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Arthur, Michael A; Dean, Walter E; Zachos, James C; Kaminski, Michael Anthony; Hagerty Rieg, S; Elmstrom, K (1989): Geochemistry of middle Eocene-lower Oligocene pelagic sediments of ODP Hole 105-647A [dataset publication series]. PANGAEA, https://doi.org/10.1594/PANGAEA.745209, Supplement to: Arthur, MA et al. (1989): Geochemical expression of early diagenesis in Middle Eocene-Lower Oligocene Pelagic sediments in the southern Labrador Sea, Site 647, ODP Leg 105. In: Srivastava, SP; Arthur, M; Clement, B; et al. (eds.), Proceedings of the Ocean Drilling Program, Scientific Results, College Station, TX (Ocean Drilling Program), 105, 111-135, https://doi.org/10.2973/odp.proc.sr.105.157.1989

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Abstract:
Geochemical analyses of the middle Eocene through lower Oligocene lithologic Unit IIIC (260-518 meters below seafloor [mbsf]) indicate a relatively constant geochemical composition of the detrital fraction throughout this depositional interval at Ocean Drilling Program (ODP) Site 647 in the southern Labrador Sea. The main variability occurs in redox-sensitive elements (e.g., iron, manganese, and phosphorus), which may be related to early diagenetic mobility in anaerobic pore waters during bacterial decomposition of organic matter. Initial preservation of organic matter was mediated by high sedimentation rates (36 m/m.y.). High iron (Fe) and manganese (Mn) contents are associated with carbonate concretions of siderite, manganosiderite, and rhodochrosite. These concretions probably formed in response to elevated pore-water alkalinity and total dissolved carbon dioxide (CO2) concentrations resulting from bacterial sulfate reduction, as indicated by nodule stable-isotope compositions and pore-water geochemistry. These nodules differ from those found in upper Cenozoic hemipelagic sequences in that they are not associated with methanogenesis. Phosphate minerals (carbonate-fluorapatite) precipitated in some intervals, probably as the result of desorption of phosphorus from iron and manganese during reduction.
The bulk chemical composition of the sediments differs little from that of North Atlantic Quaternary abyssal red clays, but may contain a minor hydrothermal component. The silicon/ aluminum (Si/Al) ratio, however, is high and variable and probably reflects original variations in biogenic opal, much of which is now altered to smectite and/or opal CT. An increase in the sodium/potassium (Na/K) ratio in the upper Eocene corresponds to the beginning of coarsergrained feldspar flux to the site, possibly marking the onset of more vigorous deep currents.
Although the Site 647 cores provide a nearly complete high-resolution, high-latitude Eocene-Oligocene record, the high sedimentation rate and somewhat unusual diagenetic conditions have led to variable alteration of benthic foraminifers and fine-fraction carbonate and have overprinted the original stable-isotope records. Planktonic foraminifers are less altered, but on the whole, there is little chance of sorting out the nature and timing of environmental change on the basis of our stable-isotope analyses.
Project(s):
Ocean Drilling Program (ODP)
Coverage:
Latitude: 53.331300 * Longitude: -45.262000
Date/Time Start: 1985-10-15T04:10:00 * Date/Time End: 1985-10-23T18:15:00
Event(s):
105-647A * Latitude: 53.331300 * Longitude: -45.262000 * Date/Time Start: 1985-10-15T04:10:00 * Date/Time End: 1985-10-23T18:15:00 * Elevation: -3869.0 m * Penetration: 736 m * Recovery: 444.6 m * Location: South Atlantic Ocean * Campaign: Leg105 * Basis: Joides Resolution * Method/Device: Drilling/drill rig (DRILL) * Comment: 75 cores; 716.6 m cored; 0 m drilled; 62 % recovery
License:
Creative Commons Attribution 3.0 Unported (CC-BY-3.0)
Size:
4 datasets

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Datasets listed in this publication series

  1. Arthur, MA; Dean, WE; Zachos, JC et al. (1989): (Table 1) Geochemistry of samples from lithologic Unit IIIC of ODP Hole 105-647A. https://doi.org/10.1594/PANGAEA.745205
  2. Arthur, MA; Dean, WE; Zachos, JC et al. (1989): (Table 7) Stable carbon and oxygen isotope record of bulk sediment, and benthic and planktonic foraminifera of ODP Hole 105-647A. https://doi.org/10.1594/PANGAEA.745208
  3. Arthur, MA; Dean, WE; Zachos, JC et al. (1989): (Table 6) Preservation of benthic and planktonic foraminifera of ODP Hole 105-647A. https://doi.org/10.1594/PANGAEA.745207
  4. Arthur, MA; Dean, WE; Zachos, JC et al. (1989): (Table 5) Whole-sediment chemsistry of ODP Hole 105-647A. https://doi.org/10.1594/PANGAEA.745206