Analyse factorielle et nuées dynamiques appliquées a l'étude de biofaciès et de leurs enchainements séquentiels: Exemple de l'Albien Portugais

Abstract

Factorial analysis of correspondences, dynamic cluster analysis and various statistic treatments allow an objective description of the distribution of fossiliferous deposits, organic population and their affinities, and bring out the ecological factors involved. They can also be used to visualize sequential evolutions and the importance of the discontinuities. Albian in Portugal is used to as an example: 6 fossil's clusters, gathering taxons which tend to cohabit or to be associated with the same taxons in similar surroundings, are revealed. The superposition to 6 deposit's clusters proves the affinities which exist between species and environments, each cluster materializing thus an ecozone. Factorial axis 1 and 2, quadratically linked by the «Guttman effect. transcribe the internal — external gradient. Consequently, regressive and transgressive ecosequences can be logically visualized by the succession along the parabolic direction of points representing deposits. Sequential discontinuities can be quantified by the distance between the representative points of the lower sequence and the first term of the upper one.