University of Cambridge > Talks.cam > Department of Earth Sciences Seminars (downtown) > SCALING LAWS FOR AGGRADATION AND PROGRADATION OF THE STRATIGRAPHIC RECORD

SCALING LAWS FOR AGGRADATION AND PROGRADATION OF THE STRATIGRAPHIC RECORD

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Aggradation, progradation and accommodation of stratified sediments are unsteady, reversible processes. Their net rates scale inversely with averaging time. Although isolated rate determinations have little predictive value, the shapes and slopes of empirical scaling law relationships between the logarithms of rate and averaging time or the logarithms of distance and averaging time reveal properties of the accumulation process, including the contributions of periodic and stochastic components. The intersections, ratios and products of pairs of scaling laws reveal characteristic dimensions of the stratigraphic record. The negative slope of the scaling law for sediment aggradation steepens with stratigraphic incompleteness; i.e. the proportion of time represented by hiatus. For peritidal carbonates, the scaling law predicts characteristic hiatus durations at Milankovitch time-scales. The intersection of two scaling laws reveals the expected time scale at which the rates balance. Thus, scaling laws for shallow marine aggradation and accommodation intersect at the characteristic time scales of upward-shallowing cyclothems. The ratio of aggradation to progradation rates is time scale dependent for floodplains and continental shelves. At averaging times shorter than Milankovitch scales, progradation shows positive feedback and aggradation has negative feedback. At longer time scales the relationship reverses. Thus, the expected shape of composite, clinoform, time-stratigraphic units is time- and size-scale dependent. The product of aggradation and progradation rates is sediment flux. For terrigenous passive margins this product is not time scale dependent. Passive margins may be characterized by a constant expected sediment flux at all time- and size-scales from ripples to whole shelves.

This talk is part of the Department of Earth Sciences Seminars (downtown) series.

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