Org or inorg? Atmospheric carbon controls that initiated the Late Paleozoic ice age 326mya

• Main Author: DeFrancis, Paco
• Format: Text
• Language: unknown
• Published: Digital Commons @ Colby 2015
• Subjects: Geology; South Pole; Ice Sheet; South pole
• Online Access: https://digitalcommons.colby.edu/clas/2015/program/166; https://digitalcommons.colby.edu/context/clas/article/1165/type/native/viewcontent/CLAS_Paco_FINAL.pptx

The Late Paleozoic Ice Age (LPIA) was a major global icehouse that initiated in the Mississippian (326 million years ago; ma) and lasted through the Early Permian (267ma). An ice sheet nucleated in southern Gondwana near the South Pole, which either paleogeography (positioning of paleocontinents) or atmospheric concentration of the greenhouse gas CO2 controlled. In this paper I accept recent findings that prove atmospheric pCO2 and not paleogeography forced global cooling that resulted in the nucleation of Gondwanan ice sheets that defined the LPIA. There remains no broad consensus of what caused pCO2 lowering in the Mississippian. Organic carbon found in extensive Carboniferous coal beds show evidence of high rates of Corg burial via peat accumulation that would have lowered pCO2 concentration, triggering the LPIA. However, these Corg-rich facies are predated by data from the Visean-Serpukhovian (331ma) boundary where glacial activity becomes evident in both near-field and far-field records. Therefore the potential of inorganic CO2 consumption must be evaluated. Here I look at weathering of silicate rocks releasing of Ca2+ and Mg2+ cations into the marine realm and sequestering atmospheric carbon as carbonate rocks. Trees evolved and proliferated globally in terrestrial regions during the Devonian and would have caused an influx in chemical weathering rates of silicate minerals. Accepting that increased silicate rock weathering resulted in the lowering of pCO2 concentration I will now evaluate the chronology and impacts that different controls had on silicate rock weathering and its relation to the initiation of the LPIA.