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WU Zhenhan, JI Changjun, WANG Tao, LIU Zhiwei, ZHAO Zhen, WANG Qian, CHEN Yun
2025,99(5):1467-1477, DOI: 10.19762/j.cnki.dizhixuebao.2025122
Abstract:
Mechanism of hydrocarbon formation caused by the Qingshuihu thrust in central Qiangtang area is revealed by field study, seismic reflection profiling and oil drilling. Jurassic marine strata as thick as 3600 m formed high quality source rocks, variety of reservoirs and good caps in the Shenglihe and its adjacent areas southern part of the north Qiangtang depression. However, the Jurassic source rocks kept in immature- low maturity in the Cretaceous due to insufficient buried depth. India- Asia continental collision led to the formation of larger- scale Qingshuihu thrust system, which is composed of northward thrust, imbricate faults and Paleogene foreland basin in north of the central Qiangtang uplift. Structural thickening derived from Paleogene thrust and Paleocene- Eocene sedimentation loading in the foreland basin reconstructed the burial, thermal and hydrocarbon generation history of the Jurassic marine source rocks. Lower- Middle Jurassic marine source rocks of the Quemoco, Buqu and Xiali formations successively strode over hydrocarbon generation threshold in Early Eocene, and formed peak of hydrocarbon generation in Middle Eocene. Paleocene- Eocene compressive stress caused fractures in Middle Jurassic limestone of the Buqu Formation, which formed fractured limestone as well as main oil reservoir beneath the Qingshuihu thrust and its foreland basin. Jurassic marine sedimentation formed source- reservoir- cap systems, and Paleogene thrust caused hydrocarbon generation and accumulation for formation of large oil and gas fields in the Qiangtang basin.
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JIANG Hua, YANG Wei, ZHAI Xiufen, GU Zhidong, LI Qiufen, LU Weihua, LIU Guixia, JIANG Qingchun, HUANG Shipeng, SHI Shuyuan
2025,99(5):1478-1491, DOI: 10.19762/j.cnki.dizhixuebao.2024072
Abstract:
The Jiulongshan structure in NW Sichuan is located in the 4th Member of the Dengying Formation in the Deyang- Anyue inner craton rift. Investigating the scale and conditions of hydrocarbon accumulation of the Jiulongshan structure has significant theoretical and practical importance for evaluating the potential of deep and ultra- deep oil and gas exploration in this region. Seismic, drilling, and outcrop data were used to analyze basic petroleum geological conditions such as source rocks and reservoirs. Focusing on the structural control of hydrocarbon accumulation, the study clarifies the formation of reservoir elements and the relationship between source and reservoir configuration within the context of structural evolution, ultimately establishing a reservoir formation model. The research results indicate that the structural control of the Sinian Dengying Formation in Jiulongshan can be divided into three important stages. First, during the syn- depositional period, the Jiulongshan structure was located within the carbonate platform of the 2nd Member of the Dengying Formation in the Deyang- Anyue rift. By the time of the 4th Member of the Dengying Formation, it had shifted to the platform margin development zone. The 4th Member exhibits well- developed platform margin sandbars, while the 2nd Member features inner platform sandbars, both representing favorable sedimentary facies zones. Secondly, during the peak development period of the Deyang- Anyue rift in the Early Cambrian, thick and high- quality mud shale layers formed in the Maidiping- Qiongzhusi formations. These, along with the underlying mud shale of the Sinian Doushantuo Formation, serve as the main source rocks for hydrocarbon supply in the Dengying Formation. The interbedding of these two sets of hydrocarbon source rocks with the large- scale reservoir of the Dengying Formation creates a high- quality reservoir formation combination. Third, the Jiulongshan structure underwent continuous local uplift and strengthening, originating from the slope of the ancient uplift in central Sichuan. Through multi- stage tectonic activities and transformation, it ultimately evolved into a local uplift structure in the western Sichuan depression. During the two key periods of oil generation (Ordovician to Early Triassic) and the main gas generation stage (Late Triassic to Early Cretaceous), the anticline structure has formed and continuously strengthened, facilitating the capture and accumulation of hydrocarbons for reservoir formation. Overall, the source- reservoir configuration conditions of the Sinian Dengying Formation in the Jiulongshan structure are superior, possessing the necessary prerequisites for large- scale hydrocarbon accumulation.
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YU Jingqiang, ZHAO Li, ZHANG Yunyin, DONG Dawei, YU Zhengjun, WANG Yongshi, ZHANG Pengfei, WEI Wen
2025,99(5):1492-1507, DOI: 10.19762/j.cnki.dizhixuebao.2023461
Abstract:
The basement dipping is an important factor controlling the structural deformation of thrust belts. However, rare attentions have been paid on the basement dipping characteristics of the Longmenshan thrust belt. Based on interpretations of seismic profiles, this paper found that the Longmenshan thrust belt in the northern, central and southern segments underwent different basement dipping. The basement dipped 2.6° toward foreland in the northern because of the uplift of thrust sheets. The basement dipped 3. 2° toward hinterland in the central due to several phases of loading. The basement dipped 2.6° toward hinterland in the southern which was the result of earlier rifting and later loading. The numerical experiment shows that the basement dipping toward hinterland or horizontal subsiding will suppress the forward propagation of thrusting deformation, and superimpose the thrusting sheets. While the control effect of the pre- existing basement dip is opposite. When the basement remains horizontal or dip toward the foreland, the thrust sheets in hinterland uplifted stronger than that of the foreland, which will cause the deformation in cover layer toward the foreland as a whole. When the basement dipped backward with syn- sedimentation will result in the back- thrusting in slope zone. Numerical simulation proved the basement evolution in southern segment of the Longmenshan thrust belt. Before the Late Cretaceous, it was in an extensional regime with thick strata in the west and thin strata in the east, which resulting its basement dipping to the west. During the Late Cretaceous- Eocene, a foreland basin developed, and the basement dipped toward hinterland because of the loading. During the Oligocene- Miocene, the thrusting deformation strongly propagated into the basin, and the basement almost had no dipping. Since the Pliocene, the basement in hinterland has been uplifted because of the Qinghai- Tibet Plateau, which resulted in the sharp topography.
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XU Yong, DENG Bao, TIAN Xiaofeng, NI Hongyu, DUAN Yonghong, XIAO Benfu, LI Junlun
2025,99(5):1508-1522, DOI: 10.19762/j.cnki.dizhixuebao.2023463
Abstract:
In order to investigate the subsurface fine structure and sedimentary characteristics of the key areas with high earthquake risk in the western margin of the Weihe basin, we deployed a dense linear array consisting of 254 short- period three- component seismometers with an average station- spacing of 200 meters in this study, which collected data for 30 days. We calculate the vertical component cross- correlation of the ambient noise, apply the recently developed extended range phase shift method to extract the fundamental mode Rayleigh wave dispersion curves ranging from 3 Hz to 3. 3 s, and then invert for high- resolution shear wave velocity structure down to the depth of 2. 5 km beneath the dense linear array. Additionally, using the collected three- component seismic noise, we apply the horizontal to vertical spectral ratio (HVSR) method to calculate peak frequencies, and then use an empirical relationship to estimate the thickness of sedimentary layers in the Weihe basin. The tomographic results show horizontal pattern with a high- low- high velocity variation, corresponding to the uplift- depression- uplift geological structure in this sedimentary basin. The result also clearly delineates three major faults and two geological structural units in the region, consistent with the profile obtained by active seismic imaging. The result from HVSR reveals that the sedimentary layers are relatively thick and exhibit a distinct and complete stratigraphic sequence deposited in the Holocene, Neogene, and Quaternary periods in the Cenozoic. A comprehensive analysis integrating results from ambient noise tomography, HVSR and active- source imaging suggests none of the three major faults beneath the 2D array penetrates through the Quaternary formation in this region. This study shows that the extendedrange phase shift and the HVSR methods based on seismic ambient noise are effective in characterizing structures in sedimentary basins.
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XIAO Kunze, TONG Hengmao, YANG Donghui, LI Xuesong, LI Xushen, CUI Hao
2025,99(5):1523-1537, DOI: 10.19762/j.cnki.dizhixuebao.2023453
Abstract:
The Yinggehai basin has long been of great interest to academics and the petroleum industry due to its special tectonic location (the area of the Red River fault zone into the sea) and its abundant natural gas resources. Since the Indo- Eurasian collision- extrusion model was proposed to explain the deformation in Southeast Asia, the Yinggehai basin has been regarded as a typical pull- apart basin. However, there is a distinct mismatch between these opinions and the structural features revealed by the 3- D (three- dimensional) seismic data. Our study is based on the “generalised fault theory”, using 3D seismic data to investigate the structural features of the No.1 fault systematically, and combining it with sandbox simulation experiments, we propose a new insight into the mechanism of the No.1 fault. The results show that the structural features and the distribution of fault distances of the boundary fault (No.1 fault) in the Yinggehai basin are not similar to those of the traditional strike- slip faults. Still, they are also strongly similar to the features of the fault deformation under oblique extension. These faults are oblique- slip normal faults with significant differences in the amount of strike- slip and dip- slip displacements at the various segments, as well as in the control of sedimentary filling of the basin. The boundary fault was an oblique- slip normal fault due to the reactivation of pre- existing structures under a north- south extensional stress regime during the Oligocene- Miocene period, and these insights were also verified by analogue modelling. A new insight into the mechanism of the No.1 fault, which theoretically reveals the mechanism of the Yinggehai basin and can provide guidance for the structural analysis of the Yinggehai basin and its later oil and gas exploration and development.
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GUAN Wei, LIU Chiyang, PENG Guangrong, HUANG Lei, SONG Lijun, LIANG Chao, LI Xin, ZHANG Lili, LI Hongbo, WU Zhe, MA Yunjie
2025,99(5):1538-1553, DOI: 10.19762/j.cnki.dizhixuebao.2023462
Abstract:
The Baiyun sag, located in the Zhu 2 depression of the central Pearl River Mouth basin, has undergone a complex evolution from a Mesozoic active continental margin to a Cenozoic passive continental margin. Recent expansion of oil and gas exploration targets to deeper buried hills necessitates a comprehensive understanding of the structure and genesis of these uplifts. This study employs 3D seismic and borehole data to analyze the structural characteristics of uplifts around the Baiyun sag and investigate their formation processes. Our findings reveal distinct genesis for these uplifts, categorized into three types: the Panyu low uplift, mainly controlled by Mesozoic thrust faults; the Yunkai low uplift, jointly controlled by Meso- Cenozoic faulting; and the Yundong low uplift, mainly governed by Cenozoic extensional faults. This diversity in uplift structures is related to the degree and type of interaction between Meso- Cenozoic faults. Mesozoic pre- existing faults determined the complexity of the basement structure, while subsequent Cenozoic faulting, both inheriting and modifying these pre- existing faults, resulted in the observed variety of uplift structures. Late- stage magmatism and fault modification further enriched this diversity. Furthermore, we investigated reservoir formation conditions in buried hills, identifying weathering, faulting, and magmatism- related fractures as the main reservoir spaces that exhibit regular planar distributions. Therefore, by studying the differences in uplift genesis, we can not only investigate the interactions between pre- existing and late extensional faults but also provide a structural basis for understanding reservoir formation and evaluating exploration targets in buried hills.
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CAI Mengke, WANG Wanyin, ZHANG Yimi, WANG Dingding
2025,99(5):1554-1575, DOI: 10.19762/j.cnki.dizhixuebao.2024352
Abstract:
The Bohai Bay basin is a principal contributor to oil and gas production not only in offshore China but also on a global scale, with its hydrocarbon resource distribution exhibiting marked differences between marine and terrestrial areas, a pattern intimately linked to the basin' s crustal structure. In order to clarify the crustal structure of the Bohai Bay basin, this study leveraged terrain and gravity data to reveal the distribution of basin faults and the fluctuations of the Moho interface. NVDR- THDR technology and Euler deconvolution were utilized to ascertain the planar locations of the faults and their apparent depth distributions. Minimum curvature technique for potential field data separation and the fast solution of forward and inverse problems for gravity fields in a dual interface model were applied to obtain the fluctuations in the Moho interface. The investigation uncovered significant contrasts between marine and terrestrial areas regarding both fault distribution and Moho characteristics: marine areas feature faults trending in both NNE—NE and WNW—NW directions, whereas terrestrial regions predominantly exhibit NNE—NE trending faults. Compared to terrestrial settings, marine faults tend to be shallower and show more intense late- stage activity. Sags in marine areas display shallower average Moho depths, thinner crustal thicknesses, and higher mean values for the sum of Moho stretching factors and crustal stretching factors relative to terrestrial sags. These findings indicate that marine areas have experienced greater tectonic deformation, creating favorable conditions for the formation of hydrocarbon- prone zones and hydrocarbon migration and accumulation. Conversely, terrestrial environments present less advantageous conditions, directly impacting the differential distribution of hydrocarbon enrichment within the basin. Consequently, the spatial distribution hydrocarbon resources in the Bohai Bay basin is tightly connected to the distribution of faults and fluctuations of the Moho interface. This research furnishes a scientific foundation for guiding further oil and gas exploration efforts in the basin.
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2025,99(5):1576-1588, DOI: 10.19762/j.cnki.dizhixuebao.2023458
Abstract:
The structural characteristics and evolution history of the eastern margin of Pamir Salient are of great significance to reveal the basin- mountain coupling relationship between the Pamir- West Kunlun orogenic belt and the Tarim basin, and to guide the exploration of oil and gas resources and earthquake disaster prevention in this region. Based on the detailed surface mapping and structural analysis of seismic profiles across key locations, the tectonic framework of the basin- range junction zone in the eastern margin of the Pamir Salient is constrained. The mapping data, field photos, seismic profiles and other data presented in this paper reveal that a dextral strike- slip fault system outcrops in the eastern margin of the Pamir Salient, and a buried compressional thrust belt develops in the adjacent basin, including the Qipan structural wedge and the Qimugen structural wedge. The growth strata of the Qipan structural wedge is located in the lower section of the Pliocene Artux Formation, while the growth strata of the Qimugen structural wedge is located at the top of the Pliocene Artux Formation, indicating that the thrust belt has been developed since the Pliocene. The eastern margin of the Pamir Salient experienced a tectonic transformation from a strike- slip tectonic system to a compressional tectonic system during the Pliocene. Before the Pliocene, deformation was accommodated by dextral strike- slip of the Wuyitake- Momoke transfer system (WMTS). Since the Pliocene, deformation in this area was dominated by eastward thrusting, and the strike- slip activity decreased.
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WANG Zhenyi, ZHANG Jin, LIU Jianfeng, QU Junfeng, ZHAO Heng, ZHANG Beihang, YANG Yaqi, ZHAO Shuo, WU Chunjiao, ZHENG Rongguo
2025,99(5):1589-1605, DOI: 10.19762/j.cnki.dizhixuebao.2024195
Abstract:
The distribution and formation age of Precambrian strata are crucial for understanding tectonic divisions, stratigraphic sequences, and fundamental geological research. The Gudongjing Group, traditionally considered the first sedimentary cover on the Precambrian basement of the Beishan Orogenic Belt, is mainly distributed in the Beishan area. However, its distribution and formation age in the northern Alxa area, north of the Enger Us ophiolitic mélange belt and south of the Sino- Mongolia border, have not been identified, which hinders the understanding of this geological body and the tectonic evolution of the northern Alxa. This study focuses on metasedimentary rocks of the Jixianian System in the Zhusileng area of the northern Alxa, in which field surveys, zircon geochronology, and Lu- Hf isotopic analyses were carried out. It is found that detrital zircon ages range from 2621 Ma to 291 Ma, mainly clustered in the Mesoproterozoic to Paleoproterozoic period. εHf(t) values are mainly concentrated in the range from 7. 5 to +5. 4, with crustal model ages TCDM plotting between 3. 29 Ga and 1. 69 Ga. These data indicate that the provenance underwent crustal remelting from the Neoarchaean to Early Paleoproterozoic and subsequent crustal growth during the mid- to late Paleoproterozoic. A maximum depositional age is constrained as 1240 Ma based on rock assemblages, metamorphism and deformation, and detrital zircon age spectra characteristics. Comparative analysis of the Jixianian System metasedimentary rocks in the Zhusileng area and the Gudongjing Group in the Beishan area reveals similarities in rock assemblages, ages, and Hf isotopic signatures. This suggests that the metasedimentary rocks from the Jixianian System can be classified as the Gudongjing Group. Based on previous work, it is confirmed that the northern Alxa, north of the Enger Us ophiolitic mélange belt, has a similar Precambrian basement, sedimentary cover, and age features of provenance to the Beishan Orogenic Belt. This suggests that the northern Alxa and the Beishan Orogenic Belt might experience a comparable Precambrian evolutionary history.
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XIA Jie, ZHANG Zunzun, LU Youyue, LI Jianfeng, FU Jianming, CHEN Xiqing, ZHOU Nianfeng
2025,99(5):1606-1631, DOI: 10.19762/j.cnki.dizhixuebao.2024131
Abstract:
Qitianling pluton is one of the most intensively researched plutons in the Nanling area. Despite this, its formation age, genetic types, and magmatic evolution process remain subjects of debate. This paper, based on detailed field investigations and U- Pb zircon dating by LA- ICP- MS, applies the theory of homologous magma evolution to divide Qitianling pluton into six lithofacies (mapping) units from early to late stages: Fine- to medium- grained porphyritic hornblende biotite monzogranite and granodiorite(ηγJ3a); medium- grained multi- porphyritic hornblende biotite monzogranite (ηγJ3b); medium- grained porphyritic (hornblende) biotite (syenogranite) monzogranite (ηγJ3c); coarse- to medium- grained porphyritic biotite (monzogranite) syenogranite (ζγJ3d); medium- to fine- grained oligoporphyritic biotite (monzogranite) syenogranite (ζγJ3e); and fine- to medium- grained biotite (monzogranite) syenogranite (ζγJ3f). U- Pb dating reveals that these units formed between 163 and 153 Ma, corresponding to the early Yanshanian of the Late Jurassic period. Geochemical analysis shows a gradual increase in SiO2 and K2 O content, a slight increase in Na2O, and a slight decrease in Al2O3. MnO, TiO2, FeO*, MgO, CaO, and P2O5 all decrease gradually. The REE distribution patterns exhibit a right- inclined pattern, with decreasing δEu and deepening negative Eu anomalies. Trace element analysis reveals enrichment in Rb, Th, U, and Nd and depletion in Ba, Sr, Nb, and Ti. The Rb/Sr and Sm/Nd ratios gradually increase, while the Nb/Ta and Zr/Hf ratios decrease, indicating progressive magma differentiation and evolution. Our findings suggest that the late- stage Qitianling granite (ζγJ3e, ζγJ3f) formed through 40%~60% fractional crystallization of the early magma (ηγJ3a). Zircon saturation temperatures range from 604 to 821℃, with an average of 760. 6℃. Combined with other data, we classify the Qitianling pluton as A2- type granite. Hf isotope analysis reveals εHf(t) values for the six lithofacies units ranging from 4. 5 to 10. 6, 4. 9 to 8. 9, 5. 2 to 7. 3, 5. 1 to 9. 4, 4. 6 to 10. 2, and 2. 7 to 8. 7, respectively. This indicates that the Qitianling pluton is primarily derived from the melting of metamorphic crustal rocks, with minor contributions from newly formed mantle material. The Hf isotope model ages for the second stage of the pluton cluster between 1658 and 1322 Ma, confirming that the source rocks separated from the mantle reservoir during the Mesoproterozoic. Therefore, the Qitianling pluton formed in an intracontinental extensional environment associated with the subduction of the Pacific plate.
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WEI Shaogang, TANG Juxing, SONG Yang, LI Baolong, LIU Zhibo, DONG Yujie, BAI Yutong, XIANG Shuo, LIU Si, BAI Yun
2025,99(5):1632-1655, DOI: 10.19762/j.cnki.dizhixuebao.2023082
Abstract:
This study investigates the petrogenesis of Mesozoic igneous rocks along the Bangong- Nujiang suture zone in Tibet, which is crucial for understanding the tectonic evolution of the Bangong- Nujiang Ocean. We focus on dacites from the Rena- Co area in the southern margin of Qiangtang, using zircon LA- ICP- MS U- Pb dating, Lu- Hf isotopic analysis, and comprehensive geochemical assessments. Our key findings are: ① The Rena- Co dacites were formed approximately 109. 6~109. 5 Ma, as determined by LA- ICP- MS zircon U- Pb dating. ② Geochemically, these rocks display medium- K calc- alkaline affinities with adakite- like characteristics. They exhibit high SiO2 (64. 79%~70. 37%), Al2O3(13. 81%~16. 13%), and Sr (517×10-6~598×10-6), coupled with low Y (8. 45×10-6~10. 7×10-6) and MgO (0. 68%~0. 88%), with Mg# values ranging from 23. 83 to 29. 65 and Sr/Y ratios from 53. 0 to 70. 8. ③ The dacites show strong enrichment in light rare earth elements and large ion lithophile elements (e. g. , Rb, U, Th, K, and Pb), but are depleted in heavy rare earth and high field strength elements (e. g. , Nb, Ta, and Ti), consistent with arc- type magmas generated in subduction zones. ④ Isotopically, they present initial 87Sr/86Sr ratios of 0. 705119~0. 705491, εNd(t) values from 0. 28 to +1. 25, and Nd model ages of 931~806 Ma. Their zircon εHf(t) values range from +3. 9 to +13. 1, indicating a young Hf- depleted mantle age of 924~332 Ma. The combined geochemical and isotopic data suggest the dacites likely originated from juvenile, thickened mafic lower continental crust, potentially incorporating partial melts of metasomatized peridotite and subduction- related fluids. Considering these findings and previous research, we suggest that the closure of the Bangong- Nujiang Ocean occurred post- early Cretaceous.
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TAO Jihua, ZHANG Zefeng, REN Zhi, XU Zhitian, SUN Junjie, CAO Jun, SU Xianyuan, LENG Chengbiao, XU Deru, YANG Yuegui
2025,99(5):1656-1675, DOI: 10.19762/j.cnki.dizhixuebao.2023386
Abstract:
The granite- hosted uranium deposits in South China are spatially associated with U- rich granites (U＞10×10-6). Understanding the petrogenesis of these uranium- bearing granites, with high U contents, is significant not only for formulating exploration strategies but also for gaining better insights into the mechanisms of U enrichment and mineralization. Here, we investigate the Xiazhuang granites,a representative suite of U- bearing granites with high U contents, using zircon U- Pb dating, zircon trace elementanalysis, and biotite and chlorite geochemistry to constrain their petrogenesis and relationship with uranium mineralization. LA- ICP- MS zircon U- Pb dating shows that the Xiazhuang granites were emplaced between 236 and 234 Ma. Their parental magmas were derived from the partial melting of F- rich Paleoproterozoic metasedimentary rocks and subsequently underwent a relatively high degree of magmatic differentiation. During magmatic evolution,oxygen fugacity decreased while U contents increased, leading to the formation of U- rich granites (U＞10×10-6) containing abundant U- rich accessory minerals such as uraninite, monazite, xenotime, and thorite. Our study suggests that these primary U- rich accessory minerals were later altered by hydrothermal fluids under relatively acidic and oxidizing conditions,likely in response to Yanshanian mafic magmatism. This alteration facilitated uranium leaching, providing a source for subsequent uranium mineralization.
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2025,99(5):1676-1689, DOI: 10.19762/j.cnki.dizhixuebao.2024118
Abstract:
This study analyzed the saturated and aromatic hydrocarbon fractions of two crude oil types from the Huangjue oilfield (Gaoyou sag) and the Wanglongzhuang oilfield (Jinhu sag) in the Subei basin using gas chromatography- mass spectrometry. We compared the distributions and compositions of long- chain n- alkylnaphthalene series and discussed the effects of biodegradation on these compounds in the different crude oils. Analysis of chain alkanes, including normal alkanes and phytane series, indicated slight biodegradation (levels 1~2 on the Peters and Moldowan (PM) scale) in some Wanglongzhuang oilfield samples. In contrast, some Huangjue oilfield samples exhibited slight to moderate biodegradation (levels 1~3 on the PM scale). Both 2- alkyl and 1- alkyl n- alkylnaphthalene series were detected in the aromatic hydrocarbon fractions of crude oils from both oilfields, with side chain carbon numbers ranging from C1 to nC26. While C0- 4 alkylnaphthalenes were dominant, the abundances of nC5- 26 alkylnaphthalene were relatively low. In unbiodegraded oils, the n- alkylnaphthalene series displayed a bimodal distribution without a clear predominance of odd or even carbon numbers. The relative abundance of 2- alkylnaphthalenes slightly exceeded that of 1- alkylnaphthalenes, with 2- alkyl- N/1- alkyl- N ratios ranging from 1.0 to 1.5, suggesting a similar biological origin. Slightly biodegraded (levels 1~2) oils showed complete n- alkylnaphthalene series, but with reduced relative abundance of nC11- 26 alkylnaphthalenes, weakening the bimodal pattern. In addition, 1- alkylnaphthalene abundances decreased, and 2- alkyl- N/1- alkyl- N ratios increased significantly compared to unbiodegraded oils, suggesting that n- alkylnaphthalenes are susceptible to biodegradation, similar to normal alkanes, with 1- alkylnaphthalenes being more vulnerable than 2- alkylnaphthalenes. In moderately biodegraded (level 3) oils, two series of n- alkylnaphthalenes became incomplete. nC4- 10 2- alkylnaphthalenes dominanted, while nC11- 26 1- alkylnaphthalenses nearly disappeared. The 2- alkyl- N/1- alkyl- N ratios increased rapidly and became irregular compared to unbiodegraded and slightly biodegraded oils. These findings suggest that n- alkylnaphthalenes exhibit biodegradation resistance similar to normal alkanes in the crude oils. However, unlike normal alkanes, higher molecular weight n- alkylnaphthalenes are more easily biodegraded than lower molecular weight components. Furthermore, 1- alkylnaphthalenes are more susceptible to biodegradation than 2- alkylnaphthalenes, the variation of their ratios reflects the extent of biodegradation.
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HE Wenyuan, BAI Xuefeng, ZHANG Jinyou, FU Xiuli, ZHAO Ying, ZHONG Jianhua, SUN Ningliang, SHENG Pengpeng
2025,99(5):1690-1710, DOI: 10.19762/j.cnki.dizhixuebao.2024062
Abstract:
The Qingshankou Formation shale and its associated light oil in the Gulong sag were studied through detailed core observation, thin section analysis, field emission scanning electron microscopy (FE- SEM), energy- dispersive X- ray spectroscopy (EDS), X- ray diffraction (XRD), and gas chromatography. The study revealed that the shale contains abundant diatoms and diatom flocs, which played a significant role in the formation of the light oil. EDS analysis indicates that the silica content of diatoms and diatom flocs is exceptionally high, the Si/Al ratio ranges from 2. 88 to 15. 20, with an average of 6. 65, significantly higher than the Si/Al ratio of illite (1. 82, based on measurements of modern clay). This suggests that a substantial portion of the silica exists as biosilica, specifically biological quartz formed by diatoms through polyamine- induced biomineralization. The biosilica particles are extremely small, with diameters of several microns, and represent the primary source of ultrafine quartz particles (diameter＜3. 9 μm) in the Qingshankou Formation shale of the Gulong sag. The bitumen and oil in the Qingshankou Formation shale are rich in N, with concentrations ranging from 7. 26% to 46. 40%. This indirectly confirms the presence of abundant diatoms, as diatoms are rich in polyamines. Polyamines and fatty acids in diatoms undergo diagenesis transformations to form hydrocarbons: polyamines contribute to the formation of gasoline, while fatty acids contribute to the formation of diesel oil in the Gulong shale light oil. Specifically, diatomaceous polyamines undergo denitration to form N- dimethylpropylamine, which further undergoes denitration and demethylation polymerization to produce alkanes below C12, with C8 as the main peak. Another prominent peak in the Gulong shale light oil is C15, which is formed by the decarboxylation and reduction of C16- dominated fatty acids derived from diatoms. Diatoms also contain a significant proportion of C16 fatty acids, accounting for 55.4% of the total fatty acids. The C15 alkane (the main peak of diesel oil) can be formed from C16 fatty acid after decarboxylation and hydrogenation. In addition, C16 fatty acids can also be converted into C16 and C17 alkanes (45. 57% of the light oil) through methylation and ethylation, respectively. Octadecenoic acid and eicosenic acid in diatoms account for about 33. 4% of the total fatty acids, closely matching the paraffin ratio (30. 70%) of octadecane, nonadecane, eicosane, and heneicosane in the shale oil of Qingshankou Formation. Both qualitative or quantitative analyses demonstrate a strong correspondence between the diesel peak in Gulong shale light oil and the carbon number and composition of modern diatom unsaturated fatty acids. This provides reliable evidence that the diesel fraction of Gulong light shale oil is formed by diatom fatty acids. Gulong shale light oil in Qingshankou Formation is a kind of fractionated light oil and not pyrolytic light oil.
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SUN Houyun, MA Feng, ZHU Xi, YU Mingxiao, CHEN Ziran, WEI Xiaofeng
2025,99(5):1711-1742, DOI: 10.19762/j.cnki.dizhixuebao.2023079
Abstract:
Geothermal fluids are a valuable source of hydrogeological and geochemical information, crucial for understanding deep circulation patterns, geothermal formation mechanisms, and guiding the development and utilization of geothermal resources. This study focuses on the Yanshan uplift- North China fault basin in northern Hebei Province. Based on regional geological and structural conditions, the geothermal system was zoned, and 91 water samples from geothermal wells and hot springs were collected. These samples were analyzed for their hydrochemical composition and isotopic characteristics to determine the recharge source, circulation path, temperature of the thermal reservoir, and the proportion of cold water mixed in during the upwelling of parent geothermal fluid in different geothermal geological zones. The results show that the study area can be divided into three geothermal geological zones: the Bashang Plateau mantle depression, the upper mantle ridge in the Yanshan platform fold belt, and the upper mantle uplift of the middle- northern North China rift depression basin. These zones were delineated based on geological structure and geothermal conditions. Correspondingly, the geologic models of geothermal systems in these zones are: a layered controlled system driven by deep depressions in volcanic sedimentary basins; a deep circulation and convection type associated with uplifted mountain faults, and a complex convection conduction type in intermountain sedimentary basins; and a complex convection and conduction hydrothermal type in buried mountains within sedimentary basins. From the Yanshan uplift to the North China fault basin, the hydrochemical evolution of geothermal fluids exhibits continuity at the macro- basin scale, with the deep hydrochemical field governed by groundwater runoff. Regionally, the hydrochemical types evolve from HCO3- Ca, HCO3- Na type to HCO3·SO4- Na, SO4- Na types, and then to Cl·SO4- Na, Cl- Na·Ca, and Cl- Na types, similar to large- scale basin groundwater systems. The temperature of the geothermal reservoir in the Bashang Plateau geothermal system ranges from 63. 44 to 137. 44℃, with fluid cycling depths of 1800 to 3770 m. The proportion of cold water mixed in during the upwelling of parent geothermal fluid is 51. 0% to 92. 2%. In the Yanshan platform fold belt, the geothermal reservoir temperature is 79. 26 to 148. 62℃, with thermal cycling depths of 2050 to 4817 m, and a cold water mixing proportion of 11. 5% to 94. 5%. The middle- northern North China rift depression basin exhibits a geothermal reservoir temperature of 71. 41 to 144. 49℃, thermal cycling depths of 2658. 2 to 3444. 6 m, and a cold water mixing proportion of 43. 0% to 97. 50%. The temperature of deep geothermal fluids in different zones, unaffected by cold shallow water mixing, is relatively consistent, ranging from 162 to 172℃. Areas where the depth of the earth' s mantle changed steeply, forming mantle scarps, where geological structures vary significantly in the deep mantle, and at the intersection zones of primary and secondary faults with high terrestrial heat flow values, are identified as potential “dessert areas” for high- temperature geothermal resources in the Yanshan uplift- North China fault basin of northern Hebei Province.
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WANG Zhuting, HU Shengbiao, ZHENG Libo, ZHANG Kesong, WANG Yibo, JIANG Guangzheng, ZHANG Chao
2025,99(5):1743-1754, DOI: 10.19762/j.cnki.dizhixuebao.2024144
Abstract:
The Dabie orogenic belt, located in the central part of China, is a product of the subduction collision between the North and South China Plates. The lack of basic geothermal measurement data has severely constrained the understanding of the geothermal field and lithospheric thermal- rheological structure in this area. This study uses temperature logging data from three boreholes, thermophysical measurements from 69 core samples, and geothermal gradient and heat flow values from surrounding areas to analyze the geothermal field and thermal- rheological structure of the Dabei orogenic belt in detail. Our results show that the Dabie orogenic belt exhibits a lower temperature field compared to surrounding structures. At a depth of 1000 m, the temperature is only 40. 0℃, significantly lower than the over 50. 0℃ observed in the southern North China basin, Tongbai orogenic belt, and the northern end of the Yangtze block. The geothermal gradient in the Dabie orogenic belt is generally lower than 26. 0 ℃/km, corresponding to a heat flow of approximately 50. 0 mW/m2. The abnormally high temperature and heat flow values in this area are mainly caused by the exceptionally high radiogenic heat production rate, averaging 7. 34 μW/m3. For the deep temperature and thermal structure of Dabie area, the temperature at the Moho depth is anomalously low, reaching only 359. 9℃. The thermal lithosphere thickness exceeds 200 km, with crustal and mantle heat flows of 30. 0 mW/m2 and 17. 5 mW/m2, respectively, and the ratio of these two values is 1. 71. The rheological structure exhibits an inverse correlation with the surface heat flow. Low heat flow values correspond to high lithospheric strength, reaching 2. 19×1014 N/m. Finally, the Dabie orogenic belt shows an extremely strong upper mantle, with a crust- to- mantle strength ratio of only 0. 04.
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LI Kefu, ZHU Chuanqing, MA Zhao, YANG Junsheng, SU Hong, XING Shudi
2025,99(5):1755-1772, DOI: 10.19762/j.cnki.dizhixuebao.2023085
Abstract:
The thermal properties of rocks are crucial for understanding the characteristics of geothermal fields and play an important role in studying geothermal fields and evaluating geothermal resources. In order to quantitatively understand the thermal properties of rocks and their impact on the geothermal field. This study systematically analyzes the thermophysical characteristics of rocks in Hainan Island through thermal property testing of outcrop samples. This provides new data and references for research in areas related to regional geothermal energy. Our results reveal that: ① Significant differences exist in the thermal properties of the three rock types in Hainan Island. Metamorphic rocks have the highest thermal conductivity (3. 16±1. 41 W/(m·K)), followed by sedimentary rocks (2. 53±0. 80 W/(m·K)), and igneous rocks (2. 40±0. 74 W/(m·K)). Conversely, igneous rocks display the highest heat generation rate (2. 68±1. 68 μW/m3), followed by sedimentary rocks (1. 90±0. 92 μW/m3), and metamorphic rocks (1. 10±0. 95 μW/m3). ② Porosity and thermal conductivity show a negative correlation, while density and thermal conductivity exhibit a positive correlation. Saturation correction of the rock samples significantly increases thermal conductivity values. Based on the specific situation of Hainan Island, we established an empirical formula for saturation correction applicable to the area. ③ U and Th are the main heat generating elements in rocks, both exhibiting a strong positive linear correlation with heat generation rate, while K shows a weaker correlation. ④ The varying thermal conductivity and heat generation rates among different strata lead to uneven temperature distribution, influencing the accumulation of strata temperature. Furthermore, temperature field simulations demonstrate differences in results when considering and neglecting rock saturation.
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LIN Xu, XIE Kejia, LIU Jing, SONG Ruizhi, LIU Haijin, LI Qingkang, RE Liping, ZHAO Shaopan
2025,99(5):1773-1791, DOI: 10.19762/j.cnki.dizhixuebao.2023071
Abstract:
Thegenesis of fluvial systems is closely related to tectonic activities and climate fluctuations. Consequently, studying the historical development of rivers is crucial for comprehending the evolutionary processes of the Earth. The formation age of the Yellow River, the largest river in northern China, remains a subject of significant controversy. To address this issue, our study focused on the Kaifeng depression, a crucial passage through which the Yellow River flows eastward to the sea. Through sedimentary drilling, paleomagnetic analysis, magnetic susceptibility measurements, grain size analysis, and detrital zircon U- Pb age dating, we obtained several significant results. The ZK02 drilling core penetrated Quaternary strata, while the bottom of the ZK04 core was dated to approximately the late Early Pleistocene. The sedimentary environment at ZK02 was primarily fluvial, whereas ZK04 exhibited a transition from fluvial and lacustrine deposition between 1. 0 Ma and 0. 15 Ma to loess deposition from 0. 15 Ma to the present. Detrital zircon U- Pb age analysis revealed that the main sediment source for ZK04 between 1. 0 Ma and 0. 15 Ma was the eastern Qinling Mountains. However, since 0. 15 Ma, sediment composition has been significantly influenced by loess derived from the Mangshan Mountains. In contrast, the sediment provenance of ZK02 is primarily connected to the evolution of the Yellow River. Material from the eastern Sanmen Gorge region has been present near Zhengzhou and the Yellow River Delta for at least 2. 2 Ma. The connection between the upper, middle, and lower reaches of the Yellow River occurred between 1. 9 Ma and 1. 6 Ma, mainly driven by the humid climate conditions in the region. During the Middle Pleistocene, the Yellow River basin experienced a period of coarser sedimentation between 0. 7 Ma and 0. 5 Ma, primarily attributed to climate transitions. This period contributed to the formation of a distribution pattern similar to the current configuration of the Yellow River and the Bohai Sea in North China. The presence of material from the Yellow River in ZK02 at 0. 15 Ma indicates that the main channel morphology of the Yellow River has not experienced significant oscillations after flowing through this region since 2. 2 Ma.
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ZHAO Long, JIANG Xiaowei, LI Yumei, LUO Yong, CUI Wenjun, TIAN Miaozhuang, WANG Shufang, TIAN Fang, XU Liang, LIU Yuanzhang, SHA Te, WANG Xinhui, QI Minghuan
2025,99(5):1792-1806, DOI: 10.19762/j.cnki.dizhixuebao.2023065
Abstract:
There is a growing concern regarding the environmental geological problems resulting from the over- exploitation of groundwater in the Beijing area. In response to this, active measures such as groundwater mining restrictions and artificial recharge have been implemented since 2010 to address the severe groundwater shortage in Beijing. To further analyze the impact of the implementation of various water management measures on regional groundwater and land subsidence since 2010, this paper analyzes the dynamic evolution characteristics of regional groundwater during the period of 2010~2020. It utilizes long- term monitoring data, quantifies the contribution of various measures in decelerating the decline of groundwater levels, and investigates the deformation characteristics of soil layers under groundwater level recovery. The results show that: ① From 2010 to 2020, the rate of decline of groundwater levels in the plains slowed down. However, groundwater levels continue to decline in most areas of the alluvial plains, while experiencing a significant rise in the root fan, middle fans, fan margins, and some areas of the alluvial plains. ② In the Chaobai River basin, the significant rise in groundwater levels at the root, middle, and margins of the alluvial fan can be attributed to the artificial recharge of the Chaobai River; groundwater extraction restrictions are the main factors contributing to the significant rise in groundwater levels in other areas of the Beijing Plain; and the continuous decline in groundwater levels in the alluvial plain is primarily driven by the increase in domestic water use. ③ From 2010 to 2020, the third and fourth aquifer groups exhibit the most significant deformation layers, with deformation rates ranging from 11. 07 to 12. 80 mm/a. On the other hand, the first and second aquifer layers show rebound, with a maximum cumulative rebound of 5. 6 mm. ④ The dilation of soil caused by the rise of groundwater levels results in two types of deformation in the soil layers. The first type is elastic deformation, which occurs synchronously with the change in groundwater level. The second type is residual deformation, which lags behind the change in groundwater level. The results of this paper provide valuable technical support for understanding the effectiveness of different water management measures. These insights can contribute to the development of regional groundwater resource management strategies and the accurate prevention and control of subsidence.
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FAN Qingkai, GUO Jinrui, GAO Min, WU Gaokui, WANG Yanyang
2025,99(5):1807-1818, DOI: 10.19762/j.cnki.dizhixuebao.2023459
Abstract:
The formation and evolution of passive continental margins are controlled by the vertical thermal- mechanical structure of pre- rifting lithosphere.In order to investigate its effect on lithospheric breakup time, faulting styles, sizes and morphology of passive continental margins, we define 3 comprehensive indexes as accumulated lithospheric yield stress (σe), average yield stress (σt) and crust- mantle rigid layers coupling degree (Coc), and reveal the influences through geodynamic numerical modelling.According to simulations, the thermal- mechanical structure of lithosphere plays a key role in controlling its rifting duration, a stronger pre- rifting lithosphere inevitably causes a longer lasting rifting, and on this basis, the decrease of the Coc will prolong this process.For the fully coupled lithosphere (Coc=1), upper crust usually breaks first, and will form symmetric margins through a ‘pure- shear’ mode.When Coc decreases, rigid layers of upper crust and upper mantle deforms separately, and an asymmetric continental margin will form by lateral migration of the rift center.Under such circumstances, the upper mantle with a relatively limited thickness will break first, while when a thick upper mantle develops, the upper crust will break first and lead to the exhumation of mantle rocks.In addition, a low Coc is necessary to generate large- scale passive continental margin basins with a broad and gentle geometry, and the lower Coc is, the greater the migration distance of the rift center and the conjugated margins are.Thickening of the crust will lead to the decreasing of Coc, which will also enlarge the scale of continental margins.Those understandings can be verified on the central segment of South Atlantic continental margins.
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ZHANG Yimi, XIONG Shengqing, HE Tao, WANG Hao, WANG Wanyin, WANG Lin
2025,99(5):1819-1831, DOI: 10.19762/j.cnki.dizhixuebao.2024006
Abstract:
Accurate interpretation of magnetic anomalies relies heavily on reduction- to- the- pole (RTP), component conversion, and tensor transformation. However, these processes often encounter instability issues in low- latitude regions, particularly near the magnetic equator. This study introduces a novel approach based on the equivalent source method to address this challenge. Our method performs RTP, component conversion, and tensor transformation of magnetic anomalies over curved surfaces in low- latitude regions. The proposed method leverages the physical relationship between the potential field and its source, employs parallel computation for the kernel function matrix, and establishes a system of linear equations. To enhance stability, we incorporate regularized sensitivity matrix weighting constraints into the objective function. The conjugate gradient method is then used to solve the objective function minimization problem, yielding the equivalent source physical property distribution. These results are subsequently substituted into relevant formulae to reconstruct or convert magnetic anomaly components and tensors, producing stable and highly accurate RTP, component, and tensor transformation results for any surface. Synthetic model tests demonstrate that this method achieves high computational accuracy for surface- observed magnetic anomalies in low- latitude regions, as well as its robustness against noise. Practical application to magnetic anomaly data from the Magur Islands study area, located at the boundary of the Caroline Plate and the Pacific Plate, has yielded highly satisfactory results.
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ZHANG Zhao, ZHANG Qunjia, LIU Lei, MEI Jiacheng
2025,99(5):1832-1847, DOI: 10.19762/j.cnki.dizhixuebao.2023460
Abstract:
Thermal infrared spectrum (TIR, 7~14 μm) has unparalleled advantages for the identification of rock- forming minerals,but currently there are few available satellite borne thermal infrared data sources, and the spatial and spectral resolution of the images is generally low. The thermal infrared spectrometer (TIS) carried by China' s Sustainable Development Scientific Satellite- 1 (SDGSAT- 1), which will be launched in 2021, is characterized by large bandwidth (300 km), high spatial resolution (30 m), and high detection sensitivity, and has a better application prospect in lithologic mapping. In this study, two kinds of thermal infrared images, ASTER and SDGSAT- 1, were selected from the East Junggar Kalamari region of Xinjiang to establish rock indices of mafic- ultramafic rocks, quartz- rich rocks, feldspar- rich rocks, and granitoid rocks, and combined with the results of the principal component analysis to analyze the distribution characteristics of the different rock types in the 2D and 3D feature spaces, and constructed the lithology identification models of the two kinds of data in the multi- dimensional spectral feature space, respectively. The results show that: ① The rock indices constructed from ASTER TIR and SDGSAT- 1 TIS data can effectively identify mafic- ultramafic rocks, quartz- rich rocks, feldspar- rich rocks and granites, with an overall accuracy of 95.16% and 98.02% for lithology identification, respectively; ② The multi- dimensional spectral feature space model constructed with two types of data also has good lithology recognition performance, with overall accuracy improved to 96. 78% and 99. 20%, respectively; ③ SDGSAT- 1 TIS has improved the accuracy of extracting mafic- ultramafic rocks by 13.26% compared to ASTER TIR, and has stronger recognition ability for rocks with smaller outcrops. It has great potential for application in lithological mapping.
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2025,99(5):202505090-202505090, DOI:
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2025,99(5):202505092-202505092, DOI:
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