A COMPARISON OF PALEOCLIMATE DATA DERIVED FROM PHOSPHATE OXYGEN ISOTOPES IN PROTEROZOIC AND PHANEROZOIC IRON FORMATIONS

Earth’s climate record is an integral source of information about the planet’s environmental history. Unfortunately, proxies for paleotemperature can be unreliable in deep-time; many potential carbonate archives have been chemically modified by diagenetic processes (Loyd et al., 2015). Phosphate, on the other hand, which is present in a wide variety of organic and inorganic material, has been proven to be fairly resilient to such post-depositional alteration. While it has traditionally been applied to biogenic, fossilized apatite as a paleothermometer, and is being refined as an indicator of biological activity (Blake et al., 2001), it has also been shown that ocean temperatures can be extrapolated from the ratio of ¹⁸O to ¹⁶O (δ¹⁸O) in dissolved inorganic phosphate preserved in sedimentary rocks (Karhu & Epstein, 1986; Blake et al., 2010). Nevertheless, phosphate oxygen isotope analyses have been performed on relatively few suites of ancient sedimentary rocks (Shemesh et al., 1983; Blake et al., 2010). Therefore, we have measured the δ¹⁸O values of dissolved phosphate in well-preserved Mesoproterozic, Neoproterozoic, and Phanerozoic iron oxide-rich rocks. This will represent the first suite of Proterozoic oxide-bound phosphate oxygen data. We will compare our findings to other sets of oxygen isotope data and paleotemperature estimates and explore the implications for long-term climate records.