Biostratigraphic Correlation of the New Devonian Timescale using Palynology
G. M. G. Hughes
University College Cork, Dept. of Geology, Cork, Ireland
A new and radical Devonian timescale has recently been proposed based on U-Pb zircon ages of volcanic ash horizons that occur throughout the Devonian succession in eastern USA and eastern Canada. These radiometric dates suggest the base of the Devonian lies close to 418 Ma and the top close to 362 Ma. This lengthens the Devonian by 20% over its previously accepted length.
The aim of this study is to produce an inter-calibration of isotopic, palynostratigraphic and stratigraphic data for the Devonian of the Appalachian Basin. Palynological samples have been collected from sequences above and below ash horizons within the Lochkovian,Emsian(?), Eifelian and Frasnian intervals in New York, Virginia, West Virginia and Tennessee. These are being studied to assign palynostratigraphical ages using spores, acritarchs and chitinozoans. Initial results from spores from the Esopus shale Formation of New York State, previously thought to be of early Emsian age, indicate a late Pragian age. An ash bed from the Esopus has been dated at 408.3+ 1.9 Ma. Samples from the top of the Briery Gap sandstone of the Foreknobs Formation,West Virginia, contain Teichertospora torquata, giving an age no older than the latest Frasnian. These, together with other localities, which are yielding good palynological assemblages, allow for the correlation of Appalachian Devonian stratigraphy and palynological zonation schemes.
AAPG Search and Discovery Article #90902©2001 AAPG Foundation Grants-in-Aid