Grain size and transport regime at shelf edge as fundamental controls on delivery of shelf-edge sands to deepwater

Earth-Science Reviews 157 (2016) 32–60

Contents lists available at ScienceDirect

Earth-Science Reviews journal homepage: www.elsevier.com/locate/earscirev

Invited review

Grain size and transport regime at shelf edge as fundamental controls on delivery of shelf-edge sands to deepwater Chenglin Gong a,⁎, Ronald J. Steel a, Yingmin Wang b, Changsong Lin c, Cornel Olariu a a b c

Department of Geological Sciences, Jackson School of Geosciences, University of Texas, Austin, Texas 78712, USA Ocean college, Zhejiang University, Hangzhou, Zhejiang Province 310058, China School of Ocean Sciences, China University of Geosciences, Beijing 100083, China

a r t i c l e

i n f o

Article history: Received 16 December 2015 Received in revised form 3 April 2016 Accepted 6 April 2016 Available online 9 April 2016 Keywords: Shelf-edge deltas Sea-level lowstand Grain size of sediment supply Transport regime Sand delivery paradigm

a b s t r a c t Relative sea-level fall and high sediment supply can be decisive in driving shelf-edge sands to form deep-water fans. However, a closer look at a series of lowstand shelf-edge deltas on flattish or downward prograding shelf margins yields two further important insights on this paradigm. Firstly, among 42 reviewed shelf-edge delta examples, only 24 river-, or wave-dominated shelf-edge deltas with supply of sand-dominated sediment fit sequence-stratigraphic models that link relative sea-level fall to submarine-fan growth. Contrary to conventional lowstand models, it is virtually impossible for lowstand shelf-edge deltas with supply of mud-dominated sediment (as evidenced by 18 reviewed examples without fan growth) to partition large volumes of shelf-edge sands into deep-water sites to form sandy basin-floor fans, even under the scenarios of river-dominated process regimes and sufficient sea-level fall. Grain size of the supply sediment (dominantly sandy or muddy, represented by the presence or absence of sandy upper delta fronts) therefore also plays a pivotal but underappreciated role in driving shelf-edge sands into deepwater, further modulating the conventional lowstand sand delivery concept. Secondly, contrary to recent suggestions that link basin-floor fan growth mainly to river-dominated shelf-edge process regimes, wave-dominated shelf-edge deltas with either high or low supply of dominantly sandy sediment (6 of 42 examples) can also foster sandy basin-floor fans, in conditions of direct linkage between deltas and slope-channel heads. These exceptional conditions, although long known, are less rare than believed, thus further modifying the evolving delivery paradigm. © 2016 Elsevier B.V. All rights reserved.

Contents 1.

2.

3.

4.

5.

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.1. 1980s–2000s: accommodation-drive mechanisms . . . . . . . . . . . . . . . 1.2. 2000s to present: supply-drive mechanisms . . . . . . . . . . . . . . . . . . 1.3. 2010–present: shelf-edge process modulation of the delivery system . . . . . . . Conventional lowstand delta database and methodology . . . . . . . . . . . . . . . . 2.1. Lowstand delta database . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2. Methodology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Relative sea-level behavior and magnitude of sediment supply . . . . . . . . . . . . . 3.1. Architectural styles of shelf-edge trajectories and associated shelf margins . . . . 3.2. Lowstand shelf-edge deltas with high or low sediment flux . . . . . . . . . . . Dominant grain size of sediment supply . . . . . . . . . . . . . . . . . . . . . . . 4.1. Lithological character of delta examples 1 to 24, 29, 32 to 34, 36, and 39 . . . . . 4.2. Lithological character of delta examples 25 to 28, 30 to 31, 35, 37 to 38, and 40 to 42 4.3. Supply of dominantly sandy or muddy sediment . . . . . . . . . . . . . . . . Process regimes of shelf-edge deltas . . . . . . . . . . . . . . . . . . . . . . . . . 5.1. River-dominated shelf-edge deltas . . . . . . . . . . . . . . . . . . . . . . 5.2. Wave-dominated shelf-edge deltas . . . . . . . . . . . . . . . . . . . . . . 5.3. Tide-dominated shelf-edge deltas . . . . . . . . . . . . . . . . . . . . . . .

⁎ Corresponding author. E-mail address: [email protected] (C. Gong).

http://dx.doi.org/10.1016/j.earscirev.2016.04.002 0012-8252/© 2016 Elsevier B.V. All rights reserved.

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6.

Sedimentary response to different types of river-dominated shelf-edge regimes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 6.1. Sandy Δr with high Qs giving rise to volumetrically significant basin-floor fans . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 6.2. Sandy Δr with low Qs fostering volumetrically less significant basin-floor fans . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 6.3. Muddy Δr with low or high Qs accompanied by deep-water mud accumulations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 7. Sedimentary response to different types of wave-dominated shelf-edge regimes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 7.1. Sandy Δw with high Qs producing volumetrically smaller sandy basin-floor fans . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 7.2. Sandy Δw with low Qs giving rise to restricted sandy basin-floor fans . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 8. Sedimentary response to different types of tide-dominated shelf-edge regimes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 8.1. Tide-dominated shelf-edge regime collectively leading to deep-water mud accumulations . . . . . . . . . . . . . . . . . . . . . . . . 49 8.2. Tide-dominated deltas with direct linkage between deltas and channel heads yielding sandy deep-water systems . . . . . . . . . . . . . 51 9. The role of grain size of sediment supply and transport regime at the shelf edge in driving sand into deepwater . . . . . . . . . . . . . . . . . 51 9.1. Sandy river-dominated shelf-edge deltas are most efficient at delivering sand into deep-water fans . . . . . . . . . . . . . . . . . . . . 51 9.2. Sandy wave-dominated shelf-edge deltas are less efficient at delivering sand into deep-water fans . . . . . . . . . . . . . . . . . . . . 52 9.3. Tide-dominated shelf-edge deltas and muddy river- or tide-dominated shelf-edge deltas appear to be inefficient in driving shelf-edge sands into deepwater . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 10. Transport regimes and dominant grain size as fundamental, but underappreciated, controls on sand partitioning into deepwater . . . . . 55 10.1. Grain size of sediment supply is all important . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 10.2. Wave-dominated shelf-edge deltas have been somewhat underestimated for delivery of deepwater sediment . . . . . . . . . . . . . . . . 57 10.3. The direct linkage between shelf-edge deltas and conduit heads, especially on narrow shelves, can be vital . . . . . . . . . . . . . . . . 57 11. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59

1. Introduction

1.2. 2000s to present: supply-drive mechanisms

What exactly drives shelf-edge sands into deep-water basins is still an elusive question, though it is the key question for the prediction of deep-water sand accumulation on the slope and floor of basins, which constitutes over 15% of siliciclastic hydrocarbon reservoirs and is still the important exploration targets worldwide (e.g., Richards et al., 1998; Carvajal and Steel, 2006; Sømme et al., 2009a; Martinsen et al., 2010; Gong et al., 2015a). After several decades of sequence stratigraphy, there have been three different schools of thought regarding the necessary condition for the delivery of shelf-edge sands into deepwater (relative sea-level fall, high sediment supply, and a particular shelf-edge process regime).

A second school of thought developed when some sedimentologists realized (partly from numerical experiments) that deltas were able to reach and maintain a shelf-edge position and to deliver large sand volumes into deepwater even during relative sea-level rise or at sea-level highstand (for example even with rise rates of some 2.1 m per ky, as was common after the last glacial maximum), provided that sediment discharge of the delivery systems was sufficiently large or shelves were narrow (e.g., Burgess and Hovius, 1998; Muto and Steel, 2002; Covault and Graham, 2010; Kim et al., 2013; Gong et al., 2016). This scenario became known as the supply-drive mechanism for partitioning of shelf-edge sands into deep-water sites (e.g., Carvajal and Steel, 2006; Covault et al., 2007). Applying this model in different depositional settings gave rise to the concept of highstand submarine fan development (e.g., Carvajal and Steel, 2006; Covault et al., 2007; Boyd et al., 2008). Representative examples of highstand submarine fans, where very high sediment flux has been demonstrated, are the Bengal fan (Weber et al., 1997), the Lewis fans of southern Wyoming (Carvajal and Steel, 2006), and fans off the southeast Australian margin (Boyd et al., 2008). However, supply-drive models will not work where the delivery systems are small rivers (e.g., Burgess and Hovius, 1998; Steel et al., 2008; Dixon et al., 2012), except where the shelf is very narrow (Covault et al., 2007; Gong et al., 2016). For example, highstand fans were interpreted to develop in the Californian borderland deep-water basins where the narrow shelf allows significant amounts of sand to be partitioned across and down from the shelf edge at present sealevel highstand (Covault et al., 2007; Normark et al., 2009; Covault and Graham, 2010).

1.1. 1980s–2000s: accommodation-drive mechanisms The early sequence-stratigraphic concept of sand delivery from outer shelves to deepwater slope and basin floors arose when ExxonMobil researchers realized that there was a repetitive pattern in their global seismic data sets. This pattern showed clearly that relative sea-level fall on or below the shelf was likely the key mechanism for slope and basin-floor sand delivery (e.g., Vail et al., 1977; Van Wagoner et al., 1990; Posamentier et al., 1992). This became known as the accommodation-drive mechanism for deep-water sand delivery (e.g., Vail et al., 1977; Posamentier et al., 1992; Catuneanu et al., 2009; Steel and Milliken, 2013). Accommodation-drive models work well with Icehouse conditions, when eustatic sea-level fall reached approximately 70 to 120 m. For example, Gong et al. (2015a) have shown that flat to slightly falling shelf-edge trajectories (proxy for falling relative sea level) were able to partition shelf-margin sands into the slope and basin floors of the northwestern South China Sea basin to form late Miocene Red River submarine fans. However, this mechanism is likely to have been less effective during Greenhouse periods when eustatic sea-level falls were only a few tens of meters or less (e.g., Carvajal and Steel, 2006; Blum and Hattier-Womack, 2009; Sømme et al., 2009b; Gong et al., 2016). The problem is that there needs to have been enough sea-level fall to drive deltas across shelves that are commonly 200 km or more wide, and that thick turbidite successions occur just as frequently in Greenhouse as in Icehouse stratigraphic intervals.

1.3. 2010–present: shelf-edge process modulation of the delivery system Irrespective of what brings a supply of sediment to the shelf-edge position, how fast or voluminous, it is by no means guaranteed that this sediment will automatically pass into the deepwater across the shelf edge, at least not at that location (e.g., Dixon et al., 2012; Laugier and Plink-Björklund, 2016). Large open ocean storm waves commonly present a formidable energy “fence” at the shelf edge, hindering sediment bypass and creating rather longshore drift and strike-feeding of the accumulating shelf-edge sediment (e.g., Carvajal and Steel, 2009;

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Dixon et al., 2012; Laugier and Plink-Björklund, 2016). Using a database of some 29 published examples where shelf-edge process regimes and the presence or absence of basin-floor fans are known, Dixon et al. (2012) concluded that river processes (rather than waves or tides) should preferentially dominate the shelf-edge area for sands to successfully bypass. These authors also noted, however, that storm-wave dominated shelf edges tend to drift sand parallel with, but above the shelf edge, and that sand can be captured by canyons or channels (Carvajal and Steel, 2009; Dixon et al., 2012) or by tidal currents (Boyd et al., 2008), to bring sand eventually down onto the basin floors. Process regimes at the shelf edge staging area therefore also play a key role in partitioning sand onto the slopes and basin floors of deep-water basins (Dixon et al., 2012; Bourget et al., 2014; Laugier and Plink-Björklund, 2016). In the present review, a conventional lowstand shelf-margin database was developed, composed of 42 shelf-edge deltas on shelf margins with slightly falling or flat shelf-edge trajectories (Table 1; Fig. 1). This screened set of examples was employed to examine the effect of the interplay of dominant grain size, sediment-transport regimes, and sediment-flux magnitudes on driving shelf-edge sands into deepwater (Table 1; Fig. 1). In contrast to the earlier emphasis given to sea-level fluctuations or magnitude of sediment supply, the current review argues that dominant grain size of sediment supply and sedimenttransport regime at the shelf edge have a fundamental but so far

underappreciated control on the delivery of shelf-edge sand to the deep-water slope and basin floor. 2. Conventional lowstand delta database and methodology One of the principle objectives of this review is to test the hypothesis that significant relative sea-level fall guarantees successful delivery of shelf-edge sands to deepwater. A conventional lowstand delta database composed of 42 shelf-edge deltas on flattish or downward prograding shelf margins has therefore been established (Tables 1–2; Fig. 1). 2.1. Lowstand delta database The chosen shelf-edge delta examples developed in different basin types, including passive continental margins (e.g., Red River margin, southern Hainan margin, Norwegian Barents margin, Gulf of Mexico, Santos Basin, and Gulf of Lions), rift basins (e.g., Porcupine Basin), passive margin platforms (e.g., Pliocene offshore Norway), rifted continental margins (e.g., northeastern Iberian margin), collisional plate boundaries (e.g., Borneo and Orinoco margins), foreland basins (e.g., Eocene Spitsbergen margin, southern Taranaki Basin, and western Siberia margin), and intermontane basin (e.g., Washakie Basin). Ages of them vary from Early Cretaceous through to Quaternary (Tables 1–2; Fig. 1).

Table 1 A summary of shelf-edge parameters for the considered shelf margins. Flattish or downward prograding margins

Cases (Fig. 1)

Red River margin

1

Borneo margin Northern Carnarvon Basin Pliocene Taranaki Basin Bay of Bengal Lower Waterford Formation in the Karoo Basin Quaternary Niger Delta Basin Early Eocene Porcupine Basin Ainsa Basin, Spain Clinoform 3 in Molo Formation, offshore Norway Clinoform 7 in Molo Formation, offshore Norway Clinoform 8 in Molo Formation, offshore Norway West Siberia margin Clinoform 14 on the Spitsbergen magrin Lower Valanginian on the Nova Scotia margin Rio Grande margin, south Texas Offshore Louisiana Delta lobe 1 on the Fuji Einstein margin Delta lobe 2 on the Fuji Einstein margin Clinoform 6 in the Washakie Basin Clinoform 10 in the Washakie Basin Clinoform 12 in the Washakie Basin Clinoform 13 in the Washakie Basin Santos Basin Southern Hainan margin

2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

Bonaparte Basin Early Pliocene Ebro margin Late Pliocene Ebro margin Middle Eocene Porcupine Basin Clinoform 1 in Molo Formation, offshore Norway Clinoform 2 in Molo Formation, offshore Norway Clinoform 4 in Molo Formation, offshore Norway Clinoform 6 in Molo Formation, offshore Norway Norwegian Barents margin Høgsnyta clinoform 1 on the Spitsbergen margin Høgsnyta clinoform 2 on the Spitsbergen margin Litledalsfjellet clinoforms on the Sptisbergen margin Middle Miocene New Jersey margin Scotian Basin Late Pliocene to early Pleistocene Taranaki Basin Pliocene Gulf of Lions margin Pleistocene Gulf of Lions margin

26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42

Examples or references

dx (km)

dy (m)

Tse (degree)

Trajectory trends

Fig. 2A Fig. 2B Fig. 5B of Koša (2015) Fig. 3A Fig. 4A Fig. 5A Fig. 11 of Jones et al. (2014) Fig. 10 of Henriksen et al. (2011) Fig. 6A Fig. 3B Fig. 7A Fig. 7B Fig. 7B Lower panel of Fig. 5 of Pinous et al. (1999) Fig. 8A Fig. 9A Fig. 5 of Banfield and Anderson (2004) Fig. 11 of Perov and Bhattacharya (2011) Fig. 9B Fig. 9B Fig. 8B Fig. 8B Fig. 8B Fig. 8B Fig. 10A Fig. 11A Fig. 11B Fig. 12A Fig. 4 of Kertznus and Kneller (2009) Fig. 4 of Kertznus and Kneller (2009) Fig. 6 Fig. 7A Fig. 7A Fig. 7A Fig. 7A Fig. 13 Steel and Olsen (2002) and Johannessen and Steel (2005)

62 52 26 32 44 12 8 3 2 16 1 4 3 342 479 10 34 6 15 15 11 14 3 10 23 42 43 17 6 6 23 4 1 1 2 34 0.5 1 1 86 23 91 41 11

−958 −974 −47 −247 −81 −261 5 −67 −4 −538 −8 −109 −41 −204 23 45 −76 −92 −206 −206 8 11 6 11 −331 −410 −295 −13 25 44 −450 −5 −6 −6 −29 −118 −13 −20 7 −114 −317 95 -331 67

−0.89 −1.08 −0.10 −0.44 −0.11 −1.27 0.04 −1.52 −0.09 −1.96 −0.67 −1.63 −0.87 −0.03 0.01 0.27 −0.13 −0.88 −0.79 −0.79 0.04 0.05 0.11 0.06 −0.83 −0.56 −0.39 −0.04 0.25 0.41 −1.13 −0.07 −0.31 −0.52 −1.09 −0.20 −1.50 −1.85 0.31 −0.08 −0.79 0.06 -4.97 0.40

Falling Falling Falling Falling Falling Falling Flat Falling Falling Falling Falling Falling Falling Falling Flat Flat Falling Falling Falling Falling Flat Flat Flat Flat Falling Falling Falling Falling Flat Flat Falling Falling Falling Falling Falling Falling Falling Falling Flat Falling Falling Flat Falling Flat

Fig. Fig. Fig. Fig. Fig.

14A 3D of Cummings and Arnott (2005) 4B 15A 15A

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Fig. 1. Global bathymetric map (map obtained from NOAA website: http://www.ngdc.noaa.gov/mgg/topo/img/globeco3.gif) showing locations of conventional lowstand delta examples documented in this review. Please refer to Tables 1 to 4 for the names and details of each of these 42 examples. Numbered white and red circles denote flattish or downward prograding shelf margins with and without fan growth, respectively.

The present review comprises unpublished subsurface data as well as published seismic, borehole, and outcrop data. Unpublished subsurface data consist mainly of 2D regional seismic lines, cores, and welllog data from the northwestern South China Sea margin, all of which were acquired and provided by the China National Offshore Oil Corporation (CNOOC) (Fig. 1). Both published and unpublished cross-sections are selected for inclusion in the study, as much as possible along the sediment feeder pathways, on which slightly falling or nearly flattish shelf-edge trajectories and shelf-slope-basin physiography are seen (Figs. 2–15). They have an average frequency of ca 30 to 60 Hz in the study interval of interest, yielding an estimated vertical resolution of ca 10 to 20 m. 2.2. Methodology The chosen shelf-edge delta examples and associated shelf-edge growth patterns have been systematically quantified, in terms of forward progradational distances of the shelf edge (dx) (Tables 1–2), vertical aggradation heights attained by the shelf edge (dy) (Table 1), angles of the shelf-edge trajectories (Tse) through the interval of interest (Table 1), and rates of shelf-edge progradation (Rp) (Table 2). Tse and Rp are defined as: T se ¼ tanȡ1 ðdy=dxÞ

ð1Þ

Rp ¼ dx=T

ð2Þ

where T is the life span of the shelf margin growth interval of interest. Taking the starting clinoform rollover of a given shelf-edge trajectory as the origin of coordinates (0, 0), dy and dx can be determined by projecting the terminal clinoform rollover (colored dots in Figs. 2–15) relative to the X-axis and Y-axis, respectively (Fig. 2B and C). For some depth-domain sections, these parameters were directly measured, using the scale bars in depth shown in the chosen cross-sections. For some time-domain profiles, direct measurements were converted from time to depth, using an average velocity of 2003 m/s for the

shallow siliciclastics and 1500 m/s for seawater. The results are numerically and graphically depicted in Tables 1–2 and Fig. 16. All of these quantitative data, averaged over a long time interval, are, thus, longterm average values, and are broadly correct. Tse is used to decode relative sea-level behavior, whereas Rp is a proxy for magnitude of sediment flux (Tables 1–2) (Gong et al., 2016). Grain size of sediment supply was deduced from the lithological character of coeval upper delta-front deposits on the outer shelves. Grain size of sediment supply to the reviewed margin examples was interpreted from seismic reflection properties (i.e., high or low amplitude seismic reflections), borehole information (i.e., sand-rich or mud-rich lithology), well logs (i.e., low or high gamma-ray responses), outcrops (i.e., sand-rich or mudrich facies), seismic attributeextraction maps (i.e., high/low root mean square (RMS) or high/low amplitude accumulations), as well as from published source articles (Tables 3–4). The lithological character of upper delta-front deposits of 42 chosen delta examples are listed in Tables 3–4. Sedimenttransport regimes for the studied shelf margin were interpreted from the distribution patterns of sandy deposits of shelf-margin deltas, sedimentary structures, well-log expression, or were directly obtained from published source articles (Tables 3–4). These quantitative and semi-quantitative data on transport regime, dominant grain size, and sediment-flux magnitudes were then taken as the input to a volumetric balance model for determining the role of variation in the interplay of these three parameters in driving shelf-edge sands into deepwater.

3. Relative sea-level behavior and magnitude of sediment supply Rates of shelf-edge progradation (Rp) and shelf-edge trajectory behavior (Tse) provide us with key information on sediment-flux magnitudes and relative sea-level changes (Carvajal et al., 2009; Gong et al., 2016). They are, thus, employed herein to semi-quantitatively estimate sediment-flux and relative sea-level changes of the studied delta examples.

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Table 2 Tabulation of architectural parameters of the studied shelf margins and their relation to magnitudes of sediment flux. Margin examples

Cases Examples or references (Fig. 1)

Ages

dx Time Rp Magnitude of (km) (My) (km/My) supply flux

Red River margin Borneo margin

1 2

Late Miocene Pleistocene

62 20

Northern Carnarvon Basin Pliocene Taranaki Basin

3 4

Fig. 2A Saller and Blake (2003) and Carvajal et al. (2009) Fig. 3A and Sanchez et al. (2012a) Fig. 4A and Salazar et al. (2015)

Bay of Bengal Lower Waterford Formation in the Karoo Basin

5 6

Fig. 5A Fig. 11 of Jones et al. (2014)

Quaternary Niger Delta Basin

7

Fig. 10 of Henriksen et al. (2014)

Early Eocene Porcupine Basin

8

Fig. 3

Ainsa Basin, Spain Clinoform 3 in the Molo Formation, offshore Norway Clinoform 7 in the Molo Formation, offshore Norway Clinoform 8 in the Molo Formation, offshore Norway

9 10 11 12

West Siberia margin Clinoform 14 on the Spitsbergen magrin

13 14

Lower Valanginian on the Nova Scotia margin

15

Rio Grande margin, south Texas

16

Offshore Louisiana

17

Delta lobe 1 on the Fuji Einstein margin Delta lobe 2 on the Fuji Einstein margin

18 19

Clinoform 6 in the Washakie Basin Clinoform 10 in the Washakie Basin Clinoform 12 in the Washakie Basin Clinoform 13 in the Washakie Basin Santos Basin Southern Hainan margin Bonaparte Basin

20 21 22 23 24 25 26

Early Pliocene Ebro margin Late Pliocene Ebro margin Middle Eocene Porcupine Basin Clinoform 1 in the Molo Formation, offshore Norway Clinoform 2 in the Molo Formation, offshore Norway Clinoform 4 in the Molo Formation, offshore Norway Clinoform 6 in the Molo Formation, offshore Norway Norwegian Barents margin Høgsnyta clinoform 1 on the Spitsbergen margin Høgsnyta clinoform 2 on the Spitsbergen margin Litledalsfjellet clinoforms on the Sptisbergen margin Middle Miocene New Jersey margin

27 28 29 30 31 32 33 34 35 36 37 38

5.00 1.70

12 12

Late Miocene (12.7 to 9.8 Ma) 32 2.90 11 Progradation rates of Pliocene Taranaki clinothems reach up to 11 to 69 km/My (Salazar et al., 2015). Pliocene 12 0.8 15 Lower Waterford Formation in the Karoo Basin is characterized by high sediment supply, as suggested by the occurrence of extensional growth faulting and oversteepened shelf-edge settings (Jones et al., 2014). Supply-dominated margins fed by one of the world's major river system with sediment discharge of 33 t/km2/yr (Reijers, 2011). Porcupine shelf-margin clinoforms seaward migrated approximately 30 km during early Eocene (~4 to 5

My), resulting in a low Rp of ca 7 km/My (Carvajal et al., 2009). Fig. 3B Early Eocene 2 0.5 4 Fig. 7A Molo Formation seaward migrated and accreted about Fig. 7B 25 km during Oligocene, is regionally localized, and is Fig. 7B only 150 to 250 m thick (Eidvin et al., 2007), all of which indicate a low sediment flux. Carvajal et al. (2009) Valanginian to Hauterivian ca 30 9 61 Fig. 8A Early Eocene Spitsbergen margin basinward accreted about 30 km during early Eocene (ca 4 to 5 My), resulting in a low migration of b10 km/My (Carvajal et al., 2009). Fig. 10A and Carvajal et al. (2009) Lower Cretaceous Nova Scotia is characterized by a low Rp of ca 5 km/My (Carvajal et al., 2009). Fig. 5 of Banfield and Anderson (2004) Late Quaternary 4 0.06 74 High Rp of N10km, together with the fact that the Rio Grande valley is filled with lowstand and early transgressive deposits, indicate a supply-dominated scenario (Banfield and Anderson, 2004). Fig. 11 of Perov and Bhattacharya (2011) Shelf edges of offshore Louisiana have basinward migrated about 5 km during Oxygen Isotope Stage 6 (0.05 My), suggesting high sediment flux. Fig. 9B Fuji Einstein shelf margins were fed by the world's Fig. 9B major river systems, resulting in volumetrically significant shelf-margin deltas (i.e., Lagniappe deltas) and high sediment supply. Fig. 8B Late Cretaceous Washakie shelf margin is Fig. 8B characterized by an extremely high shelf-edge Fig. 8B aggradation rates of 267 m/My and progradation rates Fig. 8B of 48 km/My (Carvajal and Steel, 2006). Fig. 10A Eocene 23 ca 10 ca 2 Fig. 11 Late Miocene 42 5.00 8 Fig. 12A Late Quaternary Bonaparte basin is characterized by rapid shelf-edge progradation and high sediment flux (Bourget et al., 2014). Fig. 4 of Kertznus and Kneller (2009) Early Pliocene 6 1.74 3 Fig. 4 of Kertznus and Kneller (2009) Late Pliocene 6 1.78 3 Fig. 6 Middle Miocene 23 7.70 3 Fig. 7A The Molo Formation has migrated and accreted Fig. 7A approximately 25 km during Oligocene, is regionally Fig. 7A localized, and is only 150 to 250 m thick (Eidvin et al., Fig. 7A 2007), collectively suggesting a low sediment flux. Fig. 13 Middle Triassic 34 5.10 7 Ron and Olsen (2002) and Early Eocene Spitsbergen margin has categorized as a Johannessen and Steel (2005) low supply margin by Carvajal et al. (2009) (represented by Rp of ca 5 km/My). Fig. 14A Shelf edges of the New Jersey margin has seaward accreted nearly 60 km during Middle Miocene (ca 2.9

Scotian Basin

39

Late Pliocene to early Pleistocene Taranaki Basin

40

Fig. 3D of Cummings and Arnott (2005) Salazar et al. (2015)

Pliocene Gulf of Lions margin Pleistocene Gulf of Lions margin

41 42

Fig. 15A Fig. 15A

My), resulting in a high Rp of ca 17 km/My (Steckler et al., 1999; Carvajal et al., 2009). Late Barremian 23 4.5 5 Late Pliocene to early Pleistocene Taranaki Basin is characterized by Rp of 12 to 54 km/My (Salazar et al., 2015). Pliocene 41 2.7 15 Pleistocene 11 1.6 7

High supply High supply High supply High supply High supply High supply

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Fig. 2. (A and B) Depositional dip-view seismic lines from the Red River margin showing stratigraphic architecture of shelf-edge deltas and concomitant sandy basin-floor fans seen as prograding and onlapping seismic facies. The stratigraphic position of core photographs shown in Fig. 25 is labeled. (C) Schematic illustration of the methodology employed to determine progradational and aggradational components of shelf-edge trajectories (dx and dy, respectively).

Fig. 3. (A) Seismic profile from the northern Carnarvon Basin (from Sanchez et al., 2012b) illustrating examples of sandy Δw with high Qs fronted by sandy basin-floor fans. (B) Stratigraphic crosssection of the Eocene Sobrarbe Formation in the Ainsa Basin, Spain (from Moss-Russell, 2009) showing an outcrop example of sandy Δr with low Qs and contemporaneous shelf-to-basin systems.

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Fig. 4. Depositional dip-oriented seismic lines (from Anell and Midtkandal, 2015) illustrating examples of sandy Δr with high Qs and muddy Δr with high Qs on the northern and southern Taranaki Basin (upper and lower panels, respectively). Notice that sandy Δr with high Qs gave rise to sandy basin-floor fans, whereas muddy Δr with high Qs did not. Red lines in the inset photos are regional map-view locations of the seismic sections presented in this figure.

3.1. Architectural styles of shelf-edge trajectories and associated shelf margins Table 1, coupled with Fig. 16A, shows two statistically distinct populations of shelf-edge growth. The first population contains shelf edges (red or blue dots in Figs. 2–15) that strongly prograded in a slightly downward direction, thereby exhibiting a slightly falling trajectory trend, referred to as slightly falling shelf-edge trajectories. The second population contains shelf edges (colored dots in Figs. 2–15) that are broadly seaward progradational and display, on average a flat trajectory trend, referred to herein as flat shelf-edge trajectories. Ranges in trajectory angles (Tse) of slightly falling shelf-edge trajectories are -2° to 0°, whereas flat shelf-edge trajectories have Tse of 0° to 0.3° (blue squares and red triangles in Fig. 16A, respectively). Table 2, together with Fig. 16B, show two statistically distinct populations of shelf-margin growth. The first population contains shelf margins with a lower rate of shelf-edge progradation (Rp) of ca 1 to 10 km/My (Table 2; black squares in Fig. 16B). The second population contains shelf margins with a higher Rp of ca 10 to 60 km/My (Table 2; red triangles in Fig. 16B).

3.2. Lowstand shelf-edge deltas with high or low sediment flux Shelf-edge trajectory (defined by Steel and Olsen, 2002) has been used globally and argued to be a reasonable proxy for relative sealevel behavior (e.g., Catuneanu et al., 2009; Helland-Hansen and

Hampson, 2009). Specifically, slightly falling or flattish shelf-edge trajectories are known to reflect relative sea-level fall or lowstand scenarios (e.g., Steel et al., 2008; Dixon et al., 2012; Gong et al., 2015b, 2016). All of these 42 reviewed delta examples on shelf margins with slightly falling or flat shelf-edge trajectories can thus be interpreted as shelfedge deltas developed during falling or lowstand of relative sea level, yielding so-called “conventional lowstand shelf-edge deltas” (Table 1; Fig. 1). From the perspective of sediment supply, sediment-supply magnitudes can be low or high. Studies by Carvajal and Steel (2006, 2009, 2012) and by Gong et al. (2015a, 2015b) suggest that higher Rp do reflect higher sediment-flux magnitudes and vice versa, and this was confirmed by Petter et al. (2013). Rp for the chosen margin examples 1 to 7, 13, 17 to 23, 26, 38, 40, and 41 are higher than margin cases 8 to 12, 14, 15, 24, 25, 27 to 37, 39, and 42 (Table 2; red triangles and blue squares in Fig. 16B, respectively). This suggests that the former and later groups of delta examples can be referred to as lowstand shelf-edge deltas with high and low sediment supply (represented by Rp of b10 km/My and Rp of N10 km/My) (zones 1 and 2 in Fig. 16B), respectively. There is likely to have been a relationship between Rp and the annual sediment discharge of river delivery systems. Margin examples with the lower Rp were generally fed by small river systems with low sediment discharge and vice versa. For example, the Red River margin with a higher Rp of ca 10 to 12 km/My was fed by a major river in Asia (i.e., the palaeo-Red River), which has a catchment area of ca 155,000 km2 and has transported huge amounts of clastic sediments to the margin during the late Miocene (e.g., Schoenbohm et al., 2006;

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Fig. 5. (A) Seismic examples of sandy Δr with high Qs in the Bay of Bengal, fronted by sandy Pliocene basin-floor fans (hot color-shaded areas). (B) RMS attribute map (high RMS attributes in yellow and orange) extracted from 100 ms above the basal bounding surface of Pliocene basin-floor fans combined with the time structural map showing the plan-view expression of the fans. The fans are interpreted to be sand-rich, as suggested by the widespread occurrence of high RMS-attribute accumulations.

Tamura et al., 2012). The annual sediment discharge of the Red River is approximately 1.6 × 108 t/yr, representing the ninth-largest among the world's river systems (Milliman and Syvitski, 1992). In marked contrast to the Red River margin, the southern Hainan margin has a lower Rp of ca 7 to 8 km/My and was fed by three small river systems on Hainan Island, all of which have a catchment area of only 3000 km2 and an annual sediment discharge of only 2.7 × 106 t/yr (Li et al., 2015). 4. Dominant grain size of sediment supply We analyzed the lithological character of upper delta fronts on 42 reviewed delta examples (see Tables 3–4 for a complete description and interpretation). 4.1. Lithological character of delta examples 1 to 24, 29, 32 to 34, 36, and 39 Sandy upper delta fronts or sand-rich delta lobes are also recognized in seismic profiles, stratigraphic cross-sections, outcrops, well-log profiles, and in previous studies (delta examples 1 to 24, 29, 32 to 34, and 39 in Table 3 and Fig. 18). The arguments for these shelfal sandbodies being of deltaic scale and for coarseness of grain size on the delta fronts are as follows. Firstly, sandy shelf-edge deltas seen as sigmoidal or oblique progradational seismic reflection packages (several 10s of

meters high) made up of moderate to high amplitude, continuous reflections are recognized in dip-view seismic sections from the Red River margin (Fig. 17A), northern Carnarvon Basin (Fig. 3A), Pliocene Taranaki Basin (Fig. 4A), Pliocene Bengal fan (Fig. 5A), Porcupine Basin (Figs. 6, 19A, and B), mid-Norwegian continental shelf (Fig. 7), and from Santos Basin (Fig. 10A). Secondly, upper delta-front deposits in the Porcupine Basin (see Fig. 2 of Ryan et al., 2009), Santos Basin (Fig. 10B), the Molo Formation along offshore Norway (Figs. 7, 20A, and B), and also offshore Alabama (Fig. 22B) are seismically imaged as high RMS or high-amplitude accumulations, suggesting sand-rich lithologies (Table 3). These seismic examples of shelf-edge deltas occur on outer shelves and are smaller (i.e., 10s of m high) than shelf-edge clinoforms (i.e., 100s of m high). Thirdly, some upper delta-front deposits, which are made up of thick regressive, fine- to mediumgrained sandstones and exhibit coarsening-upward well-log patterns, are identified in the Washakie Basin (Figs. 8B and 23A) and on the Nova Scotia margin (Fig. 10A). Fourthly, channelized upper delta-front deposits seen as laminated mudstones that coarsen upwards into fineto medium-grained sandstone beds are observed in outcrops, such as in the Eocene Sobrarbe Formation in the Ainsa Basin (Figs. 3B and 24). Fifthly, previous studies (see Table 3) have suggested that upper delta-front deposits on margin examples 2, 6, 7, 13, 14, 16, 17, 34, 36, and 39 are also sand-rich.

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Fig. 6. Palaeocene to middle Eocene sandy Δw with low Qs and associated shelf-to-basin systems in the Porcupine Basin (see Fig. 19A and B for their plan-view geomorphology). The shown seismic lines are compiled from Ryan et al. (2009).

Fig. 7. Depositional dip-oriented seismic sections along offshore Norway (from Bullimore et al., 2005) showing well-imaged clinoforms 1 to 8 of late Miocene to early Pliocene age in the Molo Formation. Note that clinoforms 3, 7, and 8 are accompanied by sandy submarine fans, whereas clinoforms 1, 2, 4, and 6 yielded fairly muddy deep-water systems. Refer to Figs. 20, 21, and 22A for the plan-view geomorphology of deep-water systems in front of clinoforms 2, 4, 6, 7, and 8.

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Fig. 8. (A) The early Eocene transect (30 km) across part of the Spitsbergen Basin in the Norwegian Arctic representing an outcrop example of sandy Δw with low Qs. (B) Regional well-log correlation section (line location shown in Fig. 23B) across the Late Cretaceous Washakie Basin illustrating well-log expression of sandy Δr with high Qs and their deep-water continuation in front of clinoforms C6, C10, C12, and C13. Notice that these four sandy Δr with high Qs collectively gave rise to thicker and bigger basin-floor fans with high sand content (yellow intervals represented by low gamma values).

4.2. Lithological character of delta examples 25 to 28, 30 to 31, 35, 37 to 38, and 40 to 42 Muddy upper delta fronts or mud-dominated delta lobes are recognized in seismic data, well-log data, cores, bathymetric maps, or previous studies (delta examples 25 to 28, 30 to 31, 35, 37 to 38, and 40 to 42 in Table 4 and Fig. 18), as supported by the following five lines of observations (Fig. 17B). Firstly, muddy upper delta-front deposits are seen in dip-view seismic lines as sigmoidal or oblique progradational, lowamplitude seismic reflection packages of 10s m high, developed on the southern Hainan margin, Bonaparte margin (Fig. 12A), late Miocene– early Pliocene Norwegian continental margin (Fig. 7A), and late Pliocene to early Pleistocene Taranaki margin (Fig. 4B). Secondly, mud-filled distributary channels were interpreted to have developed on the outer shelves of clinoform 2 in the Molo Formation (Fig. 21A) (Bullimore et al., 2005). These seismic examples of delta lobes or upper delta fronts developed mainly on the outer shelves and are several tens of meters high. Thirdly, muddy delta fronts, which exhibit blocky high gamma-ray patterns, are seen to develop on the middle Miocene New Jersey margin (Fig. 14A). Fourthly, well-preserved gastropod and mollusk shells in offshore siltstone deposits (Fig. 14B), together with silty or clayey prodelta sediments with sporadic occurrence of sharpbased sandy storm beds (Fig. 14C), are found on the middle Miocene New Jersey and Gulf of Lions margins. Fifthly, previous studies suggest that upper delta-front deposits on Pliocene Ebro margin and in the Upper Missisauga Formation of the Nova Scotia margin are also mud-dominated (see also Table 3).

4.3. Supply of dominantly sandy or muddy sediment The lithological character of the upper delta fronts represents a good indication of the dominant or maximum grain size of supplied sediment (e.g., Porębski and Steel, 2003). Accordingly, sandy upper delta-front deposits on the reviewed margin examples 1 to 24, 29, 32 to 34, and 39 can be regarded as having been supplied by dominantly sandy sediment (Table 3; red stars, red triangles, and red squares in Fig. 18), whereas muddy upper delta-front deposits on examples 25 to 28, 30 to 31, 35, 37 to 38, and 40 to 42 can be regarded as dominantly muddy sediment flux bypassing to deepwater (Table 4; blue stars and blue triangles in Fig. 18). 5. Process regimes of shelf-edge deltas We use the ternary classification system of river deltas proposed by Galloway (1975) to classify the likely process regimes of 42 considered shelf-edge deltas (see Tables 3–4 and Fig. 18 for a complete description and interpretation). 5.1. River-dominated shelf-edge deltas The arguments for the identification of river-dominated process regimes at shelf edge are as follows (red or blue stars in Fig. 18). Firstly, in outcrops, river-dominated shelf-edge deltas (Δr) in our database are characterized by long, gradual coarsening-upward profiles (b 100 m thick) that are relatively muddy and by a relative lack of

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wave or tidal structures on the delta fronts. The delta front is generally muddy, but thin sandy turbidites and a sandy mouth bar at the top of the delta front are common. The capping distributary channel is also usually sandy. Among the 29 river-dominated shelf-edge deltas recognized in this review (colored stars in Fig. 18), delta 9 of the Sobrarbe Formation in the Ainsa Basin offers a classical outcrop example (Table 3) (Moss-Russell, 2009). As presented in Figs. 3B, 24A, and B, distributary channels and mouth bars in the Eocene Ainsa shelf-edge deltas are composed mostly of structureless to plane-parallel laminated sandstone. No wave ripples or hummocky cross-stratification or tidal structures are present in the delta fronts of this river-dominated delta (Figs. 3B, 24A, and B). Secondly, mud-rich and sand-rich river-dominated shelf-edge deltas appear in plan-view geomorphic images as birdfoot-like lowamplitude accumulations and lobate high-amplitude sheets, respectively. For example, river-dominated shelf-edge deltas in the Molo Formation (e.g., delta cases 11, 12, and 33) show amplitude-extraction maps as protruding accumulations with localized high-amplitude anomalies or as dendritic low amplitude sheets (Tables 3–4; Figs. 20A, B, and 22A). Thirdly, published data suggest that shelf-edge delta examples 1, 2, 4, 7, 10 to 23, 25, 27, 28, 30 to 33, 35 to 38, and 40 to 42 all have a river-dominated affinity (Tables 3–4). In summary, of 42 shelf-edge deltas presented here, 73.8% (31 of 42) are categorized as river-dominated cases (colored stars in Fig. 17). They collectively developed on shelf margins where fluvial distributary channels delivered their suspended and bedload sediment immediately in front of river mouths without being significantly influenced by waves or tides. Distributary complexes, bars, delta lobes, or elongate deltaic bodies are widely developed in front of distributary mouths,

resulting in lobate, dendritic, or birdfoot-like patterns in plan form (Tables 3–4). 5.2. Wave-dominated shelf-edge deltas In outcrops, wave-dominated shelf-edge deltas (Δw) are recognized in our data sets as relatively abrupt coarsening-upward successions (contrasting strongly with the gradual upward-coarsening of the riverdominated profiles) rich in swaley and hummocky cross-stratification, as well as symmetrical wave ripples on their delta fronts. Distributary channels are much less abundant and therefore less likely to cap the delta-front units at any location compared to river–dominated deltas (Tables 3–4). Delta example 6 in the Karoo Basin offers a representative outcrop example of this type of delta (Table 3). It is composed of fairly abrupt, sometimes sharp-based, coarsening-upward bodies with swaley and hummocky cross-stratification, current-ripple lamination, symmetrical wave ripples with shallow scours filled with small mudstone chips, and limited mudstone layers on their delta fronts (Jones et al., 2014). Secondly, in plan form, wave-dominated shelf-edge deltas exhibit a smoothfronted, strongly strike-elongate morphology because of obliquely directed waves (Tables 3–4). Some representative wave-dominated shelf-edge deltas come from the Eocene Porcupine Basin (examples 8 and 29), the Fuji Einstein margin (examples 18 and 19), and the Eocene Santos Basin (case 24) (Tables 3–4). Most of them appear in RMS attribute maps as high attribute accumulations with an elongate strike-extended morphology (Figs. 10B, 19A, B, and 22B). Thirdly, published data indicate that shelf-edge delta examples 3 and 24 can also be classified as wavedominated deltas (Table 3).

Fig. 9. (A) Regional stratigraphic cross-section from the Nova Scotia margin (from Deptuck, 2011) suggesting that sandy fan complexes and channel sandstones seen in core photographs of Fig. 9C and D developed in deep-water reaches of sandy Δr with low Qs. (B) Regional stratigraphic cross-section along the axis of the Einstein channel in the Gulf of Mexico (complied from Sylvester et al., 2012) illustrating cross-sectional appearance of sandy Δw with high Qs and associated sandy channel-levee complexes and sandy submarine fans.

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Fig. 10. (A) Depositional dip-oriented seismic section illustrating cross-sectional sandy Δw with low Qs in the Eocene Santos Basin. Sandy Δw with low Qs fostered sandy basin-floor fans that are seen as wedge-shaped, high-amplitude reflection packages in section view and as lobate high RMS-attribute accumulations in plan view. Seismic line and RMS attribute-extraction maps presented in this figure are from Dixon (2013).

Fig. 11. Dip-view seismic lines from the southern Hainan margin showing examples of muddy Δr with low Qs and associated mud-dominated slope to basin-floor systems.

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Fig. 12. 2D seismic profile and coherence attribute overlain by the time structure map showing cross-sectional and plan views of muddy Δt with high Qs in the late Quaternary Bonaparte Basin. Muddy Δt with high Qs links downdip to plume-derived mud belts and mass-transport deposits. From Bourget et al. (2014).

Fig. 13. Regional 2D seismic line (courtesy of Tore Grane Klausen) showing the stratigraphic architecture of sandy Δt with low Qs on the middle Triassic Norwegian Barents margin. No indications of seismic-scale turbidite sandstone bodies are seen to develop in front of falling shelf-edge segments of this margin.

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Fig. 14. (A) Multichannel seismic profile acquired during the Integrated Ocean Drilling Program Expedition 313 (from Miller et al., 2013) showing stratigraphic architecture of muddy Δr with high Qs on the middle Miocene New Jersey margin. No indicators of seismically detectable deep-water sandstones are recognized. (B, C, and D) Enlarged core photographs (from Mountain et al., 2010) showing well-preserved gastropod and mollusk shells in offshore silts (Hole M27 core 89 sec 1), silty prodelta sediments with sporadic occurrence of sharpbased sandy storm beds (Hole 28 core 92 sec 1), and laminated silty clay in deep-water reaches (Hole 28 core 166 sec 2).

In summary, of the 42 delta examples presented here, about 16.7% (7 of 42 examples) are categorized as waves-dominated regimes (red triangles in Fig.18B). They collectively occur on shelf margins where single or very few fluvial channels terminate at coastlines to form strike-extended smooth lobes because of wave remobilization and longshore-drift redistribution of sediment from river mouths (Tables 3–4). 5.3. Tide-dominated shelf-edge deltas The arguments for the recognition of tide-dominated shelf-edge deltas are as follows. Firstly, tide-dominated shelf-edge deltas (Δt) identified in our database differ from river- or wave-dominated shelf-edge deltas by the presence of long, elongate tidal bars extending at right angles to the coastline, within funnel-shaped coastal embayments. As such they contrast strongly with the strike-oriented wave deltas. Within the very irregular upward-coarsening delta fronts, there are tidal signatures such as mud drapes, fluid mud layers, tidal bundles, lenticular lamination, flaser bedding, and bidirectional cross-strata. Classical examples of tide-dominated shelf-edge deltas from the Scotian Basin (delta example 39) are given by Cummings et al. (2006), where thickening-thinning trends of tidal rhythmites in a thick upward-coarsening succession were recognized (Table 3). Secondly, in plan form, tide-dominated shelf-edge deltas have highly elongated morphological elements, because of the elongate tidal bars (e.g., Ganges-Brahmaputra delta). For example, tide-dominated deltas on the Bonaparte shelf margin (example 26) appear in plan-view coherence images as highly elongated bands, on

which tidally influenced distributary channels developed (Fig. 12B) (Bourget et al., 2014). Thirdly, literature studies show that shelf-edge delta example 34 on the Norwegian Barents margin also had a tidedominated origin (Klausen et al., 2015). In summary, tide-dominated shelf-edge deltas are less common in our lowstand delta database, because there are only few identified in the literature, such as examples 5, 26, 34, and 39 (Table 3). Of 42 reviewed delta examples presented in Tables 3–4, only 9.5% (4 of 42 examples) are classified as tide-dominated shelf-edge deltas (squares in Fig. 18). In closing, sediment-supply magnitudes (Qs) can be high or low, grain size of sediment supply can be dominantly sandy or muddy, and shelf-edge delta regimes can be river- (Δr), wave- (Δw), or tide-dominated (Δr) (Fig. 18A and B). The interaction between these three variables results in ten main types of shelf-edge deltas, namely: (1) sandy Δr with high Qs, (2) sandy Δr with low Qs, (3) muddy Δr with high Qs, (4) muddy Δr with low Qs, (5) sandy Δw with high Qs, (6) sandy Δw with low Qs, (7) sandy Δt with high Qs, (8) sandy Δt with low Qs, (9) muddy Δt with high Qs, and (10) muddy Δt with low Qs (Fig. 18A and B). 6. Sedimentary response to different types of river-dominated shelf-edge regimes 6.1. Sandy Δr with high Qs giving rise to volumetrically significant basin-floor fans Eleven sandy Δr with high Qs (examples 1, 2, 4, 7, 13, 16, 17, and 20 to 23 in Tables 3–4 and Fig. 18) are recognized in our database. Nearly all of

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Fig. 15. (A) Regional 2D seismic line (from Leroux et al., 2016) showing classical examples of muddy Δr with high or low Qs on the Pliocene to Pleistocene Gulf of Lions margin. (B) Regional well-log correlation section (from Leroux et al., 2016) across the entire Gulf of Lions margin illustrating lithographical character of Gulf of Lions examples (penetrated by wells Sirocco1, Mistral1, Rascasse1, and Autan1) and strata at 1245 m below sea level (mbsl) (penetrated by GLP2 well).

them link downdip to volumetrically significant sand accumulations on the deeper slope and basin floors (Table 3), among which the Late Cretaceous Washakie basin and the late Miocene Red River margin provide some typical cases. The Late Cretaceous Washakie shelf margin is interpreted as a supply-dominated (high Qs) case, and it fostered 4 typical examples of sandy Δr with high Qs accompanied by fan growth (e.g., clinoforms 6, 10, 12, and 13 of Carvajal and Steel, 2006) (Table 3; Figs. 8B and 23A). For example, the analysis of the Washakie clinoform 10 by Carvajal and Steel (2006, 2009) demonstrates that a riverdominated shelf-edge regime (with some tidal influence) played the driving role in the bypass of sand to deepwater, resulting in sandy basin-floor fans with sandstone units of 50 to 100 m in thickness (Fig. 23B), as shown by low gamma-ray responses in the logs of Figs. 8B and 23A. In addition, prograding and onlapping seismic facies are seen to develop in front of sandy Δr with high Qs on the late Miocene Red River margin (hot color-shaded areas in Fig. 2A and B). They are made up mainly of parallel, high-amplitude continuous seismic clinoform reflections with wedge-shaped geometries and display very clear, sigmoidaloblique progradational configurations (Table 3; Fig. 2A and B). Core data from the basin-floor fans in this system show predominantly poorly sorted, medium- to relatively coarse-grained sandstones and gravel lags (Fig. 25), which are shown in log profiles as a blocky log pattern of low gamma ray, low density, low sonic, and moderate to high resistivity (Fig. 25), indicating a sand-rich sedimentary facies. Dimensionally,

the Late Cretaceous Washakie basin-floor fans are 1387 to 2334 km2 (averaging 1830 km2) in fan area, while the late Miocene Red River submarine fans occupy an area of several thousands of km2 (Carvajal and Steel, 2006; Gong et al., 2015a). Basin-floor fans at deep-water reaches of sandy Δr with high Qs, therefore, tend to be volumetrically significant (Table 3).

6.2. Sandy Δr with low Qs fostering volumetrically less significant basin-floor fans Six sandy Δr with low Qs are recognized in our lowstand delta database, including examples 9 to 12, 14, 15, 32, and 33 in Tables 3–4 and Fig. 18. They collectively yielded basin-floor fans at their outlying deep-water reaches, except for cases 32 and 33 (Tables 3–4). Some representative outcrop examples of this type of delta with sandy submarine fan growth come from the Eocene Sobrarbe Formation in the Spanish Pyrenees and from clinoform 14 on the Spitsbergen margin (Table 3). The former had a low sediment supply (Rp b 4.88 km/My) and contains a sandy river-dominated shelf-edge delta, in front of which submarine channels and lobes composed of structureless, amalgamated, finegrained sandstones occur (Figs. 3B and 24) (Moss-Russell, 2009; Kim et al., 2013). The latter example of the outcropping early Eocene Spitsbergen clinoform 14 contains channeled shelf edges and associated slope channels filled by sandy hyperpycnites (Fig. 8A) (Petter and

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Fig. 16. Plots of Tse and Rp of flattish or downward prograding shelf margins documented in the current study (upper and lower panels, respectively). According to Rp, the magnitude of sediment supply to the chosen margin examples can be low or high (blue and red triangles in Fig. 16B, respectively). A t-test confirms that Tse populations are statistically distinctive at the 90% confidence interval.

Steel, 2006), in front of which relatively small submarine fans (seen on Hynestabben mountain) developed (Fig. 8A). In addition, clinoforms 7 and 8 in the Molo Formation on the Norwegian continental margin offer some seismic examples of sandy Δr with low Qs accompanied by sandy submarine fan deposition (Table 3). Sandy basin-floor fans appeared in amplitude-extraction maps (Fig. 20A and B) as fan-shaped high-amplitude accumulations are seen in the dip-view seismic line (Fig. 7B) as wedge-shaped, highamplitude, laterally continuous reflections. Dimensionally, fans in front of Spitsbergen and the Eocene Sobrarbe sandy Δr with low Qs are several tens of meters in thickness and generally less than 10 km in length (Figs. 8A and 24) (Moss-Russell, 2009), while fans at the downdip extension of Molo clinoforms 7 and 8 are several kilometers in length (Fig. 20A and B). Fans in front of sandy Δr with low Qs are, therefore, dimensionally less significant compared to those associated with sandy Δr with high Qs (Table 3). 6.3. Muddy Δr with low or high Qs accompanied by deep-water mud accumulations Twelve muddy Δr with high Qs (examples 25, 27, 28, 30 to 33, 35, 37 to 38, 40, and 41 in Table 4 and Fig. 18B), together with two sandy Δ r with low Q s (cases 36 and 42), are recognized, in front of which no sandy deposition has been interpreted (Table 4). Among them, some classical examples come from the Molo clinoforms 2,

4, and 6, the Taranaki Basin, the middle Miocene New Jersey margin, and the Pliocene to Pleistocene Gulf of Lions (Table 4). Distributary channel complexes imaged as depositional dip-extended, lowamplitude accumulations were interpreted to be mud-dominated by Bullimore et al. (2005). Bullimore et al. (2005) have indicated that deep-water fan deposition was likely absent during the deposition of Molo clinoforms 2 and 4, despite sufficient fall of relative sea level (Table 4; Figs. 7, 21A, 21B, and A). In addition, some mud-dominated upper delta fronts seismically imaged as low-amplitude, laterally continuous seismic reflections developed on the late Pliocene to early Pleistocene Taranaki margin with high Rp of 12 to 45 km/My (Salazar et al., 2015), resulting in muddy Δr with high Qs (Table 4; Fig. 4B). No seismically resolvable sandstone bodies are seen in the deep-water reaches of the Taranaki system (Table 4; Fig. 4B) (Anell and Midtkandal, 2015; Salazar et al., 2015). However, sandy channel-fan systems seen as wedge-shaped, high-amplitude reflection packages developed at the downdip extension of sandy Δr with low Qs on the same margin (Table 4; Fig. 4A) (Salazar et al., 2015). The same trends were also obtained from the middle Miocene New Jersey margin, where muddy Δr with high Qs and their resultant toeset beds composed predominantly of laminated silty clay are recognized (Table 4; Fig. 14). The similar affinity is also evidenced by the borehole data from the Pliocene to Pleistocene Gulf of Lions, where muddy sedimentary prisms made up predominantly of clay or calcareous clay are interpreted to be present in the downdip extension of

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Table 3 A summary of deep-water sedimentary response to the interplay of process regime at the shelf edge, dominant grain size of supplied sediment, and magnitude of sediment flux for the tabulated examples with basin-floor fan growth. Flat or downward prograding margins

Cases Lithological character of upper delta fronts

Sediment Transport regimes at the shelf supply edge

Contemporaneous deep-water systems

Red River margin

1

Sandy upper delta-front deposits seen as sigmoid-progradational, moderate to high, continuous seismic reflections (Fig. 17A).

High

River dominated (Wang et al., 2011)

Borneo margin

2

High

Northern Carnarvon Basin Pliocene Taranaki Basin

3

West Baram Rpper delta fronts composed of blocky siltstone and sandstone sheets Koša (2015) Delta lobes 1 to 20 consisting predominantly of sandstones rich in quartz grains (Fig. 3A) (Sanchez et al., 2012a). Sandy upper delta fronts consisting of high amplitude, laterally continuous seismic reflections (Fig. 4A) (Anell and Midtkandal, 2015).

River dominated (Saller et al., 2004) Wave dominated (Sanchez et al., 2012a, 2012b)

Sand-rich basin-floor fans consisting of fine-grained turbidites, coarse-grained grain-flow deposits, and sandy debris-flow deposits (Figs. 2 and 25). Sandy basin-floor fans imaged as moderate- to high amplitude reflectors (Koša, 2015). Sandy basin-floor fans seen in dip-view seismic sections as wedge-shaped, high-amplitude reflection packages (Fig. 3A). Sinuous, deltaic channels transferred shelf-edge sands into deep-water areas, yielding sandy basin-floor fans (Fig. 4A) (Salazar et al., 2015).

Bay of Bengal

5

Lower Waterford Formation in the Karoo Basin Quaternary Niger Delta Basin Early Eocene Porcupine Basin Ainsa Basin, Spain

6

Clinoform 3 in the Molo Formation, offshore Norway Clinoform 7 in the Molo Formation, offshore Norway Clinoform 8 in the Molo Formation, offshore Norway West Siberia margin Clinoform 14 on the Spitsbergen magrin Lower Valanginian on the Nova Scotia margin Rio Grande margin, south Texas Offshore Louisiana Delta lobe 1 on the Fuji Einstein margin Delta lobe 2 on the Fuji Einstein margin

4

High

High

Gangese-Brahmaputra delta systems and associated High sand-rich upper delta fronts (Goodbred Jr and Kuehl, 2000). High Upper delta fronts with amalgamated hummockand swale-dominated sandstones (Jones et al., 2014).

River dominated, as suggested by the occurrence of sinuous channels on outer shelves (Salazar et al., 2015). Tide dominated (Goodbred Jr and Kuehl, 2000) Wave dominated (Jones et al., 2014)

Regionally extensive (12 km long and 4 km wide) Pliocene basin-floor fans containing substantial turbidite reservoirs (Fig. 5B). Basinward thickening wedge of undeformed heterolithic to amalgamated slope turbidite sandstones (Jones et al., 2014).

7

Sandy upper delta fronts on one of the largest shelf-edge deltas in the word (Reijers, 2011).

High

River dominated (Reijers, 2011)

8

Sandy delta lobes rich in medium-grained sandstones (Figs. 6B and 19A) (Ryan et al., 2009).

Low

Wave dominated (Fig. 19A) (Ryan et al., 2009)

9

Sandy upper delta fronts consisting of medium-grained sandstones (Figs. 3B and 24B).

Low

River dominated (Moss-Russell, 2009)

10

Sandy delta fronts with bypass signals on their topset compartments (Fig. 7A).

Low

River dominated (Bullimore et al., 2005)

11

Sandy fluvial rivers manifested as sinuous high-amplitude bands and upper delta fronts seen as figure-shaped high-amplitude patches (Fig. 20A).

Low

River dominated (Dixon et al., 2012)

Basin-floor fans seen in amplitude maps as fan-shaped high-amplitude sheets (Fig. 20A).

12

Sand-rich delta lobes seen as lobate high amplitude Low anomalies (Fig. 20B).

River dominated (Dixon et al., 2012)

Laterally nested basin-floor fans seen as fan-shaped high-amplitude sheets (Fig. 20B).

13

West Siberia upper delta fronts containing substantial sands (Pinous et al., 2001).

River dominated (Pinous et al., 2001)

14

Low Channelized, sandy upper delta fronts dominated by fluvial sediment supply (Figs. 8A and 25A) (Steel et al., 2000).

River dominated (Steel et al., 2000)

Thick and regionally extensive submarine fans and ramps consisting mainly of massive sandstones (Pinous et al., 2001). Hyperpycnites and sandy basin-floor fans (Steel et al., 2000; Steel and Olsen, 2002).

15

Sable island delta fronts composed of thick regressive sandstones (Fig. 9A) (Cummings and Arnott, 2005; Deptuck, 2011).

Low

River dominated (Cummings and Arnott, 2005)

Fan complexes and sandy channel fills (Fig. 9A) (Cummings and Arnott, 2005; Deptuck, 2011).

16

Sandy delta lobes (Banfield and Anderson, 2004).

High

River dominated (Banfield and Anderson, 2004)

Sand-prone Rio Grande basin-floor fans (Banfield and Anderson, 2004).

17

Sandy mouth bars on forced regressive shelf-margin deltas (Perov and Bhattacharya, 2011). Sandy delta lobes and delta fronts characterized by high amplitude reflection properties (Fig. 22B) (Sylvester et al., 2012).

High

River dominated (Perov and Bhattacharya, 2011)

Channel sandstones and sandy lobe complexes (Perov and Bhattacharya, 2011).

High

Wave dominated (Sylvester et al., 2012)

Sandy submarine channel-levee systems and sand-rich submarine fans (Fig. 22B) (Sylvester et al., 2012).

High

Wave dominated (Sylvester et al., 2012)

18

19

High

Basin-floor fans expressed as wedge-shaped, high amplitude, laterally continuous reflections (Henriksen et al., 2011). Coarse-grained submarine lobes and sandy channel sandstones (Figs. 6 and 19A). Coarse-grained submarine lobes and sandy channel fills (Fig. 24A and C) (Moss-Russell, 2009; Kim et al., 2013) Sandy basin-floor fans expressed as high amplitude laterally continuous reflections (Fig. 7A).

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Table 3 (continued) Flat or downward prograding margins

Cases Lithological character of upper delta fronts

Sediment Transport regimes at the shelf supply edge

Contemporaneous deep-water systems

Clinoform 6 in the Washakie Basin Clinoform 10 in the Washakie Basin Clinoform 12 in the Washakie Basin Clinoform 13 in the Washakie Basin Santos Basin

20

High

River dominated (Fig. 23 A) (Carvajal and Steel, 2009)

Huge amounts of shelf-edge sands were delivered into deep-water areas of clinoforms 6, 10, 12, and 13, resulting in sandy, regionally extensive basin-floor fans in front of flat shelf-edge trajectories (Figs. 8B and 23B) (Carvajal and Steel, 2006, 2009).

Wave dominated (Dixon, 2013)

Sandy basin-floor fans seen in section view as wedge-shaped, high amplitude reflections and in plain view as lobate, high RMS accumulations (Fig. 10A and B).

21

Sand-rich shelf-edge deltas and concomitant upper delta fronts contain flat-laminated sandstones and tidal influenced facies (Figs. 8B and 23A) (Carvajal and Steel, 2009).

High

22

High

23

High

24

Shelf-sand ridges seen in RMS attribute-extraction map as depositional strike-elongated, high RMS bands (Fig. 10B).

Low

contemporaneous muddy Δr with either high or low Qs (Leroux et al., 2016) (Table 4; Fig. 15). 7. Sedimentary response to different types of wave-dominated shelf-edge regimes 7.1. Sandy Δw with high Qs producing volumetrically smaller sandy basin-floor fans Four sandy Δw with high Qs are identified, including examples 3, 6, 18, and 19 in Table 3 and Fig. 18A. They are all accompanied by timeequivalent basin-floor fans, which are volumetrically smaller than those associated with sandy Δr with either high or low Qs (Table 3). The lower Waterford Formation in the Karoo Basin and the Fuji Einstein system along offshore Alabama are examples showing such affinities. Shelf-edge deltas on clinoform 4 in the lower Waterford Formation were interpreted as storm-wave-dominated shelf-edge deltas by Jones et al. (2014). The low accommodation and high sediment supply triggered by active extensional growth faulting and slope oversteepening are interpreted to have delivered shelf-edge sands into gullied shelfmargin rollovers though no fans are documented (Table 3) (Jones et al., 2014). Dixon et al. (2012) and Sylvester et al. (2012) suggested that the sandy Pleistocene Fuji delta lobes 1 and 2 imaged as lobate high RMS-attribute sheets are of wave-dominated origin (Fig. 22B). The fuji Einstein sandy Δw with high Qs gave rise to sandy channel fills in sinuous submarine channels and concomitant sandy basin-floor fans that are volumetrically small (i.e., 10s m in thickness and 100s km2 in area), which are seismically imaged as depositional diptrending, tortuous, high-amplitude bands and as fan-shaped, highamplitude lobes (Table 3; Figs. 9B and 22B), respectively. Each of these four case studies suggests that it is possible to source some sandy deep-water systems from wave-dominated shelf-edge regimes, though there are other documented cases of high-supply shelf-edge deltas where the ‘storm-wave fence’ and alongshore sediment drift at the shelf edge has prevented deepwater delivery downdip of the wave-dominated sites (e.g., Carvajal and Steel, 2009; Dixon et al., 2012). 7.2. Sandy Δw with low Qs giving rise to restricted sandy basin-floor fans Three examples of sandy Δw with low Qs are recognized in our database, including examples 8, 24, and 29 in Tables 3–4 and Fig. 18. Similar to sandy Δw with high Qs, two of them (cases 8 and 24) are accompanied by time-equivalent, small submarine fans (Table 3). The reviewed

examples 8 and 24 are characterized by low sediment supply (suggested by Rp of ca 2 to 3 km/My) (Table 2). The former Eocene Porcupine case appears in RMS attribute-extraction maps as lobate high attribute accumulations (Fig. 18A), and is categorized as a wave-dominated delta by Ryan et al. (2009). It did produce some locally restricted basin-floor fans at its outlying deep-water reaches (i.e., 10s km2 in fan area), which are imaged as lobate high RMS-attribute accumulations (Table 3; Fig. 19A). The Santos example was interpreted to be wavedominated by Dixon (2013), and contains shoreface ridges expressed as strike-elongate, high RMS-attribute bands (Fig. 10B). It fostered a series of relatively small basin-floor fans (i.e., 10s km2 in fan area) that show in seismic sections as wedge-shaped, high-amplitude reflection packages and in RMS attribute-extraction maps as fan-shaped, dipextended high RMS lobes (Fig. 10A and B), collectively indicating sand-rich properties (Dixon, 2013).

8. Sedimentary response to different types of tide-dominated shelf-edge regimes 8.1. Tide-dominated shelf-edge regime collectively leading to deep-water mud accumulations There are only few examples of tide-dominated shelf-edge regimes recognized in our database, such as examples 5, 26, 34, and 39 in Tables 3–4 and Fig. 18, so care must be taken in drawing conclusions. In marked contrast with sandy Δr or Δw with either high or low Qs, most of them (cases 26, 34, and 39), whether they are fed by dominantly sandy or muddy sediment, are not associated with the growth of sandy basin-floor fans. This suggests that little shelf-edge sand was transported across the shelf and down to the deeper slope, but was retained within the topsets of tide-dominated shelf-edge deltas (Tables 3–4). This hypothesis is supported by the following three lines of observations. Firstly, there is no seismic evidence for thick, discrete basin-floor fans in front of the flat to slightly falling shelf-edge segments of the late Barremian Nova Scotia margin, although the contorted or downward prograding nature of this system could be regarded as a signature of active delivery of shelf-edge sands into deepwater (Table 4) (Cummings and Arnott, 2005). Secondly, Klausen and Mørk (2014) suggest that there are no indications of seismically resolvable sandstone bodies or any seismic signatures of submarine channels or canyons in the deep-water areas of the middle Triassic Barents margin, although fluvial channel sandstones and sandy tide-dominated shelf-edge deltas with tidal channels, tidal flats, and tidal sand bars are recognized

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Table 4 A summary of deep-water sedimentary response to the interplay of process regime at the shelf edge, dominant grain size of supplied sediment, and magnitude of sediment flux for the tabulated examples without fan growth. Flat or downward prograding margins

Cases Lithological characters of upper delta fronts

Sediment Transport supply regimes at the shelf edge

Contemporaneous deep-water systems

Southern Hainan margin Bonaparte Basin

25

Muddy upper delta fronts typified by moderate to low, continuous seismic reflections (Fig. 17B). Mud-dominated upper delta fronts (Fig. 13) (Bourget et al., 2014).

Low

Marine mudstone sheets and mud-dominated mass-transport deposits (Fig. 11A and B). Plume-derived mud belts and mass-transport deposits (Fig. 12) (Bourget et al., 2014).

Early Pliocene Ebro margin

27

Mud-prone upper delta fronts expressed as moderate- to low-amplitude seismic reflections with oblique or sigmoidal configurations (Kertznus and Kneller, 2009).

Low

Late Pliocene Ebro margin

28

Middle Eocene Porcupine Basin Clinoform 1 in the Molo Formation, offshore Norway Clinoform 2 in the Molo Formation, offshore Norway Clinoform 4 in the Molo Formation, offshore Norway Clinoform 6 in the Molo Formation, offshore Norway Norwegian Barents margin Høgsnyta clinoforms 1 on the Spitsbergen margin Høgsnyta clinoform 2 on the Spitsbergen margin Litledalsfjellet clinoforms on the Sptisbergen margin Middle Miocene New Jersey margin Scotian Basin

29

26

30

High

Low

Sandy upper delta fronts expressed as high RMS-attribute sheets with localized high amplitude anomalies and in facies (Fig. 19B). Muddy upper delta fronts seen as sigmoidal low amplitude, continuous reflections (Fig. 7A).

Low

Low

River dominated (Li et al., 2015) Tide dominated (Bourget et al., 2014) River dominated (Jimknez et al., 1997) River dominated (Jimknez et al., 1997) Wave dominated (Ryan et al., 2009) River dominated (Bullimore et al., 2005)

Fairly muddy sedimentary prisms made up of slumps, slides, or debris-flow deposits developed on the slope of the Pliocene Ebro margin (Kertznus and Kneller, 2009).

Mud-dominated mass-transport deposits and heterolithic marine accumulations imaged as low RMS attribute sheets (Fig. 19B). Slumps, slides, and debris-flow deposits on the slope (Fig. 7A).

31

Muddy outer shelves represented by low amplitude sheets Low with sporadic occurrence of localized high amplitude patches (Fig. 21A) (Bullimore et al., 2005).

River dominated (Dixon et al., 2012)

Mud-dominated slumps and slides seen as transparent, chaotic reflection packages with sporadic occurrence of sandy debris-flow deposits (Fig. 21A) (Bullimore et al., 2005).

32

Sandy barrier bars seen as dip-elongated, high amplitude accumulations (Fig. 21B).

Low

River dominated (Bullimore et al., 2005)

Slumps, slides, and debris-flow deposits occur immediately seaward of Molo clinoform 4 (Fig. 21B).

33

Isolated channels and sand-prone delta lobes (Fig. 22A) (Bullimore et al., 2005).

Low

River dominated (Bullimore et al., 2005)

Mass-transported deposits (i.e., slumps, slides, and debris-flow deposits) developed in front of clinoform 6 (Fig. 22A) (Bullimore et al., 2005).

34

Due to a wide shelf of up to 700 km, sandy fluvial channels Low or deltas are unable to reach the shelf edge (Fig. 13A) (Klausen et al., 2015). A lack of sandy sediment supply (Plink-Björklund et al., Low 2001; Plink-Björklund and Steel, 2002).

Tide dominated (Klausen and Mørk, 2014) River dominated (Dixon et al., 2012)

No indications of seismically detectable sandstone bodies are found to occur in deep-water areas (Fig. 13B) (Klausen et al., 2015). Muddy slope aprons (Plink-Björklund et al., 2001; Plink-Björklund and Steel, 2002).

35

36

Dominantly sandy shelf-margin deltas and supply of sand-dominated sediment (Plink-Björklund and Steel, 2002).

Low

River dominated (Dixon et al., 2012)

Muddy slope aprons and mudstone sheets, due to the absence of sediment conduits (Plink-Björklund and Steel, 2002).

37

Mud-dominated delta fronts and a lack of cross-shelf incised valleys (Mellere et al., 2002).

Low

River dominated (Deibert et al., 2003)

Marine mudstone sheets (Mellere et al., 2002).

38

Silty prodelta sediment and mud-prone outer shelves (Fig. 14A, B, and C).

High

Toeset beds are composed of laminated silty and clay (Fig. 14A and D).

39

Sandy, strongly tide influenced shelf-margin deltas (Cummings et al., 2006).

Low

Late Pliocene to early Pleistocene Taranaki Basin Pliocene Gulf of Lions margin

40

Mud-dominated upper delta fronts composed of low to transparent amplitude, parallel seismic reflections (Fig. 4B).

High

41

High

Pleistocene Gulf of Lions margin

42

Mud-dominated upper delta fronts consisting mainly of clay, carbonated clay, silty clay seen in wells Sirocco1, Mistral1, Rascasse1, and Autan1 (see Fig. 15B and Leroux et al., 2016 for more details). Mud-dominated upper delta fronts consisting of clay, carbonated clay, silty clay, and silty marl recognized in wells Sirocco1, Mistral1, Rascasse1, and Autan1 (see Fig. 15B and Leroux et al., 2016 for more details)

River dominated (Steckler et al., 1999) Tide dominated (Cummings et al., 2006) River dominated (Anell and Midtkandal, 2015) River-dominated, Gilbert deltas (Lofi et al., 2003)

Low

No indications of thick, sandy basin-floor fans are found (Cummings and Arnott, 2005). No seismically resolvable sand deposits are seen (Fig. 4B) (Anell and Midtkandal, 2015).

As evidenced by well GLP2, downdip extension of Pliocene muddy Δr with high Qs in Gulf of Lions is made up mainly of clay and carbonated clay, with sporadic occurrence of thin sandstone beds (Fig. 15B). River-dominated, As evidenced by well GLP2, downdip continuation of Pleistocene muddy Δr with low Qs in Gulf of Lions is Gilbert deltas (Lofi et al., 2003) composed predominantly of clay (Fig. 15B) (Leroux et al., 2016).

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Fig. 17. Depositional dip-view seismic lines illustrating sandy Δr with high Qs developed in front of Asia's third largest river (Red River) and small rivers with a total catchment area of less than 3000 km2 on the Hainan Island (upper and lower images, respectively).

(Fig. 13). Thirdly, Bourget et al. (2014) have shown that there is a lack of turbidite reservoir development in front of the late Quaternary Bonaparte tide and wave-dominated shelf-edge deltas during lowstands (Fig. 12).

dip-view seismic lines as wedge-shaped prisms consisting of moderate- to high-amplitude, laterally continuous reflections, and manifests as high RMS-attribute fans (Fig. 5A and B, respectively), both of which are indications of sand-rich properties.

8.2. Tide-dominated deltas with direct linkage between deltas and channel heads yielding sandy deep-water systems

9. The role of grain size of sediment supply and transport regime at the shelf edge in driving sand into deepwater

As discussed above, on the basis of a very restricted database, the tide-dominated shelf-edge regime is not interpreted as a successful shelf-edge scenario for transfer of shelf-edge sands to basin-floor fans. However, some tide-dominated shelf-edge regimes with direct link between deltas and canyon heads do occur, as evidenced by the examples of sandy Δt with high Qs from the Ganges-Brahmaputra-Bengal sediment-routing system (Table 3; Fig. 18). The Ganges and Brahmaputra rivers with an annual sediment discharge of ca 5.2 × 108 t/yr discharge into an energetic marine environment characterized by very strong tidal currents, resulting in the tide-dominated GangesBrahmaputra deltas with characteristic elongate tidal bars (Fig. 18) (Milliman and Syvitski, 1992; Kuehl et al., 1997). The Swathe of No Ground Canyon, together with slope gullies or submarine channels cut deeply back into deltas, thus incising across much of the shelf (Romans et al., 2016). In this way, submarine conduits are able to maintain a connection to the nearby delta lobes and/or distributary channels, allowing abundant sand to funnel through the slope, forming an extensive Pliocene basin-floor fan (Table 3). This basin-floor fan appears in

9.1. Sandy river-dominated shelf-edge deltas are most efficient at delivering sand into deep-water fans Among the 42 shelf-edge delta examples presented in this review, nearly all cases of sandy Δr with either high or low Qs (red and blue starts in Fig. 18A) gave rise to extensive sandy accumulations on the slope and basin floor (examples 1, 2, 4, 7, 9 to 17, and 20 to 23 in Table 3). This indicates that large volumes of shelf-edge sands are commonly partitioned into deep-water areas by riverdominated shelf-edge deltas, even with low sediment supply, confirming the conclusion of Dixon et al. (2012) (Fig. 26A). Driven by relative sea-level fall as suggested by slightly falling or flat shelfedge trajectories, sandy river-dominated shelf-edge deltas become cannibalized by their own river distributaries (Mellere et al., 2002), enhancing the volumes of shelf-edge sands delivered into deepwater reaches of the recognized examples of sandy Δ r with either high or low Qs (Table 3; Fig. 26A). In fact, it is a characteristic feature of the conventional sequence-stratigraphic model that relative sea-

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Fig. 18. The classification system of the 42 chosen delta examples, based on magnitudes of sediment supply (low or high), the dominant grain size of sediment supply (dominantly sandy or muddy), and shelf-edge delta regimes (river-, wave-, or tide-dominated). Note that sandy Δr and Δw with either high or low Qs (examples 1 through 24 in Table 3) are consistent with conventional sequence-stratigraphic models that link relative sea-level fall to submarine-fan growth, but that muddy Δr, Δw, and Δt with either high or low Qs (examples 24 through 42, as listed in Table 4) have no associated sandy basin-floor fans.

level fall drives shelf-edge sands to the outlying deeper slope and basin floors. 9.2. Sandy wave-dominated shelf-edge deltas are less efficient at delivering sand into deep-water fans Of seven sandy Δw with either high or low Qs presented here (red triangles in Fig. 18), many of them also link downdip to very small sandy basin-floor fans or slope turbidite systems (examples 3, 6, 8, 18, 19, 24, and 29 in Table 3). However, sandy basin-floor fans associated with sandy Δw with low Qs are only a few kilometers in width and several tens of km2 in area, and thereby are significantly smaller than those in front of river-dominated shelf-edge deltas (Table 3). This suggests that sandy wave-dominated shelf-edge deltas are less efficient than river-dominated deltas in dispersing sand from shelfedge sites down to the deeper slope and basin floors (Fig. 26A). The main reason for this is because most of the sand on wavedominated shelf-edge deltas is reworked and driven by oblique waves as longshore drift, thereby storing the sand in longshore sand belts at the shelf edge itself (Dixon et al., 2012). However, there are exceptions where sometimes this sand can be captured by a canyon or large channel head, and funneled downslope into basin-floor fans (Fig. 26A). This may have been the case for the

Waterford clinoform 4 in the Karoo Basin, where sandy wavedominated shelf-edge deltas have delivered their sand volumes directly into upper slope gullies (Jones et al., 2014). This scenario is conceptually illustrated in Fig. 26A. 9.3. Tide-dominated shelf-edge deltas and muddy river- or tide-dominated shelf-edge deltas appear to be inefficient in driving shelf-edge sands into deepwater In contrast to sandy Δr or Δw with either high or low Qs, Δt with either high or low Qs (red squares in Fig. 18B) appear to be less likely to disperse sand to deep-water settings, as evidenced by delta examples 34 and 39 in Table 4, though we use some caution because there is very few data on this type of shelf-edge delta. Most of the examples of tidedominated shelf-edge deltas appear to have no associated submarine fan growth (Fig. 26B). A possible problem is that tide-dominated deltas may promote plume-derived fine-grained sedimentation or masswasting processes instead of coarse-grained hyperpycnal flows, as happened in the Bonaparte case during the Last Glacial Maximum (Bourget et al., 2014). In contrast to the sandy Δr or Δw with either high or low Qs, ten muddy river- or tide-dominated shelf-edge deltas with either high or low Qs are all fronted by muddy deep-water systems (examples 25 to 28, 30, 31, 35, and to 38, and 40 to 42 in Table 4 and in Fig. 18B). It

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Fig. 19. RMS amplitude-extraction maps (from Ryan et al., 2009) illustrating plan-view geomorphological appearance of sandy Δw with low Qs and associated deep-water systems. Note that sandy Δw with low Qs with channelized shelf edges gave rise to volumetrically small sandy basin-floor fans, but that sandy Δw with low Qs with non-channelized shelf edges did not.

Fig. 20. Amplitude-extraction maps (from Bullimore et al., 2005) taken at 25 ms above the basal bounding surfaces of clinoforms 7 and 8 (bases 7 and 8 in Fig. 7) (left and right panels, respectively) illustrating plan-view geomorphological manifestations of sandy Δr with low Qs and coeval deep-water systems.

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Fig. 21. (A) Muddy Δr with low Qs and associated muddy mass-transport deposits as shown on amplitude-extraction maps (from Bullimore et al., 2005) taken at 26 ms below the basal bounding surfaces of clinoform 2 (base 2 in Fig. 7A). (B) Amplitude-extraction map (from Bullimore et al., 2005) showing plan-view geomorphological expression of sandy Δr with low Qs on clinoform 4 with non-channelized shelf edges, in front of which mass-transported features (i.e., slumps, slides, and debris-flow deposits) occur.

Fig. 22. (A) Sporadic occurrence of delta lobes in non-channeled shelf-edge regions and sandy Δr with low Qs on Molo clinoform 6 as imaged on the amplitude-extraction map (from Bullimore et al., 2005). (B) Amplitude-extraction map (from Sylvester et al., 2012) showing plan-view geomorphological appearance of the Fuji Einstein sandy Δw with high Qs with densely channelized shelf edges and associated sandy submarine fans. Note that sandy Δw with high Qs with channelized shelf edges are linked downdip to submarine channels and sandy basin-floor fans (right panels), but that sandy Δr with low Qs with non-channelized shelf edges are not (left panel).

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Fig. 23. (A) Cross section through the shelf-edge outcrop of clinothem C10 on the eastern Washakie Basin showing fluvial deposits at the shelf edge and associated slope channels and submarine fans. (B) Sandstone isopach map of basin-floor fans occurring in front of the clinoform C10 in the Washakie sandy Δr with low Qs in.

is virtually impossible for a mud-dominated system to deliver large volumes of sand into deep-water sites to form sandy basin-floor fans, and this scenario is conceptually illustrated in Fig. 26B. All of these observations suggest that little significant shelf-edge sand will be delivered into deep-water areas by muddy, river- or wave-dominated shelf-edge deltas or by tide-dominated shelf-edge deltas. 10. Transport regimes and dominant grain size as fundamental, but underappreciated, controls on sand partitioning into deepwater 10.1. Grain size of sediment supply is all important All muddy river-, wave-, or tide-dominated shelf-edge deltas with either high or low supply of dominantly muddy sediments have no

associated basin-floor fans (Fig. 26B; Table 4), whereas most of the sandy river- and many wave-dominated shelf-edge deltas with either high or low supply of dominantly muddy sediments link downdip to submarine fan turbidite systems (Fig. 26A; Table 3). Of 42 conventional lowstand shelf-edge delta examples, ca 38% (16 of 42 examples) do not fit the conventional sequence-stratigraphic models that link falling relative sea level to sandy basin-floor fan growth (e.g., Vail et al., 1977; Van Wagoner et al., 1990; Posamentier et al., 1992; Catuneanu et al., 2009). The conventional accommodation-drive mechanism is, therefore, less valid in shelf-edge delta regimes with supply of dominantly muddy sediment, even when there is sufficient fall of relative sea level or high sediment flux or river-dominated regimes to drive the delta delivery system across the shelf (Fig. 26B). This deviation from the traditional sequence-stratigraphic model is simply caused by a lack of sandy sediment supply (Fig. 26B).

56 C. Gong et al. / Earth-Science Reviews 157 (2016) 32–60 Fig. 24. Interpreted photographs (from Moss-Russell, 2009; Kim et al., 2013) of a river-dominated shelf-margin delta in the early Eocene Ainsa Basin (A), fluvial channel belts located at the distal shelf (B), and turbidite lobe elements on the basin floors (C). See Fig. 3B for stratigraphic positions of the shown outcrop photographs.

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Fig. 25. Integrated well log and core photographs (stratigraphic position shown in Fig. 2A) showing core-log expression of basin-floor fans in the deep-water reaches of sandy Δr with high Qs on the late Miocene Red River margin.

10.2. Wave-dominated shelf-edge deltas have been somewhat underestimated for delivery of deepwater sediment

10.3. The direct linkage between shelf-edge deltas and conduit heads, especially on narrow shelves, can be vital

This review of 42 delta examples strongly suggests that a riverdominated shelf-edge delta regime is by far the most successful shelf-edge scenario for getting shelf-edge sands to deepwater sites, as has also been highlighted by Dixon et al. (2012); Bourget et al. (2014), and Laugier and Plink-Björklund (2016). However, the current work suggests that wave-dominated shelf-edge process dominance is also sometimes able to foster slope or basin-floor turbidite reservoirs, as reflected through examples 3, 6, 8, 18, 19, and 24 in Table 3 and in Fig. 18A. Among examples of sandy wavedominated regimes with fan growth, examples 3, 6, 18, and 19 with Rp N10 km/My are characterized by relatively high sediment flux, whereas examples 8 and 24 with Rp b 10 km/My are characterized by a low sediment flux (Fig. 18A). This suggests that, no matter how high or low sediment supply may be, sandy wave-dominated shelf-edge deltas are also sometimes able to deliver shelf-edge sands to the deepwater areas, as conceptually illustrated in Fig. 26A. In some cases the deepwater delivery site is not necessarily downdip of the wave-dominated shelf edge, but farther along strike because of longshore drift at the shelf edge.

Our results suggest that sandy river-, and to a lesser extent wavedominated shelf-edge deltas, are by far the most successful transportregime scenarios for driving shelf-edge sands down to basin-floor fans (Fig. 26A). However, this rule can be easily broken by direct linkages between shelf-edge deltas and canyon or channel heads, as supported by following two lines of evidence. On the one hand, sandy river- or wave-dominated shelf-edge deltas are unable to disperse shelf-edge sands into deepwater, if there is no conduit linkage to the slope. This is well illustrated by delta examples 29, 32, 33, and 36. Sandy wave-dominated upper delta fronts expressed as high RMS-attribute sheets and sandy barrier bars or delta lobes seen as depositional strike-elongate, high-amplitude accumulations are also seen to develop on the outer shelves of the Porcupine margin (case 29, Fig. 19B) and the Molo clinoforms 4 and 6 (examples 32 and 33, Fig. 21A), collectively suggesting a sandy river-dominated shelf-edge regime (Table 4). Examples 32 and 33, however, did not foster seismically detectable submarine fans (Tables 3–4). A closer look at them suggests that they lack active sediment dispersal conduits (i.e., canyons, channels, or slope gullies) that eat their way back on to the shelf (Figs. 19B and

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Fig. 26. Schematic illustration of the significance of dominant grain size and transport regimes at the shelf edge on driving shelf-edge sands into deepwater areas of basins. Note that sandy Δr and Δw with either high or low Qs are accompanied by sandy submarine fans (upper panel), whereas muddy Δr and Δw with either high or low Qs, together with sandy or muddy Δt with either high or low Qs, are not.

21A). Another example of sandy Δt with low Qs without fan growth comes from Høgsnyta clinoform 2, Spitsbergen (example 36 in Table 4), where a fall of sea level below the shelf edge brought no sand out onto the basin floor, although significant sand accretion and river dominance on the coeval shelf margin was recognized (Plink-Björklund and Steel, 2002). Plink-Björklund and Steel (2002) related the absence of deep-water sand accumulation, despite river dominance at the shelf edge and sufficient sea-level fall, to the absence of channels on the upper slope. On the other hand, some sandy Δt with high Qs with direct linkage between shelf-edge deltas and channel heads are able to disperse shelf-edge sands into the deeper slope, although tide-dominated transport regimes are interpreted to be less efficient in driving shelf-edge sands into deepwater (Fig. 26B). The Ganges-Brahmaputra-Bengal delta lobes (example 5) are known to be tide dominated, but were also significantly incised and cut by channels, canyons, or slope gullies (Romans et al., 2016). On this sandy Δt with high Qs, sediment dispersal conduits extended back into the shelf-edge deltas and were able to maintain connections to nearby hinterland source areas and distributary channels, thus bringing sand down to the Pliocene Bengal basin-floor fans (Fig. 5). 11. Conclusions A review of 42 lowstand delta examples on flattish or downward prograding shelf margins shows that only 24 Δr and Δw with either high

or low Qs of dominantly sandy sediment are able to deliver shelf-edge sands into deepwater to form sandy submarine-fan systems. Contrary to the classical sequence-stratigraphic models, ca 43% of the reviewed examples with either high or low supply of mud-dominated sediment have no coeval basin-floor fans. Therefore, grain size of sediment supply is a pivotal, but underappreciated, control on delivering shelf-edge sands into deepwater. Wave-dominated shelf-edge process regimes with sanddominated supply can also be efficient in creating small deepwater reservoirs on the slope or sometimes on the basin floor, as reflected by six examples of sandy Δw with either high or low Qs accompanied by concomitant submarine fan growth, particularly where there is a direct linkage between deltas and conduit heads. Our results thus aid in obtaining a more complete picture of the shelf-edge to deepwater sand delivery paradigm. Also shown are the stratigraphic positions of outcrop photographs of Fig. 24A, B, and C. Acknowledgments The RioMAR sponsor companies are greatly acknowledged for numerous discussions and their generous support of C. Gong's postdoctoral research at the University of Texas at Austin. We thank the China National Offshore Oil Corporation for providing unpublished subsurface database (Figs. 2, 11, 17, and 25). We are grateful to Jinyu Zhang of UT

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Austin for taking the time to plough through an earlier version of this manuscript and to Jae Woo Kim and to Tore Grane Klausen for providing original versions of images shown in Figs. 5, and 23B. We are indebted to Tor O. Sømme and two anonymous reviewers for the critical but constructive reviews and to André Strasser for editorial handling, both of which significantly improved the current paper. This research was partly funded by the Key National Natural Science Foundation of China (No. 91328201) and the National Natural Science Foundation of China (No. 41372115). C. Gong dedicates this work to Zhaohong Cheng and Julia (Ruoyu) Gong, whose labour and arrival, respectively, greatly encourage his vigorous pursuit of deep-water sedimentology and stratigraphy. References Anell, I., Midtkandal, I., 2015. The quantifiable clinothem — types, shapes and geometric relationships in the Plio-Pleistocene Giant Foresets Formation, Taranaki Basin, New Zealand. Basin Res. 1–21. 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