BIOGEOCHEMISTRY OF SEDIMENTARY BARITE DEPOSITS IN THE DEVONIAN SLAVEN CHERT OF CENTRAL-NORTH NEVADA

The search for life at biochemical boundaries on early Earth and extraterrestrial targets relies on developing models based on metabolically analogous systems in the modern environment and applying them to the fossil records. The biological record is often lost to deep time; however, unique mineral deposits formed as a function of these metabolisms may record ecosystem interactions.

This study focuses on large barite (BaSO₄) beds and associated limestone deposits located at the Clipper, Northumberland, Greystone, Dana, Mountain Springs, Miller, and Shasta mining regions of the Roberts Mountain Allochthon in north-central Nevada. These deposits formed on a continental slope, along an active tectonic margin, during the Antler Orogeny in the Devonian. Preliminary isotope data supports a model where flocculated barite is remobilized in highly reducing sediments, barium is transported by methane seeps, and barite is precipitated at and below the seafloor. Evidence of methane seepage is based on anomalous limestone lenses with depleted δ¹³C values (-27.31 to -31.65‰; n=13) and fossils of Dzieduszyckia—a brachiopod known to have inhabited seeps. The carbon data also show a ~5‰ fractionation difference between samples with brachiopods and those without. Sulfur isotope data (n=34) show elevated δ³⁴S values up to 20‰ above contemporaneous Devonian seawater (23‰). The low δ¹³C of seep associated limestone point to a carbon source that is influenced by subsurface anaerobic oxidation of methane, while the enriched sulfur isotope signals of barite indicate a sulfate source linked to bacterial sulfate reduction and not hydrothermal activity.

Ongoing research is aimed at linking the geographical and stratigraphic occurrences of barite and limestone with specific petrofabrics and isotopic trends. The goal of this project is to detail the various pathways by which the barium, carbon, and sulfur cycles influenced barite formation and drove the localized chemosynthetic ecosystems across the continental slope in the Devonian during a time of active tectonism. This model is significant to astrobiologists who are striving to develop models of chemosynthetic-based metabolisms that rely on simple reduction-oxidation systems that might be applicable to extraterrestrial targets.