ARE UNION SPRINGS AND OATKA CREEK MEMBERS OF THE MARCELLUS FORMATION FORMED UNDER DIFFERENT DEPOSITIONAL CONDITIONS?

The Marcellus Formation is one of the largest shale play areas in the US that is currently exploited for hydrocarbon resources. Despite the success of the shale gas “revolution,” the average recovery from shale play areas is about 25% for gas and less than 10% for tight oil. Although there are issues with the recovery of natural gas from shale play areas, there is an insufficient understanding of the paleoenvironments of the Marcellus Formation. In this study we focused on reconstructing the paleoenvironment of Marcellus Formation to better understand depositional conditions that are suitable for natural gas exploration. Using geochemical data (total organic carbon (TOC), major, trace, and rare earth elements) we observe different variations in geochemistry between Union Springs and Oatka Creek black shale members. Union Springs has significantly higher TOC, chalcophile, and siderophile concentrations; whereas Oatka Creek has a significantly higher field strength element composition. We suggest that the difference between the geochemistry of the two members may be caused by basin flexing of the Arcadian orogenic belt, instead of basin filling (e.g. Black Sea Model). In the basin flex model, we suggest Union Springs was deposited in a shallower environment and further away from the orogenic belt than the Oatka Creek member yielding higher TOC values. Due to basin flexing, the Acadian orogenic belt created a deeper depositional environment for Oatka Creek, lowering TOC preservation due to higher dissolution from deepening the basin and higher sedimentation rates.