A shellabration of early life : exploring the taphonomy, diversity, and distribution of small shelly fossils surrounding archaeocyathid reef systems in the Harkless System, Death Valley, NV
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Cambrian archaeocyathid reef systems represent the earliest metazoan-dominated topographically complex bioconstructions in the rock record and provide valuable insights into community composition with respect to the major framework builders and their small shelly fossil (SSF) inhabitants. This study focuses on lower Cambrian (Series 2, Stage 4) SSF assemblages from the Harkless Formation in southern Esmeralda County, Nevada, as a comprehensive systematic and quantitative analysis of these communities is currently lacking. The thesis is separated into two primary contributions addressing different challenges in the interpretation of SSF paleoecology at this locality. The first study aims to quantify the degree of bias introduced by the intersection of overlapping morphology and taphonomic features specifically of coniform fossils and discuss the implications for accurate taxonomic identification and paleoecological studies. Morphometric data and taphonomic scores were collected using a combination of light, electron scanning, and X-ray tomographic microscopy to survey coniform taxa. Well-preserved fossils were found to be the most abundant in the sample and could be identified with more confidence than those that were poorly preserved; however, µCT volume imaging confirms that external morphological features are insufficient alone to differentiate species from other similar coniform fossils. The second study investigates changes in SSF richness and diversity in relation to proximity to biohermal facies based on lithology and composition of SSF assemblages. Combining petrographic and quantitative analyses with a systematic review of the SSFs reveals a low diversity, but abundant assemblage. Trends in diversity and richness of species show no consistent patterns in distance from the reef across the measured sections. However, lithology serves as a major control in determining SSF biofacies, with select fauna exhibiting evidence of additional taphonomic controls.
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M.S.