Global Climate Change in the Paleozoic (Ordovician, and Carboniferous-Permian): Why it Matters to the Oil Industry Now, and in the Future

Pope, Michael Carl¹ (1) Washington State University, Pullman, WA

The state of the global climate has fluctuated, sometimes rapidly, between greenhouse and icehouse conditions since at least 2 Ga. During the Paleozoic there were three main periods of widespread continental glaciation: Late Ordovician, Late Devonian, and Carboniferous-Permian. These periods are characterized by low atmospheric pCO2 content and large-scale (>20 m) high-frequency (20-400 k.y.) eustatic sea level oscillations which partition carbonate reservoir rocks differently than they are partitioned during greenhouse periods. Late Ordovician climate change produced a long-term transitional climate phase (454 Ma-442 Ma) that is characterized in North America by carbonate parasequences indicating ~20 m sea level fluctuations, overlain by long-term sequences (1-3 Ma duration) with little or no evidence for high-frequency parasequences. The acme of continental glaciation centered on Africa was very short-lived (possibly < 1 Ma) and formed a widespread unconformity on many other continents. The Carboniferous-Permian glaciation occurred in pulses with larger continental icesheets during the late Mississippian-early Pennsylvanian, the middle Pennsylvanian and the late Pennsylvanian-Early Permian. The waxing and waning of these glaciers produced both cyclothems and larger-scale asymmetric sequences with fewer parasequences. The record of these glacial events is well-recorded in rocks, and with greater and greater emphasis on high-resolution stratigraphic studies we are beginning to gain more insight into the mode and tempo of these climate shifts. If atmospheric CO2 continues to increase at its present rate the only true analogs we may soon have to understand future rapid climate fluctuations will have to come from studies of these ancient rocks.