Small shelly fauna biodiversity from reef-adjacent facies of the lower Cambrian Harkless Formation, Nevada

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 quantified variations in the composition of SSF assemblages (richness, evenness, and diversity) in relation to proximity to biohermal facies of the lower Cambrian (Series 2, Stage 4) Harkless Formation in southern Esmeralda County, Nevada. Combining petrographic and quantitative analyses with a systematic review of the SSFs reveals a low diversity, but abundant assemblage. Trends in species richness, evenness and diversity 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 taphonomic controls. More research is needed to investigate spatial relationships of shelly faunas across these ancient carbonate archaeocyathid reefs and platforms to determine the role early reef habitats have on local biodiversity. • Studies exploring the effects of proximity to Archaeocyathid reefs on the composition of nearby SSFs biofacies are sparse. • Diversity metrics of SSFs show variability in lateral distribution away from the reef. • Lithology and paleoenvironment plays a key role in the preservation of SSF assemblages.