HR: 0800h
AN: PP41A-0578    [Abstracts]
TI: A Priori Models to Examine the Potential for Geochronology to Determine Sedimentary Cycle Durations
AU: * Rasbury, E T
EM: troy.rasbury@sunysb.edu
AF: SUNY Stony Brook, Department of Geosciences, Stony Brook, NY 11794 United States
AU: Holt, W E
EM: wholt@mantle.geo.sunysb.edu
AF: SUNY Stony Brook, Department of Geosciences, Stony Brook, NY 11794 United States
AB: Sedimentary cycles are identified in numerous depositional environments. Often they can be credibly lined to Milankovitch orbital parameters and so they provide a high resolution measuring stick for geologic processes. However few cyclic sections are dated and even those that have been dated often suffer from few and sometimes controversial ages. We generate Monte Carlo models to test the potential accuracy of cycle durations inferred from age estimates. In particular we are interested in determining the resolving capability of more, but less precise, age estimates obtained from dating syn-sedimentary carbonates, as opposed to fewer, but more precise ash ages. Our simulations consider the potential cycle duration, the number of cycles represented in a section, the precision of the ages (assumed to represent accuracy), and the number of available ages. To create the models we assumed that ashes and carbonates that can be dated are randomly distributed in the section. We use cycles as a means of partitioning time into quasi-equal increments and examine cycles that have an average duration of 20, 100, and 400 ky, consistent with well studied Milankovitch cycles. For experiments where only two high precision ages were used, we imposed the constraint that the ages had to be far enough apart to be resolvable. Such a constraint was not placed on the models where ten ages were used. Based on these parameters we ran Monte Carlo simulations to examine the potential of randomly distributed age determinations within a section with a given number of cycles to define cycle duration within that section (a least-squares fit of age determinations versus cycle position). A total of 100,000 experiments were performed for each hypothetical section to estimate the variance of determined cycle duration from the actual cycle duration. Assuming that precision does equal accuracy, a priori models demonstrate that a greater number of lower precision ages have the potential to produce a higher precision estimate of position in a section (here calculated in terms of uncertainty in cycle duration) than the case of two higher precision ages. The longer the time interval considered, the better the ability to resolve cycle duration, whatever the tool. Ten precise ash ages always perform the best but, for sections greater than 2 My in duration, ten less precise carbonates are always preferable to the two precise ash age determinations in their ability to define cycle duration.
DE: 9699 General or miscellaneous
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting