Small-scale cyclicity in stratigraphic sequences (1 mm–10 m) is often attributed to regular orbital signals. Commonly, however, these signals are overprinted by other signals. A dynamic forward model for clastic sedimentation in foreland basins suggests that this overprint can be caused by slope instability, stress variations in the lithosphere, and autocyclicity induced by climate change. Spectral analyses of predicted sedimentation rates with various external controls demonstrate the occurrence of autocyclic fluctuations in sediment flux on time scales smaller than the time scale of the variation of the original, triggering, external control. This feature probably represents the response of the sedimentary system to external variations, depending on the eigenfrequencies of this system. Because the eigenfrequencies are determined by the basin geometry, changing through time, a chaotic frequency distribution of sedimentation rates is expected. This hypothesis explains the commonly observed absence of a significant number of frequencies of the orbital spectrum in a large number of sediment sequences.

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