HR: 16:30h
AN: B54C-03    [Abstracts]
TI: Complex Plumbing Systems in the Near Subsurface: Geometries of Authigenic Carbonates From Dolgovskoy Mound (Black Sea) Constrained by Analogue Experiments
AU: Nermoen, A
EM: anderne@student.matnat.uio.no
AF: Physics of Geological Processes, Dept. of Physics and Geology, Sem Saelandsvei 24, Oslo, 0316, Norway
AU: * Mazzini, A
EM: adriano.mazzini@fys.uio.no
AF: Physics of Geological Processes, Dept. of Physics and Geology, Sem Saelandsvei 24, Oslo, 0316, Norway
AU: Ivanov, M
EM: mivanov@geol.msu.mu
AF: Moscow State University, Vorobjevy Gory, Moscow, 119992, Russian Federation
AU: Bahr, A
EM: bahr@uni-bremen.de
AF: Research Center Ocean Margins, University of Bremen, Post Box 330 440, Bremen, D- 28334, Germany
AU: Bohrmann, G
EM: gbohrmann@uni-bremen.de
AF: Research Center Ocean Margins, University of Bremen, Post Box 330 440, Bremen, D- 28334, Germany
AU: Svensen, H
EM: henrik.svensen@fys.uio.no
AF: Physics of Geological Processes, Dept. of Physics and Geology, Sem Saelandsvei 24, Oslo, 0316, Norway
AU: Planke, S
EM: planke@vbpr.no
AF: Volcanic Basin Petroleum Research, Oslo Research Park, Oslo, NOR 0349,
AB: Targeted sampling on the Dolgovskoy Mound (northern Shatsky Ridge), revealed the presence of stunning laterally extensive and differently shaped authigenic carbonates. The sampling stations were selected based on sidescan sonar and profiler images that show patchy backscatter and irregular and discontinuous reflectors in the near subsurface. The interpretation of acoustic data from the top part of the Mound supports the seafloor observations and the sampling that revealed the presence of a complex subsurface plumbing system characterized by carbonates and gas. The crusts sampled consist of carbonate cemented layered hemipelagic sedimentary Unit 1 associated with several cm thick microbial mats. Three different carbonate morphologies were observed: a) tabular slabs, b) subsurface cavernous carbonates consisting of void chambers up to 20 cm3 in size, and c) chimney and tubular conduits vertically oriented or forming a subhorizontal network in the subsurface. The methanogenic origin of the carbonates is established based on visual observations of fluids seepage structures, 13C depletion of the carbonates (d13C varying between -36.7 and -27.4 permil), by carbonates within the thick microbial mats. Laboratory experiments with a Hele-Shaw cell were conducted in order to simulate the gas seepage through contrasting grainsize media present of the seafloor. Combined petrography, visual observations, and sand box simulations allowed a characterization of the dynamics and the structures of the plumbing system in the near subsurface. The shapes of the authigenic carbonates are interpreted respectively as a) Darcian porous flow through the finely laminated clayey/coccolith-rich layers, b) gas accumulation chambers at sites where significant fluid escape was impeded by thicker clayey layers forming the laminated Unit1, and c) focussed vertical fluid venting and subhorizontal migration of overpressured fluids released from b). The Hele-Shaw cell experiments represent a promising tool for investigating shallow fluid flow pathways in marine systems.
DE: 0419 Biomineralization
DE: 0463 Microbe/mineral interactions
DE: 0466 Modeling
DE: 3045 Seafloor morphology, geology, and geophysics
DE: 8426 Mud volcanism
SC: Biogeosciences [B]
MN: 2007 Fall Meeting