The gravity-flow channel developed in continental margin zone is the preferred transportation route for the terrigenous debris to deep sea^[1], and an important location for the filling and accumulation of sandy sediments^[2], as well as the favorable hydrocarbon enrichment area^[3]. The gravity flow channel is of great research importance and significant petroleum exploration value. Since 2000, some research works related to the gravity flow channel, such as type division^[4], analysis of external morphology and internal filling architecture^[5], and exploration of depositional evolution and genetic mechanism^[6,7,8], have received considerable attention among geologists and petroleum industry all around the world and become a hot topic^[9,10,11].

The Congo Basin is one of the most typical and petroliferous basins in deep-water oil-gas exploration, within which many large-scale gravity flow channels have developed^[12]. Focusing on the classification, sedimentary environments, and characteristics of the channels as well as the controlling effects of tectonic geomorphology and salt activities on their development, a series of research work have been carried out by scholars^[13,14,15]. There are 5 types of channels known to be developed, namely axial incised valley, single erosional channel, erosional channel complex, aggradational levee-channel and aggradational lobe-channel. The levee and marine mud were generally well developed, and the tectonic uplift provided the driving force for the development of the deep-water gravity flow deposits. However, most of these studies failed to reveal the filling architecture and depositional evolution of deep-water channels systemically. In addition, the response of various controlling factors, such as deep-water channels’ filling evolution, sea-level change, paleoclimate, tectonic events-provenance supply and salt activities, still needs to be studied further^[16].

Based on an integrated analysis of around 3000 km² high-resolution 3D seismic data under 500-1200 m of sea water with a dominant frequency of 25 Hz and a bandwidth of 12-37 Hz, 10 well logs and core samples related in the study area were used to establish the high-resolution sequence stratigraphy framework, and then the main lithofacies features of the Miocene were summarized and the main sedimentary units of the gravity flow channels were identified. By jointly analyzing seismic facies and seismic attributes, the external morphology and filling architecture of the gravity flow channels were revealed, and the development and evolution model of the Miocene gravity flow channels in the study area was established. Finally, on the basis of the previous studies, we systematically discussed the main controlling factors of the development of gravity flow channels, including sea level change-paleoclimate, tectonic events-provenance and salt structure activities, which aims to provide certain reference for deep-water petroleum exploration in this basin.

The Lower Congo-Congo Fan Basin, referring to the Lower Congo Basin and part of the Congo Fan Basin, is located in the eastern side of the South Atlantic Ocean (Fig. 1a) and confined by the Pre-Cambrian basement to the east, toe of the Africa continental slope to the west, the Kwanza Basin to the south, and the Gabon Coastal Basin to the north^[17]. It covers an area of approximately 17×10⁴ km² with an outer contour of the 3000 m depth marine contour line (Fig. 1b). As a typical passive continental margin basin, the Lower Congo-Congo Fan Basin contains abundant petroleum resources^[18,19], and it has been extensively studied by geologists in recent years.

The Lower Congo-Congo Fan Basin experienced three evolution stages: the rifting phase (Late Jurassic-Early Cretaceous Barremian stage), the transition period (Early Cretaceous Aptian stage) and the drift phase (Early Cretaceous Albian Stage to present)^[18]. During the rifting period, a set of primary hydrocarbon source-rock with high-quality developed in the study area due to the intra-continental rifting. During the transition period, a set of regional evaporative salt strata were deposited. Then, during the early drift period, from the Late Cretaceous Campanian age to Maastrichtian age, the sedimentation is characterized by a set of marine shale rich in organic matter. From the Paleogene to present, the late drift period occurred. Before the Miocene, the delta and gravity flow deposits composed of continental clastic (e.g., the Paleogene Landana Formation) were developed. After the Miocene, the Congo River revived and a large amount of terrigenous detrital were accumulated within the basin and transported to deep-sea area through submarine valley^[20], which resulted in the thick gravity flow deposits, up to 6000 m (Fig. 2) and constituted the present-day West African Congo Fan system. The Miocene Malembo Formation has a thickness of 1200-1500 m^[19], as the target stratum of this paper, is the most important reservoir and oil-producer in this basin.

During the Early Cretaceous Aptian stage, the transition period, various salt structures were formed, distributed orderly from land to sea in the Lower Congo-Congo Fan Basin^[21]. The eastern extensional zone mainly consists of salt rolls or salt windows. The salt rock layer is relatively thin and missing in some area due to the tectonic deformation, forming salt windows or salt welding. In the middle transitional area, the common structures are salt arch, salt puncture and salt wall, and the salt layer is extremely thick. The western compression zone is dominated by salt awn, salt plant and thick block- shaped salt rock mass. Episodic salt tectonic deformation underwent three periods, the Early Cretaceous Albian stage, the Early-Middle Oligocene and the Late Miocene to the present, respectively^[17].

According to the five sequence boundaries of SB1-SB5 identified, the Miocene of the target layer are divided into four 3rd-order sequences, namely SQ1, SQ2, SQ3 and SQ4 respectively, and the gravity flow channels were developed in the lower system domain of each sequence. In addition, the 3rd-order sequence is further separated into seven 4th-order sequences by the 4th-order sequence interfaces sb1, sb2 and sb3 (Figs. 2 and 3). SQ1 is equivalent to the Lower Miocene, and SQ2 and SQ3 sequences are equivalent to the Miocene, and the SQ4 sequence corresponds to the Upper Miocene. Typical truncation and onlap have been observed on the top interface of the 3rd-order sequence. The deposits consist of sandwiched gravity flow channel within deep-sea mudstone, shown as bell-shaped or box-shaped GR curves. The bottom sequence boundary is characterized by onlap. The erosion to the underlying strata is observed below it. As the whole is located in a deep-water environment, dominated by mudstone deposits, it represents as conformity with truncation and onlap in certain locations (Fig. 4). In the sequence unit, sequence interfaces SB1, SB2 and SB3 are respectively Miocene bottom interface, interface of Middle Miocene and Lower Miocene and Middle Miocene internal sequence interface. Above these three sequence boundaries are generally lowstand slope fan systems, mainly defined by channel filling and overbank with fining-upward sand deposits. The GR curve exhibits as box-shaped or finger-shaped, often in contact with the underlying strata abruptly (Fig. 3). The onlap point is often seen above top sequence boundary, while the truncation point can be found below. Both SQ2 and SQ3 have developed flooding surfaces, so the highstand systems tract (HST) is often formed in the lower part of SB3 and SB4, which is mainly composed of frontal lobes. SB4 is the boundary of the Middle Miocene and Upper Miocene, where erosion unconformity is observed partially. Lowstand turbidite is developed above the interface, but it is generally in a small scale, dominated by overbank deposition. The water body is deepened upward and toplap or truncation is often shown at the interface. SQ4 sequence in the Upper Miocene is defined by the sequence boundary SB5 corresponding to the top interface of Miocene. It is characterized by a succession of thick mudstone deposits, with a high value on GR curve, revealing the deepening of water. Incised valleys are recognized in several sequences. Thinner sandstone filling in incised valley is developed above the SB5 and the logging curve is finger-like, with a sudden change on the resistivity curve at the interface (Fig. 3). In the direction being perpendicular to provenance, the SB5 interface represents obvious denudation on the seismic profile, and the corre-sponding seismic reflection shows the characteristics of medium amplitude, low frequency and high continuity, while the lower layer shows medium-strong amplitude, high frequency and medium continuity (Fig. 4).

For deep-water deposits, the lowstand systems tracts are generally formed during the relative sea level drop and early rise, and mainly developed gravity flow deposits, which are of great significance for oil and gas exploration. With the continuous rise of sea level, the terrigenous detritus in the deep-sea area decreases gradually, consisting of argillaceous debris flow and deep-sea and semi-deep-sea muddy sediments. During the early to middle Miocene, due to the tectonic uplift of continental shelf and the sharp decline of sea level, ample sediments were supplied^[20]. Low slope fan systems were developed in the lower part of SQ1 and SQ2, i.e., the SQ1-1 and SQ2-1 (Fig. 3), with a large development scale and strong erosive ability. Turbidite channel or channel complexes were mainly developed, and the development scale of channel reached its peak. From Mid-Late Miocene to Late Miocene, the scale of turbidite channel developed in the lowstand systems tract of SQ3 and SQ4 gradually decreased (Fig. 3), which was dominated by levee-channel deposits and channel complexes. Within the sequence, the SQ2-2 sedimentary sequence was mainly characterized by extensive shale mixed with a small amount of muddy siltstone or silty mudstone (Fig. 3), and its logging curve was shown as high gamma in the shape of micro-teeth and abrupt contact with the low systems tract above the interface (Figs. 3 and 4).

The gravity flow sedimentary system of the Lower Congo-Congo Fan Basin is composed of siliciclastic rocks and pelite. Based on core, logging, and seismic data, from the perspective of the combination of geomorphology and sedimentary units, the main sedimentary units are identified, including slumping deformation layers, mass transport deposits, gravity flow channel fills, levee-overbank, frontal lobes, etc.

3.1.1. Slumping deformation layers

Deformed fine sandstones with mud debris of different sizes owing to slumping deformation can be recognized in the study area. Soft deformation structures and slumping deformation structures are identified in it (Fig. 5a). The gray-black mudstone on the top and fining upward sandstone in the lower part, and the co-axial deformation of the gravity flow channel (U-shaped) (Fig. 6, debris flow collapse) suggest the slumping deposits within channel (Fig. 4).

3.1.2. Mass transport deposits

Mass transport deposits are formed by various gravity other than turbidity current, such as slide, slump and debris flow. They are originally applied to describe the sediments at the bottom of a sequence overlapped by channels or natural levees deposits^[22]. Due to the different scales of mass transport deposits, their thicknesses vary greatly, up to hundreds meters. MTDs are dominated by disorderly arrayed gravels, sands and muds with poor stratification, where thin turbidite sandstone, thick muddy debris-flow deposits and slumping and sliding structures are observed.

3.1.3. Gravity flow channel

As the most important reservoir in deep-water sedimentary system, gravity flow channel extensively developed in continental slope, lower continental slope and deep- water basin. The shape and position of the gravity flow channel are controlled by depositional process and downward erosion^[23]. It can be divided into muddy channel and sandy channel based on different types of fillings.

Muddy turbidity deposits represent the predominant portion of muddy channels. Relevant studies indicated that thick-massive glutenite can be recognized at the bottom of muddy channel^[24,25,26]. In the middle part, it is composed of fine sandstone with mud or argillaceous fine sandstone, along with fining upward grain, increasing mud content, as well as wavy bedding and ripple lamination. The upper part is dominated by deep-sea mudstone deposits.

Sandy channels are mainly filled with sandy fillings. It has been shown from cores of Well W3 in the study area that the single channel is characterized by massive sandstone with mud and gravel deposits in some parts (Fig. 5b). The bottom of the channel consists of poorly sorted sandstone, containing millimeter to centimeter-level gravel grains (Fig. 5c), and the grain size changes obviously with unclear bedding and large particles suspendedly accumulated. The main part of the channel is characterized by predominantly sandstone and regionally distributed coarse gravels, with low-angle cross bedding in the middle, showing an overall positive grain sequence. The top is dominated by thin interbeds of very fine sand and silty clay, and the deformed structure can be found in the middle muddy layer. Besides, the sandy channel is shown as box-shaped log curve pattern as a whole (Fig. 4, Well W5).

3.1.4. Levee-overbank deposits

The levee-overbank deposits are mainly developed on both sides of the channel, and the lithology is represented by interbedded sand and mud (Fig. 5d), mostly thin siltstone and mudstone, including constituent units of proximal levee, distal levee, overbank, and slumping deposits (Fig. 5d). Since sediments overflowing the bank, as a result of the gravity flow channel scouring the levee, the overbank deposited alternately with levee. It appears as a sawtooth pattern on logging curve (Fig. 4, Well W5). Generally, the thickness of the sediment on the near side of the levee is larger than that of the other side far from the levee, where a nearly wedge-shaped sediment body formed^[27].

3.1.5. Lobe deposits

The frontal lobe deposits are commonly found at the end of the channels. Owing to the limited sediments supply, the lithology is dominated by siltstone, mainly interbedded thin-layered siltstone and mudstone, with fine-medium sandstone (Fig. 5e). In some areas, narrow channels mainly affected by erosion are developed, which are filled with mixed massive sandstone from the axis to the edge of the channel, and muddy conglomerate is present at the bottom.

3.2.1. Mass transport deposits

The mass transport deposits have a series of different seismic reflection structures, such as parallel, thrust, rotating, clutter, mound-shaped, blank. It exhibits a seismic character with poor continuity, diverse amplitude (Table 1, SF1) and low-value bell shape or funnel shape on GR curve. The lithology is characterized by the messy accumulation of gravel, sand and mud, with poor stratification. In addition, thin turbidite sandstone, thick muddy debris flow deposition and folds and sliding blocks formed by slumping are recognized. This facies commonly appears in deep water areas of the continental margin, especially at the bottom of the sequence, and is covered by channels and levees on the top. It overlies the erosional bottom boundary from upward dipping direction, and displays as mound shape from downward dipping direction, pinching out laterally. Based on the comprehensive analysis of seismic, logging, and lithological characteristics, it is interpreted as mass transport deposits, which is mainly formed by slumping, generally including slider, clasolite, and block transport complexes.

3.2.2. Gravity-flow channel

The gravity-flow channel is "U" or "V" shaped in seismic profile, and "S" shaped on RMS amplitude attribute map, with strong internal amplitude and poor continuity (Table 1, SF2). The overlying strata have a seismic response of weak amplitude and a parallel-subparallel reflection pattern. The lithology is characterized by conglomerate, sandstone, mudstone and their mixed deposits, interpreted as the gravity-flow channel. In the following parts, its internal architecture units will be discussed based on the seismic reflection structure and attribute features.

3.2.2.1. Composite structure of gravity-flow channels

(1) Single channel. It is shown as small "U" or "V" shape on the seismic profile, with medium-strong amplitude, short-axis reflections and occasionally weak amplitude reflections, which is formed by one erosion and filling (Fig. 6 SQ1 and SQ4). The deposits are dominated by sandstone, occasionally covered by deep-sea mudstone on the top, showing as an obvious positive graded bedding vertically.

(2) Complex channel. It is generally composed of multiple single channels with similar characteristics, with a width to depth ratio of about 10. There are two types of complex channel, including straight channel and meander channel. On the seismic profile, it corresponds to small "U" or "V" shape, with strong amplitude, discontinuity and parallel reflection signatures (Fig. 6 SQ2). Cross bedding, parallel bedding, small wavy bedding, as well as a positive sequence in the vertical are identified.

3.2.2.2. Sedimentary unit of gravity-flow channel

(1) Debris flow deposits at the bottom of gravity-flow channel

It has the seismic response of strong amplitude at the bottom and weak amplitude with medium to low frequency in the internal. The lateral migration on the plane is inconspicuous (Table 1, SF2-1, Fig. 7). It is mainly developed in the lower system domain of sequence, dominated by coarse-grained suspended conglomerate (Fig. 5e), which is comprehensively interpreted as debris flow deposits at the bottom of gravity-flow channel.

(2) Lateral aggradation body

This facies is of strong amplitude, crescent shape, and closely arranged in different stages on RMS amplitude attribute map (Table 1, SF2-2), which are similar to point bar deposits in fluvial facies. On seismic profile, it is mainly characterized by discontinuous and shingled reflections, with an inclination of approximately 5°-10°, which towards to the axis of the previous phase of the channel. However, when the thickness of the sediment is less than the tuning thickness of the seismic profile, it is mostly manifested as a single, continuous, strong amplitude reflection (Table 1, SF2-2), which can only be identified on the amplitude attribute map, with horizontal top and bottom, covering an area of 1 to 5 km² and a thickness of up to 50 m. Thus, it is integratedly interpreted as lateral aggradation body.

(3) Abandoned channel deposits

Abandoned channel deposits are seismically characterized by a strong amplitude, intermediate frequency, parallel reflection signatures, and appear in a semicircular shape with strong amplitude on RMS amplitude attribute map (Table 1, SF2-3, Fig. 7). The lithology is dominated by conglomerate, sandstone and siltstone in the lower part and covered by deep-sea mud on the top, showing as a positive cycle in vertical, which is comprehensively interpreted as abandoned channel deposits.

(4) Overbank deposits

Overbank deposits show moderate to strong amplitude, mound shaped or inconspicuous oblique seismic reflection features, and nearly fan-shaped type on RMS amplitude attribute map (Table 1, SF2-4, Fig. 8), mainly composed of interbedded fine sandstone and mudstone. The grain size is relatively fine, with coarsening upwards sequence, which is comprehensively interpreted as overbank deposits (Fig. 5d).

(5) Slumping deposits

On the seismic profile, it shows weak-amplitude, elongated to crescent-shaped, inclining at the bottom and nearly parallel reflection pattern (Table 1, SF2-5). It is semicircular or fan-shaped on RMS amplitude attribute map, which is mostly associated with the fan-shaped collapse on the edge of the channel, but its internal structure shows great difference. There are various lithological types, such as soft deformed structures, slumped muddy debris etc. (Fig. 5a). Therefore, it is comprehensively interpreted as the slumping deposits within channel, which are mainly formed by the sedimentation of sliding block, slump, and debris flows.

3.2.3. Channel-levee complexes

On the seismic profile, weak amplitude, "U"-shaped or "V"-shaped reflection, with poor continuity can be observed in the middle. On the two sides of channel, it shows strong amplitude, good continuity and nearly wedge-shaped reflection. The overall shape is like gull wings (Table 1, SF3). Morphologically, the sedimentation slope of inner side is steep, while the outer side slope is much slower. From the inner to the outer side of the bank, the amplitude becomes weaker gradually, which indicates that the grain size of the sediment gets finer. Spatially, these deposits are generally distributed on both sides of high-curvature channel, mainly composed of fine sandstone and siltstone, whose grain size is finer than that of the sediments in inner part of channel. It appears in positive grain sequence vertically, interpreted as channel- levee complexes, which is composed of channel deposits in the middle and levee deposits caused by gravity flow overflow on the two sides.

3.2.4. Lobe deposits

The seismic reflections of lobe deposits mainly consist of strong amplitude, intermediate frequency, parallel- subparallel reflection. The mound-shaped reflection is also recognized in the study area (Table 1, SF4, Fig. 9). Composed of composite sheet sand and layered sheet sand, it is located at the end of an eroded channel or a channel-levee complex. Meanwhile, the composite sheet sand and layered sheet sand mentioned above consist of sandstone with a small amount of mudstone, and interbedded layers of sandstone and mudstone respectively. So, this facies is comprehensively interpreted as lobe deposits.

3.3.1. Evolution features

The depositional evolution of the Miocene gravity-flow channels in the study area can be classified into 4 stages.

(1) During the Early Miocene (SQ1), gull-winged, weakly restricted and unrestricted depositional channels were mostly developed in the study area (Figs. 6 and 7). Their basic characteristics are as follows: gull-winged, weakly restricted or unrestricted; a single channel is about 50 m thick with the high breadth-depth ratio; mainly aggradation and filling, without erosion at the bottom.

(2) In the early of the Middle Miocene (SQ2), W-shaped, weakly restricted erosional-depositional channels were the major part in channel systems (Figs. 6 and 8). Their basic characteristics are: W-shaped, weakly restricted, medium scale of single channel with moderate breadth-depth ratio; mainly aggradation and filling, with erosion occurring at the bottom.

(3) In the late of the Middle Miocene (SQ3), U-shaped, restricted erosional channels were considered as major categories developed in the study area (Fig. 6), and their basic characteristics are as follows: U-shaped and restricted; large-scale channel with relatively low breadth- depth ratio; the sedimentation was dominant by erosional filling; strong erosion displayed at the bottom; complex channels were formed by interaction cutting and superimposition of different single channels.

(4) In the Late Miocene (SQ4), the study area was mainly developed with V-shaped, deeply erosional isolated channels (Fig. 6). The basic characteristics are as follows: V-shaped and deep dissection with quite low width to depth ratio; the sedimentation tends to be erosional filling; the channels were isolated or randomly distributed.

3.3.2. Deposition model

Based on the rules of channels classification proposed by predecessors^[4], the sedimentary characteristics of the channels were summarized and then the development model of the Miocene gravity flow channels in Lower Congo-Congo Fan Basin was built (Fig. 10). From toe of slope-submarine plain to the lower continental slope, the middle continental slope and finally to the upper continental slope, four different types of channels were developed: (1) gull-winged, weakly restricted-unrestricted depositional channels; (2) W-shaped, weakly restricted erosional-depositional channels; (3) U-shaped, restricted erosional channels; (4) V-shaped, deeply erosional isolated channels.

At the beginning of the Miocene, the ice age occurred and the sea level started to fall^[19]. In the Early Miocene, the sea level was relatively high. The study area was located at toe of slope to submarine plain, along with very small landform slope and weak gravity flow, which contributed to the channel-levee complexes and lobes developed in the SQ1 sequence^[2]. During the Middle Miocene, the sea level continued to fall due to the glacial climate, making the location of study area gradually change from the lower continental slope to the middle continental slope. When it is situated on the lower continental slope, the slope of the landform is small and the gravity flow energy is not strong enough, resulting in the W-shaped, weakly restricted erosion-sedimentary branch channels in the SQ2 sequence^[28]. Then, with a larger landform slope and a stronger gravity flow in the middle continental slope, the U-shaped and restricted erosion-type waterways dominated the SQ3 sequence^[7]. As the sea level further fell in the Late Miocene, the study area was finally emplaced on the upper continental slope. At this point, the landform slope slightly smaller than of middle continental slope, but the gravity flow energy is relatively strong^[28,29], mainly developing V-shaped, deep eroded isolated channels in the SQ4 sequence.

In general, a continuous decline in the relative sea level caused by the Miocene glacial climate, led to the continuously rising geomorphological position of the study area, which consequently affected the strength of gravity flow and controlled the development of gravity-flow deposits.

In the Late Oligocene to Early Miocene, the African continental plate and the Iberia plate collided with orogen^[19], making the West African coast in a state of compression^[30,31]. The continental shelf was exposed to large-scale erosion and the provenance supply was sufficient. A large amount of sediments were transported to deep-sea basin, providing material conditions for the development of gravity flow and forming the initial deep-water fan. Between the Early Miocene and the Middle Miocene, the west African coast uplifted, exposed and eroded again. In response to the sudden increase of sediment supply and rapid progradation, the deep-sea area prone to form large-scale multistage superimposed gravity channels^[32]. In the Late Miocene, the west African coast continued to be uplifted. However, the uplift was relatively weak, and the sedimentary supply was limited^[33], thereby leading to small-scale gravity-flow channels and levee-channel complexes.

The salt tectonic activities in the Lower Cong-Congo Fan Basin in the Miocene were proved to be really extensive, whose influence on gravity-flow channel deposition can be divided into 3 phases: presedimentary period, synsedimentary period and postsedimentary period^[17]. Salt structure developed in presedimentary stage can redirect, restrict or block the gravity-flow channel^[34]. When the flow direction of the channel is perpendicular to the small salt structure or oblique at a large angle, the channel will change direction to bypass the salt structure. If the salt structure is too large to be bypassed or crossed, the channel will be blocked^[35]. When the flow direction of the channel is approximately parallel to the salt structure or oblique at a low angle, the channel cannot migrate laterally but develops under the restriction of the salt structure^[35]. The relationship between the synsedimentary salt structure and the channel depends on the rate of channel eroding and salt rock uplifting^[36]: If the salt rock uplift faster than channel erosion, the axis of the multi-phase gravity-flow channel will migrate laterally to the lower part of the structure^[37]. Otherwise, the vertical accretion of the channel will deposit on the active salt structure and continuously erode the salt structure, resulting in local depressions at the top of the salt structure. Furthermore, the development of postsedimentary salt structures can give rise to the denudation and destruction of channels^[17].

The Miocene can be divided into four 3rd-order sequences, which can be subdivided into seven 4th-order sequences. The gravity flow channels dominate the LST, characterized by channel fills and levee-overbank, while the HST predominately develops lobe deposits, with finer sand bodies. The lithology of the Miocene gravity-flow deposits is mainly composed of siliciclastic rocks and pelite. The main sedimentary units relevant comprise slumping deposits, MTD, channel fills, levee-overbank, and frontal lobes.

The depositional evolution of the Miocene gravity-flow channels in the study area can be divided into 4 stages from the Early Miocene to the Late Miocene. During the Early Miocene (SQ1), gull-wing, weakly restricted-unrestricted depositional channel-overbank complexes and splays-lobes were mainly deposited in the study area. When it was in the early Middle Miocene (SQ2), W-shaped and weakly restricted erosional-depositional channels (multi-phase superposition) were mainly developed. Then, U-shaped and restricted erosional channels dominated in the late Middle Miocene (SQ3). Finally, the Late Miocene (SQ4) was characterized by V-shaped and deeply erosional isolated channels.

The development of the Miocene gravity-flow channels in the study area is jointly controlled by paleoclimate, sea level change, tectonic movements, provenance and salt structures. Climate cooling and continuous fall of the sea level made the study area transit from toe of slope-submarine plain to lower continental slope, middle continental slope and finally to upper continental slope, which in turn affected the strength of the gravity flow. Three times of tectonic uplifting and climate cooling in the West African coast provided sufficient provenance for the development of the gravity flow deposits. Multistage activities of salt structures played crucial roles in redirecting, restricting, blocking and destroying the gravity flow deposits.