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HICKS, M.K., University of Nevada, Las Vegas, Geoscience Department, Las Vegas, NV

ABSTRACT: Paleoecology of Lower Cambrian Archaeocyathan Reefs in Esmeralda County, Nevada: Influences on the Collapse of Metazoan Reef Ecosystems

At the end of the Early Cambrian Epoch, metazoan-built reefs disappeared worldwide for at least 30 million years and were replaced by microbialite build-ups. The mechanism or mechanisms that brought about the demise of metazoan-built reefs is unknown, but global climatic changes are thought to have had a profound influence. Rising atmospheric CO2, global warming, and fluctuations in sea level are factors that could, in varying degrees, have affected the growth of metazoan reefs.

Five reefs found in Esmeralda County, Nevada represent the youngest episode of archaeocyathan-built reefs in western North America and are among the youngest Early Cambrian reefs in the world. In this study, I will compare the community structure and archaeocyathan diversity in reefs that developed at the end of the Early Cambrian with those that developed earlier. I will examine systematic changes in archaeocyathan generic diversity, morphology, and reef size. I will use these variations to test hypotheses on the role of changing climate on reef development.

Determining the community structure of the Lower Cambrian reefs will require a high-resolution paleoecological study of these reefs. Field and laboratory work will entail measuring reefs, performing faunal counts, measuring stratigraphic sections, and correlating the reefs across Esmeralda County. Fossils, ichnofossils, paleocurrents, carbonate diagenesis, and meteoric cements will be identified and documented.

Understanding the evolution, community structure, and demise of the Early Cambrian reef ecosystems may also shed light on the decline of modern reef ecosystems and perhaps contribute to mitigation of this problem.

AAPG Search and Discovery Article #90909©2000 AAPG Foundation Grants-in-Aid