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2013, Volume 20 Issue 2
15 March 2013 Previous Issue    Next Issue
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Sequence stratigraphy and genesis of sand bodies of the Upper Triassic Yanchang Formation in the southwestern margin of Ordos Basin. LIU Zi-Liang, SHU Xiao-Min-*, LIAO Ji-Jia, CHEN Jie 2013, 20(2): 1-9.  Abstract ( 2409 )   PDF (3768KB) ( 1149 )   Taking the Yanchang Formation in the southwestern margin of Ordos Basin as an example, by using the high resolution sequence stratigraphy theory, this paper studied the sedimentary characteristics of the Yanhe and other outcrops. It is concluded that unconformities, erosion surfaces, lithofacies contrast surfaces and flood surfaces mark the important sequence boundaries. The Yanchang Formation in the study area can be divided into one super longterm baselevel cycle, five longterm baselevel cycle and seventeen midterm baselevel cycles. It mainly developed braided fluvial and braided delta depositional system in the southwest steep slope, meandering river delta sedimentary system in northeast terrainrelief and turbidite fan deposits in the deep lake systems. The genesis of favorable sandstone reservoirs can be divided into submarine distributary channel, submarine distributary channel and composite river mouth bar, river mouth and slump turbidite fans. With changing lake level, the ratio of accommodation space (A) over sediment supply (S) affects the distribution of depositional systems from different source directions and the sedimentary evolution distribution patterns, as discussed in the paper. Related Articles | Metrics

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Provenance and depositional systems of the Upper Triassic Yanchang Formation in the southwestern Ordos Basin, China. YANG Hua, LIU Zi-Liang, SHU Xiao-Min, DENG Xiu-Qin, ZHANG Zhong-Xi, JI E-Lin 2013, 20(2): 10-18.  Abstract ( 1954 )   PDF (5650KB) ( 963 )   Taking the Yanchang Formation in the southwestern Ordos Basin as an example, based on the studies of petrology, sedimentary characteristics, measurements of paleocurrent directions shown by outcrops, as well as framework grains and minerals in sandstones and their distribution characteristics, the paper studied the provenance and depositional characteristics of the research area. The study shown that early sediment source was mainly from the southwest of the basin with some contribution from the south. This was followed by subsequent deposition of sediments sourced from the southwestern and southern areas with some contribution from the northeast of the basin. Debris of the Chang 8 sandstone is dominated by metamorphic rocks, small amount of sedimentary and volcanic rocks. Debris of the Chang 6 sandstone is dominated by sedimentary rocks, and a small amount of metamorphic rock and volcanic rocks. The presence of more felsic materials of the late Archean in the Chang 6 sandstone suggested that the western margin of the basin uplift had undergone intensive erosion, resulting in a large number of younger strata eroded and added to the source rocks. The distribution of the Yanchang Lake basin was along northwestsoutheast. It mainly developed braided fluvial and braided delta depositional systems in the southwestern slope, meandering river delta depositional system in northeastern terrainrelief and turbidite fan deposits in the deep lake systems. Related Articles | Metrics

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Sedimentary characteristics and model of shallow braided delta in largescale lacustrine: An example from Triassic Yanchang Formation in Ordos Basin. SHU Xiao-Min, DENG Xiu-Qin, LIU Zi-Liang, SUN Bo, LIAO Ji-Jia, HUI Xiao 2013, 20(2): 19-28.  Abstract ( 1798 )   PDF (5888KB) ( 969 )   The research and exploration of shallow delta have been paid much attention in recent years. A large shallow braided delta developed in Longdong Area of southwestern Ordos Basin. Based on some outcrop, core, logging, seismic data from Triassic Yanchang Formation in Ordos Basin, it is suggested that the geological setting of Ordos Basin is favorable for the formation of shallow braided delta during the period of Yanchang Formation. The shallow braided delta is characteristics of coarse grain size, many soft lithoclasts, low content and texture maturity, many cross beddings, normal cycles, many distributary channels, thick sandbodies, distal extension etc. During the sedimentation of the shallow braided delta in southwestern Ordos Basin, the sediment center was near to provenance, the width to depth ratio of the channel was big and shallow water sedimentary structures were developed. The development of the braided shallow delta was controlled by the tectonic activities and lake level changes and therefore, the shallow braided delta in southwestern Ordos Basin was formed in the form of small plain and large delta front. Related Articles | Metrics

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Sedimentary characteristics and model of gravity flow in Triassic Yanchang Formation of Longdong Area in Ordos Basin. LIAO Ji-Jia, SHU Xiao-Min, DENG Xiu-Qin, SUN Bo, HUI Xiao 2013, 20(2): 29-39.  Abstract ( 2109 )   PDF (4616KB) ( 860 )   Sedimentary characteristics and depositional model of Yanchang Formation of Longdong area in Ordos Basin were studied based on core, logging data and gravity flow theory. The gravity flow deposits of the area can be divided into turbidite, sandy debris flow sediment, muddy debris flow sediment and slump rock. The turbidite develops positive grading. The sandy debris flow sediment is characterized by freezing and massive deposition. The muddy debris flow sediment mainly contains muddy and a small number of sandy particles and clumps in its interior. The slump rock develops liquefied tectonic structure, such as convolute bedding. The differences of the development degree of gravity flow sediments are obvious. In terms of the number of drilling wells, the turbidite and sandy debris flow sediment are the major sedimentary types, and the muddy debris flow sediment is the less one. In terms of the single deposition thickness of gravity flow, the average thickness of sandy debris flow deposition is 0.986 m, which is significantly higher than other types. The average deposition thickness of turbidite is the lowest, which is 0.414 m. The gravity flow of the area is due to the slump of delta front sediments. The sandy debris flow sediment and turbidite are the main types of gravity flow deposits, followed by the slump rock and muddy debris flow sediment. The sandy debris flow sediment developed in deepwater area in front of the northeast delta front from meandering river. The turbidite mainly developed in deepwater area in front of the braided river delta front, whose provenance came from west, southwest and south. In terms of distribution area, the muddy debrisflow sediment and sandy debris flow sediment with mud gravel are very small in plane, and their distribution is not in a regular pattern. Related Articles | Metrics

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Petroleum enrichment theory and practice for low permeability reservoir in large continental basin. DAN Xin-Quan, SHU Xiao-Min, YANG Hua, LIU An-Di, FU Jin-Hua, TUN Qing-He, TAO Jing-Li, GAO Gang 2013, 20(2): 147-154.  Abstract ( 1775 )   PDF (3319KB) ( 1898 )   Related Articles | Metrics

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THE 2008 IWATE-MIYAGI EARTHQUAKE(M  7.2) AND ARC VOLCANISM:INSIGHT FROM IRREGULAR-GRID TOMOGRAPHY Wei WEI Dapeng ZHAO 2013, 20(2): 155-171.  Abstract ( 6439 )   PDF (14054KB) ( 18714 )   Related Articles | Metrics

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Archean eclogites from Belomorian Mobile Belt, Russia. LI Xiao-Li, ZHANG Li-Fei, WEI Chun-Jing 2013, 20(2): 172-185.  Abstract ( 1292 )   PDF (3989KB) ( 792 )   Related Articles | Metrics

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Characteristics of mix crystal xenolith from basaltic(shoshonitic) volcanic breccia at Maguan Area,Yunnan Province, and their geological significance. HUANG Yu-Peng, LIU Xian-Fan, LI Chun-Hui, LEI Qiu-Xia, DAO Zhuan, DIAO Fu-Feng, DONG Yi 2013, 20(2): 186-196.  Abstract ( 1432 )   PDF (2263KB) ( 680 )   Related Articles | Metrics

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Metallogenetic epoch of the Almalyk porphyry copper ore field, Uzbekistan, and its geological significance. XUE Chun-Ji, DUAN Shi-Gang, CHAI Feng-Mei, MU Ge-Da-Er-·Mai-Mai-Chi, А.Х.Туресебеков3 , JUE Wen-Dun 2013, 20(2): 197-204.  Abstract ( 2635 )   PDF (1571KB) ( 1096 )   The exploration of porphyry copper deposits in western Tianshan, Xinjiang, had attracted much attentions. The Almalyk copper deposit in western Tianshan, Uzbekistan, is one of the largest porphyry copper deposits in Asia, but has not well been dated. The Almalyk copper ore field is located in the southern part of CaledonianHercynian central Tianshan fold belt, and includes four copper deposits: Kalmakyr, Dalneye, Sarcheku and Kyzata. Copper mineralization occurred within the porphyries. The primary ores are characterized mainly by stockwork and disseminated structures, and  the  major metallic minerals are in assemblage of pyrite, chalcopyrite, molybdenite, hematite, magnetite, nature gold and bornite.  The present paper obtains the  weighted model age of 320.4±2.3 Ma and an isochron age of 317.6±2.5 Ma based on the ReOs isotopic method  by using the molybdenites from the Sarcheku coppermolybdenum ores.  On the basis of  the sequence of magmatic formation in this area, it is suggested that the  tectonomagmatic hydrothermal process in Almalyk ore field started at the early Carboniferous, developed during the late Carboniferous, and finished at the early Permian, and the porphyry copper mineralization mainly occurred during the late Carboniferous. The worldclass large and supper large porphyry copper mineralization including the Almalyk copper deposit in western Tianshan  is  closely related to the complex arc magmatic geological processes resulted from the subduction of paleoAsia ocean crust under KazakhstanYili plate, which happened mainly from the middle Devonian to the late Carboniferous (D2C2). Related Articles | Metrics