Reconstructing the Paleocommunity from the Fossil Assem- blage: Comparative Analysis of Taphonomy and Time Averagingin Modern Death Assemblages of the Marine Environment

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A major impediment in the interpretation of the fossil record has been the inadequate understanding of the biases in it caused (1) by the taphonomic alteration of the original assemblage of living organisms and (2) by the mixing or time averaging of temporally distinct faunas. The objective of this project is to improve our understanding of these biases by a comparative study of taphonomy and time averaging among the major environments of deposition found in the Gulf of Mexico and adjacent waters. Over the past 6 years, selected communities in Texas bays and the Texas continental shelf were sampled and analyzed using the best techniques available to both zoologists (for the living community) and paleontologists (for the death assemblage). Parameters investigated included taxonomic composition, trophic structure, diversity, population dynamics, biomass and the influence of physical disturbance phenomena and biological interactions in determining community structure for both the living community and the death assemblage. Processes studied included taphonomic modification and loss of shell material, local transportation of shell material, and time averaging. A good working model of how these processes affect the formation of the death assemblage from the living community and the use of the parameters listed above during paleoecological reconstruction has been developed for the Texas coastal zone and extended out onto the shelf and upper slope. A detailed taphofacies analysis has been conducted in a suite of major environments of deposition in these same areas. We will extend this analysis in depth by including, for the first time, a detailed comparative analysis of time averaging. We propose to extend this analysis in scope by broadening the study to include additional EOD's within the Gulf of Mexico and adjacent waters. In this way, we can investigate how fossil assemblages form in the marine environment and determine how broadly applicable the model developed for death assemblages in Texas bays and the Texas shelf is to a much larger fraction of the fossil record.