~ 203 m ~ 15 1 ~ 4 1m 2 1 Fig The regional geology and measuring points of the gravel fabric in the southwe

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1 ACTA SEDIMENTOLOGICA SINICA Vol. 29 No. 2 Apr jianqiang2@ 126. com P A 1 1 ~ 7 1 ~ ~ m ~ m JK181

2 ~ 203 m ~ 15 1 ~ 4 1m 2 1 Fig The regional geology and measuring points of the gravel fabric in the southwestern Ordos Basin Fig Gravel columnar comparison chart of Yijun group of Lower Cretaceous in Southwestern Ordos Basin

3 a b c ~ 4 1 ~ 2 96% 3 ~ 4 60% % 1 23% 8% 12% 9% 3 8 ~ 9 49% 18% 12% % 5% CEMP 49% ~ 17 Table ~ 7 3 a b c The compositional features of Yijun gravels of Lower Cretaceous in the southwestern Ordos basin /%

1 150 12 ~ 17 Table 1 1 2 5 ~ 7 3 a b c The compositional features of Yijun gravels of Lower Cretaceous in the

4 c 1. 3 珔 d 珔 d a 珔 d b 珔 d c 珔 d = 3 珔 d a 珔 d b 珔槡 dc 珔 d 50 珔 d 50 = 3 槡 d a50 d b50 dc50 d a50 d b50 d c50 a b c 4 S a S b S c a 2 b c d 25 d 75 S a = 槡 d 75 /d25 S b S c a b c F F = a + b /2c B B = 槡 3 abc /a 珔 d a 珔 d b 珔 d c P ~ 4 W ~ ~ % ~ 53% 2. 2 ~ 4 Fig. 3 The compositional features curve of Yijun gravels of Early Cretaceous in the southwestern Ordos Basin ~ 2 珔 d 3 ~ 6 cm a 5 ~ 8 cm 3. 3 珔 d 50 1 cm ab 4 ab a 5 a b Table 2 2 The granulometric features of Yijun gravels of Lower Cretaceous in the southwestern Ordos Basin /cm S 珔 d 珔 d 50 珔 d a 珔 d b 珔 d c 珔 d a50 珔 d b50 珔 a S b S c d c

3 The compositional features curve of Yijun gravels of Early Cretaceous in the southwestern Ordos Basin 8 2 1 ~ 2 珔 d 3 ~ 6 cm a 5 ~ 8 cm 3.

5 Fig. 4 4 a The curvilinear map of a-axon size-frequency distribution of Yijun gravels of Lower Cretaceous in the southwestern Ordos basin Fig. 5 5 a The histogram map of a-axon size-frequency distribution of Yijun gravels of Lower Cretaceous in the southwestern Ordos basin Table 3 3 The psephitic features of Yijun gravels of Lower Cretaceous in the southwestern Ordos basin F 1 B P F /B W

features of Yijun gravels of Lower Cretaceous in the southwestern Ordos basin F 1 B P F /B W 2. 08 0. 65 36. 04 3. 2 1 2 2. 42 0. 62 34. 28 3. 9 1 3 2. 35 0.

6 % WinRose R 0. 9 ab % Fig. 6 6 The palaeocurrent map of Yijun Formation of Lower Cretaceous in the southwestern Ordos Basin

7 ~ 4 cm % ~ % ~ m 4 ~ 6 cm ~ % ~ 52. 8% 60 ~ 80 m ~ m ~ ~ ~ 83 Ma

8 J Liu References Chiyang Zhao Hongge Gui Xiaojun et al. Space-time coordinate of the evolution and reformation and mineralization response in Ordos Basin 1 J. Acta Geologica Sinica J Zhu Dagang Zhao Xitao Meng Xiangang et al. Fabric analysis of gravel in Quaternary gravel beds on backbone area of Nianqingtanggulashan mountains J. Journal of Geomechanics M Geological Bureau of the Regional Geological Survey Team of Shaanxi Provincial. Cretaceous of Shaanxi M Bureau of Geology and Mineral Resources of Shaanxi Province. J. Regional Geology of Shaanxi Province M. Beijing Geological Publishing House Liu Xun Wang Jun Zhang Zha ochong et al. Relation between the components of Quaternary molasse and uplift of the Qinghai-Tibet Plateau-Preliminary understanding of the results of measurements of the Quaternary pebble composition at the Kokyar section Yecheng Xinjiang J. Geological Bulletin of China Regional Geology Survey Team of Shaanxi Province J Han Jian en Yu Geological Mining Maps and Instruction of Longxian 1967 Jia Meng Qingwei et al. Analysis of Quaternary gravels in the Zhanda basin Ngari area Tibet China J. Geological Bulletin of China Institute of Geological Survey of Shaanxi Province Geological mining Maps and Instruction of Baoji M. J Zhang Zejun. The fundamental principle and method for defining the proluvial fans in a small Peng Jianbing Zhang Jun Su Shengrui et al. Active Faults and Geological Hazards of Weihe red basin according to the statistics of gravels J. Regional Geology of China M. 5. M Wang Xin. Occurrence and Development of Geothermal Resources Zhou Anchao. The Evolution of Late Paleozoic Basins in North Margin of North China Block and the in Weihe Basin M. Xi'an Science and Technology Press 2005 Coupling Relationship between Basin and Range M. Beijing Coal Industry Press J Zhao Hongge Liu Chiyang. Approaches and prospects of provenance analysis J. Acta Sedimentologica Sinica Xi an College of Geology J Wu Leibo Ma Shengyun Shen Shumin. The gravel-directional array analysis and depositional structure of the Baishajing gravel layer discussion in Changsha and other places J. Acta Geologica Sinica M Zhang Guowei Zhang Benren Yuan Xuecheng et al. Qinling Orogene and Continental Dynamics M. Beijing Science Press anomaly and formation time in Ordos Basin J. Acta Geologica Sinica J Chen Gang Wang Zhijuan Bai Guowei et al. Meso-Cenozoic peak-age e J. vents and their tectonic-sedimentary response in Ordos Basin J. Geology in China M The Regional Geological Survey Team of Geological Bureau of Gansu Province Regional Geological Maps and Instruction of Jingchuan Basin M. Xi'an Northwestern University Press M Zhao Chenglin Zhu Xiaomin. Sedimentary Petrology M. Beijing Petroleum Industry Press J Yuan Weiguo Wang Ping. On the Caledonian movement in the southern Ordos basin J. Journal of 20. J Wang Jianqiang Liu Chiyang Yan Jianping et al. Development time and evloution characteristics of Weibei uplift in the south of Ordos basin J. Journal of Lanzhou University Natural Sciences 21. J Ren Zhanli Zhang Sheng Gao Shengli et al. Research on region of maturation Yang Youyun. Cretaceous sedimentary formation in Ordos Basin J. Oil & Gas Geology

Fabric analysis of gravel in Quaternary gravel beds on backbone area of Nianqingtanggulashan mountains J. Journal of Geomechanics 2002 8 4 323-332 11. M.

9 Fabric Analysis of Yijun Gravels of Lower Cretaceous in the Southwestern Ordos Basin WANG Jian-qiang JIA Nan LIU Chi-yang QIU Xin-wei ZHAO Hong-ge GUO Zhen State Key Laboratory of Continental Dynamics Geology Department of Northwest University Xi'an Abstract The study area is located in the southwest of the Ordos Basin with the tectonic position in the intersection of Ordos Basin and Qinling-Qilian orogenic belt and the area is adjacent to the western thrust fold belt in the west and looking at Qinling orogenic belt across Weihe graben in the south. Since the Late Triassic molasse formations were widely developed because of the neighbouring orogenic belts' multi-stage tectonic movements. Among them the Yijun conglomerate at the bottom of the Lower Cretaceous is the typical molasse formation. The study on it has great significance and value to discuss the original basin boundary and basin-mountain evolution in the southwest of the Early Cretaceous basin. Using fabric analysis method to study the composition particle size shape and preferred orientations of nine measuring points from west to east in Yijun conglomerate in the southern Early Cretaceous basin can clarify the composition source and formation environment of these gravels. The composition analysis shows that the component gravels from the west to the east in the study area can be divided into three regions Longxian- Qianyang area's gravels are mainly carbonate rocks Linyou-Yongping area's gravels are dominated by granite and metamorphic rocks Binxian area's gravels are quartzite and metamorphic rocks. Analysis on particle size shape and preferred orientations indicate that the gravels size show large-small-large-small rule from west to east generally with poor sorting subangular to subrounded and low degree weathering and the material mainly come from the southern of the basin which can be seen that the Yijun conglomerate is an alluvial fan-fluvial sedimentary gravels with arid environment and rapid accumulation to deposit in the depression at the foot of mountain. Combining with analysis of adjacent areas rock formations and regional geology we consider that the provenance of Lower Cretaceous should not come from the old strata of southern Weibei uplift or the pre-cenozoic strata of Weihe garben. Linyou-Binxian region's gravels mainly came from the North Qinling orogenic belt and Longxian-Qianyang's gravels might come from the Paleozoic of Longshan area which was the extrusion response of Qinling orogenic belt at southwestern basin in Late Mesozoic. It can be further explained by the evidence that the large-scale uplift does not exist at Weibei area or it's southern to prevent the source material from Qinling orogenic belt. We can infer that the development time of Weibei large-scale uplift may be in the late Early Cretaceous at least. While the sedimentary facies of the southern basin in Lower Cretaceous are fluvial delta and lake therefore it is considered that the southern boundary of the heyday sedimentary basin in the Cretaceous may be still extended to the south which may be at least in Weihe region or even in the northern foot of Qinling mountain. Key word Ordos Basin Early Cretaceous Yijun conglomerate fabric analysis of gravel Weibei uplift original basin boundary

and Qinling-Qilian orogenic belt and the area is adjacent to the western thrust fold belt in the west and looking at Qinling orogenic belt across Weihe graben in the south.

GLOBAL GEOLOGY Vol. 29 No. 3 Sept P531 A doi /j. issn

29 3 2010 9 GLOBAL GEOLOGY Vol. 29 No. 3 Sept. 2010 1004-5589 2010 03-0363 - 10 1 2 1. 123000 2. 110032-4 4 P531 A doi 10. 3969 /j. issn. 1004-5589. 2010. 03. 002 Characteristics of lithofacies palaeography