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 patterns of two types: (a) hierarchically cyclic variation in calcium carbonate/clay ratios forming couplets grouped into bundles at ratios of ca. 5 : 1; these are coupled with (b) a redox cycle of bottom waters, expressed in darkness of sediment (organic carbon) and variations of the ichnofauna. These patterns resemble those previously observed in the pelagic Albian Scisti a Fucoidi of Italy. Visual study and time-series analysis based on image processing provide ratios compatible with those of Milankovitch theory. Whereas the chronostratigraphic control in Angola does not afford a basis for an independent chronology, the similarity to the Italian Albian supports attribution of these rhythmicities to orbital forcing.