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Zhang Y.-P.,Xian Geological Survey Center | Ren J.-Y.,Hubei University | Zhao X.-Q.,Southwest University of Science and Technology | Tang Y.,Changan University | And 2 more authors.
Geological Bulletin of China

Great Sanjiang region is an important oil and gas resources succeeding district in eastern China. During the Early Cretaceous period, this region was once a unified lake basin, and then broken up. The problem as to the determination of the basin boundary and the reconstruction of the basin prototype is one of the key geological problems in this region. Previous study on the basin boundary was mainly focused on theoretical speculation and seemed lack of actual evidence. In this study, a set of conglomerates was found at the bottom of Muling Formation in Linkou basin. Based on an analysis of gravel composition and sorting as well as sedimentary characteristics, combined with the paleocurrent recovery and seismic data interpretation, the authors have concluded that the set of conglomerate is on the whole of alluvial fan facies, the river conglomerate deposition and overflow conglomerate deposition constitute the dominant depositions, and the provenance mainly came from the Zhangguangcai Mountain in the west of the basin. Combined with the seismic data analysis, it is held that the deposition model of the study area was the direct transition from the alluvial fan to the shallow lake subfacies in the period of Muling Formation. This study not only provides direct evidence for the determination of the western border of the Great Sanjiang Basin, but also points out the direction for the future oil and gas exploration in this region. Source

Wan Y.-Y.,Jilin University | Su X.-S.,Jilin University | Dong W.-H.,Jilin University | Hou G.-C.,Xian Geological Survey Center
Jilin Daxue Xuebao (Diqiu Kexue Ban)/Journal of Jilin University (Earth Science Edition)

In order to reduce the pressure of water supply and accelerate the development of local economy and society, the authors studied the groundwater renewal ability of the Ordos Cretaceous groundwater basin, one of major water resources areas in the Ordos basin. The dynamics of DIC in groundwater is regarded as the same as groundwater approximately. This interprets that input and output of 14C in groundwater system can provide information of its renewal ability. 14C isotopes are used to study the renewal ability of mediate and deep groundwater by the isotopic mathematic and physical model, and groundwater renewal rate is an indicator for evaluation. The results reflect that the groundwater renewal ability decreases with depth, the renewal rate of mediate groundwater in most part is 0.1%/a-1%/a, greater than that of deep groundwater with the renewal rate of less than 0.1%/a. The groundwater renewal ability in the northern part of the basin is greater than that in the southern part. Source

Jiang H.-B.,Xian Geological Survey Center | Li Z.-H.,Xian Geological Survey Center | Yang H.-Q.,Xian Geological Survey Center | Dong F.-C.,Xian Geological Survey Center | And 3 more authors.
Northwestern Geology

Metallogenic unit is a geological unit on thein terms of metallogenic significance. The latest classification scheme about Chinese metallogenic units released by the national mineral resource potential assessment project includes Level I (Metallogenic domain), Level II (metallogenic provinces) and Level III (metallogenic belts). This article revises boundaries of the five Level III metallogenic units (metallogenic belts) in the Qinling area on the basis of the inheritance of this previous classification scheme. Then the five Level III metallogenic units are divided into 15 Class IV metallogenic units (metallogenic sub-zones)) as a symbol of according to significant stratigraphic, tectonic and magmatic belt characteristics and as well as relevant majorassociated mineralization. Furthermore, there is a summary about geology and mineral characteristics features of every Class IV metallogenic unit (metallogenic sub-zones) are summarized in this paper. Source

Gu P.Y.,Xian Geological Survey Center | He S.P.,Xian Geological Survey Center | Li R.S.,Xian Geological Survey Center | Shi C.,Xian Geological Survey Center | And 4 more authors.
Acta Petrologica Sinica

The granitic gneiss of Laguigangri metamorphic core complexes in southern Tibet is characterized by high SiO2 and K2O, low Fe 2O3, MgO and MnO, with alumina saturation index (A/CNK) of 1. 07 ∼ 1. 19 and peraluminous minerals (such as muscovite and garnet). These features suggest that the granitic gneiss belongs to the high-K calci-alkaline peraluminous rocks. It is obvious that the chondrite-normalized REE shows right inclined patterns with obvious negative Eu abnormity, simultaneously, the primitive mantle normalized trace element spidergrams are characterized by enriched LILE (such as Rb, Th and U) and depleted HFSE (such as Sr and Nb), as well as evidently low contents of Ba and Hf, which are compatible with the characteristics of crustal derived S-type granites. The initial values of 87Sr/86 Sr(/Sr) are in a range of 0. 709 ∼0. 7306, the εsr(t) in arangege of 80. 65 ∼ 379 and εNd(t =514Ma) values of -7. 13 ∼ -8. 97, without significant correlation between εNd (t) and/ Sr. The ratios of (206 Pb/204 Pb)t(= 18. 1062 ∼ 18. 8085), (207 Pb/204 Pb)t(= 15. 7 ∼ 15. 8) and (208 Pb/204 Pb),(=37. 5 ∼38. 2) also reveal crustal Pb isotopic features. Therefore, the granitic magma is originated from partially melting of clay and sandstone sedimentary rocks. With the U-Pb isotopic age of 514Ma, we believe that these rocks in Laguigangri formed during the transition period from syncollision (compressional) to post collision (extensional environment) in Pan African orogenic events in the north Himalayan. This magmatic activity may play an important role in formation of the Laguigangri metamorphic core complex. Source

Zhang Y.,Xian Geological Survey Center | Li Y.,Xian Geological Survey Center | Lu J.,Xian Geological Survey Center | Li Y.,No.105 Exploration Party | And 2 more authors.
Geological Bulletin of China

In this paper, high-concentration helium was found for the first time in the coal drill hole and the mud-shale adsorbed gases in Quanjishan and Tuanyushan area on the northern margin of the Qaidam Basin. Six methane samples from these two areas were analyzed for carbon and helium isotopes. The data obtained show that two samples' carbon isotope values of methane are -38.4‰ and -39.9‰, suggesting organic origin. In addition, the 3He/4He isotope values of four samples are between 0.03×10-6 and 1.3×10-6, showing that they were mainly crust-derived matter and subordinately mantle-derived matter. Through the analysis of regional geology and geophysical data, the authors have reached the conclusion that crust-derived helium was sourced from the granite with rich uranium and thorium on the basin basement. The deep faults of the northern Qaidam Basin might have provided better conditions for migration of the helium. Helium was produced in combination with other hydrocarbon or non-hydrocarbon gases in vertical migration process, and probably formed the unique helium-rich natural gas enrichment environment under the good reservoir and sealing condition in Jurassic, Neogene and Paleogene. © 2016, Science Press. All right reserved. Source

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