下扬子鄂东南地区冷家溪群大药姑组沉积特征分析

Analysis on Dayaogu Formation of Lengjiaxi Group Sedimentary Characteristics in the Lower Yangtze Area of Southeast Hubei

通过鄂东南1∶5万沙洲店等幅区调工作,对通山县岭下大队大药姑组剖面进行测量。详细描述大药姑组地层岩性及砾石分布特征,并与邻区进行地层对比,分析大药姑组沉积环境及物源方向。研究表明,大药姑组可划分为两段,即一段以灰绿色中—厚层状变质细砂岩为主,底部及顶部发育数层细砾岩及含细砾砂岩,砾石成分主要为深灰色粉砂质砾和白色石英砾,砾径2~5 mm,圆—次圆状,分选较好,下部见明显鲍马序列,为较深水浊流沉积环境;二段以灰绿色板岩及砂质板岩为主,夹灰黄色薄—中层变质粉砂岩,与一段相比,沉积水体更深。通过与通山小洞和江西修水大药姑组地层对比表明,小洞和修水为水体较浅的斜坡带上部碎屑流沉积环境,岭下大队剖面为斜坡带下部较深的浊流沉积环境。通过上述三条剖面沉积厚度、砾径和分选度对比,表明物源由北西向南东方向搬运。

The section of the Dayaogu formation in Lingxia Brigade,Tongshan County was measured through the regional geological survey work of 1∶ 50 000 Shazhoudian sheet of Southeast Hubei. The lithology and gravel distribution characteristics of Dayaogu formation are described in detail and compared with the strata of the adjacent area,and the depositional environment and the source direction of Dayaogu formation are analyzed. The study shows that Dayaogu formation can be divided into two sections： the first section is gray green medium-thick layered metamorphic fine sandstone mainly at the bottom and the top of the development of several layers of fine conglomerate and gravel sandstone,gravel composition is mainly dark gray sandy gravel and white gravel,gravel diameter 2 - 5 mm,round and sub-round,sorting better,the lower part of the Bauma sequence,for the deeper water turbidity deposition environment; the second section of gray green slate and sand slate mainly,and gray yellow thin-middle layered metamorphic siltstone,the sedimentary water is deeper compared with the first section. Compared with Tongshan Xiaodong and Jiangxi Xiushui strata of Dayaogu formation,Xiaodong and Xiushui for the debris flow deposition environment of the upper part of the shallow water slope,Lingxia brigade section for the deeper turbidite deposition environment of the lower slope. Through the above three sections of the deposition thickness,gravel diameter and sort grade comparison,indicating that the source direction from northwest to and southeast.