Two types of modern sediment dispersal systems in the western Taiwan foreland basin: Sediment transfer from basin to basin
Abstract
The western Taiwan foreland basin (WTFB) is a classical peripheral foreland basin longitudinally bounded by the East China Sea (ECS) to the north and the South China Sea (SCS) to the south. Sediments spill longitudinally into the nearby marginal ocean basins, similar to the typical foreland basin setting. Due to oblique collision in the Taiwan region, the WTFB has evolved into two subbasins: a mature basin dominated by fluvial sediments in central-northern Taiwan and an immature one dominated by deep marine facies offshore south-western Taiwan, accompanied by two distinct sediment routing systems. In the north, the Choushui River drainage, narrow seaway of the Taiwan Strait, Huapingshu Channel/Mienhua Canyon System and southern Okinawa Trough (SOT) are integrated into a united sediment dispersal system, allowing sediments sourced by the mature basin to laterally overflow into the ECS and be deposited into the SOT. In southern Taiwan, the Kaoping River drainage, Kaoping submarine canyon, Penghu submarine canyon, deep-sea Penghu Channel and SCS basin interconnect, forming a longitudinal dispersal system for sediments mainly derived from the southern Taiwan orogen to be longitudinally transported to the northern SCS basin and the northernmost Manila Trench. The oblique collision between the Luzon Arc and the Chinese margin in the Taiwan region is the major factor in the development of two distinct sediment dispersal systems. Preferential sediment transport (axial vs. transverse), shelf width and sea-level change since the Last Glacial Maximum (~2 ka BP) are the other significant factors in the development of sediment routing systems in the WTFB. The two proposed distinct sediment dispersal systems in the WTFB clearly demonstrate how foreland basin sediments can be transferred longitudinally to adjacent marginal sea basins. Moreover, the sediment dispersal systems in the WTFB can be considered a modern analogue for interpreting ancient counterparts.
1 INTRODUCTION
Variations in sediment discharge passing through different morphodynamic segments of sediment dispersal systems are examined in source-to-sink (S2S) studies. Relevant sedimentary processes, tectonic activity, climate conditions, sea-level changes and linkages between terrestrial sources and marine sinks are revealed to better understand earth surface processes and global changes recorded in the continental margins (MARGINS, 2004). The S2S system consists of five major morphodynamic segments: mountain, plain, shelf, slope and deep-sea basin (MARGINS, 2004; Sømme et al., 2009). Studies on sediment dispersal or sediment routing in the regional S2S scheme have focused on the important roles of rivers and submarine canyons in transporting sediments sourced from mountains and plains to deep-sea basins (Chiang et al., 2020; Covault et al., 2007; Liu et al., 2016; Piper & Normark, 2009; Yu & Huang, 2009). Although the sediment dispersal patterns in foreland basins are influenced by physiography, structural framework and climate, basin-scale sediment routing is mainly controlled by tectonics (Burbank, 1992; DeCelles, 2012; De Ruig & Hubbard, 2006; Hubbard et al., 2008; Fosdick et al., 2014). It has been noted that accommodation exceeds sediment supply in narrow underfilled subaerial basins, resulting in dominant axial fluvial systems (Flemings & Jordan, 1989). In contrast, sediment supply exceeds accommodation in wide overfilled basins, resulting in prevalent sediment delivery by transverse fluvial systems (Jordan, 1995; Koshnaw et al., 2020; Schlunegger et al., 1997).
Peripheral foreland basins are longitudinally bounded by two marginal ocean basins (Figure 1A) and empty laterally into marginal or remnant ocean basins (DeCelles & Giles, 1996). The western Taiwan foreland basin (WTFB) is regarded as a classical peripheral foreland basin longitudinally bounded by the southern Okinawa Trough (SOT) to the north and the South China Sea (SCS) basin to the south, similar to the typical foreland basin setting (Figure 1B). The mountain ranges of Taiwan, under the influences of a monsoon climate with heavy precipitation during the typhoon season and frequent earthquakes caused by ongoing collision tectonics, produce high sediment yields, which partly fill the WTFB, with some sediment effectively transported by small mountainous rivers to the coastal seas and subsequently to nearby ocean basins via submarine canyons and channels (Chiang et al., 2022; Hsiung et al., 2015; Liu et al., 2009; Milliman & Kao, 2005; Milliman & Syvitski, 1992; Yu et al., 2009). Covey (1986) postulated that some orogenic sediments derived from the Taiwan orogen have overflowed to the adjacent marginal seas, maintaining shallow marine conditions in the distal foredeep of the Taiwan Strait. Recently, Nagel et al. (2018) speculated that excess sediments derived from the Taiwan orogen are most probably to be transported northwards to the SOT and southwards to the SCS. In this study, two distinct sediment dispersal systems in the WTFB are presented, with the aim of showing how foreland basin sediments are longitudinally transported to adjacent marginal sea basins (i.e. SOT and SCS basin).
The modern geological and tectonic settings of Taiwan allow for a direct observation of basin-scale axial and transverse transport systems, from small mountainous rivers via submarine canyons and channels to the marginal sea basins (Chiang et al., 2022; Hsiung & Yu, 2011, 2013; Malkowski et al., 2017; Yu et al., 2009). This helps to interpret ancient counterparts whose morphodynamic segments have been tectonically disrupted and are no longer easily recognisable. The Kaoping Canyon connected to the Kaoping River plays an important role as a major sediment conduit for delivering terrestrial sediments from an overfilled basin in southern Taiwan to a deep-water underfilled SCS basin in the north-east (Chiang et al., 2004; Yu et al., 2009). In contrast, the Choushui River, the largest river in Taiwan, is a major sediment conduit for delivering a large sediment flux from the northern Taiwan orogen to the shallow Taiwan Strait, then to the East China Sea (ECS) and finally to the SOT (Chiang et al., 2022).
The objective of this study was to propose two distinct modern sediment dispersal systems in the WTFB: the Choushui River drainage–SOT dispersal system in northern Taiwan and the Kaoping River drainage–northern SCS sediment route in southern Taiwan (Figures 1B and 2A). Tectonic, sedimentary and climatic controls of these two sediment dispersal systems are discussed, in addition to their relative contributions to the development of these two dispersal systems, in order to improve the understanding of sediment routing within the evolving WTFB. Moreover, the influence of tectonics, erosion and sediment supply on the dominant transverse and axial sediment transport in the Choushui and Kaoping dispersal systems, respectively, is addressed. Based on the two proposed dispersal systems in the WTFB, the intention is to show how foreland basin sediments can be transferred longitudinally to adjacent marginal sea basins via different sediment routing systems. This paper is a synthesis of the published literature related to sediment dispersal systems, combined with up-to-date knowledge of sediment routing systems in Taiwan. It is hoped that the sediment dispersal systems in the WTFB can be considered a modern analogue with which to interpret ancient counterparts in the context of the regional S2S scheme.
2 GEOLOGICAL AND FORELAND BASIN SETTING
The island of Taiwan (Figure 2A) was formed by oblique collision between the Chinese margin and the Luzon Volcanic Arc beginning about 5 Ma (Suppe, 1981; Teng, 1990). The central-southern Taiwan mountain belt is still actively uplifting, while the central-northern Taiwan mountain belt has reached a steady state (Suppe, 1984), with collapse in the northernmost part (Teng, 1996; Teng et al., 2001). The modern collision tip lies in the SCS between southern Taiwan and north of the Manila Trench (Lallemand & Tsien, 1997). Tectonically, Eocene to Miocene strata along the Chinese margin have been deformed into an uplifting mountain belt with west-verging folds and thrusts since the Late Miocene/Early Pliocene (Suppe, 1981, 1984). Syn-tectonically, erosion and weathering of the rising Taiwan orogen produced large amounts of sediment that were transported westwards and deposited in the down-flexed trough to form the WTFB during the Pliocene–Quaternary (Covey, 1986; Lin & Watts, 2002; Yu & Chou, 2001). The WTFB is about 150 km wide, 5 km deep and 350 km long, parallel to the N–S trending mountain belt. This foreland basin occupies the western foothills, coastal plain, eastern Taiwan Strait, and offshore Kaoping Shelf and slope region in south-western Taiwan (Figure 2A).
The WTFB is mainly filled with Pliocene–Pleistocene sediments derived from the flanking mountain belt to the east, forming an eastward thickening sediment wedge (Figure 2A). Stratigraphically, the sedimentary fill of this foreland basin is characterised by coarsening-upward sequences that grade from deep marine fine sediments to coarse fluvial sediments (Chen et al., 2001; Chiang et al., 2004; Covey, 1986; DeCelles, 2012). Based on sediment type and distribution, the western foothills and coastal plain are considered overfilled basins characterised by coarse-grained subaerial conglomerates. The eastern Taiwan Strait, covered in shallow marine fine sand and mud, is a filled basin, and the Kaoping Shelf and slope region offshore south-western Taiwan is an underfilled basin dominated by deep marine fine-grained sediments (Chen et al., 2001; Chiang et al., 2004; Covey, 1986; Kao et al., 2013; Yu, 2004). Structurally, the WTFB has been deformed by a series of thrust faults, propagating westwards to the Taiwan Strait and south-westwards to the Kaoping Shelf and slope region (Chen et al., 2001; Chiang et al., 2004; Kao et al., 2013). As a result, the strata in the coastal plain and western foothills west of the mountain belt have been deformed by a series of westward-propagating thrust faults, forming a wedge-top depozone (Chen et al., 2001; Kao et al., 2013), as shown in profile A–A' in Figure 2B. The eastern Taiwan Strait is mainly filled by undeformed shallow marine sediments and is considered a foredeep depozone. Immediately west of the foredeep depozone, the flexural forebulge appears as a subdued topographic/structural high and runs along the central axis of the Taiwan Strait parallel to the strike of the Taiwan orogen. The flexural forebulge is characterised by the presence of an unconformity where relatively thin Quaternary sediments overlie eroded Miocene strata (Chang et al., 2012; Yu & Chou, 2001). Similarly, sediments in the coastal plain west of the southern Central Range and offshore Kaoping Shelf and slope region have been deformed by thrust faults propagating southwards, producing thrust-fault-confined piggyback basins within the wedge-top depozone of the southern Taiwan foreland basin, as shown in profile B–B′ in Figure 2C (Chiang et al., 2004; Yu & Huang, 2009).
3 MODERN SEDIMENT DISPERSAL SYSTEMS IN THE WTFB
Two sediment routing systems can be identified in the WTFB. In central-northern Taiwan, the Choushui River drainage–SOT sediment dispersal system is characterised by long-range combined transverse and longitudinal sediment delivery (Figure 3). In contrast, the Kaoping River drainage–northern SCS basin sediment routing system in southern Taiwan is dominated by axial sediment supply, and submarine canyons play important roles as conduits, transporting excess sediments out of the WTFB and into the SCS basin (Figure 4).
3.1 Choushui River drainage–SOT dispersal system
The sediment dispersal system in central-northern Taiwan and its northern offshore extension is composed of six morphodynamic units: (1) Choushui River drainage, (2) coastal plain, (3) Taiwan Strait, (4) ECS shelf and slope region, (5) Huapinghsu Channel–Mienhua Canyon System and (6) SOT (Figure 3). The following sections briefly describe the main sedimentary features of each morphodynamic unit. The Choushui River drainage region is the primary terrestrial sediment source area (Jia et al., 2023; Zeng et al., 2024). The coastal plain serves as the temporary sink and is filled mainly with fluvial sediments, forming the elongated Southwest Taiwan Delta along the coastline (Hsiung & Saito, 2017). The eastern Taiwan Strait is considered a sediment bypass zone where shallow marine sediments overflow northwards to the ECS. The ECS shelf and slope are the temporary sinks for sediments mainly derived from the Choushui River drainage. The Huapinghsu Channel–Mienhua Canyon System, across the ECS shelf and slope, serves as the major conduit for sediments derived from western Taiwan rivers via the Taiwan Strait to the SOT (Chiang et al., 2022). An unnamed submarine fan in front of the Mienhua Canyon mouth located in the SOT is the ultimate sediment sink.
3.1.1 Choushui River drainage region
The largest drainage region in Taiwan, with an area of about 3160 km2, is identified as the Choushui River drainage region. The Choushui River is also the largest river in Taiwan, with a length of about 187 km and is characterised as a small mountainous river with a high sediment discharge, ranging from 34.3 to 93.8 MT/year (Dadson et al., 2003; Hsiung & Saito, 2017; Milliman & Farnsworth, 2011; Milliman & Meade, 1983). The main stream of the Choushui River runs perpendicular to the strike of the Taiwan orogen in a nearly east–west direction, and a large percentage of fluvial sediment is transported downslope transversely to the coastal plain and the Taiwan Strait.
3.1.2 Coastal plain
The Choushui River and seven other nearby smaller rivers have formed the Southwest Taiwan Delta along the coastal plain since the middle Holocene (Hsiung & Saito, 2017). This delta stretches along the shoreline for about 180 km and consists of two parts: a subaerial delta and a subaqueous delta. The northern part of the subaqueous delta extends seawards to about 40 m water depth. The central part is in front of the Choushui River and extends to about 100 m water depth, and the southern part is east of the Penghu Channel and extends to about 40 m water depth (Hsiung & Saito, 2017; Figure 3).
3.1.3 Taiwan Strait
The Taiwan Strait is located in the distal part of the WTFB. This seaway between Mainland China and Taiwan is a relatively shallow foreland shelf with an average water depth of 60 m (Chang et al., 2015; Liao et al., 2008; Yu & Hong, 2006). Foreland basins are characterised by elongated and narrow troughs, allowing the development of narrow, shallow seaways in front of and along fold-thrust belts (DeCelles & Giles, 1996; Dickinson, 1974; Kalifi et al., 2022). The floor of the Taiwan Strait is covered by a thin veneer of Late Pleistocene to Holocene sediment of varying relict, palimpsest and modern origins (Boggs et al., 1979; Liu et al., 2008). At present, shallow marine sediments in the eastern Taiwan Strait are mainly transported northwards to the ECS shelf by the Taiwan Warm Current (TWC) and north-flowing tidal currents (Liu et al., 2008; Hsiung & Saito, 2017; Figure 3).
The forebulge of the WTFB extends approximately along the central axis of the Taiwan Strait parallel–subparallel to the Taiwan fold-thrust belts (Figure 1B). As the forebulge is subdued and buried by thin layers of Late Quaternary shallow marine sediments, it does not serve as a topographic divide to block sediment transport farther cratonwards (Yu & Chou, 2001). Linear sand bodies occur along the eastern flank of the forebulge, suggesting that sandy sediments are transported northwards mainly by north-flowing tidal currents (Chang et al., 2015; Liao et al., 2008).
3.1.4 ECS shelf and slope region
The sea floor off north-eastern Taiwan is mainly constituted by the broad ECS continental shelf and narrow ECS continental slope (Figure 2A). The ECS shelf is relatively flat and wide, measuring about 400 km in width, with a north-east trending edge at about 140 m water depth. The ECS slope near Taiwan is characterised by irregular sea floor features with an average slope angle of about 1.5° (Song et al., 2000; Tsai et al., 2018). Linear depressions such as sea valleys, canyons, channels and gullies are prominent morphological features of the shelf–slope region off north-eastern Taiwan. Terrestrial sediments derived from western Taiwan rivers accumulate as elongate sediment bodies, largely in the ECS shelf immediately north of Taiwan (Chiang et al., 2022).
3.1.5 Huapinghsu Channel–Mienhua Canyon System
Located on the shelf offshore north-west Taiwan, the Huapinghsu Channel extends from its head at a water depth of 120 m, seawards across the shelf–slope region, joining the main stem of the Mienhua Canyon and finally terminating at the lower ECS slope in the SOT (Figure 3). The head of the Huapinghsu Channel extends into the shelf for about 82 km, forming a shelf-indenting channel. The Huapinghsu Channel continues downslope and joins the western branch of the Mienhua Canyon at a water depth of 215 m, forming a channel/canyon connection (Chiang et al., 2022). The head of the Huapinghsu Channel is close to shelf deposits sourced from the Choushui River and western Taiwan rivers. The river-borne sediment on the shelf edge may be a source of gravity-driven sediment flows into the head of the Huapinghsu Channel (Chiang et al., 2022). The Huapingshu Channel–Mienhua Canyon System serves as the conduit for shallow marine sediments mainly derived from Choushui River drainage to the SOT, even during the present-day sea-level highstand.
3.1.6 Southern Okinawa Trough
The Okinawa Trough (OT), located between Japan and Taiwan, is a back-arc basin that was formed by the extension within the continental lithosphere behind the Ryukyu trench–arc system (Kimura, 1985; Sibuet et al., 1998; Tsai et al., 2018; Figure 2A). Covered by the ECS, the SOT near north-eastern Taiwan is bounded by the ECS slope to the north and by the Ryukyu Islands to the south. It extends from the south-west Kyushu Island to the Ilan Plain of Taiwan (Sibuet et al., 1998). The floor of the SOT is at a water depth of less than 2300 m (Sibuet et al., 1998). Submarine fans and channels with numerous meanders appear in the SOT (Sibuet et al., 1998). In the deepest portion of the SOT, channel overflow formed levees in a low-energy environment, possibly during glacial lowstand when the shelf emerged and rivers emptied directly into the SOT (Sibuet et al., 1998). The SOT has been suggested to be an important sink receiving abundant terrigenous sediment from multiple sources, including major rivers on the Chinese mainland and small mountainous rivers in Taiwan (Bentahila et al., 2008; Chiang et al., 2022; Diekmann et al., 2008; Dou et al., 2016; Hsiung & Saito, 2017; Hu et al., 2020; Li et al., 2016). In this study, the SOT is considered the ultimate sink for river-borne sediments from western Taiwan rivers and the Choushui River since 9.5 ka BP, transported via the Huapinghsu Channel–Mienhua Canyon system.
3.2 Kaoping River drainage–SCS Basin dispersal system
The sediment dispersal system in south-western Taiwan comprises six morphodynamic units: (1) Kaoping River drainage basin, (2) Kaoping Shelf, (3) Kaoping Slope, (4) Kaoping Canyon, (5) Penghu Canyon together with deep-sea Penghu Channel and (6) northern SCS basin (Figure 4). The following sections describe the essential characteristics of each morphodynamic unit. The Kaoping River drainage basin is the major terrestrial sediment source area, the Kaoping Shelf is the sediment bypass zone and the Kaoping Slope is the temporary sink. The Manila Trench in the northern SCS is the ultimate sink, receiving sediments mainly from the Taiwan orogen (Hsiung et al., 2015; Hsiung & Yu, 2013; Liu et al., 2016; Su et al., 2015; Wang et al., 2023; Yu et al., 2009). The Kaoping Canyon/deep-sea Penghu Channel system serves as the major conduit for transporting terrestrial sediments from the Kaoping River mouth to the northern Manila Trench.
3.2.1 Kaoping River drainage basin
The Kaoping River drainage basin, extending over 3257 km2, is the second largest drainage basin in Taiwan and receives sediment derived from the southern Central Range of Taiwan. The Kaoping River is a small mountainous river characterised by a very high suspended-sediment load (49 MT/year), which frequently generates hyperpycnal flows at the river mouth during seasonal floods (Dadson et al., 2005; Liu et al., 2016; Yu et al., 2009). The main trunk of the Kaoping River flows parallel to the strike of the Taiwan orogen in a nearly north–south direction (Yu & Hong, 2006). The Kaoping River transports sediment longitudinally and accumulates over-bank deposits subaerially to form the coastal plain in south-western Taiwan (Yu & Hong, 2006).
3.2.2 Kaoping Shelf
The Kaoping Shelf is a narrow (<10 km) and shallow (<80 m) platform that is a seaward continuation of the coastal plain of south-western Taiwan (Yu & Chiang, 1997). Due to its width, it is a sediment bypass zone, rather than a terrestrial sediment sink, allowing much sediment to cross the narrow shelf to be delivered to the deep-water slope and basin floor (Yu et al., 2009). This young (<400,000 years) shelf is still growing and prograding, mainly controlled by the uplift of the Taiwan orogen and accompanying orogenic sediment supply. The Kaoping Shelf is considered a transitional facies boundary separating the proximal overfilled fluvial facies from the distal underfilled deep marine facies of the Kaoping Slope in the northern SCS.
3.2.3 Kaoping Slope
The Kaoping Slope is a broad sloping region that extends seawards from the Kaoping Shelf edge to a water depth of about 3000 m and merges with the SCS basin floor. It is divided into an upper slope and a lower slope by isobaths between 1000 m and 1200 m water depth. The boundary between these two slopes is marked by one or more scarps with more than 1000 m relief, producing a steep upper slope and a much gentler lower slope. Structurally, the Kaoping Slope is dominated by west-vergent folds and thrust faults and is associated with active mud diapirism, producing intra-slope basins ranging from 10 to 40 km long and 10 to 20 km wide that trap slope sediments (Chiang et al., 2004; Hsu et al., 2017; Yu & Huang, 2006). Sediments from localised failures of the upper Kaoping Slope are most probably transported by downslope mass wasting to the lower Kaoping Slope where they are trapped in intra-slope depressions (Yu et al., 2009). Some sediments derived from failure on the lower Kaoping Slope are transported downslope to the lower reach of the Penghu Canyon (Hsiung et al., 2015). In contrast to a basin plain fan or a terminal fan in front of the canyon mouth at the basin floor, the modern Kaoping Fan is located west of the Kaoping Canyon at the lower Kaoping Slope at water depths of between 2200 m and 3000 m (Hsiung et al., 2018). The Kaoping Fan is relatively small, confined to topographic lows and is laterally fed sediments from the Kaoping Canyon. The lower segment of the Kaoping Canyon not only feeds overflowing sediments from the Kaoping Canyon to the Kaoping Fan but also completely passes through the Kaoping Fan, delivering sediments to the lower reach of the Penghu Canyon (Hsiung et al., 2018).
3.2.4 Kaoping submarine canyon
The Kaoping Canyon, connected to the Kaoping River, extends from the river mouth, running downslope and south-westwards, crossing the Kaoping Shelf and slope region, and terminating by joining the lower reach of the Penghu Canyon, which flows southwards to the deep-sea Penghu Channel (Chiang et al., 2020; Hsiung et al., 2015; Yu et al., 2009; Figure 4). The Kaoping Canyon consists of three distinct segments along its course: an upper, a middle and a lower reach. The course of the upper reach extends south-westwards, normal to the shoreline in the shelf-upper slope region, and then extends south-eastwards along a prominent linear escarpment. The lower reach flows sinuously downslope to the base of the Kaoping Slope, where it meets the lower reach of the Penghu Canyon (Yu et al., 2009). The Kaoping Canyon serves as the major conduit for axial sediment dispersal from the Kaoping River drainage area to the northern SCS basin floor and the ultimate sink, which is the northern Manila Trench (Figure 4).
3.2.5 Penghu Canyon and deep-sea Penghu Channel
Located along the axis of the southwards tilting elongate marine trough between the SCS slope and the Kaoping Slope, the Penghu Canyon extends downslope and southwards for a distance of about 180 km, gradually merging with the deep-sea Penghu Channel (Figure 4). The upper reach of the Penghu Canyon shows a V-shaped canyon morphology and intense down cutting, while the lower reach is characterised by U-shaped cross-sections with combined erosion and deposition processes (Yu & Hong, 2006). The deep-sea Penghu Channel is about 20–30 km wide and 80 km long, with water depths of between 3500 m and 4000 m (Hsiung et al., 2015). This deep-sea channel receives sediments supplied by the Penghu Canyon and laterally merging Kaoping Canyon and feeds these sediments into the northern Manila Trench.
3.2.6 Northern SCS basin
The basin floor of the northern SCS is narrowed towards south-western Taiwan, becoming shallower and gradually merging northwards into the Taiwan Strait (Figure 4). Bathymetrically, the northern SCS basin is divided by the north-south trending Penghu Canyon into two parts: the Kaoping Slope and Kaoping Shelf to the east, and the SCS shelf and slope region characterised by a wide shelf (>300 km) and a narrow slope with rough topography (Su et al., 2015). Covered by the SCS, the northern Manila Trench shows an asymmetric trough at about 4000 m in water depth with a relatively wide (~50 km) trench bottom NE-SE (Figure 2A). More than 2500 m thick turbidite sediments are inferred to have accumulated in the northern Manila Trench (Lewis & Hayes, 1984). Recently, these accumulated turbidite sediments have been examined with a series of multichannel seismic profiles and determined to be a typical trench wedge (Underwood & Karig, 1980) with width ranging from 10 to 20 km and thickness ranging from 0.6 to 0.8 s of two-way travel time (Hsiung et al., 2015). Based on an assessment of detrital zircon geochronology and combined drainage patterns in the north-eastern SCS, Wang et al. (2023) suggested that the sediments that accumulated in the northern Manila Trench primarily originated in the Kaoping River (ca 45%). Recently, Wang and Ding (2023) have found that large amounts of sediments have accumulated along the Manila Trench in the north-east, forming fan-shaped deposits with a thickness of more than 1000 m. Therefore, it is suggested that the northern SCS receives sediments mainly from the Taiwan orogen rather than from the Luzon Arc to the east (Hsiung et al., 2015; Hsiung & Yu, 2011; Ren et al., 2024; Wang et al., 2023; Wang & Ding, 2023). Here, the northern part of the SCS basin south of the Kaoping Slope is considered the sink for the WTFB sediments and the northern Manila Trench is the ultimate sink for sediments derived from the Taiwan orogen via the Kaoping Canyon and the deep-sea Penghu Channel.
4 DEVELOPMENT OF MODERN SEDIMENT DISPERSAL SYSTEMS IN THE WTFB
The two distinct sediment dispersal systems in the WTFB are primarily governed by the oblique collision between the Luzon Arc and the Asian passive margin (Hsiung et al., 2015; Su et al., 2015). The diachronous oblique collision propagates southwards along the 400 km strike of the Taiwan orogen, with the contemporary WTFB evolving into two subbasins: (1) a mature foreland basin in central-northern Taiwan, mainly filled with terrestrial and shallow marine sediments, with balanced uplift and erosion; and (2) an immature foreland basin in south-western Taiwan, with accumulated deep marine sediments and ongoing orogen uplift and basin subsidence (Covey, 1986). In the WTFB are two distinct types of drainage systems: (1) the transverse Choushui River drainage perpendicular to the Taiwan orogen and the longitudinal Kaoping River that flows parallel to the strike of the Taiwan orogen (Figures 3 and 4). Here, the major controls of these two drainage systems in the WTFB, along with models of sediment routing for end-member foreland basin types (Burbank, 1992; Garcia-Castellanos, 2002; Johnson & Beaumont, 1995; Raines et al., 2013; Sharman et al., 2017), are discussed. The longitudinal and transverse sediment dispersal systems that evolve in a foreland basin depend mainly on the interplay of flexural subsidence and sediment supply.
Foreland basins are characterised by elongated and narrow troughs, allowing the potential development of narrow seaways in front of and along the fold-thrust belts (DeCelles & Giles, 1996; Dickinson, 1974; Kalifi et al., 2022). There is increasing interest in sedimentation and tectonics in narrow straits and seaways (i.e. Cretaceous Western Interior Seaway) in ancient foreland basins (Kalifi et al., 2022; Nielsen & Johannessen, 2008; Rosenblume et al., 2022). Here, the modern foreland basin seaway in the WTFB, with an emphasis on sediment dispersal patterns (axial vs. transverse) influenced by prevalent currents controlled by sea-level changes since the Last Glacial Maximum (LGM), is presented. The narrow seaway (Taiwan Strait) located in the distal part of the WTFB comprises the foredeep and forebulge depozones filled mainly with orogenic sediments (Chang et al., 2015; Yu & Chou, 2001). The important role of sea-level changes since the LGM in the sediment dispersal patterns in the Taiwan Strait, along with basin evolution in central-northern Taiwan, is emphasised here.
4.1 Filled to overfilled subbasins in central-northern Taiwan
The Choushui River drainage, Taiwan Strait shelf, Huapingshu Channel, Mienhua Canyon and SOT are integrated into a united S2S scheme controlled mainly by sea level, tectonics and sediment supply. At the present day, the Central Range and western foothills in northern Taiwan, which form the proximal part of the WTFB, have been uplifted to more than 3000 m, probably owing to erosional rebound, resulting in topography that slopes steeply towards the foreland side. Because of the elastic crustal uplift, the proximal foreland basin has also been uplifted, accompanied by syn-tectonic erosion, producing eroded orogenic sediments transported downslope to the coastal plain to the west across which the main rivers transversely prograde to the distal foreland.
Enhanced erosion in catchments leads to an increase in sediment flux into the basin, allowing the progradation of fluvial deposits towards the distal foreland and increasing the width of the foreland basin. The Choushui River is characterised by very high sediment discharge and transport of large amounts of sediment, producing a relatively broad (~90 km) overfilled basin compared to a relatively narrow (~40 km) overfilled onshore basin in southern Taiwan. The Choushui River is not only a main conduit for delivering sediment to the shallow Taiwan Strait, but it is also a major feeder for the shallow marine-fill in the Taiwan Strait. Clearly, the Choushui River plays an important role in the outflow of excess sediment from the overfilled basin on land to the shallow marine basin in the Taiwan Strait.
The eastern Taiwan Strait receives sediments mainly from the Choushui River (point source) and partly from the Southwest Taiwan Delta (line source) (Figure 3). Submarine canyons or channels are not present on the floor of the Taiwan Strait. Apparently, sediments supplied by the Choushui River to the floor of the Taiwan Strait are moved and redistributed mainly by marine hydrodynamic processes such as tides, waves and currents. The marine regime of the eastern Taiwan Strait is dominated by semi-diurnal tides and north-flowing tidal currents (Chang et al., 2015; Jan et al., 2004). The average velocity of tidal currents is 0.46 m/s and ranges from 0.2 to 0.8 m/s. These tidal currents are capable of transporting sandy sediment. In general, nearshore sediments along the western Taiwan coast are transported by the TWC northwards and deposited on the ECS shelf northwest of Taiwan (Hsiung & Saito, 2017; Liu et al., 2008). In extreme events such as typhoons and floods, a large portion of the nearshore muddy sediments along the western Taiwan coast is moved northwards over a relatively short time. For example, much flood-derived hyperpycnal sediment delivered to the Choushui River mouth was quickly moved away by strong currents induced by Typhoon Mindulle in July 2004 (Milliman et al., 2007).
Elongated sand bodies occur along the eastern flank of a subdued forebulge depozone dominated by strong north-flowing currents parallel to the shoreline (Chang et al., 2015; Liao et al., 2008). Thus, the presence and orientation of linear sand bodies indicate that the eastern Taiwan strait is dominated by longitudinal sediment dispersal parallel to the strike of the Taiwan orogen. The north-flowing TWC can transport excess sediment flux from the Taiwan orogen, mainly supplied by the Choushui River drainage, out of the Taiwan Strait, as proposed by Covey (1986) and Nagel et al. (2018).
It has been speculated that sediments from western Taiwan rivers are deposited in the Taiwan Strait and transported northwards by the TWC, forming thick (>20 m) sediment bodies on the ECS shelf that are finally deposited in the SOT (Hsiung & Saito, 2017; Liu et al., 2008). How are these sediments on the ECS shelf transported to the SOT? What is the possible sediment conduit or transport mechanism for the delivery of these shelf sediments to the SOT? Such questions remain to be answered. Proposed destinations of these shelf sediments are mainly based on evidence from provenance studies in the SOT. Recently, Chiang et al. (2022) inferred that the Huapinghsu Channel–Mienhua Canyon System functions as a conduit for delivering these shelf sediments to the SOT. They proposed a possible connection between the head of the Huapinghsu Channel and the sediment bodies on the shelf, allowing continued sediment input into the channel. The shelf sediments within the channel are transported farther down channel and laterally flow into the main stem of the Mienhua Canyon, where they are deposited in the unnamed submarine fan of the SOT (Figure 3).
The proposed development of the Choushui River drainage–SOT sediment routing system is based on the links between terrestrial sediments at source areas in front of the Taiwan orogen and the ultimate sink in far-field SOT. It has been suggested that eroded sediments sourced from the mountain front are transversely transported by the Choushui River and emptied onto the Taiwan Strait shelf where the TWC allows shallow marine sediments to be redistributed and transported longitudinally northwards, out of the Taiwan Strait. The overflowing sediment that accumulates on the ECS shelf may be removed and transported transversely downslope to the lower slope and finally into the SOT via the nearby Huapinghsu Channel–Mienhua Canyon System. The connections among the Choushui River, the TWC in the Taiwan Strait and the Huapinghsu Channel–Mienhua Canyon System in the ECS shelf and slope region form a far-field transport route with three distinct transport segments: (1) transversely fluvial sediment transport in the proximal overfilled basin, (2) longitudinal shallow marine sediment transport in the distal filled basin and (3) transverse shallow and deep-water sediment transport in the marginal sea basin. The shelf sediments derived from western Taiwan rivers, close to the Huapinghsu Channel head, could be reworked and removed by local currents, resulting in a connection between the channel head and nearby shelf sediments. Chiang et al. (2022) considered that the present Huapinghsu Channel remains active due to the erosion of the channel bottom, accompanied by the transport of sediment down channel to the western branch of the Mienhua Canyon, mainly due to a continuous sediment supply from the nearby shelf into the channel head. Due to the continued sediment supply from the western canyon branch, the stem of the canyon head kept the canyon segment south of the head areas active during sea-level highstand.
4.2 Underfilled to overfilled subbasin in south-western Taiwan
In southern Taiwan, the base level of the foreland basin tilts southwards along the strike of the low relief (~1000 m) southern Central Range where orogen-derived sediment is transported longitudinally by the Kaoping River, following the regional dip southwards to the coastline in south-western Taiwan. It has been noted that sediment derived from the southern Central Range is redistributed along the strike, in the proximal parts, by large alluvial fans such as the Laonung alluvial fan (Chang, 1997) and, in the distal parts, by the fluvial systems of the Kaoping River and southwest coastal plain (Figure 4). Once the Kaoping River reaches the shoreline, most river discharge directly feeds into the Kaoping Canyon and about 10% of sediment discharge is distributed through unconfined flow along the Kaoping Shelf (Yu et al., 2009). The shelf sediments are transported seawards to be deposited along the deep-water Kaoping Slope. The Kaoping Shelf is recognised as the transitional sediment facies boundary separating the proximal overfilled fluvial facies on land from the distal underfilled deep marine facies of the Kaoping Slope in the northern SCS. The Kaoping Slope is mainly fed by a line source along the outer shelf–upper slope where failed or collapsed sediments are transported seawards by downslope mass wasting processes to produce deep marine slope deposits. The Kaoping Slope as a whole is considered an underfilled foreland basin with orogenic sediments from the Taiwan orogen more than 7–10 km thick (Yu, 2004).
However, orogenic sediments from southern Taiwan that are not deposited in the Kaoping Slope are mainly transported by the Kaoping Canyon out of the foreland basin. The Kaoping Canyon is directly fed large amounts of sediment from the point source of the Kaoping River that cross the narrow Kaoping Shelf and the broad Kaoping Slope. Sediments transported along the canyon course are deposited into the lower reach of the Penghu Canyon (Figure 4). The north–south trending Penghu Canyon is located at the most distal part of the southern foreland basin. Limited sediments from localised failures of the lower Kaoping Slope are most probably transported by downslope mass wasting to the Penghu Canyon (Hsiung & Yu, 2013). Sediment supply from the upper Penghu Canyon is suggested to be low, as there is no direct sediment supply from tributary canyons and gullies from either the Kaoping Slope or SCS slope. The majority of sediment supplied to the Penghu Canyon is from the laterally merged Kaoping Canyon, linking a Kaoping River land-based drainage system to the lower Penghu Canyon and finally to the northern Manila Trench via the deep-sea Penghu Channel (Hsiung et al., 2015).
The Penghu Canyon extends southwards and merges gradually into the 80 km long deep-sea Penghu Channel, continuing southwards into the northern Manila Trench and forming a continuous canyon–channel–trench pathway for delivering sediments downslope to the northern Manila Trench (Hsiung et al., 2015; Hsiung & Yu, 2011). The Penghu Canyon, together with the Kaoping Canyon, flows from north to south, parallel to the strike of the Taiwan orogen.
The northern Manila Trench is characterised by the presence of a wedge-shaped sediment body along the lower trench slope. The northern Manila Trench wedge is a relatively flat floor with sediment waves on the outer trench walls, suggesting that sediments were transported by turbidity currents within the Manila Trench (Hsiung et al., 2015). Using detrital zircon U-Pb geochronology to study these sediments, Wang et al. (2023) found that they are primarily from Taiwan Island, transported via the Kaoping Canyon.
5 DISCUSSION
The major influences on and controls of the development of the two sediment dispersal systems in the WTFB are discussed. The important role of sea-level changes since the LGM in the sediment dispersal patterns in the Taiwan Strait, along with basin evolution in central-northern Taiwan, is emphasised. A brief comparison of the two sediment dispersal systems in the WTFB (Table 1) highlights the tectonic and sedimentary processes that contributed to their formation.
| Sediment dispersal systems | Morphodynamic units' | ||||
|---|---|---|---|---|---|
| River drainage system and coast plain | Shelf | Channel/Canyon | Slope | Basin floor | |
| Choushui River drainage–SOT | Choushui River (~186 km), transverse sediment transport, subaerial delta and subaqueous delta | Taiwan Strait shelf (>80 km) dominated by Taiwan Warm currents, axial sediment transport, wide ECS shelf (~400 km), shelf-indenting channel | Huapinghsu Channel/Mienhua Canyon System (~215 km), transverse sediment transport | ECS slope (~35 km), narrow slope, slope-confined canyon | Poorly defined and unnamed submarine fan (ultimate sink), water depth (2000–2300 m) |
| Kaoping River drainage–SCS | Kaoping River (~170 km), axial sediment transport | Kaoping Shelf (<10 km), narrow shelf, river-connected canyon | Kaoping Canyon (~260 km), axial sediment transport | Kaoping slope (~100 km), topographically complex broad slope, presence of intra-slope basins and transient submarine fan | Abyssal fan-shaped deposits (~1000 m thick), thick deposits of trench wedge (ultimate sink), water depth (~4000 m) |
- Abbreviations: ECS, East China Sea; SCS, South China Sea; SOT, southern Okinawa Trough; WTFB, western Taiwan foreland basin.
5.1 Longitudinal sediment transport: Modern and ancient analogy
Garcia-Castellanos (2002, p.90) noticed that several large, well-known foreland basins share common and conspicuous features: axial drainage systems with the main river flowing longitudinally along the distal margin of the basin. For example, the Danube River flows eastwards along the distal northern margin of the North Alpine Basin, while the Guadalquivir River runs axially along the northern external boundary of the Guadalquivir foreland basin in southern Spain. In addition, the Ganges River flows eastwards about 1000 km along the distal southern margin of the Himalaya foreland basin. The distal location of the main longitudinal river in these overfilled foreland basins is related to subsidence, uplift, erosion, sediment supply and their interactions (Burbank, 1992; Raines et al., 2013). Recently, Sharman et al. (2017) reviewed previous studies and suggested that isostatic uplift with erosional denudation of the thrust belts leads to the migration of transverse fluvial systems away from the thrust front and the main longitudinal drainages are displaced farther towards the craton close to the distal margin of the basins.
Longitudinal sediment delivery is also recognised as a significant sedimentary process in the early stage of foreland basin development in geological settings of oblique arc–continent collision, such as the longitudinal Kaoping River in the southern sector of the WTFB. Recently, Malkowski et al. (2017, p.368) have suggested that longitudinal sediment routing in the southern Taiwan foreland basin is the modern analogue for longitudinal sediment dispersal in the Cretaceous Magallanes foreland basin in the southern Andes. The Late Cretaceous Magallanes foreland basin has formed syn-tectonically by oblique arc–continental collision with progressive north–south collision. The Late Cretaceous sediments derived from uplifted terranes to the north are transported axially southwards, filling the shallow marine- and deep-water Magallanes foreland basin.
However, the longitudinal sediment routing system in the Papua New Guinea–west Solomon Sea convergent zone is considered the modern analogy for Taiwan (Hsiung & Yu, 2011, 2013). Oblique arc–continent collision between the South Bismarck Arc and Australian passive margin occurred west of the Solomon Sea Triple Junction (Whitmore et al., 1999). In Papua New Guinea, arc–continent collision resulted in the uplifted Finisterre Range (~4000 m) to the north and the Papua Peninsula to the south. In the collision zone lies an elongated basin along the Finisterre Range where the Markham River flows parallel to the strike of the Finisterre Range and empties into the west Solomon Sea. Like the sediment dispersal system in southern Taiwan, the river-connected Markham Canyon functions as the main conduit, delivering terrestrial sediment from the Markham River and shallow marine sediments to the Markham Channel farther seawards. The Markham Channel continues to flow eastwards and then sharply northwards, finally merging into the western end of the New Britain Trench at a water depth of 6500 m. On a regional scale, sediments sourced from the Finisterre Range are transported longitudinally (parallel to the strike of the Finisterre Range and the curved Bismarck Arc) to the Solomon Sea via a linear sediment dispersal system consisting of a connected river–canyon–channel–trench route. The counterpart to this modern longitudinal sediment transport system is the southern sector of the WTFB.
Here, the longitudinal sediment routing system in the southern sector of the WTFB can be considered a representative axial sediment dispersal system in an early developed foreland basin with oblique arc–continental collision. Modern and ancient examples of longitudinal sediment dispersal systems presented here not only improve understanding of the sediment dispersal systems in the WTFB but also in other foreland basins with similar characteristics.
5.2 Control exerted by sea-level change
River discharge locations on the shelf are controlled by sea-level changes. In the Taiwan Strait, land was exposed during low stands, while a marine environment was created by post-LGM sea-level rise, influencing fluvial transverse and axial drainage systems of sediment derived from the Choushui River (Figure 5). The Taiwan Strait is a relatively shallow foreland shelf (average 60 m in water depth) (Liao et al., 2008; Yu & Hong, 2006) that emerged during the LGM in the Late Pleistocene when the sea level was interpreted to have been about 140 m below the present sea level (Boggs et al., 1979), following the sea-level work of Emery et al. (1971). Boggs et al. (1979) postulated that incised valleys and palaeo-fluvial drainages occurred on the subaerially exposed Taiwan Strait (Figure 5A). During the LGM, the forebulge and foredeep depozones were situated at a lower elevation, relative to the crest of the forebulge where unconformities developed with very thin Quaternary sedimentary layers overlying Late Miocene-eroded strata (Chang et al., 2012; Yu & Chou, 2001). Both the forebulge and foredeep depozones were entirely covered in fluvial sediments mainly supplied by the Choushui River that drained from the wedge-top depozone to the east (Figure 5A).
It is possible that a north–south trending river valley, located between the Penghu Islands and south-west Taiwan, extended southwards and merged with a submarine canyon. During the LGM, the estuary and mouth of the Choushui River might have extended westwards and merged with this palaeo-river valley, feeding it orogen-derived sediment from the WTFB before finally emptying into the SCS basin to the south. Using core samples from the Choushui River delta and provenance analyses, Zhang et al. (2022) reached a similar conclusion to that of Boggs et al. (1979). During the LGM, the palaeo-Choushui River might have exported sediments from western Taiwan to the SCS basin via a linear conduit of a connected river valley–submarine canyon system.
Subsequently, the sea level began to rise and by about 9.5 ka BP, it was approximately 35 m below the present level, producing the narrow palaeo-Taiwan Strait, which connects the SCS to the south and the ECS to the north. By about 9.0 ka BP, sea level was about 15 m below the present level and the Taiwan Strait was submerged nearly to the present shorelines. Moreover, the Choushui River mouth retreated to the present position and was completely disconnected from the palaeo-river valley, which is now the Penghu Channel, allowing sediment from the Choushui River to be redistributed on the shelf. From the subsequent transgression to about 7.3 ka BP, sea level rose nearly to the present sea level and the entire Taiwan Strait was submerged with increasingly strong north-flowing currents (Hsiung & Saito, 2017), which are also responsible for the increasing terrestrial sediment supply from western Taiwan to the SOT (Hu et al., 2020). Over the last 7000 years, the sea level of the Taiwan Strait has been maintained, with variations in the intensity of the north-flowing TWC mainly influenced by seasonal winds, storms and typhoons. Apparently, the sea level has continuously risen since the LGM, allowing the crest of the forebulge to be submerged and the present-day foredeep and forebulge depozones to be filled with shallow marine sediments. This caused the sediment dispersal pattern of the foredeep depozone (i.e. eastern Taiwan Strait) to become dominated by axial transport, controlled mainly by marine processes (Figure 5B).
5.3 Delta sedimentation in response to shelf width
The width of the shelf is related to sediment accumulation in small mountainous river deltas along the coastal plain in south-western Taiwan. Sediments directly supplied from the Choushui River are mostly trapped on the wide Taiwan Strait shelf (>80 km) where riverine sediments are mainly dispersed westwards and northwards to build the northern subaqueous delta with submerged clinoforms along the western coastline (Figure 4). The widest part of the northern subaqueous delta is about 15 km and extends to a water depth of about 100 m in front of the Choushui River mouth. The southern subaqueous delta is formed by the accumulation of sediments supplied from two small mountainous rivers, the Tsengwen and Erhjen rivers. The shelf off these rivers is narrower (<30 km), and at present, ~80% of the fluvial sediment discharge is transported beyond the shelf edge (Hsiung & Saito, 2017; Hsu et al., 2014). Apparently, a certain amount of shelf sediment removed from the subaqueous delta is either transported northwards to the ECS or westwards to the Penghu Channel. Milliman and Kao (2005) have inferred that under normal conditions, the north-flowing TWC transports riverine sediments from the Tsengwen and Erhjen rivers to the north. However, during flooding events, fluvial sediment discharges from the Tsengwen and Erhjen rivers may be transported by hyperpycnal flows, easily crossing the narrow shelf to the nearby Penghu Channel. Hence, the southern subaqueous delta decreases in width to about 7 km at 40 m of water depth and terminates at the northern boundary of the Kaoping Shelf where it narrows to about 10 km.
In contrast, sediments directly supplied from the Kaoping River mouth are mostly redistributed and removed from the shelf, resulting in the absence of a river-mouth delta (Figure 4). The narrow width of the Kaoping Shelf (<10 km) is considered a main factor in the absence of a river-mouth delta on the Kaoping Shelf (Hsiung & Saito, 2017; Yu et al., 2009). In comparison with the narrow Sepik (Papua New Guinea) and Eel (northern California) shelves, the narrow Kaoping Shelf allows more than 80% of shelf sediments to bypass it and be delivered to the Kaoping Slope farther downslope. Both the Sepik and Eel shelves are at active margins with widths of <10 km, allowing more than 90% of shelf sediment to cross and be transported to the deep-water slope and basin floor seawards (Walsh & Nittrouer, 2003). Particularly, most riverine sediments are transported to the deep slope region by hyperpycnal flows associated with flood events, thus bypassing the narrow shelf (Liu et al., 2016). Therefore, the Kaoping Shelf serves as a sediment bypass zone rather than a terrestrial sediment sink, with unfavourable conditions for the building of a delta along the coastal plain in southern Taiwan.
5.4 River-connected submarine canyon: Efficient sediment conduit
Among the various types of submarine canyons, the river-connected canyon is considered the most efficient sediment conduit because of its continuous high sediment input into the canyon head, inducing the generation of turbidity currents to efficiently flush sediment down canyon (Bernhardt & Schwanghart, 2021; Chiang et al., 2020; Chiang & Yu, 2022; Yu et al., 2009). Turbidity currents within submarine canyons can be actively maintained even during sea-level highstand if the river mouth and canyon head remain connected. Examples include Congo Canyon (Babonneau et al., 2002; Khripounoff et al., 2003), Var Canyon (Khripounoff et al., 2009) and Kaoping Canyon (Chiang et al., 2020). Typhoons and frequent earthquakes are important triggering mechanisms for generating turbidity currents in the Kaoping Canyon (Chiang et al., 2020; Chiang & Yu, 2022; Hsu et al., 2008; Su et al., 2012). The Kaoping River feeds high sediment discharge (49 MT/year) directly to the Kaoping Canyon head, enhanced by typhoon-related floods and coupled with frequent earthquakes, triggering erosive sediment flows including turbidity currents in the canyon. Therefore, the river-connected Kaoping Canyon is capable of efficiently transporting large amounts of sediment out of the WTFB. Yu et al. (2009) estimated that less than 10% of sediments from the Kaoping River are distributed on the Kaoping Shelf, with the remaining more than 90% transported to the Kaoping Slope and basin floor via the Kaoping Canyon.
6 CONCLUSION
Based on morpho-sedimentary features in the WTFB and up-to-date knowledge of S2S studies in Taiwan, two distinct sediment dispersal systems in the WTFB have been identified: the Choushui River drainage–SOT system in the north and the Kaoping River drainage–SCS system in the south. The oblique arc–continent collision in the Taiwan region is the major control on the formation of these two sediment routing systems. Ongoing collision in southern Taiwan has led to the tilting of the uplifted proximal foreland basin, causing it to tilt southwards, elongate and deepen towards the SCS. This allows the Kaoping River to be a major conduit for the longitudinal transport of sediment to the distal marine basin. In contrast, owing to erosional rebound to a steady state in the north, the uplifted wedge-top basin has resulted in a steep topographic slope towards the foreland, allowing the Choushui River to transport sediments transversely to the Taiwan Strait. By about 9.5 ka BP, the formation of north-flowing currents in the Taiwan Strait allowed sediments to be transported out of the shallow marine foredeep to the ECS basin. The Huapinghsu Channel–Mienhua Canyon System functions as a sediment conduit, delivering sediments mainly from western Taiwan rivers to the ECS shelf and SOT. The river-connected Kaoping Canyon plays an important role as a sediment conduit, transporting much sediment longitudinally out of the WTFB. The sediment dispersal systems in the WTFB clearly show how foreland basin sediments are longitudinally transported to adjacent marginal sea basins.
ACKNOWLEDGEMENTS
This study received financial support from the Ministry of Science and Technology ( 111-2611-M-178-001 and 112-2611-M-178-001, now known as National Science and Technology Council, Taiwan). We greatly appreciate the use of bathymetric data from the Ocean Data Bank of the National Center for Ocean Research, Taiwan. Special thanks to Professor Guy Plint for his meticulous proofreading and positive suggestions. We are also deeply grateful to the anonymous reviewer for their thorough and insightful recommendations. The editorial effort from the editors is greatly appreciated.
CONFLICT OF INTEREST STATEMENT
The authors declare no conflicts of interest.
Open Research
DATA AVAILABILITY STATEMENT
Data are available upon request from the corresponding author.
