315 Paleontology IV - Exceptional Preservation and Taphonomy

Wednesday, 8 October 2008
1:30 PM - 5:30 PM

The Scale and Dynamics of Time-Averaging in Holocene Cave Deposits Quantified through AMS 14C Dating of Kangaroo Rat Bones

Paper number: 315-14
Program: Technical Sessions
Time: 4:45 PM – 5:00 PM

Authors

Abstract

The distribution of skeletal remain ages within a death-assemblage is of fundamental importance to paleobiological analysis. Radiometric dating provides the most direct method for obtaining such distributions. The use of radiometric dating is growing in marine systems, but has seldom been used in terrestrial vertebrate systems to evaluate the scale and dynamics of time-averaging.  Here I use 67 new AMS 14C dates from kangaroo rat femora to quantify age-frequency distributions from four strata of the Holocene Homestead Cave record to address: (1) the consistency of age-frequency distributions across strata, (2) how a stratum's effective temporal resolution relates to the maximum extent of time-averaging it represents, and (3) the extent to which a bone's overall taphonomic condition is predictive of its age.  I also use simulations to explore hypotheses regarding how varying distribution shapes may arise in this system.

Results indicate that, while the age-frequency distribution of the modern surface assemblage is near exponential, deeper strata exhibit modes at intermediate ages. While a stratum's maximum extent of time-averaging can range from 300 to 8000 years, its effective temporal resolution is often constrained by an order of magnitude.  No predictive relationship is found between a bone's age and its taphonomic condition.  Exponential decay curves cannot account for the observed age-frequency distributions. Simulations suggest a more complex interplay between decreasing rates of input over time, and loss rates that increase as a function of a bone's age.  Results from this study fill in the gap in our understanding of the scale and dynamics of time-averaging in small-bodied terrestrial vertebrate systems, and indicate that such deposits, even when significantly time-averaged, can represent valuable sources of ecological information over 102 – 103 time-scales.