PENNSYLVANIAN-CISURALIAN INTERNATIONAL TIME-SCALE AND NEW OPPORTUNITY IN ITS PRECISE RADIOMETRIC CALIBRATION

The Late Paleozoic was an important interval in Earth’s history that associated with the final assembly and early evolution of Pangaea, major eustatic changes in sea level, and global climate change from the Pennsylvanian “ice house” to the Permian “hot house”. The detailed, high-resolution conodont/foraminiferal/ammonoid zonation for the Pennsylvanian-Cisuralian contrasts sharply with the handful of useful radiometric dates employed in this time scale building. With a duration of the Pennsylvanian-Cisuralian Epochs close to 50 m.y. the zones on average give a resolution better than 1.5-1.0 my, whereas on average there is less than one radiometric date per 10 my. Worse, there are no dates for most of the Bashkirian, Sakmarian, Artinskian and Kungutian and single dates only in the Moscovian, Kasimovian and Gzhelian. The biostratigraphic calibration is also compromised in that the dates for the upper Pennsylvanian and the rest of Cisuralian come from continental sequences of Western Europe that only poorly correlate with marine sequences in the type regions. Dates assigned to biostratigraphically well-constrained western European regional stages within the Namurian and Westphalian are needed to correlate with the well-calibrated standard biozonal scales and international stages. Similar issues compromise the few available radiometric constraints on the Cisuralian from Australia. Although Permian biostratigraphy of Australia is reasonably established, it is based on provincial foraminifers, palynomorphs, and brachiopods and cannot provide reliable global correlation.

Numerous interstratified volcanic ash layers within well biostratigraphically constrained sequences were currently found in the upper Paleozoic sections of the southern Urals. In the majority of samples conodonts and radiolaria were recovered along with excellent and numerous zircons. The ability to obtain detailed paleontologic data and precise radiometric ages from the same stratigraphic horizon provides a potentially powerful tool for calibration of this interval of the time scale with quantitative approaches, as well as understanding process rates in paleobiology, paleoecology, paleoclimatology, paleotectonics and sedimentology. The project is supported by the NSF grants EAR 0106796 and EAR-ITR 0218799