Tectonic characteristics and structural styles of a ... · seismic data.” Therefore, seismic geomorphology, when integrated with seismic and sequence stratigraphy, is a powerful
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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
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
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
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-