HR: 17:45h
AN: OS42C-08    [PDF]
TI: ULTRADEEP LARGE SCALE POCKMARKS OFF CONGO - EXAMPLES FOR MASSIVE OCCURRENCE OF GAS HYDRATE, FLUID AND GAS SEEPAGE
AU: * Spiess, V
EM: vspiess@uni-bremen.de
AF: University of Bremen Dept. of Earth Science, Klagenfurter Strasse, Bremen, 28359 Germany
AU: Kasten, S
AF: University of Bremen Dept. of Earth Science, Klagenfurter Strasse, Bremen, 28359 Germany
AU: Schneider, R
AF: University of Bremen Dept. of Earth Science, Klagenfurter Strasse, Bremen, 28359 Germany
AU: Zuehlsdorff, L
AF: University of Bremen Dept. of Earth Science, Klagenfurter Strasse, Bremen, 28359 Germany
AU: Pfeiffer, K
AF: University of Bremen Dept. of Earth Science, Klagenfurter Strasse, Bremen, 28359 Germany
AU: Bohrmann, G
AF: University of Bremen Dept. of Earth Science, Klagenfurter Strasse, Bremen, 28359 Germany
AU: Sahling, H
AF: University of Bremen Dept. of Earth Science, Klagenfurter Strasse, Bremen, 28359 Germany
AU: Breitzke, M
AF: GEOMAR Research Center, Wischhofstrasse 1-3, Kiel, 24148 Germany
AU: Bialas, J
AF: GEOMAR Research Center, Wischhofstrasse 1-3, Kiel, 24148 Germany
AU: Ivanov, M
AF: Moscow State University, Vorobjevy Gory, Moscow, 119899 Russian Federation
AU: M56 Shipboard Scientific Party, .
AF: University of Bremen Dept. of Earth Science, Klagenfurter Strasse, Bremen, 28359 Germany
AU: M56 Shipboard Scientific Party, .
AF: GEOMAR Research Center, Wischhofstrasse 1-3, Kiel, 24148 Germany
AU: M56 Shipboard Scientific Party, .
AF: Moscow State University, Vorobjevy Gory, Moscow, 119899 Russian Federation
AU: M56 Shipboard Scientific Party, .
AF: Max-Planck Institute for Marine Microbiology, Celsiusstrasse 1, Bremen, 28359
AB: Deep sea pockmarks belong to the large scale features on the sea floor, where major fluxes of fluids and gases can be observed. They are also among the rare places, where gas hydrates are found near the sea floor in the reach of sampling. The southwest African continental margin off Gabon and Congo has revealed numerous such structures during recent surveys using high resolution seismic and acoustic systems, and 3 pockmark structures had been subsequently selected to be studied within the framework of the German geotechnologien gas hydrate initiative. Main objectives were the occurrence, evolution and properties of gas hydrate, fluid and gas seepage and its physical appearance within the hemipelagic sediment cover. Deep Tow Side Scan Sonar and sea floor video observations confirmed the widespread distribution of shallow carbonate precipitates and gas hydrates, contributing to high backscatter as well as very high reflection amplitudes in sediment echosounder data. Only parts of these a few to 30 meters deep sea floor depressions are affected by fluid escape on sub-circular areas of a few hundred meters diameter. Numerous samples of gas hydrates had been recovered from the vicinity of all 3 surveyed pockmarks, indicating a close relationship between fluid pathways, chemosynthetic communities as clam fields or tube worms, gas hydrate growth and carbonate precipitation. 3D seismic data collected at high to very high resolution, using seismic sources up to 1 kHz source frequency, reveal a complex nature of the fluid upflow zone and their relationship to deeper shallow gas pockets. It is assumed that they allow the spatial reconstruction of gas hydrate occurrence, gas distribution and the sediment volume, contributing to the overall fluid flow, as well as the quantification of gas hydrates stored in the vicinity of the pockmarks in the upper 200 meters of the sediment column.
DE: 3000 MARINE GEOLOGY AND GEOPHYSICS
SC: Ocean Sciences [OS]
MN: 2003 Fall Meeting