四川盆地万源地区中侏罗统湖相(砂)砾岩风暴沉积的发现及其地质意义

Discovery and significance of lake storm deposition in Middle Jurassic conglomerate of Wanyuan

四川东北部的万源中侏罗统湖泊(砂)砾岩中发育了典型的丘洼构造,揭示了湖泊粗粒沉积中也能发育风暴沉积。丘洼构造具有明显的特点:1)规模普遍较大,宽度多在数米,最大宽度可达7.85 m;高度多在数十厘米,最大可达2.53 m;2)发育在砂砾岩中,甚至可以完全发育在砾岩中。砾石的排列方式具有“八”字形和反“八”字形,与风暴浪的汇聚与发散有关;3)无论是丘状或洼状构造都具有很好的正粒序性。砾石的分选磨圆极好,多发育了双倾向叠瓦构造。砾石主要为石英岩,来自于前寒武纪变质基底,揭示了大巴山南缘在中侏罗世时已经经历了大幅隆起和大幅剥蚀,进而揭示了大巴山南缘在中侏罗世已经发生了造山作用。通过喷流模拟实验建立了最小悬浮速度公式,并计算了风暴浪的相关动力学参数。

In the Middle Jurassic lake conglomerate of Wanyuan in the northeast of Sichuan Province,typical hummocky structures and swaley structures were developed,which revealed the existence of lake storm deposits.Hummocky structures and swaley structures have obvious characteristics:1)The scale is generally large,the width of many meters,up to 7.85 m.The height is usually in the tens of centimeters,with a maximum of 2.53 m.2)Develop in the conglomerate and even completely reverse breed in the conglomerate.The arrangement of gravel has Chinese“eight”word shape and Chinese anti-“eight”word shape,and is related to storm wave convergence and divergence.3)Both hummocky structures and swaley structures have good positive grain sequence.The sorting and grinding of gravel is very good.The gravel is mainly quartzite and comes from the Precambrian metamorphic basement,which reveals that the southern margin of Daba Mountain has experienced large uplift and denudation in the Middle Jurassic,and further reveals that the southern margin of Daba Mountain has undergone orogenesis in the Middle Jurassic.Through the jet simulation experiment and the minimum suspension velocity formula established and the dynamic parameters of storm waves were calculated.