Rock Magnetic Properties Across Paleocene-Eocene Boundary Sediments from the North Atlantic, South Atlantic, and Eastern Pacific

Details Rock Magnetic Properties Across Paleocene-Eocene Boundary Sediments from the North Atlantic, South Atlantic, and Eastern Pacific Rock Magnetic Properties Across Paleocene-Eocene Boundary Sediments from the North Atlantic, South Atlantic, and Eastern Pacific

Dec 2004

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004agufmgp31b0840l&link_type=abstract

American Geophysical Union, Fall Meeting 2004, abstract #GP31B-0840

Other

4215 Climate And Interannual Variability (3309), 1505 Biomagnetism, 1512 Environmental Magnetism

Scientific paper

We present new rock magnetic data from Wilson Lake, NJ (N. Atlantic continental shelf), ODP Site 1262, (Walvis Ridge, S. Atlantic), and Lodo, CA (continental shelf, coastal California) in an effort to evaluate the comet-impact trigger hypothesis (Kent et al., 2003) for the carbon isotope excursion (CEI) associated with the Paleocene-Eocene Thermal Maximum (PETM). The comet-impact trigger hypothesis is based primarily on anomalous magnetic properties in outer shelf Paleocene-Eocene boundary sediments from the New Jersey continental margin; proponents of this hypothesis suggest these magnetic properties indicate the presence of extraterrestrial nanoparticles of magnetite. Our results suggest that these nanoparticles of magnetite may be terrestrial, not cosmic, in origin. Changes in magnetic hysteresis properties (e.g., Mr/Ms and Hc/Hcr) across the Wilson Lake section are similar to those from other regional stratigraphic sections (re: Kent et al., 2003), but similar changes are not observed at S. Atlantic or coastal California sites; thus, there may be a regional rather than global source of magnetic material. Squareness plots (Tauxe et al., 2003) and Day plots (Day, 1977) of hysteresis data suggest that Wilson Lake magnetite is single domain (SD flower structure to SD cubic), but the grain size of magnetite from the other two sites is mixed, possibly with a significant component of pseudo-single domain grains. Weak-field high temperature susceptibility experiments suggest that the primary magnetic mineral in these sections is magnetite. Low-temperature zero- and strong-field saturation isothermal remanent magnetization (SIRM) experiments indicate that the fine-grained magnetite is partially oxidized, probably to maghemite. More significant, however, the low-temperature experiments suggest that the fine-grained magnetite from the CIE portion of the Wilson Lake section may have a biogenic origin. Although it is clear that intact chains of magnetosomes are not preserved, the single-domain magnetite in the Wilson Lake section may have a significant population of isolated magnetosomes or other biogenic magnetite. We present additional comparative studies of low-temperature data to better assess the component of biogenic magnetite in the Wilson Lake section. We also present geochemical data to better understand the redox conditions that could favor or inhibit the production of biogenic magnetite at the three sampling sites.

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