Fig 7 - uploaded by Yoshiki Saito
Content may be subject to copyright.
7 Stratigraphic succession models for three major tide-dominated delta systems, ( a ) the Ganges-Brahmaputra, ( b ) the Mekong, and ( c ) the Changjiang. Each model includes the lower coarsening-up subaqueous clinothem overlain by the upper, generally fi ning-up, subaerial clinothem. The Mekong 

7 Stratigraphic succession models for three major tide-dominated delta systems, ( a ) the Ganges-Brahmaputra, ( b ) the Mekong, and ( c ) the Changjiang. Each model includes the lower coarsening-up subaqueous clinothem overlain by the upper, generally fi ning-up, subaerial clinothem. The Mekong 

Source publication
Chapter
Full-text available
Among tidally influenced sedimentary environments, tide-dominated deltas are perhaps the most variable and difficult to characterize. This variability is due in part to the major role that fluvial systems play in defining their delta, with rivers differing widely in discharge, sediment load, seasonality, and grain size. Tide-dominated deltas also t...

Contexts in source publication

Context 1
... to the prodelta. In contrast to the prevalent tide-dominated facies formed in the deltaplain distributaries and the adjacent intertidal to subtidal delta-front platform, the delta-front slope to prodelta environments are mostly infl uenced by waves, ocean currents, and storms. Because many factors can infl uence the formation of stratigraphic sequences over 10 3 –10 5 years, it is also useful to consider mesoscale facies associations that characterize the various subenvironments of tide- dominated deltas (Fig. 7.6 ; Gani and Bhattacharya 2007 ; Heap et al. 2004 ) . A facies association is a group of sedimentary facies that are typically found together and defi ne a particular environment, but also allow for local variability in lithology, structure, and stratal relationships. In deltaic settings where accretion rates are relatively high, facies associations record delta progradation and lobe development that typically occurs at timescales of 10 1 –10 3 years . For tide-dominated deltas the most frequently described facies association is that of the lower delta plain, which captures the advancing deltaic shoreline and subtidal to supratidal transition (Allison et al. 2003 ; Harris et al. 1993 ; Hori et al. 2002a, b ; Ta et al. 2002 ; Dalrymple et al. 2003 ) . As described from numerous delta-plain systems, the facies association comprises an 8–10 m thick, fi ning upward succession starting with sandy, cross-stratifi ed subtidal shoals, which grade into heterolithic intertidal mud-sand cou- plets and are capped by a rooted mud-dominated supratidal soil (Fig. 7.7 ). Other facies associations that have been described for tide-dominated deltas include tidal bars, tidal gullies and channels, incised distributary channels, and the subtidal shelf (Fig. 7.7 ; Davies et al. 2003 ; McCrimmon and Arnott 2009 ; Tänavsuu-Milkeviciene and Plink-Björklund 2009 ) . The tidal-bar facies association is variably described as a fi ning-up or coarsening-up succession of cross-stratifi ed sand with bidirectional fl ow indicators and inclined planes that is very similar to, if not the same as, the portion of the delta-plain facies association (Fig. 7.6b ). The difference between the upward-fi ning and upward- coarsening descriptions is likely related to their proximity to the active distributary mouth, the fi ning- up example being more proximal to the rivermouth and receiving abundant sediment to make a rapid transition from subtidal to vegetated intertidal setting, whereas the coarsening-up succession may be a more wave-tide dominated downdrift littoral deposit. The tidal gullies and distributary channels are regularly described as fi ning-up , current-rippled to planar-bedded deposits with a sharp, often incised, lower contact. However, the most characteristic features of these facies associations is the regular occurrence of mud clasts that refl ect the local reworking of shallow intertidal and supratidal delta-plain deposits as channels migrate, avulse, and incise (Fig. 7.6c ; Dalrymple et al. 2003 ; Davies et al. 2003 ; Tänavsuu- Milkeviciene and Plink-Björklund 2009 ) . On aver- age, though, tidal channels are relatively laterally stable (e.g. Fagherazzi 2008 ) and so the muddy deltaplain deposits that cap tidal-channel sands are commonly preserved in the upper stratigraphy of the subaerial delta clinothem. Offshore facies associations are less frequently described for tide-dominated deltas, in part because of sampling constraints in modern examples, but also because tidal signatures become increasingly weak offshore and may not be recognized in the rock record. This potential bias may explain early confusion with interpreting the Sego sandstones (Book Cliffs, USA), which are incised into marine shales and thus described as various types of forced regression deposits in a tidally infl uenced setting (Van Wagoner et al. 1991 ; Yoshida et al. 1996 ) . Willis and Gabel ( 2001, 2003 ) have since argued that the Sego Sandstone actually represent the tidal channels and inner shelf sand sheet of a tide-dominated delta system, which incised into its own muddy delta-front platform and prodelta deposits during progradation. Such a mud-incised succession of progradating tidal channel deposits has also been described from the Miocene-age record of the Ganges- Brahmaputra delta (Fig. 7.6d ; Davies et al. 2003 ) . Deltas are defi ned as discrete shoreline deposits formed where rivers supply sediment more rapidly than can be redistributed by basinal processes (Elliott 1986 ) ; thus shoreline advance is essential for distinguishing them from estuaries, which also occur at river mouths but are transgressive depositional systems. As defi ned, deltas are regressive prograding to aggrading systems (Boyd et al. 1992 ; Dalrymple et al. 1992 ) . Therefore deltaic successions will overall shallow upward, ideally including facies associations from prodelta, delta-front slope, delta-front platform, and delta-plain environments, in ascending order (Fig. 7.7 ; Dreyer et al. 2005 ) . In tide-dominated deltas that support a compound clinothem with prograding subaerial and subaqueous deltaic units, the idealized stratigraphic succession can be subdivided into two major intervals (Fig. 7.7 ). The lower portion shows an upward-coarsening facies succession from the prodelta to delta-front slope and outer platform deposits that is marked at its top by sharp- based wave and current scours. This lower interval is overlain by an upward-fi ning succession of prograding deposits from the inner delta-front platform and shoaling to subaerial delta-plain facies. The upper interval is most typically represented by the delta-plain facies association (see Sect. 7.4.1 ), but may also include local sub-environments such as tidal channel bars or estuarine distributary associations. Within the overall deltaic succession, the coarsest and most well-sorted deposits typically occur in the boundary zone between the delta-front platform and slope, and secondarily in the prograding, distributary-mouth channel bars (Coleman 1981 ; Hori et al. 2001, 2002b ; Dalrymple et al. 2003 ; Tänavsuu-Milkeviciene and Plink-Björklund 2009 ) . With only modest variation this general succession of an upward-coarsening subaqueous-delta unit overlain by an upward fi ning subaerial-delta unit has been documented in many of the world’s modern tide- dominated delta systems, including the Ganges- Brahmaputra (Allison et al. 2003 ) , Mekong (Ta et al. 2002 ) , Changjiang (Hori et al. 2001 ) , and Fly (Harris et al. 1993 ; Dalrymple et al. 2003 ) . Such similarity suggests that this stratigraphic succession may be a useful tool in distinguishing tide-dominated deltas in the rock record (Willis 2005 ) . Local variation in the tide-dominated delta succession has been recognized in the Mekong system, which has become increasingly wave infl uenced in the late Holocene and shows an upward-coarsening succession ending in wave-swept foreshore to aeolian beach-ridge deposits (cf. Fig. 7.6b , lower profi le; Ta et al. 2002 ) . In the Mahakam delta, alongshore heterogeneity in stratigraphic successions arises from the greater fl uvial infl uence relative to tidal reworking (Gastaldo et al. 1995 ) . The rate of delta progradation can strongly infl uence the delta facies succession. As the subaerial delta progrades basinward, the tidal distributary channels can incise up to 20 m into the delta-front platform deposits, and a relative rise of sea level (e.g., commonly through subsidence) is important in order to preserve topset deposits of the outer delta-front platform. The Ganges- Brahmaputra and Mahakam deltas are examples of such progradational and aggradational deltas that dis- play a largely continuous and conformable Holocene succession from prodelta to delta-plain facies (Goodbred et al. 2003 ; Storms et al. 2005 ) . If distributary channels are stable relative to delta progradation, a delta succession will form as described above. However, if the lateral migration of distributaries is fast relative to delta progradation, then much of the delta-front facies will be replaced by distributary- channel fi ll, which is thought to occur in the Fly river delta (Dalrymple et al. 2003 ) . Sea-level change can also force environmental changes that may appear similar to delta progradation in the stratigraphic record. During periods of sea-level fall there is a forced regression of the shoreline that drives delta progradation and potentially downward incision. If the drop in sea level is relatively fast compared to the rate of delta progradation, then the succession should shift toward a more fl uvially dominated stratigraphy with decreasing marine and tidal infl uence (Bhattacharya 2006 ) . However, with further sea-level fall and a narrowing of the shelf, tidal range will ultimately drop and tidal energy will decrease considerably relative to a growing wave infl uence. It might therefore be inferred that tide-dominated deltas are more generally highstand features, as adequate tidal energy is less well developed during lowstands due to narrow shelf widths. Indeed meso- to macrotidal conditions in the modern are associated exclusively with broad shelves or large drowned valleys and embayments. Regional morphology of the continental margin (e.g. rift settings, epicontinental seas) could maintain tidal amplifi cation even during lowstand, though, in such settings as the Cretaceous Western Interior Seaway (Bhattacharya and Willis 2001 ) and the Gulf of California. Sea-level rise following a lowstand leads to the transgression and marine inundation of incised valleys formed during the previous fall of sea level. Riverine sediments are effectively trapped in these valleys to form fl uvial and coastal plains, resulting in sediment starvation on the adjacent shelf and the formation of a ravinement surface and condensed section (Hori et al. 2004 ; Goodbred and Kuehl 2000 ) . Continued sea-level rise and transgression of the ...
Context 2
... of the Gulf of Papua shelf of the Fly and Kikori deltas, the delta-front platform (topset) shows massive mud with laminated sandy mud, interbedded mud and sand, and bioturbated sandy mud (Dalrymple et al. 2003 ; Walsh et al. 2004 ) . Some of these thick mud sets on the delta-front slope are likely formed by wave- supported hyperpycnal fl ows during storm events (Kudrass et al. 1998 ) and may be correlative with local wave-scoured erosion surfaces on the delta-front platform. Where wave infl uence is high at the shoreline, sediment facies in the intertidal zone change signifi cantly with the development of sandy beaches and longshore bars. The Mekong and Red river deltas of Vietnam both have beach ridges with aeolian dunes and foreshore with longshore bars in an intertidal zone in parts of the delta (Thompson 1968 ; Ta et al. 2005 ; Tanabe et al. 2006 ; Tamura et al. 2010 ) . Portions of these deltas are also tide-dominated and characterized by mangroves and tidal channels. Where changes in river, wave, and tidal infl uence vary through time, reductions in sediment supply to muddy tidal fl ats can induce erosion and the downdrift formation of sand/shell-mound along the shoreline, called ‘cheniers’. Such episodic changes locally form a series of cheniers on the prograding delta plain (Fig. 7.5a ; e.g., Changjiang, Mekong). Seaward of the muddy subaerial delta and inner deltafront platform, sediments typically coarsen again on the outer delta-front platform toward the rollover point (e.g., Changjiang, Gulf of Papua, Mekong; Hori et al. 2001 ; Ta et al. 2005 ) . This situation is common for deltas with a relatively shallow rollover where abrupt shoaling across the delta-front slope exposes the outer platform to high wave energy and tidal-current acceleration (Figs. 7.5 and 7.6 ). Structures on this outer portion of the delta-front platform include fi ne to medium-scale bedding with wave ripples, hummocky and trough cross-stratifi cation and frequent sharp- based erosional contacts formed by storm-wave scour. Subaqueous dunes are also occasionally reported from this zone of the delta-front platform (Gagliano and McIntire 1968 ; Kuehl et al. 1997 ) . Overall tidal signatures are not well developed in these deposits despite the strong cross-shelf tidal currents, because of generally lower sedimentation rates and frequent bed resus- pension by waves. At water depths below fair-weather wave base (~5–30 m), sedimentary facies of the delta-front slope are characterized by a coarsening-upward succession of alternating sand and mud deposits (e.g., Changjiang, Mekong, Ganges-Brahmaputra) or laminated to bioturbated muds (e.g., Gulf of Papua, Amazon). Individual bedding units often comprise graded (upward fi ning) and fi nely laminated sand–silt layers with sharp basal contacts, such as in the Ganges-Brahmaputra (Michels et al. 1998 ) and Changjiang deltas. Ripples are also found on the seabed of the delta front of the Changjiang (Chen and Yang 1993 ) . However, clear tidal signatures are not always present in the delta-front slope sediments of tide-dominated deltas, because tidal currents are not usually well-developed this far offshore. Similarly, prodelta sediments even further offshore are often highly bioturbated and intercalated with silt stringers and thin shell beds. The shell beds result primarily from storms, which may also transport coarser- grained sediments to the prodelta. In contrast to the prevalent tide-dominated facies formed in the deltaplain distributaries and the adjacent intertidal to subtidal delta-front platform, the delta-front slope to prodelta environments are mostly infl uenced by waves, ocean currents, and storms. Because many factors can infl uence the formation of stratigraphic sequences over 10 3 –10 5 years, it is also useful to consider mesoscale facies associations that characterize the various subenvironments of tide- dominated deltas (Fig. 7.6 ; Gani and Bhattacharya 2007 ; Heap et al. 2004 ) . A facies association is a group of sedimentary facies that are typically found together and defi ne a particular environment, but also allow for local variability in lithology, structure, and stratal relationships. In deltaic settings where accretion rates are relatively high, facies associations record delta progradation and lobe development that typically occurs at timescales of 10 1 –10 3 years . For tide-dominated deltas the most frequently described facies association is that of the lower delta plain, which captures the advancing deltaic shoreline and subtidal to supratidal transition (Allison et al. 2003 ; Harris et al. 1993 ; Hori et al. 2002a, b ; Ta et al. 2002 ; Dalrymple et al. 2003 ) . As described from numerous delta-plain systems, the facies association comprises an 8–10 m thick, fi ning upward succession starting with sandy, cross-stratifi ed subtidal shoals, which grade into heterolithic intertidal mud-sand cou- plets and are capped by a rooted mud-dominated supratidal soil (Fig. 7.7 ). Other facies associations that have been described for tide-dominated deltas include tidal bars, tidal gullies and channels, incised distributary channels, and the subtidal shelf (Fig. 7.7 ; Davies et al. 2003 ; McCrimmon and Arnott 2009 ; Tänavsuu-Milkeviciene and Plink-Björklund 2009 ) . The tidal-bar facies association is variably described as a fi ning-up or coarsening-up succession of cross-stratifi ed sand with bidirectional fl ow indicators and inclined planes that is very similar to, if not the same as, the portion of the delta-plain facies association (Fig. 7.6b ). The difference between the upward-fi ning and upward- coarsening descriptions is likely related to their proximity to the active distributary mouth, the fi ning- up example being more proximal to the rivermouth and receiving abundant sediment to make a rapid transition from subtidal to vegetated intertidal setting, whereas the coarsening-up succession may be a more wave-tide dominated downdrift littoral deposit. The tidal gullies and distributary channels are regularly described as fi ning-up , current-rippled to planar-bedded deposits with a sharp, often incised, lower contact. However, the most characteristic features of these facies associations is the regular occurrence of mud clasts that refl ect the local reworking of shallow intertidal and supratidal delta-plain deposits as channels migrate, avulse, and incise (Fig. 7.6c ; Dalrymple et al. 2003 ; Davies et al. 2003 ; Tänavsuu- Milkeviciene and Plink-Björklund 2009 ) . On aver- age, though, tidal channels are relatively laterally stable (e.g. Fagherazzi 2008 ) and so the muddy deltaplain deposits that cap tidal-channel sands are commonly preserved in the upper stratigraphy of the subaerial delta clinothem. Offshore facies associations are less frequently described for tide-dominated deltas, in part because of sampling constraints in modern examples, but also because tidal signatures become increasingly weak offshore and may not be recognized in the rock record. This potential bias may explain early confusion with interpreting the Sego sandstones (Book Cliffs, USA), which are incised into marine shales and thus described as various types of forced regression deposits in a tidally infl uenced setting (Van Wagoner et al. 1991 ; Yoshida et al. 1996 ) . Willis and Gabel ( 2001, 2003 ) have since argued that the Sego Sandstone actually represent the tidal channels and inner shelf sand sheet of a tide-dominated delta system, which incised into its own muddy delta-front platform and prodelta deposits during progradation. Such a mud-incised succession of progradating tidal channel deposits has also been described from the Miocene-age record of the Ganges- Brahmaputra delta (Fig. 7.6d ; Davies et al. 2003 ) . Deltas are defi ned as discrete shoreline deposits formed where rivers supply sediment more rapidly than can be redistributed by basinal processes (Elliott 1986 ) ; thus shoreline advance is essential for distinguishing them from estuaries, which also occur at river mouths but are transgressive depositional systems. As defi ned, deltas are regressive prograding to aggrading systems (Boyd et al. 1992 ; Dalrymple et al. 1992 ) . Therefore deltaic successions will overall shallow upward, ideally including facies associations from prodelta, delta-front slope, delta-front platform, and delta-plain environments, in ascending order (Fig. 7.7 ; Dreyer et al. 2005 ) . In tide-dominated deltas that support a compound clinothem with prograding subaerial and subaqueous deltaic units, the idealized stratigraphic succession can be subdivided into two major intervals (Fig. 7.7 ). The lower portion shows an upward-coarsening facies succession from the prodelta to delta-front slope and outer platform deposits that is marked at its top by sharp- based wave and current scours. This lower interval is overlain by an upward-fi ning succession of prograding deposits from the inner delta-front platform and shoaling to subaerial delta-plain facies. The upper interval is most typically represented by the delta-plain facies association (see Sect. 7.4.1 ), but may also include local sub-environments such as tidal channel bars or estuarine distributary associations. Within the overall deltaic succession, the coarsest and most well-sorted deposits typically occur in the boundary zone between the delta-front platform and slope, and secondarily in the prograding, distributary-mouth channel bars (Coleman 1981 ; Hori et al. 2001, 2002b ; Dalrymple et al. 2003 ; Tänavsuu-Milkeviciene and Plink-Björklund 2009 ) . With only modest variation this general succession of an upward-coarsening subaqueous-delta unit overlain by an upward fi ning subaerial-delta unit has been documented in many of the world’s modern tide- dominated delta systems, including the Ganges- Brahmaputra (Allison et al. 2003 ) , Mekong (Ta et al. 2002 ) , Changjiang (Hori et al. 2001 ) , and Fly (Harris et al. 1993 ; Dalrymple et al. 2003 ...
Context 3
... uenced by waves, ocean currents, and storms. Because many factors can infl uence the formation of stratigraphic sequences over 10 3 –10 5 years, it is also useful to consider mesoscale facies associations that characterize the various subenvironments of tide- dominated deltas (Fig. 7.6 ; Gani and Bhattacharya 2007 ; Heap et al. 2004 ) . A facies association is a group of sedimentary facies that are typically found together and defi ne a particular environment, but also allow for local variability in lithology, structure, and stratal relationships. In deltaic settings where accretion rates are relatively high, facies associations record delta progradation and lobe development that typically occurs at timescales of 10 1 –10 3 years . For tide-dominated deltas the most frequently described facies association is that of the lower delta plain, which captures the advancing deltaic shoreline and subtidal to supratidal transition (Allison et al. 2003 ; Harris et al. 1993 ; Hori et al. 2002a, b ; Ta et al. 2002 ; Dalrymple et al. 2003 ) . As described from numerous delta-plain systems, the facies association comprises an 8–10 m thick, fi ning upward succession starting with sandy, cross-stratifi ed subtidal shoals, which grade into heterolithic intertidal mud-sand cou- plets and are capped by a rooted mud-dominated supratidal soil (Fig. 7.7 ). Other facies associations that have been described for tide-dominated deltas include tidal bars, tidal gullies and channels, incised distributary channels, and the subtidal shelf (Fig. 7.7 ; Davies et al. 2003 ; McCrimmon and Arnott 2009 ; Tänavsuu-Milkeviciene and Plink-Björklund 2009 ) . The tidal-bar facies association is variably described as a fi ning-up or coarsening-up succession of cross-stratifi ed sand with bidirectional fl ow indicators and inclined planes that is very similar to, if not the same as, the portion of the delta-plain facies association (Fig. 7.6b ). The difference between the upward-fi ning and upward- coarsening descriptions is likely related to their proximity to the active distributary mouth, the fi ning- up example being more proximal to the rivermouth and receiving abundant sediment to make a rapid transition from subtidal to vegetated intertidal setting, whereas the coarsening-up succession may be a more wave-tide dominated downdrift littoral deposit. The tidal gullies and distributary channels are regularly described as fi ning-up , current-rippled to planar-bedded deposits with a sharp, often incised, lower contact. However, the most characteristic features of these facies associations is the regular occurrence of mud clasts that refl ect the local reworking of shallow intertidal and supratidal delta-plain deposits as channels migrate, avulse, and incise (Fig. 7.6c ; Dalrymple et al. 2003 ; Davies et al. 2003 ; Tänavsuu- Milkeviciene and Plink-Björklund 2009 ) . On aver- age, though, tidal channels are relatively laterally stable (e.g. Fagherazzi 2008 ) and so the muddy deltaplain deposits that cap tidal-channel sands are commonly preserved in the upper stratigraphy of the subaerial delta clinothem. Offshore facies associations are less frequently described for tide-dominated deltas, in part because of sampling constraints in modern examples, but also because tidal signatures become increasingly weak offshore and may not be recognized in the rock record. This potential bias may explain early confusion with interpreting the Sego sandstones (Book Cliffs, USA), which are incised into marine shales and thus described as various types of forced regression deposits in a tidally infl uenced setting (Van Wagoner et al. 1991 ; Yoshida et al. 1996 ) . Willis and Gabel ( 2001, 2003 ) have since argued that the Sego Sandstone actually represent the tidal channels and inner shelf sand sheet of a tide-dominated delta system, which incised into its own muddy delta-front platform and prodelta deposits during progradation. Such a mud-incised succession of progradating tidal channel deposits has also been described from the Miocene-age record of the Ganges- Brahmaputra delta (Fig. 7.6d ; Davies et al. 2003 ) . Deltas are defi ned as discrete shoreline deposits formed where rivers supply sediment more rapidly than can be redistributed by basinal processes (Elliott 1986 ) ; thus shoreline advance is essential for distinguishing them from estuaries, which also occur at river mouths but are transgressive depositional systems. As defi ned, deltas are regressive prograding to aggrading systems (Boyd et al. 1992 ; Dalrymple et al. 1992 ) . Therefore deltaic successions will overall shallow upward, ideally including facies associations from prodelta, delta-front slope, delta-front platform, and delta-plain environments, in ascending order (Fig. 7.7 ; Dreyer et al. 2005 ) . In tide-dominated deltas that support a compound clinothem with prograding subaerial and subaqueous deltaic units, the idealized stratigraphic succession can be subdivided into two major intervals (Fig. 7.7 ). The lower portion shows an upward-coarsening facies succession from the prodelta to delta-front slope and outer platform deposits that is marked at its top by sharp- based wave and current scours. This lower interval is overlain by an upward-fi ning succession of prograding deposits from the inner delta-front platform and shoaling to subaerial delta-plain facies. The upper interval is most typically represented by the delta-plain facies association (see Sect. 7.4.1 ), but may also include local sub-environments such as tidal channel bars or estuarine distributary associations. Within the overall deltaic succession, the coarsest and most well-sorted deposits typically occur in the boundary zone between the delta-front platform and slope, and secondarily in the prograding, distributary-mouth channel bars (Coleman 1981 ; Hori et al. 2001, 2002b ; Dalrymple et al. 2003 ; Tänavsuu-Milkeviciene and Plink-Björklund 2009 ) . With only modest variation this general succession of an upward-coarsening subaqueous-delta unit overlain by an upward fi ning subaerial-delta unit has been documented in many of the world’s modern tide- dominated delta systems, including the Ganges- Brahmaputra (Allison et al. 2003 ) , Mekong (Ta et al. 2002 ) , Changjiang (Hori et al. 2001 ) , and Fly (Harris et al. 1993 ; Dalrymple et al. 2003 ) . Such similarity suggests that this stratigraphic succession may be a useful tool in distinguishing tide-dominated deltas in the rock record (Willis 2005 ) . Local variation in the tide-dominated delta succession has been recognized in the Mekong system, which has become increasingly wave infl uenced in the late Holocene and shows an upward-coarsening succession ending in wave-swept foreshore to aeolian beach-ridge deposits (cf. Fig. 7.6b , lower profi le; Ta et al. 2002 ) . In the Mahakam delta, alongshore heterogeneity in stratigraphic successions arises from the greater fl uvial infl uence relative to tidal reworking (Gastaldo et al. 1995 ) . The rate of delta progradation can strongly infl uence the delta facies succession. As the subaerial delta progrades basinward, the tidal distributary channels can incise up to 20 m into the delta-front platform deposits, and a relative rise of sea level (e.g., commonly through subsidence) is important in order to preserve topset deposits of the outer delta-front platform. The Ganges- Brahmaputra and Mahakam deltas are examples of such progradational and aggradational deltas that dis- play a largely continuous and conformable Holocene succession from prodelta to delta-plain facies (Goodbred et al. 2003 ; Storms et al. 2005 ) . If distributary channels are stable relative to delta progradation, a delta succession will form as described above. However, if the lateral migration of distributaries is fast relative to delta progradation, then much of the delta-front facies will be replaced by distributary- channel fi ll, which is thought to occur in the Fly river delta (Dalrymple et al. 2003 ) . Sea-level change can also force environmental changes that may appear similar to delta progradation in the stratigraphic record. During periods of sea-level fall there is a forced regression of the shoreline that drives delta progradation and potentially downward incision. If the drop in sea level is relatively fast compared to the rate of delta progradation, then the succession should shift toward a more fl uvially dominated stratigraphy with decreasing marine and tidal infl uence (Bhattacharya 2006 ) . However, with further sea-level fall and a narrowing of the shelf, tidal range will ultimately drop and tidal energy will decrease considerably relative to a growing wave infl uence. It might therefore be inferred that tide-dominated deltas are more generally highstand features, as adequate tidal energy is less well developed during lowstands due to narrow shelf widths. Indeed meso- to macrotidal conditions in the modern are associated exclusively with broad shelves or large drowned valleys and embayments. Regional morphology of the continental margin (e.g. rift settings, epicontinental seas) could maintain tidal amplifi cation even during lowstand, though, in such settings as the Cretaceous Western Interior Seaway (Bhattacharya and Willis 2001 ) and the Gulf of California. Sea-level rise following a lowstand leads to the transgression and marine inundation of incised valleys formed during the previous fall of sea level. Riverine sediments are effectively trapped in these valleys to form fl uvial and coastal plains, resulting in sediment starvation on the adjacent shelf and the formation of a ravinement surface and condensed section (Hori et al. 2004 ; Goodbred and Kuehl 2000 ) . Continued sea-level rise and transgression of the shelf and valleys will tend to favor tidal amplifi cation and the development of tide-infl uenced or tide-dominated environments (Uehara et al. 2002 ; Uehara and Saito 2003 ) , although such responses are also dependent on shelf and ...
Context 4
... et al. 2003 ; Walsh et al. 2004 ) . Some of these thick mud sets on the delta-front slope are likely formed by wave- supported hyperpycnal fl ows during storm events (Kudrass et al. 1998 ) and may be correlative with local wave-scoured erosion surfaces on the delta-front platform. Where wave infl uence is high at the shoreline, sediment facies in the intertidal zone change signifi cantly with the development of sandy beaches and longshore bars. The Mekong and Red river deltas of Vietnam both have beach ridges with aeolian dunes and foreshore with longshore bars in an intertidal zone in parts of the delta (Thompson 1968 ; Ta et al. 2005 ; Tanabe et al. 2006 ; Tamura et al. 2010 ) . Portions of these deltas are also tide-dominated and characterized by mangroves and tidal channels. Where changes in river, wave, and tidal infl uence vary through time, reductions in sediment supply to muddy tidal fl ats can induce erosion and the downdrift formation of sand/shell-mound along the shoreline, called ‘cheniers’. Such episodic changes locally form a series of cheniers on the prograding delta plain (Fig. 7.5a ; e.g., Changjiang, Mekong). Seaward of the muddy subaerial delta and inner deltafront platform, sediments typically coarsen again on the outer delta-front platform toward the rollover point (e.g., Changjiang, Gulf of Papua, Mekong; Hori et al. 2001 ; Ta et al. 2005 ) . This situation is common for deltas with a relatively shallow rollover where abrupt shoaling across the delta-front slope exposes the outer platform to high wave energy and tidal-current acceleration (Figs. 7.5 and 7.6 ). Structures on this outer portion of the delta-front platform include fi ne to medium-scale bedding with wave ripples, hummocky and trough cross-stratifi cation and frequent sharp- based erosional contacts formed by storm-wave scour. Subaqueous dunes are also occasionally reported from this zone of the delta-front platform (Gagliano and McIntire 1968 ; Kuehl et al. 1997 ) . Overall tidal signatures are not well developed in these deposits despite the strong cross-shelf tidal currents, because of generally lower sedimentation rates and frequent bed resus- pension by waves. At water depths below fair-weather wave base (~5–30 m), sedimentary facies of the delta-front slope are characterized by a coarsening-upward succession of alternating sand and mud deposits (e.g., Changjiang, Mekong, Ganges-Brahmaputra) or laminated to bioturbated muds (e.g., Gulf of Papua, Amazon). Individual bedding units often comprise graded (upward fi ning) and fi nely laminated sand–silt layers with sharp basal contacts, such as in the Ganges-Brahmaputra (Michels et al. 1998 ) and Changjiang deltas. Ripples are also found on the seabed of the delta front of the Changjiang (Chen and Yang 1993 ) . However, clear tidal signatures are not always present in the delta-front slope sediments of tide-dominated deltas, because tidal currents are not usually well-developed this far offshore. Similarly, prodelta sediments even further offshore are often highly bioturbated and intercalated with silt stringers and thin shell beds. The shell beds result primarily from storms, which may also transport coarser- grained sediments to the prodelta. In contrast to the prevalent tide-dominated facies formed in the deltaplain distributaries and the adjacent intertidal to subtidal delta-front platform, the delta-front slope to prodelta environments are mostly infl uenced by waves, ocean currents, and storms. Because many factors can infl uence the formation of stratigraphic sequences over 10 3 –10 5 years, it is also useful to consider mesoscale facies associations that characterize the various subenvironments of tide- dominated deltas (Fig. 7.6 ; Gani and Bhattacharya 2007 ; Heap et al. 2004 ) . A facies association is a group of sedimentary facies that are typically found together and defi ne a particular environment, but also allow for local variability in lithology, structure, and stratal relationships. In deltaic settings where accretion rates are relatively high, facies associations record delta progradation and lobe development that typically occurs at timescales of 10 1 –10 3 years . For tide-dominated deltas the most frequently described facies association is that of the lower delta plain, which captures the advancing deltaic shoreline and subtidal to supratidal transition (Allison et al. 2003 ; Harris et al. 1993 ; Hori et al. 2002a, b ; Ta et al. 2002 ; Dalrymple et al. 2003 ) . As described from numerous delta-plain systems, the facies association comprises an 8–10 m thick, fi ning upward succession starting with sandy, cross-stratifi ed subtidal shoals, which grade into heterolithic intertidal mud-sand cou- plets and are capped by a rooted mud-dominated supratidal soil (Fig. 7.7 ). Other facies associations that have been described for tide-dominated deltas include tidal bars, tidal gullies and channels, incised distributary channels, and the subtidal shelf (Fig. 7.7 ; Davies et al. 2003 ; McCrimmon and Arnott 2009 ; Tänavsuu-Milkeviciene and Plink-Björklund 2009 ) . The tidal-bar facies association is variably described as a fi ning-up or coarsening-up succession of cross-stratifi ed sand with bidirectional fl ow indicators and inclined planes that is very similar to, if not the same as, the portion of the delta-plain facies association (Fig. 7.6b ). The difference between the upward-fi ning and upward- coarsening descriptions is likely related to their proximity to the active distributary mouth, the fi ning- up example being more proximal to the rivermouth and receiving abundant sediment to make a rapid transition from subtidal to vegetated intertidal setting, whereas the coarsening-up succession may be a more wave-tide dominated downdrift littoral deposit. The tidal gullies and distributary channels are regularly described as fi ning-up , current-rippled to planar-bedded deposits with a sharp, often incised, lower contact. However, the most characteristic features of these facies associations is the regular occurrence of mud clasts that refl ect the local reworking of shallow intertidal and supratidal delta-plain deposits as channels migrate, avulse, and incise (Fig. 7.6c ; Dalrymple et al. 2003 ; Davies et al. 2003 ; Tänavsuu- Milkeviciene and Plink-Björklund 2009 ) . On aver- age, though, tidal channels are relatively laterally stable (e.g. Fagherazzi 2008 ) and so the muddy deltaplain deposits that cap tidal-channel sands are commonly preserved in the upper stratigraphy of the subaerial delta clinothem. Offshore facies associations are less frequently described for tide-dominated deltas, in part because of sampling constraints in modern examples, but also because tidal signatures become increasingly weak offshore and may not be recognized in the rock record. This potential bias may explain early confusion with interpreting the Sego sandstones (Book Cliffs, USA), which are incised into marine shales and thus described as various types of forced regression deposits in a tidally infl uenced setting (Van Wagoner et al. 1991 ; Yoshida et al. 1996 ) . Willis and Gabel ( 2001, 2003 ) have since argued that the Sego Sandstone actually represent the tidal channels and inner shelf sand sheet of a tide-dominated delta system, which incised into its own muddy delta-front platform and prodelta deposits during progradation. Such a mud-incised succession of progradating tidal channel deposits has also been described from the Miocene-age record of the Ganges- Brahmaputra delta (Fig. 7.6d ; Davies et al. 2003 ) . Deltas are defi ned as discrete shoreline deposits formed where rivers supply sediment more rapidly than can be redistributed by basinal processes (Elliott 1986 ) ; thus shoreline advance is essential for distinguishing them from estuaries, which also occur at river mouths but are transgressive depositional systems. As defi ned, deltas are regressive prograding to aggrading systems (Boyd et al. 1992 ; Dalrymple et al. 1992 ) . Therefore deltaic successions will overall shallow upward, ideally including facies associations from prodelta, delta-front slope, delta-front platform, and delta-plain environments, in ascending order (Fig. 7.7 ; Dreyer et al. 2005 ) . In tide-dominated deltas that support a compound clinothem with prograding subaerial and subaqueous deltaic units, the idealized stratigraphic succession can be subdivided into two major intervals (Fig. 7.7 ). The lower portion shows an upward-coarsening facies succession from the prodelta to delta-front slope and outer platform deposits that is marked at its top by sharp- based wave and current scours. This lower interval is overlain by an upward-fi ning succession of prograding deposits from the inner delta-front platform and shoaling to subaerial delta-plain facies. The upper interval is most typically represented by the delta-plain facies association (see Sect. 7.4.1 ), but may also include local sub-environments such as tidal channel bars or estuarine distributary associations. Within the overall deltaic succession, the coarsest and most well-sorted deposits typically occur in the boundary zone between the delta-front platform and slope, and secondarily in the prograding, distributary-mouth channel bars (Coleman 1981 ; Hori et al. 2001, 2002b ; Dalrymple et al. 2003 ; Tänavsuu-Milkeviciene and Plink-Björklund 2009 ) . With only modest variation this general succession of an upward-coarsening subaqueous-delta unit overlain by an upward fi ning subaerial-delta unit has been documented in many of the world’s modern tide- dominated delta systems, including the Ganges- Brahmaputra (Allison et al. 2003 ) , Mekong (Ta et al. 2002 ) , Changjiang (Hori et al. 2001 ) , and Fly (Harris et al. 1993 ; Dalrymple et al. 2003 ) . Such similarity suggests that this stratigraphic succession may be a useful tool in distinguishing tide-dominated deltas in the rock record (Willis 2005 ) . Local variation in the ...

Similar publications

Article
Full-text available
The western Pacific subtropical high (WPSH) features lower-level southerlies or southwesterlies at its western and southern edges that transport amount of water vapor into East Asia, and it exerts a large influence on the East Asian summer climate. This paper evaluates the historical (1950–2005) spatial distribution and variability in the summer WP...
Article
Full-text available
This paper is the first to analyse a much broader range of correlates of job growth simultaneously for each country individually across all 12 East Asian and Pacific countries with stratified randomised enterprise survey data between 2009 and 2012. It acknowledges the strong data limitations and deviates from the standard approach of using pooled,...
Article
Full-text available
The precipitation over eastern China during January-March 2010 exhibited a marked intraseasonal oscillation (ISO) and a dominant period of 10-60 days. There were two active intraseasonal rainfall periods. The physical mechanisms responsible for the onset of the two rainfall events were investigated using ERA-interim data. In the first ISO event, an...

Citations

... Headless channels are ubiquitous on tide-dominated deltas in the field and are self-formed or relict abandoned distributaries maintained via bi-directional tidal flow and landward-decreasing shear stresses (Fagherazzi, 2008;Hood, 2010). These deltas also have large subaqueous platforms that extend seaward from the shoreline, consistent with field deltas subjected to significant tidal influence (Goodbred & Saito, 2012;Rossi et al., 2016). Rough shorelines are common features of tide-dominated deltas in the field such as the Orinoco delta ( Figure 2b) (Galloway, 1975;Geleynse et al., 2011;Rossi et al., 2016), and in our simulations roughness results from a combination of headless tidal channels and distributary channels perturbing the shoreline as protrusions and indentations. ...
... The Yangtze River Delta is a typical tide-dominated river delta (Figure 1; Goodbred and Saito, 2012) and there have Niu et al., 2021). (B) Locations of cores KZ01-A and KZ02 in the present-day North Channel and the turbidity maximum zone (TMZ; after Shen and Pan, 2001). ...
Article
Full-text available
Muddy sediments are the most prominent constituents of sedimentary successions in tide-dominated river deltas and have highly complex depositional mechanisms. In this study, we performed fine-grained (4–11 μm) quartz optically stimulated luminescence (OSL) dating on two sediment cores collected at a shipwreck site in the turbidity maximum zone (TMZ) of the modern Yangtze River mouth, China, which were compared with previously published dating results including 45–63 um quartz OSL dating, radionuclide dating, porcelain artifacts recovered from the wreck, macro-plastics, and the morphological history recorded in marine charts. We investigate the luminescence characteristics of muddy sediments trapped in the TMZ and discuss the implications of OSL ages in understanding depositional mechanisms in tide-dominated river mouths. The results indicate that most OSL ages of muddy sediments in the delta front setting are overestimated compared with other dating methods. We suggest that OSL age overestimation reflects the trapping of sediments from offshore in the TMZ imported by saltwater intrusions and storm events. The offshore inputs contain high percentages of residual luminescence and are also subjected to incomplete bleaching due to turbid water conditions and near-bed dispersal in the salt-wedge river mouth. We thus suggest that the reduced bleaching efficiency of muddy sediments in delta front settings needs to be accounted for in understanding sedimentary processes and distinguishing between different sedimentary facies in tide-dominated river mouths. Furthermore, we propose that differences in quartz OSL ages of fine- and medium-grained fractions may arise in response to extreme events.
... Even a casual reading of publications on the Tilje and Cook formations shows a surprising similarity of facies, suggesting that the northern and southern regions shared some common tide-dominated or tideinfluenced depositional systems within the Early Jurassic Seaway. The common thread is that they were both part of the same epicontinental seaway (Doré 1991), a basin setting that typically favours and amplifies tidal currents, and despite its long extension (hundreds of kilometres), had some tendency to suppress wave action (see also Goodbred and Saito 2012). The intriguing question is whether these two time-equivalent formations were in spatial continuity with each other along offshore Norway or comprise separate units with a similar basin setting that gave them both a strong tidal character. ...
... The shallow water depths of epicontinental shelves or seaways, as well as the tectonic partitioning of such seaways, typically suppresses wave activity and enhances tidal currents. It should also be noted that tidal currents can weaken with a narrowing of the shelf width, or if the coastal morphology changes from concave to convex (Goodbred and Saito 2012). ...
... Tide-dominated deltas have a set of distinguishing features on the scale of facies, facies successions and at the basin scale. Many of the modern examples are found in tropical areas with a wet climate and often associated with active uplift tectonism, resulting in abundant sediment yield in the mountain catchments allowing deltas to form along continental shelves (Goodbred and Saito 2012). Modern tidedominated deltas are commonly larger in size than other types of deltas because of their protruding subaqueous portion (Fig. 3), and they often have high sediment discharges bringing large volumes of very fine-grained sandstones and muddy sediment onto moderately wide shelves (Middleton 1991). ...
Article
Full-text available
The Lower Jurassic Cook Formation reservoir is a hydrocarbon-prolific unit that produces from several fields in the northern North Sea. For 40 years this formation has been interpreted as a westward-prograding deltaic unit sourced from Norway. Despite numerous discoveries, exploration targeting this unit has been hampered by well failures with lack of reservoir sand, discouraging companies from further exploration of this play. During a current re-evaluation of the process sedimentology of the Norwegian offshore basins, the Cook Formation is now interpreted as the middle to distal reaches of a very large, north-to-south-oriented delta system, variably confined within the Early Jurassic Seaway running from the Norwegian Sea into the northern North Sea. The Cook Formation is a subaqueous delta built southward during regression, whereas several internal transgressive phases produced sands that were reworked as north–south-oriented, shelf tidal ridges. The tidal ridges of the Cook Formation constitute some of the best reservoirs and are elongated with stacked, well-sorted, cross-bedded sandstone sets with mudstone drapes. Both the elongate tidal sand-ridges and intervening mudstone-rich, inter-ridge zones are proven by numerous well observations and illustrated by seismic amplitudes. In contrast to earlier eastern derivation models, these new results for the depositional system of the Cook Formation better explain the Cook well successes and failures in the northern North Sea. This work also strongly suggests that the tide-dominated subaqueous delta to transgressive-ridge system of the Cook Formation is spatially linked with the time-equivalent shorelines, subaerial tidal deltas and estuaries of the Tilje Formation in the Haltenbanken region to the north. The Tilje Formation deltas built into the Early Jurassic Seaway due to rift-initiation and rift-shoulder uplift, drained southwards and spilled eventually into the northern North Sea, becoming the entirely subaqueous Cook Formation. The relatively narrow seaway enhanced the tidal currents and suppressed wave activity, resulting in Cook subaqueous delta lobes and ridges without any delta-top facies. Overall, this elongate and extensive, Pliensbachian deltaic to estuarine system of the Early Jurassic Seaway off Norway competes in scale with some of Earth's largest present-day deltas.
... (direct linkage or canyon capture), surface mud plumes (hypopycnal flow), dilute-suspension bottom-boundary-layer dispersal sometimes enhanced by waves or tide-driven currents, and sediment gravity flows (hyperpycnal underflows and fluid-mud flows). Wave and tidal processes on the other hand, constantly rework the shoreline and shelf sediments supplied by the river, and morphological changes can be observed in a century (Dominguez 1996;Goodbred and Saito 2012;Anthony 2015;Rossi et al. 2016). ...
... The model presented herein is valid for the bypass zone where neither deposition nor erosion occurs. Adapted from Walsh and Nittrouer (2009) (Goodbred and Saito 2012). If there are only weak waves on the shelf, it is the enhanced tidal currents on the thicker subaqueous delta and its highenergy upper surface that build the delta towards the shelf-slope transition zone, supplementing river flow. ...
Article
The processes that transport sediment from the coastline to the shelf edge are key components of the sedimentary source-to-sink system, determining basin-margin building, deepwater deposition, organic-material accumulation, and the long-term carbon cycle. Research on shelf sediment transport has been aided recently by advances in modeling and marine technology. In this study we provide a much needed review of up-to-date findings on how sediment moves from the outer shelf onto the upper slope, and we summarize four dominant shelf-to-slope drivers: 1) river currents, 2) reworking storm waves and longshore currents, 3) strong tidal currents supplementing river outflow, and 4) small-scale to very large-scale gravity collapse of the shelf-edge area.
... After the Flandrian (around 6000YBP) marine transgression (Banerjee &Santra, 1999) the delta has prograded east and southeastward with coalescing lobes (Allison et al., 2003). The active delta, formed in a macrotidal (>4m) regime has acquired a typical shape of tide-dominated deltas (Goodbred and Saito, 2012) with numerous islands (104 nos in the Indian part) oriented along the strong tidal ow perpendicular to the shoreline. With the colonization of these islands by the salt tolerant halophytic Mangroves plants, the Sundarban mangroves forest on the 'Sundarban surface' came into existence since 6000-3000 YBP (Vidyanadhan & Ghosh, 1993). ...
Book
Full-text available
Field Traverse on Sundarban Delta System, approved by 36th IGC Society, has been planned to be taken up during February 25-March 01, 2020. The trip will encompass visit to geo-tourism sites of the Ramsar wetland. Processes of delta building, erosional and accretional landforms, endangered flora and fauna including variety of mangroves, archaeological relics of ancient habitation (500 to 1500AD) etc. would be showcased at Sagar Island, Bakkhali, Henry Island, Jharkhali, Dobankee, Sudhanyakhali, Sajnekhali etc. Effects of fluvio-tidal regime on habitated Satjelia island, colonial Heritage, interaction with the residents to get acquainted with their livelihood, Rangabelia women self help group and cyclone shelter are included in the traverse plan. Evidences of neotectonic activities during Holocene, imparting control on the temporal and spatial variation of lithofacies, their thickness and composition in the Sundarban Delta system would be discussed. Delta progradation and occurrence of post depositional subsidence in the Bengal could also be characterised by studies on pollen, foraminifera and nature of sediments. Sundarban being the world’s largest mangrove forest holds the credit of sequestrating a substantial amount of blue carbon, however, substantial land loss occurred in the last four decades. The geochemistry of the heavy metal concentration has been recorded from Diamond Harbour, Kulpi, Namkhana, and Nazat, and attributed to high anthropogenic activity. Shallow aquifers show high arsenic in groundwater wherein the arsenic value decreases with depth. Most of the distributaries of the Ganges like Matla, Vidya, Saptamukhi or Ichamati, etc. lost their upstream freshwater sources and were gradually silted up. The estuaries, now act as tidal inlets only. The bathymetry and current velocities are variable along and across the estuaries influencing the erosion accretion process, sediment distribution pattern and the stability of the delta in the face of Anthropocene sea level rise. The major landforms observed in Sundarban are vast alluvial plain intersected by a large number of tidal rivers, creeks, mangrove swamps, mudflats, salt flats and dune complexes. The current field traverse is planned to cover all the major rivers in the Indian part of Sundarban Delta System such as Muriganga, Saptamukhi, Thakuran, Matla and Bidya. The sediment distribution in the channels generally shows a coarsening towards estuarine end due tosouth while in the north they are generally silty or clayey in nature. The most significant issue emerged from the current status of knowledge is the highly unstable geomorphology of the islands by the effects of erosionaccretion coupled with neo-tectonism. The erosion-accretion system of islands indicates changes in shoreline which causes the erosion of the sea facing islands with aggradations/ growth of islands towards the northern side. Deployment of an Acoustic Doppler Current Profiler (ADCP) under different tidal conditions enables us to have an idea about the possible sediment transport pattern in and around the spot of sampling and to identify areas suitable for setting up of tidal turbines to generate green energy as an alternative to carbon based energy.
... The individual strata of the SH-II and ST appear in the same order. The lower to middle part of the studied sedimentary sequence (L-LS-SiC-SL) represents an intertidal to supratidal deposition sequence, which has been reported by case studies in various locations globally (Goodbred and Saito, 2011;Dalrymple and Choi, 2007;Chen et al., 2014;Olariu et al., 2012;Buatois et al., 2012). This general tidal-dominant environment setting is consistent with the interpretation of the study of molluscs and foraminifera taken from this succession previously (Lee et al., 2002;Lin, 1969), although their stratigraphical context is not clear in detail. ...
Article
Full-text available
Elevated Quaternary sedimentary complexes in the western foreland of the central mountain ranges of Taiwan are called tablelands. Their mostly flat surfaces are deeply incised by fluvial processes. The landforms and the fluvial systems in the Miaoli Tableland are investigated by high-resolution terrain analyses based on different datasets. Sediments are described in 51 outcrops and characterized by grain size composition. The outcrops revealed complete or incomplete sequences of the general scheme from bottom to top: sandy tidal–coastal units overlain by gravel- and cobble-rich fluvial deposits always with a fine-grained silt-rich top cover layer influenced by aeolian deposits. All layers are unconsolidated sediments. Three subtypes of this sequence were identified, with respect to the occurrence of the fluvial deposits. The relation of tectonic and erosional processes including the rework of gravels is discussed. The results reveal a tableland surface much more disaggregated than previously mapped, suggesting that individual tableland segments represent remnants of an inferred palaeotopography. The tableland surfaces have been separated into Sedimentary Highlands (SH-I and SH-II) and Sedimentary Terraces (ST) by geometrical properties. The Alluvial and Coastal Plains (AL) represent broad valley bottoms (“box-shaped valleys”) in the dendritic drainage systems below 150 m and the coastal plains. The landforms and predominantly the sediment sequences are discussed in the context of the existing stratigraphical schemes of the Toukoshan Formation and the so far rarely used Lungkang Formation. The latter is recommended as the stratigraphical term for the refined subdivision of the uppermost part of late Quaternary sediments in the Miaoli Tableland.
... There were only small variations in the GS distribution indicating that most samples were well sorted. The sediment types and GS characteristics of the samples reflected the common sediments of large river systems under tide-dominated deltaic settings [52], such as the Amazon River [53] and Changjiang River [54], and they were similar to the surface sediments of other tidal flats from the Red river mouth to the day river estuary [55], [56]. ...
Article
Full-text available
Sediment properties such as water content (WC) and grain size (GS) are essential to characterize the environmental conditions of tidal flats. This article aimed to develop appropriate models to estimate the WC and GS of surface sediments for an intertidal flat on the Red river delta (Vietnam) using Sentinel 2A (S2A) images. The spectral reflectance, WC, and GS of 96 sub-samples from 12 sediment samples collected on December 17, 2017 were measured to clarify their relationships. The WC was highly correlated with the reflectance ratio of two shortwave-infrared bands, R (2190)/ R (1610) ( R <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> = 0.93). The median GS ( D <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">50</sub> ) at 0%, 15%, and 20% of WC was significantly correlated with the reflectance ratio of the near-infrared band (842 nm) versus the visible-green band (560 nm) ( R <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> > 0.78). Next, D <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">50</sub> was estimated from a multivariate regression model using this band ratio, the visible-red band (665 nm), and WC. The accuracy of the models was verified by comparisons with WC and D <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">50</sub> from 20 samples collected on March 12 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sup> 2019 (RMSE of both WC and D <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">50</sub> < 15%). Then, the WC and sediment type distributions were mapped by applying these models to two S2A scenes. The maps showed high WC (>30%) in very fine sediments (silts), which is consistent with other intertidal flats with similar sediment types. This article was limited to fine sediment samples. Therefore, our next step is to incorporate coarse sediments into the models to provide more universal mapping of WC and sediment types.
... These are then examined against the fifteen point stressor analysis framework developed by Scheltinga et al. [3]. The analysis carried out is based on findings by [4][5][6][7][8][9][10][11][12][22][23][24][25]]. ...
... Goodbred and Saito [24], explain that tide dominated deltas are quiet difficult to characterize. This is due to the major role that fluvial systems have put into action in pronouncing the deltas they are associated with as the rivers vary broadly in their discharge, sediment load, seasonal behavior as well as the sediment material grain size. ...
Chapter
Full-text available
Deltas are landforms, which come into existence when sediment carried by river or stream empties its load into another water body with slow flow rates or stagnant water. Sometimes, a river may empty its sediment load on land, although this is uncommon. The world’s deltas are amongst the most productive and in some cases more populated than even land. This chapter reviews the formation of deltas, the ecology and habitats of deltas as well as the biodiversity in coastal habitats and delta habitats. Additionally, the chapter looks at recent advances in deltas such as the loss of sediment and other stressors currently facing deltas with a focus on anthropogenic activities in the Mekong River Delta (MRD) that is amongst the most resource rich deltas in the world. The Mekong River Delta (MRD) is currently known to be in peril due to anthropogenic activities such as dam construction for hydropower and irrigation, overfishing, agricultural production amongst many others. Additionally, demographical trends like population increase have also been scrutinized to see the impacts on the MRD. The results of the review process have shown that at least 85% of the deltas in the world are subsiding and losing their fertility to the sea. Finally, the chapter has endeavored to come up with suggestions on how best to overcome some of these stressors resulting from the anthropogenic activities.
... This is principally due to the higher degree of spatial variability of salinity in both shallow and deeper aquifers. It is a consequence of the complex coastal hydrogeology and land use of the active Ganges-Brahmaputra delta [21][22][23][24]. This water quality constraint, together with complex hydrogeology, leads to the unavailability of suitable freshwater aquifer layers limiting the use of tubewells. ...
Article
Full-text available
Substantial progress has been seen in the drinking water supply as per the Millennium Development Goals (MDG), but achieving the Sustainable Development Goals (SDG), particularly SGD 6.1 regarding safely managed drinking water with much more stringent targets, is considered as a development challenge. The problem is more acute in low-income water-scarce hard-to-reach areas such as the southwest coastal region of Bangladesh, where complex hydrogeological conditions and adverse water quality contribute to a highly vulnerable and insecure water environment. Following the background, this study investigated the challenges and potential solutions to drinking water insecurity in a water-scarce area of southwest coastal Bangladesh using a mixed-methods approach. The findings revealed that water insecurity arises from unimproved, deteriorated, unaffordable, and unreliable sources that have significant time and distance burdens. High rates of technical dysfunction of the existing water infrastructure contribute to water insecurity as well. Consequently, safely managed water services are accessible to only 12% of the population, whereas 64% of the population does not have basic water. To reach the SDG 6.1 target, this underserved community needs well-functioning readily accessible water infrastructure with formal institutional arrangement rather than self-governance, which seems unsuccessful in this low-income context. This study will help the government and its development partners in implementing SDG action plans around investments to a reliable supply of safe water to the people living in water-scarce hard-to-reach coastal areas.
... The sandstone facies with sigmoidal to lobed geometry characterized a thickening upward succession associated with an integrated deltaic system generated for straight crests bedforms migration in a unidirectional flow, deceleration current, and suspension process (Goodbred and Saito, 2012). The suspension process is evidenced by subcritically climbing ripple cross lamination, and mudstone (Bridge and Demicco, 2008;Tucker, 2009;Collinson and Mountney, 2019). ...
Article
Epicontinental seas dominated the central Amazonas Basin during the late Carboniferous configuring singular paleogeography of West Gondwana connected to the Panthalassa Ocean. The Pennsylvanian record is represented by 1,7 km-thick mixed siliciclastic-carbonate-evaporite deposits forming a complete transgressive-regressive megacycle in the Amazonas Basin. Outcrop and core-based stratigraphic and facies analysis carried out in 50 m-thick mixed siliciclastic-carbonate transgressive succession of the Amazonas Basin identified twenty-six facies and microfacies, representative of coastal to platform depositional systems and grouped in three facies associations: (1) coastal aeolian deposits, consisting of fine to medium-grained sandstone, lime mudstone and finely-crystalline dolostone that correspond to a complex association of aeolian dunes, sand sheets, interdunes, fluvial channels and lagoon deposits bioturbated by Palaeophycus, Lockeia, Thalassinoides, Roselia, and meniscate trace fossils; (2) a mixed tidal flat setting, constituted by fine to medium-grained sandstone, mudstone, shale, siltstone and limestone interpreted as supratidal, tidal channel, tidal delta and lagoon settings with evidence of subaerial exposure; and (3) carbonate epicontinental platform deposits, consisting of lime mudstone, wackestone, packstone and grainstone with allochemicals (ooids and peloids), terrigenous grains and abundant, diversified open shallow marine benthic and nektonic organisms,. A Bashkirian age is suggested based on the presence of the Neognathodus symmetricus, Streptognathodus sp., and Ellisonia sp. These mixed siliciclastic-carbonate deposits are correlated with several successions in the west and east Amazonia and sub-Andean basins in South America. These records indicate that the Itaituba deposits constitute a significant portion of a vast Pennsylvanian epicontinental sea connected to the west with the Panthalassa Ocean.