Geological Journal of China Universities

Structural Characteristics of the Paleogene in the Northern Depression,Beibuwan Basin and Their Control on the Sedimentary Fill

ZHANG Qiang，WU Zhiping，YAN Shiyong，LIU Yiming，PING Mingming

2018, 24(6): 787.

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The Paleogene NE-NEE-trending faults control the structural framework of the northern depression, Beibuwan Basin, and
the NEE- and NW-trending faults control the development of the sub-structural units. As a result, a NEE-trending half-graben basin
was formed, which faulted in the northwestern of the basin and overlapped in the southeastern of the basin. The basin structures of
the Weixinan sag and the Haizhong sag show characteristics of complicated half-graben and simple half-graben, respectively, and the
Weixinan low uplift is controlled by a boundary fault. The Paleogene evolution of the study area can be divided into two stages, i.e.,
rifting during the depositional period from the Changliu Formation to the Wei-3 Member, and transitional from rifting to depression
during the depositional period from the Wei-2 Member to the Wei-1 Member. The rifting stage can be further subdivided into rifting
I episode (Changliu Formation to Liu-2 Member) and rifting II episode (Liu-1 Member to Wei-3 Member). The sedimentary features
of the study area have response to the basin structure and tectonic evolution. During the rifting I episode, the tectonic activity in the
study area was intense and the sediments covered the entire lake to form a basin, which developed various sedimentary facies
including nearshore subaqueous fan in steep slope, braided deltas in gentle slope, and lake and sublacustrine fan in subsag.
During the rifting II episode, the tectonic activity was subdued and the Weixinan low uplift was exposed to the surface which
separates the Weixinan sag from the Haizhong sag, and various sedimentary facies were formed including nearshore subaqueous fan
and fan deltas in steep slope, large braided deltas in gentle slope, and lake or sublacustrine fan in sub-sag. During the transitional
stage, the tectonic activity was weak, which was dominated by shallow lacutrine facies, and plenty of braided deltas were developed
in steep and gentle slopes, whereas the Weixinan low uplift was still exposed to the surface.

Factors Control the Development of Beach Bar in the Upper Fourth Member of the Paleogene Shahejie Formation in the Shubei Area of the Western Sag, Liaohe Basin

WANG Xiabin，JIANG Zaixing，HU Guangyi，FAN Tingen，WANG Xuying，LU Huan

2018, 24(6): 800.

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Beach bar is a new exploration field for the rifted basins in the Shubei area of the western sag, Liaohe Basin. In this paper,
the main controlling factors for the development of the beach bars in the study area were addressed. Results show the factors include
the palaeogeomorphology, palaeodepth of water body, palaeosource and palaeowind. These can be summarized as a control system of
tri-end members of “wind-source-basin”. The method to quantificationally reconstruct the four factors are proposed. The beach bar in
the study area is mainly developed in underwater uplifts. The favorable palaeodepth of water body is approximately 7 m. The
palaeosource comes from the transformation of delta, erosion of buried hill and reformation of coastline bedrock. The formation of the
beach bar is influenced by the north-south monsoon, the wind force reaching 8th grade. According to the controlling factors, the study
area can be divided into five zones, including coastal zone, buried-hill drapping zone, buried-hill draping zone, northern slope zone and
deep depression zone, of which the buried-hill draping zone is most favorable for the development of beach bar.

Formation Mechanism and Factors on the Accumulations of the Quaternary Biogenic Gas in the Nuobei Area in the Sanhu Depression, Qaidam Basin

LIN Peixian，ZHANG Xia，LIN Chunming，WANG Dahua，ZHANG Kuihua

2018, 24(6): 810.

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The Nuobei area is still in the initial stage of petroleum exploration in the east part of the Sanhu Depression, Qaidam Basin.
In this paper, the characteristics of the gas source rocks and the living environments of the methanogens in the Quaternary Qigequan
Formation from the Nuobei area have been studied, based on a vast amount of data for lithology paleontology, elemental geochemistry,
organic geochemistry etc. We discussed the sedimentary environments and geochemical conditions that influenced the formation of
biogenic gas, and then to predict the favorable exploration blocks. The results show that the gas source rocks in the Nuobei area contain
low organic matter content which are dominated by type Ⅲ kerogen and still at immature stage. The Qigequan Formation was deposited
under the low temperature and alkalinity, high salinity, and strong anoxic conditions, which were favorable for the formation of the gas
source rocks. The geochemical environment affected the flourish of the Methanogens, for instance, the low temperature and high salinity
inhibited the activities of the Methanogens, and the neutral-alkaline and strong reducibility environment were suitable for Methanogens
to flourish. The inhibition effect of salinity for the Methanogens is gradually strengthened from south to north as affected by surface
runoff. The biogenic gas accumulations in the Nuobei area were dominated by vertical gas migration. According to the above analyses,
we suggested that the Central Depression is the most favorable exploration area in the Nuobei area, followed by the North Slope. In
these areas, the widely developed lacustrine mudstones supplied nutrient for Methanogens, the weak compaction during the early
diagenetic stage provided large amounts of pores in reservoirs, and the thick sedimentary strata and gypsum deposition increased the
sealing capacity of the cap rock.

Characteristics and Significances of Trace Elements of Cambrian Crude oil in Tarim Basin

QIN Huan，YANG Tao，PAN Wenqing，CHEN Yongquan，ZHANG Baoshou

2018, 24(6): 822.

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Tarim Basin is the largest inland oil and gas basin in China. The main source rocks of oil in the basin are still controversial.
Oil-oil correlation can discern the relationship between crude oils and identify the geochemical characteristics of different types of
crude oil, which is an effective method to address this problem. The crude oil from the Awatage Formation of the Middle Cambrian and
the Xiaoerbulake Formation of the Lower Cambrian in Zhongshen-1 Well and Zhongshen-1C Well serve as important end-member oils
for oil-oil comparison. In this study, trace elements characteristics of the two kinds of Cambrian crude oil and a variety of light crude oil
were investigated, and results indicate the studied oil can be classified into two groups in terms of trace elements ratios including Cr/V,
Ni/Mn and Ni/Mo. The crude oil in group I have lower Cr/V ratios and higher Ni/Mn, Ni/Mo ratios than the crude oil in group II, which
may indicate that the source rocks for group I were deposited in a relatively more reducing environment. The classification results are
consistent with previous studies based on organic geochemistry, indicating that inorganic geochemical indicators can also be used as
indexes for crude oil classification, and have great potential for further application.

Formation Mechanism of Lower Palaeozoic Dolomites in the Carbonate Buried Hill of the Shaxibei Structural Belt, Bohai Sea

HUA Xiaoli，LI Huiyong，SUN Xijia，YU Haibo，SHI Panpan

2018, 24(6): 833.

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Based on core and thin-section observations, and analyses including scanning electron microscope, carbon, oxygen and
strontium stable isotopes, X-ray diffraction and trace elements, the geochemical characteristics and genetic mechanism of dolomites in
the carbonate buried hills of the Shaxibei structural belt (Bohai Bay Basin) were studied systematically. Results show that the dolomites
can be divided into four types, including micritic dolomite, granular dolomite, muddy/limy dolomite and saddle dolomite. They vary in
distinguished characteristics. The micritic dolomite and granular dolomite are formed under penecontemporaneous environments, as
implied by δ18O greater than -7‰, 87Sr/86Sr ratio in the range of 0.7090-0.7120 that is close to the seawater value, relatively high Na2O
content with value greater than 0.06%, low degree of order, and gypsums observed under thin section. In contrast, the muddy/limy
dolomite is formed under burial environments, as implied by fine crystalline structure, relatively negative δ18O values of -8‰--10‰,
87Sr/86Sr of 0.7120-0.7140, lower Na2O content, higher degree of order, and bright secondary-enlarged edge observed under
microscope. The saddle dolomite is of hydrothermal origin, as implied by medium and coarse crystalline structure, negative δ18O
values, high 87Sr/86Sr values, and diabase observed under microscope. Therefore, the dolomites in the study area were mainly of
penecontemporaneous and burial origins, and some may be formed under hydrothermal environments along faults. The burial
dolomitization and associated dissolution during the Ordovician increase the effective porosity of dolomite, which plays a postive role
in the formation of high quality reservoirs.

Major and Trace Elements of the Late Triassic Strata in the Helan Mountain: Constraints on the Provenance and Discussions on Different Methods

LI Meng，ZHAO Hongge，LI Wenhou，REN Zhanli，LIU Wenhang

2018, 24(6): 841.

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Systematic provenance analysis of the Late Triassic strata in the Helan Mountain area have been performed, based on the
geological conditions, thickness variation, and major and trace elements. Results show that sediments of the Late Triassic Yanchang
Formation in the Helan Mountain were mainly derived from its northwest, west, south and east in the early stage (the lower two
members) and from its northwest, west and south in the later stage (the upper three members). In this study, we systemically compare
the effectiveness of various major and trace elements as provenance indicators. Analysis of the major elements /UCC, main elements of
discriminant function diagram, trace elements /UCC, La/Th and Hf, Co/Th and La/Sc，Th/Sc and Zr/Sc discrimination diagrams, and
Th/U and Th discrimination diagram yields largely similar results in term of indicating provenance, though differences exists. Besides
the above indicators, analysis of lithological discriminant, CIA index, Eu anomaly, and Rb/Sr discrimination can also provide effective
information for provenance, and can be used as important indicator for judging the complex provenance compositions. This paper
provides details about the advantages and disadvantages of various methods for provenance analysis by major and trace elements and
draws some new insights, which provided a scientific basis for further improving provenance analysis.

Genesis of Alkali-Feldspar Granite at Dawangshan Tungsten Polymetallic Ore Concentration Area in Central Jiangxi Province: Constraints from LA-ICP-MS Zircon U-Pb Chronology and Geochemistry

YANG Qingkun，GUO Fusheng，YU Yushuai，ZHANG Xiaoliang，HUA Chen

2018, 24(6): 856.

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Fine-to medium-grained two-mica alkali-feldspar granites hosting tungsten and molybdenum minerals occur in the
Dawangshan tungsten polymetallic ore field in central Jiangxi Province. LA-ICP-MS U-Pb dating of zircon from Dawangshan
ore-bearing granites yields an age of 147.8±1.9 Ma, which indicates Late Jurassic time. The intrusion of the granites as evidenced by
the U-Pb age, coincided with the ore-forming of the quartz-vein type tungsten polymetallic deposits in central Jiangxi Province and
Nanling area. The granites are strongly peraluminous with high differentiation index (DI) and contain minor dark minerals. The granites
are enriched in alkali and silicon, and are depleted in calcium and magnesium. The REE partition curve shows a“seagull pattern”.
Their primitive-mantle normalized trace element spidergrams indicate depletions in Ba, Sr, Nb, Eu, P and Ti, and enrichment in Rb,
Th, U, Pb and K. In the diagram of εNd(t) vs. T, the granite samples are projected in the area between the Proterozoic crustal region of
South China and the chondrites mantle, suggesting a source from mantle source material. The results of the T2DM ages of granites (1.39~
1.66 Ga) are relatively younger than the average age of the crust in South China (1.7~1.8 Ga). These indicate that the formation of
granites likely involved a small amount of mantle materials. By combining the Sr-Yb and Q-Ab-Or diagrams as well as the calculated
zircon saturation temperatures, we conclude that the granites belong to high-differentiated peraluminous S-type granite and they were
formed in a post-orogenic extensional environment with low temperature, low pressure and water-rich conditions.

Study of Metallogenic Chronology, Mineralogy and Ore-Forming Process of the Superlarge Tungsten Deposits in Zhuxi, Jiangxi Province

YU Quan，CHEN Guohua，KANG Chuan

2018, 24(6): 872.

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The Zhuxi tungsten deposits are superlarge ore deposits， discovered in recent years in the eastern segment of Jiangnan
orogenic belt. The ore bodies of the Zhuxi deposits mainly occur in the skarn and skarnized marble at the contact zone between
Yanshan intrusive rocks and carbonate. To better understand the characteristics and genesis of Zhuxi tungsten deposits, we collected
both granites and skarns samples, and carried out research on petrology, mineralogy, geochemistry and chronology. The petrological
and geochemical characteristics of the biotite granites are calc-alkaline and peraluminous，enriched in Rb，U，Ta，and depleted in
Ba，Nb，Sr and Ti. The rare earth elements are characterized by the relatively low total content with a slightly rightly-dipping REE
pattern. Electron microprobe analyses reveal that the garnet is mainly composed of grossularite-andradite, and the pyroxene mainly
belongs to diopside-andradite series. Sheelite coexists with many F-rich minerals such as fluorite, apatite, titantites, and vesuvianite.
The F-enriched ore-forming fluid facilitates the transfer of W and the mineralization of scheelite in the Zhuxi deposits. The fluid
characteristic reflected by the REE distribution curve and Mo content variations of scheelite indicate that the mineralization
environment of zhuxi tungsten deposits changed from oxidation to reduction environment in the skarn stage. In-situ U-Pb dating of
titanite by LA-ICP-MS shows that titanite from the skarn sample yields a weighted mean 206Pb /238U age of 153±2 Ma. The main
mineralization event occured in the Yanshanian, which is consistent with the age of Zhuxi granites .

Geochronology, Geochemical Characteristics, and Geological Significance of the Rhyolite from Tuohe Basin, in Chifeng

JIANG Shan，WU Jianhua，WANG Changdong，ZHU Hongtao，ZHAO Bo，LIU Yang

2018, 24(6): 896.

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Tuohe volcanic basin is located in the Keshiketeng, Inner Mongolia, southern segment of the Great Xing'an Range. It belongs
to the Liaoyuan block，which is located between Xar Moron River-Changchun suture zone and Kangbao-Weichang-Chifeng-Kaiyuan
fault zone. The felsic volcanic rocks unconformably overlie the lower Permian Elitu Formation and are overlain by basalts in the basin.
The zircon SHRIMP U-Pb ages of rhyolites in the base indicate a 206Pb / 238U age of 158.5±1.3 Ma, suggesting that it is the product of
the early stage of Late Jurassic magmatism, belonging to the Xinmin Formation. The Tuohe rhyolites show high content of SiO2 A/CNK <
1.1， the content of standard mineral corundum is less than 1% , high ΣREE and the LREE are enriched with an negative Eu
abnormaly, (87Sr/86Sr)i=0.709244~0.713168, εNd(t) =-8.76~-8.42, TDM2=1656~1629 Ma, (206Pb/204Pb)i=17.271~17.326, (207Pb/204Pb) i =
15.401~15.413, (208Pb/204Pb) i =37.614~37.696, δ18OV-SMOW=4.1‰~4.5‰. The main elements, trace elements and Sr-Nd-Pb-O isotopes
geochemical characteristics of rhyolite in Tuohe basin are basically the same as those of rhyolite and rhyolite porphyry in Hongshanzi
Basin and Zhirui Basin, implying that the material sources of these basins are the same. This paper supports the notion that the material
sources are related to both the crust, especially the lower crust, and the mantle, especially the EMI-type mantle. On the diagram of (Yb
+ Ta)-Rb vs. Y-Nb, the rhyolite in the Tuohe Basin shows that it is an intra-plate tectonic setting. Comparing with the rock
assemblages, geological ages, isotopic composition, and uranium mineralization characteristics of the Hongshanzi basin, the
mineralization conditions in Tuohe basin are better. This study suggests that future exploration of uranium deposits in the basin should
be conducted with the guide from the model of Hongshanzi uranium-molybdenum deposits.

Water-Rock Interaction in Jiaojia Gold Deposits and Variations of the Ore-Forming Fluid

LIU Yazhou，WANG Enjing，WANG Sirui，GUO Guangjun，LI Dapeng，ZHANG Binglin

2018, 24(6): 907.

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On the basis of detailed analysis of the alteration-mineralization time series of the Jiaojia gold deposit, and the correlative
theory of chemical thermodynamics and chemical reaction, a solid phase titration model of water-rock interaction in Jiaojia gold deposit
is established. In addition, we discussed the precipitation order, existence form, migration behavior, and concentration change of
ore-forming fluid components by using numerical simulation of thermodynamics. we further discussed the relationship between
water-rock interaction and gold mineralization. The results show that the potash feldspathization occurred at the initial stage of the
reaction due to the K+ flow into the surrounding rocks from the fluid, the concentration of Fe2+ and Al3+ increased with the continuous
reduction of H+ concentration along with proceeding of the water-rock interaction. Sericite and quartz heavily precipitated with the
disappearance of potassium feldspar, followed by precipitation of the sulfide minerals. The content of SO42-, HS- and Fe2 + in the
ore-forming fluid has a great influence on the alteration mineral assemblage, the reduction of sulphate (SO42-) and the formation of the
same amount of HS-, which was accompanied by the precipitation of ferric minerals during the process of water-rock reaction. This may
be an important mechanism of sulfide precipitation in Jiaojia gold deposits. The continuous increase of pH value during the whole
reaction process is due to the exchange of Ca, K, Na and Mg in the original rock with H+ in the solution. Also, the increased pH value
reduces the solubility of gold, resulting in Au precipitation. These results provide a new basis for understanding the mineral
assemblage, sequence of formation, and the genetic mechanism of altered zonation

Characteristics and Formation Mechanism of Inverted Structures in Bongor Basin, Chad: Evidence from Seismic Profiles and Sandbox Simulation Experiments

WU Zhenyun，YIN Hongwei，WANG Wei，DU Yebo

2018, 24(6): 918.

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Based on the analysis of regional seismic profiles and sandbox simulation experiments, the characteristics and formation
mechanism of inverted structures in Chad Bongor basin are discussed and analyzed. The results show that: (1) there are three typical
inverted structures in Bongor basin, which are compressional inverted monocline structure, compressional inverted syncline structure
and compressional inverted anticline structure. Some inverted structures are the inverted fault related folds, which are mainly
developed in the high angle boundary fault zone and the basement Horst tectonic belt in the depression zone. The formation and
evolution of these structures are closely related to existing fault activities; The others are scattered flower anticline structures (looks
liking buckle folds) caused by the upper arch of the strata, which are mainly developed between the slope fault zone or the interior of
graben; (2) The syn-tectonic erosion has an important influence on the evolution of the basin inversion. The erosion promotes the
formation of inversion fold and structural traps in the deep strata, meanwhile, hinders or destroys the evolution of the inversion folds
and structural traps in the shallow strata.

The Discussion About the Property and Formation Mechanism of the Dashibei Fault in Hushan, Nanjing

LI Tian，XIE Guoai，WANG Guangkou，TIAN Rongsong，LI Fahao，Amirdin Arkin

2018, 24(6): 930.

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The Dashibei Fault in the Hushan region, Nanjing is located in northwest flank of the Dashibei syncline and exhibits as
normal fault in section. Based on the analysis of structural elements, including the faults and joints, and the study of tectonic stress
field in study region, together with field observation, we propose that the Dashibei Fault mainly present as right-lateral strike slip with
some degree of normal fault. The NE folds (Ningzhen mountain range), NW right strike-slip faults and NNW sinistral strike-slip faults
were formed due to the NW-SE tectonic stress during in the Indosinian. The NW right strike-slip fault displays false appearance of
normal fault in NE cross section，and thus as a typical teaching case of fault effect.

Monitoring of Soil Desiccation Cracking Process Using Electrical Resistivity Tomography

LUO Xiaowei，ZHANG Kuan，TANG Chaosheng，ZENG Hao，WANG Yue，TAN Yunzhi

2018, 24(6): 939.

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In order to investigate soil shrinkage and desiccation cracking process, one-dimensional desiccation cracking tests were
conducted on Xiashu clay and monitored using the electrical resistivity tomography (ERT) technique. During the test, saturated slurry
specimens are prepared and dried under a natural condition. The evolution of electrical resistivity of soil specimen is recorded during
the drying process. Moreover, the desiccation cracking mechanisms are analyzed by comparing desiccation crack patterns and electrical
resistivity images. Experimental results show that the electrical resistivity of soil specimen decreases slightly at the beginning of the
drying process. This is because volumetric shrinkage results in an increase in the contact area between soil particles and the double
layer thickness reduces. Thus, the electrical conductivity of double layer increases. With elapsed drying time, soil specimen becomes
unsaturated and the electrical resistivity transits into the increasing phase. When crack initiates, the electrical resistivity near the crack
increases significantly. Comparing the desiccation crack patterns and electrical resistivity images, it is found that there was a
consistency in terms of crack position and condition. Therefore, the ERT technique is an effective method to dynamic monitor the
development of desiccation cracks and particularly reliable to map their positions. It can be a proper technique for further study on soil
engineering properties under extreme drought climate.

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