Geochemical features and genesis of the natural gas and bitumen in paleo-oil reservoirs of Nanpanjiang Basin, China

Bitumen from the Nanpanjiang Basin occurs mainly in the Middle Devonian and Upper Permian reef limestone paleo-oil reservoirs and reserves primarily in holes and fractures and secondarily in minor matrix pores and bio-cavities. N2 is the main component of the natural gas and is often associated with pyrobitumen in paleo-oil reservoirs. The present study shows that the bitumen in paleo-oil reservoirs was sourced from the Middle Devonian argillaceous source rock and belongs to pyrobitumen by crude oil cracking under high temperature and pressure. But the natural gas with high content of N2 is neither an oil-cracked gas nor a coal-formed gas generated from the Upper Permian Longtan Formation source rock, instead it is a kerogen-cracked gas generated at the late stage from the Middle Devonian argilla- ceous source rock. The crude oil in paleo-oil reservoirs completely cracked into pyrobitumen and methane gas by the agency of hugely thick Triassic deposits. After that, the abnormal high pressure of methane gas reservoirs was completely destroyed due to the erosion of 2000--4500-m-thick Triassic strata. But the kerogen-cracked gas with normal pressure was preserved under the relatively sealed condition and became the main body of the gas shows.     

(40)~Ar/(39)~Ar chronology and geochemistry of high-K volcanic rocks in the Mangkang basin, Tibet

Our two newly obtained high-quality 40Ar/39Ar ages suggest that the high-K volcanic rocks of the Lawuxiang Formation in the Mangkang basin, Tibet were formed at 33.5±0.2 Ma. The tracing of elemental and Pb-Sr-Nd isotopic geochemistry indicates that they were derived from an EM2 enriched mantle in continental subduction caused by transpression. Their evidently negative anomalies in HFSEs such as Nb and Ta make clear that there is an input of continental material into the mantle source. The high-K rocks at 33.5±0.2 Ma in the Mangkang basin may temporally, spatially and compositionally compare with the early one of two-pulse high-K rocks in eastern Tibet distinguished by Wang J. H. et al., implying that they were formed in the same tectonic setting.     

Sequence-stratigraphic frameworks and their palaeogeographic patterns for the Permian Lopingian of the Dianqiangui Basin and its adjacent areas of Southwestern China

The Permian Lopingian in the Dianqiangui Basin and its adjacent areas is marked by the coal measures of the Wuchiapingian and the carbonate strata of the Changhsingian stages. For the Lopingian of the Dianqiangui Basin and its adjacent areas,the diversity of sedimentary facies and the obviousness of facies change provide an advantaged condition on a study of sequence stratigraphy. Approximately,the Wuchiapingian stage constitutes a third-order sequence and the Changhsingian stage forms an-other. For the Wuchiapingian stage in the study area,coal-measures were developed on the attached platform and,in addition,a special coal-measure that is composed of both limestone beds and coal beds was also developed in the central part of some isolated platforms. Grain-bank grainstones and packstones were formed on the margin of the attached platform as well as in the windward part of iso-lated platforms. For the Changhsingian stage in the study area,open-platform limestones were formed on the attached platform,while sponge-reef limestones were developed both on the margin of the at-tached platform and on the isolated platforms. The Lopingian Series is a set of basin-facies muddy shales with interbeds of silicalites in the inter-platform basin,which appears a set of the large-thick coarse clastic strata of molasses covering direct the deep-water strata from the Devonian to the Per-mian Yangsingian in the Qinzhou-Fangcheng region in the southern part of the study area. All of these features indicate the complexity of temporal-spatial facies-changes. Sequence-stratigraphic frame-works could be established,which would illustrate two types of facies-changing surfaces and dia-chronisms in the stratigraphic records,based on the combination of both biostratigraphic and chronostratigraphic materials and the regularity reflected by temporal evolutionary succession of sediments as well as spatial distributional patterns of sedimentary facies. Ultimately,features of sedi-mentary succession and palaeogeographical evolution of the Permian Lopingian in the study area are revealed clearly in a series of the panel diagrams of sequence-stratigraphic frameworks and the outline maps showing the sedimentary-facies and palaeogeography. The Permian Lopingian formed by two third-order sequences differs from the stratigraphy of the same era characterized by the constant re-gression along Euramerica. Most specially,if the end-Guadalupian mass-extinction event is genetically related to a regressive event represented by the unconformity of the first episode of the Dongwumovement in the study area,the mass-extinction event at the turn from the Permian to the Triassic is genetically related to a rapid transgressive event re-flected by the drowning unconformity in the study area. These phenomena might reveal a complex rela-tionship between mass-extinction events and trans-gressive-regressive events.     

Geochemical characteristics of soil selenium and evaluation of Serich land resources in the central area of Guiyang City,China

Based on the results of multipurpose regional geochemical surveys of the Guizhou Province, geochemical characteristics of soil Se and Se-rich land resources in the central area of Guiyang City were studied and evaluated.Major conclusions are as follows:(1) the Se content in surface soil of the central area of Guiyang City was 0.17–2.89 mg kg~(-1), and the average was 0.78 mg kg~(-1), which were respectively 2.6 and 3.9 times of the national background value of soil and the world background value of soil.The Se content in deep soil was 0.11–1.48 mg kg~(-1), and the average was 0.44 mg kg~(-1), which were respectively 1.5 and2.2 times of the national background value of soil and the world background value of soil. The soil Se content decreased with the increase in the soil depth on the vertical profile, and the surface soil had a higher Se content.(2)Distribution of Se content was mainly affected by parent material, physicochemical properties of soil and other components, soil type, and land use type. Parent material played a key role, as the soil Se content was mainly originated from parent rock and increased with the background value of Se in parent rock, physicochemical properties of soil and other components had certain influences upon the Se content. Se was shown to have a significant linear positive correlation with S and organic carbon but no significant correlation with p H value. Se content varied with different types of soil as follows: skeleton soil yellow soil paddy soil limestone soil purple soil. Land use type also hadcertain influences upon the soil Se content as follows: dry land construction land garden plot grassland =garden plot forest land.(3) Taking 0.4 mg kg~(-1)B x(Se) 3.0 mg kg~(-1) as the standard for Se-rich soil, Se-rich soil of the study area covered an area of 2224 km~2 and 92.5% of the total area; the remaining is general soil. The study area had no Se-excess soil. Therefore, the central area of Guiyang City has a high proportion of Se-rich land, a large area of Serich land resources, and a moderate selenium enrichment strength, which have been rarely seen anywhere and provide advantageous resources for the development of Se-rich featured agriculture.     

The hydrothermal karstification and its effect on Ordovician carbonate reservoir in Tazhong uplift of Tarim Basin, Northwest China

With a detailed study on petrology, mineralogy and geochemistry of some important Ordovician carbonate well core samples in Tazhong uplift of Tarim Basin, the distinguishing symbols of hydrothermal karstification are first put forward as the phenomena of rock hot depigmentation, hot cataclasm and the appearance of typical hydrothermal minerals such as fluorite, barite, pyrite, quartz and sphalerite. The main homogenization temperatures of primary fluid inclusions in fluorite are from 260 to 310℃, indicating the temperature of hydrothermal fluid. The fluid affected the dissolved rocks and showed typical geochemistry features with low contents of Na and Mg, and high contents of Fe, Mn and Si. The ratio of 3He/4He is 0.02Ra, indicating the fluid from the typical continental crust. The hydrothermal fluid karstification pattern may be described as follows the hot fluid is from the Permian magma, containing dissolving ingredients of CO2 and H2S, and shifts along fault, ruptures and unconformity, and dissolves the surrounding carbonates while it flows. The mechanism of hydrothermal karstification is that the mixture of two or more fluids, which have different ion intensity and pH values, becomes a new unsaturated fluid to carbonates. The hydrothermal karstification is an important process to form hypo-dissolved pinholes in Ordovician carbonates of Tazhong uplift of Tarim Basin, and the forming of hydrothermal minerals also has favorable influence on carbonate reservoirs.     

Geochemical characteristics of the metapelites from the Xingxingxia group in the Eastern Segment of the Central Tianshan: Implications for the provenance and paleoweathering

Clastic sedimentary rocks record a number of in-formation about the compositions and paleoweathering conditions of the source areas, and the tectonic setting of the depositional basin[1―6]. The traditionallypetrological study commonly utilizes the major com-ponents (Quartz, Feldspar and Lithics) of the silici-clastic sedimentary rocks to investigate the source rock composition and tectonic setting[7]. However, thepetrological method is somewhat limited, because many of the mafic components f…     

Paleomagnetic data from the Late Carboniferous-Late Permian rocks in eastern Tibet and their implications for tectonic evolution of the northern Qiangtang-Qamdo block

We report paleomagnetic results from the Late Carboniferous-Late Permian strata in eastern Tibet (China), and aim to clarify the tectonic and paleogeographic evolution of the northern Qiangtang-Qamdo block, which is the key to the study of plate boundary between the Gondwanaland and the Eurasia during the late Paleozoic. Two hundred and nineteen samples-including limestone, muddy siltstone, basalt, lava, and tuff-were collected at 24 sites in the Upper Carboniferous and Middle-Upper Permian successions. A systematic study of rock magnetism and paleomagnetism yields three reliable paleomagnetic pole positions. Both hematite and magnetite occurred in the Late Carboniferous limestone samples. The demagnetization curve shows a characteristic double-component, with the remanent magnetization (ChRM) exhibiting a positive polarity (negative inclination). In the Late Permian limestone, tuff, and basalt, magnetic information were recorded primarily in magnetite, although a small fraction of them was found in hematite in basalt. The demagnetization curve illustrates a double or single component, with the ChRM showing a negative polarity (positive inclination), which has passed the classic fold test successfully. The single polarity features of the ChRM directions of the Late Carboniferous and Middle-Late Permian rocks are respectively related to the Kiaman positive and reversed polarities under the stratigraphic coordinates. This, in turn, indicates that both ChRMs directions represent the original remanence directions. By comparison with the previously published paleomagnetic results from the late Paleozoic rocks in the northern Qiangtang Range, we suggest that: (1) Qamdo and northern Qiangtang block were independent of each other during the Late Carboniferous to the Early Permian periods. The north Lancangjiang ocean basin between the two blocks may have closed before the Middle Permian and been involved in the continent-continent collision stage in the Late Permian-Early Triassic periods. (2) The northern Qiangtang-Qamdo Block paleogeographically was situated at low to intermediate latitudes in the Southern Hemisphere in the Late Carboniferous-Late Permian periods, and began to displace northward in the Early Triassic, with an amount of more than 5000 km northward transport from its current location.     

The deep structures and oil-gas prospect evaluation in the Qiangtang Basin, Tibet

The Qiantang Basin is now one of the topics of general interest in petroleum exploration in China. This paper reports a comprehensive study of geophysical and geological survey data recently obtained in this area and, combined with INDEPTH-3 deep survey results, comes to the following conclusions： 1） The hydrocarbon source formations, reservoirs, and overlying strata and their association within the basin are quite good, local structures are developed, and, therefore, the region is favorable for forming and preserving oil and gas accumulations. Faults are not a fatal problem. The future main target strata are the middle-deep structural strata composed of Upper-Triassic and middle Jurassic rocks; 2） A new classification has been made for second-order tectonic sequences inside the basin to disavow the central Qingtang uplift. It is noted that the main structures at the surface are orientated NW-SE and the crustal structure can be described as three depressions, three risees, and one deep depression, of which the prospective zone with the most potential is the inner main subsided belt and its two sides; 3） Comparatively intensive interaction between the crust and mantle and volcanic and thermal activities in the northern basin play a very important role in petroleum evaluation. The southern deeper sedimentation and less thermal activity make this area a more perfect zone for oil exploration; 4） Currently, the most important objective is determining the physical properties of the deep strata, the status of oil and gas accumulations, the source of the hydrocarbons, and the relationship between the upper and lower structures; and 5） The Lunpola Tertiary basin may be favorable for oil accumulations because petroleum may migrate from marine strata on two sides.     

Origin of seleniferous cherts in Yutangba Se deposit,southwest Enshi,Hubei Province

At the top of the Lower Permian Maokou Formation limestones are developed carbonaceous cherts(Plm3),which constitute the dominant seleniferous layer of the Yutangba Se deposit.The cherts contain as much Se as 1646×10?6 on average.In addition,they are rich in organic carbon,Al2O3,Si2O,but poor in S.In addition to Se,as well as Mo,Cd,V,and Co,etc are also highly enriched in the cherts.The chert samples are characterized by low ?REE,slight LREE enrichment,relatively heavy Si isotope enrichment,and insignificant variations in ? 30Si value within the range of 1.1‰-1.2‰.Generally,it can be judged from the major element,trace element and REE data and the Si isotopic characteristics that the Yutangba seleniferous cherts were formed in the shallow sea to semi-deep sea anoxic environments and their formation is controlled chiefly by bio-chemical processes.     

Permian-Triassic magmatic evolution of granitoids from the southeastern Central Asian Orogenic Belt: Implications for accretion leading to collision

Many orogenic belts in the world exhibit accretionary and collisional orogenic phases to varying extents. How accretion evolves into collision of the Central Asian Orogenic Belt(CAOB), the largest Phanerozoic accretionary orogenic belt,is an intriguing question. In this paper, we present new U-Pb age, geochemical and isotopic data for Permian-Triassic granitoids from middle Inner Mongolia, Northern China in the southeastern CAOB, and delineate the magmatic transition from subduction to(soft) collision. The magmatic record of soft collision is identified and characterized by thickened lower crust-derived high Sr/Y granitoids with a sub-linear distribution along the Solonker suture zone. Granitoids from Early Permian to Late Permian became more enriched in whole-rock Nd and zircon Hf isotopic compositions(ε_(Nd)(t) values from 2.4 to-19.5, ε_(Hf)(t) values from 11.6 to-33.7), indicating increasing incorporation of old crust. The change in peak timing of magmatism from west(ca. 264 Ma)to east(ca. 251 Ma) along the Solonker suture zone implies "scissor-like" closure of the Paleo-Asian Ocean. Integrated with previous studies, a three-stage tectonic model from the Permian to Triassic by accretion leading to collision on the south-eastern margin of CAOB is proposed.(1) Early Permian( ca. 285 Ma): Juvenile magmatism on an active continental margin with double-sided subduction of the Paleo-Asian Ocean;(2) Middle Permian to Middle Triassic(ca. 285–235 Ma): Magma source transition from juvenile to old crust induced by a tectonic switch from arc to "scissor-like" closure and subsequent intracontinental orogenic contraction;(3) Late Triassic( ca. 235 Ma): A-type and alkaline magmatism in response to post-collisional extension.     

Location and moment tensor inversion of small earthquakes using 3D Green’s functions in models with rugged topography: application to the Longmenshan fault zone

With dense seismic arrays and advanced imaging methods, regional three-dimensional(3D) Earth models have become more accurate. It is now increasingly feasible and advantageous to use a 3D Earth model to better locate earthquakes and invert their source mechanisms by fitting synthetics to observed waveforms. In this study, we develop an approach to determine both the earthquake location and source mechanism from waveform information. The observed waveforms are filtered in different frequency bands and separated into windows for the individual phases. Instead of picking the arrival times, the traveltime differences are measured by cross-correlation between synthetic waveforms based on the 3D Earth model and observed waveforms. The earthquake location is determined by minimizing the cross-correlation traveltime differences. We then fix the horizontal location of the earthquake and perform a grid search in depth to determine the source mechanism at each point by fitting the synthetic and observed waveforms. This new method is verified by a synthetic test with noise added to the synthetic waveforms and a realistic station distribution. We apply this method to a series of M_W3.4–5.6 earthquakes in the Longmenshan fault(LMSF) zone, a region with rugged topography between the eastern margin of the Tibetan plateau and the western part of the Sichuan basin. The results show that our solutions result in improved waveform fits compared to the source parameters from the catalogs we used and the location can be better constrained than the amplitude-only approach. Furthermore, the source solutions with realistic topography provide a better fit to the observed waveforms than those without the topography, indicating the need to take the topography into account in regions with rugged topography.     

Petrology and geochemistry of clastic sedimentary rocks as evidences for provenance of the Late Palaeozoic Madzaringwe Formation,Tshipise-Pafuri Basin,South Africa

Petrography and geochemistry(major, trace and rare earth elements) of clastic rocks from the Late Palaeozoic Madzaringwe Formation, in the Tshipise-Pafuri Basin, Northern South Africa, have been investigated to understand their provenance. Sandstone petrography and detrital modes indicates that the Late Palaeozoic succession was derived from craton interior and recycled orogen provenance. Sandstones in the Madzaringwe Formation are sub-arkosic to sub-litharenite. The sediments may represent a recycled to craton interior provenance. The geochemical data of major elements show that sandstone and shales have the same source. The study of paleoweathering conditions based on modal composition, chemical index of alteration(CIA) and A-CN-K(Al2O3-Ca O+Na2O-K2O) relationships indicate that probably chemical weathering in the source area and recycling processes have been more important in shale and sandstone rocks. The relatively high CIA values(70–90%) indicates moderate to high weathering conditions of the samples and the paleoclimate of the source area was warm. K2O/Na2 O versus Si O2 and Na2O-Ca O-K2 O tectonic setting discrimination plots, suggest a passive continental margin. In the study of trace elements, triangular Th-Sc-Zr/10 and La-Th-Sc plots both suggest a passive margin setting of the basin. Petrographic and geochemical results of the samples suggest uplifted basement source areas dominated by sedimentary rocks and/or granite-gneiss rocks. The source rocks might have been the recycled pre-Soutpansberg Karoo Supergroup rocks and the metasedimentary rocks of the Soutpansberg Group. Other source rocks may have been the pre-Beit-Bridge basement rocks(granites and gneisses).     

Major element, trace element, and Sr, Nd and Pb isotope studies of Cenozoic basalts from the South China Sea

The whole rock K-Ar ages of basalts from the South China Sea basin vary from 3.8 to 7.9 Ma, which suggest that intra-plate volcanism after the cessation of spreading of the South China Sea (SCS) is comparable to that in adjacent regions around the SCS, i.e., Leiqiong Peninsula, northern margin of the SCS, Indochina block, and so on. Based on detailed petrographic studies, we selected many fresh ba-saltic rocks and measured their major element, trace element, and Sr-Nd-Pb isotope compositions. Geochemical characteristics of major element and trace element show that these basaltic rocks belong to alkali basalt magma series, and are similar to OIB-type basalt. The extent of partial melting of mantle rock in source region is very low, and magma may experience crystallization differentiation and cu-mulation during the ascent to or storing in the high-level magma chamber. Sr-Nd-Pb isotopic data of these basaltic rocks imply an inhomogeneous mantle below the South China Sea. The nature of magma origin has a two end-member mixing model, one is EM2 (Enriched Mantle 2) which may be originated from mantle plume, the other is DMM (Depleted MORB Mantle). Pb isotopic characteristics show the Dupal anomaly in the South China Sea, and combined with newly found Dupal anomaly at Gakkel ridge in Arctic Ocean, this implies that Dupal anomaly is not only limited to South Hemisphere. In variation diagrams among Sr, Nd and Pb, the origin nature of mantle below the SCS is similar to those below Leiqiong peninsula, northern margin of the SCS and Indochina peninsula, and is different from those below north and northeast China. This study provides geochemical constraints on Hainan mantle plume.     

GPS Observation and Study on Recent Crustal Movement in the Northeastern Area of Pamir,Xinjiang

Calculation of repeated observation data at the densified GPS monitoring network in northeastern area of Pamir together with data from IGS stations in the peribphyery of the area yielded the movement rate of more than 40GPS station sites in the area,and,hence,the recent crustal deformation rate pattern and time series of fiductial GPS stations in the area were obtained.The result indicates that the principal movement direction of the GPS station sites is NNW,basically diagonal to the strike of Tianshan fold belt,i.e.a normal compression occurs in the Tianshan region.The movement pattern near Jiashi and its southwestern zone is some different from that of station sites in their surrounding areas,indicating a certain relation of tectonic deformation in Jiashi area to seismic activity during last years.The movement rate of station sites in the periphery of Taim basin less varies and its direction is basically consistent It indicates less or basically no deformation within Tarim basin.     

Zircon SHRIMP geochronology and Nd-Pb isotopic characteristics of the meta-basalt in the central part of Tibetan Plateau’s Qiangtang region

A small-sized meta-basic rock system is discovered in Qilongwuru Gully of Central Qiangtang’s Shuanghu region and contains a meta-basalt and garnet-bearing plagioclase amphibolite.The zircon U/Pb age of this meta-basalt by SHRIMP analysis is463.3±4.7 Ma,suggesting that this lava formed in the Middle Ordovician,and is consistent with that of the meta-basic rocks in the Taoxing Lake and Guoganjianian Mountain ophiolite found in the Qiangtang plate.As this lava system bears similar geochemistry to N-MORB,it might be a component of ophiolite that represents the trail of the extinction of the Proto-Tethys,suggesting that the formation of Proto-Tethys oceanic basin in the Longmu Co-Shuanghu suture zone could date as far back as to the Middle Ordovician.Isotopic geochemical analysis indicates that the magma source area consists of both depleted mantle(DM)and enriched mantle(EMII)end members and bears Dupal anomaly,similar to that of the Paleo-Tethys in the Neo-Tethys represented by the Yarlung-Tsangpo suture zone,the Paleo-Tethys represented by the Changning-Menglian suture zone,and the Paleo-Tethys in Sanjiang region.This suggests that they have inherited the attribute of the Proto-Tethys mantle domain,and the Longmu Co-Shuanghu suture zone may be a representative of the northern boundary of Gondwana.     

Hydrocarbon accumulation in network and its application in the continental rift basin

The concept of hydrocarbon accumulation in network was presented on basis of the overall analysis of the formation and evolution characteristics of the continental faulted basin and of the systemic re-search on the major controlling factors on the hydrocarbon accumulation. The hydrocarbon accumu-lation in network can be defined as hydrocarbon accumulation in a three-dimensional network system which is constituted by the hydrocarbon migration passages under multiple dynamics,following the hydrocarbon generation from source rocks. The research shows that the hydrocarbon accumulation in network is composed of four elements,i.e.,hydrocarbon source (source rock kitchen),hydrocarbon accumulation terminal (trap),network pathway connecting source and terminal (transporting system),and network potential driving hydrocarbon migration in the network pathway (migration dynamics). Compared with other networks,hydrocarbon accumulation in network has three basic characteristics: the irreversible geological process of material and information flow in the network; the loss of material and information in the flow process in the network; the multiple dynamics in the flow process. Interac-tion of all the elements in the geological process can be called hydrocarbon accumulation in network. There are three basic models for hydrocarbon accumulation in network,that is,hydrocarbon accumu-lation in the network source area,hydrocarbon accumulation in the network pathway,and hydrocarbon accumulation in the network terminal. The key in the application of the hydrocarbon accumulation models in network in practice is to confirm the major accumulation stage and the function range of the four elements controlling the hydrocarbon firstly,to predict the profitable accumulation region by su-perposition of the favorable areas confirmed by four elements consequently,and to evaluate the oil-bearing property of the trap as well as confirm drilling targets. This paper takes the Dongying De-pression in the Bohai Bay Basin as an application example.     

Rare-earth and trace elements and hydrogen and oxygen isotopic compositions of Cretaceous kaolinitic sediments from the Lower Benue Trough,Nigeria: provenance and paleoclimatic significance

This study evaluated the Cretaceous(Campanian–Maastrichtian) kaolinitic sediments of the Ajali/Mamu and Enugu/Nkporo Formations from the Lower Benue Trough of Nigeria. A combined method of inductively coupled plasma–mass spectrometry and isotope ratio mass spectrometry was used to investigate trace and rareearth element geochemistry and hydrogen and oxygen isotopic compositions. These data were then used to infer the sediments' provenance and paleoclimatic conditions during their deposition. The sediments contained low concentrations of most trace elements, with the exceptions of Zr(651–1352 ppm), Ba(56–157 ppm), V(38–90 ppm),and Sr(15.1–59.6 ppm). Average values of Co and Ni were1.5 and 0.7 ppm, respectively. Trace and rare earth element values were lower than corresponding values for upper continental crust and Post-Archean Australian Shale, with the exception of Zr. The samples showed only slight light rare-earth enrichment and nearly flat heavy rare-earth depletion patterns, with negative Eu and Tm anomalies,typical of felsic sources. Geochemical parameters such as La/Sc, Th/Sc, and Th/Co ratios support that the kaolinitic sediments were derived from a felsic rock source, likely deposited in an oxic environment.^(18 )O values ranged from+ 15.4 to + 21.2% for the investigated samples, consistent with a residual material derived from chemicalweathering of felsic rock and redeposited in a sedimentary basin(typical values of + 19 to + 21.2%). While in the basin, the sediments experienced extended interactions with meteoric water enriched in d D and d16 O. However,the variation in d D and d16 O values for the investigated samples is attributed to the high temperature of formation(54–91 °C). The d D and d^(18 )O values suggest that the sediments, although obtained from different localities within the Lower Benue Trough, formed under similar hot,tropical climatic conditions.     

Characteristics of petroleum accumulation in syncline of the Songliao basin and discussion on its accumulation mechanism

The relation between oil and water in reservoirs with low and ultra-low permeability is very complicated. Gravitational separation of oil and water is not obvious. Normal reservoirs are located in depression and structural high spot, oil and water transitions are located in their middle. Stagnation is the key fact of oil-forming reservoir in the axis of a syncline based on the research of oil, gas and water migration manner, dynamics and non-Darcy flow in the Songliao basin. In low and ultra-low permeable reservoir, gas and water migrate easily through pore throats because their molecules are generally smaller than the pore throats; but the minimum diameter of oil droplets is larger than pore throats and they must be deformed to go through. Thus, gas and water migrate in advance of oil, and oil droplets remain behind. Pressure differential and the buoyancy force in a syncline reservoir are a main fluid driving force; and capillary force is the main resistance to flow. When the dynamics force is less than resistance, oil is immobile. When the buoyancy force is less than the capillary force, a gravitational separation of oil and water does not occur. The reservoir in the mature source rock of a syncline area with the low and ul- tra-low permeability belongs to an unconventional petroleum reservoir.     

The Role of Gravity, Magnetic and Electric Prospecting Techniques in the Geological Survey of the Qiangtang Basin

The Qiangtang basin is one of the large-scale basins in China, which is located in the high-altitude and cold area. In 1994 the preliminary gravity, magnetic and electric prospecting work was undertaken in this area. Over three years the gravity, magnetic and electric reconnaissance work had been completed. The integrated interpretation of complex gravity, magnetic and electric data had identified the boundary of the basin. The relationship between the basin and mountains is a south-north ramp structure. The basin structure consisted of one uplift and two sags, five depressions and two arches. The complex evaluation showed that the regions of Baitanhu and Youyiquan in the Qiangtang basin were considered to be the most perspective ones in sense of oil-gas bearing.     

Provenance discrimination and Source-to-Sink studies from a dryland fluvial regime： An example from Kachchh,western India

Tracing the sediment delivery from its source terrain to its ultimate sink envisage multiple factors that play a vital role in understanding present day erosional engine.To accomplish this,it is significant to distinguish the variable end-members contributing to the basin.The findings from the study of dryland coastal fluvial regime in Kachchh(Western India),which is one of the end members contributing to the Gulf of Kachchh coast(partial sink) and finally to the Arabian Sea(ultimate sink) have been presented here.Multi-proxy sediment provenance proxies such as grain-size,clay minerals,geochemistry and magnetic minerals have been employed to evaluate the provenance discriminating characteristics of the Kachchh dryland fluvial system and factors influencing them.The results of different proxies indicate that the provenance signatures of uplands are quite characteristic with magnetic susceptibility(χ) values of 20×10~(-7)m~3kg~(-1) and smectite(S)/kaolinite(K) ratio between 0.26 and 0.49.The middle reaches show marked increase in magnetic mineral concentration with χ values(140×10~(-7)m~3kg~(-1))and S/K ratio(4.92),while the estuarine tract shows χ values(80×10~(-7)m~3kg~(-1)),S/K ratio(1.90) and,characteristic heavy minerals(i.e.mica minerals),probably reflect the interplay between land and sea oscillations.Major sources of sediments within catchment scale were identified,viz.,upland sedimentary rocks(Juran and Bhuj Formation sandstone-shale) and middle reaches volcanic(Deccan Trap Formation basalt) rocks.The present study draw cautions in provenance of sediment discrimination in areas influenced by Deccan basalt that has the overwhelming sediment delivery and a comparatively subdued effects of other provenance signatures.The studied proxies of mineralogy of clays,magnetic minerals and geochemistry of heavy and major elements serve as the potential for fingerprint of sediment source regions and hence behold a strong position in source to sink studies globally.