西准噶尔地区石炭纪残余洋盆充填演化的地层学记录

THE STRATIGRAPHIC RECORD OF THE FILLING EVOLUTION OF THE CARBONIFEROUS RESIDUAL OCEAN BASIN IN THE WEST JUNGGAR AREA

准噶尔盆地位于古亚洲洋构造域南部,是中亚造山带的重要组成部分。早石炭世,该盆地继承了晚泥盆世多洋岛的古地理格局,沉积了一套巨厚海相沉积物。随着古准噶尔洋持续收缩,海水逐渐退去,区内形成多个残余洋盆,并最后被充填及消亡。太勒古拉组、包古图组和希贝库拉斯组为西准噶尔地区从下到上的石炭纪沉积序列,完整记录了西准噶尔残余洋盆充填消亡的全过程。根据上述三组地层岩性及其组合特征、沉积构造特征,将残余洋盆收缩充填过程分为3个阶段:太勒古拉组以暗色硅质岩、硅质泥岩夹粉砂岩为主,代表着洋盆沉积记录,即盆地阶段;包古图组以硅质岩、粉—细砂岩和含砾砂岩为主,毫米—厘米级鲍马序列极为发育,代表洋盆缓慢收缩充填的开始,即缓慢充填阶段;希贝库拉斯组以含砾砂岩、砾岩、角砾岩夹砂岩和泥岩为主,浊流沉积和风暴沉积较为发育,水体较浅,残余洋盆进入快速充填—消亡阶段。

The Junggar Basin is located in the southern part of the Paleo-Asian Ocean and is an important part for understanding the evolution of the Central Asian Orogeny. The basin inherited the paleogeographic background that is the Devonian multi-oceanic islands. During the Carboniferous, the basin went through a changing history from relatively wide ocean to narrow one, and at the last was filled and terminated. A sequence of thick marine sediments,which are, in ascending order, the Tailegula, Baogutu and Xibeikulasi formations, were deposited to record this changing process. The Tailegula Formation is dominated by dark siliceous rock, siliceous mudstone intercalated with siltstone, which represents sedimentary record of the last stage as an oceanic basin. The Baogutu Formation is mainly composed of siliceous rock, silt-fine sandstone, and gravel-bearing sandstone. The millimeter-centimeter-level Bouma sequences are well developed, which may represent the stage of the slow shrinking and filling of the oceanic basin. The Xibeikulasi Formation mainly consists of gravel sandstones, conglomerates, breccia intercalated with sandstones and mudstones. Turbidities deposits and storm deposits abundantly occur. In the late Carboniferous, it might be a stage that very shallow and residual oceanic basin was rapidly filled, moreover the marine deposits totally disappeared in the western Junggar Basin which indicates it had entered the inland orogenic stage.