Dating of the time of sedimentation using UPb ages for paleosol calcite

Abstract

We have sampled paleosol horizons from a continuous core of a rapidly deposited Late Pennsylvanian-Early Permian marine shelf section in Texas, USA. The paleosols occur on the tops of shoaling upward cycles and, based on current time constraints, these cycles average 250 ka and cannot represent longer than 400 ka. As the unconformity which is represented 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 238U 206Pb age of brown paleosol calcite from one exposure surface is only 1 Ma. Reported uncertainties on Paleozoic boundaries are greater than 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 selected paleosol calcite. These results have implications for vastly improving time resolution of the rock record.