Table of Content

20 August 2021, Volume 27 Issue 4

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Study of Chemical Weathering and CO₂ Consumption Rate of Granite in a Small Subtropical Watershed

XIAO Sa, ZHAO Yuqing, ZHANG Youkuan

2021, 27(4):  375-384.  DOI: 10.16108/j.issn1006-7493.2020026

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A small subtropical watershed in Shenzhen was selected to investigate granite weathering process and its CO₂ consumption rate. The rainwater, springs, runoff, granite, and saprolite in the watershed were sampled regularly and their major ions and trace elements were analyzed in the lab. Hydrochemical compositions and their sources of the water samples were explored along with the weathering extent and weathering trends of rock and saprolite samples. The chemical weathering rate and CO2 consumption rate of the granite were estimated based on the hydrometeorological data. The results showed that the spring and runoff were HCO₃-Na type, mainly owing to the silicate weathering and cation exchange reaction. The Chemical Index of Alteration (CIA) values of the rock samples were 47.15-57.47, while the saprolite samples have a stronger weathering extent with CIA values of 59.24-82.71. The A-CN-K diagram shows that Na, Ca was leached first in the early weathering, then was K leached, and Al was accumulated as the weathering strength increased. The average weathering rate of the granite is 14.40 m/Myr, and is mainly controlled by lithology, ion flux, and climate conditions. The rock weathering from atmospheric acid deposition accounts for 11.73% of the total weathering amount. The average CO₂ consumption rate is 0.59×106 mol/(km2 yr). The acid precipitation in the study area may weaken the consumption of atmospheric and soil CO₂ by the chemical weathering process.

Mechanism of Poly-phosphates Sorption by Boehmite: A ³¹P Solid-state NMR Study

LI Yongfang, REN Chao, ZHOU Qiang, LI Wei

2021, 27(4):  385-393.  DOI: 10.16108/j.issn1006-7493.2020012

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Poly-Phosphate (Poly-P) is a group of very important inorganic phosphates, which exists widely in natural systems. Studying of the transport and transformation of Poly-P is critically essential to understand the biogeochemical cycling of phosphorus. Sorption reactions at mineral-solution interface control the transport and transformation of elements. In this research, the widely distributed hydrated alumina, Boehmite, was selected as the adsorbent to explore the behavior and mechanism of Poly-P sorption, as a function of initial P concentration and pH. Under the experimental conditions, the amounts of the sorbed Poly-P increase with P
concentration, whereas decrease with increasing pH. To further understand the mechanisms, we adopted several technologies, such as XRD, SEM and ³¹P solid-state NMR to characterize our samples. The results of 31P solid-state NMR indicate the occurrence of both adsorption and hydrolysis. The P-O-P bond in the middle of the long chain was randomly broken, generating short-chain Poly-P and orthophosphate, both of which were adsorbed as inner-sphere complexes on the surface of Boehmite.



Zircon U-Pb Geochronology, Geochemical Characteristics of the Mao’erjie Granite Porphyry in Southwestern Hunan Province, and Its Geological Significance

ZHOU Weifa, LU Jianjun, ZHANG Qiang, ZHANG Rongqing, WU Jinwei

2021, 27(4):  394-407.  DOI: 10.16108/j.issn1006-7493.2020031

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Based on detailed studies on zircon U-Pb geochronology, whole-rock geochemical and Nd isotope compositions of the Mao’erjie granite porphyry in the northwestern Miao’ershan-Yuechengling area, the emplacement age, genetic type and source of the granite porphyry are discussed. LA-ICP-MS U-Pb dating of the zircons from three granite porphyry samples yielded weighted mean 206Pb/238U ages of 824.3±4.5 Ma, 825.4±4.1 Ma, and 826.8±4.8 Ma, respectively, indicating that the Mao’erjie granite porphyry was emplaced in the Neoproterozoic. It is peraluminous with high silica contents and is enriched in large ion lithophile elements (LILE) such as Cs, Rb, U and K, and high field-strength elements (HFSE) such as Th and Hf, but is relatively depleted in Ba, Sr and Ti. Its chondrite-normalized REE pattern is right-inclined and has obvious Eu negative anomaly (δEu=0.37-0.43). The εNd (t) values of the granite porphyry are from -6.3 to -8.7, and the TDM2 (Nd) values are from 2.00 to 2.20 Ga, indicating that the granite porphyry was formed by partial melting of old crust-derived basement material. Ten inherited zircon grains with U-Pb ages of 852-861 Ma were found in the three dated granite porphyry samples and yield a weighted average age of 856.3±7.4 Ma, implying the existence of ~856 Ma magmatic activity in the Miao’ershan-Yuechengling district. It can be speculated that ~856 Ma magmatic rocks was involved during the formation of the Mao’erjie granite porphyry.

Zircon U-Pb Chronology, Geological and Geochemical Characteristics of Metamorphosed Basic Rocks in the Middle Reaches of Lalingzaohuo, Qimantage Area of East Kunlun Mountains

WANG Panxi, GUO Feng, WANG Zhenning, FENG Naiqi

2021, 27(4):  408-421.  DOI: 10.16108/j.issn1006-7493.2020015

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The metamorphosed basic body in the middle reaches of Lalingzaohuo intruded into the gneiss of Baishahe formation of the Paleoproterozoic Jinshuikou group. The petrography, chronology and geochemistry of basic metamorphic rocks are investigated in this study. The protolith, nature of source region, tectonic environment, ages and geological significance of these rocks are discussed. The results show that the basic metamorphic rocks are plagioclase amphibolite, metamorphosed diabases and amphibolite. The protolith belongs to subalkalic series, including tholeiite series, calc-alkaline series and shoshonitic series rocks. The contents of silica and alkali are 44.04%-54.39%, 1.97%-6.53%, and Na₂O are more than K₂O. The contents of MgO, Fe₂O₃,

and TiO₂ are 5.01%-9.58%, 7.71%-13.46%, and 0.56%-1.49%, respectively. The average values of ΣREE is 83.60×10-6 and δEu values range from 0.89 to 1.55 with an average value of 1.14, showing slightly positive Eu anomaly. The chondrite-normalized REE distribution patterns show a relatively smooth slightly right inclined curve, which has the features of slightly enriched LREE and
slightly differentiated HREE. The rocks are clearly enriched in LILEs (e. g., Cs, Rb, Ba, K, Sr, U, Pb) and significantly depleted in HFSE (e. g., Nb, Ta, Zr), slightly depleted in P and Ti. Combining SIMS zircon U-Pb dating with rock geochemical and regional geological background, it is believed that the magmatic-metamorphic events in early Neoproterozoic (928±25 Ma), the end of early Cambrian (514±11 Ma), middle-late Ordovician (451±11 Ma), and early-middle Devonian (392±12 Ma) have been recorded in the amphibolite. The zircon ages of 928±25 Ma and 514±11 Ma represent the ages of captured zircons, the crystallization age of the protolith is 451±11 Ma, the metamorphism of the amphibolites occurred at 392±12 Ma. The protolith of basic metamorphic rocks in the middle reaches of Lalingzaohuo was product result of partial melting in lithosphere mantle ever dehydrating by subduction slab and should be formed in an island-arc environment.


Tectonic Evolution from Permian to Cretaceous in Western Guangxi and Its Relation with Sedimentary Bauxite

XU Jianqi, CHEN Youbin, PANG Baocheng, LI Xuesen, CHEN Tao, LIU Wang, YIN Benchun, LI Jialong, ZHOU Yequan, LU Guanghui, XU Haipeng, LIAN Lvxing, WANG Ze

2021, 27(4):  422-431.  DOI: 10.16108/j.issn1006-7493.2021024

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Western Guangxi, one of the most important source of bauxite ore deposit in China, is located in the Youjiang Basin, which is on the Yangtze Block of the South China Plate. In order to figure out the response of sedimentary bauxite to tectonic evolution from Late Paleozoic to Early Mesozoic in this area and to study about the influence on the ore forming process of bauxite deposit, the structure information that recorded by the bauxite ore deposit and the stratigraphic lithology in surrounding areas was analyzed from the perspective of ore geological characteristics and stratigraphy. The results show that the mineralization and transformation of sedimentary bauxite ore in western Guangxi is accompanied by regional tectonic movements. It provides favorable conditions for mineralization of bauxite ore deposit by crustal uplift and volcanic eruptions during the Dongwu Movement. Under the tectonic background settings of intracontinental deformation and compression during the Indosinian and Yanshanian movement in the South China Plate, the sedimentary bauxite was transformed, manifested as the shape changing and the spatial displacement of ore bodies.


Impacts of the Sedimentation and Diagenesis on Reservior Physical Property under the Control of Sequence: A Case Study of the Cretaceous Mishrif Formation, A Oilfield in the Middle East

LI Fengfeng, GUO Rui, SONG Shiqi

2021, 27(4):  432-443.  DOI: 10.16108/j.issn1006-7493.2020027

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Strong vertical heterogeneity of thick carbonate reservoirs that led to disproportionate production. To clarify the mechanism and distribution of reservoirs and interlayers, taking based on a case study in the Cretaceous Mishrif Formation of A oilfield in the Middle East, the effects of sedimentation and diagenesis on reservoir physical properties were studied under the control of sequence stratigraphy frameworks. The results showed that there were 6 quaternary sequences in the Mishrif Formation, and the sea level controlled the evolution of the sedimentary environment, and had an important impact on the early diagenetic process. On the basis of water energy and sedimentation diagenesis characteristics, it could be divided into 5 combinations (1) High-energy environment+constructive diagenesis. The non-selective dissolution of the shoal greatly improved the reservoir physical properties of the rock forming high-quality reservoirs. (2) High-energy environment+destructive diagenesis. Different degrees of cementation occurred on the shoal, reducing the physical properties of the rocks and forming poor reservoirs or physical interlayers. Which were highly hidden and difficult to be identified, increasing the reservoir heterogeneity. (3) Lowenergy environment+constructive diagenesis. Selective dissolution and dolomitization occurred in lagoons, open shallow seas, and the back shoal, effectively improving rock physical properties, and mainly forming poor reservoirs. (4) Low-energy environment +destructive diagenesis. Under humid climate conditions, rocks in lagoon were compacted and cemented, and carbonaceous mudstone deposited at the top of the sequence, forming an exposed cemented-carbonization zone. Under the alternating conditions of arid and humid climates, rocks in lagoon were subjected to multiple stages of weathering and leaching, forming dense cemented breccia. This configuration usually developed in low system tract, forming stable interlayers. (5) Low-energy environment+weak diagenesis. The original physical properties of the rocks were poor with high lime mud, and the subsequent diagenesis had not significantly improved the physical properties, and lithological interlayers were usually formed. Under the control of multi-stage sequences, the Mishrif Formation had continuously been changing the combination of sedimentation and diagenesis. The physical interlayers, mainly distributed in high-quality reservoirs, were thin, and small in scale and unstable. The lithological interlayers were associated with poor reservoirs. Lithological interlayers developed in different environments had different continuity. The tight cement zones were stable and the formation was divided into different development layer series of development.

Genetic Types and Accumulation of Crude Oil in the Central Inversion Zone in the Liaoxi Depression, Bohai Sea

TIAN Derui, NIU Chengmin, WANG Deying, GUO Tao, PAN Wenjing, GUO Longlong

2021, 27(4):  444-458.  DOI: 10.16108/j.issn1006-7493.2020093

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The central inversion zone of the Liaoxi Depression is the enrichment area of high quality light crude oil in the Liaodong Bay exploration area. However, the genetic types, source and accumulation of crude oil have not been systematically studied. Based on the analysis and comparison of the biomarkers, three sets of effective source rocks of the Shahejie Formation were distinguished. The first, third and fourth members of the Shahejie Formation, are obviously different in the source of organic matter and sedimentary environment. It is confirmed that plankton is the main component of organic matter in the three sets of source rocks. The first member of the Shahejie Formation (E2s1) has the highest plankton content and the least terrestrial organic matter input. The content of dinoflagellate in the fourth member of the Shahejie Formation (E2s4) was significantly higher than that in the first and third members of the Shahejie Formation (E2s1, E2s3). Both E2s3 and E2s4 source rocks were deposited in the freshwater and weakly alkaline reducing environment, and the E2s1 source rock was deposited in the brackish to saline alkaline strongly reducing environment. The crude oil found in the central inversion zone can be divided into three source-related types through hierarchical cluster analysis(HCA). The oil-source correlation results show that the type Ⅰ crude oil is the mixed oil originated from the E2s3 and E2s1 source rocks, which is mainly distributed in the middle block and the middle area of the east block on the central inversion zone. The type Ⅱ crude oil is originated from the E2s4 source rocks, which is distributed in the southern area of the east block on the central inversion zone. The type Ⅲ crude oil is the mixed oil originated from the E2s3 and E2s4 source rocks, which is mainly distributed in the west block and the northern area of the east block on the central inversion zone. On this basis,

the main controlling factors of hydrocarbon accumulation in the central inversion zone of the Liaoxi sag were analyzed. Oil and gas
reservoirs on the central inversion zone are controlled by multiple factors, including the distribution of effective source rocks and the math of fault and sand bodies.


Sand Enrichment Constrained by Structural Conversion Zone：the Pinghu Formation in the Kongqueting Area of the Pinghu Slope

LI Junjie, HOU Guowei, QIN Lanzhi, XIE Jingjing, MIAO Qing

2021, 27(4):  459-468.  DOI: 10.16108/j.issn1006-7493.2020029

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Structural conversion zone is an important field of oil and gas exploration and development, which is distributed in many types of compressional or extensional basins. Based on the theories of conversion zone, it is considered that there is a significant control on sand body convergence in the Syndepositional period. The Pinghu Formation in the Kongqueting area of the Pinghu Slope records the fault-depression transition. It is of significance for further exploration and development to clarify the control on the sand and facies in the structural transformation zone composed by the synsedimentary fault system in this period. Based on the interpretation of 3D seismic data and logging data, three types of parallel, collinear and overlapping transition zones in the Kongqueting area were clarified by comprehensive analyses of structural style, fault system and growth index. The tectonic conversion zone controls the formation of the paleogeomorphology between depressions and uplifts, and further controls the unloading and enrichment of sedimentary sand bodies in low-lying areas near the fault conversion point with a large accommodation space. These sand bodies developed into sedimentary microfacies, such as deluvial fan, front underwater fan and composite sand bar. Based on the matching relationship between paleogeomorphic characteristics, transformation zone types and sedimentary sand bodies, three sand-control models of flexured-parallel transfer belt, flying-geese-like collinear transfer belt and wriggling-transformed-overlapping transfer belt were determined. The former two have good sand accumulation effects. This study provides insights into subsequent exploration of tectonic lithologic reservoirs.

Coral Reef Geomorphology of Daoming Reefs in Nansha Islands

HU Xindi, ZHANG Yongzhan

2021, 27(4):  469-479.  DOI: 10.16108/j.issn1006-7493.2020033

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Coral reefs support one of the ecosystems responding to global climate change most rapidly, and part characteristic geomorphology of coral reefs is significant proxy to determine the sea level change. Currently, most of the published results are mainly based on qualitative researches, no matter the research on the modern geomorphology or the buried palaeogeomorphology of coral reefs, quantitative research is relatively scarce. Based on the analyses of shallow seismic profile data collected at Daoming Reefs (DR) in the northern area of the Nansha Islands from August to September in 2017 combined with high resolution Google Earth images, DR is a typical atoll with an island, four cays, seven drying reefs and several submerged reefs now. It could be seen that the form ratic of DR is 0.11, the compactness is approximately 0.52 with the ductility of 4.20, while the development index of reef flat is 0.30. It is obviously that DR is still a semi-open to quasi-enclosed atoll, still in the early development stage of reefs. The zoning of the underwater geomorphic units of DR indicates that its reef structure follows the Darwin’s atoll theory of ‘Upper Truncated Cone’. Furthermore, taking the erosion interfaces and various typical seismic facies buried under the reef flat and lagoon of DR into account, the features of its modern geomorphology and buried palaeogeomorphology of DR could be revealed. It also indicates that there are several stages of its geomorphologic evolution, including three main developing phases and two stagnated phases, While sea level rose in the postglacial period, it has two relatively stable phases at the water depth of 80-90 m and 50 - 60 m. The modern coral reef in DR began to grow in the early Holocene and developed continuously till now. To collect  the core samples at its out slope, reef flat and lagoon in DR, it would be helpful to set up the reliable chronology scale and the local curve of sea level rising, which would be important to reveal the geomorphologic evolution of the coral reefs in northern area of the Nansha Islands and its responses to sea level changes since the postglacial period further.

Discussion on Geological Characteristics and Landscaping Mechanism of Gemstone Cave in Fumin County, Central Yunnan

ZHOU Yuguo, ZHANG Fan, ZHOU Kun, ZHOU Chensu, WANG Yuchao, WANG Jian, FAN Kai

2021, 27(4):  480-488.  DOI: 10.16108/j.issn1006-7493.2020054

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The karst underground river cave landscape system in Gemstone Cave, Fumin County, Central Yunnan Province is moderate in scale with various karst landscapes in the cave, treasures (agates) in the cave, beautiful ecological environment, multiethnic religious culture and potential hot spring resources outside the cave and superior traffic location which makes the tourism elements cluster with high development value. According to the regional geological background of Gemstone Cave, this paper analyzes the evolution characteristics of regional geological history, summarizes the tourism geological characteristics of Gemstone Cave according to the field exploration results of Gemstone Cave, discusses the landscape mechanism of Gemstone Cave from five aspects: lithology, structure, hydrogeology, paleogeography and landscape age, points out that multiple faults (fracture zones) jointly control the spatial pattern of Gemstone Cave landscape. Karst started in the late Yanshan period and the Himalayan period was the main landscape period of the karst underground river cave system in Gemstone Cave. The origin of the gem (agate) produced in Gemstone Cave was preliminarily inferred and explained.



Geochemical Characteristics and Genesis of Geothermal Fluids in Zhefang Jade Pool (hot spring) Sedimentary Rock Area on the Eastern#br# Side of the Longling-Ruili Fault, West Yunnan

ZHANG Qidao

2021, 27(4):  489-500.  DOI: 10.16108/j.issn1006-7493.2020011

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The Zhefang Basin in Mang City of Yunnan Province is located in the middle-south section of the Sanjiang orogenic belt. There are many faults, strong magmatism and abundant geothermal resources in this area, but research on these different aspects of this area is low at present. In this study, a geological, geophysical, hydrogeological and hydrogeochemical investigation was carried out in the sedimentary rock area on the eastern side of the Longling-Ruili Fault. Water samples were collected and subjected to hydrochemical analysis, stable isotope measurements, and quantitative calculations. The silicon-enthalpy equation method and the silicon-enthalpy diagram method were used to quantitatively evaluate the cold-water mixing ratio in hot spring water, and to estimate hot water recharge elevation, recharge zone temperature, thermal storage temperature, cycle depth, and natural heat release of the hot spring. The calculated δ13CCO2 value of CO2 is -16.56‰. The sources of CO₂ involved in water-rock reaction are a mixture of both mantle and soil. Moreover, the water-rock reaction is mainly reflected as CO₂ entering the reservoir and the surrounding rock to produce HCO₃-. The genetic type of groundwater hydrochemical components is mainly constrained by rock weathering type. The chemical characteristics of geothermal fluid, the state of occurrence of geothermal resources, the mechanism of thermal cycle and the source of heat source in Zhefang jade pool were further identified. The formation and evolution of geothermal water in the study area were analyzed. The research results provide new support for geothermal research in Zhefang area and important guidance for the sustainable development and protection of tourism resources in the jade pool.