盆-山耦合控制下塔里木盆地库车坳陷上三叠统黄山街组层序地层特征

Basin-mountain coupling-controlled sequence stratigraphic characteristics of the Upper Triassic Huangshanjie Formation， Kuqa Depression， Tarim Basin

王正和 张荣虎 岳勇 程锦翔

Zhenghe WANG Ronghu ZHANG Yong YUE Jinxiang CHENG

前人对塔里木盆地库车坳陷上三叠统黄山街组三级层序划分方案不一，导致对其内部关键界面性质及沉积演化过程的认识各异。基于库车坳陷野外露头的精细观察与分析重新划分了黄山街组的三级层序。结果表明：①黄山街组的4个岩性段构成2个三级层序。黄（黄山街组）一段—黄三段构成东薄、西厚的三级层序SQ1，黄四段构成东厚、西薄三级层序SQ2。2个三级层序均发育低位体系域（LST）、水进体系域（TST）和高位体系域（HST）。②三级层序界面SB1，SB2和SB3分别对应于黄山街组底界、黄三段顶界及黄山街组顶界。SB1和SB3都为岩性和岩相突变转换面，SB3也是侵蚀与沉积间断面。SB2是区域抬升形成的沉积间断，有区域可对比的古土壤。③盆-山耦合变化控制了黄山街组所包含的2个三级层序的形成。古天山在SQ1低位体系域和高位体系域沉积之初分别经历了2幕强烈的快速隆升，在SQ1末期被侵蚀夷平。盆地沉积响应由强烈拗陷快速沉积充填过渡为稳定拗陷沉积充填，再次强烈拗陷快速沉积充填形成SQ1。发生沉积间断后，在弱拗陷背景下持续稳定沉积充填形成SQ2。

Previous classification schemes for the third-order sequences in the Upper Triassic Huangshanjie Formation in the Kuqa Depression， Tarim Basin have different views on the nature of its internal key boundaries and the sedimentary evolution process. Following fine observation and analyses of outcrops in the Kuqa Depression， we reclassify the third-order sequences in the Huangshanjie Formation. The results indicate that the four members of the Huangshanjie Formation constitute two third-order sequences： SQ1 and SQ2. SQ1 comprises the 1， 2， and 3 members of the formation， proving thin in the east and thick in the west. SQ2 consists of the 4 member of the formation， being thick in the east and thin in the west. Both sequences contain lowstand systems tracts （LSTs）， transgressive systems tracts （TSTs）， and highstand systems tracts （HSTs）. The third-order sequence boundaries， i.e.， SB1， SB2， and SB3， correspond to the bottom boundary of the Huangshanjie Formation， the top boundary of the 3 member of the formation， and the top boundary of the formation， respectively. SB1 and SB3 exhibit sharp transitions of lithology and lithofacies， with SB3 also identified as an erosional and depositional hiatus surface. SB2 emerges as a depositional hiatus caused by regional uplifting， and forms regional paleosol that can be correlated far away. The changes of basin-mountain coupling govern the formation of the two third-order sequences in the formation， in which the paleo-Tianshan Mountain experienced two episodes of rapid uplifting during the initial deposition of the LSTs and HSTs in SQ1， and then got eroded to peneplain at the end of SQ1 deposition. Accordingly， the basin’s sedimentary response transitions from the early intense subsidence and rapid sedimentary infilling to the stable subsidence and sedimentary infilling， and then to the second phase of intense subsidence and rapid sedimentary infilling to form the SQ1. After depositional hiatus， the basin continues to be filled steadily under the background of weak subsidence， forming SQ2.

10.11743/ogg20240504