Magnetic stratigraphy and environmental magnetism of oceanic sediments

Type Thesis
Date 2006-12
Language English
Author(s) Evans Helen F1
University University of Florida
Discipline Geology

This dissertation presents the results of chronostratigraphic studies on marine sediment cores from three Oceans. Using a combination of magnetic stratigraphy, biostratigraphy and cycle stratigraphy it is possible to produce chronostratigraphies that exceed the resolution of any individual technique. In the North Atlantic, environmental magnetic records from Eirik Drift, south of Greenland, record detrital signals related to the melting of the Greenland and Laurentide Ice Sheets. The detrital layer stratigraphy has been placed in a paleointensity-assisted chronostratigraphic template, based on paleointensity and stable isotope data, to enhance correlation of detrital layers across the North Atlantic region. In the central Atlantic, on Gardar Drift, correlation of a benthic oxygen isotope record to the Greenland and Vostok Ice cores has placed cores from the drift on a revised GISP chronology. A stack of relative paleointensity records was developed and placed on the revised GISP chronology. In marine isotope stage 3, a benthic isotope record appears to record changes in bottom water temperature that are coeval with magnetic grain size changes. IODP Site U1313 from the North Atlantic produced a high-resolution polarity stratigraphy and relative paleointensity record between 2.5 and 6.0 Ma. This is one of a handful of paleointensity records for this interval. Cycles in magnetic susceptibility allowed agecalibration by correlation to a benthic oxygen isotope stack. Sediment cores from the Pacific Ocean produced excellent magnetic stratigraphies, and cycles in the sediment allowed astronomic calibration of reversal boundaries. Based on the correlation of planktonic foraminifer datums to the magnetic stratigraphy at ODP Site 1208, a new planktonic foraminifer zonation for the northwest Pacific Ocean can be precisely correlated to polarity chrons and astronomically calibrated ages. Numerous paleomagnetic excursions are tentatively identified for the first time in Pacific sediments. Oxygen isotope records from the Late Miocene (9.3-11.2 Ma) at ODP Site 1092 (South Atlantic) allowed astronomic calibration of ages of reversal boundaries and three polarity excursions within Chron 5. This is the first time astronomically calibrated ages have been assigned to these polarity excursion chrons and indicate a duration for the excursions of 3-4 kyrs.

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