| The work area is located about 150 km northwest of Amdo County,district north,South to Duozengmu Garang,West,East,Dazhuoma Gaerba close,area 700km2.The administrative division under the jurisdiction of the County Gang Ni xiang.The district is located in the southeastern part of the Qiangtang plateau,known as the southern Qiangtang,as the permafrost zone,the average 5200 m of altitude in general between 5000 and 5300 m,the relative ratio,200-300 m,of tectonic attribution to Qiangtang Changdu block,contains the Longmucuo Shuanghu-Lei Wuqi-the central uplift belt,North to the Hoh Xil Jinsha River suture zone,South to the Bangong Lake Nu River suture zone.Based on in the study area,route survey and the measured profile,and the measured profile data of regional strata,established Dazhuoma area middle Jurassic sedimentary sequence,sedimentary system formation,and the system of collecting in the north and South Qiangtang geological data and research results,to establish the nature and evolution of the basin Qiangtang basin.Sum up,This paper comes to the following conclusion:1 Stratigraphic area:through the study area location and formation of the system,and compares the Jurassic stratigraphic division and regional data,the study area for Yunnan stratigraphic area,southern Qiangtang formation zone and stratigraphic division,and the north and South Qiangtang during the same period.The formation of the general description.2 Regional stratigraphic framework established:the study area is Jurassic strata,namely a Mo wrong group,Buqu Formation and Xiali formation measured sections and regional stratigraphic comparison,transverse distribution in these strata thickness,different rocks,and the horizontal distribution of some special layer are described.Lithologic character distribution and contrast3 Understanding depositional environments and sedimentary facies:passed in front of the Jurassic three strata,combined with the sedimentary structures,fossils feature,compared with regional strata adjacent North and South Qiangtang,and define the longitudinal change of sedimentary facies and the lateral variation.In general,in the early Middle Jurassic,southern Qiangtang is mainly a deep-water slope facies,and the study area and the northern Qiangtang basin is mainly shallow littoral deposits and delta sedimentary environment.And in the Jurassic period,mainly for the carbonate ramp relatively stable phase development,local lagoon facies.The Middle Jurassic late,southern Qiangtang area are mainly sedimentary environment nearshore sandbar shelf-,and research area and the area east of tidal flat,lagoon facies with local area.4 Understanding of sea level change:The third point is divided by the deposition phase and contrast,the results of the sea in the Middle Jurassic period of the study area and adjacent regions lifting process of change,Overall,during the deposition of Quemocuo of transgressive-regressive sequences,Buqu relatively stable,the middle part of the transgressive-regressive process,to the deposition of Xiali,when there is a relatively large transgression,then gradually regressive.5 Investigate the nature and evolution of the Qiangtang Basin Basin:Mainly based on previous studies and some research data,obtained the nature and evolution of the Qiangtang basin basin.When Jinsha ocean basin closure time,in the early Triassic period,the formation of Qiang north foreland basin began to Late Triassic period,Qiang north end of the foreland basin,then Bangonghu open ocean basin,born Qiang south rift basin,as well as the rift Qiang North also become rift basin,to the Early Jurassic,the basin is relatively stable north and south Qiangtang Basin are mainly depression basin,Middle Jurassic time,Qiang North rift basin once again,to the Late Jurassic and Early Cretaceous period,Qiangtang Basin gradually shrinking,the sea receded from the north-west end of the Mesozoic sedimentary basins of the Qiangtang Basin process. |
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