新疆哈密大草滩地区早—中泥盆世浊积岩的发现及其沉积大地构造背景

新疆吐哈盆地南缘大草滩一带出露一古生代基岩“天窗”，主要为一套火山岩—火山沉积岩，前人将其归为泥盆纪大南湖组。在该区新发现的大草滩蛇绿岩两侧识别出了两套厚度较大、时代为早—中泥盆世的复理石沉积，缺乏火山熔岩和碳酸盐岩夹层，与大南湖组层型剖面存在一定的差别。北侧复理石沉积可划分为三段，南侧受构造改造，仅发育上下两段。两侧砂岩样品的粒度参数呈现典型浊积岩特征，且自下而上水动力存在增强的趋势。通过岩性组合、沉积构造、粒度特征对该浊积岩进行沉积相分析，共识别出9种浊积岩相，进而识别出浊积扇中的3种沉积环境，其中在内扇和中扇环境中各识别出3种沉积亚环境。沉积相在垂向上的分布规律显示南北两侧的复理石分别为外扇—中扇和外扇—中扇—内扇的两套进积序列，结合碎屑颗粒组分和区域大地构造背景，推断该浊积岩形成于大南湖岛弧的弧前盆地。

Identification of Lower-Middle Devonian Turbidite Succession from Dacaotan Area,Xinjiang, NW China,and Its Sedimentary Tectonic Setting

A basic rock “window” is exposed in the Dacaotan area located at the southern margin of the Tuha Basin， Xinjiang， northwestern China. It was previously identified as the Dananhu Formations， which comprise abundant volcanic and volcaniclastic rocks. Here， well?exposed Lower to Middle Devonian flysch of great thickness was reported initially on both sides of the Dacaotan ophiolite. The petrographic characteristics of the flysch are distinguished from the stratotypic Dananhu Formations by the lack of lava and carbonate rock. The flysch on the northern side of the Dacaotan ophiolites is divided into three members， whereas only two members of the flysch are exposed on the southern side as a result of regional tectonic reworking. Typical turbidite characteristics and a stratigraphically increasing trend of hydrodynamic force are evident in the grain size data from sandstone samples from the flysches. Nine lithofacies and a further three sedimentary environment types were identified， within which three sedimentary subenvironmental types were identified in an inner fan and middle fan， judging from the petrographic assemblages， sedimentary structures and grain size characteristics. Two progradational successions， including an outer?to middle?fan from the flysch on the southern side and outer?to middle?to inner?fan from the flysch on the northern side are represented by the stratigraphic sequences of sedimentary environmental types. Therefore a sedimentary setting of these turbidites， which are located in the forearc basin of the Dananhu arc， was suggested from the combination of stratigraphic succession， clastic components and regional tectonic regime.