Morphology, sedimentary features and evolution of a large palaeo submarine canyon in Qiongdongnan basin, Northern South China Sea

Morphology, sedimentary features and evolution of a large palaeo submarine canyon in Qiongdongnan basin, Northern South China Sea

Journal of Asian Earth Sciences 62 (2013) 685–696 Contents lists available at SciVerse ScienceDirect Journal of Asian Earth Sciences journal homepag...

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Journal of Asian Earth Sciences 62 (2013) 685–696

Contents lists available at SciVerse ScienceDirect

Journal of Asian Earth Sciences journal homepage: www.elsevier.com/locate/jseaes

Morphology, sedimentary features and evolution of a large palaeo submarine canyon in Qiongdongnan basin, Northern South China Sea Xiangquan Li a,b,c,⇑, Luke Fairweather d, Shiguo Wu b, Jianye Ren a, Hongjie Zhang d, Xiayun Quan a, Tao Jiang a, Cheng Zhang a, Ming Su a, Yunlong He a, Dawei Wang b a

Key Laboratory of Tectonics and Petroleum Resources of Ministry of Education, China University of Geosciences, Wuhan 430074, China Key Laboratory of Marine Geology and Environment, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China Key Lab of Submarine Geosciences, SOA, Hangzhou 310012, China d Geology Department, Meston Building, University of Aberdeen, Aberdeen AB24 3UE, UK b c

a r t i c l e

i n f o

Article history: Received 27 June 2012 Received in revised form 28 October 2012 Accepted 4 November 2012 Available online 17 November 2012 Keywords: Submarine canyon Qiongdongnan basin Canyon morphology Canyon fills Canyon evolution

a b s t r a c t The large Miocene-aged palaeo canyon that extents through the Qiongdongnan basin (QDNB) and Yinggehai basin (YGHB) of Northern South China Sea has been of considerable interest both economically and scientifically over the past decade. Stemmed from this, significant research has been employed into understanding the mechanism for its existence, incision, and sedimentary fill, yet debate remains. In the first case the canyon itself is actually quite anomalous. Alone from the size (over 570 km in length and more than 8 km in width (Yuan et al., 2009)), which is considerably more than most ancient deep-water channels (REFS), the canyon’s sedimentary fill is also distinctly different. Some explanations have been given to explain the canyon’s origin and existence, these include increased sediment supply from the Red River which is genetically linked to uplift of the Tibetan Plateau, lowstand turbidite and mass-transport activity, reactivation and dextral displacement of the Red River Fault zone inducing erosive gravityflows, regional tilt of the QDNB and YGHB, paleo-seafloor morphology and seal-level fluctuations. With the application of new data obtained from interpretations of a large number of 2D seismic profiles, core and well log data, and tectonic and sedimentary analysis this contribution aims to: (1) Present models to explain the Canyon’s sedimentary fill and basin plain deposits, which provided significant understanding of processes pre-, syn- and post-incision and; (2) review the plausibility and likelihood of each of the controlling mechanisms, hoping to shed light on this controversial aspect. We conclude that the final erosive event that shaped the canyon is dated at 5.5 Ma. The Canyon’s unusual fill is a product of variation in the interaction between turbidity currents and MTD that blocked the canyon’s axis, and the reduction in gravity flow energy through time; and therefore the complete succession represents one major erosive and cut event at 5.5 Ma and thereafter multi-gravity currents fills unlike in most slope channel-fills. Ó 2012 Elsevier Ltd. All rights reserved.

1. Introduction Submarine canyons are deep and steep incisions, generally showing V or U-shapes in profile, which act both as temporary stores of sediment and carbon (Van Weering et al., 2001; Oliveira et al., 2007) and as preferential conduits delivering sediment from the continental margin to the deep sea on both continental passive and active margins (Shepard, 1981; Laursen and Normark, 2002). Potentially they create significant deepwater hydrocarbon reservoirs because of their association with sand-rich turbidite canyon fills (Stow and Mayall, 2000; Posamentier, 2003). The downslope ⇑ Corresponding author at: Department of Marine Science and Engineering, Faculty of Earth Resources, China University of Geosciences, Wuhan 430074, China. Tel.: +86 1860 2707 959; fax: +86 27 6788 3063. E-mail address: [email protected] (X. Li). 1367-9120/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jseaes.2012.11.019

mass sediment transportation, notably slides, slumps, debris flows and turbidity currents, were found to be the principal mechanisms responsible for submarine canyon’s cutting and shaping (Babonneau et al., 2002; McHugh et al., 2002). The controlling factors of the submarine canyon development are complex, and may involve structural fabric, local tectonism, sediment supply, sea-level oscillations (Shepard, 1981; Greene et al., 1991). Until now, a general world-wide accepted valid theoretical context of the location, evolution and activity of submarine canyons is not yet available (Lastras et al., 2009). In recent years, with the advent of new geophysical techniques, such as swath bathymetry, sidescan sonar and high resolution seismic profiles, an increasing number of modern and ancient submarine canyons have been described and interpreted in detail (e.g. Popescu et al., 2004; Mitchell, 2005; Antobreh and Krastel, 2006; Mitchell et al., 2007; Mountjoy et al., 2009).

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A large-scale palaeo submarine canyon developed along the continental margin of Northern South China Sea. The maximum width of the canyon is above 20 km, the maximum depth is over 1000 m, and its total length is more than 570 km (Yuan et al., 2009). Although this canyon, whose incision mechanism was mainly thought to be by turbidity current erosion, has been documented in the past several years (Lin et al., 2001; Yuan et al., 2009; Su et al., 2009; Gong et al., 2011), there are little consistent viewpoints on its initial development time, architecture, seismic stratigraphy, evolution and controlling factors. The controlling factors of the canyon’s formation have been discussed, involving uplift of the Tibetan Plateau, lowstand turbidite and masstransport activity, reactivation and dextral displacement of the Red River Fault zone inducing erosive gravity-flows, regional tilt of the QDNB and YGHB, paleo-seafloor morphology and seal-level fluctuations (Lin et al., 2001; Yuan et al., 2009;Gong et al., 2011), however it remains lack of a clear and plausible evolution and sedimentary infill model. In this paper, based on comprehensive and multi-disciplinary data including high resolution seismic profiles, core and biostratigraphy data and regional dynamics settings, the canyon’s seismic reflection features, morphology, sedimentary and infilling characteristics, controlling factors and evolution are discussed. 2. Regional geology The continental margin basins of northern South China Sea, including YGHB, QDNB, and Pear River Mouth basin (PRMB), are located at the conjunction of the Eurasian, the Indio-Australian, the Philippine and the Pacific Plates (Hall and Blundell, 1996; Fig. 1). The QDNB and PRMB both trend in a northeast direction parallel to the present shoreline of southern China, and perpendicular to the trend of the YGHB. Their formation is believed to relate to the evolution of the South China Sea during the Cenozoic (Liang and Liu, 1990). As shown in Fig. 1, the YGHB and QDNB are separated by the No. 1 Fault which is regarded as one branch of the Red River Fault strike-slip system trending southeast (Xie et al., 2008; Su et al., 2009). These Cenozoic-aged basins show typical passive continental margin features where a two-phase history can be identified; an earlier rifting phase extending from the Paleocene to Oligocene and the post-rifting phase from the Miocene to Quaternary (Chen et al., 1993, Figs. 2 and 3). From the Late Miocene (10.5 Ma), continental shelf/slope systems began to widely develop along the Northern South China Sea margin. Stratigraphic patterns in YGHB and western QDNB are mainly characterized by progradational slope clinoforms, which result in a rapid seaward (and southeastward) shift of the shelf-slope break due to high rates of sediment supply (Xie et al., 2008). In contrast, in the eastern QDNB, the shelf margin shows a vertical aggradational or minor progradational patterns due to insufficient sediment supply. Differing from the traditional passive continental margin basins, the Yinggehai basin and Qiongdongnan basin underwent a tectonic reactivation phase from the latest Miocene (5.5 Ma) to Quaternary, with obvious anomalous high rates of post-rifting subsidence (Xie et al, 2006). 3. Methods and data set The sedimentary basins on the northern margin of the South China Sea contain significant hydrocarbon reserves. Because of this, over the past decade, large amounts of geological and geophysical data have been accumulated. The 2D seismic grid arranges from 1  1 km to 16  16 km. 39 wells, most of them are distributed on the present shelf area, were loaded to the workstation project and interpreted using Landmark 2003 suite. Seismic

interpretation has been based on both stratigraphic data and seismic stratigraphy techniques (Vail et al., 1977). The ages of stratigraphic calibration of seismic horizons are determined by planktonic foraminifera, calcareous nanoplankton and dinoflagellates collected from the boreholes in QDNB. 4. Morphology The upstream part of the paleo-canyon begins from the western side of the QDNB, and is close proximity to the No. 1 Fault which defines the boundary between the QDNB and YGHB. The canyon length of the part in QDNB is 454 km and its present bathymetry arranges from 150 m to 2600 m. The canyon trends in northeast direction which is consistent with the overall axial trend of the QDNB, and forms a low-sinuosity ’S’ shape in plan view. The geomorphology of the canyon’s axis appears elongate, slope-parallel or subparallel orientation to the strike of present shelf margin, and coincides with the present axial extension of Xisha Trough in eastern QDNB. In the western QDNB, however, the canyon head has been buried under the present shelf due to shelf-margin progradation (Fig. 4). The cross section morphologies of the canyon are shown in Fig. 5. In profile P1 in the western QDNB, the canyon displays a ‘U’ shape, the width of the canyon head being 5.5 km, and its incision depth is 370 m. To east, the width and depth of the incision become greater, and in cross section it shows a ‘V’ shape. The maximum width of the canyon is 21 km (Fig. 5, profile P16) and the maximum incision depth is 1100 m deep (Fig. 5, profile P21). The canyon becomes narrow and deep between P19 and P21; its width being slightly over 10 km, but its incision depth being over 1000 m. The accommodation of the large palaeo canyon is completely infilled and buried by the overlying strata from its origin to profile P18. The canyon is, however, only partially infilled from the P19 to P21, and the canyon’s expression is inherited by modern seafloor geomorphology. 5. Seismic and sedimentary facies and features Seismic profiles of the canyon sedimentary fills show a range of different seismic facies, from high amplitude reflections, alternations between high amplitude and low-transparent amplitude, continuous to subcontinuous, parallel to subparallel reflection or chaotic reflection. These seismic facies display the variation in the configuration, scale, location (both vertically and streamwise down canyon) and therefore represent changes in lithofacies and sediment transport mechanisms active in the canyon. The canyon is defined by the termination of the above seismic facies against surrounding strata producing an obvious discordant unconformity, which represent the ‘walls’ or sides of the canyon (Fig. 6). 5.1. Seismic facies 5.1.1. Low amplitude, chaotic seismic facies Chaotic seismic reflection packages are mainly interpreted to represent chaotic slumps and debrites (Mayalla et al., 2006). We subdivided these facies into three types based on their locations and developing scales in the canyon. The first type, named MTDI, developed at the base and almost along the whole canyon in QDNB (Fig. 6). These are interpreted to be deposited either by anomalous large-scale wall failures or lags from basin-ward mass-failures sourced from the upstream of the canyon and traveled a long distance. Based on these observations, we conclude that this type may have partially aided incision. The other two types are characterized by locally distribution in the canyon and interpreted as mass-transport deposits that traveled a short distance along the

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Fig. 1. The marginal sedimentary basins distribution in Northern South China Sea (after Li et al., 1998; Xie et al., 2008) and the tectonic sketch map of Southeast Asia (after Leloup et al., 1995; Rangin et al., 1995; Sun et al., 2003). SCS: South China Sea; NSSCS: Northwest Subbasin of South China Sea; QDNB: Qiongdongnan basin.

canyon axis. One type, named MTD-II, is restricted to the canyon sides, and is interpreted as mass-transport deposits derived from the walls of the canyon (Fig. 6, P20). Another, named MTD-III, is the interval chaotic seismic facies in the canyon, similar with the MTD-I (Fig. 6, P5, P13, P16, P18), but its space scale is much smaller and developed locally. This kind of seismic facies is developed in the middle or up part of the canyon infills, and is interpreted as mass-transport deposits sourced from the short distance, northern Hainan Island shelf/slope, not from the long distance axial gravity currents of the canyon. 5.1.2. High amplitude to low amplitude parallel and subparallel cyclities seismic facies Chaotic seismic facies pass gradually upward becoming parallel or subparallel seismic reflections showing several alternating cycles of high to low amplitude reflections (Fig. 6). From the wellseismic calibration and their seismic reflection features, the high amplitude seismic facies usually represent deposits of turbidity currents that are likely to be sand-rich. We therefore suggest that these cyclities represent the lithofacies alternations from sandstone to mudstone, respectively (Figs. 8 and 9). 5.1.3. The intra incisive channel seismic facies In some seismic profiles, the intra incisive channel seismic reflections can be identified in the canyon infill seismic facies (for example Fig. 6, P5, P16, P20), these channels developed in

the middle and up part of the canyon. Compared with the canyon, these channels distribute locally and are much smaller in width and depth, usually accompanied with MTD-III development (Fig. 6 P5, P16). These seismic facies are interpreted as the result of small-scale incisive turbidity currents or erosive mass-transport deposits sourced from the northern Hainan Island shelf/slope.

5.2. Sedimentary facies The well YC35-1-2(location in Fig. 4) was drilled aiming at the canyon’s hydrocarbon reservoir in 1995, and the sandy turbiditefill of the canyon was proved. The erosive base of the canyon corresponds to T30 seismic reflection surface. Only one well (YC35-1-2) was available for correlation and seismic facies control, located at the head of the canyon, therefore only a limited understanding of lithofacies variation is attained. Nonetheless, according to the core sedimentary log and GR logging curve which displays box or bell shape, the canyon filling can be divided three upward-fining deposition cycles (Fig. 7). The bottom of the canyon is characterized a poorly sorted, massive pebbled sandstone of a thickness of 36 m. The scour surface on the bottom of the pebbled sandstone corresponds to the erosive base of the canyon on the seismic profile. The core picture (in Fig. 7) shows rounded pebbles floating in a sandy matrix. These deposits are interpreted as high density, coarse-grained sandy debris flows or hyper-concentrated gravity currents. Thick fine sandstone deposits, summing to a

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Fig. 2. Stratigraphic table with deposition environment (after Chen et al., 1993), subsidence, regional tectonics events (after Tapponier et al., 1986; Allen et al., 1984; Leloup et al., 1995; Taylor et al., 1983; Xie et al., 2008), sea-level (after Haq et al., 1987; Xie et al., 2008), etc. of Qiongdongnan basin and Yinggehai basin. SCS: South China Sea.

Fig. 3. The representative AA0 geological cross-section of the Qiongdongnan basin, showing the structural basin framework characterized by rift and post-rift phases and the shelf/slope system developed after T40 seismic surface. Note the location of the palaeo canyon. The section location is shown in Fig. 1.

thickness of about 80 m, define the bottom of second deposition cycle. This indicates a second phase of gravity flow activity. A basal scour surface can be identified on well core but this is not visible on the seismic profile which showing its weak contribution to the basal incision. This massive fine sandstone (core picture in Fig. 7) is interpreted as turbidity currents. The third deposition cycle displays thin interbeds of fine muddy siltstone and silty mudstone (Fig. 7), and the single interval is only about 10 m.

6. Discussions 6.1. The infilling model of the canyon Two filling models (Figs. 8 and 9) of the canyon are sketched according to the seismic profile P20 and P16 in Fig. 6. Usually, the MTD-I chaotic seismic facies initially fill the canyon base and it is overlain and transition up-dip into multi-period parallel and

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Fig. 4. Present bathymetric contours and the interpretive schematic of the large palaeo canyon revealed by a large number of multi-channel seismic profiles in QDNB. P1 to P21 represent the locations of some cross section seismic profiles of the large palaeo canyon.

subparallel seismic facies from high amplitude to low amplitude or MTD-II or MTD-III seismic facies (Figs. 6–9). On the whole, the seismic reflection features and the core sedimentary log (Fig. 7) show multi-upward fining deposition cycles with the lithology from coarse to fine and the single layer thickness from thick to thin. These sedimentary features imply that there are multi-period gravity flow activities in the canyon’s incisive and filling process. Lin et al. (2001), Su et al. (2009) and Gong et al. (2011) think that the large canyon is formed by multi-period gravity flows cut and fill cycles according to the seismic interpretation. But we note that, besides the large canyon basal incisive surface, no regional erosive surface or regional thalweg can be identified from seismic profiles in the canyon. This shows the multi-period gravity flows activities might play major infilling roles and very limited contribution to the canyon incision or shaping. So it seems more likely one large initial cut event and thereafter multi-period gravity current filling processes. This is differ from the common, multi-periods cut-fill slope channel system (for example, Sprague et al., 2002; McHargue et al., 2011). In Fig. 9, a large-scale mass-transport deposits and slide plane are identified in the overlying strata of the canyon, and the frontal mini thrust faults can be recognized at the toe of the slump unit. These mass-transport deposits and slide plane can be traced and linked to the northern Hainan Island slope failures. If this kind of slide plane is connected to the canyon wall, it can induce largescale canyon wall failures and carry large amounts of mass-transport deposits into the canyon axis. This shows an important evidence that the northern Hainan Island shelf/slope subparallel to the canyon axis could affect and complicate the canyon’s infills, such as the MTD-II, MTD-III and the intra incisive channels (Figs. 8 and 9). 6.2. Origin time Generally, the canyon is narrow and shallow in western QDNB, and it only incised downward to T30 seismic reflection surface. It

becomes wide and deep in the middle of the basin and the incised depth increases to T40 and T50 seismic reflection surfaces. In eastern part of the canyon, the canyon becomes narrower again but the incision becomes deeper to T60 seismic reflection surface, and nowadays the seafloor remains a part-filled canyon geomorphology within Xisha Trough (Fig. 5, p19–p21 and Fig. 6, p20). All the features of the canyon raise a series of questions: when the canyon got its initial development and how it developed? The time of the canyon’s origin and incision especially is a controversial issue, Lin et al. (2001) first documented that the incision of the large palaeo canyon results by multi-period lowstand gravity flow events of T40 (10.5 Ma), T30 (5.5 Ma) and T27 (2.4 Ma). Su et al (2009) proposed that the distribution of the canyon during time T40 was only in eastern QDNB, then the canyon back-stepped and entrenched to west respectively corresponding to T30 and T29 horizons. The present distribution of the canyon is therefore a function of a multi-period development. They further argued that sea-level fall and sediment supply are the dominant controls in western QDNB, but in the eastern QDNB the structural subsidence and fault activities are the main controls. Yuan et al. (2009) and Gong et al. (2011) emphasized that the earliest origin time of the canyon is at latest Miocene (5.5 Ma), and the canyon is formed by Multi-period cutfill cycles controlled by seal level fluctuations. In this paper, according to the seismic reflection and filling features of the canyon, we argued that the origin time of the canyon is at latest Miocene (5.5 Ma), corresponding to T30 seismic reflection surface. And differ from all the previous studies, we think it is formed by one large gravity current erosive and cut event (at 5.5 Ma) and thereafter multi-period gravity currents fill processes (discussed in 6.1). There are two convincing pieces of evidences for this, they are: (1) The large palaeo canyon has a common erosive base, although the incision of the canyon become deeper and the incised seismic surface is from T30 to T60 from west to east, the erosive time and the regional erosive unconformity can be unified to the T30 seismic reflection surface; (2) The unusual sedimentary fill where neither internal regional erosive seismic surfaces nor internal

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Fig. 5. Cross-sectional morphology of the canyon revealed by seismic profiles. The values of the canyon bottom represent the two-way seismic reflection travel time. Locations of seismic profiles are shown in Fig. 4. Note the eastern part of the canyon is part-filled from P19 to P21 at present.

regional unconformities, although some local ones exist, can be identified leads us to reject any significant erosive periods occurring during the canyon fills. The erosive base of the canyon can be unified to the T30 seismic surface (5.5 Ma), and the canyon’s filling strata is mainly between T30 and T29 seismic surfaces (Fig. 6, P2, P5, P13). The T29 seismic surface corresponds to 4.2 Ma (Fig. 2), so we can conclude the filling process of the canyon was a relatively short time, between 5.5 Ma and 4.2 Ma. However, it is difficulty to give more detail age control to the filling strata. 6.3. Evolution model If the canyon was formed at time of T30, what is the interpretation of the canyon’s part-filled geomorphology at present day seafloor in eastern QDNB? And whether it indicates the canyon is still active nowadays? In this study, we found that there are not obvious incisive seismic reflection terminations at the canyon walls in the upper part of the canyon in eastern QDNB, and the internal

seismic facies show similarities with the outsides corresponding strata of the canyon (Fig. 6, P20), so we inferred that this part of filling strata ‘in the canyon’ is the same depositional source with its outside downslope sedimentary strata, not sourced from the canyon’s axial gravity flows (Fig. 6, P20; Fig. 8). To understand this idea better, the schematic evolution models of the canyon in west and east are established in Fig. 10. The Canyon developed at the time of T30 in western QDNB, and was full infilled by gravity flow sediments. Strata B and C which are interpreted to be transported downslope perpendicular to the canyon’s axial direction, and, thus, are sourced from Hainan Island subsequently draped on the canyon (Fig. 10a). Different from the west, the canyon was only part-filled after the time of T30 in eastern QDNB and thus strata B and C, remains sourced from the Hainan Island, inherit the canyon part-filled geomorphology, so that the present seafloor is characterized by an unhealing canyon topography (Fig. 10b). We inferred the high rates of sediment supply in west (Xie et al., 2008) is the reason that the western overlying strata thickness thicker than the east in QDNB. And the insufficient sediment

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Fig. 6. Cross-sectional seismic profiles across the canyon. Locations of seismic profiles are shown in Fig. 4. C = canyon, IC = incisive channel, GC = gas chimney, D = diapir, F = Fault, Sf = Seafloor, Sl = Slumps, SP = sliding plane, FTF = frontal mini thrust faults, LSF = Lowstand slope fan, MTD = mass transport deposition, MTD-I = MTD located along the base of the canyon, MTD-II = MTD restricted to the canyon wall sides, MTD-III = MTD developed in the middle or upper part of the canyon.

supply in east resulted in the ‘hungry’ part-filled canyon topography nowadays. 6.4. Controlling factors A submarine canyon generally originates from upper slope or outer shelf, formed by slope failure or gravity flow incision. Its formation may relate to sea-level fluctuation, fluvial sediment supply, slope failure, faults or diapir structural activities, etc. (e.g. Shepard, 1981). In QDNB, what factors contributed the formation of the unusually large palaeo canyon at latest Miocene (5.5 Ma), the controlling factors are analyzed as followed. 6.4.1. Tibet plateau rapid uplift and the Red River sediment increased The Red River sediment supply is alleged to be sourced from mountainous area of Tibet plateau, and therefore the uplift history of Tibet plateau will influence the sediment supply amount of Red

River (Lin et al., 2001; Xie et al., 2008). Although the uplift history of Tibet plateau which was caused by the India–Eurasia collision is not very clear, a multi-phase uplift history has been generally acknowledged (Zhong and Ding, 1996; Shen, 1987; Amano and Taira, 1992; Wang and Ding, 1998), and some authors believe that the real rapid uplift of Tibetan plateau initiated during the late Miocene (Fig. 2). Li (1995) proposed that the Tibetan plateau uplift was divided into three stages according to the evidence from paleomagnetic, sedimentation and architecture of surrounding basins and the distribution of palaeo fauna and flora. A last overall rapid uplift of the Tibetan plateau occurred from the latest Miocene to Quaternary; Cui et al. (1996) presented that Tibet plateau underwent three uplifts and two time plantations according to a karst denudation plane, the present altitude of Tibet plateau is mainly derived from the rapid uplift since the latest Miocene. The rapid uplift of the Tibetan plateau may cause high rates of erosion and thus of sediment supply to the Red River which leads to a rapid

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Fig. 7. Well YC35-1-2 canyon-fill sedimentary log and its correlation to corresponding seismic profile across the palaeo canyon. Well location is shown in Fig. 4.

Fig. 8. the schematic infilling model of P20 seismic profile, the raw seismic data is shown in Fig. 6, location of the profile is shown in Fig. 4.

seaward progradation in the YGHB and western QDNB (Xie et al., 2008). The Earth’s largest submarine canyons are mainly located at passive continental margins downslope from the estuaries/deltas of large rivers that feed these canyons, for example, the Amazon and Mississippi canyons (Milliman et al., 1975; Goodwin and Prior, 1989; Sawyer et al, 2007). It is suggested that the plentiful

sediment supply of Red River also should be one of the controls forming the large palaeo canyon at latest Miocene (5.5 Ma). In QDNB, subsidence rate was not high enough to provide accommodation for the increasing sediment supply, thus the gravity flows had to create accommodation through incision. It is noteworthy that this study has no further direct evidence (e.g. provenance

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Fig. 9. the schematic infilling model of P16 seismic profile, the raw seismic data is shown in Fig. 6, location of the profile is shown in Fig. 4. IC = incisive channel, D = diapir, F = Fault, SP = sliding plane, MTD = mass transport deposition, FTF = frontal mini thrust faults.

(Red River Fault) and the Red River experiencing large-scale sinistral strike-slip movement of over 700 km from Eocene to late Miocene. Allen et al. (1984) highlighted that the inland northern part of the fault displayed dextral strike slip movement. Leloup et al. (1995) presented that the transformation of Red River Fault from sinistral strike-slip into dextral strike-slip movement at about 5 Ma, over a distance of about 20–50 km. According to Physical Modeling Study, Sun et al. (2003) proved dextral movement of the No. 1 fault after latest Miocene in YGHB. No. 1 Fault acts as one of the branches of the Red River Fault that extents seaward and southeastward and forms the boundary of YGHB and QDNB. It is suggested, based on the timing of switch displacement direction from sinistral to dextral strike-slip movement and the inferred incision time of the canyon, that large-scale MTDs were subsequently triggered resulting in the incision and fill of the canyon.

Fig. 10. the schematic infilling model of the canyon in the west (a) and east (b) of Qiongdongnan basin. Note the difference of the present day seafloor topography and the thickness of overlying strata B and C between the west and east.

analysis) that relates the sediment in the canyon neither to the Red River nor to the rapid uplift history of the Tibetan plateau as suggested by Clark et al. (2004). 6.4.2. Sea-level fall and lowstand Sea-level change is one of the important factors of forming submarine canyons, most of the submarine canyons and their corresponding submarine fans are associated with the lowstand system of third-order sequences (e.g. Vail et al., 1977). During this lowstand period, the rivers are allowed to release their terrestrial sediment directly into the submarine canyons. Moreover, sea-level fall also sub-aerially exposes the shelf resulting in severe terrestrial erosion (Mattern, 2005). An obvious relative sea-level falling can be recognized at latest Miocene-5.5 Ma in QDNB (in Fig. 2). The large denudation area of the shelf at the time of T30 based on the seismic interpretation indicates that the shelf erosion also provides large amounts of sediment to the deep sea (Fig. 4), which also is a favorable factor to the formation of the large palaeo canyon. 6.4.3. Dextral strike slip movement of the Red River Fault Tapponnier et al. (1982) proposed that India–Eurasia collision led to the Eurasia plate being extruded along the boundary fault

6.4.4. Palaeogeomorphology Large submarine canyons act as principal sediment conduits and stores from shelf to deep sea basins, apart from tectonic, sedimentation and the sea level fluctuation, we suggest that the palaeogeomorphology also plays an important role on the morphology and distribution of submarine canyons and fans, especially the basin floor inclination. Generally submarine canyons originate from the shelf margin or upper slope and canyon axial is perpendicular to the shelf margin (Fig. 11a). However, the Xisha trough is a particular depositional environment with its elongated, confined trough geomorphology and tilted seafloor (type Fig. 11c). Threedimensional view of the T30 reflection in QDNB shows the large canyon originates from the western QDNB, upon reaching the deep basin floor it remains parallel to the palaeo shelf break line (Fig. 12). Fig. 12 further shows a northeast tilted palaeogeomorphology characteristic similar with the present seafloor. So we deduced that the northeast tilted seafloor palaeogemorphology and the Xisha trough topography which is confined between northern Hainan island shelf/slope and southern Xisha uplift controlled the large canyon morphology, scale and distribution in QDNB. 6.5. Development model Based on the above analyses, we put forward a conceptual development model of the large palaeo canyon in QDNB. This model is divided into two parts (A and B), part A is identified and sketched based on researches in QDNB. Part B means When the

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Fig. 11. The schematic of three types of canyon’s morphology and distribution controlled by different seafloor geomorphology setting. a: the canyon is perpendicular to the shelf margin and displays a radial fan when it gets to the low gradient open seafloor plain; b: when the sea floor is lateral titled, the submarine fan also takes place lateral extension coincide with sea floor inclination direction; c: when the sea floor is lateral tilted and with a elongated and restricted sea floor geomorphology between the shelfslope and the uplift, the canyon’s erosion ability becomes greatly stronger than a and b with a long distance canyon transportation and incision.

Fig. 12. The upper right picture shows the three-dimensional view of two-way seismic reflection traveltime of horizon T30 in Qiongdongnan basin, the left bottom table shows the statistics of submarine bottom two-way seismic reflection traveltime along the canyon axis, and the numbers of the dark dot stand for the seismic profiles whose locations are shown in Fig. 4.

canyon extends northeast out of the Xisha trough mouth, it shifts into the Northwest Subbasin of South China Sea where it becomes an open and low gradient flat seafloor plain, thereafter the canyon transforms into a radial channelized fan with a tongue-like shape (Fig. 13). However, due to the lack of seismic profiles out QDNB, part B is only an inferred evolution model, which needs further specific exploration and academic studies. At the latest Miocene (5.5 Ma), the Tibet plateau underwent a phase of rapid uplift, and because of its rapid tectonic uplift and mountainous relief, the Tibet Plateau potentially provided vast amounts of sediment to YGHB and western QDNB area through the Red River. The sea level fall at 5.5 Ma enables the sediment to transport directly to proximity of canyon origin. At the same time, the sea level fall exposes the shelf which is subsequently eroded and produces more sediment supply (T30 erosive area in Fig. 4). The structural activity of Red River Fault transformation from sinistral strike-slip movement into dextral strike-slip movement at latest Miocene maybe play the most important role in triggering large scale MTDs resulted in resedimentation and initial incision of the canyon. The tilted and confined seafloor geomor-

phology impelled gravity flows to travel long distance, eroding significantly downstream. The canyon shows a low-sinuosity ‘S’ shape in plan view, which coincides with palaeo basin depression axis. It should be noted that there are some small scale canyons, fans or slumps sourced from Hainan Island merging into the canyon axis, making the filling configuration be more complex and probably causing some local small internal erosive channels or surfaces in the canyon (Figs. 8 and 9). 6.6. Further discussion The canyon’s fill shows small incisive channels, fans and slumps that are interpreted to be sourced from the northern Hainan Island shelf/slope and deposit along the canyon axis. They merge with the canyon intra fills which makes the internal sedimentary configuration and lateral lithology continuity of the canyon more complex (Figs. 8 and 9). This needs more specific study to evaluate the canyon reservoir and hydrocarbon potential. Moreover, the maturity and sorting of the filling sedimentation in the canyon should be different between the western and eastern QDNB area. In the

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Fig. 13. Development model of the large palaeo canyon in QDNB.

Western QDNB the sedimentation will likely compose thick massive sandstone with low maturity and poor sorting because its close proximity to sediment source. But in eastern QDNB, where the canyon is filled with thin alternating sandstone and mudstone beds, the sediment should present better maturity and sorting due to its long distance transportation, this is also a worth considering factor in evaluating hydrocarbon reservoirs. Because of the large canyon’s incision, it is reasonable to deduce that there is a large submarine fan connecting to canyon mouth, but enough regional seismic profiles are the prerequisite to prove its existence. The confined seafloor geomorphology of Xisha trough is favor of the long distance incision. Meanwhile, it is also favor of oceanic current existence, especially bottom currents, because of its connection with the open sea of Northwest Subbasin of South China Sea. So proving the existence of palaeo oceanic currents and evaluate their reworking and influences on the physical property and distribution of turbidite sandstone is another significant scientific problem.

7. Conclusions Large-scale submarine gravity flow (slumps, debris flows or turbidite currents) incision is the primary formation mechanism of the Canyon. The seismic data shows the erosive base of the canyon took place at latest Miocene (5.5 Ma) corresponding to the T30 seismic surface. It is likely that the canyon has a genetic link with the Tibet plateau rapid uplift and Red River sediment supply, sealevel falling and shelf erosion, the strike-slip tectonics of No. 1 Fault activity and the palageomorphology, and the latter two factors maybe play more important roles in controlling the formation, scale, morphology and evolution of the canyon. The fact that the large palaeo canyons are filled with sediment indicates the submarine canyon not only acts as the preferential conduit of delivering sediment, but as the site of deposition. The internal sedimentary configuration of the canyon basing on the core sedimentary log and filling sedimentary model (Figs. 7–9) indicates that the canyon is composed of multi upward fining normal depositional cycles, which display a vertical evolution series of massive slumps or debris to thick massive turbidite sandstone to alternating turbidite sandstone and pelagic mudstone beds. Temporal and spatial variations, mainly the energy decrease of gravity flows and interaction with MTDs, manifests in a unique fill to any other Canyon’s fill reported in literature. The seafloor’s unhealing geomorphology within Xisha Trough at the present day in the east-

ern QDNB is the result of inherited sedimentation of the part-filled palaeo canyon geomorphology. Acknowledgements We gratefully acknowledge Institute of Petroleum Exploration and Development, Nanhai West Oil Corporation for providing geological data. This study is supported by National Natural Science Foundation of China (Nos. 41102068, 91028009, and 41002031), Open Foundation of the Key Lab of Submarine Geosciences, SOA, Hangzhou, PR China (KLSG09023), The author thanks professor Julien Bourget and Dr. Qiliang Sun for insightful comments and large number of expression revisions, which led to significant improvements of this paper. References Allen, C.R., Gillespie, A.R., Han, Y., et al., 1984. Red River and associated faults in Yunnan Province, China: quaternary geology, slip rates and seismic hazard. Geological Society of America Bulletin 95, 686–700. Amano, Kazuo, Taira, Asaira, 1992. Two-phase uplift of Higher Himalayas since 17 Ma. Geology 20, 391–394. Antobreh, A.A., Krastel, S., 2006. Morphology, seismic characteristics and development of Cap Timiris Canyon, offshore Mauritania: a newly discovered canyon preserved-off a major arid climatic region. Marine and Petroleum Geology 23, 37–59. Babonneau, N., Savoye, B., Cremer, M., Klein, B., 2002. Morphology and architecture of the present canyon and channel system of the Zaire deepsea fan. Marine and Petroleum Geology 19, 445–467. Chen, P.H., Chen, Z.Y., Zhang, Q.M., 1993. Sequence stratigraphy and continental margin development of the northwestern Shelf of the South China Sea. American Association of Petroleum Geologists Bulletin 77, 842–862. Clark, M.K., Schoenbohm, L.M., Royden, L.H., et al., 2004. Surface uplift, tectonics, and erosion of eastern Tibet from large-scale drainage patterns. Tectonics 23 (TC1006), 1–20. Cui, Z.J., Gao, Q.X., Liu, G.N., et al., 1996. Planation surfaces and palaeokarst and Tibet Plateau uplift. Chinese Science Bulletin (in Chinese) 26, 378–385. Gong, C.L., Wang, Y.M., Zhu, W.L., et al., 2011. The Central Submarine Canyon in the Qiongdongnan Basin, northwestern South China Sea: architecture, sequence stratigraphy, and depositional processes. Marine and petroleum Geology, 1–13. Goodwin, R.H., Prior, D.B., 1989. Geometry and depositional sequences of the Mississippi Canyon, Gulf of Mexico. Journal of Sedimentary Petrology 59 (2), 318–329. Greene, H., Clarke, S., Kennedy, M., 1991. Tectonic evolution of submarine canyons along the California continental margin. In: Osborne, R.H. (Ed.), From Shoreline to Abyss, vol. 46. SEPM Special Publication, pp. 231–248. Hall, R., Blundell, D.J., 1996. Tectonic Evolution of SE Asia: Introduction, vol. 106. Geological Society Special Publication, London, 7. Haq, B.U., Hardenbol, J., Vail, P.R., 1987. Chronology of fluctuating sea levels since the Triassic. Science 235, 1156–1167. Lastras, G., Arzola, R.G., Masson, D.G., Wynn, R.B., Huvenne, V.A.I., Hühnerbach, V., Canals, M., 2009. Geomorphology and sedimentary features in the Central

696

X. Li et al. / Journal of Asian Earth Sciences 62 (2013) 685–696

Portuguese submarine canyons, Western Iberian margin. Geomorphology 103, 310–329. Laursen, J., Normark, W., 2002. Late Quaternary evolution of the San Antonio Submarine canyon in the central Chile Forearc (33°S). Marine Geology 188, 365–390. Leloup, P.H., Lacassin, R., Tapponnier, P., Schärer, U., Zhong, D., Liu, X., Zhang, L., Ji, S., Trinh, P.T., 1995. The Ailao Shan-Red River shear zone (Yunnan, China), Tertiary transform boundary of Indochina. Tectonophysics 251, 3–84. Li, T.D., 1995. The uplifting process and Mechanism of the Qinhai-Tibet Plateau. Acta Geoscientia Sinica 1 (1), 1–9. Li, S.T., Lin, C.S., Zhang, Q.M., 1998. Dynamic process of episodic rifting in continental marginal basin and tectonic events since 10 Ma in South China Sea. Chinese Science Bulletin 43 (8), 797–810. Liang, D.H., Liu, Z.H., 1990. The genesis of the South China Sea and its hydrocarbonbearing basins. Journal Petroleum Geology 13 (1), 59–70. Lin, C.S., Liu, J.Y., Cai, S.X., et al., 2001. Depositional architecture and developing settings of large scale incised valley and submarine gravity flow systems in the Yinggehai and Qiongdongnan basins, South China Sea. Chinese Science Bulletin 46 (8), 690–693. Mattern, F., 2005. Ancient sand-rich submarine fans: depositional systems, models, identification, and analysis. Earth-Science Reviews 70, 167–202. Mayalla, M., Jonesb, E., Caseyc, M., 2006. Turbidite channel reservoirs-Key elements in facies prediction and effective development. Marine and Petroleum Geology 23, 821–841. McHargue, T., Pyrcz, M.J., Sullivan, M.D., et al., 2011. Architecture of turbidite channel systems on the continental slope: patterns and predictions. Marine and Petroleum Geology 28, 728–743. McHugh, C.M.G., Damuth, J.E., Mountain, G.S., 2002. Cenozoic mass transport facies and their correlation with relative sea-level change, New Jersey continental margin. Marine Geology 184, 295–334. Milliman, J.D., Summerhayes, C.P., Barretto, H.T., 1975. Quaternary sedimentation on the Amazon continental margin: a model. GSA Bulletin 86 (5), 610–614. Mitchell, N.C., 2005. Interpreting long-profiles of canyons in the USA Atlantic continental slope. Marine Geology 214, 75–99. Mitchell, J.K., Holdgate, G.R., Wallace, M.W., Gallagher, S.J., 2007. Marine geology of the Quaternary Bass Canyon system, southeast Australia: a cool-water carbonate system. Marine geology 237, 71–96. Mountjoy, J.J., Barnes, P.M., Pettinga, J.R., 2009. Morphostructure and evolution of submarine canyons across an active margin: Cook Strait sector of the Hikurangi Margin, New Zealand. Marine Geology 260, 45–68. Oliveira, A., Santos, A.I., Rodrigues, A., Vitorino, J., 2007. Sedimentary particle distribution and dynamics on the Nazaré canyon system and adjacent shelf (Portugal). Marine Geology 246, 105–122. Popescu, I., Lericolais, G., Panin, N., et al., 2004. The Danube submarine canyon (Black Sea): morphology and sedimentary processes. Marine Geology 206, 249– 265. Posamentier, H.W., 2003. Depositional elements associated with a basin floor channel-levee system: case study from Gulf of Mexico. Marine and Petroleum Geology 20, 677–690. Rangin, C., Huchon, P., Le Pichon, X., Bellon, H., Lepvrier, C., Roques, D., Hoe, Nguyên Dinh, van Quynh, Phan, 1995. Cenozoic deformation of central and south Vietnam. Tectonophysics 251, 179–196.

Sawyer, D.E., Peter, B., Flemings, R., et al., 2007. Seismic geomorphology, lithology, and evolution of the late Pleistocene Mars-Ursa turbidite region, Mississippi Canyon area, northern Gulf of Mexico. AAPG Bulletin 91 (2), 215–234. Shen, X.J., 1987. Mechanism of the thermo-tectonic evolution of the uplift of the Tibetan Plateau. Journal of Geodynamics 8, 55. Shepard, F.P., 1981. Submarine canyons: multiple causes and longtime persistence. AAPG Bulletin 65, 1062–1077. Sprague, A.R., Sullivan, M.D., Campion, K.M., et al., 2002. The Physical Stratigraphy of Deep-Water Strata: A Hierarchical Approach to the Analysis of Genetically Related Elements for Improved Reservoir Prediction. American Association of Petroleum Geologists Annual Meeting abstracts, Houston, Texas, pp. 10–13. Stow, D.A.V., Mayall, M., 2000. Deep-water sedimentary systems: new models for the 21st century. Marine and Petroleum Geology 17, 125–135. Su, M., Li, J.L., Jiang, T., et al., 2009. Morphological features and formation Mechanism of Central Canyon in the Qiongdongnan Basin. Marine Geology and Quaternary Geology 29 (4), 85–93, in Chinese with English abstract. Sun, Z., Zhou, D., Zhong, Z.H., Zeng, Z.X., Wu, S.M., 2003. Experimental evidence for the dynamics of the formation of the Yinggehai basin, NW South China Sea. Tectonophysics 372, 41–58. Tapponier, P., Peltzer, G., Armijo, R., 1986. On the mechanics of the collision between India and Asia. Geological Society Special Publication 19, 115. Tapponnier, P., Peltzer, G., Ledain, A.Y., et al., 1982. Propagation extrusion tectonics in Asia: new insights from simple experiments with plasticine. Geology 22 (4), 611–616. Taylor, B., Hayes, D.E., 1983. Origin and history of the South China Sea basin. In: Hayes, D.E. (Ed.), The Tectonic and Geologic Evolution of Southeast Asian Seas and Islands, Part 2, vol. 27. American Geophysical Union Geophysical Monograph, pp. 23–56. Vail, P.R., Mitchum, R.M. Jr., Thompson, S. III, 1977. Seismic stratigraphy and global changes of sea level: Part 2 – The depositional sequences as a basic unit for stratigraphic analysis. In: Payton, C.E. (Ed.), Seismic Stratigraphy Applications to Hydrocarbon Exploration, vol. 26. Mem. Am. Assoc. Petrol Geol, pp. 63–81. Van Weering, T.C.E., De Stigter, H.C., Balzer, W., Epping, E.H.G., Graf, G., Hall, I.R., Helder, W., Khripounoff, A., Lohse, L., McCave, I.N., Thomsen, L., Vangriesheim, A., 2001. Benthic dynamics and carbon fluxes on the NW European continental margin. Deep-Sea Research Part II 48, 3191–3221. Wang, C.S., Ding, X.L., 1998. The new researching progress of Tibet plateau uplift. Advance in Earth Sciences 13 (6), 526–532, in Chinese with English abstract. Xie, X.N., Müller, R.D., Li, S.T., Gong, Z.S., Steinberger, B., 2006. Origin of anomalous tectonic subsidence along the northern South China Sea Margin and its relationship to dynamic topography. Marine Petroleum Geology 23 (7), 745– 765. Xie, X.N., Müller, R.D., Ren, J.Y., et al., 2008. Stratigraphic architecture and evolution of the continental slope system in offshore Hainan, northern South China Sea. Marine Geology 247, 129–144. Yuan, S.Q., Lü, F.L., Wu, S.G., et al., 2009. Seismic stratigraphy of the Qiongdongnan deep sea channel system, northwest South China Sea. Chinese Journal of Oceanology and Limnology 27 (2), 250–259. Zhong, D.L., Ding, L., 1996. Rising process of the Qinghai-Xizang (Tibet) Plateau and its mechanism. Chinese Science Bulletin 39 (4), 369–379.