This research is on variations in the Nd and Sr isotopic composition and REE abundance patterns in Proterozoic and Archean chemical sediments. It's purpose is to trace the major mass fluxes in the exogenic geochemical cycle through the Proterozoic and to understand the relationship between the evolution of the sedimentary reservoir, the oceans and the atmosphere during this time period. We will concentrate on measurements of Nd and Sr isotope variations and REE abundance patterns on samples of Proterozoic marine sediments. The following specific projects are proposed: 1) Determine 143Nd/144Nd variations in Proterozoic carbonates and shales.; 2) Determine REE patterns of banded iron formations ranging in age from - 0.8 Ga to 3.5 Ga.; 3) Modeling of the Sr and Nd isotope records of the exogenic geochemical cycle through the past 3.5 Ga, emphasizing the Proterozoic.; and 4) Extend the record of high precision Sr isotopic data of carbonates from the mid-Cambrian to - 2.0 Ga ago, using well dated and documented samples from Victoria Island (N.W.T., Canada), and various sedimentary basins in Australia. We propose to establish a detailed, precise record of Sr and Nd isotopic variations of chemical sediments for the time between 0.5 and 2.0 Ga ago. During the Proterozoic, seawater Nd and Sr budgets appear to have changed from dominantly hydrothermal inputs (as in the Archean) to dominantly continental (river) inputs. Data obtained from this research will be used to constrain the changes in rates of hydrothermal circulation, continental erosion rates and variations in the mean age of continental erosion products through the Proterozoic.
