APTIAN STAGE

the fifth of six main divisions (in ascending order) in the Lower Cretaceous Series, representing all those rocks deposited worldwide during the Aptian Age (119 to 113 million years ago). No global stratotype section and point (GSSP) for the base of the Aptian Stage has been approved by the International Commission on Stratigraphy. The name of the stage is derived from the town of Apt in Vaucluse dpartement in southeastern France, for which the surrounding area serves as the classic type district for rocks of this age. In England the Aptian Stage is represented by part of the Lower Greensand formation. Elsewhere in northern Europe it consists of portions of the thick Hils Clay, while in the United States it includes the Dakota Sandstone. The first occurrence of the ammonite cephalopod Prodeshayesites marks the base of the Aptian Stage in England, Germany, and France. The calcareous nannofossil biozones of Nannoconus bucheri and N. wassalli and the fossil zones of the planktonic foraminifera Globigerinelloides algerianus and G. blowi are also considered diagnostic for rocks of this stage. Rocks of the Aptian Stage overlie those of the Barremian Stage and are overlain by rocks of the Albian Stage.