Abstract: Spectral and Markovian Analysis of Bed Thickness and Lithologic Periodicities in Turbidite Successions of Monte Antola Formation, Northern Apennines, Italy

J. H. Doveton, I. P. Martini, M. Sagri

The Monte Antola Formation of Late Cretaceous (Turonian-Maestrichtian) age crops out extensively in the northern Apennines and consists of graded units of calcareous sandstone, sandstone, marl, and shale. The Cerreto, Bruggi, and San Donato members constitute lateral facies subdivisions which range from proximal channelized turbidites to distal prograding turbidites in a generalized environment interpreted as abyssal plain.

Repetitive patterns in lithologic sequence of the turbidite associations generally are distinctive and are described satisfactorily by first-order Markov chains. The Antola Member alone has additional second-order Markov properties. Imaginary eigenvalues of the transition-probability matrices for all but the Bruggi Member demonstrate a strong cyclic character to lithologic ordering within the formation.

Systematic long-term variations in the sequence of bed thickness development in measured sections are commonly subtle and equivocal, and pose special problems in interpretation. Fourier analysis was applied to the task of partitioning fundamental wavelengths from "background noise" introduced by essentially random depositional events. In all members there is a strong short-term wavelength of 2 to 3 beds indicative of alternating thin and thick beds and judged to be typical of turbidite sequences; an intermediate wavelength ranging from about 5 beds (proximal facies), 8 beds (distal), to 9 beds (very distal); a poorly defined long-term wavelength of between 30 and 80 beds. Phase angles associated with the computed power spectra give indications as to the asymmetry (thickening, or thinning upward) or symmetry of the intermediate-term repetitive units.

AAPG Search and Discovery Article #90972©1976 AAPG-SEPM Annual Convention and Exhibition, New Orleans, LA