Controls on the Geometry of Shelf-Edge Deltas

Despite their important role in sediment dispersal to marine environments, and their influence on the geomorphology and hydrodynamic setting of continental margins, shelf-edge deltas are commonly overlooked in source-to-sink models, perhaps because few are developed during present-day highstand conditions. In subsurface and outcrop, their recognition can be difficult where information on the physiographic environment is limited. Moreover, it has yet to be determined whether specific architectural and geometric characteristics of accumulated deposits of these deltaic systems can be linked to specific attributes of their environmental setting.

To address these issues, a comparative, global-scale metastudy of >40 Permian to late Quaternary successions has been undertaken to increase our understanding of factors that govern the geometric characteristics of deltaic architectural elements (e.g. delta lobes, delta complexes) and of relationships between delta geometry and attributes of their paleoenvironmental setting.

Selected findings of the study are: (i) moderate to strong scaling is seen for lengths, widths, thicknesses and areas of delta lobes and delta complexes; (ii) the internal hierarchical organization (single lobe vs. multiple lobes) of shelf-edge deltas cannot be reliably estimated based on their geometry and vice versa; (iii) hydrodynamic conditions and margin configuration associated with open seas are associated with the development of shelf-edge deltas with greater lengths and widths compared to their counterparts in semi-enclosed and enclosed seas; (iv) deltas sourced by multiple rivers tend to be longer and more extensive than deltas supplied by a single fluvial system; (v) paleolatitude is not an effective predictor of shelf-edge delta geometry.

Our analysis confirms that shelf-edge deltas can evolve in a complex manner due to the interplay of their controlling factors. Nonetheless, tentative predictions of their geometry can be attempted based on knowledge of certain environmental controls.