米仓山隆升时代的沉积学制约

Sedimentological Restriction During the Uplift Period in Micangshan

米仓山地区位处上扬子北缘,既是四川盆地的北部边界,又是龙门山、秦岭造山带与四川盆地三者之间的盆山转换地带,是探讨秦岭造山带—上扬子北缘中生代构造演化的重要地区,其隆升时代关系到四川盆地的时空边界与区域构造演化格局。通过米仓山南、北两侧侏罗纪地层沉积层序的详细对比,可以确定米仓山侏罗纪古地理地貌与隆起特点。本研究在米仓山南侧分别选取旺苍白水镇、南江赶场镇2条侏罗系剖面进行实测和研究,并实测米仓山北侧西乡堰口侏罗系剖面。通过3条侏罗系剖面的沉积建造、层序地层特点对比分析表明,米仓山南北两侧侏罗系总体具有一定的可对比性,尤其是南北两侧下侏罗—中侏罗统下段沉积层序基本相同。这种沉积建造的可对比性表明,米仓山隆升时代至少始于中侏罗世晚期。

As the northern boundary of Sichuan Basin,The Micangshan locates in the north part of the upper Yangtze region,which is the basin and mountain transition area among the Longmenshan,Qinling orogen belt and Sichuan Basin.So it is important for researching the tectonic evolution of Qinling and upper Yangtze region in Mesozoic.The uplift period of Micangshan has a large connection with spatio-temporal boundary of Sichuan Basin and tectonic evolutional framework.We can ascertain the palaeogeographical topographic features and tectonic upwarping’s feature of Jurassic in Micangshan from the research of Jurassic sediment of its both sides.Two cross sections were surveyed at Baishui and Ganchang to the south of Micangshan,another cross section in Yankou to the north of Micangshan,and lithological column of l Jurassic was made.There is no remarkable discrepancies in sediments to both sides of Micangshan from Lias to early phase of Mid-Jurassic.In a word,our research indicates that the Micangshan uplifted was later than the early phase of Mid-Jurassic and the sedimentary environment was not separated until then.