Mathematics – Logic
Scientific paper
Dec 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004agufmos43b0574j&link_type=abstract
American Geophysical Union, Fall Meeting 2004, abstract #OS43B-0574
Mathematics
Logic
8105 Continental Margins And Sedimentary Basins, 3025 Marine Seismics (0935), 0930 Oceanic Structures
Scientific paper
We document the geologic environment of Smooth Ridge, off shore Central California, where the deep-water node associated with the MARS (Monterey Accelerated Research Site) scientific research cable is to be deployed. The MARS cable will provide internet connections and electric power at a node in 890 m of water in support of scientific observatory development and experiments. IODP boreholes are proposed which will be connected to the MARS cable. The deeply incised channels of Monterey and Soquel Canyons flank Smooth Ridge to the SW and NE and the San Gregorio faults marks its NW and upslope boundary. However, the top of Smooth Ridge, as its name implies, only has subdued bathymetric features. These include a subtle downslope channel and one distinct slump scar. A patch of acoustically reflective seafloor on the west side of the ridge, over 5 km from the MARS site, is associated with the only known large-scale biological community on the crest of Smooth Ridge. A reflection seismic survey conducted in 2003 with a high-resolution electrical sparker source reveals the stratigraphy of the Smooth Ridge in unprecedented detail. In conjunction with previously collected widely-spaced multichannnel seismic data, observations and samples obtained using remotely-operated vehicle (ROV) dives, and piston cores, this new survey reveals the erosional and depositional history of Smooth Ridge. The continuity of seismic reflections indicates nearly undisturbed deposition occurred until at least the mid-Miocene. Since that time, and especially since the upper Pliocene, the record is marked by unconformities and infill due to shifting channels, large slumps and landslides, and sediment waves. Several crossing seismic lines provide a quasi-three-dimensional view of a distinct slump scar's structure, and reveal a history of multiple headwall failures. Other subsurface structures, including a much larger, and older, slump feature, have no bathymetric expression at all. 14C dated piston cores, and ROV observations and sampling reveal that sediments have not been accumulating in the Holocene. Exposure of Plio-Pleistocene strata on the surface of Smooth Ridge in water depths of less than 1 km indicates that this is an area of active seafloor erosion. Measurements of sulfate gradients in piston cores indicate sulfate depletion occurs between 3 to 5 m below the seafloor, which is unusually shallow for continental margin sediments and suggests enhanced biogeochemical/microbiological activity occurs in the subsurface under Smooth Ridge.
Aiello I. W.
Gibbs S.
Greene H. G.
Jordahl K. A.
Mitts P.
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