Diagenesis in the AND-2A Core, Andrill Southern McMudo Sound Project, Antarctica

Z. Gui and T. D. Frank
Department of Geosciences, University of Nebraska-Lincoln, Lincoln, NE 68588-0340 USA. And the ANDRILL SMS Science Team

The purpose of the diagenetic study in the AND-2A core is to understand how the relationships between oceanographic changes, basin evolution, climate and diagenesis. Thirty-five pore water samples were collected from 9.67 to 545.01 meters below sea floor (mbsf) for analyzing alkalinity, pH, salinity, δ¹⁸O, δ¹³CDIC, and major ions. Sediment samples were collected every 10 to 20m in the core for petrographic and stable isotopic analysis. Alkalinity and salinity data show higher values than normal marine sediments, with salinity reaching 5 times normal sea water salinity. These changes are attributed to water-rock exchange between pore fluids and reactive volcanogenic particles, in particular volcanic glass, under conditions of a high geothermal gradient. Downcore increases in most major ions suggest that the hydration reactions, including zeolitization and the hydration of volcanic glass, are taking up water and expelling salts into the pore water system. Decreasing δ¹⁸O values with depth are consistent with this interpretation. δ¹³CDIC values show a decreasing trend that reflects the dominance of carbon derived from organic matter rather than marine carbonate in the pore water system. Fifth samples for XRD analysis of clays show an abundance of illite, kaolinite, chlorite and smectite in the AND-2A core. In the future work, petrographic and geochemical analyses of carbonate cements will be carried out to aid in understanding the major diagenetic processes.

AAPG Search and Discover Article #90087 © 2008 AAPG/SEG Student Expo, Houston, Texas