Filtering of Depositional Events and the Completeness of Sedimentary Sequences

The preservation of depositional events in sedimentary sequences is investigated using a Monte-Carlo model in which sedimentation rates are constant and the magnitudes of the events follow a lognormal frequency distribution. The model indicates that sedimentation processes act as a stationary, low-pass filter that preserves an amplitude-distorted record of the depositional events imposed on the modern environment. This low-pass filter gives rise to two concepts of completeness of sedimentary sequences: (1) Preservation of time lines in sedimentary sequences, or temporal completeness; and (2) Preservation of depositional events in sedimentary sequences, or spatial completeness. The model suggests that as sedimentation rate decreases, (1) the number of time lines preserved decreases exponentially and the completeness of the record of depositional events decreases linearly; and (2) low-magnitude events are progressively eliminated from the record. The latter characteristic of the model, which arises because of the assumption of stationarity of the time series, may be in conflict with observations from real sedimentary sequences. A nonstationary component can be added to the model by taking into account other depositional variations that have been observed in modern environments.