Clumped Isotope Reordering Kinetics in Carbonate Minerals: The key to accurate ocean paleotemperatures and basin thermal histories

Abstract

One of the most exciting new ideas in geochemistry is to measure two rare isotopes in calcium carbonate instead of just one and "clump" them together. This provides a new and powerful tool to study the temperature of ancient oceans and sediments and will help scientists looking at climate change, plate tectonics, and petroleum exploration. This study will help identify the calcium carbonate minerals most likely to preserve ancient temperatures. It will also provide the chemical information needed to use two minerals at the same time to better estimate the temperature history of the rocks. This project will develop this new tool by connecting atom-level processes with observed chemical reactions. The study will improve temperature estimates of ancient oceans and the temperature history of rocks related to petroleum reservoirs. The project will train graduate and undergraduate students and will add a new section of a capstone undergraduate course that will introduce seniors to the field. The project will also engage chemistry graduate and undergraduate students from underrepresented minority groups

One of the most exciting developments in geochemistry in the 21st century is the ability to measure the relative abundance of molecules with two rare isotopes ("clumped isotopes") in calcium carbonate minerals (e.g., calcite) and apply this technique to reveal the temperatures of ancient oceans or the burial temperatures of sediments now exposed at the surface. A major complication in clumped isotope paleothermometry however is reequilibration (reordering) of the signatures at elevated temperatures (>100oC) on million-year timescales. While complicating paleoclimate studies, this reordering provides great potential for measuring rates of burial, uplift, and exhumation of geologic formations, but only if the rates (kinetics) of reordering are well understood. Currently, only the reordering kinetics of the mineral calcite (CaCO3) has been studied in detail. To address this knowledge gap, experiments will be conducted in which different minerals are heated and the rate at which they reorder is measured. The mechanisms of clumped isotope reordering will be examined at an atomistic level using a range of sophisticated chemical techniques such as programmable heated-stage synchrotron X-ray diffraction, total scattering, Raman spectroscopy, and scanning transmission X-ray microscopy, in conjunction with advanced models for atomic bonding. Correlating atomic characteristics with kinetic parameters and mineralogical characterization will allow determination of detailed equations governing the rates of reordering in a variety of carbonate minerals. The project will train graduate and undergraduate students and will add a new section of a capstone undergraduate course that will introduce seniors to the field. The project will also engage chemistry graduate and undergraduate students from underrepresented minority groups

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.