Sedimentary characteristics and processes of the Paleogene Dainan Formation in the Gaoyou Depression, North Jiangsu Basin, eastern China
Sedimentary characteristics and processes of the Paleogene Dainan Formation in the Gaoyou Depression, North Jiangsu Basin, eastern China
Xia Zhang 0 1 2
Chun-Ming Lin 0 1 2
Yong Yin 0 1 2
Ni Zhang 0 1 2
Jian Zhou 0 1 2
Yu-Rui Liu 0 1 2
0 Edited by Jie Hao
1 Institute of Geological Sciences, Jiangsu Oilfield Branch Company , SINOPEC, Yangzhou 225009, Jiangsu , China
2 School of Geographic and Oceanographic Sciences, Nanjing University , Nanjing 210023, Jiangsu , China
In this paper, the type, vertical evolution, and distribution pattern of sedimentary facies of the Paleogene Dainan Formation in the Gaoyou Depression of the North Jiangsu Basin are studied in detail. Results show that fan delta, delta, nearshore subaqueous fan, and lacustrine facies developed during the Dainan Formation period and their distribution pattern was mainly controlled by tectonics and paleogeography. The fan delta and nearshore subaqueous fan facies predominantly occur in the southern steep slope region where fault-induced subsidence is thought to have created substantial accommodation, whereas the delta facies are distributed on the northern gentle slope which is thought to have experienced less subsidence. Finally, the lacustrine facies is shown to have developed in the center of the depression, as well as on the flanks of the fan delta, delta, and nearshore subaqueous fan facies. Vertically, the Dainan Formation represents an integrated transgressiveregressive cycle, with the E2d1 being the transgressive sequence and the E2d2 being the regressive sequence. This distribution model of sedimentary facies plays an important role in predicting favorable reservoir belts for the Dainan Formation in the Gaoyou Depression and similar areas. In the Gaoyou Depression, sandstones of the subaqueous distributary channels in the fan delta and the subaqueous branch channels in the delta are characterized by physical properties favorable for reservoir formation.
Sedimentary facies; Distribution pattern; Sedimentary evolution; Dainan Formation; Gaoyou; Depression; North Jiangsu Basin
State Key Laboratory for Mineral Deposits Research, School
of Earth Sciences and Engineering, Nanjing University,
Nanjing 210023, Jiangsu, China
Lacustrine rift basins are distributed widely in eastern China.
About 300 Mesozoic–Cenozoic rift basins cover a total area
of approximately 2 9 106 km2. These depressions occur as
one of the most important petroliferous basin types in China,
and have therefore been the focus of exploration for subtle
(Xian et al. 2007; Wang et al. 2014; Jiang et al.
. The sedimentary systems developed in these rift
basins in eastern China, such as the Bohai Bay Basin, the
southern part of the North China Basin, the Erlian Basin, and
the Ural Basin, tend to form favorable lithologic or
structural-lithologic reservoirs, even in the conglomerates and/or
sandy conglomerates of the nearshore subaqueous fans that
(Sui 2003; Zhao et al. 2011; Cao et al. 2014; Zhang
et al. 2014a)
. The North Jiangsu Basin is one of the richest
regions for oil and gas in eastern China, given its thick and
wide distribution of Mesozoic–Cenozoic strata. The
Paleogene Dainan Formation is one of the most productive
reservoir intervals in the Gaoyou Depression, North Jiangsu
Basin (Qiu et al. 2006). The production of most major oil
fields in the Dainan Formation is now in decline; thus, a
precise description of the sedimentary facies of these
reservoir sandstones is greatly needed. To date, studies of the
Dainan Formation have focused primarily on the
paleontological, sequence stratigraphic, and structural
compartmentalization of the basin
(Dong 1999; Lu 2000;
Zhang et al. 2005; Pang and Cao 2005; Zhu et al. 2013; Chen
et al. 2015)
. There have also been studies of the
(Chen and Wu 2006; Zhang et al. 2007; Xia et al.
2008; Ji et al. 2012; Zhao et al. 2015)
et al. 2010; Zhang et al. 2014b)
of the basin fill. However, the
regional distribution pattern and processes of sedimentary
facies have yet to be understood at a sufficiently high
temporal and spatial resolution. Such detail is crucial for reliable
predictions of depression-scale sedimentary architecture
within and/or between individual oil fields. The objectives of
this study are to (1) describe the characteristics, spatial
distribution, and evolution processes of sedimentary facies of
the Dainan Formation, and (2) reconstruct the sedimentary
system and model of the Gaoyou Depression, which may
have broad implications for other similar rift basins.
2 Geological setting
The North Jiangsu Basin is a large Mesozoic–Cenozoic
fault-depressed basin with the basement being composed of
Proterozoic metamorphic rock and Early Mesozoic
carbonate, turbidite, and clastic rocks
(Shu et al. 2005)
. It is
located east of the Lower Yangtze Plate covering an area of
approximately 35 9 103 km2 (Fig. 1a), and it can be
divided into four east-westward oriented tectonic units: the
Dongtai Depression, Jianhu Uplift, Yanfu Depression, and
the Binhai Uplift
(Qiu et al. 2006; Fig. 1b)
The Gaoyou Depression is located in the central Dongtai
Depression with an area of about 2.7 9 103 km2. It is
characteristic of a dustpan-like depression
Zeng 2007; Zhu et al. 2013; Fig. 1c, d)
resulting from the
differential subsidence of fault blocks during the Yizheng
Movement in the Late Cretaceous and the Wubao
Movement in the Late Paleocene
. The Gaoyou
Depression is bounded to the south by the Zhenwu fault
belt (separating it from the Tongyang uplift), and links to
the Zheduo low uplift through a slope in the north
(Fig. 1c). The western and eastern boundaries are the
Lingtangqiao low uplift and the Wubao low uplift,
respectively (Fig. 1c). Due to the influence of Indian and
Pacific plate movements, there are three groups of fractures
(ENE, NE, and NW orientations) developed in the Gaoyou
Depression, with those oriented ENE dominant. These
ENE faults (Zhen 1, Zhen 2, and Hanliu faults) separate the
Gaoyou Depression into three ENE trending sections from
south to north: southern step-fault zone, central deep
depression zone, and northern slope zone
(Qiu et al. 2006;
Chen 2001; Fig. 1c)
. The central deep depression zone can
be further divided into three subdepressions from west to
east: Shaobo, Fanchuan, and Liuwushe (Fig. 1e).
The Mesozoic–Cenozoic sedimentary thickness in the
Gaoyou Depression can reach up to 7000 m. Of this, the
Dainan Formation (E2d) has a thickness of approximately
1500 m and has been one of the most productive reservoir
intervals in the Gaoyou Depression over the last 30 years,
hosting over 15 oil–gas fields containing about 4.1 9 108
tons of recoverable oil. The E2d lies between the overlying
Funing Formation (E1f) and the underlying Sanduo
Formation (E2s) (Table 1), and can be divided into two
members in the ascending order: 1st member (E2d1) and
2nd member (E2d2).
3 Sedimentary characteristics and facies
Four sedimentary facies (fan delta, delta, nearshore
subaqueous fan, and lacustrine) have been identified within the
Dainan Formation in the Gaoyou Depression based on the
variations in lithology, sedimentary structures, and vertical
3.1 Fan delta
Fan deltas occur mainly in the southern steep slope of the
Gaoyou Depression, with three subfacies: fan delta plain,
fan delta front, and profan delta. The fan delta plain
subfacies is the subaerial part of the fan delta and contains
distributary channels and back swamps. It is comparable
with high-energy gravel-rich braided river facies
McPherson 1994; Lin et al. 2003; Kre´zsek et al. 2010)
Distributary channels, which are the dominant microfacies
of the fan delta plain, consist of gray or mottled
conglomerate, gray conglomeratic sandstone, and coarse
sandstone. The conglomerate gravels are common poorly
sorted, subangular to subrounded in shape, and randomly
distributed in a matrix of fine- to coarse-grained sands
which indicate proximal deposition. Also, they have
complex compositions, which include siliceous rocks, phyllite,
limestone, mud pebbles and gypsum, and have diameters
ranging from 1 to 8 cm. The structureless conglomerates
overlie basal scour surfaces and progressively change
upwards into parallel-bedded conglomeratic sandstones
and coarse-grained sandstones. These characteristics
suggest deposition from waning high-density flows. The
spontaneous potential logs (SP) are jagged with low to
moderate amplitudes. The brown mudstones and silty
mudstones are interpreted as deposits of a back-swamp
Fan delta front subfacies consist primarily of
subaqueous distributary channels and interchannels, and
subordinate mouth bar and sand sheet deposits (Fig. 2).
Subaqueous distributary channel microfacies are
characterized by light gray conglomeratic sandstones, and gray to
Beijing Lower Yangtz block
brown fine sandstones and siltstones which exhibit an
upward-fining trend (Fig. 2). From bottom to top,
sedimentary structures include a scour surface (Fig. 3a), graded
bedding, tabular cross bedding (Fig. 3b), parallel bedding
(Fig. 3b), climbing-ripple cross stratification (Fig. 3c),
wavy bedding, and convolute bedding (Fig. 3d).
Furthermore, mud pebbles are pervasively present above the scour
surface, having diameters ranging from 0.5 to 2.5 cm, and
2 2 E d 3
their abundance and grain size become progressively lower
abundant plant remains. Mudstones of subaqueous
disand smaller, respectively, towards the top (Fig. 3a). Single
tributary interchannels usually display significant scour and
subaqueous distributary channels are 5–10 m thick, but
can even be completely removed by successive
high-disthey can amalgamate and superimpose upon one another
charge events. Such mudstones are commonly laminated as
with resultant thicknesses reaching more than 50 m. SP
indicated by the SP curves close to the shale line and
curves display an obvious negative anomaly. Subaqueous
resistivity log (R) curves displaying a low-magnitude
jagdistributary interchannel microfacies are composed of gray
ged pattern (Fig. 2). Mouth bar microfacies mainly contain
silty mudstones, and purple red, brown, dark gray
mudgray to brown siltstone and fine-grained sandstone with a
stones, which together are occasionally intercalated with
thickness of 4–6 m. These exhibit an upward-coarsening
muddy siltstones. Horizontal, wavy, and lenticular
bedsuccession, as shown by the funnel-shaped SP curve. Cross,
dings are also present, commonly having bioturbation and
parallel, and wavy beddings are common. The sandstones
te ilga& irneagLithology
of subaqueous distributary channels and mouth bars were
vulnerable to being reworked by wave processes
1988; Johnson and Levell 1995; Hoy and Ridgway 2003)
forming a thin-bedded, widely distributed sand sheet in the
distal part of the fan delta front. Sand sheets consist mainly
of siltstone and muddy siltstone and display an intimate
association with the mudstones of the shallow lacustrine
facies (finger-like pattern in the SP curve). The thickness of
individual sand sheets is 2–3 m.
Profan delta subfacies mainly consist of grayish brown
mudstones with sand strips and masses. Horizontal bedding
is most common, with wavy and lenticular beddings being
less common. The SP curve is relatively straight, while the
R curve displays a low-amplitude jagged pattern.
Delta facies occur predominantly in the northern gentle
slope of the Gaoyou Depression, and are marked by
finegrained sandstones with less conglomerate and more
mudstone compared to the fan deltas (Table 2). Seismic
profiles occur as parallel to subparallel reflection
configurations. The deltas can be divided into three distinct yet
genetically related subfacies: delta plain, delta front, and
prodelta, with the delta front as the majority of those found
in the Gaoyou Depression. The delta plain constitutes the
subaerial part of the delta and mainly consists of branch
channels and branch interchannels. The basal sections of
branch channels are erosionally based and are typified by
medium- to coarse-grained sandstones with scattered mud
pebbles. They can be structureless, or contain pervasive
trough-cross and parallel beddings. The upper portion of
the branch-channel succession is primarily composed of
fine-grained sandstones and siltstones (with occasional
mudstones), containing wavy bedding and climbing-ripple
cross stratification. The thickness of individual successions
ranges from 6 to 8 m.
The delta front includes subaqueous branch channels,
subaqueous branch interchannels, branching mouth bars,
and sheet sands (Fig. 4). Subaqueous branch channels are
erosionally based, and are mainly composed of grayish
brown fine-grained sandstones and siltstones, with many
rounded mud pebbles at the base. Sedimentary structures
comprise graded bedding, parallel bedding, cross bedding,
climbing-ripple cross stratification, and horizontal bedding
from bottom to top. In general, subaqueous branch
channels represent an upward-fining succession with the
corresponding SP curve characteristically bell-shaped
(Fig. 4). The thickness of individual successions is 5–7 m.
Subaqueous branch interchannels are located between
adjacent subaqueous branch channels and consist of
brownish-gray mudstones and muddy siltstones. Horizontal
and wavy beddings, plant remains (Fig. 3e), and
bioturbations are common.
Branching mouth bars usually occur as an
upwardcoarsening succession with grayish brown muddy
siltstones at the bottom, and siltstones and fine-grained
sandstones towards the top. Parallel, wavy, and cross
beddings are pervasive (Fig. 4). The thickness of
individual successions is 3–5 m. Sheet sands are located in
the distal part of the delta front, and are mainly composed
of thin-bedded fine-grained sandstone and siltstone
(Fig. 4) with wavy, cross, and horizontal beddings
involved. The thickness of individual successions is
commonly 2–3 m. Prodelta subfacies mainly consist of
gray-brown mudstones and shales intercalated with
thinbedded siltstones. The SP curve displays a finger-like
pattern within the low-magnitude range.
,m sa g
thp g inLithology
eD li&O reab
3.3 Nearshore subaqueous fan
The term ‘‘nearshore subaqueous fan’’ refers to a
coarsegrained fan that lacks a subaerial component. It develops
where an alluvial river or fan debouches directly into
excessively deep coastal waters
(Colella and Prior 1993)
and is derived from gravity flow
(Zhang and Tian 1999;
. Deposits of these systems have been commonly
found in Mesozoic–Cenozoic rift basins of eastern China
(Zhang and Shen 1991; Zhou et al. 1991; Zhang and Tian
In the study area, nearshore subaqueous fans developed
in the Shaobo, Xiaoliuzhuang, and Zhouzhuang areas
during the E2d1 period, and these can be further divided
into three microfacies: inner fan, middle fan, and outer fan.
The inner fan subfacies is characterized by one or a few
main channels which can be described as
undercompensated incised valleys
. The main channel consists
of poorly sorted mottled conglomerates and sandy
conglomerates that have complex compositions and are
commonly matrix-supported and/or grain-supported. Those that
are matrix-supported are interpreted to have been deposited
by debris flows, characterized by gravels floating randomly
in a fine-grained matrix (appearing structureless) (Fig. 3f).
Resultant successions have sharp boundaries or scour
surfaces at their base and load structures developed towards
the underlying unit. Grain-supported conglomerates, on the
other hand, are thought to have been deposited by
highdensity turbidity currents. Deposits of such turbidity
currents (turbidites) are typified by normal and reverse graded
bedding, occasional crude cross bedding, and slump
deformation structures. The corresponding SP curve of
such successions displays a jagged bell- or cylinder-shaped
The middle fan facies includes braided channels and
interchannels, with deposits of the former constituting the
majority of the succession (Fig. 5). The braided channels
are typified by gray and grayish-white sandy conglomerates
and conglomeratic sandstones with low compositional
maturity and moderate textural maturity. Clasts
constituting these conglomerates involve limestone and quartz
fragments with diameters of 10–20 mm. Scour surfaces
and flute casts are common at the bottom of the braided
channel successions. Graded, parallel, and cross beddings
are most common. The fine-grained sediments formed in
the interchannels are easily washed away
The corresponding SP curve displays a bell-shaped or
jagged cylinder-shaped pattern (Fig. 5).
The outer fan is located in the seaward extremity of the
nearshore subaqueous fan and consists mainly of dark
mudstones intercalated with siltstones, muddy siltstones,
and locally thinly bedded fine-grained sandstones.
Sedimentary structures mainly include wavy and horizontal
beddings, reflecting a relatively lower flow regime and
quiet environment. The corresponding SP curve is flat with
Compared to the deltas and fan deltas, the nearshore
subaqueous fan is characterized by the strongest
hydrodynamic force and poor sorting (Table 2), which is clearly
reflected in the probability cumulative grain-size
distribution curves (Fig. 6). Figure 6 shows that (1) the grain-size
range of saltation components for nearshore subaqueous
fans is between -1.0 and 3.0 U, whereas those of fan delta
and delta are 0.5–3.5 and 1.0–4.0 U, respectively, which
indicates that the hydrodynamic force of nearshore
subaqueous fans is the strongest
(Lin et al. 2005)
; (2) the slope
of saltation components for delta, fan delta, and nearshore
subaqueous fan is about 71 , 65 , and 52 , respectively, of
which the latter is the smallest, suggesting poor sorting; (3)
the abundance of the suspension component for the
idem trsu 0
Well Sha 5, 2317.4 m
Well Sha 5, 2347.8 m
Grain size, Φ
Grain size, Φ
nearshore subaqueous fans is the greatest, generally more
than 30 %, supporting a graywacke classification.
3.4 Lacustrine facies
Lacustrine facies mainly occur at the center of the
Gaoyou Depression, as well as on the flanks of the fan
deltas, deltas, and nearshore subaqueous fans.
Shoreshallow lacustrine and semideep lacustrine subfacies are
identified in the study area. The nature of the
shoreshallow lacustrine subfacies is controlled by the
provenance and hydrodynamic force. If the provenance is
typified by gravel and sand, then gravelly and/or sandy
lacustrine beaches form. However, if the terrain of the
lacustrine beach is gentle, the hydrodynamic force will be
weak, and supplied sediment will consist mainly of mud,
allowing mudflats to form
(Lin et al. 2003)
. In the study
area, the shore-shallow lacustrine subfacies comprise
mainly of siltstones and mudstones with a variety of
colors: brownish-gray, dark-purple, and dark-brown
(Fig. 2). Horizontal and wavy beddings, bioturbation
(especially vertical worm burrows), and plant remains are
common. The corresponding SP curve is linear and low
in amplitude, while the R curve is jagged having low to
moderate amplitudes (Fig. 2). Semideep lacustrine facies
are located under the fair-weather wave base, i.e., a
generally anoxic environment. Sedimentary rocks are
mainly composed of dark mudstones with high organic
matter contents, with horizontal and lenticular beddings
4 Sedimentary distribution and processes
The sedimentary succession of the Dainan Formation in the
Gaoyou Depression exhibits a complete
transgressive–regressive cycle with sediment grain sizes displaying a
coarse–fine-coarse pattern in the ascending order. As a
result, there are two major sedimentological periods for the
Dainan Formation: E2d1 and E2d2. E2d1 consists of three
stages: E2d13, E2d12, and E2d1, and E2d2 is composed of five
stages: E2d2, E2d24, E2d2, E2d22, and E2d21 (Table 1).
4.1 Sedimentary period of E2d1
During the E2d1 period, the Dainan Formation began to
form and overlay the Funing Formation by an
unconformity which had resulted from Wubao Movement.
Deposition during the E2d1 is thought to have been in phase with
the uplifting of the basement and the development of
northeastern faults in the Gaoyou Depression
(syndepositional). The strata are thick in the south and gradually thin
towards the north. The subsidence center was located in the
Shaobo and Fanchuan subdepressions with strata thickness
up to 900 m. The fan delta, delta, nearshore subaqueous
fan, and lacustrine facies developed within this period,
representing a transgressive succession with the grain size
of clastic particles fining upwards and the relative thickness
of sandstones reducing gradually upwards (Fig. 7).
In E2d13, the strong movements of the Zhen 2 and Hanliu
faults controlled and limited the distribution of sediments
, so that the Zhen 2 fault acted as a southern
boundary and the Hanliu fault formed a fault-step zone as
the northern margin. The subsidence center is located in the
Shaobo subdepression with stratum thickness up to 400 m
(Fig. 8a). The total sandstone thickness is greater in the
east than in the west, reaching up to 60 m in the Fumin area
(generally 20–40 m) (Fig. 8b). Four fan deltas (Huangjue
(HJ), Zhenwu–Caozhuang (ZC), Fumin (FM), Zhouzhuang
(ZZ)) and a nearshore subaqueous fan (Shaobo (SB))
developed along the Zhen 2 fault. Four small-scale and
independent deltas involving the western part of
Lianmengzhuang (LLZ), and eastern parts of Lianmengzhuang
(RLZ), Yong’an (YA) and Fumin–Huazhuang (FH) were
formed on the gentle northern slope (Fig. 9a).
Shore-shallow lacustrine facies occurred mainly in the center of the
depression (Fig. 9a).
In E2d1, the sedimentary area extended with the
boundary crossing the Zhen 2 and Hanliu faults because of
the small-scale increase of lake water and decrease in
tectonic activity (Fig. 9b). The stratigraphic overlap in the
northern part of the Gaoyou Depression is easily observed
in the seismic profile. The subsidence center was also
located in the Shaobo and Fanchuan subdepressions with a
thickness of 300 m (Fig. 8c). The gross sandstone
thickness is greater in the east than towards the west, with
maximum thickness reaching 80 m in the Fumin and
Yong’an areas (20–40 m in general) (Fig. 8d). Compared
to the E2d13, the range and scale of the E2d12 period fan delta,
delta deposits, and nearshore subaqueous fan sediments
expanded due to augmented accommodation and sufficient
sediment supply. Four fan deltas (HJ, ZC, FM, and ZZ) and
three nearshore subaqueous fans (SB, Xiaoliuzhuang
(XLZ), and ZZ) developed along the steep southern slope
zone (Fig. 9b). Also, the four deltas of E2d13 in the northern
slope of the Gaoyou Depression merged to form one larger
delta, and the Majiazui (MJZ) area started receiving
sediment in this stage, resulting in the formation of two
detached deltas (Fig. 9b). Shore-shallow lacustrine
deposits mainly accumulated in the center of the depression, as
well as on the flanks of the fan deltas, deltas, and nearshore
subaqueous fans (Fig. 9b).
During the E2d11 period, the lake transgression reached a
maximum and the lateral extent of deposition continued to
expand with the ‘‘five high-conductivity’’ dark mudstones
representing the sedimentary boundary of the Gaoyou
Depression. The subsidence center was still located in the
Shaobo, Fanchuan, and Liuwushe subdepressions with
strata thickness of 200 m (Fig. 8e). The gross sandstone
thickness is generally 20 m, but can be locally greater, such
as in the Fumin, Yong’an, and Shanian areas, where
thicknesses can reach up to 40 m (Fig. 8f). Compared to
the E2d13 and E2d12, the scales of fan deltas, deltas and
nearshore subaqueous fans of the E2d11 period were reduced
20 30 40
Stratigraphic pinch-out line
b Fig. 8 Isopach maps of the strata (left side) and gross sandstone
layers (right side) in different stages for the Dainan Formation,
Gaoyou Depression. a, b The E2d13 stage; c, d: the E2d12 stage; e, f the
E2d11 stage; g, h the E2d2 stage
and these moved back towards the lakeshore. The ZC and
ZZ fan deltas of E2d12 were each replaced with two
detached and small-scale fan deltas. In the northern slope,
the delta was still a unified delta as that of E2d1. The
Wazhuang (WZ) area started receiving sediment in this
stage occurring as the WZ delta. The ZZ nearshore
subaqueous fan was substituted by shore-shallow lacustrine
subfacies. Semideep lacustrine subfacies developed in the
Shaobo, Fanchuan, and Liuwushe subdepressions, and the
shore-shallow lacustrine subfacies deposited mainly on the
flanks of fan deltas, deltas, and nearshore subaqueous fans
4.2 Sedimentary period of E2d2
During the E2d2 period, the Gaoyou Depression was
characterized by weak movement of faults and basement
uplift, resulted in a shallowing water depth, a decreasing
slope gradient, and disappearance of nearshore subaqueous
fans in the southern slope (Figs. 9d, 10). The stratum
thickness is still thick in the south and thins out towards the
north (Fig. 8g). Subsidence centers were located in the
Shaobo and Fanchuan subdepressions with strata
thicknesses up to 700 m (Fig. 8g). The sandstones were
primarily deposited in the eastern Gaoyou Depression,
including the Shanian and Yong’an areas of the northern
slope, as well as the Fumin and Fanchuan regions of the
southern slope, with thicknesses commonly reaching
100–300 m. These thicknesses generally thin out towards
the western Gaoyou Depression to approximately \50 m,
with only a few areas reaching 100 m (Fig. 8h). In general,
the sedimentary framework of E2d2 occurs as a regressive
succession composed of a second-order
transgressive–regressive cycle, with the grain size and thickness of the
sandstone displaying a coarse–fine-coarse and
thick-thinthick trend upwards, respectively (Fig. 7).
During the E2d25 depositional period, the dispersal of
sediment reduced and water depth became shallower
compared to E2d11. Due to the sufficient supply of sediment,
the fan deltas in the steep southern slope and the deltas in
the northern gentle slope prograded into the center of the
depression with their lateral extent amplified. In the Fumin
area, the fan delta front and delta front converged (Fig. 9d).
The Zhenwu and Caozhuang fan deltas of the E2d11 period
also joined together as one unified fan delta. Semideep
lacustrine subfacies were replaced by shore-shallow
lacustrine subfacies (Fig. 9d).
In E2d24, the lateral extent of sediment deposition
extended and water depth increased compared to E2d2.
Together, this resulted in the retrogradation of the fan
deltas and deltas with the scale of such systems reduced.
The fan delta fronts and delta fronts, however, still
converged in the Fumin area. The Zhenwu–Caozhuang and
Shaobo fan deltas and Lianmengzhuang–Yong’an–Fumin
delta of the E2d25 period were each replaced by two
detached and small-scale fan deltas and deltas.
Shoreshallow lacustrine subfacies developed in the center of the
depression and on the flanks of deltas/fan deltas (Fig. 9e).
In E2d23, the water depth continued to increase, which
resulted in the persistent retrogradation of the fan deltas
and deltas. The fan delta front and delta front separated in
the Fumin area. The Lianmengzhuang and Yong’an–Fumin
delta of the E2d24 period converged into a unified delta, and
the two separated fan deltas in the Shaobo area also joined
together. Shore-shallow lacustrine subfacies developed in
the center of the depression and on the flanks of deltas/fan
deltas (Fig. 9f).
In E2d22, the distribution pattern of sedimentary facies is
similar to that of the E2d23 period; however, the deltas and
fan deltas prograded into the center of the depression with
the scale of lateral deposition increased due to the shallow
water depth and sufficient supply of sediment (Fig. 9g).
In E2d21, the deltas and fan deltas continued to prograde
into the center of depressions with the scales increased due
to the shallow water depth and sufficient supply of
sediment. In the Fumin area, the fan delta front and delta front
met and blended together again. The Huangjue and Shaobo
fan deltas also merged together to form a unified fan delta
(Fig. 9h). In addition, during the late stage of the E2d2
period, the Gaoyou Depression uplifted as a result of
Zhenwu Movement leading to the denudation of Dainan
Formation which was unconformably overlain by the
Sanduo Formation (Table 1).
5 Sedimentary architecture and implications
Continental rift basin sediment filling patterns are mainly
controlled by tectonics
(Lin et al. 2001)
, and subordinate
lake-level fluctuations and sediment supply
(Yu et al.
. Tectonics primarily determines the type of
sedimentary facies present and the associated spatial
distribution pattern. The southern slope of the Gaoyou Depression
was steep and narrow such that the increased rate of
accommodation creation, triggered by tectonically induced
subsidence (fault movements), exceeded the rate of
sediment supply (A [ S). As a result, small-scale and
coarsegrained fan deltas and nearshore subaqueous fans
preferentially developed (Fig. 11). For instance, in step-fault
zones such as the Huangjue and Fumin areas, the slope was
Z W w
Fan delta plain Fan delta front Pro-fan delta Delta plain Delta front Prodelta Inner fan Middle fan Outer fan Shore-shallow Semi-deep Fault
Zhen1 Fault Tongyang0Uplift
b Fig. 9 Diagrams showing the distribution pattern of the different
sedimentary facies in plan view for different stages during the
development of the Dainan Formation, Gaoyou Depression. a E2d1
stage; b E2d12 stage; c E2d11 stage; d E2d25 stage; e E2d24 stage; f E2d2
stage; g E2d22 stage; h E2d21 stage. FM Fumin; ZZ Zhouzhuang; YA
Yong’an; FH Fumin–Huazhuang; RLZ Right part of the
Lianmengzhuang; LLZ Left part of the Lianmengzhuang; HJ Huangjue;
SB Shaobo; ZC Zhenwu–Caozhuang; MJZ Majiazui; XLZ
Xiaoliuzhuang; WZ Wazhuang; ZW Zhenwu; CZ Caozhuang; LMZ-YA-FH
Lianmengzhuang–Yong’an–Fumin–Huazhuang; FC Fanchuan; LWS
Liuwushe; LMZ Lianmengzhuang; YA-FH
Yong’an–Fumin–Huazhuang. Arabic numbers show the town locations in the study area, 1
Huangjue; 2 Shaobo; 3 Zhenwu; 4 Yong’an; 5 Xiaoliuzhuang; 6
Huazhuang; 7 Zhuhong; 8 Hanliu; 9 Huangsi
(a) First member of the Dainan Formation (E2d1):
large slope angle and high lake level
(b) Second member of the Dainan Formation (E2d2):
small slope angle and low lake level
Fig. 10 Schematic map showing how the slope gradient and lake
level control the formation of the nearshore subaqueous fan and fan
delta. H1 represents the water depth; A1 indicates the slope angle
relatively gentle enough to allow for the development of
fan deltas. In the monofaulted zone, like the Shaobo area,
however the slope was sufficiently steep to form nearshore
subaqueous fans (Figs. 10, 11). The northern slope was
broad and gentle characterized by decreased subsidence as
a result of reduced movement of faults, therefore favoring
the generation of large-scale fine-grained deltas (Fig. 11).
Lake-level fluctuations and sediment supply modulated the
distribution pattern and scale of sand bodies by modifying
the interrelationship between the rates of accommodation
space creation and sediment supply. The rate of sediment
supply was able to keep pace with, or exceeded, the
increased rate of accommodation space creation. Numerous
studies have shown that lake-level fluctuations can cause a
shift in the depocenter, which results in the deposition of a
wide range of sedimentary facies in the same area of the
basin through each transgressive–regressive cycle as shown
in Fig. 7
(Posamentier et al. 1988; Hoy and Ridgway
Economically important reservoirs in the Gaoyou
Depression consist predominantly of deltaic and fan deltaic
sandstones which are mainly distributed along the margins
of depressions. Additionally, the reservoir quality of
sandstones in the subaqueous branch channels of the deltas
is generally better than that of sandstones in the
subaqueous distributary channels of the fan deltas. Porosity of the
former ranges from 10 % to 30 %, and the permeability
ranges from 1 to 100 mD. The porosity and permeability of
the latter, however, are 10 %–20 % and \1 mD,
respectively. The sandstones of nearshore subaqueous fans
represent a second reservoir type, consisting mainly of
thickbedded, turbiditic channel-fill sandstones. Some turbiditic
channel sandstones have been proven to be important oil
reservoirs in the Gaoyou and other depressions
Tian 1999; Gao et al. 2009)
. Thus, a comprehensive
understanding of the vertical evolution and distribution
patterns of the sedimentary facies of the Dainan Formation
in the Gaoyou Depression is of significance in predicting
optimal reservoir targets for exploration and exploitation.
The Dainan Formation in the Gaoyou Depression was
generated during two major sedimentation periods (E2d1
and E2d2), involving four main sedimentary facies, which
include fan delta, delta, nearshore subaqueous fan, and
lacustrine facies. In addition, the nearshore subaqueous fan
facies were absent during the E2d2 period due to the weak
movement of faults, shallowing of the water depth, and
reduction of the slope gradient. Fan delta and nearshore
subaqueous fan facies are distributed predominantly in the
southern steep slope, whereas deltaic facies occur in the
northern gentle slope. The lacustrine facies are present in
the center of the depression and on the flanks of the three
facies above. Vertically, the Dainan Formation exhibits an
integrated transgressive–regressive cycle with the grain
size and relative thickness of sandstones displaying a
coarse–fine–coarse and thick–thin–thick trend upwards,
respectively. This sedimentary framework and distribution
patterns of facies are thought to have been controlled
primarily by tectonics, and less by lake level and sediment
supply. This study provides a valuable model for the
exploration and exploitation of oil and gas in the study
area, as the sandstones of the subaqueous distributary
channel and subaqueous branch channel facies have
favorable physical properties for major lithologic reservoir
Zhenwu B′ B
Fan delta plain Fan delta front Pro-fan delta
Prdoirveecntaionnce dCehparensnseilosninedthgee Seislomciactipornofile Slope break
Acknowledgments This research was financially supported by the
National Natural Science Foundation of China (Grants Nos. 41272124
and 41402092), Natural Science Foundation (Youth Science Fund
Project) of Jiangsu Province (BK20140604), the Fundamental Research
Funds for the Central Universities (20620140386), and the State Key
Laboratory for Mineral Deposits Research of Nanjing University (Grant
No. ZZKT-201321). We thank X.D. Yue, Y.L. Li, Z.P. Zhang, Y.L.
Yao, and L.K. Gao for their helpful discussions, and assistance in field
and core observations, and the laboratory work. Especial thanks are
given to Y.J. Ma and Q.D. Liu of Jiangsu Oilfield Branch Company,
SINOPEC for their invaluable support. Special thanks should be
extended to the Petroleum Science editors and anonymous reviewers for
their constructive suggestions and comments, and to D.T. Canas of
Queen’s University, Canada for checking the English presentation.
Open Access This article is distributed under the terms of the
Creative Commons Attribution 4.0 International License (http://crea
tivecommons.org/licenses/by/4.0/), which permits unrestricted use,
distribution, and reproduction in any medium, provided you give
appropriate credit to the original author(s) and the source, provide a
link to the Creative Commons license, and indicate if changes were
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