张掖鹦鸽嘴剖面白垩系碎屑岩层序地层序列:祁连山白垩纪隆升的沉积学响应

Sequence Stratigraphic Succession of the Cretaceous Clastic Rock System in Zhangye City: Sedimentological Response to the Cretaceous Uplift of the Qilian Mountains

早白垩世期间,青藏高原东北缘的祁连山隆升明显,在区域性构造运动和气候变化的综合影响下,在祁连山山前盆地中堆积了一套特殊的碎屑岩序列。甘肃张掖鹦鸽嘴白垩系发育完整,虽局部被第四系覆盖,但总体出露良好,其特殊相序单元构成的非常规体系域概念框架下的陆相层序地层模式,对研究祁连山隆升的沉积学响应及环境效应具有重要意义。鹦鸽嘴剖面下白垩统包括赤金堡组、下沟组和中沟组,可以识别出10个三级层序(S.1—S.10),LAST单元由冲积扇和河流相粗碎屑岩地层组成,湖泊相细碎屑岩沉积物构成三级层序的HAST单元。鹦鸽嘴剖面赤金堡组中下部的4个三级层序和下沟组中普遍发育的风成砂岩,是祁连山隆升造成的"焚风效应"的产物,对研究祁连山阶段性隆升特征具有重要的指示意义。早白垩世,研究区经历了从半干旱气候—干旱气候—潮湿气候的演变,在一定程度上反映了祁连山隆升过程从幕式隆升—快速隆升—均衡稳定隆升的阶段性特征。早白垩世末期,祁连山进入快速强烈隆升阶段,研究区区域性抬升为剥蚀区,整体缺失上白垩统。因此,鹦鸽嘴剖面下白垩统层序地层序列,不仅是早白垩世祁连山隆升过程的物质记录,还为早白垩世东亚大气环流格局变化的研究提供了物质基础。

In the Early Cretaceous,controlled by the uplift of Qilianshan Mountains and the climate,a set of clastic rocks developed in the continental basins before Qilianshan Mountains. The Cretaceous strata develope and outcrop well in Zhangye city of Gansu province,which are made up of particular sedimentary facies successions under the concept framework of the unconventional system tracts,and are very important to the study of Qilianshan Mountains uplift and its impacts on the environment of Asia. The Lower Cretaceous strata of Yinggezui cross-section include the Chijinpu Formation,the Xiagou Formation,and the Zhougou Formation,which can be divided into 10 third-order sequences（ S. 1—S. 10）. Generally speaking,the LAST is composed of alluvial fan facies and fluvial facies coarse clastic rocks,while lacustrine facies fine clastic rocks constitute the HAST. The eolian sandstones in the middle-low Chijinpu Formation and the Xiagou Formation,are the products of＂foehn effect＂caused by Qilianshan Mountains uplift,which are meaningful to the study of the Qilianshan Mountains uplift. In the Early Cretaceous,the climate experienced a series of changes,from semi-arid climate to arid climate to wet climate,which reflects that the Qilianshan Mountains uplift in this period can be charactered by four different stages,i. e. the early episodic uplift stage,the middle fast uplift stage,and the last isostatic uplift stage. In the transition period of Early to Late Cretaceous,the Qilianshan Mountains uplifted fast and intensively,which caused the study area turned into a denuded zone,so the Upper Cretaceous strata have not developed. The Lower Cretaceous sequences of Yinggezui cross-section,not only are the material records of Qilianshan Mountains uplift,but also can provide an important record to the reconstruction of the pattern of the atmospheric circle in the East Asia.