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Differential Deformed Salt-Related Tectonics of the Kuqa Foreland Fold-Thrust Belt, Tarim Basin, Northwest China*
By
Liangjie Tang1, Yixin Yu1, Chengzao Jia2, and Zhijun Jin3
Search and Discovery Article #30052 (2007)
Posted September 23, 2007
*Adapted from extended abstract prepared for presentation at AAPG Annual Convention, Long Beach, California, April 1-4, 2007
1Basin & Reservoir Research Center, China University of Petroleum, Beijing 102249, China ([email protected])
2PetroChina Company Limited, Beijing 100011, China
3Petroleum Exploration and Production Research Institute, SINOPEC, Beijing 100083, China
The
differential deformed salt-related tectonics in the Kuqa foreland fold-thrust
belt have been observed by field geological observation, geographic information
system (GIS) analysis, 3-D visualization, analysis of the salt-related
structural
styles, and restored
cross
-
sections
, as well as estimation of the
shortening rates. The differentially deformed salt-related tectonics is mainly
displayed as the structurally differentiation in various levels, the zonation in
transverse, and the segmentation in longitudinal
sections
. The boundaries
between the
structural
segments are mainly strike-slip faults or tear faults
revealed by terminal facets, scratches, steps, misplaced hills and river
valleys. The GIS analysis may indicate some characteristic details about
structural
segmentation. Several segments of buried residual salt pillows are
revealed by 3-D visualization. Distinct
structural
styles occur in different
segments. The analysis of balanced
cross
-
sections
may estimate the differential
amounts and rates of shortening in different segments. The origin of
differentially deformed salt-related tectonics may have a bearing upon the
segmentation of Tianshan Mountains, the differential sedimentation and
distribution of the salt beds, the pre-existent faults and basement uplifts as
well as paleotectonic-ramps.
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Geological Setting Tectono-Stratigraphic Sequences The Kuqa foreland fold-thrust belt is located in the northern Tarim basin and strikes east-west approximately. With an area of about 2.85x104 km2, it is a foreland depression south of the Tianshan Mountains and north of the north Tarim uplift. Three tectono-stratigraphic sequences--subsalt, salt, and suprasalt sequences--can be recognized. The subsalt sequences include the Upper Permian—Lower Cretaceous and their main characteristics are summarized as follows: (1) The 300-m-thick Upper Permian Biyelbaoguz Group is composed of continental purple sandy mudstone with interbedded gray conglomerate, sandstone, and black carbonaceous shale. It overlies the Lower Permian volcanics or the Carboniferous limestones. (2) The Lower Triassic consists of pluvial-alluvial purple granulite with interbedded sandstone and mudstone. The Middle-Upper Triassic is composed of flood-plain/shallow-lakeshore/deltaic dark mudstone with interbedded gray-green granulite. The thickness of the entire Triassic is up to 2000 m. (3) The Jurassic, with a thickness of 400-2000 m, consists of fluvial/delta/swamp/lacustrine gray conglomerate, sandstone, dark mudstone, shale, and coal seams. (4) The Lower Cretaceous, with a thickness of 400-2000 m, is composed of pluvial-fluvial/delta/lakeshore/lacustrine purple conglomerate, sandstone, and mudstone. The
salt sequences are special successions in the middle part of Kuqa
foreland fold belt and are characterized by thick halite and gypsum
beds. Plastic flow was clearly observed in the sequences. The main
detachment surface was developed within the salt sequences, which
controlled The supra-salt sequences include the Oligocene—Quaternary and has the following main features: (1) The Oligocene Suwiyi Formation is characterized by red siliciclastics with thin, interbedded halite and gypsum with a thickness of 150-600 m. (2) The lower Miocene Jidik Formation consists of purple sandstone and mudstone and has a thickness of 200-1500 m. (3) The upper Miocene Kanchun Formation, 650-1500 m thick, is dominated by interbedded brown sandstone and mudstone. (4) The Pliocene Kuche Formation, 450-4000 m thick, is composed of gray-yellow sandstone, silty mudstone with interbedded conglomerate. (5) The Quaternary is dominated by fluvial-pluvial loose gravel, sand, and clay beds.
The
Kuqa foreland fold-thrust belt can be divided into six (1) Northern monocline belt is mainly composed of Mesozoic strata. The south-dipping Triassic and Jurassic monocline was formed because of uplifting and thrusting of the south Tianshan Mountain wedge. (2)
Klasu—Yiqiklik (3)
Baicheng—Yanxia sags contains over 9000 meters of Meso-Cenozoic
sediments. One of the reasons for its intense subsidence is that the
deep salt flowed plastically toward the Klasu (4)
Qiulitag (5)
Northern Tarim forebulge is at the northern part of the north
Tarim uplift and is composed of the Yaken anticline belt, Yaha fault
belt, Luntai (6) Wushi sag is the western segment of the Kuqa foreland fold-thrust belt. It contains thick Meso-Cenozoic and deep-seated pre-Sinian basement. A series of anticlines, fault-anticlines, and fault-nose traps were developed in the sag.
Main Characteristics and Marks of the Differentially Deformed Salt-Related Structures and Segmentation Difference in Salt Distribution The salt strata occur in the Lower Paleogene in the western part of the Kuqa foreland fold-thrust belt; they were developed in the Neogene Jidik Formation in the eastern part of the belt. It is characterized by pure salt and gypsum in the west and interbedded gypsum and mudstone in the east. It is more widely distributed and thicker in the west than in the east.
Surface Characteristics and GIS Analysis The
strike-slip faults or tear faults perpendicular to the regional
Terminal facets, scratches, steps, misplaced hills and river valleys are commonly observed on outcrop. The terminal facets are perpendicular to the regional tectonics. The scratches are mainly horizontal. The
GIS analysis is thought to indicate some characteristic details
about
The 3-D visualization of the thickness of the Paleogene Kumglimu Formation in the Kuqa foreland fold-thrust belt indicates that the salt bed thickens in the Klasu and Qiulitag belt and thins in the Beicheng sag (Figure 3). Salt-related structures are distributed irregularly around the Baicheng sag. The well developed salt pillows are mainly distributed along the Qiulitag belt, whereas the relict salt pillows, which are distributed along the Klasu belt, are apparently transected by strike-slip fault and segmentation.
Differentiated Deformed The
difference of the salt-related The alternating salt beds and clastics are developed in the Miocene Jidik Formation in the eastern part of the Kuqa foreland fold-thrust belt. The flowage of the salt beds is weaker and the salt pillow is smaller than in the west segment. No salt nappes, sub-salt imbricated thrust faults, or duplex structures exist in the eastern part of the belt. The broad synclines and anticlines were formed in the supra-salt Kacun Formation (N1k), Kuqa Formation (N2k), and Quaternary. It is thought that the complex thrusts, fault-blocks, and folds were developed in the foothills of the south Tianshan Mountains (Figure 4 D-D’).
Balanced
Mechanisms of Differentiated Deformation and Segmentation of the Salt-Related Structures Differentiated Deformation of Tianshan Orogenic Belt and Kuqa Foreland Fold-Thrust Belt
There exists segmentation in the Tianshan Mountains and adjacent
basins. The difference of the texture and habitat of
Pre-existing basement structures controlled differentiated
deformation and segmentation of salt-related structures of the Kuqa
foreland fold-thrust. Pre-existing basement fault belts exist in the
Qiulitag and Klasu, and they controlled the development of salt
pillows and salt nappes. The mechanisms of basement tectonics
controlling the development of the salt-related structures are as
follows: (1) The
development of the salt pillows is in accordance with the existence
of the sub-salt paleo-uplifts; (2) The pre-existing basement faults
are present in both limbs of the salt pillows; and
(3) The formation
of the salt nappes may have a bearing on the paleo-
The differentially deformed salt-related tectonics in the Kuqa
foreland fold-thrust belt has been observed by field geological
studies, geographic information system (GIS) analysis, 3-D
visualization, analysis of the salt-related |