Table of Content

10 April 2018, Volume 32 Issue 02

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Sedimentology

Provenance of Late Triassic Xujiahe Formation in Huize Area, Upper Yangtze: Based on Heavy Mineral Analysis and Detrital Zircon U-Pb Dating

ZHANG Yingli, WANG Zongqi, JIA Xiaotong, CHEN Muyin

2018, 32(02):  213-226.  DOI: 10.19657/j.geoscience.1000-8527.2018.02.01

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The Late Triassic Xujiahe Formation in Huize area, Upper Yangtze consists of braided river and shallow lacustrine sandstones and mudstones. The direction of provenance restored by cross bedding mainly comes from the southeast. The heavy mineral assemblages of ilmenite, anatase, chromian spinel and magnetite indicate that they can be provided by magmatic rocks and part of mafic rocks. In this paper, the tourmaline and detrital zircon in Xujiahe sandstone are respectively tested and analyzed by electron microprobe analysis and detrital zircon LA-ICP-MS U-Pb dating. The chemical compositions of tourmaline are mainly dravite and schorl. They are mainly from metapelites and metapsammites, and a small amount of Li-poor granitoids and associated pegmatites and aplites. The detrital zircon U-Pb age spectrum shows that the source rocks of Xujiahe Formation mainly come from 257 to 362 Ma, 420 to 492 Ma, 782 to 876 Ma and 1,690 to 2,176 Ma rocks. The paleocurrent direction, heavy mineral assemblages, tourmaline electronic microprobe analysis and detrital zircon dating show that the source was mainly from the Dianqiangui Oldland. The 257 to 362 Ma source rocks are mainly Emeishan basalt and intrusive rocks; 420 to 492 Ma and 782 to 876 Ma ones are from granite and sandstones, and 1 690 to 2 176 Ma ones are from sandstones. Compared with the provenance of Feixianguan Formation, the source area of Xujiahe Formation is obviously different, which may be related to tectonic movement. Detrital zircon dating indicates that there existed Paleoproterozoic magmatism and Neoarchean crystalline basement. These data provide sedimentological evidence for tectonic evolution of the Upper Yangtze.

Analysis of the Sedimentary Environment in the North of Dongpu Depression During the Deposition of the Middle Section of the Third Member of the Shahejie Formation

LI Bei, LIU Chiyang, HUANG Lei, JIANG Feihu, GUO Pei, LU Kun

2018, 32(02):  227-239.  DOI: 10.19657/j.geoscience.1000-8527.2018.02.02

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The salt rocks and source rocks are extensively developed in the middle section of the third Member of Shahejie Formation in the North of Dongpu Depression and the two seemingly coexisting substances are intermixed here. In this period, the sedimentary characteristics of the study area were the continuous deposition of multi-salt rhythm and multi-layer hydrocarbon source rocks. Individual salt rhythms vary in thickness from a few meters to more than ten meters, the hydrocarbon source rocks have high organic matter abundance and the type is good. In the plane, the two are symbiotic with the sedimentation center of the lake basin, and in the vertical, high organic matter abundance, good kerogen type and high salinity formation have a better correspondence.Therefore, it has become an important research object for the restoration of paleoclimate and paleoenvironment. We studied the sedimentary environment of the middle section of the third Member of Shahejie Formation in the North of Dongpu Depression through petrology, paleontology, and the methods of Sr/Ba,B/Ga,(V+Ni+Mn),Fe/Mn,Sr/Cu,Mg/Ca,V/(V+Ni),as well as REE content and chlorine isotope. The results showed that the sedimentary environment of the middle section of the third Member of Shahejie Formation in the North of Depression was the reduction environment of the deep-water deposition, and the ancient salinity was a little high,which is semi-saltwater-saltwater deposition. The trace elements and the spore fossils indicate the environment of the middle section of the third Member of Shahejie Formation in the study area was warm and humid.

Elemental Geochemistry Characteristics of Mudstones from Benxi Formation to Lower Shihezi Formation in Southeastern Ordos Basin

CHEN Jing, HUANG Wenhui, HE Mingqian

2018, 32(02):  240-250.  DOI: 10.19657/j.geoscience.1000-8527.2018.02.03

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Based on the coring samples of mudstones in the southeastern Ordos Basin, this article focuses on the analysis of trace elements and rare earth elements in different horizons and studies the evolution of sedimentary environment and provenance from Benxi Formation to Lower Shihezi Formation. Core data show that from Benxi Formation to Lower Shihezi Formation the color of mudstones varies from deep to shallow and the reducibility of sedimentary environment changes from strong to weak. According to the analysis of environmental sensitive trace elements (such as V, Ni, Sr, Cu, etc.) and Ce_anom, from the Benxi Formation to the Lower Shihezi Formation, the sedimentary environment is generally the weak reducing-reducing environment, and the reducibility tends to decrease gradually; the climate is generally warm and humid with the wettability of climate gradually decreasing from bottom to top. The Benxi Formation is marine saline deposits, and the Shanxi Formation and Lower Shihezi Formation are dominated by continental fresh water deposits. The depth of water is shallow in Benxi Formation, more deeper in Shanxi Formation, which is more deeper than in Lower Shihezi Formation. The REE indexes analyses, such as δEu,(La/Yb)_N, Gd/Yb and so on, show that the sediments in the study area are mainly from upper crust rocks and there are two sources respectively from south and north. The northern provenance is from Alanshan-Yinshan ancient continent in the northern basin and the southern provenance is from the northern Qinling orogenic belt. Under the control of the south and north sedimentary origins, the value of Al₂O₃/CaO of the proximal sediments in the southern area is generally higher than that of the far-source sediment in the northern area.

Sedimentary Fabrics for the Stromatolitic Bioherm of the Cambrian Fengshan Formation in Chengde, Hebei

ZHANG Rui, ZHAO Xinwei, WANG Long

2018, 32(02):  251-259.  DOI: 10.19657/j.geoscience.1000-8527.2018.02.04

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The stromatolitic bioherm in the middle part of the Furongian Fengshan Formation at the Lutonggou section of Hebei Province was masked by a bed of stromatolite bioherm, and formed forced-regressive system tract within three-order sequences of drowning unconformity type, which suggested the stromatolite developed in a medium-high energy coastal sea. Macroscopically, this bioherm consisted dominantly of columnar stromatolite with the ambiguous lamination. Microscopically, the bioherm was characterized by dense micrite and microspar, and it was well seen in bioherm that involved peloids, benthic oolites and aggregate grains, all of which represented complicated microbial activities, thus it differed from the Precambrian stomatolites. Furthermore, more lithocodium-like colonies of calcified cyanobacteria remnants and some filamentous calcified cyanobacteria fossils developed in the dense micrite matrix of the stromatolitic bioherm, and it demonstrated the microbial mats forming stromatolite were composed of mats leading by cyanobacteria. In general, the complicated and special carbonate sedimentary fabrics within stromatolitic bioherm of the Fengshan Formation provided a precious geological case for the understanding of complicated microbial metabolism in the growth of stromatolites.

Depositional Environments of the Bedrock of Danxia Landform in Xiangshan Geopark of Jiangxi Province, SE China

LIU Xin, CHEN Liuqin, LI Xinmin, LI Yuliang

2018, 32(02):  260-269.  DOI: 10.19657/j.geoscience.1000-8527.2018.02.05

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Owing to the rise of tourism geoscience and the requirement of geoscience popularization, the research of redbeds and Danxia landform is attracting more and more attention. The Xiangshan Geopark of Guixi City in northeastern Jiangxi Province is featured by the prominent reddish cliffs. The bedrock of the Danxia landform is the conglomeratic strata of the Late Cretaceous Hekou Formation of the Guifeng Group, which is characterized by erosional bases, graded beddings and cross beddings. The sedimentary structures are useful to interpret depositional environments. A detailed centimeter-scale outcrop section was measured to describe lithofacies. Moreover, two conglomerate outcrops were chosen to perform pebble counting. In the measured 40-meter-thick stratigraphic column of the Hekou Formation, seven lithofacies were distinguished: normal graded conglomerate (facies A), inverse graded conglomerate (facies B), structureless conglomerate (facies C), parallel bedding conglomerate (facies D), cross bedding conglomerate (facies E), concentrated conglomerate (facies F), and sandstone (facies G). Clast sizes are mainly 2 cm to 5 cm, although it can range from 0.5 cm to 12.5 cm. Clasts are poorly rounded and moderately weathered. They are composed dominantly of tuff (58%-66.5%) with minor quartzite, granite, and sandstone, which is indicative of the dominant sediment derivation from the Early Cretaceous volcanic-intrusive complex outcropped along the southern margin of the basin. Based on the measured section and pebble counting, the alluvial fan depositional system is envisaged for the formation of the redbeds of the study area. The sediment increments were produced by the combination of faulting along the basin margin with episodic strong rainfalls and transported by braided streams on the alluvial fan lobes. As a result, the frequent interstratification of the conglomerate and sandstone beds, erosions, prevalent fining-upward units were preserved in the outcrops. In addition, under an overall arid climate regime during Late Cretaceous in Southeastern China, the stream-dominated alluvial fan systems were indicative of a climate change towards greater humidity which possibly resulted in abundant streams transporting coarse sediments to the basin area.

Tectonics

Study on the Cyclic Stratigraphy Activity of Nankou-Sunhe Fault in Beijing Plain Since Quaternary and Its Tectonic Significance

BAI Lingyan, LI Xiao, QIN Haomin, ZHANG Xiaoliang, ZHANG Yueze

2018, 32(02):  270-278.  DOI: 10.19657/j.geoscience.1000-8527.2018.02.06

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As one of buried faults, Nankou-Sunhe Fault is the only one northwest striking active fault in Beijing plain. In order to study its activity, this study analyzed characteristics of magnetic susceptibility and natural gamma ray for drillholes of ZK17 and ZK18, and the spectrum analysis was conducted on the magnetic susceptibility and natural gamma ray data of the two drillholes.ZK17 is located at the hanging wall and ZK18 is at the lower wall. Significant Milankovitch sedimentary cycles were respectively identified in the two drillholes, revealing that the Quaternary paleoclimate and deposition process in Beijing plain were controlled by orbital forcing. A continuous astronomical time scale was established by tuning the bandpass filtered-100ka-short eccentricity signal from initial age constrained time series to the astronomical solutions, thus it got a fine way to study the fault’s activity. Six phases which are relatively active have been identified by the comparative study on deposition rate of the two walls, and four of them are in Early Pleistocene and the active period is 0.4 Ma. The first and third phases are correspond to the B (2.6 Ma) and C(1.7 Ma) periods of Qingzang Movement; the activity characteristics in the Middle Pleistocene are related to Kunhuang Movement; so the characteristics of neotectonic movement in Beijing plain have a good relationship to Qingzang and Kunhuang movements.

Characteristics and Tectonic Stress Field of Joints in Xujiahe Formation of Jiudianya-sangmuchang Structure

ZHONG Cheng, QIN Qirong, WEI Zhihong, LI Hu, DENG Yi, HE Wei

2018, 32(02):  279-288.  DOI: 10.19657/j.geoscience.1000-8527.2018.02.07

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The study of paleotectonic stress field and division of tectonic stages in the Southeastern Sichuan, is one of the key research object for the analysis of the evolution of the Sichuan basin in recent years. It is of great significance to clarifying the relationship between tectonic evolution and paleo-stress field, and to further studying the stress evolution of the margin of Sichuan basin and guiding oil and gas exploration in the later period. Based on the analysis of the 452 group joints observed in the Xujiahe Formation of the Jiudianya-sangmuchang structure, using the structural geometrical analysis method and the apatite fission track and the acoustic emission experiment combined with the relevant regional tectonic evolution history, the phases and the tectonic stress field in the study area were analyzed. The results show that there are two sets of structure joints in this area, which are the joints formed by the two main tectonic stresses of nearly NW-SE direction and near NE-SW direction. This region has at least two or more tectonic movements which have a great influence on the area since the Triassic: the first phase is the middle and late period of the Yanshan Movement. The direction of the maximum principal axes of stresses is 133°, mainly forming tectonic system with a large scale in NE and NNE directions. The fracture is relatively developed. The second stage is the late stage of the Yanshan Movement-early Himalayan Movement. The direction of the principal axes of stresses is 51°, mainly forming structural system in NW direction with a small scale, but the fracture is still relatively developed.

Petrology

LA-ICP-MS Zircon U-Pb Dating,Hf Isotopic Composition and Ce⁴⁺/Ce³⁺ Characteristics of the Yanshanian Acid Magma in the Xidamingshan Cluster,Southeastern Margin of the Youjiang Fold Belt,Guangxi

XIAO Changhao, SHEN Yuke, WEI Changshan, SU Xiaokai, LE Xingwen, ZHANG Liang

2018, 32(02):  289-304.  DOI: 10.19657/j.geoscience.1000-8527.2018.02.08

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The Xidamingshan cluster is located along the southeastern margin of the Youjiang fold belt,South China. LA-ICP-MS zircon U-Pb dating constrains the crystallization of the quartz porphyry,monzogranite and biotite granite at (93.11±0.64) Ma,(92.92±0.69) Ma and (92.5±1.1) Ma,respectively.They have the same ages with each other within errors,suggesting they are magmatism coevally emplaced during the Later Cretaceous.The ε_Hf(t) values of the quartz porphyry vary from -18.4 to -1.2 with an average value of -7.1,with two-stage model Hf ages (T_DM2) of 1 236 to 2 326 Ma with an average value of 1 609 Ma. And the values of the monzogranites and biotite granite are from -19.4 to +0.3 with an average value of -5.6 and -12.2 to -3.6 with an average value of -6.7,correspond to two-stage model Hf ages (T_DM2) of 1 139 to 2 385 Ma and 1 386 to 1 933 Ma,respectively.It indicates that the source material was derived from the partial melting of the Paleo-and Mesoproterozoic crust.Comparing with Hf isotopic characteristics of the Yan-shanian granites in the boundary of the Youjiang fold belt,we suggest that all of the granites may have the same magma sources.The average Ce(Ⅳ)/Ce(Ⅲ) ratios of monzogranite and biotite granite are 23.65 and 33.76,respectively.It suggests that the Luowei concealed intrusion is with low oxygen fugacity.Combined the results from this study coupled with previous research,we proposed that the magmas formed in a regional extensional setting along the southeastern margin of the Youjiang fold belt in the South China during the Later Cretaceous.This caused the partial melting of the Paleo-and Mesoproterozoic crust due to the lithosphere relaxation and collapse,which meanwhile resulted in the large-scale magmatism in the Xidamingshan cluster.In the light of tectonic settings and geochronology,we deduct that the Yanshanian granites along the margin of the Youjiang fold belt are related to both Pacific and Tethyan tectonic domain.

Chronology,Geochemistry Characteristics and Petrogenesis of Wufenglou Lamprophyres in Northern Hebei, China

DONG Pengsheng, DONG Guochen, SUN Zhuanrong, LI Huawei, WANG Shushu, ZHAI Tianlei, WANG Weiqing, GENG Jianzhen

2018, 32(02):  305-315.  DOI: 10.19657/j.geoscience.1000-8527.2018.02.09

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Mesozoic lamprophyres with lithological minette are developed as dykes near Shouwangfen-Wufenglou in Yanshan region, North China Craton. Chemically, the lamprophyres are basic (SiO₂ from 48.25% to 51.47%), have high values of sodium (Na₂O/K₂O values from 1.13 to 2.31), alkali (K₂O+Na₂O values from 6.61% to 7.40%), Mg^# (67.84 to 71.34) and TiO₂(1.31% to 1.65%), belonging to high-Ti, Na-rich calc-alkaline lamprophyres. The rock is enriched in LREE, LILE and P, depleted in HREE and HFSE (Nb, Zr, Ta), and has no Eu anomalies. LA-ICP-MS zircon U-Pb dating got an age of (135.2±1.3)Ma, indicating that the lamprophyres were intruded at the same period of magmatic activity with the nearby granitic complex at Shouwangfen area in the Early Cretaceous. The ε_Hf(t) values of lamprophyres are ranging from -19.3 to -13.3, the two stage Hf model ages are much older than the age of diagenesis, indicating an enriched mantle source. The high values of Ba/Th (123.09 to 436.34) and Sr (915.4×10^-6 to 1 257×10^-6) imply the magma formation was effected by the subduction-zone fluids. The low values of Rb/Sr(0.02 to 0.11) and the high values of Ba/Rb(10.8 to 80.9) showed that the source contained amphibole. It is concluded that the lamprophyres were derived from partial melting (0.5% to 1.5%) of garnet-amphibole lherzolite of enriched mantle that formed by the interaction between sodium rich subduction fluid and mantle wedge, and the origin depth is 75 km to 100 km.

Zircon U-Pb Ages, Geochemical Characteristics and Tectonic Implications of Xigongka Granodiorite Around Gonghe Basin, West of Western Qinling Mountains

YANG Hanwen, SHEN Junfeng, WEI Liyong, ZHANG Zhen, LIU Mannian, FENG Boxin, ZHANG Luoning

2018, 32(02):  316-328.  DOI: 10.19657/j.geoscience.1000-8527.2018.02.10

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Xigongka granodiorite is located in Gonghe Basin, west of the Western Qinling mountains Orogenic Belt, and the main composition of rock is gray, fine-grained, block granodiorite. In this paper,we carried out the petrography, zircon U-Pb geochronology and geochemistry of Xigongka granodiorite. Zircon LA-ICP-MS U-Pb dating yielded a weighted mean age of (227.2±7.3) Ma, which is interpreted as the emplacement age of the Xikongka intrusion.The Xigongka intrusion is weakly peraluminous and high-K calc-alkaline with A/CNK values of 0.99-1.20 and high contents of SiO₂(69.86%-70.94%),K₂O(3.20%-4.08%),K₂O+Na₂O(5.61%-7.03%), and belongs to I-type granite. It is characterized by enrichment in LILE(such as K, Rb, Ba, Th, U), and by depletion in HFSE(such as Nb, Ta, Ti, P) with high LREE/HREE ratios of 11.04-13.13 and moderate negative Eu anomalies (δEu=0.72-0.84). The geochemical characteristics of the Xigongka granodiorite suggested that it was partial melting of crustal components. In combination with previous studies, the Xigongka intrusion was formed in the Late Triassic,which is consistent with the ages of other intrusions in the region. Therefore, they were all formed in the same tectonic environment of post-collision. This finding indicated that the west part of Western Qinling Orogen turned into the tectonic environment of post-collision in the Late Triassic and it also provided new constraints on the tectono-magmatic evolution of Gonghe Basin in Western Qinling Orogen.

Zircon U-Pb Ages and Geological Significance of Volcanic Rocks from Maoniushan Formation in the Northern Margin of Qaidam Basin

ZHANG Yaoling, NI Jinyu, SHEN Yanxu, WANG Chaoqun, GAO Wanli, HU Daogong

2018, 32(02):  329-334.  DOI: 10.19657/j.geoscience.1000-8527.2018.02.11

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The molasses of Maoniushan Formation rest unconformably on pre-Devonian strata and record the closure time of the Early Paleozoic ocean in the northern margin of Qaidam Basin. This research determinates zircon U-Pb isotopes from two rhyolite-tuff samples of volcanic rock member of upper Maomiushan Formation of Maoniushan mountain, northern margin of Qaidam Basin. The weighted mean ²⁰⁶Pb/²³⁸U ages of magmatic zircons from two samples are (396.5±2.4) Ma(n=17,MSWD=3.3)and (395.8±1.2) Ma(n=20,MSWD=1.1), interpreted as the formation time of the volcanic rocks. Combining past dating results about Maoniushan Formation of East Kunlun orogenic belt, we concluded that the formation time of the Maoniushan Formation around Qaidam Basin should be Late Silurian to Late Devonian, and the Caledonian movement of East Kunlun and northern margin of Qaidam Basin ended before Early Devonian instead of Late Devonian, as traditional thought.

Metallogenic Prediction and Evaluation

3D Metallogenic Prediction and Prediction Evaluation:A Case Study in Hongqigou-Shenshuitan Gold Deposit in the Eastern Kunlun Metallogenic Belt

HU Qiao, CHEN Jianping, TIAN Ye

2018, 32(02):  335-343.  DOI: 10.19657/j.geoscience.1000-8527.2018.02.12

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Hongqigou-Shenshuitan gold deposit belongs to a kind of tectonic altered rock type gold deposits in the eastern Kunlun metallogenic belt, and the orebodies are controlled by the fracture zone within mine district. Through an integrated analysis of geological setting and gold mineralization, the 3D digital mine is modeled. We have extracted the favorable range of controlling factors and constructed prospecting prediction model with the spatial analysis of GIS, and the prospecting information content method was used to synthesis metallogenic prediction. Moreover, from the three aspects of the optimal classification analysis, the accuracy analysis and the result analysis, we have done the research on the following aspects: the information content grading evaluation, the prospecting area grading evaluation, the data accuracy evaluation, validity evaluation on the prospecting prediction model and the positioning precision evaluation of the prospecting target area, and estimate of resource reserves and prospecting probabilistic assessment.In this study, 4 prospecting targets have already preliminarily delineated, and the estimated gold reserves are about 165 tons in this area. The study results show that the Hongqigou-Shenshuitan gold deposit has considerable prospecting potential and attention should be paid to the deep area and the border area of the known orebodies in the study area.

Geological-Geochemical Modeling and Deep Exploration of Jiaochong Au Deposit in Tongling District of Anhui Province

PANG Zong, WANG Gongwen, ZHANG Shuai, GUO Dongwei, CHEN Linjie, XIE Jiayu

2018, 32(02):  344-356.  DOI: 10.19657/j.geoscience.1000-8527.2018.02.13

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The Yangtze River’s middle and lower reaches are important Cu (Au) metallogenic belts in China. Tongling ore concentration area of Anhui Province is located in the belt and it is also a deep mineral exploration demonstration district in China. The study area (Jiaochong gold deposit) is located in a favorable prospecting zone at the southwest of Shizishan ore field in Tongling district. In this paper, the three-dimensional models of orebodies, Au-bearing rocks and lithologic strata in the study area are constructed using GOCAD modeling method, which is based on the middle section of -420 m to -820 m levels and drillhole dataset in Jiaochong gold deposit. Geological characteristics, the thermoelectricity features of pyrite as regularity of Au-bearing standard mineral were analyzed, and two prospecting targets were identified. The research results have an important reference for the deep mineral exploration and mining in the Yangtze River’s middle and lower reaches.

Petroleum Geology

Characteristics of the Feldspar Corrosion and Migration Enrichment of Al in the Clastic Reservoir of Dongying Depression

ZHANG Yongwang, LI Feng, QU Zhengyang

2018, 32(02):  357-363.  DOI: 10.19657/j.geoscience.1000-8527.2018.02.14

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The leaching and corrosion of feldspar as framework grain of sandstone is an important role of the formation of secondary porosity in diagenesis. Because the mobility of Al is the lowest in the corrosion of feldspar, Al can be migrated under strong hydrodynamic conditions of fluid. The kaolinite distribution and feldspar corrosion are controlled by migration and enrichment ability of Al. So it has important significance to study the migration of Al. In this paper, the diagenetic characteristics of reservoir in Dongying depression are analyzed through quantity thin section analysis, core observation, scanning electron microscope and X-ray powder diffraction. The feldspar corrosion of sandstone reservoir is general and the characteristics of migration and enrichment of Al are obvious in Dongying depression. We calculate the kaolinite contents through chemical reaction equation of the formation of kaolinite by plagioclase dissolution on well He 140(2,921.3 to 2,925.8 m). The difference between the theoretical calculation and the actual formation of kaolinite content shows that the migration and accumulation characteristics of Al in the relatively open system. Through the study of kaolinite distribution of the sandstone in the Niuzhuang sag, we find the enrichment of kaolinite occurs near the sand body at the interface of sandstone and mudstone. It shows that the Al as feldspar dissolution product has migrated and enriched under certain hydrodynamic conditions. The distribution of kaolinite from feldspar corrosion is controlled by the sandstone-mudstone boundary where the fluid activity is active and reservoir physical property in research area. Taking the formation of kaolinite and quartz from albite and potash feldspar as examples, we have calculated the volume changes before and after diagenesis. The results show that if the Al of the feldspar dissolution does not have a large scale migration, the nearly equal volume of secondary minerals after feldspar dissolution will precipitate and fill the pores. Petrographic criteria of secondary porosity alone are an insufficient measure that the rock has undergone leaching resulting in porosity enhancement. It only means redistributional secondary porosity, dissolution of framework grains and reservoir heterogeneity. The kaolinite content is not the mark of effective porosity on the sandstone reservoir. The reservoir physical property can be increased if the Al is moved out.

Detailed Study of Lake Fine Grained Deposition Characteristics: A Case Study from Chang 7 of Yanhe Section, Ordos Basin

LÜ Qiqi, LUO Shunshe, FU Jinhua, NIU Xiaobing, XU Liming, FENG Shengbin, LI Shixiang

2018, 32(02):  364-373.  DOI: 10.19657/j.geoscience.1000-8527.2018.02.15

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Field geological outcrops play a significant role in meticulous depiction of the internal structure of sedimentary deposits and establishing accurate underground geological model. This paper takes Chang 7 of Yanhe outcrop section in Ordos basin for instance, adopts the methods of petrology and field outcrop sedimentology, and detailedly analyses the lithofacies type, characteristies, vertical combination and sedimentary environment of lake fine grained sediments. The results show that Chang 7 of Yanhe outcrop section develops 9 types of lithofacies, including parallel bedding fine sandstone facies, flowing water crossbedding fine sandstone facies, wave forming crossbedding fine sandstone facies, ripple cross lamination siltstone facies, deformation bedding siltstone facies, horizontal bedding(argillaceous )siltstone facies, bulk mudstone facies, horizontal bedding(sandy)mudstone facies, big wavy-straight laminae shale facies. On the basis of combining regional geological characteristics, this paper regards the Chang 7 as distal sources meandering stream deltaic front and shallow-semi-deep lake sedimentary, further divided into 7 categories sedimentary units, among which underwater distributary channel and bar between branches developed well, subsea natural barrier, distal bar and sheet sand developed small scale, shallow-semi deep lake sedimentary only developed at the lower part of the Chang 7₂ subsegment, mouth bar developed hardly, only partial visible. Thorough research on the vertical distribution characteristics of every sedimentary unit, 4 vertical distribution forms of Ⅰ,Ⅱ, Ⅲ, Ⅳ are recognized. Ⅰ、Ⅱ combination mainly distributed at the research area Chang 7₁ and Chang 7₃ subsegments. Ⅲ、Ⅳ combination mainly distributed at the research area Chang 7₂ subsegments. Section facies analysis shows that during integral Chang 7 deposition period, a fine grained sedimentary sequence of thin to coarse was formed, showing meandering stream deltaic front sedimentary-shallow lake-semi-deep lake sedimentary-meanderiing stream deltaic front sedimentary.

Petroleum Geology and Exploration Potential of Key Basins in Bolivia

TIAN Naxin, JIANG Xiangqiang, GUO Jinrui, ZENG Yuxin

2018, 32(02):  374-384.  DOI: 10.19657/j.geoscience.1000-8527.2018.02.16

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Based on the analysis of the regional tectonic evolution and sedimentary filling characteristics in Bolivia, the differences in geological conditions of hydrocarbon accumulation in the basin, such as source rocks, reservoirs and cap rock are studied, and the exploration potential of basins is analyzed. The three major basins, Chaco, Beni and Madre De Dios basins in Bolivia, are superimposed basins developed on the basis of the Precambrian basement, and the basins are sequentially filled with the marine sedimentary sequence of the Paleo-generation craton margin, the Triassic Cretaceous rift marine facies-marine-continental transitional sedimentary sequence and foreland continental sedimentary sequence since Late Cretaceous. Comprehensive analysis of geological conditions of hydrocarbon accumulation shows Devonian main source rocks develope in 3 basins, Devonian-Carboniferous and Cretaceous sandstones are reservoirs, and Paleozoic carbonate rock and Paleogene mudstone are multiple sets of caprocks. Mature source rocks are mainly distributed in the thrust belt and the foredeep region, and the oil and gas must be migrated vertically and laterally so as to accumulate, which has the characteristics of late hydrocarbon generation and late accumulation. Low amplitude structural traps and stratigraphic traps in foredeep and slope areas of Madre De Dios basin and thrust fold belt of tectonic traps in Chaco and Beni basins are the main exploration targets.

Experimental Study of Hydrate

Experimental Study of Thermophysical Properties of Reservoirs Bearing Gas Hydrates in Qilian Mountain Permafrost

WAN Lihua, LIANG Deqing, LI Dongliang, GUAN Jin’an

2018, 32(02):  385-391.  DOI: 10.19657/j.geoscience.1000-8527.2018.02.17

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In this paper, the reservoir microstructures of mudstone and sandstone from Qilian Mountain permafrost were tested by electron microscopy. Under the microscope, the mudstone is composed of tiny and uniform flaky polygonal blocks, so that the hydrate immerses in the mudstone. The sandstone has dispersed pores inside, thus the hydrate exists in the sandstone by pore-type filling. The thermal conductivity and thermal diffusi-vity of reservoirs bearing methane hydrate were measured by transient plane heat source method. At the temperature range of about -9.41 to 9.41 ℃, the thermal conductivities of the dried mudstone and the mudstone bearing methane hydrate are 0.577-0.853 W·m^-1·K^-1 and 0.704-1.050 W·m^-1·K^-1, respectively. At the temperature range of about -8.11 to 9.28 ℃, the dried sandstone and the sandstone bearing methane hydrate have thermal conductivity of 0.828-1.271 W·m^-1·K^-1 and 3.850-4.555 W·m^-1·K^-1, respectively. At the temperature range of about -9.41 to 9.41 ℃, the thermal diffusivities of the dried mudstone, the mudstone bearing methane hydrate, the dried sandstone, and the sandstone bearing methane hydrate are 0.712-0.894 mm²·s^-1, 0.792-1.006 mm²·s^-1,1.198-1.674 mm²·s^-1, and 1.403-1.769 mm²·s^-1,respectively. The data show that it is a good means to explore the existence of hydrate by measuring the thermal conductivity of intervals bearing gas hydrate.

Remote Sensing Geology

Remote Sensing Monitoring on Mine of WorldView-2 Satellite: A Case Study of the Luobusa Area, Tibet

YANG Weiguang, ZHENG Youye, LIU Ting, WANG Chengsong

2018, 32(02):  392-397.  DOI: 10.19657/j.geoscience.1000-8527.2018.02.18

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Remote sensing monitoring of mine is an important survey work for exploitation of mineral resources, reorganization and standardization the order of mining industry by Ministry of Land and Resources in recent years. Chromitites mining area in Luobusa is the main chromitites production mine region in China.The exploitation intensity of mineral resources increases year by year due to the rapid development of national economy. In order to promote the sustainable development of the mining economy and environment, this article selects the WorldView-2 remote sensing data and profoundly analyzes remote sensing image characteristic of different surface features in the mine development process. Through field verification, we take advantage of WorldView-2 high spatial resolution remotely sensed data to establish the remote sensing interpretation keys of mine features so as to clarify development situation and ecological environment of this mineral area, and then conduct statistics and analysis of mining conditions and environment. Based on remote sensing monitoring of mine, reasonable suggestions about mine environmental recovery are given. Results show that WorldView-2 are with rich information and high precision of interpretation due to its high spatial resolution, panchromatic and eight multi-spectral bands, can obtain good effect in the remote sensing monitoring.

Geophysics

Three-dimensional Modeling of Controlled Source Audio Magnetotelluric Data with Topography

ZHONG Sumei, LIN Changhong, XIE Yuchun

2018, 32(02):  398-405.  DOI: 10.19657/j.geoscience.1000-8527.2018.02.19

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The topography has a strong effect on the controlled source audio magnetotelluric (CSAMT) data, therefore, the topography should be considered when interpreting the CSAMT data. The real subsurface geolo-gical structure and the topography of the surface are usually more complex and are three-dimensional spaces in most cases. Based on the three-dimensional finite-difference CSAMT modeling algorithm for flat surface, this paper presents a new method to calculate the total electric field at the air-earth interface with topography from the total magnetic fields at subsurface staggered sampling points, modeling the three-dimensional CSAMT responses on topography. In the new algorithm, the pseudo-delta function is used to replace the source to directly calculate the total field, avoiding the limitation of selecting the appropriate background resistivity structure under complex geological structure conditions when the total field is separated into the background field and the secondary field. In order to simulate the total field directly, this study used the new boundary condition of the three-dimensional forward equation in the three-dimensional CSAMT modeling algorithm with topography. The correctness and validity of the algorithm are verified by comparing the response results obtained from the two models (the flat surface model with 3D anomaly and the three-dimensional trapezoidal-hill model) with the results of the previous algorithms.

Inversion Method Based on High-resolution Waveform and Its Application on Predicting Sweet Spots: An Example from Shale Gas Reservoirs in Jiaoshiba Area of Sichuan Basin

GUO Peng, YUAN Yijun, LIU Xiwu, ZHANG Yuanyin, WU Xuemin, LI Hong

2018, 32(02):  406-414.  DOI: 10.19657/j.geoscience.1000-8527.2018.02.20

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The resolution of the conventional post-stack sparse pulse inversion method is low, and the traditional geostatistical inversion method also lacks the lateral geological significance. For these limitations, this paper proposed an inversion method based on high-resolution waveforms. This inversion method was employed to portray the distribution profile of wave impedance of the thin shale reservoir on Longmaxi Formation in Jiaoshiba area of Sichuan Basin, and to describe the plane distribution profile of thickness of high quality shale reservoirs in time domain. In the performance for random-well detection on the distribution profile of wave impedance in target reservoirs, the accuracy of this method had doubled comparing with the conventional post-stack sparse pulse inversion method. This inversion method was further applied to simulate the distribution profile of TOC in the target reservoir, and the results laid a foundation for the later ‘sweet spots’ evaluation and fine evaluation of shale reservoirs.