U-Pb calcite age of the Late Permian Castile Formation, Delaware Basin:: a constraint on the age of the Permian-Triassic boundary (?)

Organic-rich calcite laminated with gypsum in the evaporitic, non-fossiliferous Castile Formation of the Delaware Basin, southwest USA, yields a Total Pb/U isochron age of 251.5 +/- 2.8 Ma (MSWD = 1.3). The Castile Formation is almost certainly Late Permian based on its Sr-87/Sr-86 value of 0.706923, identical to the distinct minimum in the late Permian Sr curve. In this paper we explore the potential for using U-Pb calcite ages to date traditionally undatable sections and show how this southern-midcontinent USA (far west Texas and southeast New Mexico) deposit can be correlated to the type section in China. We accept that diagenetic alteration can bias U-Pb results, but the data set we present shows no evidence for such alteration. Clearly with alteration the age we present would represent a minimum age for the Castile Formation. If the age actually dates the Castile Formation then it requires the Permian-Triassic boundary to be younger than 251.5 2.8 Ma. (C) 2002 Elsevier Science B.V. All rights reserved.