ORBITAL CYCLICITY IN THE EOCENE OF ANGOLA - VISUAL AND IMAGE-TIME-SERIES ANALYSIS COMPARED

Photographic coverage of hemipelagic Eocene marls of Angola (Africa), supplemented by limited sampling, shows rhythmic stratification patter ns of two types: (a) hierarchically cyclic variation in calcium carbon ate/clay ratios forming couplets grouped into bundles at ratios of ca. 5: 1; these are coupled with (b) a redox cycle of bottom waters, expr essed in darkness of sediment (organic carbon) and variations of the i chnofauna. These patterns resemble those previously observed in the pe lagic Albian Scisti a Fucoidi of Italy. Visual study and time-series a nalysis based on image processing provide ratios compatible with those of Milankovitch theory. Whereas the chronostratigraphic control in An gola does not afford a basis for an independent chronology, the simila rity to the Italian Albian supports attribution of these rhythmicities to orbital forcing. (C) 1998 Elsevier Science B.V. All rights reserve d.