GLACIOEUSTASY, METEORIC DIAGENESIS, AND THE CARBON CYCLE DURING THE MID-CARBONIFEROUS

Mid-Carboniferous carbonates in the western United States have undergone Pleistocene Bahamas-style meteoric diagenesis that may be associated with expanding late Paleozoic ice sheets. Here we present fourteen stratigraphic sections from mid-Carboniferous carbonate platforms to illustrate the regional distribution and variable intensity of physical and chemical diagenesis just below the unconformity. Each section contains top-negative carbon isotopic excursions that terminate in a regional exposure surface associated with karst towers, desiccation cracks, fabric destructive recrystallization, and extensive root systems. The timing of the diagenesis is synchronous with similarly-scaled top-negative carbon isotope excursions observed by others in England, Kazakhstan, and China. If global, the mass flux of light carbon required to generate similar isotopic profiles across the areal extent of middle Carboniferous platform carbonates is a significant and unrecognized component of the global carbon cycle. We present a simple carbon box model to illustrate that the delta-13 C of dissolved inorganic carbon in the ocean could be elevated by up to 1 - 2 permil as light remineralized organic carbon weathering from the terrestrial carbon pool reacts with exposed platforms before reaching the ocean and atmosphere. These results represent an improvement on global biogeochemical models that have struggled to provide a congruent solution to the heavy delta-13 C of the late Paleozoic icehouse.