扬子陆块震旦纪—寒武纪之交的地壳伸展作用:来自沉积序列与沉积地球化学证据

Crust Extensional Activity during the Transition from Sinian(Ediacaran) to Cambrian in Yangtze Block:Evidences from the Depositional Sequence and Its Geochemical Data

震旦纪(埃迪卡拉纪)—寒武纪之交(SCB)是华南裂谷盆地到被动大陆边缘盆地演化的重要转折期,也是华南古生代最重要的烃源岩发育时期。铜仁坝黄SCB附近的沉积序列和沉积地球化学研究表明,该时期沉积具有热液活动和缺氧沉积的双重特征,并伴有火山活动,结合区域地质调查成果,作者提出了地壳伸展—差异升降—热液上升(伴随火山活动)—快速海侵(伴随上升洋流)—缺氧事件复合沉积动力学模式。即在伸展构造背景下,热液上升伴随着火山作用,在扬子东南缘发育了广泛的硅质岩沉积;持续的拉张,出现了强烈的差异沉降,促使台地相区进一步隆升剥蚀、而在斜坡和陆棚相区硅质岩持续发育;扩张晚期,海平面快速上升,在火山活动、热液流体和生物爆发共同作用下,进一步加剧了海底缺氧,使得有机质大量埋藏和保存。因此,早古生代第一套区域性优质烃源岩是区域伸展构造背景下被动大陆边缘盆地形成早期的产物。

It was a very important transition from Precambrian to Cambrian Period,because during this time the basin nature not only had accomplished the change from rifting basin into passive margin basin,but also the most important source rocks of Paleozoic had developed in south China.So,deep studying the sedimentary sequence and depositional environment of this time is the key to recognize and understand the developing mechanism of high grade source rocks,and the dynamic setting of basin evolution.The research of sedimentary sequence and geochemistry near Sinian（Ediacaran）—Cambrian Boundary（SCB） in the Bahuang section indicate that there were double characteristic of anoxic event and hydrothermal activity,and companied with volcano activity.Based on these data and regional geological survey,authors bring out a complex sedimentary dynamic model：Crust extension—differential subsidence—hydrothermal water rising（companied with volcano）—quick transgression（companied with rising ocean current）—anoxic event.It is to say,because of crust extension,the volcano was taken place,and the siliceous rocks developed widely in shelf facies in southeast margin of Yangtze block,persisting extension increased differential subsidence,and made the platform facies farther uplifting and being eroded,and on the other hand,the siliceous rocks developed continually in slop and shelf facies.In late stage of extension,it is sea level quickly rising,accompanied with hydrothermal activity and bio-radiation which aggravated the sea floor anoxia further,that resulted in more organic matter buried and preserved.Therefore,the first set regional high grade source rocks of Paleozoic was the product of extensional setting during the primary stage of passive continental margin basin from rift basin.