ID-TIMS U-Pb ZIRCON RADIOMETRIC AGES FOR THE PENNSYLVANIAN-CISURALIAN TIME SCALE: IMPLICATIONS FOR GLOBAL CORRELATION AND RATES OF PROCESSES

点击翻译按钮获取中文摘要

Schmitz0418703The Late Pennsylvanian through Early Permian was an important interval in Earth's history.Significant events of this age include the final assembly and early evolution of Pangea, major eustaticchanges in sea level, and global climate change from the Pennsylvanian 'ice house' to the Permian 'hothouse.' Unfortunately, the poor temporal resolution of the geologic time scale during this intervalsubstantially limits our ability to clarify and correlate many aspects of late Paleozoic geologic history.Commonly cited time scales differ by as much as 14 Ma in the estimated age of the Pennsylvanian-Permian boundary, and vary by 500% in the inferred duration of various stages. Significant uncertaintiesin this part of the time scale arise because numerical ages assigned to period and stage boundaries arebased on linear interpolation between relatively sparse control points. Moreover, the existing controlpoints were obtained from geographically disparate stratigraphic sections, assigned positions in the timescale using several different taxa, and dated by several different radiometric techniques. Because muchfundamental research depends directly on the accuracy and precision of the geologic time scale,improving its age calibration is critical, and requires a robust, well-constrained, and internally-consistentframework of biostratigraphic and geochronologic data for the Late Carboniferous to Early Permian.This is a three-year multidisciplinary research effort to calibrate this interval of the time scaleusing the type sections and principal reference sections in the southern Ural foreland of Russia-Kazakhstan. Three aspects of the southern Urals make this an excellent laboratory for age calibration:first, the internationally accepted definition of the chronostratigraphic scale for Early Permian(Cisuralian) comes from this region, and it is a principal reference area for the Late Pennsylvanian aswell; second, late-Paleozoic marine fauna (including small foraminifera, fusulinids, conodonts, andammonoids) are numerous and well preserved, allowing precise biostratigraphic control; and third,interstratified volcanic ashes are common, making precise radiometric age control achievable. The proposed study will have truly global significance. Researchers worldwide working on a broadrange of Late Paleozoic problems will benefit directly and measurably from the results.