Bed-thickness distributions of alternating coarse and fine layers in flysch sequences can be regarded as the realization of a stochastic point process. The study is similar to that of earthquakes, if the log thickness of the coarse layer is treated as earthquake magnitude and the linear thickness of the fine layer is considered as the waiting time between earthquake events. A set of 489 sandstone-shale couplets measured in a flysch sequence totalling 420 ft in thickness from the Upper Cretaceous Cedar District Formation in southwest British Columbia, demonstrates that the frequency-log-thickness diagram for the sandstone beds is similar to that observed for magnitude-frequency diagrams of present-day earthquakes. Sandstone beds greater than 2 in. in thickness are essentia ly Poisson distributed over the interval studied, whereas beds less than 2 in. are nonrandomly distributed. The lack of correlation in thickness between successive sandstone-shale, shale-sandstone, and shale-shale beds is indicative of a renewal rather than a Markov process. The process is nonstationary, however, in that the sandstone/shale ratio decreases systematically from a value of approximately 2 to a value of approximately 1, although the number of sandstone beds per unit thickness of shale essentially triples from older to younger strata. The data are consistent with the hypothesis of a progressively deepening basin and a progressively diminishing sand supply, with sand being delivered from more widely distributed source areas.

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