鄂东南新元古界冷家溪群大药菇组地质特征及区域对比  

GEOLOGICAL CHARACTERISTICS AND STRATIGRAPHIC CORRELATION OF THE NEOPROTEROZOIC DAYAOGU FORMATION OF THE LENGJIAXI GROUP IN SOUTHEASTERN HUBEI PROVINCE

作　　者：何垚砚 牛志军[2,3] 宋芳[3] 杨文强[2,3] 

机构地区：[1]中国地质大学(武汉),湖北武汉430074 [2]中国地质调查局古生物与生命一环境协同演化重点实验室,湖北武汉430205 [3]中国地质调查局武汉地质调查中心,湖北武汉430205

出　　处：《地层学杂志》2017年第2期195-208,共14页Journal of Stratigraphy

基　　金：中国地质调查局地质矿产调查评价专项(编号:12120114039301,1212011120117,DD20160031)项目资助

摘　　要：鄂东南位于江南造山带中部区段,是扬子地块与华夏地块结合带,自东向西从明确到争议的过渡区域,区内新元古界冷家溪群顶部普遍发育一套含砾层位——大药菇组。调查发现,通山小洞剖面是研究冷家溪群顶部层位的理想剖面,剖面中大药菇组可分为上下两个岩性段:下段以含砾层为主,结合药菇山剖面可将大药菇组砾岩分为五种类型;上段以粉砂质板岩为主。碎屑锆石研究表明大药菇组至少形成于~826 Ma之后,甚至有可能略晚于820 Ma,与武陵运动的年龄范围十分接近,说明大药菇组沉积时限短,为近源快速堆积的产物,结合沉积特征的研究,认为大药菇组下段的砾岩以斜坡碎屑流沉积为主,而非前人认为的浊积物。相对而言,小洞剖面的大药菇组沉积于斜坡之上,碎屑流沉积占主导地位;药菇山剖面的大药菇组沉积更靠近坡底,浊流沉积比重略有增加。Southeastern Hubei Province is located in the middle part of Jiangnan Orogen, which is a key ar- ea in the juncture between the Yangtze and Cathaysia cratons. In this area, a gravel-bearing unit occurs in the Neoproterozoic Dayaogu Formation of the uppermost Lengjiaxi Group. In this study, we investigate the Dayaogu Group at the Xiaodong Section in Tongshan County. At this section, the Dayaogu Formation can be divided into two units： the lower unit is dominated by gravel-bearing lithologies, and in combination with lithostratigraphic data from the Yaogushan Section, can be classified into five different facies~ the up- per unit is dominated by silty slate. Results of detrital zircon analysis show that the Dayaogu Formation was deposited after ~826 Ma, or even after 820 Ma, very close to the Wuling Orogeny. This age con- straint implies a short duration and rapid sediment accumulation of the Dayaogu Formation. Based on sedi- mentological observations, we argue that the lower Dayaogu Formation is mainly debris flow sediments, rather than turbidites as previously thought. Overall, the Dayaogu Formation at the Xiaodong Section was deposited in a slope environment dominated by debris flow sedimentation, whereas the Yaogushan Section represents deposition in a bottom slope environment where turbidites are more common.

关 键 词：岩石地层 砾岩 碎屑流 大药菇组 冷家溪群 新元古代 江南造山带 鄂东南 湖北省 

分 类 号：P534.3[天文地球—古生物学与地层学]