If the base of the Maastrichtian Stage is placed at the first appearance ofthe belemnite Belemnella lanceolata in Western Europe, the boundary between the Campanian and Maastrichtian stages in the U.S. Western Interiormay lie between the zones of Baculites jenseni and Baculites eliasi. The B. jenseni Zone can be shown to be latest Campanian in age on the basis of the occurrence of Nostoceras (N.) hyatti Stephenson and Jeletzkytes nodosus (Owen), which range to the top of the Campanian in the well-dated Vistula Valley sequence in Poland, but disappear before the first appearance of B. lanceolata. So defined the numerical age of the Maastrichtian lies between 73.2 ± 0.7 and 70.1 ±0.7 Ma, based upon dates from high temperature chronometers in bentonites in the Western Interior. © 1992, Cambridge University Press. All rights reserved.
