Compensational Stacking of Channelized Sedimentary Deposits
Compensational stacking, the tendency for sediment transport systems to preferentially fill topographic lows through deposition, is a concept widely used in the interpretation of the stratigraphic record. We propose a metric to quantify the degree of compensation by comparing observed stacking patterns to what would be expected from simple, uncorrelated stacking. This method uses the rate of decay of spatial variability in sedimentation between picked depositional horizons with increasing vertical stratigraphic averaging distance. We present data from six sedimentary basins where this decay can be measured. The depositional environments range from river deltas to deep water minibasins and in scale from the laboratory to 1.2 km of thickness. The decrease in standard deviation of sedimentation/subsidence with increasing vertical averaging distance is well described by a power law in each study basin. We term the exponent in this power law the compensation index, kappa. The value of kappa is 0.5 for uncorrelated stacking and 1.0 for perfect compensational stacking. Parameters controlling the magnitude of kappa include the frequency of system-scale avulsions and the variability of deposition rates. Data describing the decay in the standard deviation of sedimentation/subsidence from all studied basins collapse onto a single power law trend when the measurement window is nondimensionalized by each system’s mean channel depth. This observation indicates that regardless of depositional environment, the key parameter controlling stratigraphic architecture is channel depth.
AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009