A New Look at Sedimentation Rates and the Completeness of the Stratigraphic Record

Abstract

Several recent papers have suggested that completeness of stratigraphic sections can be estimated by using the ratio of long-term sedimentation rates to short-term rates. We show that the median short-term sedimentation rates used in these papers are erroneous and are mostly an artifact arising from improper data manipulation. To demonstrate the artificial character of short-term median rates, we have generated a series of plots assuming a constant sedimentation rate with fixed variance and defined limits of measurement precision. These plots demonstrate that increasing variance in the time required to deposit sediments will result in spuriously high short-term median sedimentation rates. A new method for calculating median sedimentation rates, which eliminates the problem of spurious median rates, is then applied to make an improved estimate of expected completeness. Recalculated median values show that sedimentation rates for pelagic sediments are close to identical for both short-term and long-term tim...