NUMERICAL-ANALYSIS OF SEDIMENTARY COMPONENTS - A KEY FOR INTERPRETATION OF MACROSCOPIC AND MICROSCOPIC FEATURES IN AMMONITICO ROSSO FACIES (UPPERMOST JURASSIC LOWERMOST CRETACEOUS)

The relationship between macroscopic and microscopic features in the w idespread Tethyan ammonitico rosso facies, traditionally considered co mparatively uniform, is analyzed for the first time using the discrimi natory power of numerical analysis, This methodology has been applied to selected sedimentary components in four macroscopically distinguish ed type facies and 91 thin sections studied in three uppermost Jurassi c (Tithonian)-lowermost Cretaceous (Lower-Middle Berriasian) sections from the Sierra Norte (Mallorca, Spain). Cluster analysis (17 variable s) and principal-component analysis (7 variables) reveal microfacies g rouping by stratigraphy and depositional conditions, Without resedimen tation, high values of the D-link/D-max ratio in cluster analysis are interpreted as caused by synsedimentary and early diagenetic dissoluti on phenomena, bioturbation, and time-averaging effects related to low sedimentation rates, In addition, the resulting information provided b y principal-component analysis (Components 1, 2, and 3 explaining 75% of variance) emphasizes subtle depositional trends (differential fabri cs) id such a homogeneous facies by skeletal composition, in which win nowing and slow sedimentation were relevant, Biological, taphonomic, a nd sedimentary processes affected significant variables, explaining 85 % of the total variance.