Compound Delta Clinoforms: A Geospatial Quantitative Analysis of Modern Deltas and Their Relation to Ancient Deposits

Compound delta clinoforms have long been recognized in modern (Holocene) deltaic systems, where they exhibit a platform (meters to tens of meters deep) between their shoreline and subaqueous rollovers. While their morphology is noticeable on bathymetry maps and shallow seismic surveys, little effort has been dedicated to spatially delineate subaqueous deltas morphologies at and away the sediment sources, and relate these architectures to stratigraphically constrain ancient deposits. This study utilizes high-resolution bathymetry grids of over 20 modern deltas to establish a foundational understanding of compound clinoforms morphologies supported by a robust geospatially quantitative analysis across deltas dominated by wave and tide processes. Gradient maps consistently show two main rollovers that display varying delineated geometries at and away from the main riverine sediment source. This spatially geometric mosaic between the bedforms—shoreline clinoform, subaqueous clinoform, and the platform in between—suggest an intricate sediment discharge rate and transport interaction at river mouths and their delivering basins, where dominant signatures of fluvial, tidal, and wave energies vary along the basin and can morph each bedform uniquely along the entire delta. A review of grainsize distribution in front of some Holocene deltas shows that subaqueous platform and subaqueous clinoform are not entirely smooth and muddy as usually assume but can have sand accumulations and irregular surfaces. Extracting geospatial frameworks from modern observations support delta numerical models and facilitate reinterpretation of the Cretaceous Kenilworth Member outcrops in the Blackhawk Formation along the Book Cliffs, Utah, where we suggest a new compound delta clinoform hypothesis.