Compound delta clinoforms : an analysis of its morphology and deposits from modern and ancient examples

Abstract

Recent recognition of compound delta clinoforms reveal pillars to understanding delta progradation and uncover a significant misunderstanding in deltaic architecture. Little effort has been dedicated to spatially delineate delta 3-D morphologies at and away the sediment sources and relate these architectures to stratigraphically constrain ancient deposits. Our assessment of over 35 Holocene deltas allowed the consolidation of a robust geospatial qualitative and quantitative analysis where we consistently observe two main gradient breaks at tens of meters water depth that display varying delineated geometries. The resulting geospatial framework reflects relatively steep shoreline and subaqueous clinoforms – reaching up to 0.49 degrees – separated by a gently dipping platform of maximum 0.11 degrees, and variability in geospatial distance relative to the sediment source and basinal energies. As a result, the extracted geospatial frameworks from modern observations facilitate reinterpretation of ancient deposits, where most compound delta clinoform recognition difficulty arises from the lack of facies criteria, especially for the subaqueous delta, and the limited incorporation of modern systems’ insights. We evaluate the Cretaceous Kenilworth Member of the Blackhawk Formation along the Book Cliffs outcrop belt in Utah, and suggest a new compound delta clinoform hypothesis. Outcomes of this study extend to anchoring the understanding of sediment transport in deltas and shallow marine systems and supporting delta numerical models. Concurrently, this study has direct industry implications in expanding hydrocarbon reserves, increasing CO₂ sequestration potential, and improving facies models for reservoir characterization.