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2002 Vol. 13, No. 3

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Ordovician Graptolite Rhabdosome Complication and Its Implications on Sea Level Changes
Chuanshang Wang, Xiaofeng Wang, Xiaohong Chen
2002, 12(3): 203-206.

A total of four times of rhabdosome complication events, i. e., the lateralbranching of graptolite stipes during the Late Middle Ordovician, the secondary branching ofgraptolite stipes at the earliest Upper Ordovician, the early Qiantangjiangian of Upper Ordovicianand the middle Qian-tangjiangian, respectively, is discussed in this paper. These events and otheradaptation events demonstrate close relationships between a diverse graptolite fauna and sea levelchanges, and consequently can be employed to study sea level fluctuations. It is safe to concludethat the complication of rhabdosome started at the maximum flooding surface (MFS) and terminated atthe beginning of regression.

Reexamination of Radiolarian Biostratigraphy in Permian in Pelagic Chert Sequences at Dachongling Section, South China
Dongying Sun, Wenchen Xia, Dongjie Liu
2002, 12(3): 207-214.

Permian radiolarian biostratigraphy was reexamined in the bedded chert section in Qinzhou area of southeast Guangxi Zhuang Autonomous Region, South China. On the basis of the analyses of characteristic radiolarian composition, six radiolarian zones are recognized, namely, Pseudoalbaillella longtanensis Zone, Pseudoalbaillella globosa Zone, Follicucullus monacanthus Zone, Follicucullus scholasticus Zone, Follicucullus charveti Zone and Neoalbaillella ornithoformis Zone, in ascending order. Correlation of these radiolarian zones with those in Japan is presented. The Neoalbaillella ornithoformis Zone was firstly discovered in Dachongling Section, which may indicate that pelagic chert of the late Permian existed there, according to the co occurring conodonts.

Guanling Biota: A Rare Biota in Sea Early Late Triassic
Shangyan Wang, Yangeng Wang, Liting Wang, Gongzheng Yin
2002, 12(3): 215-216.

Guanling biota has been found at the bottom of Wayao Formation of UpperTriassic (Carn-ic stage) near Xinpu town, Guanling County, Guizhou Province, China. There are a lotof crinoids and marine reptiles, which is a characteristic of Guanling biota, including ammonites, bivalve, brachiopod, fish, conodont and plant. These fossils are featured not only with the largequantity, but also with their extraordinary perfect forms. This paper explores the meaning, geological background, present situation of study and scientific significance of Guanling biota.

Cenozoic Volcanism in South China Sea and Its Vicinity and South China Sea Spreading
Hailing Zhao, Jinfu Deng, Kaiming Li, Yongjun Di, Junji Yu, Jianhua Zhao, Yonghua Li
2002, 12(3): 217-224.

The rock series, rock types and Sr Nd isotopic dating of the Cenozoic volcanic rocks in the South China Sea are similar to those in its vicinity. On the basis of the spreading age of the South China Sea, the Cenozoic volcanic rocks are divided into three stages: the pre spreading stage, the spreading stage and the post spreading stage. The deep process characteristics of the asthenosphere and lithosphere may be inferred from the study on primary basaltic magma. The top layers of the asthenosphere both in the spreading stage and in the pre spreading stage are closer to the earth surface than that in the post spreading stage. From the pre spreading stage to the spreading stage, the top layer of the asthenosphere decreased in depth, while the amount of interstitial partial melts increased. The evolution of the primary basaltic magma shows a progressive evolution sequence of the rifting volcanism and a faster lithospheric spreading velocity. From the spreading stage to the post spreading stage, the top layer of the asthenosphere gradually increased in depth, but the amount of interstitial partial melts decreased. The evolution of primary basaltic magma shows a retrogressive evolution sequence of the rifting volcanism and a gradual decrease in the lithospheric spreading velocity. The depth recognized by the study on the Cenozoic volcanism demonstrates the deep environment for the formation and evolution of the South China Sea.

Study on Mineralization Age of Xiaoban Gold Deposit, Fujian Province
Bailin Chen, Ganguo Wu, Da Zhang, Rensheng Huang, Jianshe Wu
2002, 12(3): 225-233.

The Xiaoban gold deposit is a large size deposit recently found in middle area of Fujian Province. It belongs to magmatic hydrothermal type occurred in Mayuan Group metamorphic rocks of Middle Proterozoic and is controlled by low angle fault (detachment) structures. The contents of Au in Mayuan Group metamorphic rocks, Caledonian Indosinian deformed granite and early Yanshanian granite are higher with Au enrichment coefficient of 2.06-5.68, 5.11 and 6.67 than those in other geological bodies. And the higher enrichment coefficients (> 2) of Ag, S, Sn and Te are similar to those of gold ore. Meanwhile, the distribution of Au in Mayuan Group metamorphic rocks and early Yanshanian granite with a low D-value (0.58 and 0.67) is favorable to gold mineralization. REE characteristics of gold ore, ratios of (LREE/HREE), (La/Sm)n, (Yb/Lu)n, (La/Tb)n and (Sm/Nd)n are similar to Mayuan Group metamorphic rocks, only non or little normal Eu abnormal of ore is dissimilar to metamorphic rocks. The δ(34S) of the gold ore, with a high homogenization, is (-4.7×10-3) - (-2.7×10-3). The study of inclusion indicates 180-249 ℃ of mineralization temperature, 3.69 %-11.81 % of salinities and 0.869-0.991 g/cm 3 of densities of mineralization fluid. Based on hydrogen and oxygen isotope (δ(18O) =11.0×10-3 -11.7×10-3, δ (D) = (-48×10-3) - (-62×10-3)) and initial w(87Sr)/w(86Sr)=0.715, combining to the analysis of geological history, regional metamorphism and magamtic activity, the authors confirm that the source for the ore fluid was mainly from magmatic, partly from metamorphic water, and with a little influence of meteoric water. Isotopic dating made on Rb Sr isochron age of 182 Ma, by using alteration minerals of gold ores from the deposit, indicates that the mineralization occurs in early Yanshanian epoch. This is close to the age of 187 Ma of the Anchun magmatite with a similar alteration and gold mineralization to the Xiaoban gold deposit. The age of early Yanshanian epoch of the Xiaoban gold is indentical with the characteristics of southern China gold metallogenic belt and the geotectonic evolution of the transition from paleo Asian system and paleo Tethyan system to paleo Pacific active continental margin in eastern Asia.

Study of Sand Dunes and Their Effect on Desertification of Cultivated Lands in Shaanxi Province, China Using Remote Sensing Techniques
Jabbar Mushtak Talib, Guangdao Hu, Jianguo Chen
2002, 12(3): 234-239.

About half of the arid and semi arid lands in the world are deserts that comprise various types of aeolian sand dunes deposits. In Shaanxi Province, aeolian sand dunes cover considerable areas of the Yulin desert and northern Jinbian. Sand dunes are moving in the main wind direction and converting some agricultural area to wasteland. Remote sensing of sand dunes helps in the understanding of aeolian process and desertification. Remote sensing data combined with field studies are valuable in studying sand dunes, regional aeolian depositional history. In particular, active and inactive sand dunes of the north Shaanxi Province were studied using remote sensing and geographic information system. In this study, we describe the Landsat thematic mapper (TM) images, covering north Shaanxi Province, which were used to study the distribution, shape, size, trends, density and movement of sand dunes and their effect on desertification of cultivated lands. Estimation was made depending on soil erodibility factor (Ⅰ) and local climatic factor (C) during the period (June to September). The result indicates that soil erosion caused sand drift of 8.957 5, 7.03 ton for Yulin and Jinbian, respectively. The mean sand dunes movement rate were 4.37, 3.11 m, whereas, monthly sand dune advance rate were 1.092 5, 0.777 5 m, for the two locations, respectively. The study reveals that cultivated lands extended obliquely to the direction of sand dune movement are extremely affected, while other segments that extend parallel to the direction of the movement are not affected. Accordingly the north Shaanxi Province was divided into areas of different classes of potential risk. Moreover, blown sands and sand movement from neighboring highlands also affect the area of western desert.

Thermodynamic Modeling of Fluid-Bearing Natural Gas Inclusions for Geothermometer and Geobarometer of Overpressured Environments in Qiongdongnan Basin, South China Sea
Honghan Chen, Shuzhen Yao, Jiahao Wang, Chunquan Li
2002, 12(3): 240-247.

It is a very difficult problem to directly determine fluid pressure during hydrocarbon migration and accumulation in sedimentary basins. pVt modeling of coupling hydrocarbon fluid inclusion of its coeval aqueous fluid inclusion provides a powerful tool for establishing the relationship of formation pressure evolution with time. Homogenization temperature of fluid inclusion can routinely be measured under microthermometric microscopy. Crushing technique has been employed to obtain the composition of fluid inclusions, and the commercial software VTFLINC easily and rapidly completes the construction of p-t phase diagram. The minimum trapping pressure of hydrocarbon fluid inclusion would be then determined in the p-t space. In this paper, three samples of YC21 1 1 and YC21 1 4 wells at YC21 1 structural closure, Qiongdongnan basin, South China Sea, were selected for the pVt modeling practice, and the formation pressure coefficient (equals to fluid pressure/hydrostatic pressure) changing trend with time has primarily been established. The modeling results also indicate that the reservoirs of Lingshui and Yacheng formations in YC21 1 structure are within a very high potential system and would have undergone a discharging of thermal fluids through top seal rupture, which depicts that there is a very high risk for natural gas exploration in this area.

Development Plan of East Unity Oil Field, Sudan, Using Reservoir Simulation Study
Tagwa A Musa, Ahmed A Ibrahim, Zhenliang Guan
2002, 12(3): 248-251.

Simulation study was applied in the development planning of East Unity oilfield, Sudan. A grid consisting of 2 000 cells was constructed. A major challenge of the study wasto evolve a full field development and future reservoir management strategy that would ensuremaximum recovery of oil based on well Un51. Simulation shows that Un51 as injection well inAradiebaC would yield better oil recovery than to be production well.

Primary Study on Quantitative Reconstruction of Middle-Late Eocene Climate in Jianghan Basin
Guobang Tong, Zhiming Liu, Mianping Zheng, Weiming Wang
2002, 12(3): 252-259.

This paper reports our primary effort in the quantitative reconstruction of paleoclimate based on the thrine in phytoecology of the affinity parent plants in the stratigraphic pollen records. The Eocene pollen data come from our former study on the Mingjia borehole 1 in the Jianghan basin. The fluctuating trend in the parameter curve of climate shows that the climate in the Middle Eocene in the Jianghan basin was more or less comparable with that of the present 22°-26°N, characteristic of a humid, semi humid central southern subtropical climate. The annual temperature at that time dropped by 1 ℃-4 ℃ in the Late Eocene, approximately equal to that of the present 23°-28°N of northern central subtropical climate. However, the climate composite at that time, characterized by higher temperature, small annual range and big fluctuation in precipitation, was quite different from the present one. The average temperature in January in the Middle Eocene, higher than that of today, ranged between 5 ℃ and 9 ℃, indicating that no effect of winter monsoon occurred in the Middle Eocene, though such an effect may have occurred occasionally in the Late Eocene. Major temperature decline is recognized at the depth of 2 100 m in the borehole, as was indicated by the decline in average January temperature, the increase in annual range, and the increase in the deciduous broad leaved types of trees in the spore pollen assemblage. The sharp fluctuation in the annual precipitation, usually raging from 300 to 1 700 mm, was favorable for the migration and accumulation of salty deposit. When the precipitation was lower than 1 000 mm, ephemera shrub increased at the same depth as that of the salty deposit. It is, therefore, deduced that the formation of the salty deposit was attributed mainly to the dry and hot environment in the high mountains and deep basins. The small annual precipitation and the intense fluctuation are favorable for the sustainable accumulation of the salts, which is different from the present salty accumulation in the Northwest China.

Shear Strength Behavior of Two Landfill Clay Liners
Wenxing Jian, Kamon Masashi, Inui Toru, Katsumi Takeshi
2002, 12(3): 260-265.

Direct shear tests were conducted to obtain both the shear strength of compacted clay liners (CCLs) specimens and the interface shear strength between compacted clay liner and base soil. These experiments were conducted under the conditions of five different water contents. The experimental results show that shear strength of both CCLs and CCLs/base interface decreases with the increase in the water content of CCLs and base soil. In addition, the considerate concentration of NaCl in leachate has no deteriorating effect on the shear strength of liners. Triaxial shear tests were also conducted on clay liner specimens to obtain total and effective shear strength under a fast compression. The shear strength parameters with total stress are ϕ =18.5° and c =30 kPa for clay bentonite, and ϕ =48.5° and c =90 kPa for sand bentonite and those with effective stress are ϕ'=27.2° and c' =25 kPa for clay bentonite, and ϕ '=35° and c '=100 kPa for sand bentonite, respectively. These results indicate that the compacted clay bentonite shows normal consolidation, but that the compacted sand bentonite exhibits over consolidation.

Entropy-Based Approach to Remove Redundant Monitoring Wells from Regional-Scale Groundwater Network
Zhihua Chen, Juanli Jing, Gang Chen
2002, 12(3): 266-273.

An entropy-based approach is applied to identify redundant wells in thenetwork. In the process of this research, groundwater-monitoring network is considered as acommunication system with a capability to transfer information, and monitoring wells are taken asinformation receivers. The concepts of entropy and mutual information are then applied to measurethe information content of individual monitoring well and information relationship betweenmonitoring well pairs. The efficiency of information transfer among monitoring wells is the basis tojudge the redundancy in the network. And the capacity of the monitoring wells to provideinformation on groundwater is the point of evaluation to identify redundant monitoring wells. Thisapproach is demonstrated using the data from a regional-scale ground-water network in Hebei plain, China The result shows that the entropy-based method is recommendable in optimizing groundwaternetworks, especially for those within media of higher heterogeneities and ani-sotropies.

Engineering Geological Mapping and Land-Capability Analysis in Tangshan City
Xianzhong Li, Zousheng Yang, Huizhu Yang, Zunguo Hu, Minglei Shi
2002, 12(3): 274-277.

Geological environment in Tangshan City is under investigation with reference to the Tangshan Urban Earth Science, geo hazards maps. The expected loss for urban land utilization is calculated by employing relevant economic mathematic models. Quantitative analysis and comprehensive evaluation are then exercised for the capability of land utilization and a series of charts for the analysis of land use capability are worked out to provide the basis for the formulation of controlling measures for urban planning and to ensure the utmost conformity between land use and geological environment in urban planning.

Deformation Control of Deep Excavation Pit and Numerical Simulation with Finite Element Method
Yun'an Li, Xiurun Ge, Huiming Tang
2002, 12(3): 278-288.

The authors firstly introduce deformation control of deep excavation pit in detail, and then put forward new conceptions such as: effective coefficient of excavation pit, effective area, ineffective area and critical line, and also put forward the referential criteria of deformation control. The System of Optimization Design with Deformation Control of Deep Excavation Pit and Numerical Simulation with Finite Element Method (SDCDEFEM) is also briefly introduced. Factors influencing deformation of excavation pit are analyzed by the system. The measured and simulated data of maximum deformations (settlement, displacement and upheaval) and their positions are analyzed and discussed. The statistic formula estimating maximum deformations and their positions was gained, and economical effective measures of deformation control were brought forward.

Sedimentary Basins in the Western White Nile, Sudan, as Indicated by a Gravity Survey
I A Mohammed, Jiaying Wang, Tianyou Liu, A G Farwa
2002, 12(3): 289-296.

An academic geophysical research as a regional gravity survey was made during 1994 in the Western White Nile to infer the shallow crustal structures in the area. The result of the survey was compiled as a Bouguer anomaly map with a contour interval of 2 ×10 -5 m/s 2. It is found that the negative residual anomalies are related to the Upper Cretaceous sediments (Nubian Sandstone Formation) filling all depressions in the Basement complex surface while the positive residual anomalies are attributed to the relatively shallow or outcropping Basement rocks and the steep gravity gradients are resulting from the sharp contacts between the sedimentary infill and the Basement rocks. To define the geological structures in the area, 9 profiles were studied. For each of the profiles, measured and computed Bouguer gravity anomalies, crustal density model, subsurface geology evaluation were performed. A G model computer program was applied in the gravity modeling, which is based on the line integral method of gravity computation. A geological/structural map was proposed showing inferred sedimentary basins, faulting troughs and uplifted Basement block and tectonic trends. The basins are believed to be fault controlled which developed by extensional tectonics (pull apart mechanism). As for the mechanism and cause of faulting, the area is considered as a part of the Central Sudan rift system which had been subjected to several tectonic events since Early Cambrian to Tertiary times which resulted in the formation of several fracture systems associated with block subsidence, rifting and basin formation.