ELSEVIER Earth and Planetary Science Letters 160 (1998) 147–161 Orbital cyclicity in the Eocene of Angola: visual and image-time-series analysis compared B. D’Argenio a,c,Ł , A.G. Fischer b , G.M. Richter d , G. Longo e , N. Pelosi c , F. Molisso c,f , M.L. Duarte Morais g a Dipartimento di Scienze della Terra, Universita ` di Napoli, Largo San Marcellino, 10, 80138 Naples, Italy b Department of Earth Sciences, University of Southern California, Los Angeles, CA 90089-0740, USA c Istituto di Ricerca GEOMARE, CNR, via A. Vespucci, 9, 80142 Naples, Italy d Astrophysikalisches Institut Potsdam, ander Sternwarte, 16, 14482 Potsdam, Germany e Osservatorio Astronomico di Capodimonte, via Moiariello, 16, 80131 Naples, Italy f Institut und Museum fu ¨r Geologie und Pala ¨ontologie, Universita ¨t Tu ¨bingen, Tuebingen, Germany g Departamento de Geologia da Universita ` A. Neto, Luanda, Angola Received 21 August 1997; accepted 24 April 1998 Abstract 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.  1998 Elsevier Science B.V. All rights reserved. Keywords: periodicity; cyclic processes; image analysis; Eocene; Angola 1. Introduction The stratigraphy of many pelagic and hemipelagic sediments contains rhythmic oscillations in carbon- ate content, optically expressed in colour and resis- tance to weathering. In some cases this rhythmicity is simple, but commonly it takes a hierarchical form. In this, high-frequency oscillations (couplets of a more clayey bed followed by a more limy one) are Ł Corresponding author. Tel.: C39 (81) 597-9220; Fax: C39 (81) 597-9222; E-mail: dargenio@gms01.geomare.na.cnr.it modulated by a longer-period oscillation in which progressively more clayey couplets are followed by progressively more limy ones, and back, so that the couplets become grouped into bundles. Such bun- dled sequences in turn may be similarly modulated on a yet longer scale, in which successive bun- dles become more calcareous and less calcareous, to divide the sequence into superbundles. Examples of such sequences are the Aptian–Albian of cen- tral Italy [1–4], the late Maastrichtian of northern Spain [5], and the Quaternary of the eastern Gulf of Mexico. 0012-821X/98/$19.00  1998 Elsevier Science B.V. All rights reserved. PII S0012-821X(98)00074-0