Abstract

On the basis of the recent data set published by Thomel [1992], the ammonoid biochronology of the Cenomanian Stage of southeastern France is reevaluated. A data set comprising 138 ammonite species from 40 sections is processed with the unitary association method [Guex, 1977, 1991]. A logical succession of analyses optimizes these data and stresses the major inconsistencies in the original documentation. It leads to the construction of a sequence of 27 unitary associations which are grouped into 7 laterally reproducible association zones. Application of this revised zonation highlights lateral facies changes even in the distal part of the basin as well as some diachronism at the species level (inclusive of some index species). It also suggests a sequence of progressively dampened pulsations in the rates of faunal turnovers during the early and middle Cenomanian, until equilibrium was reached during the late Cenomanian to the early Turonian, without any apparent change at the Cenomanian-Turonian boundary. This trend was also accompanied by significant changes in species diversity, with an abrupt doubling during the late early Cenomanian and a protracted decrease from the late-middle Cenomanian onwards. Finally, this zonation is compared to the current synthetic scales of southeastern France and of the Anglo-Paris Basin.

First Page Preview

First page PDF preview
You do not currently have access to this article.