Geological Society of London
2 files

High-precision U–Pb zircon CA-ID-TIMS dates from western European late Viséan bentonites

posted on 2016-06-21, 11:38 authored by Michael A. Pointon, David M. Chew, Maria Ovtcharova, George D. Sevastopulo, Bernard Delcambre

Three new U–Pb zircon chemical abrasion isotope dilution thermal ionization mass spectrometry dates obtained from late Viséan Belgian bentonites are reported and are used to estimate the periodicity of early Warnantian shallowing-upwards carbonate parasequences that are interbedded with the dated bentonites. Early Warnantian parasequences exhibit mean cycle periodicity values that are consistent with the c. 100 ka Milankovitch cycle, which is the dominant Milankovitch frequency recognized from recent Pleistocene glacial records, and thus strengthen the arguments for (1) these sedimentary cycles being of glacio-eustatic origin and (2) the initiation of the main phase of late Palaeozoic glaciation before the start of or during earliest Warnantian times. The new dates also provide additional high-precision age constraints for the improved calibration of the Mississippian time scale. Using the new dates, the stratigraphical age of the Clyde Plateau Volcanic Formation, Midland Valley of Scotland, is revised from Holkerian to early Asbian.