Break Belt Research Articles

Characteristics and geological significance of early carboniferous soft-sediment deformation structures in the Kushanhe section, southwest Tarim Basin, Northwest China

The early Carboniferous Kushanhe Formation and Hantiereke Formation in the Kushanhe section in the piedmont of the southwestern margin of Tarim Basin are in a medium-deep water sedimentary environment with a stratigraphic thickness of more than 500 m, and the sedimentary facies is slope-shelf facies. Among these deposits, soft-sediment deformation structures (SSDS) are common, dominated by various types of slumps. The appearance of SSDS is related to the geotectonic environment of early Carboniferous in southwest Tarim Basin. In the Early Carboniferous, the Paleo-Tethys ocean dived under the Tarim plate, forming a back-arc structure, and a structural slope break belt easily appeared along the basin edge, which provided topographic conditions for the development of marginal platform marginal belt and slope facies. Under this background, the ultra-thick volcanic rocks of Wulate Formation accumulate along the subduction zone, and earthquakes with M≥ 5.0 are prone to occur. Landslides related to earthquakes and corresponding SSDS are easily triggered at the outer edge of the slope break zone. The large earthquake induced by tectonic environment is an important trigger factor of early Carboniferous SSDS. Therefore, the appearance of early carboniferous SSDS in Kushanhe section is an important sedimentary response to the early carboniferous piedmont tectonic activities in southwestern Tarim.

A Method for Defining Sedimentary Characteristics and Distributions and Its Application in Qinnan Depression, Bohai Bay Basin

A new method incorporating geophysical analysis and geological analysis is proposed to define the sedimentary characteristics and distributions in basins with few drilling wells to promote the exploration of reservoirs. This method is applied to a study, through which its principles, closed-loop workflow and technologies are introduced in detail and the sedimentary characteristics and distributions of the study area are accurately defined. During the application process of the method, a compatible geological model is established, based on which the seismic data are interpreted and the results derived from the interpretation are further verified via seismic forward modeling. The study results exhibit a successive sand-rich deposition from the retrogradational gully-filling gravity flow deposition including near-shore fans, slope fans and basin-floor fans delimited by different slope break belts in transgressive sequences to the progradational delta deposition in a retrogressive sequence including braided river deltas with a long extension distance and fan deltas developed along a steep slope belt. And the potential reservoirs are located at the point-out sites of sand bodies with lower average P-wave velocities than those of muddy sediments. The proposition and application of this method are of great significance for oil and gas exploration.

Sedimentary characteristics and model of gravity flow channel - lobe complex in a depression lake basin: A case study of Chang 7 Member of Triassic Yanchang Formation in southwestern Ordos Basin, NW China

To reveal the development characteristics and distribution of gravity flow sedimentary system under micro-paleogeomorphologic units of the Chang 7 Member of Triassic Yanchang Formation in the southwestern Ordos Basin, on the basis of the restoration of the paleogeomorphological form of the Chang 7 depositional period by the impression method, each micro-paleogeomorphologic unit was depicted in-depth, and the characteristics and development models of gravity flow deposits in the study area were studied in combination with outcrop, core, mud logging and log data. The results show that: (1) The paleogeomorphology in the Chang 7 depositional period was an asymmetrical depression, wide and gentle in the northeast and steep and narrow in the southwest. Three sub-paleogeomorphologic units were developed in the basin, including gentle paleo-slope, paleo-slope and paleo-depression, and they can be further subdivided into eight micro-paleogeomorphologic units: bulge, groove, slope break belt, plain of lake bottom, deep depression of lake bottom, paleo-channel, paleo-ridge of lake bottom, and paleo-uplift of lake bottom. (2) There are 9 types of lithofacies and 4 types of lithofacies assemblages of Chang 7 Member. According to lithofacies composition and lithofacies vertical combination, the gravity flow deposit is further divided into 5 types of microfacies: restricted channel, unrestricted channel, natural levee, inter-channel, lobe. (3) Paleogeomorphology plays an important role in controlling sediment source direction, type and spatial distribution of sedimentary microfacies, genetic types and distribution of sand bodies in Chang 7 Member.

Cenozoic Depositional Evolution and Stratal Patterns in the Western Pearl River Mouth Basin, South China Sea: Implications for Hydrocarbon Exploration

Investigating the deposition evolution and stratal stacking patterns in continental rift basins is critical not only to better understand the mechanism of basin fills but also to reveal the enrichment regularity of hydrocarbon reservoirs. The Pearl River Mouth Basin (PRMB) is a petroliferous continental rift basin located in the northern continental shelf of the South China Sea. In this study, the depositional evolution process and stacking pattern of the Zhu III Depression, western PRMB were studied through the integration of 3D seismic data, core data, and well logs. Five types of depositional systems formed from the Eocene to the Miocene, including the fan delta, meandering river delta, tidal flat, lacustrine system, and neritic shelf system. The representative depositional systems changed from the proximal fan delta and lacustrine system in the Eocene–early Oligocene, to the tidal flat and fan delta in the late Oligocene, and then the neritic shelf system in the Miocene. The statal stacking pattern varied in time and space with a total of six types of slope break belts developed. The diversity of sequence architecture results from the comprehensive effect of tectonic activities, sediment supply, sea/lake level changes, and geomorphic conditions. In addition, our results suggest that the types of traps are closely associated with stratal stacking patterns. Structural traps were developed in the regions of tectonic slope breaks, whereas lithological traps occurred within sedimentary slope breaks. This study highlights the diversity and complexity of sequence architecture in the continental rift basin, and the proposed hydrocarbon distribution patterns are applicable to reservoir prediction in the PRMB and the other continental rift basins.

Source-to-Sink Comparative Study between Gas Reservoirs of the Ledong Submarine Channel and the Dongfang Submarine Fan in the Yinggehai Basin, South China Sea

The Ledong submarine channel and the Dongfang submarine fan, two remarkable sedimentary systems developed during the late Miocene, are considered promising hydrocarbon reservoirs in the Yinggehai Basin of the South China Sea. A comparative study was conducted to reveal the differences between the source-to-sink characteristics of the two gas-bearing and gravity-driven depositional systems to determine their provenances, formation mechanisms and migration paths as well as their key controlling factors. The heavy mineral assemblages and detrital zircon U-Pb dating results suggest that the Ledong channel was fed by the Hainan provenance from the eastern margin, whereas the Dongfang fan was supplied by northwestern terrigenous sources. The relative sea level transgression and sufficient sediment supply triggered the delivery of deltaic loads toward the continental shelves. Seismic data show that fracture activity had a great impact on the tectono-morphologic features of the margins. During downward flow, the gravity flow along the Yingdong Slope encountered steeply falling faulted slope break belts and formed the Ledong incised channel, and the gravity flow of the Yingxi Slope moved through the gently dipping flexural break slope zone and formed the Dongfang dispersed lobe deposits. Since ca. 30 Ma, the sedimentary center has been migrating from the north to the southeast, which produced a clear control of the southeastward distribution pattern of these two sedimentary systems. Observations of cores and thin sections indicate that the rock structures and their compositions are more mature in the Dongfang channel than in the Ledong fan. This study documents significant differences and similarities by comparing the source-to-sink processes of the two gravity-driven systems that developed in the Yinggehai Basin and provides analogies for understanding similar submarine sedimentary systems that developed under similar geological contexts worldwide.

Geophysical characteristics of a focused fluid flow system in the western South China Sea

High-resolution multichannel seismic data and multibeam terrain data are used to analyse and identify a focused fluid flow (FFF) system in the central and northern parts of the Zhongjiannan Basin in the western South China Sea. The authors classify and summarise the geophysical characteristics of an FFF system in the study area. It is divided into a fault-related FFF system and a column-related FFF system. In addition, the FFF system in the study area is mainly located within the tectonic activity area, thin slope break belt and land slope area. The rich FFF system in the study area is an important channel for fluid migration, which is conducive to gas hydrate accumulation. The FFF system in the study area is poorly studied, and the distribution research results of the FFF system in this area can be used more widely in hydrocarbon and gas hydrate exploration and must be taken into account when assessing seabed stability.

The Major Controlling Factors and Different Oolitic Shoal Reservoir Characteristics of the Triassic Feixianguan Formation, Eastern Longgang Area, NE Sichuan Basin, SW China

AbstractBased on comprehensive analyses of occurrence, petrological observation, pore structure and geochemistry, the different reservoir characteristics and reservoir evolutionary pathways between different oolitic shoal reservoir types of the Feixianguan Formation on the west side of the Kaijiang‐Liangping Trough have been studied. There exist three stages of high‐energy slope break belts in the Feixianguan period, the corresponding three stages of oolitic shoals gradually migrating in the direction of the trough. Three types of oolitic shoal reservoirs, namely, residual‐oolitic dolomite, mold‐oolitic dolomite and sparry oolitic limestone, were formed during sedimentary‐diagenetic evolution, the pore types being intergranular dissolved pore, mold pore (or intragranular dissolved pore) and residual intergranular pore, respectively. The petrology, physical properties and pore structure of the different types of oolitic shoal reservoirs are quite different. Residual‐oolitic dolomite reservoirs have the best quality, while sparry oolitic limestone reservoirs have the poorest. Combined with analyses of trace elements, rare earth elements and carbon‐oxygen isotopes, it is suggested that the formation of residual‐oolitic dolomite reservoirs is jointly controlled by penesaline seawater seepage‐reflux dolomitization and hydrothermal dolomitization. Mold‐pore oolitic dolomite reservoirs are controlled by penesaline seawater seepage‐reflux dolomitization and meteoric water solution. The burial dissolution of organic acid not only further improves the reservoir qualities of previously formed oolitic dolomite reservoirs, but also preserves residual intergranular pores in the sparry oolitic limestone reservoirs.

Formation of the Neoproterozoic Rifting Depression Groups of the Tarim Basin and its Hydrocarbon Potential: Responded to the Initial Opening of the Proto‐Tethy Ocean

AbstractThe largest and superimposed Tarim basin developed on the one of the three bigger craton, Tarim Craton, in China. The early Paleozoic is the heyday of its development and cratonization, and then changes to the different property basin. The reserved sedimentary strata of Neoproterozoicare recognized mainly in the local of outcrops periphery orogenic belts, but drilling core in the basin reveals them seldom. The proto‐type of the initial Tarim Basinis always a mystery. The vast desert, huge‐thickness of sedimentary strata, multiple tectonic movements, and a low quality of deep data are the keys to getting to know him. We comprehensive field outcrops, wells, seismic reflection profiles with higher SNRs and aeromagnetic data, recognized about 20 normal fault‐controlled rifting depressions of the Cryogenian and Ediacaran, which scattered throughout the basin, and developed on the Precambrian metamorphic and crystalline basement. The structural framework is clearly different from that of the overlying Phanerozoic. The rifting depressions consist of mainly half grabens, symmetrical troughs and horst‐grabens. From the northeast to southwest of the basin, they are divided into three rifting depression groups (RDG) with the WNW, ENE, and NW‐trends that are mainly controlled by normal faults. From the Cryogenian to Ediacaran, most of the main inherited faults to active and eventually ceased at the end of the Ediacaran or Early Cambrian, while subsidence centers appeared and migrated eastward along the faults. They formed under the NNE‐SSW oriented and NNW‐SSE‐oriented extensional paleo‐stress fields (relative to the present) during the Neoproterozoic, and were accompanied by clockwise shearing. According to the analysis of the activities of syn‐sedimentary faults, filling sediments, magmatic events, and coordination with aeromagnetic anomalies, the tectonic properties of the fault depressions are different and are primarily continental rifts or intra‐continental fault‐controlled basins. The formation of the rifting depression was associated with the initial opening of the South Altun‐West Kunlun Ocean and the South Tianshan Ocean, which were located at the northern and southern margins of the Tarim Block, respectively, in response to the break‐up of the Supercontinent Rodinia and the initial opening of the Proto‐Tethys Ocean.Inthe RDG developedfluvial, shallow marine and carbonate platform facies, accompanied with multiple phases of magma activities and glaciations during the Cryogenian and Ediacaran. The structural architectures of interfaces between the Neoproterozoic and Cambrian are mainly angular and parallel unconformities in the RDG. Over the parallel unconformities in the RDGs are beneficial for the organic‐rich and /or phosphorites of the Yuertus Formation of the Lower Cambrian. The main fault belts of RDGs also controlled the small platform margin and slope break belt of in the Cambrian. The Neoproterozoic and the Lower Cambrian petroleum systems of the basin might be controlled by the RDGs in the initiation of the Tarimcraton.

Sedimentary infill of shallow water deltaic sand bodies controlled by small-scale syndepositional faults related paleogeomorphology: Insights from the paleogene Shahejie formation in the Dongying depression, Bohai Bay Basin, Eastern China

Formed in extensional structural system, syndepositional faults are widely distributed in rift basins. Large basinal scale syndepositional faults play important roles in controlling the development and dispersion of depositional systems in rift basins. When it comes to the intensively developed small-scale syndepositional faults related to those large basinal scale syndepositional faults in complex fault blocks, the controlling effects to sedimentary architecture in the finer scale are still not well understood in the depositional systems. Thus, commonly used sedimentary models without considering small-scale syndepositional faults related paleogeomorphology are difficult to apply in complex fault blocks of rift basins. In this study, using the interpretation of 3D seismic profiles, wire-line log curves, and cores, patterns of small-scale syndepositional faults and their related finer scale stratigraphic sequences are described in the upper Es2 member, Shahejie Formation of the W43 complex fault block area, Dongying Depression, Bohai Bay Basin. The syndepositional faults are intensively distributed in the W43 complex fault block area. Based on the interpretation of sequence boundaries, four types of syndepositional faults related paleogeomorphology units were identified. They are named the micro slope break belt, micro-horst belt, and the micro-graben belt. The stacking patterns and development scale of individual deltaic sand bodies in the parasequences are controlled by activity of the syndepositional faults. In the hanging wall area near the syndepositional fault of the micro-step and micro-graben, thickened multi-stage continuously individual sand bodies are deposited controlled by low topography during the depositional period with sufficient sediment supply. In the footwall area of single micro syndepositional fault and micro-horst belt, individual sand bodies became thinner and less aggraded in vertical direction. The small-scale syndepositional fault-related paleogeomorphology is a new important factor that controls the sedimentary architecture of the shallow water deltaic sand bodies in the rift basin. This study provides insights into tectonic control of finer-scale sedimentary architecture and hydrocarbon reservoirs development in continental rift basins.

Tectono-sedimentary characteristics in the area with distributed normal faults: Lower Cretaceous Prosopis Formation in the northern slope of Bongor Basin, Chad

Based on an integrated database (e.g., core observations, well logs, and seismic data), the characteristics of depositional systems, as well as the response to tectonics, are systemically delineated in the Prosopis Formation of the Lower Cretaceous at Bongor Basin, Chad. The tectonic setting of this study area experienced multiple, active sub-basins with narrow-spaced intra-basinal normal faults. The multiple normal faults formed in the initial rifted stage leading to the development of a corridor-shaped basin consisting of small-scale sub-basins. As this basin is attracting increased attention due to further hydrocarbon exploration, deciphering the process of sediment partition, especially in the initial rifted stage, would provide a further understanding of the tectono-sedimentary evolution in lacustrine rift basins. Based on core observations, well logs, and three-dimensional seismic data, fan-delta and sub-lacustrine-fan depositional systems are widely developed in this area. Two depositional systems (e.g., fan-delta and sub-lacustrine-fan) and three categories of slope break belts (single-faulted, step-faulted, and flexure types) have been identified. Overall, during the initial rifted stage, the formation of multiple normal faults mainly dominates the geomorphology and sediment supplies that generate the spatio-temporal features of depositional systems in semi-closed lacustrine basins. Climatic perturbations, furthermore, regulated the composition of sediments (coarse versus fine deposits). For the economic perspective, this study highlights the significance of fault systems in further hydrocarbon exploration during the initial rifted stage of lacustrine basins.

Sequence stratigraphic architectures and responses to syndepositional tectonic evolution in the Paleogene Lingshui Sag, Qiongdongnan Basin, northwestern South China Sea

ABSTRACT The syndepositional tectonic evolution and sequence stratigraphic architecture of the Paleogene Lingshui Sag, Qiongdongnan Basin, South China Sea, are investigated with seismic profiles, boreholes and well logs. First, according to the recognized sequence boundaries, the Paleogene sequence stratigraphic framework is established. Then, based on analyzing the subsidence history and paleogeomorphology evolution, the Paleogene Lingshui Sag is clarified to present episodic tectonic evolution, showing tectonic stage-I, stage-II and stage-III. From stage-I to stage-III, the major basin-marginal faults gradually lost control over the subsidence center, which moved away from the initial basin margin to the late central basin. Structural slope break belts, such as fault slope break belts and gentle slope break belts, formed through the above three tectonic stages and controlled the formation of four types of relevant distinct sequence stratigraphic architectures, namely, Types A1, A2, B1 and B2. Finally, the responses of sequence stratigraphic architectures to tectonic evolution are described, and the favorable hydrocarbon reservoirs in the different architectures are discussed, which constitute stratigraphic traps, fault traps, lenticular lithologic traps and updip wedge-out traps. This information is beneficial in prospecting for subtle traps in basins located in deepwater areas.

Depositional model for peat swamp and coal facies evolution using sedimentology, coal macerals, geochemistry and sequence stratigraphy

As one of the most important source rocks and reservoirs of unconventional natural gas, the sedimentary environment and mode of peat swamp (the predecessor of coal seam) is important to the coal seam’s spatial distribution, material composition, hydrocarbon generation potential, reservoir physical properties, etc. To reveal the depositional characteristics and history of environmental change in a terrestrial basin during a period of peat accumulation, the Middle Jurassic aged #7 coal from Gaoquan in the Qaidam Basin (NW China) was investigated using sedimentology, maceral composition, geochemistry and sequence stratigraphy. Based on identification of the sedimentary shoreline break belt, wave energy depletion point and position of wave base, the peat swamp system can be subdivided into (1) lakeside plain, (2) low energy lakeshore, (3) high energy lakeshore, and (4) shallow lake subfacies. A new method for determining coal facies is proposed based on the combination of environmental parameters including oxidation-reduction levels, energy conditions and the influence of terrigneous sediments. The evolution of the coal seam shows that peat was deposited mainly in the low energy lakeshore and lakeside plain subfacies. Five types of sequence stratigrpahic surface and two types of parasequence were identified. Forced lake regressions and normal lake regressions are attributed as the causes of sequence boundaries. The sequence stratigraphic framework comprises six sequences and corresponding system tracts, and the curve of base-level for each demonstrates a characteristic initial period of slow rising followed by fast rising and then returning to slow rising. A model indicating the relationship among base-level changes, coal facies evolution, and the environmental features in the swamp is proposed that shows the environmental features of the swamp were controlled by both base-level changes and coal facies. Accompanying depositional environment changes from a lakeside plain to lakeshore and shallow lake caused by increasing rate of base-level rise, water paleosalinity, acidity and the percentage of woody plants decrease, and the bog type alters from the low marsh to raised bog.

Estimation of palaeo-slope and sediment volume of a lacustrine rift basin: A semi-quantitative study on the southern steep slope of the Shijiutuo Uplift, Bohai Offshore Basin, China

The sequence architecture and depositional systems of the Palaeogene lacustrine rift succession in the southern steep slope of the Shijiutuo Uplift (SU) in Bohai Offshore Basin (BOB) were investigated using combined 3-D seismic, well log and core data. Four second-order/composite sequences and seven third-order sequences were identified. A detailed analysis revealed fan delta, braid delta and lacustrine depositional systems in the third-order sequences 7 (SQ7). Eleven seismic facies were chosen in the SQ7 to calculate the area and sediment budget. We also calculated the palaeo-slope parameters in the southern steep slope of the SU, including the gradient of basin margin fault slope belt, the shape, average width, average height, width/height ratio and cross sectional area of palaeo-valley. The gradient of the fault slope break belt was inversely proportional to the area and volume of sediments. The higher gradient corresponded to the smaller area and volume of sediments. The width and cross sectional area of palaeo-valleys dominated the volume and facies of sediments. A larger cross sectional area of a palaeo-valley involved much more sediments supply and more favorable conditions for the origin of large-scale deltas. Because of favorable sediment transportation path and existence of large-scale braid delta, the eastern part of the SU formed better quality reservoir than that in the west.

A seismic quantitative identification method of slope break belt

Abstract Based on the slope variation characteristics of slope break belt and slope theory in geomorphology, a method, which can quantitatively identify the slope break belt based on the precise seismic horizon data and slope gradient and aspect attribute, was established, and the mathematic surface model, dip logging, seismic attributes, and formation thickness contours were used to verify this method. Then, this method was used to quantitatively identify the distribution range and geometric parameters of the slope break belt in the Lower Cretaceous Qingshuihe Formation in Chepaizi area of Junggar Basin, NW China, the results show that the formation slope gradient calculated by this method is consistent with that reflected by the dip logging data, the distribution range of the slope break belt identified by this method is in line with the trend of the formation thickness and the distribution range of the discovered stratigraphic-lithologic reservoir, and the slope gradient attribute is better than formation dip attribute in identifying the slope break belt. The geometric parameters of the slope break belt which this method can identify are the accurate location of slope break and slope toe, the value of the slope gradient and the height difference and width between the slope break and slope toe.

Three-dimensional forward stratigraphic modelling of the gravel-to mud-rich fan-delta in the slope system of Zhanhua Sag, Bohai Bay Basin, China

An important hydrocarbon reservoir is hosted by the third member of the Shahejie Formation (Es3) in the Zhanhua Sag, Bohai Bay Basin. Seismic stratal slices reveal different characteristics of channels and fan-delta lobes between the south (slope break belt) and southwest (gentle slope) areas combined with lithology, wire-line logs and three-dimensional (3-D) seismic data in the southern slope of Zhanhua Sag. And an excellent analogue has been provided for understanding various key depositional evolution of fan-deltas in the slope system (from base to top: Es3L, Es3M and Es3U). The Sedsim, a three-dimensional stratigraphic forward modelling programme, is applied to simulate the evolution of fan-deltas in the southern slope break systems and southwestern gentle slope systems of the Zhanhua Sag by considering a number of key processes and parameters affecting the fan-deltaic deposition from 43 Ma to 38.2 Ma. Modelling results indicate that depositional types and scales evolved from the thickest medium-scale gravel- or sand-rich fan deltas (43 Ma ∼41.4 Ma, Es3L) to the thinnest small-scale mud-rich fan deltas and lacustrine mud (41.4 Ma ∼39.8 Ma, Es3M), and lastly to less thicker larger-scale mixed sand-mud fan deltas (39.8 Ma ∼38.2 Ma, Es3U). The types of slope system, sediment supply and lake-level change are three controlling factors for determining the source-to-sink architecture of the gravel-to mud-rich fan-deltas and sediment-dispersal characteristics. This study has demonstrated that the process-based modelling approach can be effectively used to simulate complex geological environments and quantify controlling factors.

Tectonic characteristics and structural styles of a continental rifted basin: Revelation from deep seismic reflection profiles

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 hydrocarbon-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 sedimentary 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 development 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 controlling factors mainly focused on subsidence history and background tectonic activities such as volcanic activity and earthquakes. The analysis of structural styles and tectonic 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.

Paleogene tectonic evolution controls on sequence stratigraphic patterns in the Fushan sag, northern South China Sea

Tectonism is of extreme importance to sequence stratigraphic patterns in continental sedimentary basins, affecting both the architectures and internal makeup of sequences. Sequence stratigraphic framework of the Paleogene system in the Fushan sag, northern South China Sea, was built using 3D and 2D seismic data, complemented by drilling cores and well logs data. One first-order, three second-order and seven third-order sequences were identified. Analysis of paleotectonic stress field, unconformities and subsidence history showed that the Paleogene tectonic evolution presented significant characteristics of multistage and episode, and can be divided into three stages: rifting stage I (initial rifting period), rifting stage II (rapid subsidence period), rifting stage III (fault-depressed diversionary period). Partition of the west and east in tectonic activity was obvious. The west area showed relatively stronger tectonic activity than the east area, especially during the rifting stage II. Episodic rifting and lateral variations in tectonic activity resulted in a wide variety of structural slope break belts, which controlled both the sequence architectures and interval makeup, and strongly constrained the development of special facies zones or sand bodies that tended to form hydrocarbon accumulation. This paper classifies the genetic types of slope break belts and their relevant sequence stratigraphic patterns within the Fushan sag, and further discusses the tectonic evolution controls on sequence stratigraphic patterns, which suggests that vertical evolution paths of structural slope break belts and relevant sequence stratigraphic patterns as a response to the Paleogene tectonic evolution were strongly controlled by sag margin types and lateral variations of tectonic activity.

Sedimentary characteristics and facies model of gravity flow deposits of Late Triassic Yanchang Formation in southwestern Ordos Basin, NW China

Abstract Based on cores and logging data, and gravity flow theory, the sedimentary characteristics and facies model of gravity flow deposits in the Longdong area in southwestern Ordos Basin were analyzed. Five types of gravity flow deposits are recognized: slides, slumps, sandy debris flows, muddy debris flows and turbidity currents. Affected by multiple provenances, paleogeomorphology and triggering mechanisms jointly, the gravity flows resulted in sublacustrine fans and slump olistoliths in the basin center. Containing channels, the sublacustrine fans can be divided into three subfacies, inner fan, middle fan and outer fan and subdivided into six microfacies, main channel, main channel lateral margin, distributary channel, distributary channel lateral margin, inter-channel and sheeted turbidite sand. It is inferred that they are caused by seasonal floods. The slump olistoliths, with no channels, consist four parts: slide rock, slump rock, debris flow lobe and sheeted turbidite sand, and are inferred to be the product of collapse of break belts triggered by events like earthquakes. Combining facies models with types of gravity flow deposits can reveal the sedimentary characteristics and genetic models of gravity flow deposits in deep water more directly and provide theoretical basis for deep water oil and gas exploration.

Characteristics of the Paleozoic slope break system and its control on stratigraphic-lithologic traps: An example from the Tarim Basin, western China

Based on comprehensive analyses of seismic and log data, this study indicates that mainly four widespread angular to minor angular unconformities (Tg8, Tg51, Tg5 and Tg3) were formed during the Paleozoic. Through the interpretation of structural unconformities, calculation of eroded thickness, correction of palaeo-water depth and compaction and compilation of the Early Paleozoic structural maps, the Early Paleozoic slope break belt (geomorphologic unit) of the Tarim Basin is subdivided into uplift area, subaqueous uplift area, rift slope break belt, flexure slope break belt (slope belt), depression area and deep basin area. Palaeogeomorphology of the Cambrian-Early Ordovician was approximately in EW trend within which three tectonic units including the Tabei Palaeo-uplift, the northern Depressional Belt and the southern Palaeo-uplift developed respectively and are grouped into two slope break systems namely as the Tabei Palaeo-uplift and the southern Palaeo-uplift. These tectonic units obviously control the deposition of isolated platform, open platform, restricted platform and deep basin. Influenced by extrusion in the Mid-Late Ordovician, the southern and northern subaqueous uplifts gradually elevated and then were eroded. Resultantly two slope break systems developed, namely as the northern and central Palaeo-uplifts which obviously controlled the deposition of provenance area, isolated platform, mixed continental shelf, slope and basin facies. The intensive extrusion of the Mid-Late Ordovician leads to significant tectonic deformation of the Tarim Basin: large area of uplifting and erosion and development of EW trending anticline and syncline. Deposition of shore, tidal flat, delta, shallow marine clastics and deep marine facies is obviously controlled by the Tabei, the southern and the Tadong Palaeo-uplifts. Slope break systems control development of stratigraphic unconformity and thus truncation and onlap unconformity zones become favorable areas in a palaeo-uplift and at a palaeo-slope belt for forming important unconformity traps; Whereas slope (slope break) belt along a palaeo-uplift margin is a geomorphologic unit where high-energy sedimentary facies widely develops, such as reef, oolitic sandy clastics or bioclastic limestone beach bar facies, thus litho-structural composite hydrocarbon accumulations usually develop when tectonic condition is suitable. In addition, large-scale palaeo-uplifts are the most favourable areas for hydrocarbon accumulation development

The Control of Palegeomorphology on Sedimentary Systems in Southeast Qianjiang Depression, Lower Xingouzui Formation, Jianghan Basin

The pale geomorphology of Lower Xingouzui Formation is controlled by synsedimentary faults. The pale geomorphology controls the distribution of depositional systems, the development of underwater distributary channel controlled by groove and structural slope break belt, combination features of underwater distributary channel and mouth bar controlled by sedimentary slope break, beach bar developed in paleo-uplift, shore-shallow lacustrine and semi-deep lake developed in sag zone.