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Abstract
The Cenozoic structures in northern marginal area of the Qaidam Basin consisted mainly of a series of fault-band folds and fault-propagation folds, where could be separated into three belts. The Northeastern Anticline Zone, along the foothill of the Qilian Mountains, consisted of small scale and relatively gentle fault-propagation folds and break-through faults, which started to form during Paleocene to the early stage of Pliocene. The Central Anticline Zone composed of fault-band folds and a few fault-propagation folds, which started to form during Miocene to the middle stage of Pliocene. The Southeastern Anticline Zone, far away from the foothill of the Qilian Mountains, created during the late stage of Pliocene to Pleistocene. The flat-ramp faulting and fault-related folding in northern margin of the Qaidamu Basin migrated from foothill of the Qilian Mountains to the basin in sequence of piggyback, and they were formed from Paleocene to now.
... Though it is generally believed that the Cenozoic deformation in the NQB is dominated by reverse faulting and folding [2,36] , the kinematic process associated with the deformation re- 121 mains controversial, and multiple models like thrusting [14] , dextral slip faulting [1,18] , sinistral slip thrusting [1920] and structural wedge [2] , etc were proposed to explain the process. Both field survey and seismic profiles (Figs. 3, 5 and 6) show that the Yuqia -Jiulongshan region is an overall box-shaped anticline controlled by a number of high-angle reverse faults, such as the Sainan, Yubei and Longbei faults, etc., which is characterized by overall basement uplift but has no long-distance low-angle thrusting or complex structural wedge. ...
Based on field geological survey, interpretation of seismic reflection profile and thermochronology dating, this paper systematically studied the structural deformation of the Yuqia-Jiulongshan region in northern Qaidam Basin during the Cenozoic. The results show that the area is primarily dominated by a large box-shaped anticline, with steep limbs and a wide and gently-deformed core. The Mahaigaxiu and Jiulongshan anticlines are secondary folds controlled by secondary faults in the limbs of the box-shaped anticline. Whereas the Yuqia and the Northern Yuqia anticlines are secondary folds within the wide core of the box-shaped anticline. The geometry of the box-shaped anticline is mainly controlled by some high-angle reverse faults with certain right-lateral strike-slip components, displaying distinct positive flower structures in section view. Combining the sedimentary correlation and detrital apatite fission track analysis, we believe that the Yuqia-Jiulongshan region was a paleo-uplift that developed slightly in the early Cenozoic, resulting in the relatively thin Cenozoic strata. The intense deformation that shaped the present-day structural framework occurred in or after the sedimentary period of Shizigou Formation. The Yuqia – Jiulongshan paleo-uplift is adjacent to the Sainan depression that is rich in Lower-Middle Jurassic source rocks, and thus has high potential for future hydrocarbon exploration. Key words: Qaidam Basin, Yuqia-Jiulongshan region, Cenozoic, structural deformation, box-shaped anticline, paleo-uplift
... In addition, southwestern Qaidam Basin is a region with frequent tectonic activities and complex tectonic evolution history. Different from the north margin of the Qaidam Basin controlled by the Qilianshan-Nanshan thrust belt since Paleocene (Liu et al., 2005; Yin et al., 2008a), southwestern Qaidam Basin is dually controlled by the Altyn Tagh and Qimen Tagh-East Kunlun fault zones. Owing to the complex tectonics of the southwestern Qaidam Basin, it is difficult to clearly define the regional tectonicsedimentary evolution. ...
Based on the analysis of heavy mineral assemblages in Cenozoic southwestern Qaidam Basin, we found that different areas have variable heavy mineral assemblage characteristics, which suggested that there were two source areas—the Altyn Mountains and the Qimen Tagh-East Kunlun Mountains. In Ganchaigou-Shizigou-Huatugou (Area A), which was mainly source from the Altyn Mountains, its heavy minerals were mainly composed of zircon, Ti-oxides, and wollastonite in the Paleocene-early Eocene and mainly of unstable minerals, especially amphibole, in the middle Eocene-Oligene. Since the late Oligocene-Miocene, the heavy minerals were still mainly unstable minerals, but the content of epidote increased and the content of amphibole decreased. In Qigequan-Hongliuquan (Area B), which was the mixed source from the Altyn Mountains and the Qimen Tagh-East Kunlun Mountains, its heavy minerals were mainly garnet, epidote, and amphibole. The source of Lücaotan-Dongchaishan-Kunbei (Area C) was mainly from the Qimen Tagh-East Kunlun Mountains, heavy minerals in the sediments in Area C were mainly zircon and Ti-oxides in Paleogene and garnet, epidote, and amphibole in Neogene. In Yuejin-Youshashan (Area D), where the stable minerals and unstable minerals were present simultaneously, the heavy mineral assemblages was controlled by multi-direction source. The variation of heavy mineral assemblages in southwestern Qaidam Basin shows that Altyn Mountains was of low-lying topographic relief in Paleocene-early Eocene, and the rapid uplift of Altyn Mountains started from the middle Eocene. In Paleogene, the Altyn Tagh Fault had a slow strike-slip velocity, but the strike-slip velocity increased greatly since the late Oligocene, leading to a strike-slip displacement above 300 km since Neogene. Meanwhile, the Qimen Tagh-East Kunlun fault zone was under a stable tectonic stage in Paleogene with the Qimen Tagh Mountain being low-lying hills; since the late Oligocene, the fault zone started to activate and the Qimen Tagh Mountain began to uplift rapidly.
Constraining the shortening rate, timing, and deformation pattern in the frontal parts of the southern Qilian Shan (China) is helpful to further understand the strain distribution model and the tectonic deformation mechanism of the Qilian Shan. The Santai fold belt is one of the active thrust and fold belts parallel to southern Qilian Shan in the northern margin of the Qaidam Basin. It has experienced the structural evolution and interactions between itself and surrounding areas throughout the Late Cenozoic. Based on the geological and geomorphic mapping, landform profile surveys, and seismic line interpretations, the Santai anticline is considered to be a fault-propagation fold that is controlled by basement-involved faulting and limb rotation. In the late Quaternary, the shortening rate of the Santai anticline was almost 0.4 ± 0.17 mm/a, accounting for about 8% of the crustal shortening across Qilian Shan, and with the assumption of a constant shortening rate, latest rapid deformation occurred at about 3 ± 1.1 Ma. This indicates that the loci of deformation sequentially migrated southward in the foreland.
According to the ground geological, geophysical and drilling data, characteristics of distributions and section structures of Maxian fault belt in northern Qaidam Basin are analysed. Its formation and development time and kinematic characteristics are detailed researched. On the basis, a reasonable kinematics model of the active fault is proposed. The results are that Maxian fault is formed in Late Cretaceous, and has a long-term activity in Cenozoic, controlling basin structures, sedimentary distributions and oil and gas accumulations, The fault dips to south and is a left-lateral strike-slip thrusting fault. The kinematic characteristics of Maxian fault derive from the differential pushes of south Qilian Mountains to Qaidam Basin.
Confined water in deep sandy gravel layer is newly-discovered large-scale pore brines in Heibei concave in the western Qaidam basin, which poses as an alternative area for potash development due to the following features: medium to strong water yield property, closeness to the surface with water level ranging from 8 to 24 m, high degree of mineralization, high KCl content fit for commercial development, and small salt buildup when mined. The statistical results show that concentration changes of TDS, Cl-, Na+, Cs+, B2O3, Ca2+, Mg2+, Sr+, NO3-, and Rb+ in the brine are small with even distribution. On the contrary, concentration changes of SO42- are big with uneven distribution; concentration changes of Br-, I-, Li+, K+ and uniform degree fall in the range in-between those of the two above-mentioned groups of elements; Na+, Cl-, Ca2+ and Sr2+, TDS show normal negatively skewed peak distribution, K+, SO42-, Li+ show non-normal positively skewed peak distribution. In component clustering analysis diagram, K+, SO42-, Li+ fall into a sub-class, whereas Cl-, TDS and Na+ fall into another sub-class The ion content change curve shows that content of Na+ and Cl- share the same change trend with that of mineralization degree and B2O3 in the pore brine from east to west. Compositions of K+, SO42-, Mg2+ are consistent, with the same change trend with that of Li+. Ratio of CNa/CCl in pore brine is 0.85-0.96, and bromine chloride coefficient is 0.01-0.34, similar to those of salt karst filter brine. It finds two laws of salting, namely, magnesium sulfate and chloride in the metastable phase diagram (25 ℃) of the quaternary system of Na+, K+, Mg2+//Cl--H2O and quinary system of Na+, K+, Mg2+//Cl-, SO42--H2O, which might have formed due to interaction of intercrystalline brine in the sedimentary formation and pore water in the sandy gravel.
The Qaidam Basin, located in the northern margin of the Qinghai-Tibetan Plateau, was a large Mesozoic-Cenozoic basin and deposited huge thick continuous Cenozoic strata, which recorded well the geological events of collision between the India and Eurasian plates since - 55 Ma. Based on latest new progress in high resolution dating of the magnetostratigraphy, a technique of balanced section across the whole basin was applied to a NE-SW seismic-geological profile in the central Qaidam Basin to reconstruct the crust shortening history from collision and to understand the nature of the basin. The results showed that the Qaidam Basin began to deform nearly synchronous to the early collision, manifesting as a weak compression; the deformation increased significantly in the Middle and Late Eocene, and then weakened slightly, and began to accelerate rapidly from the Late Miocene, especially since the Pleistocene, implying the maximal shortening of the basin and rapid uplift of the northern Tibetan Plateau during that time.
The reverse S-shaped fold-and-thrust belts in the northern Qaidam Basin were interpreted as a result of lateral traction by sinistral strike slip of the Altyn fault in the north edge of the basin. However, the deformation features of the Qaidam Basin indicated that the area influenced by strike slipping of the Altyn fault was very narrow. To further study the mechanism of the reverse S-shaped fold-and-thrust belts, a set of sandbox models of arcuate boundaries with different substrate were designed according to the actual geological conditions. The experimental results showed that the strikes and structural patterns of fold-and-thrust belts were mainly controlled by the boundary geometry of rigid blocks and partially by the mechanical properties of substrates. Based on analyses of the experiments and deformation characteristics of the northern Qaidam Basin, it was proposed that the reverse S-shaped fold-and-thrust belts there could be simply interpreted as the "combination effect of arcuate boundaries of rigid blocks", namely, 1) the Lenghu reverse S-shaped fold-and-thrust belt being a combination effect of arcuate block boundaries of the Saishiteng Mountains and the Kunteyi Sag; 2) the Eboliang reverse S-shaped fold-and-thrust belt being a combination effect of arcuate block boundaries of the Kunteyi Sag and Yiliping Sag; 3) the fold-and-thrust belt, along southwest edge of the Yiliping Sag and with a reverse traction relation to sinistral strike slipping of the Altyn, being related to the southwestward curved boundary of the sag.
There were two situations for cap rock destructed by faulting: one was reduce of successive distribution area of cap rock, another was reduce of thickness of cap rock. The main influencing factors of distribution of cap rock destructed by faulting were fault throw, dip angle and thickness of cap rock itself. A new concept, the effective juxtaposition thickness, was presented and discussed. By the study of influence factors, the logarithmic relation between effective juxtaposition thickness of cap rock destructed by fault and gas column height sealed by cap rock was found. Based on it, a new method evaluating seal ability of cap rock destructed by fault was established. Taking the gypsum-mudstone cap rock of the Kumugeliemu Group in the Kuqa Depression, Tarim Basin, as an example, the effective juxtaposition thickness was calculated and an isopleth map was drawn out. The results were well coincident with the exploration practice, which showed our new evaluation method should be useful and practical for oil-gas exploration.
The development of the Qaidam Basin in Cenozoic was coupled with two orogenic processes: the Neotethyan orogenics (the Kumlun mountain chains) and the shear-orogenics of the Altun fault. In the western part of Qaidam, the Altun fault played a more important role in the basin development. Based on a systematic description of the Cenozoic strata, an analysis of the carbonate-argillaceous rocks in the Xiayoushashan Formation and a comparison with the neighboring North Xorkol Basin, the following knowledges could be drawn. 1) The Altun fault was a dextral strike-slip fault in Paleogene, and become a sinistral one from Miocene. Correspondingly, the related thrusting of early generation (the latest Cretaceous-Eocene) in the northern margin of the basin expanded towards the northeast, and the thrusting of later generation (Pliocene-Pleistocene) expanded towards the southwest. 2) The oblique-thrusting occurred in Eocene and Pliocene respectively, which resulted in a high sedimentary ratio of the Upper Member of Xiaganchaigou Formation and the Shizigou Formation, and the sedimentary centers immigrating eastwards obviously during that time. 3) The Miocene might be a relaxation period of the Altun fault owing to collapse of the Neotethysides. Co-operated with the NE-striking normal faults, a pull-apart basin might be occurred in western Qaidam where the sediments were dominated by the carbonate-argillaceous rocks, obviously different from the sediments in the neighboring North Xorkol Basin. 4) The Altun fault experienced an intracontinental cycle of extension-compression during Neogene in a background of sinistral strike-slipping.
On the basis of the detailed geological interpretation of seismic profile in northern margin of Qaidam basin, combined with the result of field geological survey, the author concluded the studying area converted from the Jurassic NE-SW trending extensional structure framework to the NEE-SWW trending compressional structure framework during the Cretaceous Period, which formed the NNW trending fault-related folds and inverted structures, the nature of northern Qaidam basin is compression-depression basin. The variation of sedimentary rhythm, lithology and thickness of Cretaceous System and the variation of its contact with overlying and underlying strata from conformity to disconformity to conformity are mainly affected by the spatial and temporal variation of the intensity of activity of syn-tectonic fault-related folds and inverted structures. During the Cretaceous Period the deformation features of northern margin of Qaidam basin differed greatly from those basins in the East of China which indicated that structural evolution of the West of China and the East of China were controlled by different tectonic regimes, the NEE-SWW compression in northern margin of Qaidam basin during the Cretaceous Period were possibly related with the collision between the Gangdise landmass and the Eurasian continent in the Tethyan tectonic domain.
The age of stratum might have an influence on the evolution of porosity, so that the age, as well as the depth of stratum, should be taken in account to solve the restoration of palaeo-burial depth, palaeo-geopressure and palaeo-fluid potential of stratum. To synthesize the results of palaeo-geotemperature study, the evolution of geotemperature-pressure systems during the main stages of hydrocarbon accumulation in the western Qaidam Basin was analyzed in detail. Fluid potential, which was combined action on the underground fluid, including geotemperature, geopressure, etc., was introduced to the study of geotemperature-pressure systems in this paper. The underground hydrodynamic field and its control function to hydrocarbon migration and accumulation could be analyzed both qualitatively, semi-quantitatively and quantitatively, also both vertically and planarly. Based on what mentioned above, the oil-gas distribution and the characteristics of oil-gas migration and accumulation were explored. In the western Qaidam Basin, high pressure compound T-P systems developed both in middle Miocene and late Pliocene. The latter had more potential of migration and accumulation. Planarly, the hydrocarbon pools usually occurred in the areas of lower energy. In addition, some pools were discovered in the areas with high energy, which were original ones, such as lithologic hydrocarbon reservoirs and palaeostructure pools with better conservation and better seals. The paper presented that most of undiscovered reserves might be in the deep and high pressure T-P system, and the deep reservoirs should be important exploration targets in future.
The Cenozoic compressional basins in central-western China is a very important area for oil-gas exploration. According to development location, basement, sedimentary succession, structural superposition and basin evolution, 4 type Cenozoic compressional basins, namely, the northwestern Junggar Basin, the western margin of Sichuan Basin, the northern Qaidam Basin and the southern Junggar Basin, could be identified in central-western China. The forland basin was developed in northwestern Junggar and western Sichuan in Late Hercynian and Early Indosinian, whose basin-orogeny relation was decoupled by the Himalayan orogeny. The Cenozoic foreland basin was developed in northern Qaidam and southern Junggar in Himalayan movement, in the latter the Hercynian - Indosinian foreland basin once well occurred. The 4 type Cenozoic compressional basins had various features for reservoir formation conditions such as source rocks and reservoir-seal associations, with obvious control function on source rock thermal evolution in the Cenozoic foreland basins. According to study on the typical hydrocarbon reservoirs in different compressional basins, it could be concluded that the main hydrocarbon accumulation for the northwestern Junggar and western Sichuan Basins occurred before and in the period of Late Yanshannian, with reservoir adjusting in western Sichuan Basin and reservoir preservation in the northwestern Junggar Basin in the period of Himalayan movement, the main hydrocarbon accumulation in the northern Qaidam Basin being the period of Late Himalayan movement, and hydrocarbon accumulation occurring in several periods in the southern Junggar Basin with most important period being in Late Himalayan movement.
NanyishanJiandingshan area is in the northwest of Qaidam Basin, and it is adjacent to Aerjin slope zone. A series of NW trending tight anticlines and the gentle synclines in the between constitute the structural framework of the area. Research shows the study area underwent mainly two stages of deformation since Mesozoic: (1)during Early to Middle Jurassic, the area was mainly dominated by extension and featured by the formation of the dustpan-like faults; and (2)during Shizigou Period to present, the area has been controlled by the SWNE trending compression. The formation of Jiandingshan anticline started in Shizigou Period, and the underlying early depression-controlling normal fault was inverted because of compression, forming large scale fault-propagation folds. The formation of Nanyishan anticline started in Qigequan Period, which was formed by a shallow anticline superimposed on a deep one, the deep anticline was a large scale faultpropagation fold, while the shallow one was a box anticline similar to detachment fold which was formed above the fault by the opposite thrust of two step thrust faults which forming Type-I triangle zone. The forms of Nanyishan anticline and Jiandingshan anticline are relatively integrated, the formation time of structure matches the time of maturity and migration of oil and gas well, indicating very favorable oil and gas exploration prospect.
The active left-lateral Altyn Tagh Fault (ATF) defines the tectonic northern edge of the Tibetan Plateau, and is one of the largest and most important faults worldwide. The fast slip along the fault is regarded as one of the major ways to absorb the India-Tibet convergence. However, when did Cenozoic left-slip on the ATF initiate remains a subject of hot debate possibly due to the complexity of the fault itself. In this paper, we focus on the various geological responses to the left-slip on the fault, and figure out their formation time which is helpful in understanding the timing of left-slip along the ATF. They are: (1) provenance change in western Qaidam Basin; (2) Late Cenozoic flexural SE Tarim Basin; (3) NE-SW directed upper-crustal shortening in NE Tibetan Plateau; (4) strike-slip related basins and (5) the linear mountain along the ATF. The result shows that these slip-related phenomena all formed after Mid-Miocene (ca. 15 ±2Ma), which we accordingly interpret as the initial time of left-slip along the ATF. We also analyze the possible reason for the discrepancy between Cenozoic long-term slip rates and reported Quaternary slip rates along the ATF, and discuss the ways how the activities of the ATF formed the Altyn Mountain and controlled the Mid-Miocene tectonic reorganization in NE Tibetan Plateau.
The timing of uplift of the Tibet Plateau has a central role in the development of tectonic models for the Tibet Plateau and Cenozoic global climate change. A detailed magnetostratigraphic study of the Dahonggou section, northern Qaidam Basin, reveal that the section spans from ~ 34 to ~ 8.5 Ma and the ages of the Shang Ganchaigou, Xia Youshashan and Shang Youshashan formations are from > 34 to 22-20 Ma, 22-20 to 13 Ma and 13 to < 8.5 Ma, respectively. Variations in lithofacies, sedimentation rate and magnetic susceptibility (K) suggest that the southern Qilian Shan was tectonically inactive and didn't respond to the rapid slip on the Altyn Tagh Fault at 30 Ma. In contrast, the similar sedimentary records in the Dahonggou section, the Xishuigou section along the Altyn Tagh Fault, and even more localities along much of the Qilian range front imply that the Qilian Shan and the Altyn Tagh Fault were synchronously tectonically active at about 12 Ma. The lower K between ~ 12 Ma and ~ 8.5 Ma in the sediments of the Dahonggou section is interpreted to be due to long-distanced oxidation and sorting, which cause not only that magnetite was oxidated to hematite, but also that magnetic minerals are enriched in fine-grained sediments and coarse-grained sediments bear few magnetic mineral.
Three magnitude >6 earthquakes struck Qaidam, Qinghai province, China, in November 10th 2008, August 28th and 31st 2009 respectively. The Zongwulongshan fault has often been designated as the active seismogenic structure, although it is at odd with the data. Our continuous GPS station (CGPS), the Xiao Qaidam station, located in the north of the Qaidam basin, is less than 30 km to the southwest of the 2008 earthquake. This CGPS station recorded the near field co-seismic deformation. Here we analyzed the co-seismic dislocation based on the GPS time series and the rupture processes from focal mechanism for the three earthquakes. The aftershocks were relocated to constrain the spatial characteristics of the 2008 and 2009 Qaidam earthquakes. Field geological and geomorphological investigation and interpretation of satellite images show that the Xitieshan fault and Zongwulongshan fault were activated as left lateral thrust during the late Quaternary. Evidence of folding can also be identified. Integrated analyses based on our data and the regional tectonic environment show that the Xitieshan fault is the fault responsible for the 2008 Qaidam earthquake, which is a low dip angle thrust with left lateral strike slip. The Zongwulongshan fault is the seismogenic fault of the 2009 earthquakes, which is a south dipping back thrust of the northern marginal thrust system of the Qaidam basin. Folding takes a significant part of the deformation in the northern marginal thrust system of the Qaidam basin, dominating the contemporary structure style of the northern margin of the Qaidam basin and Qilianshan tectonic system. In this region, this fault and fold system dominates the earthquake activities with frequent small magnitude earthquakes.
The Riwat thrust, with a surface trace of over 50 km, is one of the major faults in the footwall of the main boundary thrust in the Himalayan foreland of Pakistan. Surface geology shows that the Riwat thrust is a foreland-vergent thrust along which lower to middle Siwalik molasse strata are thrust southward over upper Siwalik strata. Seismic reflection interpretation shows that the Riwat thrust developed as a roof thrust of a hinterland-vergent tectonic wedge (triangle zone) underlain by evaporites. The Riwat thrust propagates upsection from depth of about 4 km at the base of the Siwalik Group. At this depth, it merges into a hinterland-vergent blind thrust that propagates upsection as a ramp from Eocambrian evaporites covering the basement at a depth of about 6 km. Bounded between this set of conjugate faults, a tectonic wedge of Eocambrian (evaporites) to Neogene strata is thrust toward the hinterland to form a triangle zone. The roof thrusts of triangles zones have been widely mapped as backthrusts in deformed mountain fronts. Hinterland motion of tectonic wedges as in the Riwat thrust triangle zone may be a feature of the fold-and-thrust belts underlain by evaporites acting as an extremely weak decollement layer. Their recognition, with a trap-forming geometry below a thrust, is important for interpreting particular fold belts and for hydrocarbon exploration. These structures could be predicted by the surface geology data where hinterland vergence of a fold below a thrust is apparent; however, seismic reflection data appear to be critical in recognizing these structures.
The purpose of this paper is to analyze the regional fault systems of Qaidam basin and adjacent orogenic belts. Field investigations and seismic interpretations indicate that five regional fault systems occurred in the basin and adjacent mountain belts and that they control the development and evolution of the Qaidam basin. These fault systems are; (1) Qilianshan-northern marginal Qaidam fault systems; (2) East Kunlunshan-southern marginal Qaidam fault systems; (3) Altun strike-slip fault systems; (4) Elashan strike-slip fault systems; (5) Gansen-Xiaochaidan fault systems. It is indicated that the fault systems have great control over the orientation of the Qaidam basin, the formation and distribution of secondary faults within the basin, the migration of sedimentary center and the distribution of hydrocarbon accumulation belts.
It is indicated that tectonic evolution of the Qaidam basin in Sinian-Triassic time underwent Sinian-Mid-Devonian and Late Devonian-Triassic open-close cycles. The cyclicity of the basin evolution is mainly related to the extension, subduction and closure of Qilian, Saishiteng - Xitieshan, Kulun and Altun Oceans surrounding the paleo-Qaidam The time span of the former cycle is up to 423 Ma (800 - 377 Ma). The latter revealled Late Devonian-Triassic back-arc extension and orogenesis, and lasted about 169 Ma (377-208 Ma). The basin evolution of the Qaidam in Sinian-Triassic can be further divided into four second-level tectonic stages, that is, (1) the formation of intra-cratonic extensional basin in Sinian-Mid-Ordovician (800-464 Ma), (2) the development of intracratonic compressional basin in Late Ordovician-Mid Devonian (464-377Ma), (3) the evolution of back-arc extension basin in Late Devonian-Early Permian (377-260Ma), and (4) the formation of back-arc foreland basin in Late Permian-Triassic (260-208Ma). The basin type experienced changes from extension to compression alternately in different stages.
Based on the study on tectonic features and tectonic evolution, the Qaidam Basin was divided into four first-order units: the North Block-faulted Belt, the Mangya, Sanhu and Delingha Depressions, which could be subdivided into 21 second-order units mainly according to the nature and relief of basement, stratigraphic distribution, style of structural deformation, feature of basin evolution, the fault- and mountain-cutting and the distribution of petroleum systems. On the authority of the distribution of hydrocarbon source rocks, source-reservoir-seal association, the development of structure trap, the second-order units were assessed on hydrocarbon potential in accordance with type I beneficial zone, type II less beneficial zone and type III potential zone. The type I beneficial zone included the following units: the Kunyite Sag, the the Lenghu and Eboliang Belts of the North Block-faulted Belt, the Gasi Sag, the Youquanzi and Qibei Belts of the Mangya Depression, and the Yanhu Belt of the Sanhu Depression.
A thick succession of Cenozoic fluvial-lacustrine sediments deposited in the Qaidam Basin accompanied with strong uplifting of the Qinghai-Tibet (Xizang) plateau. Intensive tectonic deformation and abrupt shift of basinal sedimentary environments from 2.5 Ma ago revealed the Qinghai-Tibet plateau having experienced the most fierce uplift since the late Cenozoic. The integrated studies of sedimentary environments, Ostracoda fossils, sporo-pollen and magnetic stratigraphy indicated that the prolonged period of tectonic quiescence of the Qinghai-Tibet plateau were punctuated by brief, intense interval of deformation and uplifting. Five episodic uplift movements were recognized, which occurred during 2.52 ∼ 2.28 Ma ago, 1.94 ∼ 1.66 Ma ago, 1.38 ∼ 1.1 Ma ago, 0.71 ∼ 0.5 Ma ago and 0.24 ∼ 0.09 Ma ago respectively, and corresponding to the episodes B and C of the Qingzang orogeny, episodes A and B of the Kunhuang orogeny and the Gonghe movement. A comparative study of tectono-sedimentary records in nine basins distributed in wide range of the Qinghai-Tibet plateau further revealed a coincident and episodic uplift feature of the Qinghai-Tibet plateau as a whole.