DATING OF THE TIME OF SEDIMENTATION USING U-PB AGES FOR PALEOSOL CALCITE

We have sampled paleosol horizons from a continuous core of a rapidly deposited Late Pennsylvanian-Early Permian marine shelf section in Tex as, USA. The paleosols occur on the tops of shoaling upward cycles and , based on current time constraints, these cycles average 250 ka and c annot represent longer than 400 ka. As the unconformity which is repre sented by the paleosol can only be a fraction of the time allowed for deposition of the cycle, the age of minerals that form in the paleosol is effectively the time of sedimentation. The uncertainty on the U-23 8-(206)pb,ge of brown paleosol calcite from one exposure surface is on ly 1 Ma. Reported uncertainties on Paleozoic boundaries are greater th an 10 Ma. Our early results suggest that the marine sedimentary record may be dated to a precision of 1 Ma with U-Pb analyses of carefully s elected paleosol calcite. These results have implications for vastly i mproving time resolution of the rock record. Copyright (C) 1997 Elsevi er Science Ltd.