REEF-LECTING ON CAMBRIAN COMMUNITIES: TAXONOMIC REVISION AND LATERAL DISTRIBUTIONS OF SMALL SHELLY FAUNAS FROM REEF-ADJACENT FACIES OF THE UPPER HARKLESS FORMATION, NEVADA

Cambrian archaeocyathid reef systems represent the earliest metazoan-dominated topographically complex bioconstructions in the rock record and offer valuable insights into community composition with respect to the major framework builders and their small shelly fossil (SSF) inhabitants. However, studies investigating the effects of inter-reef substrates as well as the level of connectivity between on-and off-reef facies and their reef-dwelling communities is comparatively sparse. This study provides a formal systematic assessment and quantitative analysis of lower Cambrian (Series 2, Stage 4) SSF assemblages from the Harkless Formation in southern Esmeralda County, Nevada. Limestone blocks were collected along three lateral transects, both between and at an increasing distance away from mapped archaeocyathid biohermal facies. Moreover, three separate lithofacies situated below, adjacent to, and above the biohermal facies were sampled in order to investigate changes in SSF richness, evenness, and diversity based on lithology and proximity to the reef. Acid digested residues typically reveal low diversity but abundant SSF assemblages. Trends in diversity and richness of species show no consistent patterns in distance from the reef across the measured 3 . However, lithology serves as a major control in determining SSF biofacies, with select fauna exhibiting evidence of additional taphonomic controls. More research is needed to understand spatial relationships and biodiversity across these ancient carbonate archaeocyathid reefs and platforms to determine key factors in maintaining biodiversity hotspots.