甘肃岷县－宕昌地区下二叠统粗碎屑硅质浊积岩

甘肃岷县－宕昌地区属酉秦岭的中秦岭分区南带。下二叠统的硅质岩主要有：砾屑硅质岩、砂屑硅质岩、放射虫硅质岩和条带状硅质岩。本文主要讨论了碎屑硅质岩的沉积特征、岩石特征、沉积构造、颗粒大小、地球化学特征及沉积序列特征．从而论证了该地区的粗碎屑沉积是拉张环境深海盆地中的内源碎屑硅质浊积。通过与Ｓｔｏｗ等硅质浊积模式和经典的陆源碎屑浊积模式的对比，讨论了它的新特点，并由此进一步建立了一个深海硅质法积岩的完整沉积序列。粗碎屑硅质岩在国内外的报道还不多见，它的发现对丰富深海沉积类型及了解西秦岭的古海洋演化具有重要意义。

LOWER PERMIAN COARSE CLASTIC SILICEOUS TURBIDITES IN THE MINXIAN-DANGCHANG REGION, GANSU

The Lower Permian siliceous rocks in southern zone of western Qinling Mountains in the Minxian-Dangchang region,Gansu consist mainly of gravel-sized siliceous rocks, sandsized siliceous rocks,radiolarian siliceous rocks and banded siliceous rocks. In terms of sedimentological and petrographical characteristics, sedimentary structures, grain size, geochemical properties and depositional sequences, the present paper demonstrates that the coarse elastic deposits in the study area are ascribed to the endogenetic elastic siliceous rocks in the deep-sea pull-apart basins. A complete depositional sequence of deep-sea siliceous turbidites has been proposed by comparison with the Stow's siliceous turbidite models and clasic terrigenous elastic turbidite models.The coarse elastic siliceous rocks are less known both at home and abroad. Their discoverly is of great importance to the further understanding of deep-sea sediment types and palaeo-oceanic evolution in western Qinling Mountains.