RECONSTRUCTING THE MIDDLE DEVONIAN PALEOCLIMATE USING MARCELLUS SHALE GEOCHEMICAL SIGNATURES

Geochemical signatures preserved in the Union Springs member of the Marcellus shale can be utilized to reconstruct the paleoclimate during the middle Devonian (416-359.2ma). Recent reconstructions place the Appalachian basin in the southern tropics between (15-30°S) where the Acadian Orogen likely formed a major rainshadow resulting in a seasonally variable semi-arid climate subject to intense storms. By utilizing major element abundances obtained via ED-XRF analysis, provenance as well as weathering trends within the stratigraphic profile can be determined. Currently, we are conducting analysis on major elemental abundances to infer continental precipitation and weathering trends.

In addition to weathering trends associated with the source rocks, we aim to determine redox conditions that were present in the depositional basin throughout the period of deposition. Here we will utilize several redox sensitive trace element proxies obtained via ICP-MS instrumentation to draw inferences on the depositional environment which was favorable for black shale formation. The presence of uranium and vanadium are interpreted to be associated with iron sulfides or catalyzed by interactions with hydrogen sulfide. Conversely, the concentrations of elements such as nickel, copper, cobalt, and chromium are reflective of organic carbon concentrations in sediments. Therefore, creating ratios between elements associated with hydrogen sulfide and elements associated with organic matter we can infer redox conditions throughout the stratigraphic profiles. Examples of trace element proxies to be utilized in my research include V/(V+Ni), V/Cr, and U/Th. Moreover, organic carbon will be compared to the aforementioned trace element proxies in order to further validate the reliability of the ratios used to determine redox conditions. Here we should observe a positive relationship between organic carbon content and the associated trace elements of Cu, Ni, Co, and Cr. Thereby creating a better understanding of the conditions favorable for black shale deposition within the Appalachian basin during the middle Devonian.