RELATIONSHIP BETWEEN AVULSION BEHAVIOR AND BASIN-FILLING SEDIMENTATION PATTERNS: LESSONS LEARNED FROM PHYSICAL EXPERIMENTS

The evenness or unsteadiness with which sedimentary systems move across and fill basins imparts fundamental patterns into the stratigraphic record. Recent studies show that paleoenvironmental (allogenic) signals preserved in the stratigraphic record may be contaminated or overprinted by internally generated (autogenic) sedimentation patterns; however, it is currently unclear over what temporal and spatial scales autogenic patterns are most prevalent. Basin-filling patterns are heavily influenced by avulsion dynamics in channelized systems; consequently, constraining long-timescale avulsion behavior provides a way of evaluating autogenic stratigraphic patterns and scales in sedimentary deposits. Utilizing recently developed statistical methods, we quantify basin filling trends in three laboratory experiments and compare stratigraphic organization to avulsion behavior. Specifically we use the compensation index, a measure of the rate of decay of spatial variability in sedimentation between picked depositional horizons with increasing vertical stratigraphic averaging distance, to estimate stratigraphic organization. In the three experiments topography of channelized deltas formed by weakly cohesive sediment were monitored along flow-perpendicular transects at a high temporal resolution relative to channel kinematics. Over the course of the experiments a uniform relative subsidence pattern, designed to isolate autogenic processes, resulted in the construction of stratigraphic packages in excess of 25 times the depth of the experimental channels. We explore how the compensation index, and thus the degree of stratigraphic organization varies as functions of 1) time-scale of measurement, 2) relative proximal to distal location in a basin, 3) the ratio of sediment discharge to water discharge and 4) the size of a sediment transport system relative to the basin it is filling.