ASSESSING THE POTENTIAL EFFECTS OF DOLOMITIZATION ON THE SULFUR ISOTOPIC COMPOSITION OF LATE ORDOVICIAN-EARLY SILURIAN DOLOMITES FROM THE BASIN AND RANGE PROVINCE, NEVADA

The sulfur isotopic composition of carbonate-associated sulfate (δ³⁴S_CAS) has proven to be an important geochemical tool for understanding and quantifying the past oxygenation state of seawater. There are, however, many processes that can potentially alter the δ³⁴S_CAS signal, including dolomitization. This study assesses the effects of dolomitization on the sulfur isotopic composition of carbonate-associated sulfate in Ordovician and Silurian dolomites from north-central Nevada, in the Basin and Range Province. These strata were deposited as limestones on a passive continental margin that extended along the coast of western North America during the Early Paleozoic and were later dolomitized by mixing zone fluids. The rocks analyzed in this study were sampled from three ranges in central Nevada (South Eagan Range, Pancake Range, and Lone Mountain), representing a nearshore-offshore environmental transect. Because of their varying positions on the carbonate shelf, the strata at each range experienced different degrees of dolomitization, with the nearshore deposits being more significantly exposed to dolomitizing fluids originating from the mixing zone. An independent correlation scheme based on sequence stratigraphy allows for a direct comparison of the δ³⁴S_CAS record of coeval strata. The goals of this project are threefold: 1) to determine whether dolomitization has changed the original isotopic composition of the sampled rocks, 2) to quantify isotopic variation as a function of the degree of dolomitization in coeval rocks across ranges, and 3) to track secular variations in the isotope record caused by dolomitization of limestones at a single locality. The δ³⁴S_CAS data are derived from CAS extracted from bulk rock powders. Major and trace element compositions serve as geochemical proxies for diagenesis and dolomitization, and we attempt to quantify the effects of these processes on sulfur isotopic composition. These results will help guide the interpretation of δ³⁴S_CAS data from carbonate rocks of other ages that have undergone similar degrees and types of dolomitization.