Towards understanding the Behaviour of the Clumped Isotope Signal During Marine Diagenesis; Implication for Reading the Ancient Record

重建地球早期历史的化学和物理条件通常是通过分析浅水沉积物的化学成分来完成的。 这些研究中的一个关键假设是，沉积物/岩石在沉积后没有发生重大变化，无论测量的是什么，都代表了沉积物形成时的原始条件。本项目旨在通过使用一种相对较新的地球化学技术，即同位素聚集法，来检验这一关键假设。 成团同位素是一种元素的两种或多种稀有同位素的组合。 该项目将使用聚集同位素方法调查现代海洋沉积物以及这些现代沉积物变成岩石的条件。这将允许从所研究的系统中获得以前无法获得的信息，即地层温度。 它还将允许对用于解释地球早期历史的化学记录进行评估。该项目为研究生提供培训，并为本科生和高中生提供研究机会。具体而言，研究人员将测量各种不同类型的现代碳酸盐沉积物中C和O同位素（δ 47）的聚集，并通过海洋埋藏领域的重结晶追踪这一特征。 在表征不同类型的现代碳酸盐沉积物中聚集的同位素信号方面已经取得了重大进展，初步数据表明骨架和非骨架主导的沉积物之间存在差异。 这项工作的目标是：（i）更详细地研究各种现代化的他化岩在三角洲47中的差异，以及它们是如何控制块状沉积物的三角洲47的，以及（ii）利用两个不同碳酸盐岩边缘沿着断面的三角洲47研究成岩行为，其中一个以非骨架产物为主一个主要是骨骼沉积物（马尔代夫（IODP站点U1466-68）和/或大堡礁（站点819- 823））。 这些数据将与一个远洋地点（807号地点）进行比较。 使用三角洲47的成岩速率将被建模，并与其他地球化学代理，包括Sr，Ca和O同位素确定的速率进行比较。 这项工作将建立在30年的ODP巡航（Legs 101-359）以及与年轻科学家的互动和合作的基础上，使用其他新的成岩作用示踪剂。

Reconstruction of the chemical and physical conditions of Earth's early history is often accomplished by analyzing the chemical composition of shallow water sediments. A critical assumption made in such studies is that there have been no significant modifications of the sediments/rocks after they were deposited, and that whatever is measured represents the original conditions present when the sediments were formed. This project aims to test this critical assumption through the use of a relative new and novel geochemical technique, namely the clumped isotope method. Clumped isotopes are combinations of two or more of the rare isotopes of an element. This project will use the clumped isotope method to investigate modern marine sediments and the conditions under which these modern sediments are changed to rock. This will allow previously unavailable information to be obtained from the system under study, namely the temperature of formation. It will also allow an assessment of the chemical records that are used to interpret the early history of Earth. This project provides training for a graduate student as well as research opportunities for undergraduate and high schools students.Specifically, the researchers will measure clumping of C and O isotopes (delta47) in a variety of different types of modern carbonate sediments and trace this signature through recrystallization in the marine burial realm. Significant headway has already been made into characterizing the clumped isotopic signal in modern carbonate sediments of differing types, and preliminary data suggest a difference between skeletal and non-skeletal dominated sediments. The goals of this work are to: (i) examine in more detail the difference in the delta47 of various type of modern allochems and how these control the delta47 of the bulk sediments, and (ii) study the diagenetic behaviour using delta47 along transects at two different carbonate margins, one dominated by non-skeletal production (ODP Sites 1003, 1005, and 1006) located off the western margin of the Bahamas), and one dominated by skeletal sediments (Maldives (IODP Sites U1466-68) and/or the Great Barrier Reef (Sites 819- 823). These data will be compared with a pelagic site (Site 807). The rates of diagenesis using the delta47 will be modelled and compared with rates determined from other geochemical proxies, including Sr, Ca, and O isotopes. This work will build on 30 years of ODP cruises (Legs 101-359) and interactions and collaborations with young scientists using other novel tracers of diagenesis.