Charcoal remains and bulk lignites collected from the late Pliocene Jinsuo Basin in Yunnan, southwestern China, have been studied to reveal changes in the wildfire regime related to changes of the ...palaeoenvironment, palaeoclimate, and paleobotany. Different types of wildfire occurred in this paleomire with a predominance of low-temperature surface fires, as indicated by mean inertinite reflectance (Ro) values ranging from 1% to 2% in most samples. High-temperature fires are less recorded and occurred more frequently in dark layers compared with pale layers and charcoal layers, as deduced from the elevated proportion of high Ro values (>3%) produced by crown fires or high-temperature surface fires. Wildfire distribution in pale and dark layers was probably influenced by, changes of both plant community and of the depositional environment during their formation. Charcoal layers represent in situ surface and ground fires, whereas pale and dark layers probably record both in situ and remote fire events inside and/or around the basin. PAH were detected in all samples throughout the whole lignite seam, indicating that burning temperatures were low (<400 °C) in most cases in the peatland. Evidence of pre-charring decay observed in some macro-charcoal fragments and pyrogenic inertinite, along with the relatively high content of perylene, shows that decaying wood materials could be a part of the source fuel for the combustion during ground or surface fires. The occurrence and spread of wildfires in the basin during the formation of pale layers probably owe to the drought conditions driven by climate, whereas seasonality of precipitation and temperature was probably the major factor for the occurrence of wildfires recorded from dark layers. The distribution of wildfires within the profile may be relate to climate changes during the mid-Piacenzian.
•Low-temperature surface and/or ground fires predominated the palaeomire.•Conifers, angiosperms, and their decaying materials are the fuel for wildfires.•PAHs concentrations are influenced by several factors.•The main factor for the occurrence of wildfires in pale and dark layers is different.•The profile-varied wildfires may be related to temperature and climate change.
Lacustrine organic-rich shales are well developed in the Dameigou Formation within the Yuka Depression of the Qaidam Basin. These fine-grained sediments have been proven to have good hydrocarbon ...generation potential; therefore, understanding the sedimentary palaeoenvironment of these shales and organic matter enrichment mechanism is essential to increase prospects for shale oil and gas resources. The mineralogy, elemental geochemistry, and organic geochemical data combined with lithology of ZK23-1 well from the Yuka Depression, Qaidam Basin have been comprehensively analyzed to determine the hydrocarbon potential, palaeoenvironmental changes, and tectonic setting of the lacustrine organic-rich shales in the seventh member of Middle Jurassic Dameigou Formation (J2d7). The profile of the ZK23-1 well is composed of three stages (Stages I to III) based on variations in bulk geochemical parameters and lithological observations. Mineral compositions of studied samples are dominated by clay minerals and quartz, with small amount of pyrite, calcite, dolomite, and plagioclase. Interestingly, all samples contain siderite, which is closely related to palaeoenvironment changes. Total organic carbon (TOC) content and hydrogen index (HI) vary significantly in the various lithologies, suggesting that oil shale holds the best hydrocarbon potential, followed by shales and mudstones. A warm-humid palaeoclimate prevailed in the Qaidam Basin during the Middle Jurassic; however, significant palaeoclimatic fluctuations occurred from Stages I to III in the J2d7, especially in Stage II. The climate varies from hot-arid to warm-humid in Stage II, likely resulting in changes in palaeowater column, chemical weathering intensity, as well as palaeoproductivity. The results of this study suggest that the Yuka Depression in the Middle Jurassic could be located at an active continental margin. Warm and humid conditions, as well as the tectonically quiescent setting with stable subsidence rate, are considered as two primary drivers for the enrichment and preservation of OM in the sediments of the J2d7. Ultimately, a comprehensive depositional model is proposed to interpret the evolution of deposition of the J2d7, providing new insights into the deposition of lacustrine organic-rich sediments linked to palaeoenvironment conditions and tectonic setting.
•Three stages have been identified from ZK23-1 in the J2d7.•An obviously environmental fluctuation occurred from stage I to III of the J2d7.•Depositional models have been proposed to interpret the enrichment of OM.•The warm and humid condition and tectonically quiescent setting are popular.•Palaeoclimate and tectonic setting are primary drivers for OM enrichment.
•Amber layers and particles were found in the Shenbei lignite deposit.•Ambers within Eocene Shenbei lignite originated from gymnosperms (Taxodium, Pinus)•Diterpenoids in the ambers improve botanical ...information during Eocene in NE China.•The δ13C values of terpenoid biomarkers help delineate diagenetic pathways.•High δ13C values of diterpenoids reflect decreased MAP during middle-upper Eocene.
The molecular and (bulk and compound-specific) stable carbon isotope composition of ambers from the Shenbei coalfield, northeastern China, were analysed to determine their origin and palaeobotanical affinitions. The applicability of the δ13C data of saturated diterpenoid hydrocarbons for palaeoenvironmental reconstruction was addressed by comparison with published carbon isotope ratios of diterpenoids from adjacent areas. The detected sesquiterpenoids are common biomarkers for the gymnosperm families of Pinaceae and Cupressaceae. The diterpenoids dominate the saturated hydrocarbon fraction with high abundances of kaurane-type compounds. Abietane-type, cadalene-type and alkylated compounds are the main biomarkers in the aromatic hydrocarbons in the ambers. Proposed typical biomarkers for amber (e.g., amberene and homoamberene) have also been detected and probably derived from the diagenesis of the abietane-type terpenoids in the studied ambers. The biomarker composition suggest that the ambers probably originated from gymnosperms such as Taxodium and Pinus. The δ13C values of bulk amber and individual compounds fall within the range of ancient ambers, but the δ13C values of bulk amber are isotopically more enriched than modern ambers. The δ13C values of compounds in hydrocarbon fractions vary in broad ranges. In the saturated hydrocarbon fraction, the δ13C value of sesquiterpenoids (–28.0‰ to –24.5‰) fluctuates more than that of diterpenoids (–22.5‰ to –21.8‰), and the average δ13C value of the latter is approximately 4‰ higher than the former. Aromatic hydrocarbons are on average enriched in 13C by around 2‰ compared to the δ13C of non-aromatic compounds, the result is influenced by isotopically light sesquiterpenoids in the saturated fraction. The similar carbon isotope compositions of aromatic abietane-type compounds and abietane confirm that progressive aromatization does not have a significant impact on the δ13C value of compounds. The obtained higher δ13C values of saturated diterpenoids in contrast to that of lower Eocene lignite from the nearby regions provide evidence for growth of the precursor plants of the amber in dryer habitats or differences in precipitation distribution between different locations and ages.
Paleo-wildfires are of great significance in the study of paleomire ecosystems. The products of such fires preserved in paleomires can provide detailed information for the reconstruction of wildfire ...regimes. This study analyzed the distribution of charcoal and aromatic biomarkers in a coal seam from the Middle Jurassic Yan'an Formation in the Ordos Basin, China. The results showed very high content of pyrogenic inertinite (38%–62%) and common occurrence of pyrogenic polycyclic aromatic hydrocarbons (PAHs) in the studied coal seam, suggesting that wildfires occurred frequently during the period of peat accumulation. The mean reflectance of pyrogenic inertinite (1.50%) in all samples indicates a dominance of low-temperature wildfires in the paleomire, which is also supported by the high abundance of 2- to 3-ring PAHs. Furthermore, the common observations of high-reflectance pyrogenic inertinite (∼ 4.47%RIo) and 4- to 6-ring PAHs suggest the repeated occurrence of high-temperature wildfires. Various parameters of 3- to 4-ring PAHs indicate a relatively high proportion of charred material contributing to the organic matter in the paleomire. The dimethylphenanthrene ratios of the studied samples were inconsistent with those of modern experimental results, which can be probably attributed to the non-analogous vegetation composition in the Jurassic paleomire, and caution should thus be exercised when applying dimethylphenanthrene ratios to ancient sediments. The ratio of retene to 3-ring PAHs implies the contribution of conifers to the fires in the paleomire. The pyrogenic PAHs originated from both, combustion residues and smokes produced by in situ and local wildfires. The high O2 level during the Middle Jurassic promoted the frequent occurrence of wildfires in the studied paleomire. In addition, the occurrence of wildfires was collectively affected by the wet/humid climates, seasonality, and depositional environment.
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•Frequent wildfires occurred in the studied Middle Jurassic paleomire.•Low-temperature wildfires dominate the studied paleomire.•DMP ratios are difficult to interpret the source plants of wildfires in the Jurassic.•The frequent wildfires were influenced by the high O2 level and humid climate.
Three different lithotypes (xylitic, gelified and matrix) of Pliocene lignite from the Velenje Basin, Slovenia, were investigated to establish the variations of biomarker compositions in solvent ...extracts and the stable isotope (carbon and nitrogen) compositions of bulk material. From the biomarker results, the xylitic lithotype almost exclusively originates from gymnosperms (conifers such as Taxodiaceae), as indicated by the very high contents of sesquiterpenoids and diterpenoids but very low abundances of n-alkanes and non-hopanoid triterpenoids. The relative proportion of gymnosperms to angiosperms in the paleomire is reflected by the ratio of diterpenoids to the sum of diterpenoids and non-hopanoid triterpenoids (Di-/(Di-+Tri-terpenoids)), which is close to 1 (av. 0.99) in the xylitic lithotype. The predominance of diterpenoids from conifers in the xylitic lithotype is associated with high C/N ratios and intermediate total sulfur (TS). The very low abundance of hop-17(21)-ene and the absence of further hopanoids in the xylitic lithotype indicate a restricted influence of bacterial degradation under relatively dry conditions in the paleomire. The matrix lithotype also originated preferentially from gymnosperms under dry depositional conditions, as indicated by the high Di-/(Di-+Tri-terpenoids) ratio (0.95), low amounts of hopanoids and low TS content. The gelified lithotype is characterized by a high content of n-alkanes and wide variation of the Di-/(Di-+Tri-terpenoids) ratio (0.13–0.88), indicating a fluctuating contribution of angiosperms to the plant community in the paleomire during formation of this lithotype. In addition, the high abundance of hop-17(21)-ene and TS in the gelified lithotype compared with the other two lithotypes suggests the effect of bacterial activity under relatively wet/humid conditions during formation of the gelified lithotype, which is also supported by the considerable content of mid-chain n-alkanes.
The high correlation between the δ13C and δ15N values (R2 = 0.68) indicates that the stable carbon and nitrogen isotope composition in the Velenje lignites were probably influenced by the same factors (e.g. precursor plants and/or microbial activity). The stable carbon isotopic values (av. −25.44‰) and nitrogen isotopic values (av. 2.15‰) of the xylitic lithotype are higher than those of the gelified lithotype (av. δ13C = −27.48‰, δ15N = 1.37‰) and the matrix lithotype (av. δ13C = −27.09‰, δ15N = 1.10‰). The relatively high correlation between the diterpenoid content and both δ13C and δ15N values suggests that the stable carbon and nitrogen isotopic composition of the three lithotypes might reflect the composition of the original plant material in the paleomire. The dominance of conifers as precursor plants in the xylitic lithotype might be the main reason for the higher δ13C values and probably also the higher δ15N values. The relatively higher δ15N values in the xylitic lithotype than in the other types could be explained by the high amount of decay-resistant xylem and low mineral (e.g. clay) content in the xylitic lithotype. The slightly lower δ13C but higher δ15N values in the gelified lithotype than in the matrix lithotype can be explained by variation of parent plant materials and the influence of bacterial activity.
•Different lithotypes (xylitic, gelified and matrix) of Pliocene lignite from the Velenje Basin, Slovenia, were analyzed for biomarkers and stable isotope (C and N) compositions.•The ratio of diterpenoids/(diterpenoids + triterpenoids) reflects the relative proportions of gymnosperms and angiosperms.•Xylitic and matrix lithotypes originate from gymnosperms, while gelified lithotypes are characterized by a fluctuating contribution of angiosperms.•The highest δ13C and δ15N values were measured in xylitic lithotype samples.•The δ13C and δ15N composition is preferentially influenced by the composition of the precursor plants community.
Continental organic-rich shales are well developed in the Dameigou Formation within the Yuka Depression of the Qaidam Basin. Here, the Rock-Eval pyrolysis, biomarkers, organic petrology, and stable ...carbon isotope have been carried out on the Middle Jurassic Dameigou Formation source rocks from the northwest part of Yuka Depression, Qaidam Basin in order to study their thermal maturity, source of organic matter (OM), and palaeoenvironment changes. The Rock-Eval pyrolysis data (e.g.,
T
max
), vitrinite reflectance, and biomarker-derived thermal maturity parameters (e.g., carbon preference index, Ts/(Ts+Tm), C
29
Ts/(C
29
Ts+C
29
αβ hopane), C
30
αβ/(αβ+βα) hopanes, C
29
ααα 20S/(20S+20R) steranes, and C
29
αββ/(αββ+ααα) steranes) suggest all studied samples stay between immature and low mature stage. The maceral compositions, stable carbon isotope compositions,
n
-alkane distributions, and biomarker-derived source parameters (e.g., C
27
/C
29
ααα 20R sterane, ternary diagram of C
27
-C
28
-C
29
steranes, C
24
tetracyclic terpane) indicate both aquatic organisms and higher plants are the source of OM in the shales, but land plants are dominant. Generally low gammacerane concentration and environment-related parameters (e.g., cross-plots of C
27
/C
29
ααα 20R sterane
vs.
Pr/Ph) indicate these source rocks may be derived from lacustrine and fluvial-deltaic environments with fresh water, which is also supported by the variations of stable carbon isotopes from OM in the source rocks. However, the stable carbon isotope compositions of OM in the source rocks were influenced by multiple factors (e.g., source types and depositional environment) in the Yuka Depression. Slightly brackish condition is recorded in the upper part of the ZK6-1 well favor the formation of lacustrine algae, as confirmed by high contents of C
27
steranes and short-chain
n
-alkanes. The variation of reducing to oxidizing condition of study area is possibly associated with the periodical flooded river-influenced aquatic condition during the deposition of the Middle Jurassic Dameigou Formation.
This paper discusses the volcanic influence on the mineralogical and elemental geochemistry of No. 6 coal from Nanyangpo Mine in the Datong coalfield, north China. Sixteen samples (14 coal and 2 ...partings) were analyzed by different geochemical methods. The results revealed that the No. 6 coal is a medium–high volatility, highly calorific, bituminous coal with a low-ash and medium-sulfur content. The minerals mainly consisted of kaolinite, calcite, dolomite, and pyrite. In addition, traces of apatite, sphalerite, and anatase were also found. Calcite, dolomite, and pyrite in the coal samples were mainly derived from epigenetic hydrothermal solutions, whereas kaolinite and apatite originated from volcanic ash. Harmful trace elements including Pb, Cu, Mo, Tl, and Hg in the No. 6 coal samples were higher than those of common global coals. These harmful elements mainly occurred in sulfide minerals, which were probably influenced by hydrothermal inputs.
The Iqe coalfield is one of the most significant coal production bases in the Qaidam Basin. Over the last few decades, core explorations have targeted the Dameigou Formation for No. 7 coal seam (M7). ...Although many M7 coal samples have been analyzed for coal components in the laboratory, the systematic understanding of the components and changes of coal in the whole Iqe coalfield is still inadequate. In this study, we focus on building log interpretation models to accurately calculate the content of coal components of M7, including ash yield (A
ad
), volatile matter (V
daf
), fixed carbon (FC
ad
), and moisture (M
ad
). Multiple regression analysis and statistical method, combined with the rock volume model, were used to establish log interpretation models of coal components. A total of 28 coal samples from ZK1, ZK2, ZK11-5, ZK23-4, and ZK36-9 wells in the Iqe coalfield were involved in the modeling, as well as well-logs parameters, such as radioactivity (GR), compensation density (DEN), acoustic (AC), and resistivity (RLLD). According to sensitivity analysis, the fitted A
ad
and V
daf
contents of M7 increase with the increasing of DEN and GR values, whereas the FC
ad
content shows the opposite way. Furthermore, the positive relationship between A
ad
and V
daf
( R
2
= 0.59) and the negative relationship between A
ad
and FC
ad
( R
2
= 0.92) as well as V
daf
and FC
ad
( R
2
= 0.69) indicate that A
ad
is a key factor in coal and should be prior determined. Finally, based on the multiple regression analysis and rock volume model, we proposed log interpretation models for M7 coal components in the Iqe coalfield, these models have been examined successfully by the case studies from the same coalfield and will provide new insights into the application of geophysical log parameters for coal quality evaluation.
The occurrence of Rb and Cs in coal samples from Iqe coalfield was analyzed by a sequential chemical extraction experiment. Five types of Rb and Cs were determined in the coal: water soluble, ion ...exchangeable, organic bonded, carbonate, and silicate. The results indicated that the occurrence of Cs is similar with Rb in coal, and nearly all Rb and Cs are distributed in silicate. The occurrence of Rb and Cs is most likely associated with silicate minerals in coal. With the high correlation between Rb, Cs, and K, and the high content of kaolinite and illite in these coal samples, it can be inferred that illite probably is the main carrier of Rb and Cs. Minor amounts of Rb and Cs may also be adsorbed by kaolinite in Iqe coal, and Cs may exist in other states, such as an exchangeable ion.
•Geochemistry of coal in the Laoyaogou Mine from Shanxi Province have been studied.•The No. 5 Coal is enriched with several valuable elements, especially Li, Zr and Hf.•Most of the enriched elements ...have inorganic affinities, except for Sr and REY.•Valuable elements, especially Li, are enriched in Ningwu coalfield and Qinshui Basin.•The coals from Shanxi Province have a potential value with these valuable elements.
This paper provides new geochemical data focussing on valuable elements and their origins in the coals from the Laoyaogou mine, Ningwu coalfield, Shanxi Province, northern China. Kaolinite, pyrite, calcite, and boehmite are the main minerals, along with a small amount of illite and anatase, present in the coals studied.
The studied coals are enriched with Li, Ga, Zr, Zn, Hf, Sr, Nb, Sn, Th, and REY, especially the case of high average concentration of Li (163.42 μg/g) which is more than ten-times higher than that in world hard coals. Zirconium and Hf, the average concentrations of which are more than five-times higher than those in world hard coals. Lithium, Ga, Zr, Hf, and Th have strong inorganic affinities, whereas Sr and REY have organic affinities. The main carrier of Li in the No. 5 Coal is kaolinite, illite, and boehmite. Gallium, Zr, Hf, and Th probably have the same origin and are largely associated with kaolinite and Ti/Ca-bearing minerals which originate from the source region. In Shanxi Province, the main coalfields are enriched in several valuable elements (e.g. Li, Ga, Zr, Hf, and Th), especially the high average content of Li in the Ningwu coalfield (116 μg/g) and the Qinshui Basin (110 μg/g). The Laoyaogou coals and the coals from the main coalfields in Shanxi Province have economic significance as hidden treasures of the coals themselves and in their by-products.
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