扬子地台北缘城口地区上寒武统洗象池组风暴沉积特征及其地质意义

Sedimentary characteristics and geological significance of tempestites in the Upper Cambrian Xixiangchi Formation, Chengkou area, northern margin of the Yangtze Platform

王瀚 李智武 刘树根 宋金民 冉波 赖冬 韩雨樾

WANG Han LI Zhiwu LIU Shugen SONG Jinmin RAN Bo LAI Dong HAN Yuyue

成都理工大学 油气成藏地质及开发工程国家重点实验室, 成都 610059

State Key Laboratory of Oil and Gas Reservoir Geology and Exploration, Chengdu University of Technology, Chengdu, Sichuan 610059, China

上寒武统洗象池组是四川盆地的一个潜在勘探层位，但对其沉积相带展布及储层主控因素的认识还十分薄弱。在扬子地台北缘洗象池组发现的风暴沉积可以为此提供一些重要的约束。通过野外剖面实测和室内薄片鉴定，对扬子地台北缘城口地区洗象池组风暴沉积特征进行了深入分析，并探讨了其古地理含义及其对川东北地区洗象池组储层发育的指示意义。研究区洗象池组风暴沉积的典型识别标志包括底冲刷-充填构造、风暴撕裂构造、粒序层理和丘状交错层理等。根据风暴沉积标志组合的不同，划分出5种风暴沉积序列：序列1、序列2、序列3、序列4及序列5，且风暴段自下而上整体表现为由序列1向序列5逐渐过渡。根据沉积构造、岩性组合及风暴序列变化，结合经典浅水碳酸盐岩风暴沉积的发育模式，认为风暴段沉积环境整体以中缓坡为主，且自下而上由内缓坡、中缓坡向外缓坡变化，构成向上变深序列。结合区域地质背景，推测扬子地台北缘洗象池组在城口以北东地区处于中-外缓坡地带，而城口以南西地区则为内缓坡地带，从而认为洗象池组在城口南西方向的川东北地区具备发育大规模优质颗粒滩储层的地质条件，值得进一步勘探。

The Upper Cambrian Xixiangchi Formation has been considered as a potential target for hydrocarbon exploration in the Sichuan Basin, but little is known about its sedimentary facies and controls on reservoir quality. The tempestite deposition found in the Xixiangchi Formation at the northern margin of the Yangtze Platform may provide some important constraints for that. Through field survey and thin section analysis, we present a detailed description on the tempestite deposition of the Upper Cambrian Xixiangchi Formation in Chengkou area on the northern margin of the Yangtze Platform, and further discuss the significance for paleogeography and implications for hydrocarbon reservoir in the northeastern Sichuan Basin. Many diagnostic sedimentary structures can be recognized in these Upper Cambrian tempestites of the Xixiangchi Formation in Chengkou area, such as basal scour-and-fill structures, rip-up clasts, hummocky cross stratification (HCS), graded bedding, and so on. Five types of tempestite sequences were recognized in terms of variant assemblies of storm-induced sedimentary structures, with a gradual transition from Type 1 at the bottom to Type 5 on the top. According to tempestite deposition, lithological association and sedimentary sequence, combined with the classical mode of tempestites developed in shallow water carbonate environments, we suggested that the sedimentary environment of tempestites of the Upper Cambrian Xixiangchi Formation in Chengkou area were dominated by middle ramp, and evolved from inner ramp at the bottom to mid-outer ramp on the top, with a deepening-upward trend. Integrated with regional geological background, it is speculated that the Upper Cambrian Xixiangchi Formation on the northern margin of the Yangtze Platform is dominated by mid-outer ramp facies to the northeast of Chengkou, and inner-ramp facies to the southwest. This implies that there were many geologic advantages for high quality shoal reservoirs in the Upper Cambrian Xixiangchi Formation developed in the northeastern Sichuan Basin to the southwest of Chengkou, worthy to be explored in the future.

十三五国家科技重大专项（2017ZX05005003-007）和国家重点基础研究发展计划（973计划）项目（2012CB214805）联合资助。

https://doi.org/10.11781/sysydz201902176