Influence of syntectonic sedimentation on kinematic evolution of fold‐and‐thrust belts with lateral changes in shallow décollement properties and basement inherited structures: insights from analogue modeling

International audienceStructural deformation of fold-and-thrust belts is influenced by the properties of décollements (number, rheology, thickness, etc.), the presence of inherited structures in the basement as well as the amount of syntectonic sedimentation, among others. Although the effect of each of these parameters has been well constrained with a series of numerical and experimental works in the literature, few sandbox models comprehensively consider all these parameters together, and particularly investigate the effect of their lateral variation. In this context, we carried out several 3-D sandbox models to investigate the effect of increasing syntectonic sedimentation rate on kinematic evolution of fold‐and‐thrust systems which contain a basal brittle detachment layer and a shallow detachment layer that changed from a brittle to a viscous domain along the mountain strike. The influence of different basement width structures, affecting the kinematics and geometry of the interbedded viscous décollement, has been also tested.Results indicate that the rate of syntectonic sedimentation exerts a first-order control on the kinematic evolution of fold‐and‐thrust belts since increasing syntectonic sedimentation rate stops (in the brittle domain) or delays (in the viscous domain) the propagation of deformation towards the foreland. Moreover, syntectonic sedimentation prohibits the propagation of deformation in the deep décollement level due to the modification of the taper angle. Structural evolution of the transfer zone in between the brittle and viscous domain is also affected since if becomes narrower and more orthogonal to the mountain front at higher sedimentation rates. Specifically, in the brittle domain, the fault dip angle increases with the increase in syn-sedimentation rate and its cross-sectional geometry becomes straighter. In the viscous domain, syntectonic sedimentation affects the partitioning of deformation with development of long-lived and complex 3-D salt structures near the hinterland (such as squeezed diapirs, salt welds and salt tongue), whereas frontal structure becomes more cylindrical. Toward the hinterland, syntectonic sedimentation increases backthrust activity, which becomes increasingly different between the brittle and viscous domain. For instance, the increase in backthrust displacement in the ductile domain is greater than the one in the brittle domain. About the basement high, our study reveals that it has a strong controlling effect on the viscous domain, dominating the development of structural belt on the top of the basement high and promoting the propagation of deformation front to the pinch-out of the salt layer. Besides, syntectonic sedimentation simplifies the structural style between the basement high and the hinterland. It strengthens the structural influence of the transfer zone, which localizes into a single strike-slip transfer fault which increases the frontal fault displacement.Our experimental results are compared with structures in the Wushi-Kuqa fold-and-thrust belts in Southern Tianshan (Central Asia) and help better understanding interaction between syntectonic sedimentation, décollement properties and basement configuration

Fault characteristics and control on hydrocarbon accumulation of middle-shallow layers in the slope zone of Mahu sag, Junggar Basin, NW China

The development, evolution and formation mechanism of faults and their control on the migration and accumulation of Mesozoic oil and gas in the middle-shallow layers of the slope zone of Mahu sag were studied by the interpretation of seismic and drilling data. Two types of faults, normal and strike-slip, are developed in the middle-shallow layers of the slope zone of the Mahu sag and they are mostly active in the Yanshanian period. They are divided into four grade faults: The grade I strike-slip faults with NWW to near EW direction are related to the left-lateral transpressive fault zones in the northwest of Junggar Basin since the end of the Triassic. The grade II faults with NE to NNE direction are the normal faults located at the junction of the fault zone and the slope zone, and their formation is related to the extension at the top of the nose-like structures in the fault zone. The grade III faults, which are also the normal faults, are the result of the extension at the top of the lower uplifts in the slope zone and differential compaction. The grade IV faults with NE direction are normal faults, which may be related to the extension environment at the tip of the lower uplifts. Faults not only are the channel for the vertical migration of oil and gas, but also control the oil-gas accumulation. There are two types of oil-gas reservoirs in the middle-shallow layers of slope zone of Mahu sag: fault block reservoirs and fault-lithologic reservoirs. They have large traps and promising exploration potential. Key words: Junggar Basin, slope zone of Mahu sag, middle-shallow layers, fault, genetic mechanism, nose-like structure, lower uplift, hydrocarbon accumulatio

Analogue modeling of the kinematic evolution of fold-and-thrust belts under various syntectonic sedimentation rates, shallow décollement properties and basement inherited structure configurations

International audienceStructural deformation of fold-and-thrust belts is influenced by the properties of décollements (number, rheology, thickness, etc.), the presence of inherited structures in the basement as well as the amount of syntectonic sedimentation, among others. Although the effect of each of these parameters has been well constrained with a series of numerical and experimental works in the literature, few sandbox models consider all these parameters together, and particularly investigate the effect of their lateral variation.To gain insight on this issue, we carried out several 3-D sandbox models and investigated the effect of increasing syntectonic sedimentation rate on the kinematic evolution of fold-and-thrust systems. Models contain a basal brittle detachment layer and a shallow detachment layer that changed from a brittle to a viscous domain along the model strike. The effect of basement high and syntectonic sedimentation are also considered meanwhile. Model results are compared with field data from the Wushi-Kuqa fold-and-thrust belt (FTB) in Southern Tianshan, Tarim basin, Central Asia.The Wushi-Kuqa is one of the south-vergent FTBs that developed in the southern Tian Shan orogen, within the Tarim basin (Fig. 1). The Wushi (W) and Kuqa (E) FTBs are separated by the Kalayuergun right-lateral strike- slip fault. According to geological maps and drilling data, the shallow décollement involved in the deformation of both FTBs changes laterally in rheological properties. The Neogene Jidike mudstones in the Wushi FTB (W) are considered as frictional, whereas the Paleogene evaporites in the Kuqa FTB (E) are viscous. This leads to different deformation styles along the strike, single fault and fold to the W, and salt nappe and folds to the E.In both FTB, two basement high structures, the Wensu (to the W) and Xiqiu (to the E) basement high, have been interpreted from seismic profiles and affected the décollement continuity and thickness (Fig. 1.c). Thus, the Jidike mudstones in the Wushi FTB decreases in thickness toward the south (Line-1, Fig. 1.c). In the Kuqa FTB, the Xiqiu basement high is closer to the mountain front to the west than to the east. Its arcuate shape is likely responsible for the similar shape of the Qiulitage belt (Line-2 and 3, Fig. 1.c).Analogue modeling approachWe set up two series of experimental models at Lille University, France, to test the influence of syntectonic sedimentation rate magnitude and basement high configuration on FTB development. In Series 1, we test variable syntectonic sedimentation rates, including low (0.3 mm/h), medium (0.6 mm/h) and high (0.9 mm/h) rates. Then we combined basement high and syntectonic sedimentation together in Series 2, and we particularly tested the along-strike change in the width of the basement high.The experimental models were typically made up of three materials that simulate different lithologies of rocks, including: (1) quartz sand, simulating the frictional behavior of brittle sedimentary rocks, (2) glass microbeads, simulating frictional brittle décollement and (3) silicone, simulating a viscous décollement, like salt layers.Modeling results and conclusionModeling results of Series 1 show that the rate of syntectonic sedimentation exerts a first-order control on the kinematic evolution of fold-and-thrust belts which concentrates deformation along the mountain front and delays the propagation of both deep and shallow deformation in the brittle and viscous domains.Modeling results of Series 2 (Fig. 2), indicate that: (1) syntectonic sedimentation reduced the number of fore- thrusts that nucleate between the basement high and the hinterland, in the viscous domain, and reduced the shallow thrust in the brittle domain; (2) basement high controlled the deformation process and distribution of deformation only in the viscous domain. Besides, modeling results can be used to explain salt-influenced deformations on the Xiqiu basement high and in Wushi-Kuqa FTB, which shows that Xiqiu basement high acts as a weak stress zone in the deformation process resulting in localized deformation in the Qiulitage structural belt

Analogue modeling of the kinematic evolution of fold-and-thrust belts under various syntectonic sedimentation rates, shallow décollement properties and basement inherited structure configurations

International audienceStructural deformation of fold-and-thrust belts is influenced by the properties of décollements (number, rheology, thickness, etc.), the presence of inherited structures in the basement as well as the amount of syntectonic sedimentation, among others. Although the effect of each of these parameters has been well constrained with a series of numerical and experimental works in the literature, few sandbox models consider all these parameters together, and particularly investigate the effect of their lateral variation.To gain insight on this issue, we carried out several 3-D sandbox models and investigated the effect of increasing syntectonic sedimentation rate on the kinematic evolution of fold-and-thrust systems. Models contain a basal brittle detachment layer and a shallow detachment layer that changed from a brittle to a viscous domain along the model strike. The effect of basement high and syntectonic sedimentation are also considered meanwhile. Model results are compared with field data from the Wushi-Kuqa fold-and-thrust belt (FTB) in Southern Tianshan, Tarim basin, Central Asia.The Wushi-Kuqa is one of the south-vergent FTBs that developed in the southern Tian Shan orogen, within the Tarim basin (Fig. 1). The Wushi (W) and Kuqa (E) FTBs are separated by the Kalayuergun right-lateral strike- slip fault. According to geological maps and drilling data, the shallow décollement involved in the deformation of both FTBs changes laterally in rheological properties. The Neogene Jidike mudstones in the Wushi FTB (W) are considered as frictional, whereas the Paleogene evaporites in the Kuqa FTB (E) are viscous. This leads to different deformation styles along the strike, single fault and fold to the W, and salt nappe and folds to the E.In both FTB, two basement high structures, the Wensu (to the W) and Xiqiu (to the E) basement high, have been interpreted from seismic profiles and affected the décollement continuity and thickness (Fig. 1.c). Thus, the Jidike mudstones in the Wushi FTB decreases in thickness toward the south (Line-1, Fig. 1.c). In the Kuqa FTB, the Xiqiu basement high is closer to the mountain front to the west than to the east. Its arcuate shape is likely responsible for the similar shape of the Qiulitage belt (Line-2 and 3, Fig. 1.c).Analogue modeling approachWe set up two series of experimental models at Lille University, France, to test the influence of syntectonic sedimentation rate magnitude and basement high configuration on FTB development. In Series 1, we test variable syntectonic sedimentation rates, including low (0.3 mm/h), medium (0.6 mm/h) and high (0.9 mm/h) rates. Then we combined basement high and syntectonic sedimentation together in Series 2, and we particularly tested the along-strike change in the width of the basement high.The experimental models were typically made up of three materials that simulate different lithologies of rocks, including: (1) quartz sand, simulating the frictional behavior of brittle sedimentary rocks, (2) glass microbeads, simulating frictional brittle décollement and (3) silicone, simulating a viscous décollement, like salt layers.Modeling results and conclusionModeling results of Series 1 show that the rate of syntectonic sedimentation exerts a first-order control on the kinematic evolution of fold-and-thrust belts which concentrates deformation along the mountain front and delays the propagation of both deep and shallow deformation in the brittle and viscous domains.Modeling results of Series 2 (Fig. 2), indicate that: (1) syntectonic sedimentation reduced the number of fore- thrusts that nucleate between the basement high and the hinterland, in the viscous domain, and reduced the shallow thrust in the brittle domain; (2) basement high controlled the deformation process and distribution of deformation only in the viscous domain. Besides, modeling results can be used to explain salt-influenced deformations on the Xiqiu basement high and in Wushi-Kuqa FTB, which shows that Xiqiu basement high acts as a weak stress zone in the deformation process resulting in localized deformation in the Qiulitage structural belt

Cenozoic Shortening and Propagation in the Eastern Kuqa Fold-And-Thrust Belt, South Tian Shan, NW China

International audienceIn an orogen-foreland basin system, syn-orogenic sedimentation and deformation records within the foreland basin provide critical evidence for understanding uplift and erosion processes of adjacent orogenic belts. Foreland fold-and-thrust belts (FTBs) are widely developed around the Tian Shan range, Central Asia. Problem of how crustal shortening accumulates and propagates from the Tian Shan to adjacent foreland basins is essential for understanding the overall dynamics of Tian Shan. In this study, we interpreted three high-resolution seismic reflection profiles to estimate the magnitude and distribution of Cenozoic shortening across the Eastern Kuqa FTB, South Tian Shan foreland. Combined with well-dated syntectonic stratigraphy, we further evaluate the timing, rate, and migration of the deformation front of the Kuqa FTB. Our results suggest that the Kuqa FTB's total crustal shortening increases westward. The distribution of crustal shortening across secondary structural belts shows a gradual, basinward decrease, which can be explained by the telescoped mechanism. Propagation rates of the Kuqa FTB's deformation front indicate an episodic propagation of the foreland thrust wedge, with an acceleration after ∼12 Ma. Similar episodic propagation pattern has also been observed in other foreland FTBs around the Tian Shan, but they show significant spatio-temporal variations in the propagation stages and related rates