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The Lower Jurassic clastic rocks in the Qiangtang Basin, northern Tibet, are generally regarded as the early sediments of the new Mesozoic Qiangtang Basin (Late Triassic to Early Cretaceous). However, little attention has been paid to the palaeoenvironment, provenance, and tectonic setting of this unit. The QZ‐16 well, located in the east of the northern Qiangtang Basin, firstly recovered the Lower Jurassic strata (Quemo Co Formation) in the Qiangtang Basin. In this paper, the whole‐rock major‐trace elemental characteristics of 34 mudstone samples and detrital zircon geochronology of one sandstone, collected from the Quemo Co Formation of the QZ‐16 well, are reported in order to infer the palaeoenvironment, provenance, and tectonic setting. Quemo Co mudstones are dominated by SiO2 and Al2O3, while Fe2O3, CaO, K2O, and MgO are the second most abundant oxides. They are generally characterized by high REE concentrations, enrichment in light rare earth elements (LREEs), marked negative Eu and Ce anomalies. The REE contents of the mudstones are mainly controlled by terrigenous detrital minerals input. The Lower Jurassic mudstones have relatively high chemical index of alteration (79.1–83.6) values, indicating moderate to high degree of chemical weathering conditions of the source area. Sr/Ba and Rb/K ratios reflect that the marine transgression impact was limited and the mudstones were generally deposited in a brackish water environment. Major, trace, and REE contents indicate that the mudstones were mainly derived from intermediate igneous rocks with subordinate felsic igneous rocks. Prominent age peaks at ca. 200 ~ 400 Ma, 700 ~ 970 Ma, 1,700 ~ 1,900 Ma, and 2,100 ~ 2,700 Ma of the detrital zircon grains suggest that the Lower Jurassic clastic rocks were derived from the Central Qiangtang and Songpan–Ganzi complex. Moreover, tectonic discrimination diagrams based on major and trace elements show that the source of the Lower Jurassic sediments were most likely derived from a collision tectonic setting. [ABSTRACT FROM AUTHOR]

The Kaixinling coal is located in the eastern part of the North Qiangtang Basin, which were the important coal resources in Tibetan Plateau. A total of thirty coal samples were collected from the Kaixinling area to determine the concentrations, distribution patterns, occurrences and origins of platinum group elements (PGEs) in the Permian coal. The total contents of PGEs are low ranging from 0.56 to 1.89 ng/g with a weighed mean value of 1.21 ng/g. The contents in Os exhibit considerably positive anomaly compare to the Upper Continental Crust and the ordinary Chinese coal. The individual PGEs in coal samples from the Kaixinling area exhibit various modes of occurrence. Pd and Pt are mainly concentrated in clay minerals and P-bearing minerals. Ir is probably present in clay minerals and partly controlled by other Fe-bearing and P-bearing minerals. Os is associated with organic matter and partly related to calcite. Three possible origins of PGEs were identified in coal seams in the Kaixinling area. Pd, Pt and Ir are mainly terrigenous inputs. Rh and Ru are derived from mixed sources (seawater and terrigenous supply), while Os is mainly derived from seawater. [ABSTRACT FROM AUTHOR]

The geochemistry and detrital zircon geochronology of the Quemoco sandstones from the Woruo Mountain area, North Qiangtang Basin, are analysed to discriminate their provenance and tectonic setting. The sandstones were classified as litharenite according to their geochemical data. The index of chemical variability and SiO2/Al2O3 ratio values suggest that the compositional maturity and recycling are weak to moderate. The weathering indices, such as chemical index of alteration, plagioclase index of alteration, and chemical index of weathering, and A–CN–K (Al2O3–(CaO* + Na2O)–K2O) ternary plot reflect that the source areas have undergone a weak degree of weathering. The TiO2 versus Zr, La/Th versus Hf, and Co/Th versus La/Sc bivariate diagrams and multimajor elements discrimination diagram of Quemoco sandstones indicate that the provenances were primarily derived from felsic igneous rocks and may also have less intermediate igneous source rocks. The paleocurrent data and low composition and textural maturity of the Quemoco sandstones suggested that the provenances are mainly from the southwest of the study area and with proximal source features. The U–Pb ages studied here could be divided into 8 groups: 206–219 Ma, 268–283 Ma, 446–630 Ma, 700–970 Ma, 1006–1346 Ma, 1457–1843 Ma, 2087–2214 Ma, and 2331–2587 Ma. The provenances are mainly from the Central Uplift Belt and surrounding of the study area according to the detrital zircon ages and rare earth element parameters, which are composed of Late Triassic tuff, Permian basalt, Early Ordovician granite, Cambrian granite gneiss, and Precambrian crystalline basement. Two multidimensional tectonic discrimination diagrams based on major elements show a complicated tectonic setting composed of a collision, rift, and minor arc setting for the Quemoco sandstones, which is consistent with the nature of a rifted margin during the late Late Triassic. [ABSTRACT FROM AUTHOR]

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The early Jurassic black shales are the most important source rocks in the Qiangtang Basin, Tibet. These black shales may provide a useful example for understanding the sedimentary conditions during the early Jurassic in the eastern Tethys. Thirty-two black-shale samples were collected from the Qiangtang Basin to reconstruct the depositional environments during the early Jurassic in the eastern Tethys. The palaeoclimate index Σ(Fe + Mn + Cr + Ni + V + Co)/Σ(Ca + Mg + Sr + Ba + K + Na) varies between 0.58 and 1.14, together with low Sr/Ba (0.20-0.60) and Sr/Cu (1.68-7.88) ratios, indicating a warm humid to semi-humid climatic condition during black-shale deposition. The early Jurassic black shales exhibit slight Ce anomalies (0.89-0.94) and Mn enrichment (EF = 1.2), suggesting a slightly oxic depositional environment. The conditions of the sedimentary water system during black-shale deposition were apparently brackish as evidenced by middle B/Ga (3.96-5.73) and Th/U (3.96-6.51) ratios. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract The Upper Triassic Bagong mudstones are considered to be the most significant source rocks in the eastern part of North Qiangtang Basin, Tibetan Plateau. This study investigates the vertical variation of total organic carbon (TOC) contents as well as mineral compositions, carbon isotope, palynology, major and trace element concentrations of the Upper Triassic sediments from Geladandong area of North Qiangtang Basin to understand the mechanism of organic matter accumulation. The TOC concentrations of Bagong Formation mudstone range from 0.77 to 1.37% (mean 1.04%), while the Boni La Formation micritic limestone displays lower TOC contents (0.18–0.37%, average 0.26%). Terrigenous flux proxies including Al, Si, Ti, Th, and Zr concentrations suggest that relatively high detrital flows originate from aluminosilicate compositions during the Upper Triassic sediment deposition. The paleoredox indicators (Mo EF /U EF and C org /P) reflect an oxic-suboxic condition during deposition of the Bagong mudstones and Boni La micritic limestones. The correlation between TOC and P org and Ba bio indicates that the Upper Triassic Bagong mudstone has a higher primary productivity compared with most of the Boni La micritic limestone. The palynological investigation and climate proxy (B/Ga and illite/smectite) reflect warm and humid to hot and sub-humid climate condition during the Bagong mudstone deposition. The warm and humid climate condition is favorable for the survival of organisms, which in turn would enhance the primary productivity of surface water. Relatively high primary productivity is the main factor for the organic carbon accumulation in the Upper Triassic Bagong mudstones. In addition, the relatively fast sedimentation rate resulting in preservation a high TOC content of Bagong mudstone deposit in an oxic-suboxic condition. The low primary productivity and the high carbonate production lead to the dilution of organic matter with respect to the low TOC content of Boni La micritic limestone. Highlights • The Upper Triassic marine sediments are considered to be the most significant source rocks in the North Qiangtang Basin, Tibetan Plateau; • Organic–rich sediments deposition in neritic shelf is a good example for understanding the mechanism of organic accumulation; • Organic matter accumulation in this study was mainly controlled by high primary productivity and relatively fast sedimentation rate. [ABSTRACT FROM AUTHOR]

The Late Triassic mudstones are considered to be the most significant hydrocarbon source rocks (TOC: 0.54%–3.29%) in the North Qiangtang Depression, eastern Tethys. Here, we present geochemical data from the Woruo Mountain Carnian mudstones, in order to investigate their paleoclimate, paleoenvironment, and provenance and to analyze the mechanism of organic material accumulation. The paleoclimate condition was warm and humid during the Carnian mudstones deposition, as indicated by moderate chemical index of alteration (CIA; 73–76), which may be connected with the Late Triassic Carnian stage global climate event in the Tethys. The low U/Th (0.17–0.25) and C org /P tot (7–33) ratio values and moderate manganese contents, reflect the oxidizing conditions during the Carnian mudstones deposition. The relatively high primary productivity in this study is supported by the relatively high P concentrations. The Al 2 O 3 –(CaO* + Na 2 O)–K 2 O ternary plot and Th/Sc–Zr/Sc crossplot reflect that the source areas have undergone a medium chemical weathering with weak sedimentary recycling. The TiO 2 –Zr, Co/Th–La/Sc, La/Th–Hf, and La/Yb–∑REE bivariate diagrams indicate that the provenance of Carnian mudstones was primarily from felsic igneous rocks. The collision setting has been identified based on the multi-major elements discriminate plots in the present study. The Riwanchaka and Mayigangri masses to the southwest and south of the study area consisting mainly of Middle-Triassic granodiorite and Late-Triassic granite are likely responsible for supplying provenance to the Woruo Mountain Carnian mudstones, which have similar REE patterns. The relatively high TOC contents of Carnian mudstones are related to high paleoproductivity and fast sedimentation rates, which will lead to preservation of some organic matter even when bottom waters are completely oxidizing. The detrital input during the Carnian mudstones deposition would result in dilution of organic matter. [ABSTRACT FROM AUTHOR]

The Shengli River–Changshe Mountain oil shale zone in northern Tibet represents a large marine oil shale resource in China. Thirty-four samples of oil shale were collected from the Changshe Mountain West oil shale, a new oil shale deposit discovered in this oil shale zone, to evaluate the minerals and geochemical anomalies in the oil shale. Minerals identified in the oil shale include calcite, dolomite, quartz, illite, and trace amounts of siderite, hematite, feldspar, apatite, zinc oxide, pyrite, sphalerite, barite, celestite, and Fe(Si, Al)-oxysulfate minerals. The oil shale samples are rich in trace elements compared to post-Archean average shales including Co (up to 15.8 μg/g), Ni (up to 83.6 μg/g), Cu (up to 101 μg/g), Zn (up to 775 μg/g), As (up to 255 μg/g), Se (up to 6.91 μg/g), Sr (up to 738 μg/g), Mo (up to 87.9 μg/g), Pb (up to 17.4 μg/g), Cd (up to 13.0 μg/g), Bi (up to 0.38 μg/g), and U (up to 7.10 μg/g), and to a lesser extent, Li, F, Sc, V, Cr, Ga, Sn, Hg, and rare earth elements. Trace elements of probable terrigenous origin in the oil shale were derived from two possible sources: a felsic volcanic rock source and a limestone source. High concentrations of lithophile elements (e.g., Li, Sc, Ga, and REEs) were derived from these provenances. However, the enrichment factor for these elements also is low. In addition, seawater and hydrothermal activity may have influenced the geological and geochemical compositions of the oil shale. Minerals such as calcite, dolomite, and a large proportion of pyrite are of marine origin, and the enrichment of V, Cr, Co, Ni, Cu, Se, Sr, Mo, Pb, and U in the oil shales was probably due to marine influence. Barite, celestite, sphalerite, Fe(Si, Al)-oxysulfate minerals, and fracture-filling pyrite are of hydrothermal origin, and F, Zn, and Cd were derived from hydrothermal fluids. [ABSTRACT FROM AUTHOR]

The organic-rich Changliang Mountain oil shale, located in the North Qiangtang depression, northern Tibet, is considered to be excellent mineral resource in China. The Changliang Mountain oil shale reported here was deposited in a tidal flat-lagoon environment and is characterized by black thin-layered oil shales intercalated with dark-gray marls. Here, we present geochemical data from the Changliang Mountain oil shale profile, in order to investigate the mechanism of organic matter (OM) accumulation and to establish the formation model for the marine oil shale deposition. Total organic carbon (TOC) values range from 2.96 to 23.47% in the oil shale samples, while the marl samples contains low TOC contents, ranging from 0.06 to 0.21%. In the organic-rich oil shale sediments, many redox indicators, including Mo/Al ratios, V/Cr ratios, Th/U ratios, Ni/Co ratios, and the relationship of Mo to TOC suggest a deposition under dysoxic to anoxic environments. Subsequently, the bottom water evolved into an oxic water body when the organic-poor marls were deposited. However, the negative and/or weak relationship between TOC and productivity indices P/Ti and Ba/Al indicates that OM accumulation was not controlled mainly by primary productivity, but dysoxic/anoxic bottom water environment. A stratified water column may be initiated by the supply of fresh water from the continent nearby, combining with warm and humid climate, which is beneficial to the reproduction of marine organisms. The death and bury of these organisms could lead to the formation of dysoxic/anoxic bottom waters and enhance the preservation of OM. In this study, a preservation model of the Changliang Mountain oil shale was established. The model implies that excellent preservation is the major controlling factor for OM enrichment in the oil shale layer. In addition, factors such as mixed deposition with clay minerals, and detrital matter input cannot be ignored for their influence on OM enrichment. [ABSTRACT FROM AUTHOR]