratigraphic information as well as having conveniently high concentrations of most of the elements of interest, so that analyses can be made on single individuals or fragments in most cases. We will carefully investigate possible diagenetic effects, and attempt to delineate much more precisely than has been done previously the timing and magnitude of the observed large changes in Sr and Nd isotopic ratios in seawater during this time period. The data will be examined in terms of current knowledge of paleotectonics, paleoclimate and paleogeography. In addition, we will explore the feasibility of U-Th dating of conodonts in this time interval, in order to refine the temporal framework for our isotopic studies and to aid in section-to-section correlation.