Mathematics – Logic
Scientific paper
Dec 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agufm.t21d..03f&link_type=abstract
American Geophysical Union, Fall Meeting 2001, abstract #T21D-03
Mathematics
Logic
1035 Geochronology, 1050 Marine Geochemistry (4835, 4850), 3022 Marine Sediments: Processes And Transport
Scientific paper
One approach to the determination of how time is distributed within sediments is the use of a constant-flux tracer, whose concentration is inversely proportional to sediment mass accumulation rate. This technique can be applied to spot samples, so can potentially provide higher temporal resolution than cyclostratigraphy. Successful use of such a tracer requires a) delivery at a constant and determinable rate, b) immunity to sedimentary redistribution and diagenesis, c) easy measurement such that large data sets can be obtained. The concentration of interplanetary dust particles (IDPs), few to 10's of μ m grains derived from comets and asteroids, may provide such a tracer. Although IDPs comprise <1 ppb of most sediments, they are enriched in the terrestrially-rare isotope 3He, which is easily measured in carbonates with LSR <4 cm/kyr. The 3He signal is preserved for >150 Myr on the seafloor, and other than possible diffusive loss at elevated temperatures, no obvious diagenetic effects have been discerned. Our preliminary survey of most of the Cenozoic indicates <2x variability in the IDP-derived 3He flux, excluding transient increases at 35 Ma and over the last 1 Myr. The Late Eocene increase is probably associated with a geologically rare comet shower. Variability post 1 Ma is not well-understood; it may derive from solar system processes, or may be a sedimentary artifact. This is the greatest source of uncertainty with the method: both IDP focusing and transport with the fine fraction have been suggested, and these may or may not be responsible for factor few variability in local flux. We have taken an empirical approach to the application of this tool. At the Gubbio K/T boundary, 3He data suggest an ~10 kyr hiatus (the clay layer) followed by decreasing then increasing sedimentation. These observations are consistent with independent constraints. During the Late Paleocene Thermal Maximum, 3He data support the cyclostratigraphic age model through the first part of the event, but towards its conclusion the two techniques suggest extremely discordant sedimentation rates (Eltgroth and Farley, this volume).
Eltgroth S.
Farley Ken A.
Mukhopadhyay Subhadeep
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