Delta‐to‐fan source‐to‐sink coupling as a fundamental control on the delivery of coarse clastics to deepwater: Insights from stratigraphic forward modelling

Abstract

We propose that a more readily studied, secondary source-to-sink (S2S) systems can be formed on direct-fed margins, in which shelf-edge deltas are 'sources' and deep-water fans are terminal depositional 'sinks', with channels working as delivery 'conduits' in between. DionisosFlow stratigraphic-forward model, coupled to seismic and borehole data from middle Miocene Pearl River margin, are used to explore physical and conceptual linkages of delta-to-fan S2S systems, with a focus on the predictability of when and how coarse clastics are delivered from the deltas down to the submarine fans. Middle Miocene Pearl River delta-to-fan S2S coupling was stratigraphically enacted in three main ways: (a) deltas that lack downdip fans: high sea level or low sediment supply caused coarse clastics to be stored mainly on inner to outer shelf areas; (b) deltas that are linked downdip to fans: coarse clastics were funneled to submarine fans through slope channels, via direct delta-to-fan S2S linkages created by delta overreach at shelf break or channels extending back to shelf-margin prodeltas; (c) fans that lack updip, coeval deltas: coarse shelf clastics were carried laterally by longshore or other shelf currents, but eventually captured by canyon heads, and then delivered directly to the basin floor. Moreover, our DionisosFlow stratigraphic-forward models suggest that an oscillation in sea-level behaviour from slowly falling to rapidly falling would result in a within-system tract surface occurring within the falling-stage systems tract. This surface is identified as a significant lower-order unconformity in its proximal reaches and as a correlative conformity distally. Within-system tract surfaces are identified by a change in shelfedge trajectory regimes from flat to slight falling to moderately falling and in architecture from mixed progradation and degradation to dominant degradation. They are coeval with the onset of the deposition of submarine fans linked updip to deltas or lacking updip deltas, highlighting that sandy deposits can be compartmentalized even within a single systems tract. K E Y W O R D Sdelta-to-fan S2S coupling, forward stratigraphic model, sequence stratigraphy, source-to-sink system, within-system tract surface F I G U R E 1 (a) Topographic map showing the geographical location and context of the Pearl River S2S systems and map-view locations of seismic lines shown in Figures 1b and 2. Larger study area signifies the domain of DionisosFlow forward numerical modelling (white box). (b-d) Depositional dip-oriented seismic transects and borehole data showing cross-sectional seismic manifestations and lithologies of late Quaternary Pearl River delta-to-fan S2S linkages. T dr and T dp are two basinwide unconformities interpreted to have formed during the middle Pleistocene marine oxygen isotope stage (MIS) 20 (814 ka) and MIS 12 (478 ka) periods of the most pronounced sea-level fall, respectively (see Gong et al., 2018 for full details) F I G U R E 3 (a) Regional seismic line (see line location in Figure 2) a...

Evolution of groundwater system in the Pearl River Delta and its adjacent shelf since the late Pleistocene

“…The deposition center is primarily situated outside the present-day Pearl River Estuary ( Fig. 3A ), due to the abundant sediments transported by the river system ( 22 ). From 4 to 10 ka before the present (B.P.…”

“…S1), was developed on the northern shelf of the South China Sea, associated with the deltaic floodplain (Fig. 1A) (21)(22)(23). In the subaerial delta, we derived the spatial distribution of groundwater salinity using 113 drilled boreholes, farm wells, and three multilevel groundwater monitoring and sampling wells (refer to the "Sampling sites and field works" section) (8,24).…”

Highstand sublacustrine fans: The role of a sudden increase in sediment supply

“…The development of highstand sublacustrine fans in this research area indicates a sudden increase in sediment supply may be another important factor controlling the formation of hyperpycnal flows (Figure 11d). Source to sink investigation of the subaqueous systems is another route to reveal the formation of hyperpycnal flows (Covault et al, 2011; Gong et al, 2019, 2021; Turmel et al, 2015). A sudden increase in sediment supply may also be the main reason for highstand fans caused by hyperpycnal flows in marine basins (Gan et al, 2022; Pattison, 2005; Pattison et al, 2007; Steel et al, 2016, 2018).…”

Relative sea‐level control on the building of two distinct shelf‐margin clinothems on the late‐Quaternary Pearl River margin: Insights from numerical stratigraphic forward modelling

“…Sediment transport in Dionisos is determined by a long‐term hillslope creeping equation and short‐term nonlinear continental and marine water driven equation:where Q s is sediment flux, K c and K w are, respectively, the gravity‐ and water‐driven diffusion coefficient, q w is the water flux, n and m are exponents with values between 1 and 2 that affect sediment transport capacity, and S is the local slope (Granjeon, 2014; Tucker & Slingerland, 1994). All of these sediment‐transport input values are listed in Table 1 and are set within the range of values used in other applications of diffusion‐based modelling (Table 1) (Csato et al, 2013; Gong et al, 2021; Harris et al, 2016, 2018, 2020; Prince & Burgess, 2013). Perhaps more importantly, the modelled results suggest the selected diffusion coefficient are reasonable because resulting stratal geometries are similar to those documented in seismic profiles of our previous studies (Gong et al, 2018; Gong, Steel, et al, 2019; Qi et al, 2022).…”