Windward vs. leeward variability of faunal distribution in a Silurian (Wenlockian) pinnacle reef complex—Ray Reef, Macomb County, Michigan

ABSTRACT Despite extensive research on Silurian (Niagaran–Wenlockian) reefs, most studies concerning faunal abundance and distribution have been qualitative studies with an emphasis on taxonomy, paleoecology, and evolution. This study is the first quantitative study of relative abundance and distribution of fauna throughout a single Wenlockian reef located in the southern trend of the Michigan Basin. Building on an established sequence stratigraphic framework with wind directions surmised from known paleogeographic location, the purpose of this study was threefold: (1) to quantitatively determine the relative abundances of fauna from subsurface cores of Ray Reef and show how they are tied to the established sequence stratigraphic framework; (2) to determine if the probable wind and current directions, along with water depth, influenced the morphology and distribution of fauna on the reef; and (3) to analyze the influence of wind and current on syndepositional marine cementation. Relative faunal abundance differed among the leeward, windward, and reef crest locations. Overall faunal density was highest in the crest and lowest along the leeward side of the reef complex. Diversity was highest in the crestal portion of the reef complex and in the reef core facies, in general. Changes in faunal morphology and community replacement were seen repeatedly through all cores in association with shallowing-upward conditions, which coincided with third-order stratigraphic and higher-frequency sequence stratigraphic cyclicity. The percentage of syndepositional marine cement was highest on the windward side and lowest on the leeward side. As has been reported in other reef complexes of varying geological ages, results of this study indicate that the core of the Silurian reef was composed mostly of rubble or debris, relative to the smaller proportion of in situ fauna.