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

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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.