The Importance of Diagenesis upon the C, S, and B Isotopic Composition of Carbonates: Implication for Reading the Rock Record

University Of Miami, Coral Gables FL

Investigators

Abstract

The study of diagenesis in carbonates uses classic tools of C and O isotopes and trace elements and now there are a number of additional geochemical proxies and methods that are potentially available. The PI proposes to examine the influence of diagenetic process upon the isotopic systematics of two of these proxies, sulfur and boron, as well as take a new look at factors controlling the carbon isotopes of organic material and inorganic carbonates. This work will be carried out mainly in Plio-Pleistocene sediments using material collected by shallow water and land drilling as well as the ODP. Material will include unaltered samples as well as those affected by diagenesis involving freshwater and marine fluids. In addition to the more Modern samples, the PI will also study B within older, Neoproterozoic, sections which have been proposed by some to have both retained their original geochemistry and by others to have been influenced by diagenesis. The PI will test one of the most established criteria for determining that the carbon isotopic signals are original, rather than diagenetic, mainly the presence of a correlation between the carbon isotopes of organic and inorganic material, which has recently been questioned. The work has implications for paleoclimatic and paleoceanographic studies. Other broader impacts include graduate and undergraduate training, outreach to high school students and collaboration with the Miami-based Creative Learning and Engagement Opportunities program. The PI suggests that the study of diagenesis in carbonate rocks using geochemistry is at an exciting point. Not only have the classic tools of C and O isotopes and trace elements continued to improve in terms of their accuracy, sensitivity and microsampling ability, but there are a number of additional geochemical proxies and methods of applying these proxies potentially available. Some of these proxies need to be refined while others wait to be discovered and developed. The PI will examine the influence of diagenetic process upon the isotopic systematics of two of these, sulfur and boron, as well as take a new look at factors controlling the carbon isotopes of organic material and inorganic carbonates. This work will be carried out mainly in young carbonate sediments (Plio-Pleistocene) deposited on the flanks and surface of carbonate platforms using material collected by shallow water and land drilling as well as the ODP. Material will include supposedly unaltered samples as well as materials which have been unequivocally affected by diagenesis involving freshwater and marine fluids. The rationale for this proposal is that the isotopes of C, B, and S have already been used over a wide ranges of geological time scales to interpret changes in the Earth?s geochemical systems. Such work is being undertaken without some of the fundamental understanding of the processes which may alter these proxies. In addition to the more Modern samples, the PI will also study B within Neoproterozoic sections which have been proposed by some to have both retained their original geochemistry and by others to have been influenced by diagenesis. Finally, one of the most established criteria for determining that the carbon isotopic signals are original, rather than diagenetic, mainly the presence of a correlation between the carbon isotopes of organic and inorganic material, has recently been questioned. Hence there is a need to establish to what extent such correlations indicate that the signals are original or whether in fact the presence of a correlation indicates that diagenesis has actually occurred. The work has implications for paleoclimatic and paleoceanographic studies. Other broader impacts include graduate and undergraduate training, outreach to high school students and collaboration with the Miami-based Creative Learning and Engagement Opportunities program.