Sedimentary differences between different segments of the continental slope-parallel Central Canyon in the Qiongdongnan Basin on the northern margin of the South China Sea

Sedimentary differences between different segments of the continental slope-parallel Central Canyon in the Qiongdongnan Basin on the northern margin of the South China Sea

Accepted Manuscript Sedimentary differences between different segments of the continental slope-parallel Central Canyon in the Qiongdongnan Basin on t...

16MB Sizes 0 Downloads 28 Views

Accepted Manuscript Sedimentary differences between different segments of the continental slope-parallel Central Canyon in the Qiongdongnan Basin on the northern margin of the South China Sea Chao Li, Ming Ma, Chengfu Lv, Gongcheng Zhang, Guojun Chen, Yingkai Yan, Guangxu Bi PII:

S0264-8172(17)30299-4

DOI:

10.1016/j.marpetgeo.2017.08.009

Reference:

JMPG 3026

To appear in:

Marine and Petroleum Geology

Received Date: 11 December 2016 Revised Date:

27 July 2017

Accepted Date: 8 August 2017

Please cite this article as: Li, C., Ma, M., Lv, C., Zhang, G., Chen, G., Yan, Y., Bi, G., Sedimentary differences between different segments of the continental slope-parallel Central Canyon in the Qiongdongnan Basin on the northern margin of the South China Sea, Marine and Petroleum Geology (2017), doi: 10.1016/j.marpetgeo.2017.08.009. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

ACCEPTED MANUSCRIPT 1

Sedimentary differences between different segments of the continental slope-parallel

2

Central Canyon in the Qiongdongnan Basin on the northern margin of the South

3

China Sea

4

Chao Li a, Ming Ma

5

Yan b, Guangxu Bi b

6

a Key Laboratory of Petroleum Resources Research, Chinese Academy of Sciences,

7

Lanzhou 730000, China

8

b University of Chinese Academy of Sciences, Beijing 100049, China

9

c Research Institute of China National Offshore Oil Corporation, Beijing 100028,

a, ∗

SC

RI PT

, Chengfu Lv a, Gongcheng Zhang c, Guojun Chen a, Yingkai

China

11

Abstract: Submarine canyons have been the subject of intense studies in recent years

12

because of their academic significance to studies of climate signals, eustasy and

13

tectonic movement of the neighbouring area and their economic significance for

14

hydrocarbon exploration in deep-water areas. The Central Canyon in the

15

Qiongdongnan Basin runs parallel to the continental slope, and has a length, width

16

and depth of 520 km, 2-15km and 270-800 m. Using seismic and well log data, we

17

analyses the sedimentary differences and controlling factors of the sediments in the

18

different segments of the Central Canyon. The sediments within the Central Canyon

19

can be subdivided into five phases of the secondary canyon filling. The most typical

20

features of each phase of the secondary canyon are high- and low-density turbidity

21

currents developed in the phase 1-2 of the secondary canyon, the muddy debris flows,

22

turbidity currents and mass transport deposits in the phase 3, the high-density

23

turbidity currents in the phase 4, the hemi-pelagic mudstone and mass transport

AC C

EP

TE D

M AN U

10



Corresponding author at: Postal address: No.382 West Donggang Road, Chengguan District, Lanzhou, 730000, PR China. E-mail address: [email protected] (M. Ma).

1

ACCEPTED MANUSCRIPT deposits in the phase 5. There are four depositional models corresponding to the head

25

area, upstream segment, middle reaches and downstream segment of the Central

26

Canyon were established. It is characterized by muddy matrix-supported

27

conglomerates and thickly massive sandstones with the feature of upward fining and

28

thinning deposited in the head area, the thickly high net to gross sandstone infilled in

29

the upstream segment, the thinly interbedded sandstones and mudstones and muddy

30

mass transport deposits developed in the middle reaches, and the extensive

31

hemi-pelagic mudstone infilled in the downstream segment. The transformation of the

32

debris flows into turbidity currents and high-density turbidity currents into

33

low-density turbidity in the head and upstream segment, supersaturated filling in the

34

upstream segment, extensive development of mass transport deposits in the middle

35

reaches, under-compensation filling and widely development of canyon wall collapse

36

in the downstream segment are the main reasons contributing to the sedimentary

37

differences between different segments of the Central Canyon.

38

Keywords: Central Canyon; Sedimentary differences; Gravity flows transformation;

39

Qiongdongnan Basin

40

1. Introduction

EP

TE D

M AN U

SC

RI PT

24

Deep-water canyons are primary conduit through which gravity flows transport

42

shelf and upper slope sediments into deep-sea plains (Babonneau et al., 2013; Bayliss

43

and Pickering, 2015; Covault and Graham, 2010; Janocko et al., 2013; Lastras et al.,

44

2011; Macauley and Hubbard, 2013; Qin et al., 2016; Reimchen et al., 2016). Gravity

45

flow deposits in the deep-water canyons are usually composed of coarse-grained

46

sediments, including gravelly sandstones, massive or graded sandstones, and

47

relatively fine-grained sediments, including siltstones, silty mudstones and mudstones

48

(Bayliss and Pickering, 2015; Corella et al., 2016; Flint et al., 2011; Macauley and

AC C

41

2

ACCEPTED MANUSCRIPT Hubbard, 2013; McHargue et al., 2011; Nielsen et al., 2015; Talling, 2014; Umar et

50

al., 2011; Zhou et al., 2015). These sediments can not only accumulate large amounts

51

of oil and natural gas resources, but also archive enormous amounts of regional

52

structural evolution, environmental and climatic change and sea-level changes

53

information (Flecker et al., 2015; Hale et al., 2014; Samaras and Koutitas, 2014;

54

Talling, 2014; Umar et al., 2011; Vesely et al., 2015; Yoshikawa and Nemoto, 2010;

55

Zhang et al., 2015).

RI PT

49

Submarine canyons generally run perpendicular to the slope break and are

57

usually sourced by a large river or delta on the continental shelf. Compared with

58

submarine canyons developed in other basins worldwide, the Central Canyon in the

59

Qiongdongnan Basin runs parallel to the continental slope, and has a length, width

60

and depth of 520 km, 2-15km and 270-800 m, respectively (Fig. 1). The genetic

61

mechanism for the continental slope-parallel particularity is that the earlier

62

provenance of the Central Canyon was eastern Vietnam rather than Hainan Uplift, and

63

the sediments crossed the Yinggehai Basin before entering the Central Canyon in the

64

Qiongdongnan Basin (Li et al., 2017). The distribution of the Yinggehai Basin and its

65

continental slope are nearly north-south direction, while the Qiongdongnan Basin and

66

its continental slope are west-east direction (Fig. 1). The sediments transport conduit

67

in the western margin of the Yinggehai Basin is perpendicular to the slope break, but

68

under the restriction of west-east negative relief, after gravity flows enter into the

69

Qiongdongnan Basin, it can only transport along west-east direction and forming the

70

continental slope-parallel Central Canyon. The sediments in the Central Canyon

71

contain hundreds of billions of cubic metres of natural gas (Huang et al., 2016; Wang

72

et al., 2015b; Xie, 2014), record the tectonic evolution of Tibetan Plateau uplift, South

73

China Sea extension, Red River Fault strike-slip movement and sea-level changes of

AC C

EP

TE D

M AN U

SC

56

3

ACCEPTED MANUSCRIPT the northern part of the South China Sea, and archive information on regional

75

environmental and climatic changes of eastern Vietnam and Hainan Island during the

76

late Miocene and Pliocene (Gong et al., 2011; Li et al., 2017; Ma et al., 2017; Su et al.,

77

2014; Yuan et al., 2009a; Zhao et al., 2015a). Previous studies have documented the

78

Central Canyon in terms of its sequence stratigraphy architecture, seismic and

79

sedimentary facies, depositional processes and infilling models (Gong et al., 2011; Li

80

et al., 2013; Su et al., 2014; Yuan et al., 2009a). Based on well 3 (see Fig. 1 for well

81

location) and seismic facies analysis, Yuan et al. (2009a) built a Central Canyon-fill

82

model, which is consisted of basal lag slumps or debris flows deposit, stacked high

83

net to gross sand-rich channel fill and low net to gross mud-rich channel complex.

84

Based on the seismic data analysis, Gong et al. (2011) and Li et al. (2013) identified

85

the seismic facies infilled in the Central Canyon, and interpret it into deep-water

86

sedimentary processes. The results indicate that there are four sedimentary processes

87

developed in the Central Canyon, including turbidity currents, debris flows, slumps

88

and hemi-pelagic deposits. Finally, a model contain four developmental stages of the

89

Central Canyon were created (Gong et al., 2011). However, under the control and

90

influence of paleogeomorphy, rate of source supply, transformation of the gravity

91

flows process, the relative sea-level changes and geometrical morphology (i.e. the

92

length, width, depth, curvature and morphology of the canyon), the sediments in

93

different sections of the Central Canyon have different features. Therefore, a single

94

depositional model cannot account for the complex filling characteristics of the

95

Central Canyon. Su et al. (2014) also noticed this problem, and the sedimentary

96

characteristics of different segments of the Central Canyon were analyzed, three

97

possible depositional models corresponding to the head area, western and eastern

98

segment of the Central Canyon were created. However, there is a lack of comparative

AC C

EP

TE D

M AN U

SC

RI PT

74

4

ACCEPTED MANUSCRIPT analysis of the sedimentary differences between different segments of the Central

100

Canyon, and the main factors controlling the sedimentary differences between

101

different segments of the Central Canyon also have not been clarified. In fact, the

102

sediments in the Central Canyon were consists of multi-phases of the secondary

103

canyon fill (Li et al., 2017), and the sedimentary characteristics of the sediments in

104

different segments of each phase of the secondary canyon are different, this results in

105

significant sedimentary variations in the different segments of the Central Canyon.

106

Then, what reasons and factors result and control the sedimentary differences between

107

different segments of the Central Canyon?

SC

RI PT

99

Using seismic and well data, the current study identified the developmental

109

phases of the Central Canyon and analyses the sedimentary characteristics of each

110

phase of the secondary canyon, through summarizes the sedimentary characteristics of

111

each phase of the secondary canyon in different segments of the Central Canyon, the

112

possible depositional model consists of secondary canyons for different segments of

113

the Central Canyon were established. And the sedimentary characteristics of the

114

different segments of the Central Canyon were comparative analysed, and the main

115

factors controlling the sedimentary differences of the Central Canyon were concluded.

116

Our results indicate that the transformation of the gravity flow process in the head and

117

upstream segment, supersaturated filling in the upstream segment, extensive

118

development of mass transport deposits in the middle reaches, under-compensation

119

filling and widely development of canyon wall collapse in the downstream segment

120

are the main reasons for the sedimentary differences between different segments of

121

the Central Canyon.

122

2. Geological background

123

AC C

EP

TE D

M AN U

108

The Qiongdongnan Basin is located on the northern continental shelf of the

5

ACCEPTED MANUSCRIPT South China Sea between 108°52'E-113°47'E and 16°47'N-19°00'N, has an area of

125

82,900 km2 (Fig. 1). It is one of the Cenozoic gas-bearing marine basin in China

126

(Huang et al., 2016; Hui et al., 2016; Su et al., 2012; Wang et al., 2015b; Xie, 2014;

127

Xie et al., 2008; Yu et al., 2009). The basin is bounded by the Yinggehai basin to the

128

west and the Pearl River Mouth Basin to the east and neighbours Hainan Island to the

129

north and the Xisha Uplift to the south (Ma et al., 2017; Zhu et al., 2009).

RI PT

124

The Qiongdongnan Basin formed in response to the rifting associated with the

131

opening of the South China Sea. The structural evolution of the basin can be divided

132

into two stages: the rift stage during Eocene and Oligocene and the post-rift thermal

133

subsidence stage during Neogene and Quaternary (Fig. 2) (Franke et al., 2014; Hu et

134

al., 2013; Morley, 2016). Multiple episodes of rifting occurred during the early stage.

135

The first episode of rifting occurred during the late Cretaceous to early Eocene. The

136

second episode of rifting occurred during the Eocene to early Oligocene. This phase

137

can be divided into two stages: rapid subsidence occurred during the middle to late

138

Eocene and stable subsidence occurred during the late Eocene to the early Oligocene.

139

The third episode of rifting occurred in the late Oligocene (Franke et al., 2014; Hu et

140

al., 2013; Morley, 2016).

EP

TE D

M AN U

SC

130

The Qiongdongnan Basin is developed on Mesozoic basement and contains a

142

thickness of 6000-12,000 m Tertiary to Quaternary sediments (Fig. 2) (Huang et al.,

143

2016). Rifting commenced in the Eocene and finished around the late Oligocene,

144

leaving a series of sags that are downthrown to the south and filled with lacustrine

145

sediments. The Yacheng Formation was deposited during the early Oligocene and

146

received mostly neritic and coastal plain coal-bearing sediments. Immediately above

147

the Yacheng Formation are the littoral to neritic Lingshui Formation. Following the

148

rifting stage, the Qiondongnan Basin experienced post-rift thermal subsidence until

AC C

141

6

ACCEPTED MANUSCRIPT present and was filled with a thick sequence of marine sediments that are dominated

150

by mudstones, with occasional turbidite channel and submarine fan sandstone bodies

151

in the Miocene to Pliocene Sanya, Meishan, Huangliu and Yinggehai Formations (Fig.

152

2) (Cao et al., 2015; Gong et al., 2014; Wang et al., 2013; Wang et al., 2015a; Yuan et

153

al., 2009b; Yubo et al., 2011; Zhao et al., 2015b). It is noteworthy that the Central

154

Canyon in the Qiongdongnan Basin, was developed during the late Miocene and

155

Pliocene.

156

3. Data and methodology

SC

RI PT

149

The seismic, calibrated by well logs data utilized in this study were provided by

158

the China National Offshore Oil Corporation (CNOOC). The density of the 2D

159

seismic lines covered on the Central Canyon is approximately 2×2 km. The original

160

seismic collecting data were processed by CNOOC, and uploaded to the Geoframe

161

workstation and interpreted with IESX modules. A whole suite of well logs containing

162

gamma, sonic, density and resistivity data were collected from five deep-water wells

163

(see Fig. 1 for well names and locations). The sonic and density logs were calibrated

164

so that synthetic seismic traces could be derived and used for seismic-well tie points.

165

Based on the integrated interpretation of the well and seismic data, the ages of

166

sequence surfaces and the lithology and geological significance of key seismic

167

reflectors were determined, and seismic facies were tied to sedimentary processes and

168

facies.

TE D

EP

AC C

169

M AN U

157

The top and bottom boundaries of the each phase of the secondary canyons in the

170

Central Canyon are defined in terms of strata termination relationships such as on-lap

171

and truncation, and canyon-wall seismic reflector, dipping angel differences of

172

formation in each phase of secondary canyons. The more detail marks and procedure

173

of the division of the Central Canyon into phases please see the article written by (Li

7

ACCEPTED MANUSCRIPT et al., 2017). Based on the closure interpretation of secondary canyon boundaries in

175

the seismic profiles, the corresponding demarcation points of the gamma logs are

176

calibrated for top and bottom boundaries of the each secondary canyon in the

177

well-cross seismic profiles. Then, the demarcation points of the gamma logs are used

178

to complete the division of the secondary canyon boundaries in the well and united

179

wells geological section. Based on the amplitude, continuity, internal configuration

180

and external geometry of seismic reflectors, the seismic facies were identified and

181

linked to different depositional processes and facies based on information from the

182

core, drilling and observations from previous seismic facies analysis of Central

183

Canyon fills.

184

4. Results and discussion

185

4.1. The division of the Central Canyon into phases

M AN U

SC

RI PT

174

It is critical to subdivide the top and bottom boundaries and analyze sedimentary

187

characteristics of each secondary canyon for analyzing the sedimentary differences

188

between different segments of the Central Canyon. There are five phases of secondary

189

canyon developed in the Central Canyon. The detail marks, procedure and result of

190

the division of the Central Canyon into phases please see the article written by (Li et

191

al., 2017).

192

4.2. Primary lithofacies of the sediments in the Central Canyon

193

4.2.1 Matrix-supported conglomerates

EP

AC C

194

TE D

186

The matrix-supported conglomerate consists of two main groups: (1) the

195

conglomerates with sandy matrix were found in the upper part of the head area of the

196

Central Canyon. Conglomeratic units exhibit bed thickness on the scale of 10 cm in

197

axial areas, consist of angular to sub-angular, poorly sorted and inversely graded

198

pebbles (2-4 mm). Its formation could be related to levee collapse because

8

ACCEPTED MANUSCRIPT thin-bedded turbidites are incorporated into the sandy matrix (Fig. 3A). (2) The

200

conglomerates with a muddy matrix are found in the basal part of the head area of the

201

Central Canyon fills, just above an erosional surface cutting into the underlying

202

hemi-pelagic mudstones (Fig. 3B). The muddy matrix conglomerates are interpreted

203

to be the product of cohesive debris flow that results mostly from the incorporation of

204

hemi-pelagic mudstones eroded during transport.

205

4.2.2 Medium- to thick-bedded, fine-grained sandstone

RI PT

199

The axis of the Central Canyon is typically filled by light grey, massive,

207

medium- to thick-bedded, fine-grained sandstones deposited from turbidity currents.

208

Very few sedimentary structures are preserved (Fig. 3C) except for graded bedding

209

(Fig. 3D), which indicates turbulent flow. These sandstones represent Bouma Ta-b

210

divisions. Graded Ta and paralleled Tb units are the most common and thickest

211

Bouma divisions in the core. They are interpreted to reflect the fill of mixed

212

erosive-depositional to depositional channels (Olariu et al., 2011).

213

4.2.3 Thin-bedded, fine-grained sandstone interbedded with siltstone

M AN U

Thin-bedded,

TE D

214

SC

206

planar

stratified,

fine-grained

sandstone

deposited

from

low-density turbidity currents are separated by centimeter-scale siltstone and

216

mudstone (Fig. 3E). They are interpreted to represent Bouma Tb, c, and d divisions.

217

Individual sandstone beds have sharp bases. Ripple cross-lamination and climbing

218

ripples are common in this sandstone (Fig. 3F).

219

4.2.4 Mudstone

AC C

EP

215

220

Thick-bedded mudstone is more common in the upper part of the Central Canyon

221

fills. The grey-black thick-bedded mudstone developed mainly during the latest

222

Central Canyon filling. This facies is interpreted either as hemi-pelagic deposits or

223

shale drapes deposited during the waning stage of the Central Canyon filling (Fig.

9

ACCEPTED MANUSCRIPT 224

3F).

225

4.3. Seismic facies of the sediments in the Central Canyon Based on the amplitude, continuity, internal configuration and external geometry

227

of seismic reflections, ten types of seismic facies of the sediments in the Central

228

Canyon were identified (Fig. 4) that are linked to different depositional processes and

229

lithological facies determined from cores, drilling and observations from previous

230

seismic facies analysis of submarine canyon fills (Schwenk et al., 2005; Mayall et al.,

231

2006; Cross et al., 2009; Gong et al., 2011; Su et al., 2014). Finally, four major

232

sedimentary processes and facies are interpreted: (1) turbidity currents, (2) debris

233

flows, (3) slumps and (4) hemi-pelagic deposits.

234

4.3.1 Turbidity currents

M AN U

SC

RI PT

226

Five seismic facies related to turbidity currents are identified from the seismic

236

profile: seismic facies 1 is characterised by onlapping filling with high-amplitude,

237

low-frequency and high-continuity features (Fig. 4A) (Gong et al., 2011; Su et al.,

238

2014). The information from drilling and well logs indicates that the lithofacies of this

239

seismic facies are blocky sandstones that fine upward and thin (Fig. 6B). Olariu et al.

240

(2011) documented the same lithofacies with upward fining and thinning present in

241

outcrops, which represent the Bouma Ta division of turbidity currents. Seismic facies

242

2 is characterised by onlapping filling with high-amplitude, high-frequency and

243

high-continuity features (Fig. 4B) (Su et al., 2014). The information from drilling and

244

well logs indicates that the lithofacies of this facies is interbedded with sandstone and

245

mudstone (Fig. 6C). Olariu et al. (2011) documented the same lithofacies present in

246

outcrops from Pennsylvanian deepwater deposits at Big Rock Quarry, Arkansas,

247

which can be interpreted as the Bouma Tb-d division of the low-density turbidity

248

currents. Seismic facies 3 consists of transparent, chaotic reflector packages with high

AC C

EP

TE D

235

10

ACCEPTED MANUSCRIPT amplitude and good continuity that appear only on the top and bottom boundaries (Fig.

250

4C); these represent thick, well-sorted sandstone deposits. Seismic facies 4 is

251

characterized by a parallel, sheet-like configuration with high amplitude and good

252

continuity and is surrounded by seismic facies with chaotic reflectors, weak amplitude

253

and poor continuity (Fig. 4D). This facies can be considered to be turbidites that were

254

eroded by later gravity flows. Seismic facies 5 is characterized by sub-parallel,

255

high-amplitude, and moderately to highly continuous reflectors with gull-wing-shaped

256

elements, where the dip angle of reflectors steepens upwards and decreases laterally

257

away from the canyon (Fig. 4E). This can be interpreted as the levee formed by the

258

overspill of the turbidity currents.

259

4.3.2 Debris flows

M AN U

SC

RI PT

249

The seismic facies of transparent, chaotic on-lapping fill with a weak amplitude

261

and low continuity is considered to be debris deposits (Fig. 4F) (Su et al., 2014). The

262

chaotic reflectors and weak amplitude are related to the poor sorting of the debris.

263

Another form of debris flow is mass transport deposits (MTDs). Seismic facies of

264

parallel, chaotic progradation with weak-amplitude reflectors is considered to be

265

MTDs (Fig. 4G) (Gong et al., 2011; Su et al., 2014). The drilling from well 5 indicates

266

that the lithofacies of this process is pure mudstone (Fig. 6C).

267

4.3.3 Slumps

EP

AC C

268

TE D

260

Two seismic facies are considered to be slumps: (1) the chaotic wedge-like

269

reflector packages with weak amplitude, which reflects small-scale slumping of the

270

canyon wall, where the boundary of the canyon has disappeared (Fig. 4H) (Su et al.,

271

2014). (2) The chaotic, sheet-like, low- to medium-amplitude reflectors; a small-scale

272

fault has developed at the bottom of this facies (Fig. 4I).

273

4.3.4 Hemi-pelagic deposits

11

ACCEPTED MANUSCRIPT Seismic facies of parallel, sheet-like configuration with middle-amplitude,

275

high-continuity reflectors is considered to be hemi-pelagic sediments (Fig. 4J) (Gong

276

et al., 2011; Su et al., 2014).

277

4.4. Sedimentary characteristics of the sediments in the secondary canyons

278

4.4.1. Phase 1 of the secondary canyon

RI PT

274

There was only well 5 (located at the middle reaches of the Central Canyon)

280

drilled into the sediments of the phase 1 of the secondary canyon, which reveals that

281

the lithofacies are thinly interbedded fine sandstones and mudstones. Olariu et al.

282

(2011) documented the same lithofacies present in outcrops from Pennsylvanian

283

deep-water deposits at Big Rock Quarry, Arkansas, which can be interpreted as the

284

Bouma Tb-d division of the low-density turbidity currents. The well-seismic

285

correlation analysis shows that the lithofacies are characterized by bidirectional

286

on-lapping fill with high-amplitude, high-continuity and high-frequency on the well

287

5-cross seismic profile (Fig. 5C1, Fig. 6C), and this seismic facies was developed in

288

all seismic profiles that cross the Central Canyon in the middle reaches. Therefore, it

289

can be concluded that all sediments in the middle reaches of the phase 1 of the

290

secondary canyon are composed of Tb-d division of the low-density turbidity currents,

291

which are thinly interbedded fine sandstones and mudstones.

M AN U

TE D

EP

AC C

292

SC

279

The seismic reflection of the sediments in the head and upstream segment of the

293

phase 1 of the secondary canyon is characterized by bidirectional on-lapping fill with

294

high-amplitude and low-frequency (Fig. 5A1, B1). Compared the seismic facies of the

295

sediments in the head and upstream segment with middle reaches of the phase 1 of the

296

secondary canyon (Fig. 5C1), the differences are mainly seismic frequency. Generally,

297

the seismic frequency is proportional to the number of the wave impedance interface.

298

The high-frequency seismic reflection of the sediments in the middle reaches of the

12

ACCEPTED MANUSCRIPT phase 1 of the secondary canyon is thinly interbedded fine sandstones and mudstones

300

in well 5 (Fig. 6), it is believed that the high-amplitude and low-frequency seismic

301

reflection of the sediments in the head and upstream segment of the phase 1 of the

302

secondary canyon is relative thickly interbeded fine sandstones and mudstones.

303

Mayall et al. (2006) documents the same seismic facies and interpreted as the thickly

304

interbedded fine sandstone and mudstone sediments deposited by Ta division of the

305

turbidites.

RI PT

299

The sediments in the downstream segment of the phase 1 of the secondary canyon

307

are seismically characterized by bidirectional on-lapping fill with low-amplitude and

308

medium frequency (Fig. 5D1). Compared the seismic facies of the sediments in the

309

downstream segment with middle reaches of the phase 1 of the secondary canon, the

310

differences are mainly seismic amplitude, which is proportional to the difference

311

between the wave impedance above and below the interface. The main factor

312

determining the value of the wave impedance of sediments is the density of detrital

313

grains, which can be used to predict the lithology of the sediments. The seismic

314

reflection of the conglomerates and sandstones and the mudstone with strong

315

calcareous cement are characterized by high-amplitude. In contrast, the seismic

316

reflection of relatively fine-grained sediments, including siltstones, silty mudstones

317

and mudstones are characterized by low-or medium amplitude. Therefore, we

318

considered that the sediments in the downstream segment of the phase 1 of the

319

secondary canyon are mainly mud-rich deposits.

AC C

EP

TE D

M AN U

SC

306

320

In summary, the head and upstream segment of the phase 1 of the secondary

321

canyon developed mainly thickly interbedded fine sandstones and mudstones, which

322

deposited by high-density turbidites. And the middle reaches of the phase 1 of the

323

secondary canyon are mainly composed of thinly interbedded fine sandstones and

13

ACCEPTED MANUSCRIPT 324

mudstones deposited by low-density trubidites, while the downstream segment

325

gradually evolved into hemi-pelagic mud-rich sediments (Fig. 6).

326

4.4.2. Phase 2 of the secondary canyon Similar to the phase 1 of the secondary canyon, there was only well 5 drilled into

328

the sediments of the phase 2 of the secondary canyon, and reveals that the lithofacies

329

of the sediments in the middle reaches are thinly interbedded fine sandstones and

330

mudstones (Fig. 6C). This lithofacies on the seismic profiles are characterized by

331

bidirectional on-lapping fill with high-amplitude, high-continuity and high-frequency

332

(Fig. 5C2), it is believed that the sediments are the same as those in the phase 1 of the

333

secondary canyon, which is mainly composed of the Tb-d divisions of low-density

334

turbidity currents.

M AN U

SC

RI PT

327

The sediments in the upstream segment of the phase 2 of the secondary canyon

336

are seismically characterized by transparent, chaotic reflector packages with

337

high-amplitude and high-continuity that appear only on the top and bottom boundaries

338

(Fig. 5B2). This seismic facies are dominated by massive sandstone with Ta and Tb

339

turbidites (Mayall et al., 2006). In the subsurface, the biggest pitfall with this

340

facies can be indistinguishing it seismically from the slump/debris flows facies.

341

When the net to gross is high, there may be no internal reflectors to resolve the

342

individual channels, and only a top and base reflector may be present with the

343

internal seismic character being opaque or weak and discontinuous giving it a very

344

similar seismic appearance to the slump/debris flow facies (Mayall et al., 2006).

AC C

EP

TE D

335

345

The seismic reflection of the sediments in the downstream segment of the

346

phase 2 of the secondary canyon are characterized by bidirectional on-lapping fill

347

with medium amplitude and frequency (Fig. 5D2), which is considered to be

348

mud-rich sediments.

14

ACCEPTED MANUSCRIPT In summary, the upstream segment of the phase 2 of the secondary canyon

350

developed mainly thick-bedded fine sandstones. And the middle reaches of the phase

351

2 of the secondary canyon are mainly composed of thinly interbedded fine sandstones

352

and mudstones, while the downstream segment gradually evolved into hemi-pelagic

353

mud-rich sediments (Fig. 6).

354

4.4.3. Phase 3 of the secondary canyon

RI PT

349

At present, there were wells 2-5 (See Fig. 1 for well locations) drilled into the

356

sediments of the phase 3 of the secondary canyon. And well 2 and well 3 reveals that

357

the lithofacies of the sediments in the head area of the phase 3 of the secondary

358

canyon is muddy matrix-supported conglomerate facies (Fig. 6). The muddy matrix

359

conglomerates are interpreted to be the product of cohesive muddy debris flows.

360

The lithofacies on the well 2- and well 3-cross seismic profiles are characterized

361

by chaotic fill with low-amplitude and continuity (Fig. 5A3), which is consistent

362

with the seismic reflection characteristics of the debris flows summarized by

363

(Mayall et al., 2006). This seismic facies is found in the basal part of the Central

364

Canyon fills, just above an erosional surface cutting into the underlying

365

hemi-pelagic mudstones (Fig. 5A3). The chaotic reflectors and low-amplitude are

366

related to the poor sorting of the debris deposits.

M AN U

TE D

EP

AC C

367

SC

355

Well 4 reveals that the lithofacies of the sediments in the upstream segment of

368

the phase 3 of the secondary canyon evolved into thick-bedded fine sandstones in

369

the lower part and siltstone deposits in the upper part. The set of the sediments on

370

the well 4-cross seismic profile is characterized by bidirectional on-lapping fill

371

with high-amplitude and continuity (Fig. 5B3), and it is interpreted as the turbidity

372

current deposits of deep-water canyon and over-bank deposits.

373

Well 5 reveals that the lithofacies of the lower sediments in the middle

15

ACCEPTED MANUSCRIPT reaches of the phase 3 of the secondary canyon evolved into thin-bedded fine

375

sandstone, while the upper part is mainly hemi-pelagic mudstone deposits (Fig. 6).

376

There was no well drilled into the downstream segment of the phase 3 of the

377

secondary canyon. Its sediments on the seismic profile are characterized by

378

parallel sheet-like fill with medium-amplitude, high-continuous and frequency (Fig.

379

5D3), which is interpreted as hemi-pelagic mud-rich depositions.

380

4.4.4. Phase 4 of the secondary canyon

RI PT

374

Well 2 and Well 3 shows that the lithofacies of the sediments in the head area

382

of the phase 4 of the secondary canyon is thick-bedded massive finestone with the

383

feature of upward fining and thinning (Fig. 6B). The lithofacies on the well 2- and

384

well 3-cross seismic profiles are characterized by bidirectional parallel on-lapping

385

fill with high-amplitude, high-continuity and low-frequency (Fig. 5A4). (Olariu et

386

al., 2011) documented the same lithofacies with upward fining and thinning

387

present in outcrops, which represents the Bouma Ta division of turbidity currents.

TE D

M AN U

SC

381

Well 4 and Well 5 reveals that the sediments in the upstream segment and

389

middle reaches are mainly hemi-pelagic mudstone deposits, and there is no

390

sandstone deposits were found (Fig. 6A). The seismic reflection of the sediments in

391

the upstream segment, middle reaches and downstream segment of the phase 4 of

392

the secondary canyon is characterized by sub-parallel sheet-like fill with low to

393

medium amplitude and continuity (Fig. 5B4, C4, D4), which represents

394

hemi-pelagic mudstone sediments.

395

4.4.5. Phase 5 of the secondary canyon

AC C

EP

388

396

Well 2 and well 3 reveals that the lithofacies of the sediments in the head area

397

of the phase 5 of the secondary canyon is thick-bedded massive siltstone (Fig. 6B).

398

The seismic reflection of the sediments on the well 3-cross seismic profile is

16

ACCEPTED MANUSCRIPT 399

characterized by sub-parallel sheet-like fill with medium amplitude and continuity

400

(Fig. 5A5). This seismic facieses extensively developed in the head area of the

401

phase 5 of the secondary canyon, and interpreted as turbidity current deposits. Well 4 and Well 5 reveals that the sediments in the upstream segment and

403

middle reaches are mainly hemi-pelagic mudstone depositions (Fig. 6A). The

404

seismic reflection of the sediments in the upstream and downstream segment of the

405

phase 5 of the secondary canyon is characterized by sub-parallel sheet-like fill

406

with medium amplitude and continuity (Fig. 5B5, D5), which represents

407

hemi-pelagic mudstone sediments.

SC

RI PT

402

The seismic reflection of the sediments in the middle reaches of the phase 5

409

of the secondary canyon is characterized by parallel, chaotic pro-gradation with

410

weak-amplitude reflectors (Fig. 5C5), it is interpreted as mass transport deposits

411

(MTDs). The drilling from well 5 indicates that the lithofacies of the MTDs is pure

412

mudstone (Fig. 6C).

413

4.5. Sedimentary characteristics of the sediments in the different segments of the

414

Central Canyon

TE D

M AN U

408

The depositional characteristics of different sections of the secondary canyons

416

are quite different, resulting in greater sedimentary differences of the sediments in the

417

different segments of the Central Canyon. Based on secondary canyon fills as unit,

418

this paper respectively established the depositional models of the head area, upstream

419

segment, middle reaches and downstream segment of the Central Canyon (Fig. 7), and

420

the sedimentary differences were analyzed.

421

4.5.1. The head area of the Central Canyon

AC C

EP

415

422

The head area of the Central Canyon is consists of the phase 3-4 of the secondary

423

canyons and with a total depth of approximately 380 meters. The phase 3 of the

17

ACCEPTED MANUSCRIPT secondary canyon as the lower part of the Central Canyon in the head area, infilled by

425

muddy debris deposits (Fig. 7A). The drillings indicates that the lithofacies of the

426

phase 3 secondary canyon is muddy matrix-supported conglomerates. The phase 4 of

427

the secondary canyon constituted the upper part of the Central Canyon in the head

428

area, infilled by thickly massive sandstones with the feature of upward fining and

429

thinning, which were deposited by turbidity currents (Fig. 6B, 7A). Stated thus, the

430

depositional model of the head area of the Central Canyon is revealed by figure 6A.

431

4.5.2. The upstream segment of the Central Canyon

SC

RI PT

424

The depth of the Central Canyon in the upstream segment is increasing to

433

approximately 560 meters, and the whole of the five phases of the secondary canyons

434

were developed. The sediments filled in the phase 1 and 3 of the secondary canyons

435

with the seismic reflector of high-amplitude, high-frequency and continuity

436

on-lapping fill (Fig. 7B), it was interpreted as the turbidity. The thickly well-sorted

437

sandstone deposited by the turbidity currents filled in the phase 2 of the secondary

438

canyon, which displayed on the seismic profile with the feature of transparent

439

reflector internally and high amplitude that appear on the top and bottom boundaries

440

(Fig. 7B). The phase 4 and 5 secondary canyon infilled by the seismic facies of

441

sub-parallel, sheet-like configuration with low amplitude and continuity which occurs

442

frequently at the upper part of the Central Canyon infills is considered to be

443

hemi-pelagic sediments (Fig. 7B). Based on the analysis, the depositional model of

444

the Central Canyon in the upstream segment is revealed by figure 6B.

445

4.5.3. The middle reaches of the Central Canyon

AC C

EP

TE D

M AN U

432

446

There are five phases of the secondary canyons developed between sequence

447

boundaries of T29-T30 in the middle reaches of the Central Canyon. The depth of the

448

Central Canyon in the middle reaches is approximately 700 m, and the thick-bedding

18

ACCEPTED MANUSCRIPT sediments deposited on the sequence surface of T29. The phase 1-2 of the secondary

450

canyon was infilled by the on-lapping filling with high-amplitude, high-frequency and

451

continuity seismic reflector features (Fig. 7C). It was interpreted as turbidity currents

452

deposits, and the drillings indicates that the lithofacies filled in the phase 1-2 of the

453

secondary canyon are interbedded sandstones and mudstones. The phase 3 and 5 of

454

the secondary canyon were infilled by the MTDs and the seismic reflector characters

455

of parallel pro-gradation with weak-amplitude, (Fig. 7C). The seismic reflector of the

456

parallel, sheet-like configuration with middle-amplitude and high-continuity is filling

457

in the phase 4 of the secondary canyon, which is considered to be hemi-pelagic

458

sediments (Fig. 7C). Based on the above analysis, the depositional model of the

459

Central Canyon in the middle reaches is revealed by figure 6C.

460

4.5.4. The downstream segment of the Central Canyon

M AN U

SC

RI PT

449

The most typical feature of the Central Canyon in the downstream segment is

462

insufficient compensation. The phase 1-2 of the secondary canyon was infilled by the

463

second seismic facies of the turbidity currents which indicates interbedded sandstones

464

and mudstones. The later fillings were consisted of the seismic facies of the parallel,

465

sheet-like configuration with medium amplitude and high-continuity which is

466

considered to be hemi-pelagic sediments (Fig. 7D). The both side of the canyon wall

467

collapsing at upper part in the downstream segment. The depositional model of the

468

Central Canyon in the downstream segment is revealed by figure 6D.

469

4.6. The factors contributing to the depositional variability of the Central Canyon

470

4.6.1. Transformation of the gravity flow process in the head and upstream segment

AC C

EP

TE D

461

471

The gravity flow processes in different sections of the each phase of the

472

secondary canyons were identified, and it was found that the different gravity flow

473

processes were developed in different sections of the each phase of the secondary

19

ACCEPTED MANUSCRIPT canyons. This indicates that there exists the phenomenon of gravity flows

475

transformation during sediments transported in the Central Canyon. There are two

476

kinds of gravity flows transformation phenomenon, including debris flows transform

477

into turbidity currents and high-density turbidity currents transform into low-density

478

turbidity. The different gravity flow processes developed in the different sections of

479

the each phase of the secondary canyons determines that the great sedimentary

480

differences of the sediments in the different segments of the Central Canyon.

RI PT

474

The transformation of the debris flows into turbidity currents was mainly

482

developed in the phase 3 of the secondary canyon. Seismic facies analysis shows that

483

the debris flows was developed in the head area of the phase 3 of the secondary

484

canyon, but with the increase of transport distance, the gravity flow process evolved

485

into turbidity currents in the upstream segment of the phase 3 of the secondary canyon

486

(Fig. 8). This process resulted in the thick-bedded muddy matrix-supported

487

conglomerate deposited in the head area of the phase 3 of the secondary canyon,

488

while the interbedded sandstones and mudstones deposited in the upstream segment

489

and middle reaches (Fig. 7). With transport distance increased further, the turbidity

490

currents eventually stopped and resulting in hemi-pelagic mudstone deposited in the

491

downstream segment of the phase 3 of the secondary canyon.

M AN U

TE D

EP

AC C

492

SC

481

The high-density turbidity currents transformed into low-density turbidity

493

currents determines the sedimentary characteristics of the phase 1-2 and 4 of the

494

secondary canyons. The higher net to gross sediments of the interbeded sandstone and

495

mudstone of the high-density turbidity currents were deposited in the upstream

496

segment of the phase 1 and 2 of the secondary canyon. With the transformation of the

497

high-density turbidity currents into low-density turbidity currents, the middle reaches

498

of the phase 1 and 2 of the secondary canyon are mainly filled with low net to gross

20

ACCEPTED MANUSCRIPT 499

interbeded sandstone and mudstone sediments. With the increase of the transport

500

distance, the mud-rich sediments with lower net to gross were developed in the

501

downstream segment. The higher net to gross sediments of the interbeded sandstone and mudstone of

503

the high-density turbidity currents were deposited in the head area of the phase 4 of

504

the secondary canyon. With the increase of transport distance, the sediments evolved

505

into low net to gross interbeded sandstones and mudstones deposited by low-density

506

turbidity currents in the upstream segment of the phase 4 of the secondary canyon. To

507

the middle reaches and downstream segment of the phase 4 of the secondary canyon,

508

the development of low-density turbidity currents gradually ceased and instead of the

509

hemi-pelagic mudstone (Fig. 7).

510

4.6.2. Supersaturated filling in the upstream segment

M AN U

SC

RI PT

502

At the upstream segment of the Central Canyon, it has the minimum depth and

512

width. In a limited accommodating space, with the sufficient sediments sources

513

supply from eastern Vietnam and Hainan Island (Li et al., 2017), the sediments fill of

514

the Central Canyon is supersaturated. Compared with the middle reaches and

515

downstream segment of the Central Canyon, the sediments in the phase 5 of the

516

secondary canyon are located on the top of the Central Canyon, rather than in the

517

interior of the Central Canyon. The sequence boundary of T29 is also much higher

518

than the top of the Central Canyon, rather than at the top in the middle reaches of the

519

Central Canyon (Fig. 7A).

520

4.6.3. Extensive development of MTDs in the middle reaches

AC C

EP

TE D

511

521

The biggest difference between the middle reaches and other areas of the Central

522

Canyon is extensive and multi-stage development of large-scale mud-rich MTDs (Fig.

523

7C). The dipping angle of the pro-grading package is approximately 75° in the

21

ACCEPTED MANUSCRIPT 524

seismic profile and shows a crescent-shaped compressional fold in planar view (Gong

525

et al., 2014; Li et al., 2015). It was sourced by Hainan Island and runs perpendicular

526

to the Central Canyon. It continued to develop after phase 5 of the secondary channel.

527

4.6.4. Under-compensation filling in the downstream segment At the end of the Central Canyon, its depth reaches the maximum. The sediments

529

supply is reduced due to long-distance transport, and the sediments transported by the

530

Central Canyon is about to unload into Shuangfeng Basin (Li et al., 2017). Then, the

531

Central Canyon is filled with starvation, and the thickness of the sediments filled in

532

the Central Canyon accounts for about sixty percent of the total depth (Fig. 7D). The

533

present depth of the seafloor in the Central Canyon is much deeper than that on both

534

sides of the Central Canyon. The seismic reflection of the sediments is characterized

535

by sheet-like fill with low-or medium amplitude, high-continuity and high-frequency

536

reflector, it represents hemi-pelagic mud-rich deposits.

537

4.6.5. Widely development of canyon wall collapse in the downstream segment

TE D

M AN U

SC

RI PT

528

The downstream segment of the Central Canyon has characteristics of

539

under-compensated filling, and the canyon wall is relatively steep, which creates

540

favorable conditions for the slumping action. Therefore, there is extensive

541

development of the hemi-pelagic muddy slumping in both sides of the Central Canyon.

542

On the seismic profiles, there are two seismic facies are considered to be slumps: (1)

543

the chaotic wedge-like reflector packages with low-amplitude, which reflects

544

small-scale slumping of the channel wall, where the boundary of the channel has

545

disappeared. The left side of this facies is hemi-pelagic deposits and consists of

546

sheet-like reflectors with high amplitudes. (2) The chaotic, sheet-like, low- to

547

medium-amplitude reflectors, a small-scale fault has developed at the bottom of this

548

facies (Fig. 7D). The extensive development of the slump deposits is the biggest

AC C

EP

538

22

ACCEPTED MANUSCRIPT difference between the downstream segment and other regions of the Central Canyon.

550

5. Conclusions

551

(1) The sediments within the Central Canyon can be subdivided into five phases of the

552

secondary canyon filling. The most typical features of each phase of the

553

secondary canyon are high-density turbidity currents and low-density turbidity

554

currents developed in the phase 1-2 of the secondary canyon, the muddy debris

555

flows, turbidity currents and mass transport deposits developed in the phase 3 of

556

the secondary canyon, the high-density turbidity currents developed in the phase

557

4 of the secondary canyon, and hemi-pelagic mudstone and mass transport

558

deposits developed in the phase 5 of the secondary canyon.

M AN U

SC

RI PT

549

(2) Based on secondary canyon fills as unit, there are four depositional models

560

corresponding to the head area, upstream segment, middle reaches and

561

downstream segment of the Central Canyon were established. The most typical

562

features of each model are muddy matrix-supported conglomerates and thickly

563

massive sandstones with the feature of upward fining and thinning deposited in

564

the head area, the thickly high net to gross sandstone infilled in the upstream

565

segment, the thinly interbedded sandstones and mudstones and mass transport

566

deposits developed in the middle reaches, and the extensive hemi-pelagic

EP

AC C

567

TE D

559

mudstone infilled in the downstream segment.

568

(3) The transformation of the debris flows into turbidity currents and high-density

569

turbidity currents into low-density turbidity in the head and upstream segment,

570

supersaturated filling in the upstream segment, extensive development of mass

571

transport deposits in the middle reaches, under-compensation filling and widely

572

development of canyon wall collapse in the downstream segment are the main

573

reasons contributing to the sedimentary differences between different segments

23

ACCEPTED MANUSCRIPT of the Central Canyon.

574 575

Acknowledgments This study was financially supported by the National Science and Technology

577

Major Project of the Ministry of Science and Technology of China (Grant

578

No.2016ZX05026-007-05). We are grateful to the CNOOC Research Centre for

579

providing the seismic and well data and permission to use and publish this proprietary

580

data.

581

References

582

Babonneau, N., Delacourt, C., Cancouët, R., Sisavath, E., Bachèlery, P., Mazuel, A.,

583

Jorry, S.J., Deschamps, A., Ammann, J., Villeneuve, N., 2013. Direct sediment

584

transfer from land to deep-sea: Insights into shallow multibeam bathymetry at La

585

Réunion Island. Marine Geology 346, 47-57.

M AN U

SC

RI PT

576

Bayliss, N., Pickering, K.T., 2015. Transition from deep-marine lower-slope erosional

587

channels to proximal basin-floor stacked channel–levée–overbank deposits, and

588

syn-sedimentary growth structures, Middle Eocene Banastón System, Ainsa

589

Basin, Spanish Pyrenees. Earth-Science Reviews 144, 23-46.

TE D

586

Cao, L.C., Jiang, T., Wang, Z.F., Zhang, Y.Z., Sun, H., 2015. Provenance of Upper

591

Miocene sediments in the Yinggehai and Qiongdongnan basins, northwestern

593

AC C

592

EP

590

South China Sea: Evidence from REE, heavy minerals and zircon U–Pb ages. Marine Geology 361, 136-146.

594

Corella, J.P., Loizeau, J.L., Kremer, K., Hilbe, M., Gerard, J., le Dantec, N., Stark, N.,

595

González-Quijano, M., Girardclos, S., 2016. The role of mass-transport deposits

596

and turbidites in shaping modern lacustrine deepwater channels. Marine and

597

Petroleum Geology 77, 515-525.

598

Covault, J.A., Graham, S.A., 2010. Submarine fans at all sea-level stands:

24

ACCEPTED MANUSCRIPT 599

Tectono-morphologic and climatic controls on terrigenous sediment delivery to

600

the deep sea. Geology 38, 939-942. Flecker, R., Krijgsman, W., Capella, W., de Castro Martíns, C., Dmitrieva, E., Mayser,

602

J.P., Marzocchi, A., Modestou, S., Ochoa, D., Simon, D., Tulbure, M., van den

603

Berg, B., van der Schee, M., de Lange, G., Ellam, R., Govers, R., Gutjahr, M.,

604

Hilgen, F., Kouwenhoven, T., Lofi, J., Meijer, P., Sierro, F.J., Bachiri, N.,

605

Barhoun, N., Alami, A.C., Chacon, B., Flores, J.A., Gregory, J., Howard, J., Lunt,

606

D., Ochoa, M., Pancost, R., Vincent, S., Yousfi, M.Z., 2015. Evolution of the

607

Late Miocene Mediterranean–Atlantic gateways and their impact on regional and

608

global environmental change. Earth-Science Reviews 150, 365-392.

M AN U

SC

RI PT

601

Flint, S.S., Hodgson, D.M., Sprague, A.R., Brunt, R.L., Van der Merwe, W.C.,

610

Figueiredo, J., Prélat, A., Box, D., Di Celma, C., Kavanagh, J.P., 2011.

611

Depositional architecture and sequence stratigraphy of the Karoo basin floor to

612

shelf edge succession, Laingsburg depocentre, South Africa. Marine and

613

Petroleum Geology 28, 658-674.

TE D

609

Franke, D., Savva, D., Pubellier, M., Steuer, S., Mouly, B., Auxietre, J.-L., Meresse, F.,

615

Chamot-Rooke, N., 2014. The final rifting evolution in the South China Sea.

616

Marine and Petroleum Geology 58, 704-720.

AC C

EP

614

617

Gong, C.L., Wang, Y.M., Hodgson, D.M., Zhu, W.L., Li, W.G., Xu, Q., Li, D., 2014.

618

Origin and anatomy of two different types of mass–transport complexes: A 3D

619 620

seismic case study from the northern South China Sea margin. Marine and Petroleum Geology 54, 198-215.

621

Gong, C.L., Wang, Y.M., Zhu, W.L., Li, W.G., Xu, Q., Zhang, J.M., 2011. The Central

622

Submarine Canyon in the Qiongdongnan Basin, northwestern South China Sea:

623

Architecture, sequence stratigraphy, and depositional processes. Marine and

25

ACCEPTED MANUSCRIPT 624

Petroleum Geology 28, 1690-1702.

625

Hale, R.P., Ogston, A.S., Walsh, J.P., Orpin, A.R., 2014. Sediment transport and event

626

deposition on the Waipaoa River Shelf, New Zealand. Continental Shelf

627

Research 86, 52-65.

629

Haq, B.U., Hardenbol, J., Vail, P.R., 1987. Chronology of fluctuating sea-levels since the Triassic. Science 235, 1156–1167.

RI PT

628

Hu, B., Wang, L.S., Yan, W.B., Liu, S.W., Cai, D.S., Zhang, G.C., Zhong, K., Pei, J.X.,

631

Sun, B., 2013. The tectonic evolution of the Qiongdongnan Basin in the northern

632

margin of the South China Sea. Journal of Asian Earth Sciences 77, 163-182.

633

Huang, B.J., Tian, H., Li, X.S., Wang, Z.F., Xiao, X.M., 2016. Geochemistry, origin

634

and accumulation of natural gases in the deepwater area of the Qiongdongnan

635

Basin, South China Sea. Marine and Petroleum Geology 72, 254-267.

M AN U

SC

630

Hui, G.G., Li, S.Z., Guo, L.L., Zhang, G.X., Gong, Y.H., Somerville, I.D., Zhang, Y.,

637

Zheng, Q.L., Zang, Y.B., 2016. Source and accumulation of gas hydrate in the

638

northern margin of the South China Sea. Marine and Petroleum Geology 69,

639

127-145.

TE D

636

Janocko, M., Nemec, W., Henriksen, S., Warchoł, M., 2013. The diversity of

641

deep-water sinuous channel belts and slope valley-fill complexes. Marine and

AC C

642

EP

640

Petroleum Geology 41, 7-34.

643

Lastras, G., Canals, M., Amblas, D., Lavoie, C., Church, I., De Mol, B., Duran, R.,

644

Calafat, A.M., Hughes-Clarke, J.E., Smith, C.J., Heussner, S., 2011.

645

Understanding sediment dynamics of two large submarine valleys from seafloor

646

data: Blanes and La Fonera canyons, northwestern Mediterranean Sea. Marine

647

Geology 280, 20-39.

648

Li, C., Lv, C.F., Chen, G.J., Zhang, G.C., Ma, M., Shen, H.L., Zhao, Z., Guo, S., 2017.

26

ACCEPTED MANUSCRIPT 649

Source and sink characteristics of the continental slope-parallel Central Canyon

650

in the Qiongdongnan Basin on the northern margin of the South China Sea.

651

Journal of Asian Earth Sciences 134, 1-12. Li, W., Alves, T.M., Wu, S.G., Völker, D., Zhao, F., Mi, L.J., Kopf, A., 2015.

653

Recurrent slope failure and submarine channel incision as key factors controlling

654

reservoir potential in the South China Sea (Qiongdongnan Basin, South Hainan

655

Island). Marine and Petroleum Geology 64, 17-30.

RI PT

652

Li, X.Q., Fairweather, L., Wu, S.G., Ren, J.Y., Zhang, H.J., Quan, X.Y, Jiang, T.,

657

Zhang, C., Su, M., He, Y.L., Wang, D.W., 2013. Morphology, sedimentary

658

features and evolution of a large palaeo submarine canyon in Qiongdongnan

659

basin, Northern South China Sea. Journal of Asian Earth Sciences 62, 685-696.

M AN U

SC

656

Ma, M., Li, C., Lv, C.F., Chen, G.J., Yang, F., Yan, Y.K., Yin, N., Zhang, G.C., 2017.

661

Geochemistry and provenance of a multiple-stage fan in the Upper Miocene to

662

the Pliocene in the Yinggehai and Qiongdongnan basins, offshore South China

663

Sea. Marine and Petroleum Geology 79, 64-80.

TE D

660

Macauley, R.V., Hubbard, S.M., 2013. Slope channel sedimentary processes and

665

stratigraphic stacking, Cretaceous Tres Pasos Formation slope system, Chilean

666

Patagonia. Marine and Petroleum Geology 41, 146-162.

AC C

EP

664

667

Mayall, M., Jones, E., Casey, M., 2006. Turbidite channel reservoirs—Key elements

668

in facies prediction and effective development. Marine and Petroleum Geology

669

23, 821-841.

670

McHargue, T., Pyrcz, M.J., Sullivan, M.D., Clark, J.D., Fildani, A., Romans, B.W.,

671

Covault, J.A., Levy, M., Posamentier, H.W., Drinkwater, N.J., 2011. Architecture

672

of turbidite channel systems on the continental slope: Patterns and predictions.

673

Marine and Petroleum Geology 28, 728-743.

27

ACCEPTED MANUSCRIPT 674

Morley, C.K., 2016. Major unconformities/termination of extension events and

675

associated surfaces in the South China Seas: Review and implications for

676

tectonic development. Journal of Asian Earth Sciences 120, 62-86. Nielsen, M.T., Weibel, R., Friis, H., 2015. Provenance of gravity-flow sandstones

678

from the Upper Jurassic–Lower Cretaceous Farsund Formation, Danish Central

679

Graben, North Sea. Marine and Petroleum Geology 59, 371-389.

680

RI PT

677

Olariu, M.I., Aiken, C.L.V., Bhattacharya, J.P., Xu, X., 2011. Interpretation of channelized

using

three-dimensional

photo

real

models,

682

Pennsylvanian deep-water deposits at Big Rock Quarry, Arkansas. Marine and

683

Petroleum Geology 28, 1157-1170.

M AN U

architecture

SC

681

Qin, Y.P., Alves, T.M., Constantine, J., Gamboa, D., 2016. Quantitative seismic

685

geomorphology of a submarine channel system in SE Brazil (Espírito Santo

686

Basin): Scale comparison with other submarine channel systems. Marine and

687

Petroleum Geology 78, 455-473.

TE D

684

Reimchen, A.P., Hubbard, S.M., Stright, L., Romans, B.W., 2016. Using sea-floor

689

morphometrics to constrain stratigraphic models of sinuous submarine channel

690

systems. Marine and Petroleum Geology 77, 92-115.

692 693 694

Samaras, A.G., Koutitas, C.G., 2014. Modeling the impact of climate change on

AC C

691

EP

688

sediment transport and morphology in coupled watershed-coast systems: A case study using an integrated approach. International Journal of Sediment Research 29, 304-315.

695

Su, L., Zheng, J.J., Chen, G.J., Zhang, G.C., Guo, J.M., Xu, Y.C., 2012. The upper

696

limit of maturity of natural gas generation and its implication for the Yacheng

697

formation in the Qiongdongnan Basin, China. Journal of Asian Earth Sciences

698

54–55, 203-213.

28

ACCEPTED MANUSCRIPT 699

Su, M., Xie, X.N, Xie, Y.H., Wang, Z.F., Zhang, C., Jiang, T., He, Y.L., 2014. The

700

segmentations and the significances of the Central Canyon System in the

701

Qiongdongnan Basin, northern South China Sea. Journal of Asian Earth Sciences

702

79, 552-563. Talling, P.J., 2014. On the triggers, resulting flow types and frequencies of

704

subaqueous sediment density flows in different settings. Marine Geology 352,

705

155-182.

RI PT

703

Umar, M., Khan, A.S., Kelling, G., Kassi, A.M., 2011. Depositional environments of

707

Campanian–Maastrichtian successions in the Kirthar Fold Belt, southwest

708

Pakistan: Tectonic influences on late cretaceous sedimentation across the Indian

709

passive margin. Sedimentary Geology 237, 30-45.

M AN U

SC

706

Vesely, F.F., Trzaskos, B., Kipper, F., Assine, M.L., Souza, P.A., 2015. Sedimentary

711

record of a fluctuating ice margin from the Pennsylvanian of western Gondwana:

712

Paraná Basin, southern Brazil. Sedimentary Geology 326, 45-63.

TE D

710

Wang, D.W., Wu, S.G., Qin, Z.L., Spence, G., Lü, F.L., 2013. Seismic characteristics

714

of the Huaguang mass transport deposits in the Qiongdongnan Basin, South

715

China Sea: Implications for regional tectonic activity. Marine Geology 346,

716

165-182.

AC C

EP

713

717

Wang, D.W., Wu, S.G., Yao, G.S., Wang, W.W., 2015a. Architecture and evolution of

718

deep-water cyclic deposits in the Qiongdongnan Basin, South China Sea:

719

Relationship with the Pleistocene climate events. Marine Geology 370, 43-54.

720

Wang, Z.F., Sun, Z.P., Zhu, J.T., Guo, M.G., Jiang, R.F., 2015b. Natural gas

721

geological characteristics and great discovery of large gas fields in deep-water

722

area of the western South China Sea. Natural Gas Industry B2, 489-498.

723

Xie, Y.H., 2014. Significant breakthrough in proprietary deepwater natural gas

29

ACCEPTED MANUSCRIPT 724

exploration in the northern South China Sea and its inspiration. Natural Gas

725

Industry B1, 221-229. Xie, Y.H., Wang, Z.F., Tong, C.X., 2008. Petroleum geology of Yacheng 13-1, the

727

largest gas field in China's offshore region. Marine and Petroleum Geology 25,

728

433-444.

RI PT

726

Yoshikawa, S., Nemoto, K., 2010. Seasonal variations of sediment transport to a

730

canyon and coastal erosion along the Shimizu coast, Suruga Bay, Japan. Marine

731

Geology 271, 165-176.

SC

729

Yu, J.F., Pei, J.X., Xu, J., 2009. New insight into oil and gas exploration in Miocene

733

and Late Oligocene strata in Qiongdongnan basin. Journal of Earth Science 20,

734

811-823.

M AN U

732

Yuan, S.Q., Lü, F.L., Wu, S.G., Yao, G.S., Ma, Y.B., Fu, Y.H., 2009a. Seismic

736

stratigraphy of the Qiongdongnan deep sea channel system, northwest South

737

China Sea. Chinese Journal of Oceanology and Limnology 27, 250-259.

TE D

735

Yuan, S.Q., Yao, G.S., Lü, F.L., Hu, B., He, X.S., Wang, B., Li, L., 2009b. Features of

739

late cenozoic deepwater sedimentation in southern Qiongdongnan Basin,

740

northwestern South China Sea. Journal of Earth Science 20, 172-179.

742 743 744

Ma, Y.B., Wu, S.G., Lü, F.L., Dong, D.D., Sun Q.L., Lu, Y.T., Gu, M.F., 2011.

AC C

741

EP

738

Seismic characteristics and development of the Xisha carbonate platforms, northern margin of the South China Sea. Journal of Asian Earth Sciences 40, 770-783.

745

Zhang, Q.W., Dong, Y.Q., Li, F., Yang, Z.L., Huang, X.J., Lei, T.W., 2015.

746

WITHDRAWN: Estimation of the sediment transport capacity in eroding

747

ephemeral gullies with a flume experiment method. Catena.

748

Zhao, M., Shao, L., Liang, J.S., Li, Q.Y., 2015a. No Red River capture since the late

30

ACCEPTED MANUSCRIPT 749

Oligocene: Geochemical evidence from the Northwestern South China Sea. Deep

750

Sea Research Part II: Topical Studies in Oceanography 122, 185-194. Zhao, Z.X., Sun, Z., Wang, Z.F., Sun, Z.P., Liu, J.B., Zhang, C.M., 2015b. The high

752

resolution sedimentary filling in Qiongdongnan Basin, Northern South China Sea.

753

Marine Geology 361, 11-24.

RI PT

751

Zhou, W., Gao, X.Z., Wang, Y.M., Zhuo, H.T., Zhu, W.L., Xu, Q., Wang, Y.F., 2015.

755

Seismic geomorphology and lithology of the early Miocene Pearl River

756

Deepwater Fan System in the Pearl River Mouth Basin, northern South China

757

Sea. Marine and Petroleum Geology.

759

Zhu, M.Z., Graham, S., McHargue, T., 2009. The Red River Fault zone in the

M AN U

758

SC

754

Yinggehai Basin, South China Sea. Tectonophysics 476, 397-417. Figure captions:

761

Figure 1. (a) Topographic map showing the locations of the main basins and the

762

distribution of the Central Canyon (outlined by the yellow line). (b) Bathymetric map

763

showing the distribution of the sags and locations of the Central Canyon in the

764

Qiongdongnan Basin. Also shows the locations of the utilized boreholes and seismic

765

profiles in Figure2-5.

766

Figure 2. The left seismic profile and interpretation profile showing the internal

767

structure, tectonic stage, sequence classification, sedimentary facies and evolution of

768

the Qiongdongnan Basin. The right sketch map showing the sequence classification,

769

seismic reflector, geologic age, lithologic characteristics, relatively sea-level changes

770

of the Qiongdongnan Basin. The ages of the sequence boundaries, formations and

771

relatively sea-level changes in the Qiongdongnan Basin were provided by the

772

Research Institute of China National Offshore Oil Corporation, and the global eustatic

773

curve was taken from Haq et al. (1987).

AC C

EP

TE D

760

31

ACCEPTED MANUSCRIPT Figure 3. Primary lithofacies of the sediments in the Central Canyon. A) Sandy

775

matrix-supported conglomerates. The Conglomeratic units are angular to sub-angular,

776

poor sorted, inversely graded and range in grain-size is 2-4 mm. B) Muddy

777

matrix-supported conglomerates, which was interpreted to be the product of cohesive

778

muddy debris flow. C-D) Medium- to thick-bedded fine-grained sandstone. Light-grey,

779

very few sedimentary structures except for graded bedding. There sandstones

780

represent Bouma Ta divisions and are interpreted to be deposited from turbidity

781

currents. E) Interlaminated sandstone and siltstone. Thin-bedded, planar stratified,

782

fine-grained sandstone and parallel laminated siltstone deposited from low-density

783

turbidity currents (Bouma Tb, c, d divisions). F) Thick-bedded massive mudstone.

784

Figure 4. Seismic profiles showing the ten major seismic facies identified in the

785

Central Canyon based on the amplitude, continuity, internal configuration and texture

786

and external geometry of seismic reflectors. A) On-lapping filling with

787

high-amplitude, low-frequency and high-continuous. B) On-lapping filling with

788

high-amplitude, high-frequency and high-continuous. C) Transparent, chaotic

789

reflection packages with high-amplitude appear only on the top and bottom boundary.

790

D) Parallel, sheet-like configuration with high-amplitude and continuous. E)

791

Sub-parallel, high-amplitude, high continuous reflections with gull-wing shaped

792

elements.

793

low-continuous. G) Parallel, chaotic pro-gradation with weak amplitude. H) Chaotic

794

wedge-like reflection packages with weak amplitude. I) Chaotic, sheet-like, low to

795

middle amplitude, a small-scale fault has being developed at the bottom. J) Parallel,

796

sheet-like configuration with high-continuous, which occurs frequently at the upper

797

part of the Central Canyon.

798

Figure 5. The typical seismic facies, which corresponding to the head area, upstream

AC C

EP

TE D

M AN U

SC

RI PT

774

F)

Transparent,

chaotic

on-lapping

32

fill

with

weak

amplitude,

ACCEPTED MANUSCRIPT segment, middle reaches and downstream segment of the sediments in each phase of

800

the secondary canyons. The seismic facies identified are based on the amplitude,

801

continuity, frequency, internal configuration and external geometry of seismic

802

reflectors. The seismic facies were linked to different depositional processes and

803

facies based on information from the drillings and observations from previous seismic

804

facies analysis of Central Canyon fills (Gong et al., 2011; Su et al., 2014).

805

Figure 6. A) The united wells geological section showing the lithological evolution of

806

the sediments in the head area, upstream segment and middle reaches of the Central

807

Canyon. B) The thickly turbidite sandstones infilled in the head area of the phase 4 of

808

the secondary canyon has the feature of upward fining and thinning. C) The thinly

809

interbedded sandstones and mudstones deposited in the middle reaches of the phase

810

1-3 of the secondary canyons.

811

Figure 7. The possible depositional models correspond to the head area, upstream

812

segment, middle reaches and downstream segment of the Central Canyon in the

813

Qiongdongnan Basin.

814

Figure 8. The pattern diagram showing the muddy debris flows in the head area of the

815

phase 3 of the secondary canyon transform into turbidity currents in the upstream

816

segment of the phase 3 of the secondary canyon.

AC C

EP

TE D

M AN U

SC

RI PT

799

33

Figure 1

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

1

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE D

Figure 2

2

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE D

Figure 3

3

AC C

Figure 4

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

4

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

Figure 5 5

AC C

Figure 6

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

6

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

Figure 7

7

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

Figure 8

8

ACCEPTED MANUSCRIPT Highlights ·The sediments within the Central Canyon can be subdivided into five phases of the secondary canyon filling. ·The sedimentary characteristics of the sediments in each phase of the secondary canyons were analyzed. ·In units of secondary canyons, four depositional models for different segment of the Central Canyon were established.

AC C

EP

TE D

M AN U

SC

RI PT

·The gravity flows transformation is the mainly factor contributing to the sedimentary differences of the Central Canyon.