A NEW δ13CCARB AND δ18OCARB RECORD FROM THE CARBONIFEROUS OF ALASKA

The Carboniferous (359–299 Ma) and early Permian (~299–273 Ma) were intervals of pronounced climatic and tectonic change, during which the Pangean supercontinent underwent assembly, and a severe and widespread high-latitude glaciation occurred across the Gondwanan subcontinent. These events had a large influence on silicate weathering and the carbon cycle, resulting in major perturbations to global atmospheric and ocean chemistries. Subsurface carbonate rocks of the Carboniferous–Permian Lisburne Group in Alaska may contain a near-continuous isotopic record of these events and present a rare opportunity to obtain C and O isotope data from a previously understudied stratigraphic unit deposited on the northern margin of Pangea. Here, we present a preliminary dataset of over 600 analyses of δ¹³C_carb from several drill cores (10–30-cm resolution) and well cuttings (3-m resolution), which reveal generally negative isotopic values in the Meramecian-Chesterian, followed by a shift to more positive values across the Mississippian-Pennsylvanian boundary and into the Morrowan-Atokan (from ~+2 to +6‰). δ¹⁸O_carb values are decoupled from this trend, with both positive- and negative-trending intervals occurring within the Pennsylvanian. Higher-resolution sampling in cores (10-cm interval) reveals smaller-scale cyclicity within the larger-scale changes identified in well cuttings. Although the Late Pennsylvanian positive shift in isotope values has been observed in other basins, regional variations preclude precise stratigraphic correlation. Our initial findings suggest a large sequestration of light carbon during the late Pennsylvanian, which is consistent with contemporaneous widespread organic carbon deposition in marine environments, or conversely, other mechanisms such as the weathering of ¹³C-enriched sources. Furthermore, ongoing research documenting the relationships between carbonate facies and isotopic values has the potential to reveal new insights into the biologic partitioning of stable isotopes in ancient carbonates. The results presented here constitute the first extensive δ¹³C_carb and δ¹⁸O_carb data set from the late Paleozoic of Arctic Alaska, a mid-latitude paleogeographic region located hundreds of km or more from existing isotopic records during this time frame.