塔里木盆地库车坳陷北部典型露头剖面白垩系巴什基奇克组三段高分辨率层序地层特征

High-resolution sequence stratigraphy of the third member of Cretaceous Bashijiqike Formation in a typical outcrop section，northern Kuqa Depression， Tarim Basin

王胜军 唐永亮 朱松柏 谢伟 单长安 聂延波 王勇 王益民 蒋国军 邵剑波 叶璁琛

Shengjun Wang Yongliang Tang Songbai Zhu Wei Xie Changan Shan Yanbo Nie Yong Wang Yimin Wang Guojun Jiang Jianbo Shao Congchen Ye

基于丰富的野外露头实测资料，并结合地表自然伽马测量、元素（Fe，Ca，Mg，B）分析及井下数据，对塔里木盆地库车坳陷北部露头剖面白垩系巴什基奇克组三段层序地层特征进行了系统研究。结果表明，巴什基奇克组三段发育3个特征明显的岩性段，其下部为两期厚层褐灰色中、细砂岩-棕褐色厚层泥岩旋回；中部为大套厚层褐色、褐灰色粉砂岩、细砂岩夹薄层红褐色泥岩；上部为褐灰色粉砂岩、细砂岩与红褐色泥岩互层。地表自然伽马值范围为5 ~ 40 API，以齿化钟形和箱形夹齿化平直段为主，这些曲线形态可以较好地与井下进行对比。Fe和Fe含量、Ca/Mg含量比及B元素含量在剖面上的变化趋势表明地层旋回特征十分明显，巴什基奇克组古水体经历了浅—深—浅—深—浅—深—浅的变化过程。巴什基奇克组三段长周期旋回界面在野外露头区易于识别对比，根据露头岩性、颜色和层理构造等特征可识别出“向上变深的非对称”和“向上变深再变浅的近对称”两种短期基准面旋回叠加样式，结合自然伽马曲线特征和元素分析可以明确中期旋回。基于此方法，露头剖面巴什基奇克组三段可划分为3个中期旋回（四级层序），6个短期旋回（五级层序），部分剖面缺少1个短期旋回。与更加靠近湖盆中心的钻井相比，露头区往往少发育1个中期旋回和4个短期旋回。露头区MSC1，MSC2与MSC3中期旋回分别对应于井下MSC2，MSC3和MSC4中期旋回，其砂体与泥岩隔夹层具有较为相似的规律。研究成果有利于库车坳陷北部气区优质储层的追踪对比和预测，可以高效指导深层天然气的勘探开发。

A systematic analysis was carried out on a combination of field outcrop data with surface natural gamma ray measurement and element contents （Fe， Ca， Mg and B） as well as well data to characterize the sequence stratigraphy of the third member of Bashijiqike Formation in an outcrop section from the northern Kuqa Depression. The results show that the member has three distinct lithologic intervals， with the lower interval characterized by two sedimentary cycles （periods） of thick brownish-gray medium to fine sandstone and thick brown mudstone， the middle interval by a large set of thick brown and brown-gray siltstone， fine sandstone with thin reddish brown mudstone interbeds and the upper interval by alternating brown-gray siltstone， fine sandstone and reddish-brown mudstone. The surface natural gamma curves values range between 5 and 40 API and occur mostly as dented bell curves or flattened boxes with dents in between， which can be readily compared with well logs. The variation trends of Fe and Fe， Ca/Mg ratio and B in the section show striking stratigraphic cycles， corresponding to the paleo-water variation in an order of shallow - deep - shallow - deep - shallow - deep - shallow for the Bashijiqike Formation. These long-period cycle interfaces in the third member of Bashijiqike Formation are contrastive and can be easily identified in outcrops. Observation of the lithology， color， bedding and other characteristics of the outcrop section reveals two types of short-term base-level cycle superposition patterns， i.e.， the “upward-deepening asymmetric” pattern and the “upward-deepening followed by upward-shallowing near-symmetric” pattern； and if combined with the characteristics of natural gamma curves and elemental analysis， medium-term cycles can also be identified. Based on this method， the third member of Bashijiqike Formation in the outcrop can be divided into three medium-term cycles （fourth-order sequences） and six short-term cycles （fifth-order sequences）， with one short-term cycle missing from parts of the outcrop. However， compared with data gathered from wells drilled closer to lake basin center， absence of one medium-term cycle and four short-term cycles are often observed in the outcrop. The medium-term cycles of MSC1， MSC2 and MSC3 in the outcrop correspond respectively to the medium-term cycles of MSC2， MSC3 and MSC4 in subsurface， and they share the similar alternating patterns of sand body with mudstone interlayers/barriers. The study may be used to guide gas exploration in the deep of northern Kuqa Depression.

10.11743/ogg20220406