HR: 0800h
AN: OS21A-1511    [Abstracts]
TI: Pore Water Chemistry as Sensitive Indicators for Fluid Flow in Brazos-Trinity Basin #4 and Ursa Basin, Northeast Gulf of Mexico (IODP Expedition 308)
AU: * Jiang, S
EM: shyjiang@public1.ptt.js.cn
AF: State Key Lab for Mineral Deposits Research, Dept. of Earth Sciences, Nanjing University, 22 Hankou Road, Nanjing, 210093 China
AU: Gilhooly, W
EM: wpg6n@virginia.edu
AF: Dept. of Environmental Sciences, University of Virginia, Clark Hall, Charlottesville, Virginia, Charlottesville, 22904 United States
AU: Takano, Y
EM: takano@fox25.hucc.hokudai.ac.jp
AF: Dept. of Earth and Planetary Sciences, Hokkaido University, N8W10, Kita-ku, Sapporo, Hokkaido, 060-0810 Japan
AU: Flemings, P
EM: flemings@geosc.psu.edu
AF: Dept. of Geosciences, Penn State University, 305 Deike Building, University Park, Pennsylvania, 16802 United States
AU: Behrmann, J
EM: Jan.Behrmann@geologie.uni-freiburg.de
AF: Geologisches Institut, Albert-Ludwigs-Universitat Freiburg, Albertstrasse 23B, Freiburg, Baden-Wurttemberg, Freiburg, D-79104 Germany
AU: John, C
EM: cjohn@pmc.ucsc.edu
AF: Dept. of Earth Sciences, University of California Santa Cruz, Santa Cruz, Santa Cruz, 16802 United States
AB: Rapid sediment loading drives overpressure in marine sedimentary basins around the world. During IODP Expedition 308, two basins (Brazos-Trinity Basin #4 and Ursa Basin) with large different sedimentary loading of turbidite and hemipelagic sediments in the northeast Gulf of Mexico, were investigated to characterize in-situ spatial variations in temperature, pressure, and rock and fluid physical properties and chemistry. Pore water chemical compositions including alkalinity, salinity, pH, anions (Cl, SO4, PO4, H4SiO4), cations (Na, K, Ca, Mg), trace metals (Li, B, Sr, Ba, Fe, Mn), were analyzed in four drill holes at sites U1319, U1320, U1322, and U1324, in the Brazos-Trinity Basin #4 and Ursa Basin. At all sites, pore water chemistry shows great variability at shallow depths with maximam or miminum values corresponding well to seismic reflectors and lithostratigraphic units. The sulfate profile shows a dramatic decrease in SO4 content with a sulfate-methane interface (SMI) of 15 mbsf at Site 1319 and 22 mbsf at Site 1320 in the Brazos-Trinity Basin #4 Basin. In contrast, the sulfate- methane interfaces (SMI) are much deeper in Ursa Basin, i.e., 74 mbsf at Site 1322, and 94 mbsf at Site 2324. The deep SMI in Ursa Basin suggest relatively slow anaerobic degradation of organic matter considering the location of drilling site though we do not determine sulfate reducing rate with organic matter or methane as substrate at this leg. The downhole consumption of sulfate coincides with a concomitant increase in alkalinity and a decrease of Mn, Ca, Mg, Sr, and Li. Furthermore, initial pore water chemistry results appear to be influence by hydrogeologic fluid flow in both basins. Coincidence between pore water profile concentration maxima and parallel seismic reflectors may suggest that these seismic surfaces occur along specific stratigraphic units, which serve as channels for lateral fluid flow. Overall, the downhole variations in interstitial water chemistry may reflect a combination of processes, including anaerobic degradation of organic matter, diagenetic carbonate precipitation/dissolution, and fluid flow pathways.
DE: 1050 Marine geochemistry (4835, 4845, 4850)
SC: Ocean Sciences [OS]
MN: Fall Meeting 2005