The Relationship Between Ecological Variability and Time Averaging In Different Habitats (Copano Bay, Texas)

Establishing the duration of death assemblage accumulation is critical in deterermining the time available for postmortem processes to act and the length of death assemblage memory of past ecological conditions. Death assemblages with species compositions inconsistent with known present-day living communities are either more time averaged than death assemblages that match their current habitat conditions, are sourced from living communities that are more variable, or both. To test this hypothesis, six sites in Copano Bay, Texas where chosen; two from each of three major living biofacies in the bay (dominated by mud, sand, and shelly substrate). Three sites have death assemblages matching the corresponding living communities, whereas the other three have death assemblages that do not appear to match present-day living communities. (The three sites in each category represent the three biofacies.) Age spectra of all six sites will be determined by dating shell material via C14 and amino acid racemization using the abundant bivalve Mulinia lateralis, providing a direct estimate of time averaging. It is expected that sites with live-dead inconsistency will have a greater degree of time averaging than sites with live-dead consistency. Alternatively, similar degrees of time averaging regardless of biofacies or degree of live-dead consistency would indicate independence of ecology and/or preservation at local sites.