CARBON AND SULFUR GEOCHEMISTRY OF POSSIBLE MARINE ZONES WITHIN THE PENNSYLVANIAN JOGGINS FORMATION, NOVA SCOTIA, CANADA

The Pennsylvanian Joggins Formation is a 932.4 m thick unit that contains 15 cyclothems, each of which records an initial flooding event followed by progradation of terrestrial facies. Although long considered to be nonmarine, recent paleontological discoveries suggest that flooding zones at the base of the formation record marine conditions. We assess the paleohydrology of cycle-bounding shales and limestones by examining their sulfur isotope geochemistry and ratio of organic carbon to pyrite sulfur. Sulfur isotope values of pyrite can be used to assess circulation patterns because bacterial sulfate reducers are free to process largely light sulfur in open circulation conditions, but forced to use increasing amounts of heavy sulfur in restricted conditions. δ³⁴S values of pyrite ranged from -8.76‰ to +23.00‰, indicating that the basin was relatively restricted and did not regularly and freely exchange water with the open ocean. The ratio of organic carbon to pyrite sulfur can be used as a measure of “marineness” because pyrite formation is limited by the availability of sulfate in freshwater environments and organic matter in marine environments. Organic carbon to pyrite sulfur values increased from 0.71 near the base of the formation to 3.50 at the top of the formation, suggesting a waning marine influence. This work supports recent paleontological studies that proposed decreasing marine influence through time, provides some of the first geochemical evidence of restricted marine conditions, and highlights geochemical analyses that may be used to supplement the sparse paleontological record of marine conditions.