Response of Th/U in deep Labrador Sea sediments (ODP Site 646) to changes in sedimentation rates and paleoproductivities

Online Access: Get full text
doi: 10.1130/0091-7613(1990)018<0162:ROTUID>2.3.CO;2
Author(s): Hillaire-Marcel, C.; Aksu, A.; Causse, C.; de Vernal, A.; Ghaleb, B.
Author Affiliation(s): Primary:
Univ. Qué, GEOTOP, Montreal, QC, Canada
Other:
Mem. Univ. Newfoundland, Canada
Univ. Marseille, France
Volume Title: Geology (Boulder)
Source: Geology (Boulder), 18(2), p.162-165. Publisher: Geological Society of America (GSA), Boulder, CO, United States. ISSN: 0091-7613 CODEN: GLGYBA
Note: In English. 34 refs.; illus. incl. sketch map
Summary: The Labrador Sea is a particularly suitable high-latitude basin for investigating U and Th behavior in deep-sea sediments. During the late Quaternary, the cyclic development and decay of huge ice sheets on adjacent land masses resulted in large-amplitude changes in sedimentation rates and organic paleoproductivities. The resulting magnification of U and Th response is well illustrated by high-resolution studies on piston-cored sediments from the Greenland continental rise at Ocean Drilling Program Leg 105 Site 646 spanning isotopic stages 8 to 1. Our results show a clear positive correlation of 238U/232Th ratios with organic paleoproductivity indicators (e.g., dinocyst) due to U uptake in the water column and/or during the early early diagenesis of organic matter responding to carbon fluxes and to their climate forcing. 230Th excesses over 234U exceed the theoretical value of the 230Th rain from the overlying water column, indicating lateral input possibly from the Greenland slope and shelf. Because these horizontal fluxes of 230Th may be partly controlled by physical parameters, 230Th excesses cannot be unequivocally correlated with sedimentation rates and/or productivity as reported elsewhere. In this subarctic basin characterized by low overall organic carbon burial, the 238U/232Th ratio appears to be a sensible geochemical indicator of organic activity and paleoproductivity.
Year of Publication: 1990
Research Program: ODP Ocean Drilling Program
Key Words: 02 Geochemistry; 07 Marine Geology and Oceanography; 24 Surficial Geology, Quaternary Geology; Absolute age; Actinides; Atlantic Ocean; Biochemistry; Cenozoic; Deep-sea environment; Diagenesis; Dinoflagellata; Foraminifera; Fractionation; Geochemistry; Globigerinacea; Interpretation; Invertebrata; Isotopes; Labrador Sea; Leg 105; Marine environment; Marine sedimentation; Marine sediments; Metals; Microfossils; Miospores; Neogloboquadrina; Neogloboquadrina pachyderma; North Atlantic; O-18/O-16; ODP Site 646; Ocean Drilling Program; Organic compounds; Organic materials; Oxygen; Paleoecology; Palynomorphs; Planktonic taxa; Pollen; Protista; Quaternary; Radioactive decay; Radioactive isotopes; Rotaliina; Sedimentation; Sedimentation rates; Sediments; Stable isotopes; Th/U; Thorium; U-238/Th-232; Uranium
Coordinates: N581236 N581236 W0482206 W0482206
Record ID: 1990016493
Copyright Information: GeoRef, Copyright 2017 American Geosciences Institute.