Integrated Ocean Drilling Program Expedition 307 preliminary report; Modern carbonate mounds; Porcupine drilling; 25 April-30 May 2005

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doi: 10.2204/iodp.pr.307.2005
Author(s): Ferdelman, Timothy; Kano, Akihiro; Williams, Trevor; Gaillot, Philippe; Abe, Kohei; Andres, Miriam S.; Bjerager, Morten; Browning, Emily L.; Cragg, Barry A.; de Mol, Ben; Foubert, Anneleen; Frank, Tracy D.; Fuwa, Yuji; Gharib, Jamshid J.; Gregg, Jay M.; Huvenne, Veerle Ann Ida; Léonide, Philippe; Li Xianghui; Mangelsdorf, Kai; Tanaka, Akiko; Novosel, Ivana; Sakai, Saburo; Samarkin, Vladimir A.; Sasaki, Keiichi; Spivack, Arthur J.; Takashima, Chizuru; Titschack, Jürgen; Dorschel, Boris; Monteys, Xavier
Integrated Ocean Drilling Program, Expedition 307 Scientists, College Station, TX
Author Affiliation(s): Primary:
Max-Planck-Institute of Marine Microbiology, Department of Biogeochemistry, Bremen, Federal Republic of Germany
Other:
Hiroshima University, Japan
Lamont-Doherty Earth Observatory, United States
Japan Agency of Marine-Earth Science and Technology, Japan
University of Tsukuba, Japan
Rosenstiel School of Marine and Atmspheric Science, United States
University of Copenhagen, Denmark
Cardiff University, United Kingdom
Universitat de Barcelona, Spain
Universiteit Gent, Belgium
University of Nebraska-Lincoln, United States
Toyama University, Japan
University of Hawaii at Manoa, United States
University of Missouri-Rolla, United States
Southampton Oceanography Centre, United Kingdom
Université de Provence, France
Chengdu University of Technology, China
GeoForschungsZentrum Potsdam, Federal Republic of Germany
Geological Survey of Japan, Japan
Rice University, United States
University of Georgia, United States
Kanazawa Gakuin University, Japan
University of Rhode Island, United States
Universität Erlangen-Nürnberg, Federal Republic of Germany
University College Cork, Ireland
Geological Survey of Ireland, Ireland
Source: Preliminary Report (Integrated Ocean Drilling Program), Vol.307, 58p. Publisher: IODP Management International, College Station, TX, United States. ISSN: 1932-9423
Note: In English. 54 refs.
Summary: Challenger Mound, a putative carbonate mound structure covered with dead deepwater coral rubble and located in Porcupine Seabight on the southwest Irish continental margin, was the focal point of twelve days of scientific drilling aboard the JOIDES Resolution during Integrated Ocean Drilling Program Expedition 307. Specific drilling objectives included the following: 1. Establish whether the mound base rested on a carbonate hardground of microbial origin and whether past geofluid migration events acted as a prime trigger for mound genesis. 2. Define the relationship, if any, between mound initiation, mound growth phases, and global oceanographic events. 3. Analyze geochemical and microbiological profiles that define the sequence of microbial communities and geomicrobial reactions throughout the drilled sections. 4. Examine high-resolution paleoclimatic records from the mound section using a wide range of geochemical and isotopic proxies. 5. Describe the stratigraphic, lithologic, and diagenetic characteristics, including timing of key mound-building phases, for establishing a depositional model of deepwater carbonate mounds and for investigating how they resemble ancient mud mounds. In addition to the mound, one site immediately downslope of Challenger Mound and an upslope site were drilled to (1) constrain the stratigraphic framework of the slope/mound system, (2) identify and correlate erosional surfaces observed in slope sediment seismics, and (3) investigate potential gas accumulation in the sediments underlying the mound. Drilling revealed that the mound rests on a sharp erosion boundary. Sediments below this erosion surface consist of glauconitic and silty sandstone drift deposits of middle Miocene age that grade upward toward more clay rich intervals. The latter are tentatively interpreted to represent relatively low energy environments in the late Miocene-Pliocene succession. The Pliocene strata end abruptly in a firmground that is overlain by the Pleistocene mound succession. Biostratigraphic results suggest that the hiatus between the two successions spans at least 1.65 m.y. The mound flanks are draped by late Pleistocene (<0.26 Ma) silty clay deposits that frequently contain dropstones. The mound succession just above the firmground is represented by interbedded grainstone, floatstone, rudstone, packstone, and wackestone in decimeter thicknesses, all reflecting relatively rapidly changing depositional realms. Above this lower level, the mound succession shows pronounced recurring cycles of Pleistocene coral floatstone, rudstone, wackestone, and packstone on a several meter scale that are well represented in the carbonate content change and are most probably associated with Pleistocene glacial-interglacial cycles. A role for hydrocarbon fluid flow in the initial growth phase of Challenger Mound is not obvious either from the lithostratigraphy or from initial geochemistry and microbiology results. We found no significant quantities of gas in the mound or in the subbasal mound sediments, nor were carbonate hardgrounds observed at the mound base. Microbial effects on mound and submound diagenesis are more subtle. We detected the methane-sulfate transition only in the deeper-lying Miocene silt and sandstones underlying the mound, where methane concentrations and prokaryotic cell abundances increase with increasing depth. In the mound itself, interstitial water profiles of sulfate, alkalinity, Mg, and Sr suggest a tight coupling between carbonate diagenesis and microbial sulfate reduction. Decomposition of organic matter (organoclastic) by sulfate reduction may drive the biogeochemical processes of mineralogical transformation by (1) producing CO2, which enhances aragonite dissolution and (2) increasing overall dissolved inorganic carbon concentration, which allows dolomite or high-Mg calcite to precipitate. Furthermore, periods of rapid sedimentation overlying hiatuses apparently left distinct signals in the interstitial water chemistry of the Pleistocene sediments that surround and partially bury the carbonate mounds of Porcupine Seabight.
Year of Publication: 2005
Research Program: IODP Integrated Ocean Drilling Program
Key Words: 07 Marine Geology and Oceanography; 20 Geophysics, Applied; Atlantic Ocean; Biogenic processes; Biostratigraphy; Boreholes; Bottom features; Carbonate rocks; Cenozoic; Challenger Mound; Chronostratigraphy; Continental margin; Cores; Drilling; Erosional unconformities; Europe; Expedition 307; Gas seeps; Genesis; Geochemistry; Geophysical methods; Geophysical profiles; Geophysical surveys; Hydrocarbons; IODP Site U1316; IODP Site U1317; IODP Site U1318; Integrated Ocean Drilling Program; Ireland; Lithostratigraphy; Magnetic inclination; Magnetostratigraphy; Marine drilling; Marine sediments; Microfossils; Mounds; North Atlantic; Ocean basins; Ocean floors; Organic compounds; Paleo-oceanography; Paleoenvironment; Porcupine Basin; Pore water; Quaternary; Sedimentary rocks; Sediments; Seismic methods; Seismic profiles; Seismic stratigraphy; Surveys; Tectonics; Tertiary; Unconformities; Well logs; Western Europe
Coordinates: N512300 N512300 W0114400 W0114400
N512300 N512300 W0114300 W0114300
N512600 N512600 W0113300 W0113300
Record ID: 2008016935
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