Seismic geomorphology and depositional system of delta and terminal fan: A case study of the Neogene Shawan Formation in the Chepaizi Uplift, Junggar Basin, China

Seismic geomorphology and depositional system of delta and terminal fan: A case study of the Neogene Shawan Formation in the Chepaizi Uplift, Junggar Basin, China

Accepted Manuscript Seismic geomorphology and depositional system of delta and terminal fan: A case study of the Neogene Shawan Formation in the Chepa...

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Accepted Manuscript Seismic geomorphology and depositional system of delta and terminal fan: A case study of the Neogene Shawan Formation in the Chepaizi Uplift, Junggar Basin, China Yanlei Dong, Mengyu Zhang, Xiaomin Zhu, Qiang Jiang, Lei Guo, Minpeng Wei PII:

S0264-8172(16)30344-0

DOI:

10.1016/j.marpetgeo.2016.10.006

Reference:

JMPG 2699

To appear in:

Marine and Petroleum Geology

Received Date: 31 January 2015 Revised Date:

17 August 2016

Accepted Date: 4 October 2016

Please cite this article as: Dong, Y., Zhang, M., Zhu, X., Jiang, Q., Guo, L., Wei, M., Seismic geomorphology and depositional system of delta and terminal fan: A case study of the Neogene Shawan Formation in the Chepaizi Uplift, Junggar Basin, China, Marine and Petroleum Geology (2016), doi: 10.1016/j.marpetgeo.2016.10.006. 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.

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Seismic Geomorphology and depositional system of Delta and terminal fan: A Case Study of the Neogene Shawan Formation in the

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Chepaizi Uplift, Junggar Basin, China

DONG Yanlei1,2, , ZHANG Mengyu1,2, ZHU Xiaomin1,2

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JIANG Qiang1,2, GUO Lei1,2, WEI Minpeng1,2

1. College of Geosciences, China University of Petroleum, Beijing 102249, China 2. State Key Laboratory of Petroleum Resources and Prospecting, China University of Petroleum, Beijing 102249, China

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* Email:[email protected],+86-10-18911226755

Abstract: The mainpurpose of this article is to demonstrate the utility of stratal slice images for exploring the sequence stratigraphy and sedimentology of complex depositional systems. A seismic sedimentological study was performed to map sediment dispersal characteristics of the Neogene Shawan Formation in the Chepaizi Uplift of the Junggar Basin, China. The Chepaizi

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Uplift is developed on the Carboniferous igneous rock basement that lies at the western boundary of the Junggar Basin. The data sources primarily include lithology, well-logging and seismic data. In the main target strata, the Neogene Shawan Formation can be divided into three fourth-order sequences (SQN1s1, SQN1s2, and SQN1s3), and the sequence SQN1s1 is subdivided into three

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fifth-order sequences (SQN1s11, SQN1s12, and SQN1s13). Based on the established fine-sequence

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stratigraphic framework, the sedimentary facies types have been identified, they are shallow braided-river deltas, fan deltas, shore-shallow lakes, braided rivers, and terminal fans. Then, stratal slices have been used to clearly depict the boundaries of sedimentary facies. Accurate results have been obtained that characterize braided river channels, terminal fans, shore-shallow lake beaches, and subaqueous distributary channels in the braided-river delta front. Additionally, this seismic sedimentology study reflects variations in source area and evolution history. Keywords: seismic sedimentology; stratal slice; Neogene; Chepaizi Uplift; Junggar Basin

Introduction The Junggar Basin is located in the northern Xinjiang region, 1

covers a total

ACCEPTED MANUSCRIPT area of 13 × 104 km2 and forms an approximately triangular shape (Fig. 1A). It is surrounded by mountains, with the Zaire, Hala’alate mountains as the western boundary, the Qinggelidi and Kelameili Mountains as the northeastern boundary, and the Eren Habirga and the Bogda Mountains as the southern boundary. The Junggar

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Basin is a large-scale hydrocarbon-bearing basin characterized by complex -superimposed and formed in a compressional tectonic environment, and the central of the basin covered by the Desert (Fig. 1B).

The Chepaizi Uplift lies at the western boundary of the Junggar Basin and has a

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simple tectonic structure, which is a monocline tilted to the southeast and lifted in the northwest (Fig. 2B). The uplift is bounded by the Hongche Fault Zone in the east and

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approaches the Zaire Mountain in the west and north, with the Sikeshu Sag as the southern boundary (Fig. 1B). The favorable exploration area is approximately 3000 km2 in the Chepaizi Uplift.

Previous research indicates that the Sikeshu Sag developed two sets of hydrocarbon source rocks: coal-bearing source rocks of the Jurassic and dark

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mudstone of the Paleogene Anjihaihe Formation.. There are favorable conditions of forming massive oil and gas fields because the area has the characteristics of multiple oil sources, multiple accumulation stages, multiple oil-bearing strata, multiple

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reservoir types and multiple oil products. This study is focused on Block P10, located at the center of the Chepaizi Uplift (Figs. 1C, 1D). Oil and gas exploration activities have been conducted for many years in the

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Chepaizi area. In 2012, four “oil bright spots” were discovered in the sandstone pitchout belt of the sandgroup 2, Sha-1 Member. Wells drilled at these “oil bright spots" included C22, C27, C32 and C33, and all of them produced high-yield industrial oil flow. Additionally, oil tests indicated daily oil production of 2.35 m3 from Paleogene strata (1955.6–1958.8 m interval) in Well C29 which revealed the significant oil-bearing prospects of Block P10. To rapidly implement the favorable target, 3-D data were collected from Block P10 in 2012 and covered a full-coverage area of 480 km2. In 2013, a number of exploration wells (Su1, Su2, Su3, Su1-x1, Su101, and Su1-3) were drilled, however, oil and gas breakthroughs were not 2

ACCEPTED MANUSCRIPT achieved from Neogene strata in any of these wells, and questions related to the distribution of sand bodies must be made clear. A large number of studies have been conducted on the sequences and sedimentary facies types in the Chepaizi area of the Junggar Basin. Zhang et al.

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(2008) analyzed drilling, logging and seismic data and they suggested that braided rivers, shallow braided-river deltas front, and shallow lakes are the major types of sedimentary facies that developed in this area. Zhao et al. (2010) divided the Shawan Formation into one second-order sequence and two third-order sequences. In

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sequence I, the braided-river delta developed in the most of the study area, whereas in sequence II, a major lake expansion occurs, and braid deltas developed at the lake

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margin. Su et al. (2010) studied the provenance of the Neogene Shawan Formation in the Chepaizi Uplift and indicated that two major provenance systems occur in the northwest and northeast. Zhong et al. (2010) studied depositional characteristics and proposed the following sedimentary facies types: gentle-slope fan delta, shallow braided-river delta and shore-shallow lake beach bar. Additionally, these authors

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analyzed the planar distribution characteristics of each sandgroup and summarized the depositional model of the Shawan Formation. Liu (2010) investigated depositional characteristics of the Shawan Formation in the Chepaizi area and proposed that the

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major sedimentary facies types are braided-river delta front and shore-shallow lake deposits. Yang et al. (2011) discussed identification characteristics of sequence boundary and studied depositional characteristics of the Neogene Shawan Formation;

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the major sedimentary facies are braided-river delta and shore-shallow lake. Yang et al. (2012) analyzed the provenance of the Shawan Formation in the Chepaizi area and suggested that two source areas have been developed, i.e., Eren Habirga Mountain in the southwest and Zaire Mountain in the northwest. The southwestern provenance extends for a longer distance and involves a wider range, and the major sedimentary facies types are fan delta, braided-river delta, and shallow lacustrine deposits. Several previous studies have been completed on the sequence stratigraphy and sedimentary system in the Chepaizi area( 人名及时间,张梦瑜?). Despite extensive work on sedimentary systems, such work has not been able to provide detailed 3

ACCEPTED MANUSCRIPT characterizations of thin sand bodies (meters to dozens of meters). The ability to truly characterize such thinly bedded reservoirs is problematic when relying only on drilled well data and conventional seismic. Seismic geomorphology and sedimentology are incomparably superior in depicting thin sand bodies (Posamentier,2003; Zeng et al,

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1998b; Zeng and Hentz, 2001b, 2004; Gee et al., 2007). The analysis is based on the common observation that depositional systems has a broader lateral extent than vertical thickness. The present study takes full advantage of seismic geomorphology and employs the techniqueof stratal slicing,, conducted the seismic geomorphology

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analysis on the Shawan Formation in Block P10, and a detailed depiction of the target strata has been performed to identify the types of sedimentary facies, to clarify the

zones in the study area.

1. Data and workflow

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distribution pattern of favorable sand bodies, and to predict favorable exploration

The background data of the study area has more than 30 drilling wells. The

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locations of the data used in the study area in Figure 1D. Post-stack 3-D seismic volumes are characterized by bandwidth of 10–100 Hz, with a dominant frequency of approximately 40 Hz. The signal-to-noise ratio is

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relativelt high. An excellent well-to-seismic tie was obtained using synthetic seismograms from 18 local wells. Additionally, seismic data interpretation and Stratal

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slice preparation were performed using the software of Landmark and Paleoscan. The research process of seismic geomorphology studies is as follows: firstly, a

fine sequence stratigraphic framework is established; secondly, the major depositional systems developed in the study area are analyzed according to lithology and well-logging data in combination with the depositional background of regional tectonics; thirdly, the boundary of sedimentary facies and the distribution characteristics of reservoir sand bodies are depicted using the strata slicing technique.

2. Geological settings The Chepaizi area is located on the hinge wall of the Hongche fault belt. Permian 4

ACCEPTED MANUSCRIPT strata were not developed, thin Triassic and Jurassic strata remained in local areas, and Cretaceous and Tertiary strata overlap deposits on Carboniferous igneous basement (Fig. 3). Overall, the formation and evolution of the Chepaizi area in the

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Junggar Basin can be divided into three stages (He et al., 2008).

2.1.1 Intense uplifting stage from Late Carboniferous to Jurassic

The Junggar Basin was a intermontane basin. At the end of the Carboniferous, orogeny in the northwest of the basin led to continuous uplifting of the West Junggar

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fold belt and nappe movement towards the southeast. Because of the barrier of the North Tianshan orogenic belt, the entire southwestern area was intensively uplifted

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and formed the Chepaizi Uplift. In addition, the Hongche Fault occurred at the front of the uplift, with eastward extrusion and thrusting. Because the Hongche Fault had high-angle and short nappe movement distance, the Chepaizi Uplift mainly underwent vertical uplift and erosion at the late stage.

The basin formed until the Permian sediments deposited, so the base of Permian

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marks the basin-forming phase. During the Permian-Jurassic (late Hercynian Age to early Yanshanian Orogeny), the Chepaizi Uplift continued to uplift, resulting in the loss of Permian, Triassic, and Jurassic strata in themost area. The activity of the uplift

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was especially intense with fault development during the Indosinian-Yanshanian Orogeny. A number of small fault sags were formed in parts of the northeastern areas of the Chepaizi Uplift, with relatively thin Upper Triassic and Middle-Lower Jurassic

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deposits. During the same period, the Hongche Fault continuously underwent intense activity. Because of the relatively low tectonic elevation, thin Permian, Triassic, and Jurassic strata were still deposited in parts of the Hongche fault belt.

2.1.2 Slow subsidence stage from Cretaceous to Paleogene From the Early Cretaceous, the Chepaizi uplift zone underwent slow differential subsidence. Overall, subsidence only occurred at a relatively low rate of subsidence in the eastern area of the uplift zone, where thin Cretaceous strata were deposited. The western area remained uplifted and received no Cretaceous deposits. From the 5

ACCEPTED MANUSCRIPT Paleogene, the activity of the Chepaizi Uplift was still dominated at low rate of subsidence, and differential subsidence became more obvious. The subsidence only occurred in a small range in the southeastern area associated with thin deposits of Paleogene strata. Vast areas in the middle-west of the Chepaizi Uplift remained

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denuded and lacked Paleogene strata.

2.1.3 Rapid subsidence stage from Neogene to Quaternary

Since the Neogene, the Himalayanian Orogeny has caused a strong uplift of the

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North Tianshan, and the northward thrusting resulted in flexural subsidence in the southern Junggar Basin. The basin tilted southward, and the North Tianshan piedmont

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foreland basin began to develop. As part of the foreland basin, the Chepaizi Uplift rapidly subsided at a high rate of subsidence, too, but the Shawan Formation was not deposited in the northeastern regions of the Chepaizi Uplift. After that, the subsidence of the Chepaizi Uplift continued over a larger range at high rate of subsidence until a deepening-upward succession was deposited with the thick Neogene Taxihe

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Formation, Dushanzi Formation, and Quaternary strata. 2.2 Sedimentary environment

The sedimentary evolution process of the Chepaizi area is summarized below.

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Following the late Indosinian Orogeny, Chepaizi began to receive deposits. The coarse clastic deposits can be seen in the Early Jurassic, such as alluvial fans and fluvial conglomerates; during the middle stage, the tectonic uplifting-subsidence

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activitie mainly produced fluvial-deltaic coarse clastic deposits, with shore-shallow lake fine clastic deposits in the southern area. The influence of the Yanshanian Orogeny caused the study area to be extruded and uplifted. Because of denudation, Early Jurassic

conglomerates strata were only remained in local valley areas.

Cretaceous strata were generally "thin in the west and thick in the east." During the Early Cretaceous, lowstand fan sand bodies were developed; in the mid-late stage, rapid expansion of lake levels and relatively insufficient sediment supply promoted the dominance of mudstone deposits, and the reservoirs were formed by beach sand bodies. Because of the intensive activity of the late Yanshanian 6

ACCEPTED MANUSCRIPT Orogeny, the study area again experienced tectonic extrusion, uplift, and denudation, which resulted in residual Cretaceous strata only in the eastern area. During the Paleogene period, the tectonic activity was dominated by vertical uplift-subsidence, and deposits were only accommodated in a small range in the

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southeastern area. During the depositional stage of the Shawan Formation, the deposits spread over the entire study area, with thin deposits in the northwest and thicker deposits in the southeast, which overlapped layer by layer. This depositional stage can be subdivided

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into three depositional phases. (1) Depositional stage of Member One of the Shawan Formation: A wide range of fan-delta thick-bedded conglomerate-sandstone coarse

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clastic deposits was developed from two source areas: Zaire Mountain in the northwest and Eren Habirga Mountain in the southwest. (2) Depositional stage of Member two of the Shawan Formation: The elevation difference in the paleo-topography and supply of sediment were reduced, the scale of the fan-delta body was significantly diminished, and wave-modified beach sandstone deposits in

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lakes were developed. (3) Depositional stage of Member three of the Shawan Formation: The water body became shallower, and shore-lake brown-mudstone deposits were primarily developed in an oxidizing environment (Fig. 4).

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2.3 Reservoir characteristics

Previous research indicates that the Sikeshu Sag developed two sets of hydrocarbon source rocks: coal-bearing source rocks of the Jurassic and dark

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mudstone of the Paleogene Anjihaihe Formation. There are favorable conditions of forming massive oil and gas fields because the area has the characteristics of multiple oil sources, multiple accumulation stages, multiple oil-bearing strata, multiple reservoir types and multiple oil products.

3. Sequence stratigraphic framework Seismic geomorphology studies are based on the establishment of a fine sequence stratigraphic framework (Abdullayev, 2000). The study of defining and analyzing sequence stratigraphic architecture includes several approaches. Seismic 7

ACCEPTED MANUSCRIPT lines that crossed the Chepaizi uplift were used to perform initial seismic interpretation of sequence stratigraphy frameworks. In seismic lines along the uplift margins, surfaces of seismic onlap, offlap, downlap, toplap, and truncation were recognized. Secondly, more than 25 well-calculated synthetic seismograms were used

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to establish the relationships between the well log and core-derived interpretations of lithology and the seismic sequences and surfaces (Fig.5). Third, a series of

stratigraphic strike- and dip-oriented wireline-log correlations were conducted basing on wireline correlation integrated with seismic data, which establish the sequence

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stratigraphy framework for further detailed depositional research.

Many studies on sequence stratigraphy were performed in Chepaizi Uplift (Chen

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et al., 2008; Zhao et al., 2010; Liu et al., 2010; Yang et al., 2011). This study comprehensively analyzes lithological, seismic and logging data in combination with the characteristics of tectonic evolution, sedimentary sequences and cyclical climate change. A new stratigraphic sub-division scheme is proposed. The Neogene Shawan Formation is divided into three fourth-order sequences (SQN1s1, SQN1s2 and SQN1s3).

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The sequence SQN1s1 is further divided into three fifth-order sequences (SQN1s11, SQN1s12 and SQN1s13) (Fig. 6).

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3.1 Stratigraphic surface characteristics

Sequence stratigraphic surfaces help to build the chronostratigraphic framework for the sedimentary succession under analysis. Such surfaces can be identified on the

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basis of several criteria, including (1) the nature of the contact (conformable or unconformable); (2) the nature of depositional systems that are in contact across that surface; (3) types of stratal terminations associated with that surface; and (4) depositional trends that are recorded below and above that stratigraphic contact (Octavian, 2005). For sequence divisions, stratigraphic surfaces are first determined in the seismic cross-section according to the stratal termination (definitions from Mitchum, 1977). The characteristics of onlap and truncation are typical in the study area. Truncation is 8

ACCEPTED MANUSCRIPT termination of strata against an overlying erosional surface, whereas onlap is termination of low-angle strata against a steeper stratigraphic surface. In the seismic cross section, significant truncation can be observed below SB1 (green arrows in Fig.7). Additionally, the major seismic reflection termination patterns above SB1 to

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SB6 are onlap (red arrows in Fig. 7) and reflect the process of sediment area gradually enlarge from SQN1s11 to SQN1s3. Thses six strapraphic surfaces can be tracked in the entire survey.

Then the change of lithology, well-logging data and depositional systems should

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be considered to define the stratigraphic surfaces. Fig.6 reflects the above characteristics, such as below SB2, is mainly the thick-bedded gery-yellow sandy

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conglomerat, but above SB2, is mainly the mudstone interbedded fine sandstone. Well-logging curve transfer from the box-shaped to the serrate straight line. The deposotional system is also change from braided delta to the lacustrine. 3.2 Sequence stratigraphic characteristics 3.2.1 SQN1s11

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The distribution of SQN1s11 is a sequence thickens to the southeast. SQN1s11 is only distributed in the south of the study area and pinchout in the north of well Su2. Lithologically, the sequence is mainly composed of thick-bedded grey-yellow sandy

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conglomerate, light-gray fine sandstone, and sand % is more than 85%. The well-log curve shows a block pattern (Fig. 6, Fig. 8A).

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3.2.2 SQN1s12

The distribution characteristics of SQN1s12 are similar to those of SQN1s11, with

thick strata in the south and thin in the north. This sequence is widely distributed across the entire study area, with a maximum thickness of 80 m and minimum thickness of 25 m. Lithologically, the sequence

are mainly composed of thick

muddy intervals and silty mudstone with thin-bedded fine sandstone and mud % is more than 90%. The well-log curve displays a relatively flat spontaneous potential (SP) baseline with high Gamma ray (GR) and low Resistivity log (RT) (Fig. 6, Fig. 8B). 9

ACCEPTED MANUSCRIPT 3.2.3 SQN1s13 The distribution of SQN1s13 thickens to the east. The maximum thickness is 35 m, and the minimum is 10 m. Lithologically, SQN1s12 is mainly composed of thin-bedded light-gray fine sandstone and mudstone-silty mudstone. Sandy sediments

shape (Fig. 6,

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account for more than 50% of the succesion. The well-log curve exhibits a block Fig. 8C).

3.2.4 SQN1s2

The distribution of SQN1s2 is a sequence thickens to the south. SQN1s2 is widely

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distributed across the entire study area, with a maximum thickness of 40 m and minimum thickness of 25 m. Lithologically, SQN1s2 is mainly deposited with

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interbedded light-gray fine sandstone and silty mudstone-mudstone. Sandy sediments account for approximately 30% of the total thickness and constitute a vertical sedimentary sequence with more mud and less sand. The well-log curve shows smooth finger-like shape for sandstone and a flat or slightly serrate straight section for mudstone and silty mudstone (Fig. 6, Fig. 8D).

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3.2.5 SQN1s3

The distribution pattern of SQN1s3 is generally consistent with that of SQN1s2. SQN1s3 is widely distributed throughout the study area, with a maximum thickness of

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280 m and minimum thickness of 30 m. Lithologically, the sequence strata are composed of thick muddy intervals with fine sandstone. Sandy sediments account for approximately 10% of the succession. The well-log curve shows a large flat intervals

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with serrate linear log (Fig. 6, Fig. 8E).

4. Depositional system analysis based on well data This study analyzes the

depositional system of the Neogene Shawan Formation

through a comprehensive analysis of the geological settings (tectonic history, sediment supply and climate) of the Chepaizi area using lithology, sedimentary succession, well-logging and seismic data. The following depositonal system types are developed in the study area: shore-shallow lake, fan delta, shallow braided-river 10

ACCEPTED MANUSCRIPT delta, and terminal fan. The depositional characteristics of the major sedimentary facies

(including

lithology,

sedimentary

succession,

sandstone/strata

ratio,

andwell-logging curve) are summarized in Table 1 and Fig. 9. 4.1 Shallow braided-river delta

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Shallow braided-river delta is the main type of depositional systems in the study area. Shallow braided-river delta developed in many basins, such as, the Holocene Guadalupe delta in the US and Songliao, Ordos and Junggar Basin in China (Donaldson, 1974; Tye,1989; Zou et al., 2008; Zhu et al., 2008, 2012, 2013; Liu et al.,

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2011; Xu et al., 2013). In Chepaizi Uplift, the main depostional element is a shallow braided-river delta front, which can be subdivided into inner and distal front. The

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delta front is associated with slumps and turbidites in the prodelta environment or in the lake center (Smith, 1995; Feng et al., 2010).

The inner front of the shallow braided-river delta is situated between average dry season and wet season water level, is dominated by river process.

In the inner front,

the scoured base is obvious, and an intermittent upward-fining succession is

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developed above the sourced base. Typical sedimentary structures include small- to medium-sized wedge-shaped cross bedding and parallel bedding with vertical burrows. The sedimentary facies include subaqueous distributary channels and

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subaqueous distributary interchannels.

The distal front of the shallow braided-river delta is located between

average

dry season water level and wave base level. It is dominated by river process too, but

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lake wave exert more impact than in the inner front. The lithological composition mainly includes grayish-green and grayish-black mudstone and siltstone-muddy siltstone. Positive, complex, or upward-coarsing succession are developed, and the typical sedimentary structures include small ripple laminations and wavy bedding that contain horizontal burrows. The major sedimentary facies include subaqueous distributary channels and subaqueous distributary interchannels, too. 4.1.1 Front subaqueous distributary channel The subaqueous distributary channel is the reservoir which favorable for hydrocarbon accumulation and is the important exploration target. Because of the 11

ACCEPTED MANUSCRIPT gentle basin floor, the interactions of fluvial inout and basin reworking processes are particularly important during the long-distance propogation towards the lakeshore (Reading, 1996). The tide-wave energy is reduced, which increases the prominence of the fluvial process at the delta front. In addition, because of the shallow water depth,

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the lake water body causes no significant backwater in the river, resulting in dispersed currents. Therefore, the shallow delta has well-developed subaqueous distributary channels with frequent bifurcation and diversions, which forms a unique, well-developed

sedimentary facies of subaqueous distributary channels.

channel

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In the study area, the lithological composition of the subaqueous distributary mainly consists of fine sandstone and siltstone. There are small wedge-,

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wavy- or trough cross-bedding and structureless bedding, with a small scoured base that can be observed obviously at the bottom of the channels. Natural gamma ray curves show bell- and blocky-shaped patterns (Fig. 9A). The seismic facies of the shallow braided-river delta subaqueous distributary channel is moderate- to high-amplitude/moderate

continuity/subparallel

facies

and

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moderate-amplitude/moderate- to high-continuity/foreset seismic facies, and the amplitude is negative (red color) (Fig. 9A’). 4.1.2 Front subaqueous distributary interchannel

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The front subaqueous distributary interchannel has fine-grained sediments, and during delta propogation, a series of wedge-shaped muddy deposits are formed between the subaqueous distributary channels. The sediments mainly consist of brown,

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grayish-green and gray mudstone with siltstone andfine sandstone (Fig. 9A). Sandy deposits mostly result from the subaqueous crevasse sub-deltas and deposition of the riverbed during the flood season, and the vertical sedimentary sequence is sand wrapped by mud.

In the subaqueous distributary interchannel, sandstones commonly develop horizontal bedding, lenticular bedding, wave bedding, and highly bioturbated structures that are associated with intense bioturbation. The gamma ray logs show an extremely low to low amplitude or a slightly serrated flat pattern. The seismic facies of the shallow braided-river delta subaqueous distributary interchannel facies has a 12

ACCEPTED MANUSCRIPT moderate to weak amplitude/moderate to poor continuity/ subparallel seismic facies, but the amplitude is positive (black color) (Fig. 9A’). 4.2 Fan delta The fan delta front commonly occurs in shallow water areas between the

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shoreline and normal wave base where flluvial interact with waves and tides (McPherson, 1987; Lin et al.,2001; Liu et al., 2008). The fan delta front

is

subdivided into several facies, including a subaqueous distributary channeland distributary

interchannel.

The

fan-delta

front

exhibits

moderate

to

high

4.2.1 Front subaqueous distributary channel

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amplitude/moderate continuity/foreset seismic facies (Fig. 9B’).

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The subaqueous distributary channel deposit is the underwater extension of the distributary channels that form in the plain environment.

The subaqueous distributary channels developed in SQN1s3 within well Su2 are mainly composed of fine sandstone and argillaceous sandtone. The single-bed thickness is approximately 4 m. The diagenesis is weak, and the rocks are mainly

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fine-grained, well-sorted and it would consist of subangular to angular clasts with argillaceous matrix. Parallel bedding, tabular cross bedding, and trough cross bedding are developed in an obvious upward-fining succession. The well-logging curves show

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a combination of apparently bell-blocky shapes (Fig. 9B). 4.2.2 Front subaqueous distributary interchannel The subaqueous distributary interchannels are deposited in a relatively stable

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low-energy environment. The lithological composition mainly consists of grayish-green mudstone with thin-bedded silty mudstone that shows wavy bedding, horizontal bedding, and lenticular bedding. The spontaneous potential curve (SP log) of this facies is smooth and nearly a straight line, and resisitivity (RT log) is a low amplitude of abnormalities (Fig. 9B). 4.3 Shore-shallow lake Because of the small transversal deltas are commonly developed in gentle slope areas near the lake margin, the fluviation is weak and sediments carried into the lake basin along the transversal direction are easily modified through lake waves and 13

ACCEPTED MANUSCRIPT shore currents. As a result, sediments move laterally along the lake shoreline to form beach at the lateral margin of the delta (Zhu et al., 1994; Xiang et al., 2008). 4.3.1 Beach Representative shore-shallow lake beach bar facies, such as the SQN1s12 deposit

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in well Su1-x1, are lithologically characterized by brownish-yellow and grey fine sandstone. The single-bed thickness is 3–4 m, the single-well cumulative thickness is 7 m, and the vertical sequence shows a upward-coarsing succession that is finer in the lower part and coarser in the upper part. The sandstone thickness accounts for

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10–30% of the entire succession thickness. In the spontaneous potential curve, the beach mostly corresponds to a symmetric finger pattern (Fig. 9C).

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In the seismic cross-section, the beach corresponds to mound reflection characterized by a flat bottom and bulged top. 4.3.2 Lacustrine mud

(Fig. 9C’).

Shore-shallow lacustrine mud is formed near the wave base with weak hydrodynamic force and low energy. It mainly consists of gray mudstone, which

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develops horizontal laminations and ripple laminations. For example, shore-shallow lacustrine mud in the upper part of SQN1s12 in well Su1-x1 are mainly composed of brownish-red mudstone with a small amount of silty mudstone. The well-log curve

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shows a flat and straight baseline (Fig. 9C). Shore-shallow lacustrine mud mainly exhibits moderate amplitude/moderate to high-continuity/subparallel sheet seimic

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facies (Fig. 9C’).

4.4 Terminal fan

Terminal fan is to describe fluvial distributary systems in which the drainage is

wholly dissipated internally via a distributary network from which no water escapes by surface flow to a take or the sea during normal conditions (Kelly and Olsen, 1993). Terminal Fans can be subdivided into single entry systems (supplied from a point source) and multiple entry systems (Mukerji, 1975, 1976; Glennie, 1970), which consist mainly of two processes including the break-up of a stream into a network and 14

ACCEPTED MANUSCRIPT subsequent water loss through evaporation and infiltration (Kelly and Olsen, 1993). Based on the modern sedimentation, the terminal fans can be subdivided into feeder, distributary, and basinal zones (Kelly and Olsen, 1993; Rhee et al.,1993). The commonality of ancient terminal fan systems has been noted by Friend

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(1978). Many units are thick (hundreds to thousands of (metres) and accumulated in relatively small basins < 105 km 2) near to uplifting mountain sources. Terminal fan sequences are most readily distinguished from other fluvial systems by consistent downstream trends in various sedimentary parameters. The grain size and scale of

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individual channel sandstone bodies will show a general decrease downstream (Friend, 1978).

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The acreage and size of the river are reduced because of evaporation, low precipitation, and high seepage discharge. Thus, terminal fan deposits commonly develop in water-deficient arid and semi-arid regions, and two processes are involved: the river channel branches into a network and river system disappears through evaporation and seepage (Rhee et al., 1993; Sean et al., 1993; Sadler et al., 1993;

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Zhang et al., 1999; Zhu et al., 1999, 2007; Stuart et al., 2004; Pitambar et al., 2012). During Neogene period, the main sedimentary background in research area was shore-shallow lacustrine. During sedimentary stage of Member one of Shawan

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Formation, climate is moist with plentiful debris supply. While it was principally developed shallow braided river delta during sedimentary stage of Member two of Shawan Formation with arid climate and receding lake, distribution range of alluvial

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plain facies continuously extend. The major lithology was brown-red mudstone and silty mudstone. During sedimentary stage of Member three of Shawan Formation, the dominating deposition was continental alluvial plain facies as coarse clastic supply decrease (Zhong, 2010). In the study area, the terminal fan deposit is mainly developed in the eastern part in SQN1s3, and it can be subdivided into fluvial trunk upstream, distributary channels and terminal distributary channels. Fluvial trunk upstream has a similar lithological composition to the river channel, although it has a slightly finer grain size and is 2–5 m thick and several hundred meters wide. 15

Distributary channels is a

ACCEPTED MANUSCRIPT combination of the river channel sand body and sheetflood sand body, and it is less than 2 m thick and tens to hundreds of meters wide.

5. Seismic geomorphology study

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The following steps were included in the process of seismic geomorphology. Firstly, 6 horizons that can be correlated on both wireline logs and seismic reflections were selected and interpreted as reference surfaces. Secondly, a stratal-slice volume

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was generated for this study by flattening the 6 reference horizons in the Neogene Shawan Formation. Next, One hundred stratal slices are generated by using Paleoscan software according to the fine interpretation of each sequence boundary. The final

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step was to interpret each depositional sequence generated through integration of lothlogy, wireline logs (Van Wagoner et al., 1990; Mitchum et al., 1991) and stratal slices (Zeng et al.,1998). 5.1 Stratal slice preparation

Seismic slicing is one of the key techniques in seismic geomorphology, and it has

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played an increasingly important role in oil and gas exploration (Zeng et al., 1998, 2007; Miall et al., 2002). Currently, the commonly used seismic slices include time slices, horizon slices, and Stratal slices. In the Junggar Basin, sequences of the

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Neogene Shawan Formation in the Block P10 belong to a monoclinal slope. The use of the stratal slicing technique can reflect the areal distribution of depositional

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elements, but the slices used in other methods tend to cross the reference time surface (Fig. 10).

One hundred Stratal slices are prepared using Paleoscan (a software package)

according to the subtle interpretation of each sequence boundary. In total, stratal slices 11, 9, 10, 25, and 45 have been obtained for sequences SQN1s11 to SQN1s3, respectively (Table 2). These slices can reflect

vertical variations in seismic

attributes from the SQN1s11 to top SQN1s3. 5.2 Stratal slice calibration Prior to the interpretation of Stratal slices, the exact lithological properties 16

ACCEPTED MANUSCRIPT represented by the seismic events should be clarified. Therefore, we must examine the relationship between lithological and impedance in the study area. Fig. 10 presents the gamma ray versus impedance cross-plot for well C32. The Y-axis represents the gamma ray signal, the X-axis is the impedance, red and yellow points represent high

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sand %, and blue and greenpoints represent high mud%. Sandstone is charactered with low gamma ray, whereas the mudstone mostly features high gamma ray. At the boundary between sandstone and mudstone, the gamma ray is from 75 to 85 API. So we can draw a conclusion that sandstone and mudstone are direct correlation with the

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gamma ray. However, the impedance of most sandstone’s points (generally are low) and impedance of most mudstone (generally are high) are overlapped in some area, so

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the impedance is not the sensitive character with the lithology (Fig. 11). In order to supply the unambiguous relationship between sandstone and mudstone, the relationship between the gamma ray and root mean square of amplitude (RMS) are discussed. The method is using the key wells to calibrate the relationship between

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lithology and RMS amplitude (Fig. 12).

For a discussion of sandstone-mudstone boundary, the reference well is C32 located in the middle-eastern part of the study area. In Fig.12, black arrow points to the fine

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sandstone interval (1630–1634 m) with daily 33 t oil production, correlate the bright yellow RMS amplitude in Fig. 14F. Green arrow points to the mudstone (1510–1540 m), correlate the blue RMS amplitude in Fig. 15F.

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Except to the lithology, the fluid accumulated in the reservoir can affect the RMS

amplitude too. But, the effect of fluid is much more weaker than the effect of lithology. Besides, although the impedance boundary is not distinct between sandstone and mudstone, most of the sandsone points’ impedence are low and RMS amplitude are high. If the sandstone which bearing the oil and gas will be the lower impedence and higher RMS amplitude. The fluid will not affect the interpretation of stratal slices. Stratal slices are interpreted according to depositional background and lithology-logging features.

Analysis of stratal slices using amplitude shows that the 17

ACCEPTED MANUSCRIPT interpretation of different sedimentary facies is highly consistent with lithology, which can truly reflect the lateral distribution of sand bodies. These data provide a good reference for subsequent interpretations of stratal slices. 5.3 Stratal slice description and interpretation

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To analyze the sedimentary facies of the Shawan Formation, one representative stratal slice is selected from each of the following sequences: SQN1s11, SQN1s12, SQN1s13, SQN1s2, and SQN1s3, and they are slice 10, 12, 26, 38 and 88. The locations of the selected slices are shown in Fig. 13.

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5.3.1 SQN1s11

Fig. 14A represent the stratal slice without interpretation, Fig. 14B is the stratal

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slice with interpretation and Fig.14C is sedimentary facies map of SQN1s11. The moderate- to high-RMS amplitude zone (>4000) is mainly distributed in the middle of the study area.

The lithology, well-logging and available data from previous research have been combined to interpret the sedimentary facies of the stratal slices. The results indicate

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that the primary source area is the southern region of the study area, which mainly developed shallow braided-river delta with progradation from southwest to northeast (a system spread over an area of ~280 Sq km ). There are three main river channels.

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The delta river channel in the southwestern area is approximately 11 km long, and the30~50 m thick and coarse grain size of the sandstone indicate the proximity of the depositional provenance and high sedimention rate. The delta river channel in the

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central and southeastern area are approximately 15 km and 18 km, respectively (Fig. 14C) (Yang et al., 2011; Zhong et al., 2009). 5.3.2 SQN1s12

Fig. 14D represent the stratal slice without interpretation, Fig. 14E is the stratal

slice with interpretation and Fig.14F is sedimentary facies map of SQN1s12. The moderate- to high- RMS amplitude zone (>4000) is mainly distributed in the northern and southeastern parts of the study area. Scattered moderate RMS amplitude area distributed in the middle of the study survey. A comprehensive assessment indicates that during the depositional period of 18

ACCEPTED MANUSCRIPT SQN1s12, the provenance is the southern part of the study area. The braided main channel is approximately 12 km long, and the range of the entire delta deposit is 120 Sq km. The distal front of the shallow braided-river delta has developed subaqueous distributary channels, and a large amount of fan-delta deposits have been developed in

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the northern area. The central and western areas are mainly covered with shore-shallow lake beach and lacustrine mud. The beaches extends in parallel to the lakeshore and their thickness are relatively thin (5~7 m). In the vicinity of the southern provenance, the beach occurs in a nearly elliptical shape with a deposition

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range of approximately 12 km2. In the northern area, the beach extends in a banded pattern with a small range of approximately 4 km2 (Fig. 14F).

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5.3.3 SQN1s13

Fig. 15A represent the stratal slice without interpretation, Fig. 15B is the stratal slice with interpretation and Fig.15C is sedimentary facies map of SQN1s13. The moderate- to high-RMS amplitude zone (>4000) is mainly distributed in the southwestern and eastern parts of the study area.

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Further analysis suggests that during the deposition of SQN1s13, the main body of the shallow braided-river delta developed in the southeastern part of the study area, and the source area was in the south. Thus, a bird-foot delta was formed, and it

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extends from south to north and spreads over an area of ~108 Sq km. The subaqueous distributary channels of the delta extend up to 9 km , and they are also extensively developed on the distal front of the delta. Additionally, two small deltas are developed

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in the southwestern and central parts of the study area, and they extend from south to north over a short distance. The channel extends for 4 km. Fewer subaqueous distributary channels are developed on the distal front of the delta (Fig. 15C). 5.3.4 SQN1s2

Fig. 15D represent the stratal slice without interpretation, Fig. 15E is the stratal slice with interpretation and Fig.15F is sedimentary facies map of SQN1s2. The moderate- to high- RMS amplitude zone (>4000) is mainly distributed to the west of well Su3 in the vicinity of well P4 in the western area as well as to the north of well Su2. 19

ACCEPTED MANUSCRIPT A comprehensive analysis shows that during the early deposition of SQN1s2, the source supply from the western region and the northern region. The shallow braided-river delta mainly developed in the south, whereas delta and shore-shallow lacustrine deposits developed in the north. The water channel extends for

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approximately 16 km, and the widest area of the delta front deposit is 6 km, whereas the system spreads over ~80 Sq km. The subaqueous distributary channels are relatively well developed. In the prodelta of shallow braided-river delta, small-scaled slumps and turbidites have a scattered distribution

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5.3.5 SQN1s3

(Fig. 15F).

Fig. 16A represent the stratal slice without interpretation, Fig. 16B is the stratal

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slice with interpretation and Fig.16C is sedimentary facies map of SQN1s3. The moderate- to high- RMS amplitude zone (>4000) with a scaly distribution characteristics is mainly in the central west, whereas the zone with the streaky distribution characteristics is in the northeast.

The zone with a scaly distribution characteristics can be interpreted as the

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shallow braided delta. The zone with the streaky distribution characteristics is terminal fan. A comprehensive assessment shows that during the deposition of SQN1s3,

braided river

and terminal fan were developed in the northeastern area,

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whereas the shallow braided delta were developed in the middle and west part. The shallow braided delta extends from north to south and the channel is approximately 16 km long and covers an area of 20-40 km2. In the northeastern area, braided river

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channels are generally 20 km long. In the eastern area, the density of braided rivers is relatively high, with 3–5 rivers of 10 km width. In the western area, the density of braided rivers is relatively small at only 1–2 rivers (Fig. 16C).

6. Discussion

The study of seismic geomorphology better delineates the spatial and temporal distributions of reservoir sand bodies in the Neogene Shawan Formation of the Block P10. More details of the sandbodies can be depicted through the use of stratal slices.Stratal slices can reflect the overall distribution patterns of different 20

ACCEPTED MANUSCRIPT sedimentary facies types and depict subtle variations in sedimentary facies. For example, during the depositional stage of SQN1s3 (slice74), the braided-river delta deposits were developed in the southwest of the study area, and the spread of subaqueous distributary channels along the delta front are clearly shown in the

features of a terminal fan (SQN1s3-slice88) (Fig. 18).

7. Conclusions

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sedimentary facies map (Fig. 17). In addition, the Stratal slice shows depositional

(1) In the Junggar Basin, the formation and evolution of the Chepaizi Uplift can

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be divided into three stages: Late Carboniferous-Jurassic intensive uplifting stage, Cretaceous-Paleogene slow subsidence stage, and Neogene-Quaternary rapid

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subsidence stage.

(2) A comprehensive analysis of the study area was performed using seismic and loggingdata in combination with geological settings, which includes the tectonic evolution and sedimentary sequence,. The Neogene Shawan Formation is divided into three forth-order sequences (SQN1s1, SQN1s2, and SQN1s3). Furthermore, SQN1s1 is

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subdivided into three fifth-order sequences (SQN1s11, SQN1s12, and SQN1s13). (3) The process of seismic geomorphology studies is as follows: a fine sequence stratigraphic framework is established, major sedimentary facies types in the study

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area are analyzed according to lithology, well-logging and seimic data in combination with the depositional background of regional tectonics; and the boundary of

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sedimentary facies and distribution characteristics are depicted using the stratal slicing technique.

(4) The major sedimentary facies developed in the study area include shallow

braided-river delta, fan delta, shore-shallow lake, braided river, and terminal fan. The seismic geomorphology study method can clearly depict the boundaries of sedimentary facies, and accurate results are obtained when characterizing braided river channels, terminal fans, shore-shallow lake beach bars, and subaqueous distributary channels in braided-river delta fronts. (5) The seismic geomorphology study presented here shows that in the study 21

ACCEPTED MANUSCRIPT area, the source area experienced directional changes during the deposition of the Shawan Formation from the south to the west and north. These changes reflect a continued uplifting process of the source area of sediments in the northern part of the study area. Regarding the distribution of sedimentary facies, the southern area

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experienced a depositional evolutionary process, which is illustrated in the development of the large-scaled braided-river delta, reduction of the braided-river delta area, and disappearance of the braided-river delta. The northern work area evolution is shown in the development of small-scaled subaqueous fan delta, complete

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exposure onto land, and development of briaded river and terminal fan.

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ACCEPTED MANUSCRIPT Yang Shaochun, Meng Xiangmei, Chen Ningning, et al. Depositional characteristics of Shawan formation in Neogene of Chepaizi area, Junggar Basin, Journa l of China University of Petroleum, 2011, 35(2):20-38 (in China) Zeng, H., Henry, S. C., & Riola, J. P., 1998. Stratal slicing, part ii: real 3-d seismic

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data. Geophysics, 1998, 63(2):514-522 Zeng, H., Loucks, R. G., & Brown, L. F., 2007. Mapping sediment-dispersal patterns and associated systems tracts in fourth- and fifth-order sequences using seismic sedimentology: example from corpus christi bay, texas. Aapg Bulletin, 2007, 91(7):981-1003

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Chepaizi area of Junggar Basin. China University of Petroleum (East China), Qingdao (Master thesis), 2010

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Zhu Rukai, Wei Wei, Zhang Yundong. The study on the terminal fans and reservoir quality during Neozoic Era in Kuche down Warping Region in Tarmin Basin, Acta Sedimentologica Sinica, 1999(Supplement) :752-757 (in China) Zhu Xiaomin, Deng Xiuqin, Liu Ziliang, et al. Sedimentary characteristics and model of shallow braided delta in large-scale lacustrine: An example from Triassic Yanchang Formation in Ordos Basin[J], Earth Science Frontiers, 2013,20(2):19-28 (in China) Zhu Xiaomin, Liu Yuan, Fan Qing, et al. Formation and sedimentary model of shallow delta in 25

ACCEPTED MANUSCRIPT large-scale lake. example from Cretaceous Quantou Formation in Sanzhao Sag,Songliao Basin. Earth Science Frontiers, 2012, 19(1):89-99 (in China) Zhu Xiaomin, Xin Quanlin, Zhang Jinren. Sedimentary characteristics and models of the beach-bar reservoirs in faulter down lacustrine basins. Acta Sedimentologica Sinica,

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1994,12(2):20-28 (in China) Zhu Xiaomin, Zhang Yina, Yang Junsheng, et al. Sedimentary characteristics of the shallow Jurassic braided river delta , the Junggar Basin, Oil & Gas Geology, 2008, 29(2):244-251 (in China)

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Zou Caineng, Zhao Wenzhi, Zhang Xingyang, et al. Formation and Distribution of Shallow2water Deltas and Central2basin Sandbodies in Large Open Depression Lake Basins, Acta

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Geologica Sinica, 2008, 82(6):813-825 (in China)

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ACCEPTED MANUSCRIPT Table 1 Characteristics of the depositional system in the Neogene Shawan Formation, Chepaizi Uplift, Junggar Basin element

Subaqueous distributary Shallow braided-river delta

channel

Front

Lithology

Fining-

and siltstone

upward

Subaqueous Grayish-green distributary

and gray

interchannel

mudstone

distributary channel

Front

Subaqueous Mudstone, silty

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/

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interchannel muddy siltstone Brownish-red silty fine Coarseningsandstone and Beach upward pebbled fine Shore-shallow 0.4–2 m sandstone lacustrine Brownish-red Lacustrine mudstone and / mud muddy siltstone Gray and Fluvial grayish-yellow Finingpebbled upward, 2– trunk sandstone and 5m upstream Terminal fan sandstone FiningDistributary Brownish-red upward, siltstone and channels muddy siltstone >2 m

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Terminal fan

upward,

>45%

Well-log pattern Bell and block

<10%

Flat

>50%

Block and bell

>5 m

distributary mudstone and

Lacustrine

/ Fining-

Glutenite

Sand %

pattern

Fine sandstone

Subaqueous

Fan delta

Stacking

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system

Facies

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Depositional Depositional

<10%

Flat and straight

10–30%

Finger and funnel

<10%

Flat and straight

>30%

Bell and block

<10%

Finger

ACCEPTED MANUSCRIPT Table 2 Sequence slices of the Neogene Shawan Formation in the Block P10, Chepaizi Uplift, Junggar Basin Sequence

Number of Stratal slices

Strata 3rd order Member

4th order SQN1s3

Member Two

SQN1s2 SQN1s

Formation

25 (31–55)

SQN1s13 SQN1s1

SQN1s12

10 (21–30) 9 (12–20)

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Member One

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45 (56–100)

Three

Shawan

(Slice No.)

5th order

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SQN1s11

11 (1–11)

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Fig.1 Maps showing the: (A) Location of the Junggar Basin in China. (B) Location of the Chepaizi

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Uplift. (C) Well location of the Chepaizi uplift and the outline of 3-D seismic shown in figure 1D.

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(D) 3-D seismic survey (Block P10) and wells used in the study.

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Fig.2 Cross section showing the pre-Mesozoic tectonic profile from the Chepaizi Uplift to central

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depression. See Figure 1C for the location of the cross-section and wells.

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Fig. 3 Profile of the evolutionary history of the Chepaizi Uplift, Junggar Basin (Zhuang, 2009). Red rectangle is the work area. N2d=Neogene Dushanzi Formation; N1t=Neogene Taxihe Formation; N1s=Neogene Shawan Formation; E=Paleogene; K=Cretaceous ; J=Jurassic; T=Triassic;P=Permian;C=Carboniferous. See Figure 1C for the location of the seismic

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Fig. 4 Sedimentary facies map in Member One of Shawan Formation, Chepaizi Uplift (Xinjiang

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Oilfield, 2014)

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Fig. 5 Sequence division and synthetic seismograms of the Neogene Shawan Formation in well

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Su2, Chepaizi Uplift. See Figure 1D for the location of the seismic cross-section and well.

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Fig. 6 Sequence division scheme for the Neogene Shawan Formation, Chepaizi Uplift

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Fig. 7 Seismic reflection characteristics of sequence boundaries in the Neogene Shawan Formation, Chepaizi Uplift (Line 96896). Red arrows represent onlap, and green arrows is

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truncation. See Figure 1D for location of seismic cross-section.

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Fig. 8 Stratigraphic isopach map of thickness in the Neogene Shawan Formation, the Block 10,

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Chepaizi Uplift. A. SQN1s11, B. SQN1s12, C. SQN1s13, D. SQN1s2, E. SQN1s3.

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Fig. 9 Lithological, electrical, and seismic reflection characteristics of the key sedimentary facies. See Figure 1D for the location of the seismic cross-section and wells.

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Fig. 10 Schematic of different slicing methods with typical measuring lines in the 3D block west of well P10, Junggar Basin (Line 97892). See Figure 1D for the location of the seismic

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cross-section and well.

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Fig. 11 Cross-plot of gamma ray versus wave impedance in well C32 of the Neogene Shawan Formation in Block 10, Chepaizi Uplift, Junggar Basin. Different color points represent different lithology

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Fig. 12 Synthetic seismogram calibration of well C32 in the Shanwa Formation in Block P10,

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Junggar Basin (SQN1s12-Slice12). Black arrow points to the fine sandstone interval (1630–1634 m) with daily 33 t oil production, correlate the bright yellow RMS amplitude in Fig. 14F. Green arrow points to the mudstone (1510–1540 m), correlate the blue RMS amplitude in Fig. 15F. See Figure

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1D for the location of the seismic cross-section and well.

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Fig. 13 Location of the representative Stratal slices from the Shanwa Formation in the 3D block west of P10, Junggar Basin. See Figure 1D for the location of the cross-section and wells.

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Fig. 14 Representative Stratal slices and depositonal system maps of sequences SQN1s11 to SQN1s12 in Block P10, Junggar Basin.

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Fig. 15 Representative Stratal slices and depositional system maps of SQN1s13 to SQN1s2 in the Block P10, Junggar Basin

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Fig. 16 Representative Stratal slices and depositional system maps of SQN1s3 in the Block P10,

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Junggar Basin

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Fig. 17 Stratal slice and sedimentary interpretation of subaqueous distributary channels in the

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braided-river delta front (SQs3-Slice74).

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Fig. 18 Stratal slice and sedimentary interpretation of terminal fans in the meandering river facies (SQs3-Slice88).

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Fine sequence framework is the foundation of sedimentary facies analysis.

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Reveal high-resolution sediment dispersal characteristics of delta and terminal fan

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Seismic geomorphology study predition thin reservoirs successfully.