Sedimentation rates off SW Africa since the late Miocene deciphered from spectral analyses of borehole and GRA bulk density profiles; ODP sites 1081-1084

Author(s): Gorgas, Thomas J.; Wilkens, Roy H.
Author Affiliation(s): Primary:
University of Hawaii, School of Ocean and Earth Science and Technology, Honolulu, HI, United States
Other:
Universite Bordeaux I, France
Office of Naval Research, United States
Volume Title: Neogene and Quaternary evolution of the Benguela coastal upwelling system
Volume Author(s): Christensen, Beth A., editor; Giraudeau, Jacques
Source: Marine Geology, 180(1-4), p.29-47; Evolution of major upwelling systems , American Geophysical Union 1999 fall meeting, San Francisco, CA, Dec. 13-17, 1999, edited by Beth A. Christensen and Jacques Giraudeau. Publisher: Elsevier, Amsterdam, Netherlands. ISSN: 0025-3227 CODEN: MAGEA6
Note: In English. 63 refs.; illus., incl. sketch map
Summary: Sedimentation rates (SRs) off SW Africa were calculated by performing spectral analyses in the depth domain on borehole and gamma-ray attenuation (GRA) bulk density data from ODP Sites 1081-1084. Inversion and integration of SRs versus depth from spectral analysis yielded detailed SR profiles in the time domain. Our technique allowed the detection of excursions in calculated SRs that not only often differed from those established through coarse-scaled biostratigraphic data, but also revealed a greater regional variability in the sediment accumulation over time. High-resolution bulk density data exhibited distinct periodicity in the waveband of Milankovitch cycles (precession at 19-23 kyr; obliquity at 41 kyr; eccentricity at 100 kyr). The pronounced Milankovitch cyclicity suggests that climate variability and trends in SRs along the Benguela Current System (BCS) were responding to insolation patterns during the past 6 Myr. We find relatively low SRs when evolutive amplitude spectra are dominated by obliquity and eccentricity periods. In contrast, significant SR peaks at all sites often occur when strong precessional amplitudes coexist with obliquity and eccentricity cycles. Episodes of high SRs often coincide with peaks in organic carbon mass accumulation rates (MAR Corg) and reduced sea surface temperature (SST) in the southern Walvis Basin, which have been associated with increased regional upwelling. This suggests that the high SRs reflect high productivity (high MAR Corg) attributed to strong wind and upwelling intensity during cool climate periods (low SSTs) in accordance with orbital forcing patterns observed in our spectra. Abstract Copyright (2002) Elsevier, B.V.
Year of Publication: 2002
Research Program: ODP Ocean Drilling Program
Key Words: 12 Stratigraphy, Historical Geology and Paleoecology; Africa; Atlantic Ocean; Benguela Current; Boreholes; Cape Basin; Cenozoic; Climate forcing; Currents; Data processing; Density; Eccentricity; Fourier analysis; Gamma-ray methods; Insolation; Inverse problem; Leg 175; Marine sediments; Milankovitch theory; Neogene; ODP Site 1081; ODP Site 1082; ODP Site 1083; ODP Site 1084; Obliquity of the ecliptic; Ocean Drilling Program; Ocean circulation; Ocean currents; Orbital forcing; Paleo-oceanography; Paleocirculation; Paleoclimatology; Paleocurrents; Paleoecology; Periodicity; Productivity; Quaternary; Sea-surface temperature; Sedimentation; Sedimentation rates; Sediments; South Africa; South Atlantic; Southeast Atlantic; Southern Africa; Tertiary; Time domain analysis; Upwelling; Well logs
Coordinates: S193712 S193712 E0111910 E0111910
S210539 S210539 E0114914 E0114914
S205342 S205342 E0111304 E0111304
S253049 S253049 E0130140 E0130140
Record ID: 2002026682
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands