Print this pageAAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
Isotope Signature as the Tool for Meteoric Diagenesis in Pleistocene Reef, Southern Dominican Republic
(1) Marine Geology and Geophysics, RSMAS, University of Miami, Miami, FL.
The Pleistocene reef terraces that are well-developed in the Southern Dominican Republic over the past 1.8 Ma have been exposed and undergone several episodes of meteoric diagenetic. These diagenetic overprints provide a valuable opportunity to understand the meteoric diagenetic history of Caribbean reefs. Furthermore, this understanding will be useful for the reconstruction of the depositional history and ultimately understanding Pleistocene sea-level history. In accordance with this aim, the isotopic composition of carbon and oxygen and X-ray mineralogy have been determined in a series of eight short cores were taken from a series of reef terraces which formed during glacial stage 9 to 11. In addition three cores, 0 to 50 meters in length were taken through reefs which formed during glacial stage 5, 7, 9 and 11. The geochemistry of the reefs formed during stage 9 or 11, which experienced multiple episodes of meteoric diagenesis, were compared to the stage 5 reefs, which only has experienced one episode.
The result of stable isotopic measurements from the short cores taken through different reef terraces show a wide range of δ13C values and narrow distribution of δ18O values. The δ13C values depend on the values of groundwater bicarbonate, limestone, and soil gas, while the δ18O is controlled by the value of local rainfall. Strong negative excursions of carbon isotope values from normal indicate the presence of subaerial exposure with the values becoming heavier with increasing distance from surface. This high amount of calcite reveals that the oldest cores have undergone a longer period of meteoric diagenesis than the younger cores. In addition, a plot of δ18O against δ13C shows that the oldest cores have the lightest oxygen isotopic values. In the younger samples, the heavier carbon isotopic values are correlated to amount of aragonite.