Multidisciplinary insights into the origin of natural gas from hydrocarbon generation and charging history of Permian dolomite reservoir in Sichuan Basin

Ni Z., Zhao J., Feng Y., Liu H., Liu F., Zhou W., Luo B.

The origin of Precambrian dolomites has attracted research interest as a result of their association with petroleum resources. The long diagenetic history of these dolomites and multiple periods of hydrothermal activity mean that dating and identifying different periods of dolomite formation is challenging. This study focuses on dolomites in the Precambrian Dengying Formation of the Sichuan Basin, central China, and presents new petrographic, in situ laser ablation inductively coupled plasma mass spectrometry U–Pb and trace element, and Sr–C–O isotopic data to characterize three types of dolomite and constrain their age and origin. In situ U–Pb dating of type I dolomite yielded a lower intercept age of 637 ± 35 Ma. The rare earth element (REE) patterns, 87Sr/86Sr ratios (0.70827–0.70903), and δ13CVPDB (0.8‰ to 1.0‰) and δ18OVPDB (−1.5‰ to −1.0‰) values of type I dolomite indicate their derivation from seawater or a precursory source with seawater characteristics. Type II dolomite yielded an age of 636 ± 15 Ma and has lower ΣREE and slightly higher δ13CVPDB (1.2‰–1.5‰) and δ18OVPDB (−0.9‰ to −0.3‰) values than type I, as well as similar 87Sr/86Sr ratios and parallel REE patterns that are indicative of formation by reflux seepage dolomitization. The type III dolomite is characterized by large crystals, unique REE patterns, high 87Sr/86Sr values (0.70942–0.70975), and negative δ18OVPDB values (−6.4‰ to −3.1‰) that indicate a hydrothermal origin. The relationships between hydrothermal dolomite and bitumen indicate that the paleo-oil charging within the Dengying Formation reservoir occurred after the hydrothermal activity at 516 ± 49 Ma. The early hydrothermal activity provided space for the subsequent fluid movement, and oil and gas charging. Our integrated approach, incorporating petrographic, geochemical, isotopic, and geochronological data, constrains the ages of different dolomite phases and an oil-charging event within the Dengying Formation reservoir and provides new insights into the evolution of petroleum systems in general.

Li L., Bao Z., Li L., Li Z., Ban S., Li Z., Wang T., Li Y., Zheng N., Zhao C., Chen L., Chen J.

Organic-rich shale in the Cretaceous succession of the large non-marine Songliao Basin in northeastern China, especially the Qingshankou Formation of the Turonian and Coniacian stages, provides a unique record for studying the role of global climate control on organic matter accumulation. Organic enrichment in the Qingshankou Formation along the Southeastern Uplift of the basin has been widely reported and is implicated in the formation of algal blooming and a saline anoxic water environment. However, studies on the Qingshankou Formation in the Changling Sag are relatively few, which leaves a significant gap to understand the controlling factors of organic enrichment at a basin scale. In this study, the sedimentary environment of the first member of the Upper Cretaceous Qingshankou Formation (K2qn1) is reconstructed from petrological and geochemical data to discuss the sources and preservation mechanisms of lacustrine shale organic matter in the Changling Sag (southern Songliao Basin). The K2qn1 is subdivided into three stratigraphic units: Sq1 phase, Sq2 phase, and Sq3 phase. Biomarker (abundance of tricyclic terpane and regular steranes) and petrographical (maceral composition) data indicate that the organic matter in K2qn1 was mainly from terrigenous plants, with some algae input. Inorganic minerals (major and trace elements) and petrological (framboidal pyrite size) data suggest a humid climate and saline anoxic water environment at the Changling Sag during the most organic-rich Sq1 phase. During the Sq2 and Sq3 phases, a relative low lake level and semi-arid climatic conditions likely prevailed. Moreover, these results imply that apart from a saline anoxic water environment, the persistence of continentally derived organic matter in lacustrine shale is mainly controlled by clay minerals. Accordingly, this study proposed a new enrichment model for lacustrine shale organic matter. The new model complements existing lacustrine shale sedimentary models for sources of organic matter and emphasizes the role of clay minerals in preserving organic matter.

Bhattacharya S., Sharma S., Agrawal V., Dix M.C., Zanoni G., Birdwell J.E., Wylie A.S., Wagner T.

This study focuses on understanding the association of rare earth elements (REE; lanthanides + yttrium + scandium) with organic matter from the Middle Devonian black shales of the Appalachian Basin. Developing a better understanding of the role of organic matter (OM) and thermal maturity in REE partitioning may help improve current geochemical models of REE enrichment in a wide range of black shales. We studied relationships between whole rock REE content and total organic carbon (TOC) and compared the correlations with a suite of global oil shales that contain TOC as high as 60 wt.%. The sequential leaching of the Appalachian shale samples was conducted to evaluate the REE content associated with carbonates, Fe–Mn oxyhydroxides, sulfides, and organics. Finally, the residue from the leaching experiment was analyzed to assess the mineralogical changes and REE extraction efficiency. Our results show that heavier REE (HREE) have a positive correlation with TOC in our Appalachian core samples. However, data from the global oil shales display an opposite trend. We propose that although TOC controls REE enrichment, thermal maturation likely plays a critical role in HREE partitioning into refractory organic phases, such as pyrobitumen. The REE inventory from a core in the Appalachian Basin shows that (1) the total REE ranges between 180 and 270 ppm and the OM-rich samples tend to contain more REE than the calcareous shales; (2) there is a relatively higher abundance of middle REE (MREE) to HREE than lighter REE (LREE); (3) there is a disproportionate increase in Y and Tb with TOC likely due to the rocks being over-mature; and (4) the REE extraction demonstrates that although the OM has higher HREE concentration, the organic leachates contain more LREE, suggesting it is more challenging to extract HREE from OM than using traditional leaching techniques.

HE D., JIA C., ZHAO W., XU F., LUO X., LIU W., TANG Y., GAO S., ZHENG X., LI D., ZHENG N.

Based on the recent oil and gas discoveries and geological understandings on the ultra-deep strata of sedimentary basins, the formation and occurrence of hydrocarbons in the ultra-deep strata were investigated with respect to the processes of basin formation, hydrocarbon generation, reservoir formation and hydrocarbon accumulation, and key issues in ultra-deep oil and gas exploration were discussed. The ultra-deep strata in China underwent two extensional-convergent cycles in the Meso-Neoproterozoic Era and the Early Paleozoic Era respectively, with the tectonic-sedimentary differentiation producing the spatially adjacent source-reservoir assemblages. There are diverse large-scale carbonate reservoirs such as mound-beach, dolomite, karst fracture-vug, fractured karst and faulted zone, as well as over-pressured clastic rock and fractured bedrock reservoirs. Hydrocarbons were accumulated in multiple stages, accompanied by adjusting and finalizing in the late stage. The distribution of hydrocarbons is controlled by high-energy beach zone, regional unconformity, paleo-high and large-scale fault zone. The ultra-deep strata endow oil and gas resources as 33% of the remaining total resources, suggesting an important successive domain for hydrocarbon development in China. The large-scale pool-forming geologic units and giant hydrocarbon enrichment zones in ultra-deep strata are key and promising prospects for delivering successive discoveries. The geological conditions and enrichment zone prediction of ultra-deep oil and gas are key issues of petroleum geology.

Huang S., Jiang Q., Jiang H., Tang Q., Zeng F., Lu W., Hao C., Yuan M., Wu Y.

The Middle Permian Qixia and Maokou formations (Fms), are important targets for current gas exploration in the Sichuan Basin. In recent years, high-yield industrial gas flow has been obtained in different structural zones of the basin. Based on the molecular and isotopic compositions of natural gas and reservoir bitumen, biomarker composition, and geological conditions, the genetic types, maturity, and sources of natural gas reservoired in the Qixia and Maokou Fms in different structural zones in the basin were analyzed. The following conclusions can be drawn: (1) the molecular and isotopic compositions of natural gas reservoired in the Middle Permian Qixia and Maokou Fms from different areas in the Sichuan Basin differ considerably; (2) the Middle Permian natural gas is oil-type gas, which is mainly generated by oil cracking; (3) most of the natural gas reservoired in the Qixia and Maokou Fms in the Sichuan Basin has reached the over-mature stage. The maturity of the natural gas from the northwestern Sichuan Basin is the highest, followed by gas from eastern and southern Sichuan, and part of natural gas in Southern Sichuan is high-maturity; (4) except for the slight thermochemical sulfate reduction (TSR) secondary alteration in the central Sichuan Basin, an effect of TSR was not observed in other areas; and (5) natural gas is controlled by the regional hydrocarbon kitchen. Gas in the eastern and southern Sichuan areas mainly originates from the Lower Silurian Longmaxi Fm shale, with a small contribution from marl in the Maokou Fm. The gas of the first member of the Maokou Fm has self-generation and self-storage characteristics, with a small contribution of the Longmaxi Fm shale. The Middle Permian gas in northwestern Sichuan is a mixture of gas generated from source rocks of the Lower Cambrian Qiongzhusi and Maokou Fms, whereas that in central Sichuan mainly originates from source rocks of the Qiongzhusi Fm. The Middle Permian gas in southwestern Sichuan mainly originates from its own source rock, and the natural gas reservoired in Permian volcanic rocks in the Chengdu–Jianyang area was generated by the mudstone of the Qiongzhusi Fm.

Li Y., Ding W., Zeng T., Xia W., Cheng X., Shi S., Ding S.

Integrated geological and geophysical methods have been used to describe the geometric characteristics and kinematic evolution of the No. 15 fault zone (ES15FZ) in the eastern Sichuan Basin (ESB). The geometric evidence of strike-slip fault activity includes a single subvertical fault and a composite flower structure with deeper positive relief and shallower negative relief in cross-sectional view, as well as a transpressional stepover between fault segments located above the principal displacement zone (PDZ) in map view. The structural relief amplitude and vertical displacement of the ES15FZ along strike provide insights into the formation and multistage development of the fault zone. The ES15FZ originated in a convergent setting, resulting in positive flower structures near the upper Cambrian strata. At shallower depths, the northern ES15FZ is composed of two large-scale negative relief regions and two small-scale positive relief regions, and the southern ES15FZ is composed of one large-scale positive relief region and one small-scale negative relief region. After progressive deformation, the ES15FZ exhibits composite flower structures with a cross-sectional pattern of deeper positive and shallower negative relief and a map-view pattern of northern negative, central positive, and southern negative relief. From the Late Ordovician to the Early Triassic, the transpressional setting and the subsequent transtensional setting were consistent with the tectonic evolution history and stress field environment of the study area. In cross-sectional view, the stress reduction effect of the ductile detachment layer caused the tectonic activity after the Middle Triassic to have little impact on the pre-existing strike-slip faults.

Wang W., Pang X., Wang Y., Chen Z., Li C., Ma X.

Hydrocarbon expulsion features and resource potential evaluation of source rocks are crucial for the petroleum exploration. High-maturity marine source rocks have not exhibited a hydrocarbon expulsion mode owing to the lack of low-maturity source rocks in deep petroliferous basins. We considered the Ediacaran microbial dolomite in the Sichuan Basin, the largest high-maturity marine gas layer in China, to exhibit a method that quantitatively characterizes the hydrocarbon expulsion of high-maturity marine source rocks. The experiment of fluid inclusion, rock pyrolysis, and vitrinite reflectance (Ro) of 119 microbial dolomite core samples obtained from the Dengying Formation were performed. A hydrocarbon expulsion model of high-maturity source rock was established, and its resource potential was evaluated. The results showed that the Ediacaran microbial dolomite in the Sichuan Basin is a good source rock showing vast resource potential. The hydrocarbon expulsion threshold is determined to be vitrinite reflectance at 0.92%. The hydrocarbon expulsion intensities in the geologic history is high with maximum of 1.6 × 107 t/km2. The Ediacaran microbial dolomite expelled approximately 1.008 × 1012 t of hydrocarbons, and the recoverable resource was 1.5 × 1012 m3. The region can be categorized into areas I, II, III, and IV, in decreasing order of hydrocarbon expulsion intensity. Areas with a higher hydrocarbon expulsion intensity have a lower drilling risk and should be prioritized for exploration in the order I > II > III > IV. Two areas, northern and central parts of Ediacaran in the Sichuan Basin, were selected as prospects which had the drilling priority in the future gas exploration. The production data of 55 drilled wells verified the high reliability of this method. This model in this study does not require low-maturity samples and can be used for evaluating high-maturity marine source rocks, which has broad applicability in deep basins worldwide.

Peng J., Hu Z., Feng D., Wang Q.

Despite the sedimentology of deep-water fine-grained sedimentary rocks from marine environments having received highlighted attention in recent years, their counterparts from the lacustrine environments are rarely reported. Based on a complete sedimentological, petrographic, and geochemical analysis of three continuous cored wells of the Lower Jurrasic Dongyuemiao Formation, Sichuan Basin, West China, this study illustrates the range of lithofacies, cyclicities, and transportation and deposition mechanisms of this lacustrine deep-water succession. The aim of this research is to establish a synthesis depositional model for lacustrine deep-water fine-grained sedimentary systems in the Sichuan Basin. The results indicate that seven lithofacies were developed in the Dongyuemiao Formation and they were stacked in a repeated pattern to constitute ca 10–20 m thick composite cycle sets. A typical composite cycle set comprises an upper and lower unit. Specifically, the lower unit is characterized by basal relatively coarse-grained detrital-rich lithofacies interpreted to record gravity flows that grade upward into relatively fine-grained detrital-lean lithofacies interpreted as suspension deposits from the water column. The upper unit is stacked in a reverse pattern and characterized by basal relatively fine-grained detrital-lean lithofacies that grade upward into relatively coarse-grained detrital-rich lithofacies. Such cyclicities in the Dongyuemiao Formation are associated with third-order lake level variations. Specifically, the relatively coarse-grained detrital-rich lithofacies is interpreted to be deposited from low-density turbidity currents, likely hyperpycnal turbidity flows, during maximum lake level regression when terrigenous fluvial and delta systems developed in the basin margin. The relatively fine-grained detrital-lean lithofacies is interpreted to be deposited from suspension fallout during maximum lake level transgression. This cyclicity pattern and frequent occurrence of sediment gravity flow deposits in the Dongyuemiao Formation suggests a dynamic hydrographic condition in the deep-water lacustrine environment of the Sichuan Basin. • The range of lithofacies in lacustrine deep-water Dongyuemiao Formation was reported. • A wide range of depositional processes (from gravity flows to suspension fallout) was revealed in lacustrine deep-water environments. • Cyclicity and sediment provenance of the deep-water Dongyuemiao Formation was regulated by lake level variation. • Deep-water organic-rich mudrocks can be deposited in dynamic hydrographic conditions rather than a consistent quiescent condition.

He Z., Li S., Li Y., Gao J.

Based on the analysis of the deformation styles in different tectonic belts of the Middle-Upper Yangtze region, as well as the dissection of typical hydrocarbon reservoirs, this study determined the controlling effects of deformations on the hydrocarbon accumulations, obtaining the following results. The Middle-Upper Yangtze region experienced significant deformations during the Late Indosinian (T2–T3), the Middle Yanshanian (J3–K,), and the Himalayan, and five styles of tectonic deformations mainly occurred, namely superimposed deep burial, uplift, compressional thrusting, multi-layer decollement, and secondary deep burial. The distribution of hydrocarbon reservoirs in the piedmont thrust belts is controlled by the concealed structures on the footwall of the deep nappe. The gentle deformation area in central Sichuan experienced differential uplift, structural-lithologic hydrocarbon reservoirs were formed over a wide area. The eastern Sichuan-western Hunan and Hubei deformation area experienced Jura Mountains-type multi-layer detachment, compressional thrusting, and uplift. In relatively weakly folded and uplifted areas, conventional structural-lithologic hydrocarbon reservoirs have undergone adjustment and re-accumulation, and the shale gas resources are well preserved. In the strongly deformed areas, conventional hydrocarbon reservoirs were destroyed, while unconventional hydrocarbon reservoirs have been partially preserved. The marine strata in the Jianghan Basin experienced compression, thrusting, and denudation in the early stage and secondary deep burial in the late stage. Consequently, the unconventional gas resources have been partially preserved in these strata. Secondary hydrocarbon generation become favorable for conventional hydrocarbon accumulations in the marine strata.

Kendrick M.A., Zhao J., Feng Y.

Abstract Newly formed oceanic crust is altered by seawater and carbonated at low temperatures over poorly defined periods of time. We applied in situ U-Pb dating to investigate 28 carbonate veins from Ocean Drilling Program Hole 801C, which is situated in the oldest Jurassic-age oceanic crust preserved in the western Pacific Ocean. Our results indicate that Pacific Ocean crust began accreting at 192 ± 6 Ma, which is ~25 m.y. earlier than previously recognized. Carbonation peaked at 171 ± 5 Ma and continued at a low rate for more than ~65 m.y. after accretion. Jurassic carbonation rates varied over ~10 m.y. timescales but encompassed a range similar to that observed today. These data suggest that carbonation rates are relatively insensitive to changes in atmospheric CO2, but confirm the longevity of seafloor alteration as a critical control in global volatile cycling.

Yang T., Azmy K., He Z., Li S., Liu E., Wu S., Wang J., Li T., Gao J.

The mechanism of fault-controlled hydrothermal dolomitization has long been controversial due to its complicated tectonic and diagenetic conditions, especially for the source of dolomitizing fluids and its hydrological driving models. In the southeastern Sichuan Basin, fracture-related dolomite bodies are well developed in a Middle Permian carbonate succession, providing an example of dolomitization and its relationship with regional tectonic activities. Previously, many of the dolomites in the Sichuan Basin have been interpreted as of hydrothermal origin but are usually poorly defined since it is hard to determine the nature and timing of dolomitization. In the current study, new petrographic, geochemical, and chronological data of Middle Permian dolomites have been integrated and allowed the classification of those dolomites into two categories (replacive dolomites of D1–D2 and fracture-/vug-filling dolomites of D3–D5). Calcite (C1–C3) and other non‑carbonate cements have also been found. The near-micritic dolomite (D1) was formed at the near-surface to early burial stage, likely from modified seawaters, which was reflected by its similar δ 18 O fluid estimates of the parent dolomitizing fluids and rare earth element patterns to matrix lime mudstone, as well as the fabric retentive texture. The fabric destructive (D2) and fracture-/vug-filling dolomites (D3–D5) are characterized by the high estimates of δ 18 O fluid of their parent dolomitizing fluids, high 87 Sr/ 86 Sr ratios, high Fe and Mn concentrations, positive Eu anomalies, high T h values, and high salinity estimates, indicating a hydrothermal origin. However, the limestone-like δ 13 C VPDB and strongly negative Ce anomalies of D2–D5 suggest that these dolomites may have originally evolved from seawater-derived fluids which circulated in the basal clastic rocks and flowed upwards by thermal convection through fault systems. New U–Pb ages bracketed a time range of these dolomites from 251 ± 11 Ma to 264 ± 10 Ma, coinciding with the emplacement of the Emeishan Large Igneous Province (~257–260 Ma). This may imply that the contemporary basement faulting and associated abnormal thermal event in southeastern Sichuan Basin still remotely echoed with the activities of the Emeishan Large Igneous Province, although the study area was far away from its eruption center. It facilitated the fluid circulation through fault systems and underlying sandstone aquifers and thus drove fault-controlled hydrothermal dolomitization at shallow burial backgrounds. • The fault-related dolomites formed at shallow burial depths from hydrothermal fluids. • New U–Pb dating results bracket a dolomitizing time range of 251 ± 11 Ma to 264 ± 10 Ma. • The dolomitizing period was coincident with the emplacement of ELIP. • Basement faulting and thermal convection facilitated hydrothermal dolomitization.

Li Q., Li B., Mei W., Liu Y.

Fold-and-thrust belts are important locations for oil and gas exploration, but due to the complex sources, migration, and charging histories the exploration risk is extremely high. The Longmenshan belt in the NW Sichuan Basin offers an excellent opportunity to study the genesis and sources of natural gas in fold-and-thrust belt. We synthesize existing geochemical data from ∼1100 samples from various strata in the Sichuan Basin. Among them, the bitumen biomarkers and the natural gas molecular compositions and stable carbon isotopes in the Middle Permian of different structural belts were analyzed to investigate the gas genetic types and sources. Then, they were compared with natural gas from other strata in the Sichuan Basin. Results indicate that the Middle Permian natural gases in the NW Sichuan Basin are dominated by hydrocarbon gases, with a small amount of CO 2 and N 2 . The identification of the gas origin and gas-source correlation indicate that there are significant differences between the Middle Permian natural gas in different structural belts of the Longmenshan belt. The natural gas in the thrust nappe belt is mainly oil-cracking gas from the Qiongzhusi Formation (Fm) source rock, and the natural gas in the thrust front belt shows obvious mixed-source characteristics, with both kerogen-cracking gas of the Permian source rocks and oil-cracking gas from the Qiongzhusi Fm source rock. However, the natural gas in the unfaulted belt mainly comes from the kerogen-cracking gas in the Permian source rocks. Overall, from the thrust nappe belt to the thrust front belt, and then to a belt that is largely unfaulted, the contribution of deep source rocks controlled by fault migration channels decreases with gradually weakening deformation. This study will help to better understand the petroleum system in the fold-and-thrust belt and optimize the future exploration strategy. • The Middle Permian natural gas in the NW Sichuan Basin are typical dry gas. • Oil cracking gas from deep source rock exists in the Middle Permian. • Genesis and sources of natural gas in each structural belt are distinct. • The results are helpful to understand the petroleum system in fold-and-thrust belt.

Chen J., Guo X., Tao Z., Cao Z., Wang B., Zhang X., Xu H., Zhao J.

Abstract Direct dating of oil charge in superimposed basins is essential to understanding the evolutionary histories of petroleum systems, especially in sedimentary basins with complicated tectonic evolution and thermal histories. Based on analyses of different phases of calcite veins and primary oil inclusions, episodes of oil charge were determined by laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) in situ U-Pb dating of calcite veins from an Ordovician reservoir within the Tahe Oilfield of the Tarim Basin, NW China. This basin has been subjected to multiple uplifts and erosions and repeated oil charges. The U-Pb dating results indicate that the first phase of oil charge occurred from 329.7 ± 1.6 Ma to 308.1 ± 4.1 Ma, and the second phase occurred from 249.3 ± 2.6 Ma to 220.5 ± 7.3 Ma. The timing of oil charge determined by fluid inclusion analysis alone can lead to great uncertainties due to the existence of multiple phases of oil charge and complex thermal evolution in superimposed basins. Our study demonstrates that U-Pb dating of calcite veins originating from the reservoirs offers a unique solution to determining the oil charge history, which avoids the multi-solution uncertainties in the timing of oil charge inferred from fluid inclusion analysis in superimposed basins.

Kotarba M.J., Więcław D., Jurek K., Waliczek M.

The Carpathian Foredeep is one of the largest Miocene sedimentary basins in Central Europe. Biomarkers, polycyclic aromatic hydrocarbons (PAHs), stable carbon isotope and maceral compositions were determined to evaluate the depositional conditions, source of Miocene dispersed organic matter (DOM) in claystones as well as the effect of thermal maturity on these parameters based on hydrous pyrolysis (HP) experiments at 330 and 355 °C for 72 h. DOM is represented mostly by humic particles of Type III with an admixture of Type IV kerogens; therefore, they only have hydrocarbon gas potential. Alginite, which originates from marine or lacustrine organic material, was recorded in some samples. Vitrinite reflectance increases from 0.27 to 0.44% R r for Original samples to 1.01–1.14% for samples After HP at 330 °C, and 1.38–1.53% after 355 °C. During HP experiments, the optical and chemical properties and maceral composition change with maturation, and the generated char and liptinite macerals mainly undergo vitrinitization and are transformed into liquid hydrocarbons. The distribution of biomarkers, selected PAHs and sulphur-containing compounds in recovered extractable organic matter (EOM) fraction indicates that (i) the DOM of the Miocene claystones was mainly deposited in an estuarine environment in the shallow Miocene sea, generally under anoxic conditions, (ii) they were accumulated in siliciclastics with marine/lacustrine shales and marls, and (iii) the contribution of terrigenous DOM was usually associated with deltaic environments during the deposition of the Miocene strata. Both geochemical and petrographic parameters change with thermal maturity. Sofer's (1984) genetic graph was constructed based on analyses of the isotopic composition of oils generated from DOM, however, our carbon isotope data reveal this graph is not always useful for genetic characterization of EOM. The observed shift could stem from isotopic fractionation during thermal maturation of EOM. • Simulation of thermogenic processes by means of hydrous pyrolysis (HP) at 330 and 355 °C in the Miocene strata of the Carpathian Foredeep. • Determining sources and depositional conditions of dispersed organic matter (DOM) based on biomarkers, PAHs, carbon isotopes and macerals. • Variations of selected biomarkers, PAHs and bitumen fraction and maceral compositions under HP heating. • Variation of carbon isotopes of saturates and aromatics under HP heating. • Correlations of HPP ratio and TA(I)/TA(I + II) triaromatic steroids versus vitrinite ratio after HP heating.

Qiu N., Chang J., Zhu C., Liu W., Zuo Y., Xu W., Li D.

Thermal regime and thermal history are of significant important in basin dynamics and hydrocarbon generation of source rocks. The sedimentary basins in three typical cratons of China, North China Craton (NCC), Yangtze Craton (YC) and Tarim Craton (TC), underwent completely different tectonic background and dynamic mechanism, which resulted in the differentials of their thermal regimes. In this paper, the thermal regimes of the Bohai Bay Basin in the eastern NCC, Tarim Basin in TC, and Sichuan basin in the Upper YC were studied. There has some lower thermal background in the area of western China than eastern side of the NCC. The mean heat flow value of Tarim basin is 42.5 mW/m 2 , 53.8 mW/m 2 in the Sichuan basin and 66.7 mW/m 2 in the eastern NCC. And the temperature at 10000 m ultra-depth in the Tarim Basin also shows lower values than that of Sichuan and Bohai Bay basins. The thermal history, modeled from thermal indicators of vitrinite reflectance (R o ), equivalent vitrinite reflectance data (R equ ), fission track and (U Th)/He data of apatite and zircon, evolved differently because of the different tectonic history in these basins. The Tarim basin underwent a cooling history with the heat flow of 55–65 mW/m 2 in the Cambrian decreasing to the present-day of 40–50 mW/m 2 . The Meso-Cenozoic thermal history of the Bohai Bay basin experienced four evolutionary stages with two heat flow peaks in the late Early Cretaceous and in the Middle to Late Paleogene, which correspond to the destruction peaks of the eastern NCC and had heat flow values of 82–86 mW/m 2 and 81–88 mW/m 2 , respectively. The Sichuan basin was stable with heat flow value of less than 65 mW/m 2 from the Late Sinian to Late Paleozoic, and the heat flow increased rapidly to the peak value (75–100 mW/m 2 ) at the end of Early Permian by thermal effect of the Emeishan mantle plume. From Mesozoic to present, the heat flow decreased to the present value (60–70 mW/m 2 ). In addition, the comparation of thermal characteristics of typical cratons around the world, including heat flow, thermal history, lithospheric thermal structure and thermal lithospheric thickness, also have been caried out. The differential thermal histories of Tarim and Sichuan basins resulted in the different thermal evolution of Cambrian source rocks. This study may provide some new geothermal evidence for hydrocarbon generation and phase distribution of oil and gas in the deep and/or ultra-deep basin. Thermal regime and thermal history of typical sedimentary basins in three typical cratons of China underwent completely different evolution. The Tarim basin underwent a cooling history, the Bohai Bay basin experienced four evolutionary stages with two heat flow peaks, and the Sichuan basin was stable with heat flow but to a peak at the end of Early Permian. Nansheng Qiu, Chang Jian, Zhu Chuanqing, Liu Wen, Zuo Yinhui, Xu Wei, Li Dan. • Three typical cratons of China show great differences in heat flow and deep-temperature. • Three typical cratons of China show great differences in lithospheric thickness from 76–170 km. • Thermal histories of Bohai Bay, Sichuan and Tarim basins are summarized. • Thermal regime between stable and destabilized cratons are compared. • Three thermal evolution patterns of source rocks are obtained.