Source Rock Types Research Articles

Influencing factors of the Tmax parameter in Rock-Eval pyrolysis

The rock pyrolysis parameter Tmax is an important index to evaluate the maturity of organic matter in source rocks. However, during the use of Tmax, it is found that the Tmax value of some samples does not conform to the thermal evolution law of organic matter when evaluating the maturity of organic matter, which affects the accuracy of geological applications. Studying the influencing factors of the rock pyrolysis parameter Tmax analysis data is beneficial to improve the experimental method to ensure the accuracy of the experimental data, and it is of great significance to the correct evaluation of the source rock type and maturity of the source rock. In this paper, the effects of sample mixing uniformity, sample weight, soluble organic matter and minerals on the rock pyrolysis parameter Tmax are analyzed experimentally. It is concluded that the degree of sample uniformity and the amount of sample will affect the results. Soluble organic matter will lead to a decrease in Tmax. With the change of kerogen/clay mineral ratio, the influence of clay mineral on the pyrolysis parameter Tmax.

Development patterns of source rocks in the depression lake basin and its influence on oil accumulation: Case study of the Chang 7 member of the Triassic Yanchang Formation, Ordos Basin, China

During the Mesozoic, the T-J1 oil system of the Ordos Basin, whilst the degree of oil enrichment, main production layer, and source rock distribution exhibit strong regional differences, no systematic study has been conducted to investigate these differences. At this time, the total organic carbon abundance and vertical distribution of the eight long core wells in different areas of the basin within the Chang 7 member source layers were calculated by means of the ΔLogR method. According to the industrial oil well and the low production well, the favorable oil distribution areas of the Chang 8, Chang 7, and Chang 6 reservoirs are demarcated. The current study confirmed five distribution styles and strong regional differences in the longitudinal direction of source rocks. To be more specific, the Jiyuan area in the northwestern part of the lake basin is dominated by the bottom rich type and the full section rich type. The northeastern Shaanxi region is mainly dominated by the middle rich type and the top rich type. Meanwhile, the central area of the basin is mainly the interlayered type, and the southwestern Longdong region is mainly the bottom rich type. The comprehensive analysis of source rock type and oil favorable zone revealed that source rock type has a controlling effect on the crude oil distribution. The bottom rich type and full section rich type dominate the Jiyuan area and multiple layer oil production. In northern Shaanxi, the top rich type and middle rich type accumulate on the upper portion. Also, the Chang 6 reservoir was the main production layer. The bottom rich type of the Longdong area accumulates under the source, while the Chang 8 reservoir is the main production layer. The central parts of the lake basin are dominated by the interlayered type with multiple layers of production oil. The close relationship between the distribution pattern of source rocks and oil accumulation indicates an improvement on the distribution law of the continental lake with significance practical implication on the optimization of the field of near-source-in-source oil and gas exploration.

Characteristics of coal-measure source rock and gas accumulation belts in marine-continental transitional facies fault basins: A case study of the Oligocene deposits in the Qiongdongnan Basin located in the northern region of the South China Sea

This study carried out the development and distribution prediction research on coal-formed gas accumulation belts from the perspectives of the development and distribution of the coal measure source rock and the thermal evolution degrees of those rock masses in marine-continental transitional facies fault basins. The purpose of the current study was to improve the accuracy of gas reservoir explorations in the sea areas. The methods used in this study were based on the systematic analyses of the drilling, logging, geochemistry, and seismic data of the Oligocene deposits in the Qiongdongnan Basin of the northern region of the South China Sea. It had been previously established that the sedimentary processes of the fault basin were mainly controlled by faulting, and (fan) deltas had often developed in the fault bending sections, tectonic transformation sections, and fault ends. The distribution along the fault zone was observed to be beaded. During the early Oligocene period of the Qiongdongnan Basin, there were strong extensional actions, and the marine and continental transitional facies strata had developed forming the northern fault depression and the central fault depression. Three (fan) delta belts were formed in the slope belt in the northern fault depression and also in the slope belts located in the north and south of the central fault depression. Due to the superposition of the humid and hot climate during that period, the majority of the coal measure source rocks were developed in each (fan) delta. Also, three macroscopic coal measure source rock belts were formed. The types of source rock had mainly included autochthonous coal, allochthonous coal, and terrigenous marine mudstone, with terrigenous higher plant organic matter accounting for more than 50%. After the deposition of the lower Oligocene period, the basin continued to sink, and the coal measure source rock masses continued to be heated. During that period, the maturity of the organic matter had continued to rise. In the northern slope belt of the northern fault depression, the maturity of the organic matter in the coal measure source rock belt were low and the gas generation abilities were weak, which was advantageous to the formation of potential gas accumulation belts. The coal measure source rock belt on the northern side of the central fault depression had a high maturity of organic matter and strong gas generation ability, forming a macroscopic gas accumulation belt. In addition, the Yacheng 13–1 large coal-formed gas field had been discovered. The maturity of the organic matter had varied greatly in the coal measure source rock belt on the southern side of the central fault depression. The coal measure source rock masses with high maturity had strong gas generation abilities and had also formed a macroscopic gas accumulation belt, and three large and medium-sized coal-formed gas fields (such as Lingshui 17–2) had been discovered. The gas accumulation belts on the southern and northern sides of the central fault depression were favorable areas for coal-formed gas explorations. Furthermore, the trap zones in and near the coal measure source rock belts with mature thermal evolution were determined to be the most favorable areas for coal-formed gas explorations.

Carbon and Hydrogen Isotopic Reversals in Highly Mature Coal-Derived Gases: A Case Study of Paleozoic Gases in the Southern Ordos Basin, China

The compositional carbon isotopic seriesδ13C-CH4<δ13C-C2H6<δ13C-C3H8<δ13C-C4H10is common in thermogenic gases. With the exploration of deeper strata, however, isotopic reversals (δ13C-CH4>δ13C-C2H6>δ13C-C3H8) in overmature unconventional shale gases and conventional (coal-derived) gases have been identified. Paleozoic gases in the southern Ordos Basin, China, with partial or complete isotopic reversals, were studied as examples of isotopic fractionation in overmature coal-derived gases. Isotopic compositions of gases of different maturities from the Ordos Basin and shale gases from around the world were compared. Results indicate that carbon isotopic series are related to maturity. Complete isotopic reversal occurs mostly in regions with vitrinite reflectanceRo>2.4%. Where2.4%>Ro>2.0%, almost all gases display partial isotopic reversal, withδ13C-CH4>δ13C-C2H6orδ13C-C2H6>δ13C-C3H8. Carbon isotopic reversal in coal-derived gases is not caused by abiotic origin, the mixing of gases from different types of source rock, abiotic polymerization, wet gas cracking, and other mechanisms that contribute to reversal in shale gases. Based on the unique structure of coaly source rock and the geology of the Ordos Basin, closed-system aromatization-polycondensation reactions are considered the most likely cause of carbon isotopic reversal. During the reactions, isotopically light gases are generated by recombination of previously formed hydrocarbons and residual kerogen-coal. Hydrogen isotopic reversal in the southern Ordos Basin might also be caused by aromatization-polycondensation reactions.

Comparison on Rare Gas Geochemical Characteristics and Gas Originations of Kuche and Southwestern Depressions in Tarim Basin, China

The Kuche Depression is considered as the most important gas resource potential and gas exploring area with great gas resource potential and prospect in the Tarim Basin. Based on geochemical experimental analyses and comprehensive geological studies, the general geochemical characteristics of molecular and isotope compositions of rare gases as well as hydrocarbon gases and nonhydrocarbon gases are comparatively studied in the Kuche and Southwestern Depressions. Then, their genetic types are separately identified and gas originations are comprehensively discussed. The main results are as follows. (1) Gas fields in the Kuche Depression have a higher methane abundance, accompanied with low N2and CO2abundances, but the Akemomu gas field in the Southwestern Depression has a relatively lower average methane abundance, accompanied with high average N2and CO2abundances. The helium abundance of natural gases in gas fields from the Kuche Depression general has 1 order of magnitude higher than the air value. Comparatively, it has more than 2 orders of magnitude higher than the atmospheric value in the Akemomu gas field from the Southwestern Depression. The neon, argon, krypton, and xenon abundances in both Kuche and Southwestern Depressions are lower than the corresponding air values. (2) Natural gases from gas fields in the Kuche Depression and the Southwestern Depressions are generally typical coal-formed gases. The rare gases in the Kuche Depression have typical crustal genesis, mainly deriving from the radioactive decay of elements in the crust, while in the Akemomu gas field from the Southwestern Depression, the rare gases have main crustal genesis with a proportion of 92.5%, probably accompanied with a little mantled genetic contribution. (3) Natural gases in the Kuche Depression are generally derived from coal measure source rocks of Jurassic and Triassic, which principally originated from Jurassic in strata period and coals in source rock types. The Jurassic source rocks account for 55%-75% and the Triassic source rocks account for 25%-45% approximately, while coals occupy 68% and mudstones occupy 32% separately. Natural gases from the Akemomu gas field in the Southwestern Depression mainly originated from humic mudstones of marine and continental transitional source rocks of Carboniferous to Permian.

Palynological and organic geochemical studies of the Upper Jurassic-Lower Cretaceous successions, Western Desert, Egypt: Implications for paleoenvironment and hydrocarbon source rock potential

The Upper Jurassic-Lower Cretaceous successions in the north Western Desert of Egypt are one of the most prolific hydrocarbon plays in North Africa. However, the source rock characteristics and depositional environments are still poorly understood. The current work assesses these sedimentary sections utilizing an integrated palynofacies and organic geochemical approach for a comprehensive source rock characterization. The investigation was carried out on 70 samples from the OBA. 3-1/1A (interval: 2540 to 3650 m) and OBA. S-C (interval: 2705 to 3782 m) wells. The results obtained are sufficient to categorically establish two types of organofacies linked to depositional environments and kerogen types, namely palynofacies PF I and PF II. The first facies (PF I) is characterized by kerogen type II and III and occurs in the Alamein and Alam El Bueib members of the Lower Cretaceous Burg El Arab Formation. This is further confirmed by pyrolysis results that revealed fair organic richness and gas generation potential in the Alamein Member with TOC ranges from 1.0 to 2.5 wt% and HI from 64 to 112 mg HC/gTOC). The Alam El Bueib Member illustrated better organic richness and quality with TOC ranges from 1.6 to 3.1 wt% and HI from 121 to 318 mg HC/gTOC. The thermal maturity assessment indicates that the Alamein Member is immature and the Alam El Bueib Member is early to oil-mature. PF II occurs in the Jurassic Masajid Formation, which is a transitional mature to overmature, fair to good source rock with mixed kerogen type II and III (TOC 1.3 to 2.4 wt% and HI 148 to 238 mg HC/gTOC). The paleoenvironmental conditions were deduced mainly from the APP ternary plot. The Alamein and Alam El Bueib members were deposited in a suboxic to anoxic basin, whereas the Masajid Formation was deposited under distal, dysoxic to anoxic basinal or proximal, suboxic to anoxic shelf conditions. In summary, it is concluded that the Late Jurassic and Early Cretaceous witnessed deposition of gas-prone source rocks similar to those found in the southern onshore Nile Delta Basin. The results have significant implications for the understanding of the source rock types in the northern onshore and offshore Egyptian basins and the future of the gas exploration.

Geochemical characteristics and Thermal Evolution of Paleogene Source Rocks in Lunpola Basin, Tibet Plateau

Lunpola Basin is the first exploration area with industrial oil flow in the hinterland of Tibetan Plateau and the target horizon is the Paleogene Niubao formation and Dingqinghu formation. Based on drilling data from multiple wells, the organic matter abundance, type and maturity of Paleogene source rocks in Lunpola Basin were measured and analyzed using organic geochemistry method. The 67 samples data from middle Niubao formation show that the average of TOC (wt.) is 3.50, S1+S2 is 30.55 mg/g; and the Tmax is 427 ∼ 442 °C, δ13CPDB is -25.6‰ ∼ -29.3‰ and Ro is 1.37%∼1.84%. The 53 samples data from upper Niubao formation show that the average of TOC (wt.) is 4.16%, S1+S2 is 30.16 mg/g. and the Tmax is 421 ∼ 440 °C, δ13CPDB is -26.9‰ ∼ -28.7‰ and Ro is 0.61%∼1.35%. The 70 samples data from lower Dingqinghu formation show that the average of TOC (wt.) is 4.16%, S1+S2 is 30.16 mg/g and Ro is 0.58%, and the Tmax is 421 ∼ 440 °C, δ13CPDB is -26.9‰ ∼ -28.7‰. These three sets of source rocks have high organic abundance and kerogen type of I- II1. Based on the previous studies of W-1 well in JiangjiaCo depression, XL-3 well in JiangriaCo depression and Z-1 well PaCo depression, a 2D model of north-south tectonic and thermal evolution in Lunpola basin is simulated by Schlumberger's PetroMod method. The results show that the XL-5 well of Niubao formation in Diezong area of Lunpola basin began to generate oil at 41.3Ma and reached the peak of hydrocarbon generation at 36.4Ma; and upper Niubao formation began to generate oil at 38.4Ma and hydrocarbon generation peaked at 31.9Ma. The lower Dingqinghu formation began to generate oil at 24.2Ma. At the end of upper Dingqinghu formation, the basin began the uplift and denudation stage at 23Ma, but the middle and upper Niubao formation and the Lower Dingqinghu formation are still active for hydrocarbon generation. The simulation also shows that the primary deposits in main source rocks are thin in the thrust uplift belt of southern basin and have not entered the stage of oil generation, and that the main oil source area is the Paleogene depression in central basin.

Provenance and palaeoenvironment of Upper Devonian Shetianqiao Formation mudstones in Shaoyang Sag, Xiangzhong Depression, Central China

The Upper Devonian Shetianqiao Formation mudstones are considered to be the most petroliferous shale gas source rocks in the Shaoyang Sag of Xiangzhong Depression in China. These Shetianqiao dark mudstones have been collected systematically to investigate their geochemical characteristics by analysing their major elements, trace elements, and rare earth elements (REEs), in order to reveal their provenance, palaeoenvironment and tectonic setting. The results show that the total REEs content (ΣREE) of dark mudstone is 34.22–246.62 ppm (average 131.66 ppm) and characterized by low ΣREE, light rare earth element (LREE) enrichments, negative Eu anomalies, and minor negative Ce anomalies. The normalized distribution pattern of REE, Eu anomaly, as well as discrimination diagrams of trace elements and REEs, are applied to explain the source rock types and properties of Shetianqiao mudstones. The results indicate that the sediments have a weak sedimentary recycling and mainly originated from the upper continental crust, and the source rocks of the black mudstones are mainly constituted by felsic granite. The Ce anomaly, Th/U, V/Sc, V/Cr, and V/(Ni + V) ratios of the dark mudstones suggest a long‐term oxidizing depositional environment interrupted by a short period of a dysoxic/anoxic depositional environment in the middle section of the formation. This short period corresponds to a dramatic marine transgression with relatively high TOC. The La/Ce, LaN/SmN, Ce anomaly, and normalized REE distribution pattern characteristics indicate that the depositional process of the Shetianqiao mudstones has consistently been influenced by the regional upwelling hydrothermal activities. The chemical index of alteration (CIA) and Al2O3‐(CaO* + Na2O)‐K2O triangular plot reveal that a warm and humid climate with moderate chemical weathering in the source areas of the Shetianqiao mudstones occurred during the deposition. The ratio of major elements, trace elements, and REEs are used to analyse the tectonic setting of the depositional area which suggests that the source area is dominated by continental island arc tectonic setting. Combined with the previous regional studies, it is concluded that the continental island arc granite formed by plate collisions in the Caledonian stage constitutes the main source of the Shaoyang Sag during the Shetianqiao period. The depositional environment was not stable due to the lasting influence of deep hydrothermal activities. The upwelling currents controlled by hydrothermal activity transport nutrients to the study area, resulting in the formation of organic‐rich mudstones.

Some Technical Considerations of Gas-Hydrate Development From Chinese Permafrost Regions

Summary Review of published geological data shows that permafrost regions in China's Mohe Basin, Qilian Mountain, and Qinghai-Tibet Plateau hold promise for gas-hydrate accumulation according to identifiable source rock, migration path, and reservoir seal, among others. In addition, they show some common characteristics: source rock consisting mostly of shale, relatively poor reservoir quality, and gas migration through fractures. However, formation lithology, source-rock type, origin of organic matter, and total organic carbon (TOC) exhibit significant differences.

Canning Basin - Petroleum Systems Analysis

New high resolution geochemical information was acquired for fluids from recent Canning Basin wells and interpreted in context with previous work on fluid typing and correlation by Geoscience Australia (GA). Ungani field oils are interpreted to be derived from the same/very similar clastic source rock, comprising bacterial and marine algal matter deposited under anoxic to sub-oxic conditions, and generated within the peak oil window for a high quality marine source rock. Observed low GOR’s are the consequence of both source rock type and gas removal. Liquids from the Yulleroo field are derived from a similar source to the Ungani oils, with the addition of dry gas from a higher maturity and/or more gas prone source, and generated and expelled at slightly higher maturity. The current lean gas condensate phase is the result of the addition of dry gas combined with minimal water washing. In nearly all aspects the Ungani and Yulleroo liquids resemble the L4 family previously attributed by GA to a probable Carboniferous age source. Gas-condensate from the Valhalla North-1 field was derived from a more mature source rock deposited in an oxic environment and containing more gas prone (terrigenous) organic matter. Map based modelling incorporated eleven 1D models in the Ungani-Yulleroo and Valhalla-Asgard region, and a map based burial history and maturity model. The source rock model was derived from the liquid geochemistry results rather than the poor quality source rock potential data gathered to date. Burial history modelling and maturity modelling at the top of the Lower Laurel Carbonate shows maturity for gas expulsion in the main trough and oil to light oil expulsion on the flanks of the basin. Maximum burial in the basin took place immediately prior to the Fitzroy Uplift, resulting in the main phase of oil generation and expulsion taking place around 200Ma.

Provenance information recorded by mineral inclusions in detrital garnet

Garnet single-grain analysis is an often used and well established tool in sedimentary provenance studies, especially when metamorphic source rocks are involved. So far, however, solely the geochemical composition of detrital garnets is considered to draw conclusions concerning probable source rocks. The gained information is often limited by (i) geochemical overlap of garnets derived from different lithology and metamorphic grade, (ii) similar probabilities of belonging to more than one source rock type, and (iii) the limitations of discriminating different protolith compositions. Here we present the first attempt of using mineral inclusions in detrital garnet as a provenance tool. We analyzed the inclusions of ~300 fine to medium sand-sized detrital garnets from two proximal modern sand samples taken in the HP/UHP Western Gneiss Region of SW Norway. All mineral inclusions ≥2 μm were identified by Raman spectroscopy, showing that (i) most garnets from HP/UHP metamorphic source rocks contain mineral inclusions ≥2 μm, (ii) Raman spectroscopy is a very powerful tool to characterize the inclusion types, and (iii) less stable mineral phases like kyanite, omphacite, diopside, enstatite, coesite, amphibole group, and epidote group minerals occur as inclusions in garnet. These minerals, which are important for provenance studies, can thus be preserved in the sedimentary record as long as garnet is stable. The combination of inclusion types in garnet and geochemical garnet classification shows that (i) inclusions well reflect the geological characteristics of the sampled catchments, implying that they are useful indicators for HP/UHP provenance, and (ii) inclusions in garnet can be used to support and enhance the provenance information obtained by garnet geochemistry.

Geochemical characteristics and hydrocarbon generation potential of the first member of Shahejie Formation (E2s1) source rocks in the Dongpu Depression, East China

The Dongpu Depression, containing huge amounts of hydrocarbons, is a typical petroliferous province in the Bohai Bay Basin, east China. As one set of the main source rocks, the first member of Shahejie Formation (E2s1) shows huge exploration potential with approximately 0.83 × 108 t resources remaining to be discovered. However, the geochemical characteristics and thermal evolution history of E2s1 source rocks have still not been determined. In this study, the sedimentary features were firstly analysed based on the geological data. Then the organic matter abundance, kerogen type, and thermal maturity of E2s1 source rocks in the present day were evaluated according to the Rock‐Eval pyrolysis, micro‐components of kerogen, total organic carbon (TOC), and vitrinite reflectance analysis. Furthermore, the evolution of thermal history and hydrocarbon generation was determined using the PetroMod procedure. The results show that dark mudstones and salt rocks were well developed in E2s1, which are propitious for organic matter to grow and preserve. E2s1 source rocks contain abundant organic matter and moderate to good generative source rock potential. E2s1 source rocks mainly consist of Type II kerogen and have entered early to maturation stage for hydrocarbon generation. Due to the limited buried depth, E2s1 source rocks only attained lower thermal maturity and generated finite hydrocarbons. The initial rapid subsidence and the second rift after uplift erosion resulted in the higher geo‐temperature at the end of E3d and the present day. Corresponding to the geo‐temperature evolution, there are two stages of hydrocarbon generation for E2s1 source rocks: The first stage was in the late E3d period, and the late stage was from the late Neogene to the present day. Moreover, the hydrocarbon generation rate and quantity of the late stage are much higher than the first stage, indicating the major hydrocarbon generation stage. Due to the limited hydrocarbon generation capacity, oils generated from E2s1 source rocks are low maturity; thus, it cannot migrate for a long distance and only accumulated around the sag belts.

Late gas generation potential for different types of shale source rocks: Implications from pyrolysis experiments

Gas generation from shale source rocks typically occurs via cracking of both kerogen and retained oils, such that it is difficult to predict and compare gas generation potentials of different shales because they are related not only to the kerogen type but also to the oil expulsion efficiency. In this study, five different shale kerogen samples were pyrolyzed in sealed gold tubes to investigate how kerogen type and oil expulsion efficiency affect their gas generation after oil-window maturity. The results illustrate that the maximum extractable organic matter (EOM) and gas generation potentials of different original shale kerogens (O-kerogen) in a closed system vary widely in the range of 229–790 mg/g TOCOK and 308–594 mL/g TOCOK, respectively. However, the gas yields of different residual shale kerogens (R-kerogen) with a starting equivalent vitrinite reflectance (EqVRo) value of approximately 1.22% are quite similar and vary between 131 and 145 mL/g TOCRK. Pyrolysis experiments also reveal that the late gas generation potential (EqVRo > 1.22%) of shale is mainly controlled by the amount of retained EOMs rather than kerogen type. When the shale source rocks containing types I and II kerogens have the same amount of retained EOMs, their gas generation potentials are quite similar. Under most geological conditions, the late gas generation potentials of shale source rocks, normalized to the TOC of matured shale at 1.22% EqVRo (TOCShale), vary approximately in the range of 180–300 mL/g TOCShale. To reach a gas content of 3 m3/ton shale for the present-day overmature shale gas exploration in the Lower Palaeozoic shales of South China, a conservative present-day TOC (TOCpd) value of 2.0% is proposed as a screening parameter that can eliminate the risk of insufficient gas generation potential as much as possible.

Quantitative evaluation of gas generation from the Upper Paleozoic coal, mudstone and limestone source rocks in the Ordos Basin, China

Significant quantities of tight gas resources have been discovered in the Upper Paleozoic interval in the Ordos Basin, central China. The gas is believed to have been derived primarily from the Upper Paleozoic coal, mudstone and limestone source rocks. An integrated organic geochemistry and basin modeling approach was applied to quantitatively evaluate gas generation from the three types of source rocks. Source-specific gas generation kinetics were first established on the basis of sealed gold tube pyrolysis experiments. Gas generation was then modeled in 1D and 3D using the source-specific kinetics obtained. The results show that (1) near the depositional and thermal center (e.g., Well ZT-1), gas generation occurred much earlier and was greater than that of the Sh-360 well, which is away from the depositional and thermal center; (2) C2-C5 gases in the ZT-1 well underwent thermal cracking, while gases in the Sh-360 well did not experience any secondary thermal alteration; (3) hydrocarbon gases were mainly generated during the Early Cretaceous (135–96 Ma) and the Late Jurassic (161–135 Ma); (4) the cumulative amounts of gas generation from the coal, mudstone and limestone source rocks are 147.23 × 1012, 57.85 × 1012 and 12.73 × 1012 m3, respectively, with coal seams being a major contributor (about 67.6%) to the Upper Paleozoic gas system, followed by the mudstone (about 26.6%) and limestone (about 5.8%). By comparing with previous work and a default kinetics basin model, our source-specific kinetics basin model is more suitable for simulating gas generation in the Upper Paleozoic source rocks within the Ordos Basin.

Late Triassic granites from the northwestern margin of the Tibetan Plateau, the Dahongliutan example: petrogenesis and tectonic implications for the evolution of the Kangxiwa Palaeo-Tethys

ABSTRACTThe Dahongliutan granitic pluton consists of two-mica granites and is located in the eastern part of the Western Kunlun Orogen, northwestern Tibetan Plateau. Zircon separates from the pluton yield a SIMS U–Pb age of 217.5 ± 2.8 Ma. Rocks from the pluton contain relatively high and uniform SiO2 (72.32–73.48 wt%) and total alkalis (Na2O + K2O = 8.07–8.67 wt%) and are peraluminous and high-K calc-alkaline to shoshonitic in composition. The Dahongliutan granites are relatively depleted in the high-field-strength elements and the heavy rare earth elements (HREEs) and have relatively high Rb, and low Ba and Sr concentrations. They contain low total rare earth element (REE) concentrations. The light REEs are strongly enriched relative to the HREEs, with (La/Yb)N values of 28.56–37.01. The εNd(t) values range from −10.6 to −8.8, and (87Sr/86Sr)i = 0.7142–0.7210. Zircons from the pluton yield εHf(t) values of −13.8 to −1.6, and δ18O = 10.5–11.6‰. Petrographic and geochemical features of the pluton indicate that the granites are S-type and were derived from parting melting of a mixture of metasedimentary and minor metaigneous sources in the middle–lower crust. Magmatic differentiation was dominated by the fractional crystallization of plagioclase, K-feldspar, muscovite, biotite, and accessory monazite, allanite, and Fe–Ti oxides. Regional granitoids were emplaced in the Early-to-Middle Triassic. Other younger granitoids, with ages of 240–200 Ma, are mostly I-type in character and were likely derived from multiple types of source rock, suggesting the source was heterogeneous Triassic crust. Such a scenario is consistent with their formation in a post-collisional setting. Our new data, combined with other geological evidence, suggest that the collision between the Tianshuihai and southern Kunlun terranes occurred between ca. 250 and 240 Ma, resulting in the closure of the Palaeo-Tethys. Post-collisional tectono-magmatic events may have occurred between 240 and 200 Ma.

Petroleum source rocks of Western Australia

Petroleum geochemical analysis of samples from the Canning, Carnarvon, Officer and Perth basins identified several formations with source potential, the: • Triassic Locker Shale and Jurassic Dingo Claystone of the Northern Carnarvon Basin; • Permian Irwin River Coal Measures and Carynginia Formation, Triassic Kockatea Shale and Jurassic Cattamarra Coal Measures of the Perth Basin; • Ordovician Goldwyer and Bongabinni formations, Devonian Gogo Formation and Lower Carboniferous Laurel Formation of the Canning Basin; • Devonian Gneudna Formation of the Gascoyne Platform and the Lower Permian Wooramel and Byro groups of the Merlinleigh Sub-basin of the Southern Carnarvon Basin; and • Neoproterozoic Brown, Hussar, Kanpa and Steptoe formations of the Officer Basin. Burial history and geothermal basin modelling was undertaken using input parameters from geochemical analyses of rock samples, produced oil, organic petrology, apatite fission track analysis (AFTA), heat flows, subsurface temperatures and other exploration data compiled by the Geological Survey of Western Australia (GSWA). Of these basins, the Canning, Carnarvon, and Perth basins are currently producing oil and gas, whereas the Southern Carnarvon and Officer basins have no commercial petroleum discovery yet, but they do have source, reservoir, seal and petroleum shows indicating the presence of petroleum systems. The Carnarvon Basin contains the richest identified petroleum source rocks, followed by the Perth and Canning basins. Production in the Carnarvon Basin is predominantly gas and oil, the Perth Basin is gas-condensate and the Canning Basin is oil dominated, demonstrating the variations in source rock type and maturity across the state. GSWA is continuously adding new data to assess petroleum systems and prospectivity of these and other basins in Western Australia.

Törmelékes rétegsorok komplex eredetvizsgálata (KEVi). Ötelemes, összehangolt törmelékeskőzet-elemző vizsgálatsor

It is well known, that clastic rocks have great economical and scientific importance as for example they are hydrocarbon- and water reservoires and remnants of totally eroded, disappeared mountains. The precise mineralogical-petrological determination (petrography) of their detrital grains and identification of their source area can be important research direction for both areas. Traditionally, two main trends have been developed for the provenance examination of unconsolidated clastic sequences: The petrography of the larger pebbles, which performs the macroscopic determination and thin-section examination of the individual pebbles larger than a few centimetres and the examination of the heavy minerals, which deals with the sandy size minerals of the layer. Both methods have serious deficiencies. To eliminate some of these deficiencies, fine-grained pebble examination (FPE) method have been introduced into the petrographic examinations in the last few years. But it didn’t resolve the problem to connect surely the different heavy minerals with source rock types. With this work, our aim is to present such a grain determination procedure that allows to determine and identify more accurately and certainly the source rock types for clastic deposites, and with the help of which the deficiences of separately used methods can be eliminated. The system of research we call Expanded Provenance Analysis (EPAn) is a coordinated joint application of five different grain determination methods on clastic deposites. It includes previously used and newly presented methods as well. In this article, we present in detail the method description, the conditions of use, advantages and disadvantages of each steps of the „EPAn” method, and the role and the usefulness of the test ranks. At the end of the presentation, we will discuss the evaluation of the „EPAn” test series.

Geochemical Characteristics and Identification Criteria of effective source rock in Mesozoic Yanchang Formation, Southern Margin of Ordos Basin

The geochemical characteristics of source rock in Mesozoic Yanchang Formation, southern margin of Ordos Basin have not been introduced in literature. In this study, a number of geochemical experiments were conducted to discuss the geochemical characteristics and to establish the identification criteria. It is shown that source rock in the study area can be divided into five types: A1, A2, A3, A4 and B. Based on the detailed oil source correlation, the source rock types in the study area can be identified as: 1) A1, Chang 7 oil shale, is the excellent source rock with large hydrocarbon-generation potential; 2) A2 and A3, mainly Chang 7 dark mudstone, are the effective source rocks with medium hydrocarbon-generation potential; 3) A4 and B, mainly the thin mudstone or carbonaceous mudstone intervals, are the potential source rock with small hydrocarbon-generation potential. [Received: April 22, 2018; Accepted: May 27, 2018]

Geochemistry of Selected Kaolins from Cameroon and Nigeria

AbstractThe geochemical characteristics of selected kaolins from Cameroon and Nigeria are presented, with an attempt to elucidate on their possible industrial applications by comparing them to world-known kaolin deposits. Major oxides concentrations were subjected to factor analyses in interpreting their relationships. Geochemical indices, including chemical index of alteration (CIA), chemical index of weathering (CIW) and the index of compositional variability (ICV) were computed and plotted on binary and ternary diagrams to determine the intensity of weathering of the kaolins and discriminate their different source rock types. Kaolinite was the major phase, followed by quartz, illite and goethite as minor phases. Minerals in trace phases included smectite, anatase, muscovite, gibbsite, microcline, palygorskite and calcite. Mean abundances of major oxides in wt% were: SiO

The effect of organic matter type on formation and evolution of diamondoids

A series of anhydrous pyrolysis experiments, using sealed gold tubes, were performed on three types of kerogen to investigate the effect organic matter type has on the generation and evolution of thermogenic diamondoids. Based on the compositional variation of pyrolysis products, the cracking of kerogens can be divided into three stages: oil generation (0.6%–1.5% EasyRo), wet-gas generation (1.5%–2.1% EasyRo) and dry-gas generation (>2.1% EasyRo). The experimental results indicate that diamondoids were mainly generated in the oil and wet-gas generation stages and decomposed in the dry-gas generation stage. In addition to thermal maturity, the formation of diamondoids is also influenced by the type of organic matter. Type I and IIA kerogens produced more diamondoids than Type III kerogen, and diamondoids generated from Type III kerogen were dominantly adamantanes. Therefore, the concentration and concentration ratios of diamondoids can be used to assess the maturity of source rocks (1.0%–1.5% EasyRo) and determine the type of organic matter (1.0%–2.0% EasyRo). Isomerization ratios of diamondoids depend mainly on thermal maturity and the type of organic matter has little effect. The use of isomerization ratios to determine thermal maturity is best for source rocks at higher maturity levels (1.5%–3.0% EasyRo). Therefore, bivariate diagrams of concentration versus isomerization indices of diamondoids (e.g., DMAs/MDs vs. DMAI-1 and DMAs/MDs vs. TMAI-1) can be used to evaluate the source rock maturity over a wider EasyRo range (1.0%–3.0% EasyRo) than single diamondoid parameters. As there are differences in the concentration and distribution of diamondoids in the extracts of three source rocks, the possibility exists to use diamondoid indices of immature rocks to determine the type of source rock.