LPIA Isotope Stratigraphy from the Alaska North Slope

In northern Alaska, subsurface archives of sediments from the Carboniferous–Early Permian Lisburne Group present an opportunity to obtain new carbon and oxygen isotope records. Consisting of a relatively continuous succession of carbonate lithologies deposited in both platformal and deeper environments, the Lisburne Group records δ13Ccarb and δ18Ocarb values on the northern margin of Pangaea during much of the Late Paleozoic Ice Age (LPIA). We present 1,200+ analyses from both core and well cuttings, revealing low and negative δ13Ccarb values in the Meramecian–Chesterian, followed by a positive shift across the Mississippian-Pennsylvanian boundary and into the Morrowan–Atokan (from ~+2 to +6‰). δ18Ocarb values are decoupled from δ13Ccarb, with both positive- and negative-trending δ18Ocarb phases occurring within the Pennsylvanian. High-resolution sampling in cores (10 cm interval) reveals smaller-scale cyclic changes than can be identified using well cuttings. The overall pattern of both C and O isotopic values through time in the Lisburne Group differs from that seen in other basins around the world. However, a similar shift toward more positive values in the Late Pennsylvanian has also been observed in several other localities on both the Panthalassan and Paleotethyan margins, though at different magnitudes and rates. This trend suggests that the relative sequestration of light carbon, or conversely, the weathering and erosion of 13C sources during this interval, may have been a global phenomenon. The results presented here constitute the first extensive δ13Ccarb and δ18Ocarb data set from this time in the arctic, and represent a mid-latitude paleogeographic location significantly distant from existing records.