重庆秀山志留系小溪组的发现与迴星哨组的厘定

DISCOVERY OF THE LATE SILURIAN XIAOXI FORMATION IN THE XIUSHAN AREA,CHONGQING CITY,CHINA,AND THE REVISION OF THE HUIXINGSHAO FORMATION

依据对重庆秀山地区微体化石(主要指植物碎片和疑源类)和大型虫管遗迹化石研究,对迴星哨组进行了厘定,将它一分为二,上部为志留纪晚期的小溪组,下部为厘定后的迴星哨组。厘定后的迴星哨组以紫红色粉砂质泥岩为主,与下伏秀山组呈整合接触,与上覆小溪组呈假整合接触,地质时代为Llandovery世Telychian晚期。基于对贵州印江、重庆秀山和湖南龙山—张家界地区志留纪晚期地层的研究,指出:在"扬子上升"后,在华南块体的中心地带——湖南张家界地区至贵州印江地区发育有志留纪晚期沉积,进一步论证了华南块体在志留纪晚期曾一度遭受过海侵,并在一定区域内沉积了具有一定厚度的地层。

Based on the studies of microfossils（including phytodebris and acritarchs）and large stout tubular trace fossils,the upper part of the originally defined Huixingshao Formation in the Xiushan area,Chongqing city,is recognized the Ludlow-Pridoli Xiaoxi Formation.The original Huixingshao Formation is revised,and subdivided into two parts,the upper part being the Xiaoxi Formation and the lower part being the Huixingshao Formation（sensu stricto）.The redefined Huixingshao Formation mainly consists of the purple silty mudstones,conformably overlying the Xiushan Formation and disconformably underlying the Xiaoxi Formation.The geological age of the redefined Huixingshao Fromation is late Telychian of the Llandovery.A survey of Ludlow-Pridoli strata in the Yinjiang area of Guizhou,Xiushan area of Chongqing,and Longshan-Zhangjiajie area of Hunan shows that,after the ＂Yangtze Uplift＂,Ludlow-Pridoli strata were deposited the interior of the Yangtze Plaform from the Zhangjiajie area of Hunan to the Yinjiang area of Guizhou,suggesting that the Yangtze Paltform was flooded by shallow seawater in the late Silurian.