THE VARVE MICROCOSM: PROPAGATOR OF CYCLIC BEDDING

Changes in the proportion of seasonal components within varves accumulate over time to produce cyclic bedding. A varve couplet is therefore a microcosm of bedding at a larger scale within the same stratigraphic unit. Cyclic bedding arises from a differing physical response or a phase-shifted temporal response to climatic forcing. An example from the Permian Castile formation suggests that the skipping of climatic cycles by the bedding response may be a common occurrence leading to erroneous estimates of the frequency of cyclic bedding. Seasonal changes that generate cyclic bedding occur in two domains of episodic sedimentation, separated by a megathreshold between pelagic and advective environments. Cumulative changes responsive to seasonality within either domain, can produce several types of cyclic bedding over a broad range of frequencies, extending into the Milankovitch band.