U-PB DATING OF A REMAGNETIZED PALEOZOIC LIMESTONE

The Upper Ordovician Trenton Group of New York State is one of a number of Appalachian limestones which yields paleomagnetic poles suggesting disturbance in the late Paleozoic. Calcite fractions dissolved from samples of the Trenton Limestone define a U-238-Pb-206 age of 454 +/- 8 Ma (MSWD = 12.8) in excellent agreement with 40Ar-39Ar and U-Pb ages for the deposition of the underlying Diecke Bentonite. This requires that the U-Pb system in the calcite has been preserved since deposition and early diagenesis. If late Paleozoic remagnetization of this limestone was induced by fluids, these fluids did not interact with significant amounts of carbonate. The apparent robustness of the U-Pb system, and the large spread in mu-values (18.17 -118.8), offers potential precision of +/- 1 Ma in determining the Paleozoic time scale.