Tectonic features,genetic mechanisms and basin evolution of the eastern Doseo Basin,Chad

The features of the unconformity,fault and tectonic inversion in the eastern Doseo Basin,Chad,were analyzed,and the genetic mechanisms and basin evolution were discussed using seismic and drilling data.The following results are obtained.First,four stratigraphic unconformities,i.e.basement(Tg),Mangara Group(T10),lower Upper Cretaceous(T5)and Cretaceous(T4),four faulting stages,i.e.Barremian extensional faults,Aptian–Coniacian strike-slip faults,Campanian strike-slip faults,and Eocene strike-slip faults,and two tectonic inversions,i.e.Santonian and end of Cretaceous,were developed in the Doseo Basin.Second,the Doseo Basin was an early failed intracontinental passive rift basin transformed by the strike-slip movement and tectonic inversion.The initial rifting between the African and South American plates induced the nearly N-S stretching of the Doseo Basin,giving rise to the formation of the embryonic Doseo rift basin.The nearly E-W strike-slip movement of Borogop(F1)in the western section of the Central African Shear Zone resulted in the gradual cease of the near north-south rifting and long-term strike-slip transformation,forming a dextral transtension fault system with inherited activity but gradually weakened in intensity(interrupted by two tectonic inversions).This fault system was composed of the main shear(F1),R-type shear(F2-F3)and P-type shear(F4-F5)faults,with the strike-slip associated faults as branches.The strike-slip movements of F1 in Cretaceous and Eocene were controlled by the dextral shear opening of the equatorial south Atlantic and rapid expanding of the Indian Ocean,respectively.The combined function of the strike-slip movement of F1 and the convergence between Africa and Eurasia made the Doseo Basin underwent the Santonian dextral transpressional inversion characterized by intensive folding deformation leading to the echelon NE-SW and NNE-SSW nose-shaped uplifts and unconformity(T5)on high parts of the uplifts.The convergence between Africa and Eurasia caused the intensive tectonic inversion of Doseo Basin at the end of Cretaceous manifesting as intensive uplift,denudation and folding deformation,forming the regional unconformity(T4)and superposing a nearly E-W structural configuration on the Santonian structures.Third,the Doseo Basin experienced four evolutional stages with the features of short rifting and long depression,i.e.Barremian rifting,Aptian rifting–depression transition,Albian–Late Cretaceous depression,and Cenozoic extinction,under the control of the tectonic movements between Africa and its peripheral plates.

Temporo-spatial Coordinates of Evolution of the Ordos Basin and Its Mineralization Responses

The Ordos basin was developed from Mid-Late Triassic to Early Cretaceous, and then entered into its later reformation period since the Late Cretaceous. Its main body bears the features of an intra-cratonic basin. The basin also belongs to a multi-superposed basin which has overlapped on the large-scale basins of the Early and Late Paleozoic. Currently, Ordos basin has become a residual basin experienced reformation of various styles since the Late Cretaceous. It＇s suggested that there were at least four obvious stages of tectonic deformations existing during the basin＇s evolution, dividing the evolution and sedimentation into four stages. The prior two stages were of the most prosperous, during which the lake basin was broad, the deposition range was more than twice larger than the current residual basin, resulting in major oil- and coal-bearing strata. The two stages were separated by regional uplift fluctuations in the area. At the end of the Yan＇an Stage, the depositional interruption and erosion were lasting for a short period of time. The third one is the Mid- Jurassic Zhiluo-Anding stage, in which the sedimentation extent was still broad but the lake area was obviously reduced. In the Late Jurassic tectonic deformation was intensive. A thrust-nappe belt was formed on the basin＇s western margin while conglomerate of different thickness were accumulated within the foredeep of the eastern side. The central and eastern parts of the basin were subject to erosion and reformation. A regional framework with ＂uplift in the east and depression in the west＂ took shape in the area west of the Yellow River. In the Early Cretaceous sediments were widely distributed, unconformably overlapping the former western margin thrust belt and the ridges on the northern and southern borders. There are abundant energy resources such as oil, natural gas, coal and uranium deposits formed in Ordos Basin. The main stages of generation, mineralization and positioning of the multiple energy resources have obvious responding connection and close coupling relationships with those of the Mesozoic and Cenozoic evolution and reformation in Ordos Basin.

Salt Tectonics and Basin Evolution in the Gabon Coastal Basin,West Africa

The Gabon Coastal Basin is a typical saliferous basin located in the middle portion of the West African passive continental margin. Complex salt tectonics make sedimentary sequences and structural frameworks difficult to interpret and can lead to difficulties in construction of balanced cross-sections and reconstruction of basin evolutionary processes. Sedimentary facies and salt structur- al patterns displaying zonation are based on seismic reflection profiles and drilling data. Two near-vertical fault systems, NW-SE and NE-SW, caused basin to be subdivided E-W zoning and N-S partitioning. Scarp slopes and extension faults formed in the Hinge belt III zone where salt diapir piercement occurred and numbers of salt pillars, salt stocks and salt rollers developed under transten- sion of coupled near-orthogonal fault systems. The zone east of Hinge belt III is characterized by small-scale salt domes and salt pillows. To the west are large-scale salt walls and salt bulge anticlines caused by diapirism promoted by tension and torsion that also resulted in formation of numerous salt pillars, salt stocks and salt rollers. Our modeling of salt tectonic structures indicates that they were produced by plastic rheological deformation of salt under regional stress fields that varied during three distinct phases of extension, compression and re-activation. Hinge belt III was active from Coniacian to Early Eocene, which was a critical period of formation of salt structures when many extension-related salt structures formed and salt diapirism controlled the distribution of turbidite fans. Rootless extrusion-related salt stocks developed throughout the Late Eocene to Early Oligocene as a result of lo- cal ephemeral low-intensity tectonic inversion. Post Oligocene salt diapirism was weak and salt tecton- ics had a weak influence on sedimentation. Balanced cross-sections of two saliferous horizons crossing different tectonic units from east to west reveal that the basin tectonic evolution and sediment filling processes can be divided into three stages containing seven episodes of rifting, transition and drifting.

Geochemistry of the Late Paleozoic cherts in the Youjiang Basin:Implications for the basin evolution

We analyzed the major and rare earth element compositions of siliceous deposits from the Upper Devonian Liujiang Formation,Lower Carboniferous Luzhai Formation,Lower-Middle Permian Sidazhai Formation and Tapi Formation,which are widely distributed as bedded cherts in the interplatform basinal successions of the Youjiang Basin.The Liujiang Formation and Luzhai Formation cherts generally have high Al/(Al+Fe+Mn) values(0.38-0.94) and are non-hydrothermal cherts.These cherts are generally characterized by moderately negative Ce anomalies and high Y/Ho values relatived to PAAS,indicating that the Youjiang Basin might have evolved into an open rift basin during the Late Devonian-Early Carboniferous.The Sidazhai Formation cherts from Ziyun generally have high Al/(Al+Fe+Mn) values(0.60-0.78),suggesting negligible contribution from a hydrothermal component.The Sidazhai Formation cherts from Hechi and the Tapi Formation cherts from Malipo generally have low Al/(Al+Fe+Mn) values(0.09-0.41),indicating an intense hydrothermal input.Relatived to the Sidazhai Formation cherts,the Tapi Formation cherts have higher Ce/Ce*values(0.68±0.19) and lower Y/Ho values(41.83±13.27),which may be affected by the terrigenous input from the Vietnam Block.The Sidazhai Formation cherts from Ziyun and Hechi exhibit negative Ce anomalies(0.43±0.12,0.33±0.17,respectively) with high Y/Ho values(57.44±16.20,46.02±4.27,respectively),resembling the geochemical characteristics of open-ocean basin cherts.These cherts were deposited on a passive continental margin adjacent to the Babu branch ocean,which may have contributed to upwelling.Detailed spatial studies on geochemical characteristics of the Late Paleozoic cherts can unravel the evolution of the Youjiang Basin.

Upwelling Process of the Western Himalaya Mountains:Height and Velocity Estimation Evidenced by Formation and Evolution of the Zanda Basin,Tibet,China

Based on field geological survey, stratigraphic section measurement and indoor comprehensive investigation, the Zanda Basin＇s tectonic location in the Himalaya Plate was ascertained, and the formation and evolution of the Zanda Basin during the Pliocene to Early Pleistocene was classified as six stages： （a） primary rift-faulting stage, （b） quick rift-faulting Stage, （c） intensive rift-faulting stage, （d） stasis stage, （e） secondary rift-faulting stage, and （f） secondary quick rift-faulting stage. Based on this six-staged formation-evolution theory of the Zanda Basin, the upwelling process of the Western Himalaya Mountains from the Pliocene to Early Pleistocene was classified as the following five stages： （a） slow upwelling stage （5.4-4.4 Ma）, （b） mid-velocity upwelling stage （4.4-3.5 Ma）, （c） quick upwelling stage （3.5-3.2 Ma）, （d） upwelling-ceasing stage （3.2-2.7 Ma）, and （e） quick upwelling stage （2.7 Ma）. Research has shown that in the duration from the Early Pliocene （4.7 Ma） to the End of Pliocene （2.67 Ma）, which lasted 2.03 million years, the Himalaya Mountains had uplifted 1500 m at a velocity of 0.74 mm/a; this belongs to a mid-velocity upwening. During the 1.31 million years in the Early Stage of the Early Pleistocene, the Himalaya Mountains had risen up another 1500 m at a velocity of 1.15 mm/a; this is a rather quick upwelling. All of these data have shown that the upwelling of the Western Himalaya Mountains is along a complicated process with multi-stages, multi-velocities, and non-uniformitarian features.

Numerical Simulation for Evolutionary History of Three-Dimensional Basin

Numerical simulation or evolutionary history of an oil and gas-bearing basin is to repeat geological and thermodyanomic history of basin evolution on a computer and then to quantitate petroleum generation,accumulation and migration.The mathemat-ical model describing geological and thermodynamic history of the basin evolution ischaracterised by an initial-boundary value problem of a system of nonlinear partial dif-ferential equations. In the present paper, a numerical method for three-dimensionalproblem and the analysis of its stability are established and a numerical result for apractical model is given, which shows that the abnormal pressure and paleo-temperat-ure computed are reasonable and display physical characteristics clearly as well.

Lacustrine basin evolution and coal accumulation of the Middle Jurassic in the Saishiteng coalfield, northern Qaidam Basin, China

Based on an extensive borehole survey of the Middle Jurassic coat-bearing sequences in the Saishiteng coalfield, northern Qaidam Basin （NQB）, a total of 20 rock types and 5 sedimentary facies were identified, including braided river, meandering river, braided delta, meandering river delta, and lacustrine facies. The distribution of rock types and sedimentary facies contributed to the reconstruction of three periods＇ sedimentary facies maps of the Middle Jurassic in the Saishiteng coalfield, namely, the Dameigou age, the early Shimengou age and the late Shimengou age. That also provided the basis for the development of a three-stage depositional model of the Middle Jurassic in the NQB, indicating the lacustrine basin of the NQB in the Dameigou age and early Shimengou age were corresponding to an overfill basin, and that in the late Shimengou age was related to a balanced-fill basin. The analysis of the stability and structure of coat seams based on sedimentary facies maps showed that the preferred coal-forming facies in the Saishiteng coalfield were inter-delta bay and interdistributary bay of lower delta plain in the Dameigou age. In particular, the swamps that developed on the subaqueous pataeohigh favored the development of thick coat seams. Thus, ruinable coal seams may also be found along the Pingtai pataeohigh in the western part of the Saishiteng coalfield.

Evolution of the Paleogene succession of the western Himalayan foreland basin

The Paleogene succession of the Himalayan foreland basin is immensely important as it preserves evidence of India-Asia collision and related records of the Himalayan orogenesis.In this paper,the depositional regime of the Paleogene succession of the Himalayan foreland basin and variations in composition of the hinterland at different stages of the basin developments are presented.The Paleogene succession of the western Himalayan foreland basin developed in two stages,i.e.syncollisional stage and post-collisional stage.At the onset,chert breccia containing fragments derived from the hanging walls of faults and reworked bauxite developed as a result of erosion of the forebulge. The overlying early Eocene succession possibly deposited in a coastal system,where carbonates represent barriers and shales represent lagoons.Up-section,the middle Eocene marl beds likely deposited on a tidal flat.The late Eocene/Oligocene basal Murree beds,containing tidal bundles,indicate that a mixed or semi-diurnal tidal system deposited the sediments and the sedimentation took place in a tidedominated estuary.In the higher-up,the succession likely deposited in a river-dominated estuary or in meandering rivers.In the beginning of the basin evolution,the sediments were derived from the Precambrian basement or from the metasediments/volcanic rocks possessing terrains of the south.The early and middle Eocene（54.7-41.3 Ma） succession of the embryonic foreland possibly developed from the sediments derived from the Trans-Himalayan schists and phyllites and Indus ophiolite of the north during syn-collisional stage.The detrital minerals especially the lithic fragments and the heavy minerals suggest the provenance for the late Eocene/Oligocene sequences to be from the recycled orogenic belt of the Higher Himalaya,Tethyan Himalaya and the Indus-suture zone from the north during post-collisional stage.This is also supported by the paleocurrent measurements those suggest main flows directed towards southeast,south and east with minor variations.This implies that the river system stabilized later than 41 Ma and the Higher Himalaya attained sufficient height around this time.The chemical composition of the sandstones and mudstones occurring in the early foreland basin sequences are intermediate between the active and passive continental margins and/or same as the passive continental margins.The sedimentary succession of this basin has sustained a temperature of about 200 C and undergone a burial depth of about 6 km.

China Continental Conductive Layers and Its Relationship with Basin Evolution

? This paper plots out two deep distribution maps of the China continental crustal and upper mantle conductive layers, and discusses the origin of two kinds of conductive layers, based on the results of the magnetotelluric(MT) sounding research made by Chinese scientists in the last two decades. The MT prospecting shows that the conductive layers possibly exist in upper mantle and middle-lower crust in the Mesozoic and Cenozoic stretching basins, and they coincide with the uplifting of two kinds of conductive layers. These characteristics help to illustrate the deep dynamic settings that control the basin evolution.

Earthquake-related Tectonic Deformation of Soft-sediments and Its Constraints on Basin Tectonic Evolution

The authors introduced two kinds of newly found soft-sediment deformation-synsedimentary extension structure and syn-sedimentary compression structure, and discuss their origins and constraints on basin tectonic evolution. One representative of the syn-sedimentary extension structure is syn-sedimentary boudinage structure, while the typical example of the syn-sedimentary compression structure is compression sand pillows or compression wrinkles. The former shows NW-SE-trendlng contemporaneous extension events related to earthquakes in the rift basin near a famous Fe-Nb-REE deposit in northern China during the Early Paleozoic （or Mesoproterozoic as proposed by some researches）, while the latter indicates NE-SW-trending contemporaneous compression activities related to earthquakes in the Middle Triassic in the Nanpanjiang remnant basin covering south Guizhou, northwestern Guangxi and eastern Yunnan in southwestern China. The syn-sedimentary boudinage structure was found in an earthquake slump block in the lower part of the Early Paleozoic Sailinhudong Group, 20 km to the southeast of Bayan Obo, Inner Mongolia, north of China. The slump block is composed of two kinds of very thin layers-pale-gray micrite （microcrystalline limestone） of 1-2 cm thick interbedded with gray muddy micrite layers with the similar thickness. Almost every thin muddy micrite layer was cut into imbricate blocks or boudins by abundant tiny contemporaneous faults, while the interbedded micrite remain in continuity. Boudins form as a response to layer-parallel extension （and/or layer-perpendicular flattening） of stiff layers enveloped top and bottom by mechanically soft layers. In this case, the imbricate blocks cut by the tiny contemporaneous faults are the result of abrupt horizontal extension of the crust in the SE-NW direction accompanied with earthquakes. Thus, the rock block is, in fact, a kind of seismites. The syn-sedimentary boudins indicate that there was at least a strong earthquake belt on the southeast side of the basin during the early stage of the Sailinhudong Group. This may be a good constraint on the tectonic evolution of the Bayan Obo area during the Early Paleozoic time. The syn-sedimentary compression structure was found in the Middle Triassic flysch in the Nanpanjiang Basin. The typical structures are compression sand pillows and compression wrinkles. Both of them were found on the bottoms of sand units and the top surface of the underlying mud units. In other words, the structures were found only in the interfaces between the graded sand layer and the underlying mud layer of the flysch. A deformation experiment with dough was conducted, showing that the tectonic deformation must have been instantaneous one accompanied by earthquakes. The compression sand pillows or wrinkles showed uniform directions along the bottoms of the sand layer in the flysch, revealing contemporaneous horizontal compression during the time between deposition and diagenesis of the related beds. The Nanpanjiang Basin was affected, in general, with SSW-NNE compression during the Middle Triassic, according to the syn-sedimentary compression structure. The two kinds of syn-sedimentary tectonic deformation also indicate that the related basins belong to a rift basin and a remnant basin, respectively, in the model of Wilson Cycle.

Basin Fluid Mineralization during Multistage Evolution of the Lanping Sedimentary Basin,Southwestern China

The Lanping sedimentary basin has experienced a five-stage evolution since the late Paleozoic： ocean-continent transformation （late Paleozoic to early mid-Triassic）; intracontinental rift basin （late mid-Triassic to early Jurassic）; down-warped basin （middle to late Jurassic）; foreland basin （Cretaceous）; and strike-slip basin （Cenozoic）. Three major genetic types of Ag-Cu polymetallic ore deposits, including the reworked hydrothermal sedimentary, sedimentary-hydrothermally reworked and hydrothermal vein types, are considered to be the products of basin fluid activity at specific sedimentary-tectonic evolutionary stages. Tectonic differences of the different evolutionary stages resulted in considerable discrepancy in the mechanisms of formation-transportation, migration direction and emplacement processes of the basin fluids, thus causing differences in mineralization styles as well as in genetic types of ore deposit.

The Type and Evolution of Neoproterozoic Sedimentary Basin in the Dahongshan Region,Northern Margin of the Yangtze Block:An Insight from Sedimentary Characteristics of the Huashan Group

Objective The Huashan group（composed of the lower Hongshansi Formation and the upper Liufangzui Formation）is an important Neoproterozoic stratigraphic unit along the northern margin of the Yangtze Block.Previous documents have focused on the geochronological and geochemical aspects of the Neoproterozoic sedimentary basin in the Dahongshan region.However.

The Lithofacies Paleogeography and Paleoenvironmental evolution of the Cenozoic in the Weihe Basin, China

The Weihe Basin,which is known as a Cenozoic rift Basin,is special for its location where not only enrich oil,gas and water,but also is a"sweet"for environment evolution research.It sits in the transition area between the ordos basin with full of oil and gas resources in the north and the Qinling Orogenic Belt with rich mineral

Geological and geochemical evolution of forming of kalium-rich brine in Sichuan Basin

1 Introduction Sichuan Basin is basically a salt brine reservoir,large closed and semi-closed artesian sedimentary basin with an area of 200,000 Km2 in southeast China.During the forming and evolution of the basin,it has been affected by

Geothermal Field and Tectono-Thermal Evolution since the Late Paleozoic of the Qaidam Basin,Western China

The Qaidam basin is the largest intermountain basin inside Tibet, and is one of the three major petroliferous basins in western China. This study discussed the geothermal field and tectono-thermal evolution of the basin, in an effort to provide evidence for intracontinental or intraplate continental dynamics and basin dynamics, petroleum resources assessment, and to serve petroleum production.

Cretaceous Stress Fields Evolution and Its Geodynamic Implications in Jiaolai Basin, Northern China

The Tan-Lu fault zone(TLFZ)along the East China continental margin experienced sinistral movement at the beginning of Early Cretaceous(ca.145)due to fast oblique subduction of the Izanagi Plate in the Pacific Ocean.It can

Evolution of the Carboniferous Reef in Eastern Qaidam Basin and its Hydrocarbon Significance

Objective Reef reservoirs have recently been receiving more and more attention due to their important role in petroleum exploration.Large-scale reefs have been previously discovered in the Paleozoic strata of western China,suchas the Late Permian of the Sichuan Basin,Late Ordovician of the Ordos Basin,and Late Ordovician of the Tarim Basin,which are all important hydrocarbon reservoirs in these areas.