Sharp‐based shoreface successions reconsidered in three‐dimensions: A forward stratigraphic modelling perspective

Abstract

Sea-level fall is commonly inferred to generate a sharp-based shoreface succession that displays an abrupt vertical transition from heterolithic, lower shoreface to sandy, upper shoreface deposits across a marine erosion surface. Threedimensional, process physics-based, coupled hydrodynamic-morphodynamic models are constructed to compare bedding architecture and facies patterns of wave-dominated delta deposits preserved during normal (static sea level) and forced (falling sea level) regression and then transgression during subsequent sea-How to cite this article:

Impact of wave, tides and fluid mud on fluvial discharge across a compound clinoform (Pliocene Orinoco Delta)

“…This resulted in the shoreline succession having a generally high net-to-gross character, and in places a sharp, erosive base (cf. Willis et al, 2022), as seen also in the Horseshoe Canyon Formation, Canada (Vakarelov et al, 2012). Furthermore, the individual lobes of the Lower Morne L'Enfer shoreline clinothems were thin (only up to 8 m) compared to the subaqueous clinothem lobes.…”

“…As this system prograded, it actively winnowed mud and transported it basinward. Flow energy decreased around the rollover point of the distal clinoform, as sediment fell out from suspension and progressively got finer‐grained down the subaqueous foreset (Elliot, 1986; Walker & Plint, 1992; Patruno et al ., 2015; Peng et al ., 2020; Willis et al ., 2022). This coarsening‐upward profile also mirrors the grain‐size observations along the modern subaqueous profiles of the Atchafalaya and Amazon deltas that get progressively finer‐grained from the subaqueous rollover point down the gently dipping subaqueous foreset (Kuehl et al ., 1986; Jaramillo et al ., 2009).…”

“…Notably, however, the Bridport Formation lacks mud on its platform, but it shows a strong distinction between subaqueous delta (net-to-gross: 38%) and platform facies (net-to-gross: 100%), related to phosphatic grainstones forming on the energetic platform (Hampson & Premwichein, 2017). Without observing a clear disparity in net-to-gross between the subaqueous delta and associated platform, it may be difficult to identify the compound clinoforms, because the entire section might appear as a single coarsening-upward succession (Willis et al, 2022), similar to observations in the Gulf of Papua, Horseshoe Canyon and Deguynos Formation (Fig. 15).…”

Spatial Analysis of Holocene Delta Compound Clinoforms

“…The subaqueous platform is developing smooth but asymmetrically along strike (Fig. 3a) mimicking the subaerial asymmetry of wave-delta lobes (Bhattacharya & Giosan, 2003;Olariu, 2014;Willis et al, 2022) while in tidal dominated deltas extends in front with variable widths(Goodbred & Saito, 2012; Kuehl et al, 1997) (see Appendix A). For example, the Ganges-Brahmaputra Delta has variable platform widths and patterns; the platform at the inactive Ganges side is slightly narrower with prominent erosional lineaments, while the platform on the active Brahmaputra side is slightly wider and smoother (see Appendix A).…”

“…As recognition of compound clinoforms is adopted in the scienti c community (Patruno et al, 2015;Patruno & Helland-Hansen, 2018), it is critical to understand their 3-D morphology and behavior across the entire shelf. Previous studies on Holocene and modern deltaic systems allowed insight on the compound delta clinoform morphologies formed under different wave and tide energy regimes (Goodbred & Saito, 2012;Kuehl et al, 1997Kuehl et al, , 2005Rossi et al, 2017;Swenson et al, 2005;Willis et al, 2021Willis et al, , 2022 but have been limited in capturing their spatial extent and geometry variability away from the riverine sediment source, though recent 3D modeling of wavegenerated compound deltas is helping (Willis et al, 2022). Failing to capture spatial variability and clinoform behaviors signi cantly inhibits our understanding of sediment transport and dynamics in shallow marine systems, and causes errors in deltaic sediment budgeting, basin stratigraphy models, and mis-management of environmental and economic projects.…”