The effect of differential compaction on shelf-edge trajectories

Abstract

Clinoforms are sigmoidal strata that prograde toward the deep part of a basin. Their geometry allows us to define shelf-edge trajectories, which are then used to infer temporal and spatial variations in sediment transfer, relative sea-level change and paleobathymetric configurations. Trajectory analysis is typically conducted on deeply buried successions, in which the primary stratigraphic architecture is modified by sediment compaction. Furthermore, the impact of dip-oriented lithological heterogeneity within clinothems during compaction is not considered. Here, we present a new approach to decompaction of clinothems that accounts explicitly for the down-dip variation in their lithology. This approach reveals that greater, or preferential, compaction of fine-grained foresets and bottomsets results in a basinward rotation of trajectories. In some cases, shelf-edge trajectories can change from rising, normal regressive trajectories to apparently falling, forced regressive trajectories, leading to erroneous interpretations for the timing and volume of sediment transfer. Also, preferential compaction counter-intuitively steepens and vertically extends rather than compresses clinothems after burial. This opposes the results of decompaction methods that do not account for basinward variations in lithology and affects interpretations of paleobatymetry and slope processes, thus implying a lithologically controlled component onto the traditional understanding of trajectory analyses, sequence stratigraphy and clinoform geometry analysis.