SYSTEMATIC DIAGENETIC CHARACTERIZATION OF THE UPPER ORDOVICIAN (RICHMONDIAN) SALUDA FORMATION, CINCINNATI ARCH REGION, USA

The Richmondian aged (Cincinnatian Series) Saluda Formation is typically described as a lens shaped unit comprised of interbedded dolomitic limestones and silty dolostones bound by coral biostromes. Fine laminations, symmetrical ripple marks, rip-up clasts, desiccation cracks, and the lack of marine biota, suggest the Saluda Formation was deposited in a restricted, lagoonal setting. Previous investigations of the Saluda have focused on the sedimentology and stratigraphy. However, diagenetic studies are far less common. Two competing models have been proposed for the timing, fluid, and mechanism of dolomitization, both are based on limited datasets. On the basis of petrographic relationships, some researchers suggest that dolomitization of the Saluda occurred early via hypersaline reflux. Other researchers interpret co-varying δ¹³C and δ¹⁸O values and cathodoluminescence zonal stratigraphy to reflect dolomitization that occurred later in a marine-meteoric mixing-zone.

In an attempt to resolve this debate and add to the general knowledge of Richmondian-age strata, this study applies a systematic approach to investigating diagenesis in the Saluda Formation. Centimeter-sampling was conducted at the HWY 421 outcrop near Madison, Indiana. Thin section petrography, powder X-ray diffraction (XRD) data, X-ray fluorescence (XRF) elemental concentrations, and δ¹³C and δ¹⁸O data are used to investigate vertical patterns in dolomite texture, mineralogy, and geochemistry, which have been documented and used collectively in recent studies to further understand the timing and mechanism of dolomitization in peri-tidal carbonate settings.