COLLABORATIVE RESEARCH: Time-Averaging in Mixed Brachiopod- Mollusk Assemblages along a Depth Gradient across a Modern Tropical Shelf

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The limits to temporal resolution imposed by processes of time-averaging (i.e., age mixing of fossils that determines the temporal resolution of the fossil record) have broad implications for interpretation of the fossil record in a wide variety of types of studies. Almost no information on time-averaging is currently available for brachiopods, the predominant organism comprising Paleozoic and many later marine shell assemblages. We propose to use a combination of amino acid racemization and radiocarbon dating to document time-averaging in surficial accumulations of mixed brachiopod-mollusk shells on the southern Brazilian shelf. The resulting data will provide quantitative estimates of age structures of dated shells of brachiopods and mollusks from seven sites along a depth gradient. The study is expected to produce (1) the first quantitative estimates of time-averaging for brachiopod shell accumulations, (2) the first comparative data on time-averaging for two groups of biomineralized organisms (brachiopods vs. mollusks), and (3) the first estimates of time-averaging along an onshore-offshore bathymetric gradient. By adding taxonomic and environmental dimensions to the current knowledge of time-averaging, this study will provide a significant contribution to our understanding of the temporal resolution of the fossil record.