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Tectonic characteristics and structural styles of acontinental rifted basin: Revelation from deepseismic reflection profiles

Yuan Lia,b,*, Yannan Zhaoa,b, Zhengliang Linc, Qinlin Mad

a Key Laboratory of Earthquake Geodesy, Institute of Seismology, China Earthquake Administration, Wuhan 430071,

Chinab Wuhan Institute of Earthquake Engineering Co., Ltd, Wuhan 430071, Chinac Sinopec Geophysical Research Institute, Nanjing 210014, Chinad Exploration and Development Corporation, PetroChina, Guangzhou 510000, China

a r t i c l e i n f o

Article history:

Received 23 June 2016

Accepted 7 July 2016

Available online 25 August 2016

Keywords:

South China Sea

Continental rifted basin

Structural style

3-D seismic-reflection

Seismic geomorphology

* Corresponding author. Key Laboratory of430071, China.

E-mail address: liyuan_28@163.com (Y. L

Peer review under responsibility of Instit

Production and Hosting by Elsev

http://dx.doi.org/10.1016/j.geog.2016.07.006

1674-9847/© 2016, Institute of Seismology, Ch

Communications Co., Ltd. This is an open acce

a b s t r a c t

The Fushan Depression is a half-graben rifted sub-basin located in the southeast of the

Beibuwan Basin, South China Sea. The Paleogene Liushagang sequence is the main hy-

drocarbon-bearing stratigraphic unit in the sub-basin. Using three-dimensional (3-D)

seismic data and logging data over the sub-basin, we analyzed structural styles and sedi-

mentary characteristics of the Liushagang sequence. Five types of structural styles were

defined: ancient horst, traditional slope, flexure slope-break, faulted slope-break and

multiple-stage faults slope, and interpretations for positions, background and develop-

ment formations of each structural style were discussed. Structural framework across the

sub-basin reveals that the most remarkable tectonic setting is represented by the central

transfer zone (CTZ) which divides the sub-basin into two independent depressions, and

two kinds of sequence architectures are summarized: (i) the western multi-stage faults

slope; (ii) the eastern flexure slope break belt. Combined with regional stress field of the

Fushan Depression, we got plane combinations of the faults, and finally built up plan

distribution maps of structural system for main sequence. Also, we discussed the con-

trolling factors mainly focused on subsidence history and background tectonic activities

such as volcanic activity and earthquakes. The analysis of structural styles and tectonic

Earthquake Geodesy, Institute of Seismology, China Earthquake Administration, Wuhan

i).

ute of Seismology, China Earthquake Administration.

ier on behalf of KeAi

ina Earthquake Administration, etc. Production and hosting by Elsevier B.V. on behalf of KeAi

ss article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

g e o d e s y and g e o d yn am i c s 2 0 1 6 , v o l 7 n o 5 , 3 2 9e3 3 9330

evolution provides strong theoretical support for future prospecting in the Fushan sub-

basin and other similar rifted basins of the Beibuwan Basin in South China Sea.

© 2016, InstituteofSeismology, ChinaEarthquakeAdministration, etc. Productionandhosting

by Elsevier B.V. on behalf of KeAi Communications Co., Ltd. This is an open access article

under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

How to cite this article: Li Y, et al., Tectonic characteristics and structural styles of a continental rifted basin: Revelation fromdeep seismic reflection profiles, Geodesy and Geodynamics (2016), 7, 329e339, http://dx.doi.org/10.1016/j.geog.2016.07.006.

1. Introduction

Structural characteristic of continental rifted basin in-

fluences the process of sedimentary filling and hydrocarbon

accumulation [1e5]. It is a more useful approach to integra-

tion of geomorphology and seismic data analysis. Within the

last decade, the most logical workflow of using seismic data

follows the transition from seismic stratigraphy, to sequence

stratigraphy, to seismic geomorphology [6e10]. Seismic geo-

morphology was defined by Posamentier et al. [11] as “the

application of analytical techniques pertaining to the study

of landforms and to the analysis ancient, buried

geomorphic surface as imaged by three-dimensional (3D)

seismic data.” Therefore, seismic geomorphology, when

integrated with seismic and sequence stratigraphy, is a

powerful and effective tool for analyzing the stratigraphy,

understanding structural styles, processes and basin

evolution, and predicting the spatial-temporal distribution

of sedimentary facies under a sequence stratigraphic

framework [12].

The FushanDepression is an extensional sub-basin formed

during the Mesozoic and Cenozoic rifting located in the

southeast of the Beibuwan Basin, South China Sea [13e15].

Pervious seismic- and well-based investigations have been

mainly focused on the slope andmarginal areas of the Fushan

sub-basin [16]. As a result, slope studies have been more

extensive than that for the sub-lacustrine areas [17]. With an

increasing demand on petroleum resources in China, the

Liushagang formation has become a significant

hydrocarbon-bearing formation in the Fushan Oilfield.

Although there has been some documentation of the

tectonics, stratigraphy, sedimentology, and petroleum

exploration and development of the sub-lacustrine area, the

deep-water area is still only moderately explored and will

likely be an area for future reserve additions [18,19].

Different from a classic marine basin, there existed com-

plex structures in such a rift lacustrine depression. The

forming of the deep-water reservoir was not only determined

by unconformity style, but also the main hydrocarbon

migration phase or the paleotopography [1e3,20e22]. There-

fore, a better understanding of the sub-lacustrine structural

movement and distribution is help for further sedimentary

research and hydrocarbon exploration. However, traditional

geological research based on logging data and 2-D seismic

reflector data is hard to well understand the complex char-

acters and distributions of the sub-basin structure. The best

way to extend the well data to the entire investigation area

and further study on previously identified area is by using 3-D

seismic data [23,24]. Given this, in this study, new logging

data, three-dimensional (3-D) seismic reflection data have

been examined in the light of three main objectives: (i) inter-

preting available 3-D seismic data and few well data to

analyze the characteristics of seismic geomorphology in the

Fushan sub-basin; (ii) providing a new case using seismic

geomorphology to characterize structural styles over the sub-

basin, including the slope area and sub-lacustrine area; (iii)

mapping the structural distribution of the Paleogene Liush-

agang formation in detail and discussing the controlling

factors.

2. Regional geological setting

The Fushan Depression is a half-graben rifted sub-basin,

located in the southeast of the Beibuwan Basin, South China

Sea, with a total area of 2920 km2. It is a “dustpan” shaped

depression bounded by the Qiongzhou Strait to the north, the

Hainan Uplift to the south, the Lingao Uplift to the west and

the Yunlong Uplift to the east (Fig. 1) [13,15]. Accumulating

sediments is supplied through braided river deltas mainly

from the southern margin [18,19]. In a similar manner to

many other continental basins [20,25], it is characterized by

multiphase structural superposition of deposits and

multistage volcanic activity, and is therefore a challenging

environment to explore for hydrocarbons [13,15]. Lei et al.,

(2015) make a detail study on the Yinggehai-Song Hong

Basin before, which is an adjoining basin of the Beibuwan

Basin separating by the Lingao Uplift. The result shows that

to the east of the Yinggehai-Song Hong Basin, the structures

are closely related to rifting and oceanic spreading of the

South China Sea.

Using the sequence stratigraphic principles of Vail et al.

[26], in combination with modern sedimentology techniques

and sequence stratigraphic data (e.g. seismic reflection

characteristics, cores, well logs and geological studies), the

Paleogene unit of the Fushan Depression is divided into

three 2nd-order depositional sequences (SSQ1, SSQ2, SSQ3)

which lasted approximately 41.5 Ma [27], and the

Liushagang formation (SSQ2) can be further subdivided into

three third-order sequences (SQEls3, SQEls2, SQEls1)

(Fig. 2a). Based on the interpretation of wireline-log patterns,

lithological combinations and 3D seismic successions,

transgressive surface (ts) and maximum flooding surface

(mfs) were recognized in the SQEls2 formation.

Corresponding to the highest lake-level (Fig. 2b), the study

formation (SQEls2) formed in the biggest extension period of

the Paleogene.

Fig. 1 e a e Location of South China Sea and the Beibuwan Basin. b e Simplified geological map of the Beibuwan Basin and

location of the Fushan sub-basin. c e Geological profile across the Beibuwan Basin showing the geometrical relationships

between the various units. d e Geological map of the Fushan sub-basin.

g e o d e s y and g e o d yn am i c s 2 0 1 6 , v o l 7 n o 5 , 3 2 9e3 3 9 331

3. Material and methods

This study uses a subsurface dataset consisting of logging

data and seismic-reflection data from the Fushan oilfield

survey provided by the China National Petroleum Corporation

(CNPC) Corporation. The seismic-reflection dataset used in

this study comprises a 2D survey and a 3D survey which cover

the extensive sub-basin. The 3D seismic survey is time-

migrated, however, true thickness data are estimated and

presented here based on well data which indicates that at the

interval of interest the acoustic velocity is ca. 1750 ms m�1;

Therefore, depth and thickness was converted from millisec-

onds two-way travel time (i.e. ms TWTT) to meters; Inline and

crossline spacing is 32 m and sample rate is 2 ms. The seismic

data are zero-phase processed and displayed in this paper so

that a downward increase in acoustic impedance is repre-

sented by a positive (black) reflection event, with the converse

being the case for a downward decrease in acoustic imped-

ance. Data quality is generally excellent throughout the sur-

vey area, although basic extrusive basalts caused by the

Cenozoic volcanic activities have partly compromised the

quality of seismic data in the eastern area of the study area.

4. Interpretation and results

4.1. Structural framework across the sub-basin

4.1.1. WeE direction seismic cross sectionCentral transfer zonedFrequent multiphase tectonic and

volcanic activities occurred during the MesozoiceCenozoic

period, and generated prototypical formation of the present

sub-basin configuration. The structural evolution can be

divided into an early (Eocene to Oligocene) extensional phase

which is marked by fault bounded and rifted strata, and a late

(Miocene to recent) passive margin phase with relatively un-

structured strata, leading to two distinctive vertical structural

layers (Figs. 3 and 4). Another remarkable tectonic setting is

represented by the central transfer zone (CTZ) (Fig. 3) which

divides the sub-basin into two independent depressions (the

western Huangtong Depression & the eastern Bailian

Depression), characterized by distinct structure superposition,

palaeogeomorphology and consequent depositional systems.

During the SQEls2 period, affected by the Meitai slip Fault,

an obvious boundary generates in the western depression for

distinguishing the slope and base-of slope (basin floor) parts,

Fig. 2 e a e General stratigraphy of the Palaeogene infill of the Fushan sub-basin. The succession comprises three cycles, the

Changliu unit, the Liushagang unit and theWeizhou unit, each being interpreted as a 2nd-order depositional sequence. The

study succession represents a lowstand prograding complex as a progradational 3rd-order unit. Letter symbols:

SB ¼ sequence boundary; SSB ¼ second sequence boundary; ts ¼ transgressive surface; mfs ¼ maximum flooding surface;

FSS ¼ forward-stepping (regressive) sequence set; BSPS ¼ backstepping (transgressive) parasequence set;

APS ¼ aggradation sequence set; LST ¼ lowstand systems tract; EST ¼ extension systems tract; HST ¼ highstand systems

tract. b e Simplified relative sea-level curve represents the three extension 2nd-order cycles of the Early, Middle and Late

Palaeogene, respectively. The Lowstand Prograding Complex occupies the lowstand segment of the second cycle and forms

the maximum flooding surface of Palaeogene sedimentation, corresponding to the largest curve radian.

g e o d e s y and g e o d yn am i c s 2 0 1 6 , v o l 7 n o 5 , 3 2 9e3 3 9332

with a series of rift-parallel faults developed in the deeper area

(Fig. 5). Conversely, with no developed faults and folds, it is a

smooth monocline with an SeN dip of nearly 3� in the eastern

depression (Fig. 3). Most of the Cenozoic strata in the sub-

basin were developed on a basement consisting of the

Paleozoic and Mesozoic granites and classic rocks. As a

result of three separate episodes of Cenozoic volcanic

activities, basic extrusive basalts and diabase have

encountered in all of the Cenozoic strata which have

severely compromised the quality of seismic data and

impeded the hydrocarbon exploration efforts (Figs. 3 and 4).

4.1.2. SeN direction seismic cross sectionWestern structural styledDuring the Paleocene, controlled

by the NNE trending boundary fault (Lingao Fault), there

generated strong extension and consequent WE trending step

faults system in the western sub-basin. According to the

analysis of fault activity rate, we found a relatively higher

value up to 60 m/Ma comparing with the maximum value of

15 m/Ma in the eastern study area during the SQEls2 period.

Multi-stage faults slope presents as step-shaped on profile and

parallel or broom-like or echelon like combination on plane.

The palaeogeomorphology of the multi-stage faults belt is

characterized by a multi-level fault-terrace that is jointly

controlled by a number of frequently active synsedimentary

faults (Fig. 4a). Many of these faults have a ladder-like profile

while fault-terraces developing at the foot of each fault,

where clastic materials typically deposit.

During the Liushagang period, playing as the major sec-

ondary fault, Meitai Fault divided the western depression into

two main components, multi-stage faults slope zone and

depression (the basin floor area) (Figs. 4a and 6). From the

Fig. 3 e Seismic cross section AeA′ alongWeE direction, showing the central transfer zone (CTZ) divides the depression into

western and eastern sub-depressions. See Fig. 1 for detailed location, see Fig. 2 for details on marked horizons.

g e o d e s y and g e o d yn am i c s 2 0 1 6 , v o l 7 n o 5 , 3 2 9e3 3 9 333

seismic section we can see that the multi-stage faults

distribute above the Meitai Fault are consequent synsedi-

mentary faults with bigger fault displacement and get the

maximum value at the foot of the Meitai Fault, then a series of

fault blocks formed which are advantageous to the formation

of hydrocarbon traps. Also somewhere are obvious to find

high-amplitude reflection which may indicate channel de-

posits, and the discontinuous reflection is assumed to be

destroyed channels caused by frequent activates of step faults

(Fig. 4a). Moreover, a rollover anticline formed at the basin

floor area below the Meitai Fault, with a series of consequent

faults and antithetic faults.

Central structural styledThe seismic cross section repre-

sents a complete profile throughout the sub-basin from the

southern slope belt into the deep-lacustrine area, which is

mainly composed by multiple-stage faults belt (Fig. 4b).

Comparing with the western slope, a significant feature is

the “double fault structure”, bounding by the T5 surface with

upper consequent strike-slip faults and lower antithetic

faults from the section. It is obvious to find that the fault

distance of the upper faults is much larger than lower ones,

which indicates that the lower antithetic faults has little

effect on the deposition process whereas the upper

consequent faults are synsedimentary faults. Combined

with basin formation mechanism, we supposed that the

development process of the “double fault structure”, can be

divided into three phases: (i) Strong transverse extension

happened to the depression during the SQEls3 period, which

may provide power source to form the embryo of the lower

antithetic faults mainly distributed form the central slope to

the eastern slope area; (ii) the rapid uplift of the Hainan

Uplift impels the development of the gravity sliding growth

faults in the upper structural layer; (iii) the intrusion of

volcanic rock during the SQEls2 period finally leads the

forming of the “double fault structure”.

Eastern structural styledFlexure slope break belt is

generated by draping onto the paleo-ridge, paleo-faults and

buried paleo-hill which shows an obvious thickening of the

strata due to on-lap fill in the slope break zone. Strata

truncations and unconformity interfaces are observed on

the upper slope break belt. Flexure slope break belt has

characteristics similar to a typical, passive continental

margin type I sequence. In Fushan sub-basin, flexure slope

break belts mainly developed near the southern margin in

the eastern study area since the SQEls2 period and the slope

gradient gradually decreases along the WE direction (Figs. 4c

and 6).

Comparing with the western multi-stage faults slope, the

eastern seismic profiles present a relative continuous slope

pattern with obvious slope break point which divides the

Fig. 4 e a e Seismic interpretation of line BeB′ traversing along WeE direction. b e Seismic interpretation of line CeC′

traversing along WeE direction. c e Seismic interpretation of line DeD′ traversing along WeE direction. d e The location of

the lines BeB′, CeC′, DeD′. See Fig. 1 for detailed location, see Fig. 2 for details on marked horizons.

g e o d e s y and g e o d yn am i c s 2 0 1 6 , v o l 7 n o 5 , 3 2 9e3 3 9334

slope into three main components: gentle slope zone near the

sub-basin margin, flexure slope break and base of slope.

However, synsedimentary faults and associated blocks are not

well developed in the eastern study area, then the maximum

flooding surface (mfs) is easier to recognize by using lithologic

logs in combination from gentle formation. Another note-

worthy feature in the eastern seismic sections is the abnormal

continuous reflectors with high-amplitude distribute along or

intrude into the SQEls2 stratum, representing igneous intru-

sion produced by strong volcanic activities.

4.2. Structural styles in the sub-basin

Based on the logging data and 3-D seismic reflection data,

we have summarized the structural styles in the sub-basin

into five types below. Table 1 presents the descriptions of each

structural style and provides interpretations for the positions,

background and development formations.

Ancient horstdAncient horst mainly developed in the

central transfer zone, which presents as a paleo-uplift

controlled by the normal faults located on each side. From the

Fig. 5 e a eWeE Stratigraphic cross-section (along line AeA′) showing the depocentres of the twomainwestern and eastern

depressions separated by the central transfer zone (CTZ). b e Total subsidence rate curves (m/Ma) derived by backstripping

of the cross-line (AeA′) showing significant subsidence distinction between the western depression and eastern

depression. c e Subsidence rate curve (m/Ma) derived by backstripping of the cross-line (AeA′) showing significant

subsidence distinction between the western depression and eastern depression.

g e o d e s y and g e o d yn am i c s 2 0 1 6 , v o l 7 n o 5 , 3 2 9e3 3 9 335

seismic section (Fig. 3, Table 1), we can find that the ancient

horst is a relative lower uplift in the deep-lacustrine area,

experiencing exposure and erosion, providing deposits to the

surrounding areas as a sub-provenance. Also it has deposit

source supplements from both the southern and northern

slopes, and continues developing through the Liushagang

formation.

Traditional slopedIt mainly distributed in the western

sub-depression and part of the eastern sub-depression during

the Liushagang period, belongs to smooth and gentle palae-

ogeomorphology type, and usually be associated with the

multi-stage fault belt (Table 1). Such a gentle slope is a

prototype for various slope palaeogeomorphology styles,

with the characteristics of widely distribution and also

provides ideal location for braided river delta deposition.

Flexure slope-breakdFlexure slope break belt is generated

by draping onto the paleo-ridge, paleo-faults and buried

paleo-hill which shows an obvious thickening of the strata

due to on-lap fill in the slope break zone. Strata truncations

and unconformity interfaces are observed on the upper slope

break belt (Table 1). In the Fushan sub-basin, flexure slope

break belts mainly developed near the southern margin in

the eastern study area since the SQEls2 period and the slope

gradient gradually decreases along the WE direction.

Faulted slope-breakdUsually formed due to the reforma-

tion of the traditional slope by the basin margin fault or sec-

ondary fault. Angle difference of the stratum attitude

happened along with the expand of the large displacement,

which is more easily to form rapid accumulation of alluvial

fan deposits. In the Fushan Depression, we mainly identified

two types of faulted slope-break (Table 1): (i) structural style of

gentle lower slope which mainly developed near marginal

basin faults, and deposited fan delta sand body at the down-

thrown side; (ii) structural style of steep higher slope which

was associated with secondary fault and deposited near

shore subaqueous fan at the down-thrown side.

Multiple-stage faults slopedControlled by the NNE trend-

ing boundary fault (Lingao Fault), there generated strong

extension and consequent WE trending step faults system in

the western sub-basin. According to the analysis of fault ac-

tivity rate, we found a relatively higher value up to 60 m/Ma

comparing with the maximum value of 15 m/Ma in the

Fig. 6 e a e Plan distribution maps of lower structural system. b e Plan distribution maps of upper structural system.

g e o d e s y and g e o d yn am i c s 2 0 1 6 , v o l 7 n o 5 , 3 2 9e3 3 9336

eastern study area during the SQEls2 period. Multi-stage faults

slope presents as step-shaped on profile and parallel or

broom-like or echelon like combination on plane. The palae-

ogeomorphology of themulti-stage faults belt is characterized

by a multi-level fault-terrace that is jointly controlled by a

number of frequently active synsedimentary faults (Table 1).

Many of these faults have a ladder-like profile while fault-

terraces developing at the foot of each fault, where clastic

materials typically deposit.

4.3. Structural system of the sub-basin

Our study used seismic coherence technique and 3-D

seismic interpretation, combined with regional stress field of

the Fushan Depression to make plane combinations of the

faults, finally built up plan distribution maps of structural

system for main sequence. Overall, the plan distribution di-

rections of most faults in the two structural systems are

closely to unanimous, which present as three groups: the

north-east direction group, the north-west direction group

and the nearly east-west direction group. The fault system of

the lower structural layer appeared to be nearly parallel

distributed (Fig. 6a), as the faults in the western sub-

depression mainly represent to be north-east direction

whereas the faults in the eastern sub-depression mainly

distributed in a nearly east-west direction. The fault system

of the upper structural layer also appeared to be nearly

parallel distributed (Fig. 6b), which represented to be north-

east and nearly north-east directions, but the fault system in

the eastern sub-depression appears to be obviously

simplistic than that in the lower structural layer, and the

north-west direction faults only developed in the eastern

sub-depression area.

Another remarkable tectonic setting is represented by the

central transfer zone (CTZ) (Fig. 1d) which divides the sub-

basin into two independent depressions (the western

Huangtong Depression & the eastern Bailian Depression),

characterized by distinct structure superposition,

Table 1 e Classification scheme for structural styles in the sub-basin.

g e o d e s y and g e o d yn am i c s 2 0 1 6 , v o l 7 n o 5 , 3 2 9e3 3 9 337

palaeogeomorphology and consequent depositional systems.

The major faults in two sub-depressions are not continuous

throughout the entire sedimentary basin, but instead stop at

termination points in the axial part of the central structural

zone, corresponding to a large-scale accommodation zone.

Overall, the structural systems of the sub-basin can be

described from three aspects: (i) the direction of the fault

system is mainly north-east, followed by the north-west di-

rection, then the nearly east-west direction; (ii) the faults of

the lower structural layer are scattered distributed, but the

consistency of the direction of the faults of the upper struc-

tural layer is better (Fig. 6); (iii) with respect to the lower

structural system, the fault strike of the upper structural

system has a certain clockwise rotation.

5. Discussion

In a continental rift setting, the structural evolution of

lacustrine system ismainly controlled by tectonic geometry of

the basin which depends on the subsidence features. Subsi-

dence history analysis was applied to the Paleogene Fushan

Sag for better insights into the interplay of tectonics and

subsidence. Considering of the complicated and variable

characteristics in the lacustrine basin, the Standard

Backstripping Technique was chosen to analyze the subsi-

dence history by using the EBM software. The technique of

backstripping is commonly applied to extensional basins to

determine the magnitude of lithospheric thinning from the

observed post-rift subsidence [28]. Stratigraphic units within a

sediment column are removed progressively from top

downwards. The remaining sediments are decompacted and

isostatically restored by using Airy isostasy. Thus, the

restoration accounts for new load conditions, paleo-water

depths, and the isostatic response to the change in loads,

and our general analysis process can be summarized as

follows: tectonic subsidence ¼ total subsidence�[deposits &

water load deposits þ sedimentary compaction þ water level

changes]. According to the result, the Fushan sub-basin

experienced several tectonic evolution stages during

Paleogene, in which SQEch and SQEls compose the synrift

stage. In this paper, we mainly chose two observation points

respectively located in the western and eastern depression

to describe territorial subsidence characters of the

Liushagang formation which will be helpful for structural

system analysis.

The vertical evolution of subsidence rate along the WE-1

cross-line reflects different subsidence features between the

western and eastern depression during the same rifting stage

whichmay relate to different structure styles and inconsistent

g e o d e s y and g e o d yn am i c s 2 0 1 6 , v o l 7 n o 5 , 3 2 9e3 3 9338

fault activities (Fig. 5). Specifically describing, the subsidence

rate mainly controlled by tectonic activities in the western

depression during the Liushagang period but less in the

eastern depression which results in relative depth and

distinct depression in the western area. We have shown that

the Fushan sub-basin has experienced an apparently

anomalous fast subsidence history since the

PlioceneeQuaternary, which is similar to the adjacent

YinggehaieSong Hong Basin.

In addition, there is an evidence of volcanic activity on the

northeast regions of the Fushan sub-basin. On the base of

evidence for volcanic activity in the region and the evidences

in cores, we suggest that volcanic earthquake played a major

role in triggering complex rifted sub-basin.

6. Conclusions

In this study, using deep 3-D seismic data, we analyzed

structural styles and tectonic evolution model of a classic

continental rifted basin in the Beibuwan Basin, South China

Sea. The research result shows:

1) Using available 3-D seismic data and few well data to

analysis the characteristics of seismic geomorphology of

the Fushan sub-basin, we built up structural framework

across the sub-basin mainly in two directions. The most

remarkable tectonic setting is represented by the CTZ

which divides the sub-basin into two independent de-

pressions, and two kinds of sequence architectures are

summarized: (i) the western multi-stage faults slope; (ii)

the eastern flexure slope break belt.

2) We have summarized the structural styles in the sub-basin

into five types: ancient horst, traditional slope, flexure

slope-break, faulted slope-break and multiple-stage faults

slope, and discussed each structural style and provided

interpretations for their positions, background and devel-

opment formations;

3) Mapped the structural distribution of the Paleogene

Liushagang formation, which divided the structural sys-

tem into upper structural layer and lower structural layer.

Respecting to the lower structural system, the fault strike

of the upper structural system has a certain clockwise

rotation. Also, we discussed the controlling factors mainly

focused on subsidence history and background tectonic

activities such as volcanic activity and earthquakes.

Overall, the analysis of structural styles and tectonic evo-

lution provides strong theoretical support for future pro-

specting in the Fushan sub-basin and other similar rifted

basins of the Beibuwan Basin in South China Sea.

Acknowledgements

We thank the National Natural Science Foundation of

China (NSFC) program (41472084) and the China Earthquake

Administration, Institute of Seismology Foundation

(IS201526246) for providing funding and for allowing publica-

tion of this paper, and China Exploration and Development

Corporation, PetroChina for allowing publication of seismic

data.

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Yuan Li, graduated from China Universityof Geosciences and obtained a doctoral de-gree on mineral resource prospecting andexploration in 2015. She has been to theFaculty of Earth Sciences and Environment,University of Ottawa for two-year JointDoctoral Education from 2012 to 2014. Nowshe is an assistant researcher at theWuhanInstitute of Earthquake Engineering, ChinaEarthquake Administration. Her mainresearch fields are structural geology, sedi-

mentary geology and seismic geology.