Arguments against biograded age estimates (and their application to chronology and sequence stratigraphy) in southwest France

The biograded age estimates calculated from a morphometric index based inte rpolation procedure using the Rosita (Contusotruncana) lineage have been us ed to document the geology of deposits of the Pyrenees in the late Cretaceo us. These estimates show geological inconsistencies whose size is greater t han the precision (relative uncertainty) assumed by the theory. For example, in the sub-Pyrenean basin, a lithological interface was said t o be synchronous according to the biograded age estimates; in contrast, amm onites put this interface into three different biozones, covering several M a, depending on the locality. In the Bale de Loya succession (Basque countr y), the biograded age estimates would indicate a continuous depositional se quence; in fact, the tectonic structure and calcareous nannofossil data pro ve that the succession has been duplicated, each repetition containing bioz ones several m.y. long. In the Coniacian - Santonian stages in the eastern Pyrenees, biograded age estimates have been published; comparison with the ammonite fauna whose North American equivalents have been radiometrically d ated, shows inconsistencies of 1 to 3 Ma. Finally, the use of the interpola tion theory for sequence interpretation of the Aquitaine deposits (sub-Pyre nean basin and the reference-section at Tercis-les-Bains) leads to inconsis tencies which are difficult to explain: (a) a sequence boundary has been gi ven different dates (for a single reference calibration using the same foss ils at the same place) with no explanation; (b) biograded estimates of age suggest a diachronism of the internal systems-tracts within homologous sequ ences with synchronous external limits which seems difficult to accept; (c) "changes" in dates larger than the assumed precision of the interpolation procedure as published from one paper to another, but without explanation. The variation in the published dates for the top and bottom of a unit may b e greater than the duration of the unit itself. These facts establish that the precision and reproducibility of biograded age estimates have been fund amentally over estimated. The variations suggest that the method is unappro priate for solving problems of age. In fact, we suspect that we have demons trated that the published biometric indices are influenced by factors other than time alone.