咸水湖泊细粒重力流沉积及油气意义:以柴达木盆地英西地区下干柴沟组上段为例  

Fine-grained gravity flow deposits and their petroleum significance in saline lacustrine basins:a case study from the Upper Member of Lower Ganchaigou Formation in Yingxi area of Qaidam Basin,China

作　　者：王小妮 杨智[1] 冯有良[1] 蒋文琦 龙国徽 伍坤宇 张洪[1] 侯鸣秋 邢浩婷 张天舒[1] 刘畅[1] 魏琪钊 WANG Xiaoni;YANG Zhi;FENG Youliang;JIANG Wenqi;LONG Guohui;WU Kunyu;ZHANG Hong;HOU Mingqiu;XING Haoting;ZHANG Tianshu;LIU Chang;WEI Qizhao(Research Institute of Petroleum Exploration and Development,PetroChina,Beijing 100083,China;Research Institute of Petroleum Exploration and Development,PetroChina Qinghai Oilfield Company,Gansu Dunhuang 736200,China;School of Earth and Space Sciences,Peking University,Beijing 100871,China)

机构地区：[1]中国石油勘探开发研究院,北京100083 [2]中国石油青海油田分公司勘探开发研究院,甘肃敦煌736200 [3]北京大学地球与空间科学学院,北京100871

出　　处：《古地理学报》2024年第4期985-1004,共20页Journal of Palaeogeography：Chinese Edition

基　　金：中国石油天然气集团“十四五”前瞻性基础性重大科技项目“页岩油勘探开发理论技术研究”(编号:2021DJ18)和“陆相页岩细粒沉积源储特征与页岩油有利区段评价研究”(编号:2021DJ1802)联合资助

摘　　要：细粒重力流可以将滨浅湖的碎屑物质和有机质搬运至半深湖—深湖,形成沉积粒度小于0.0625 mm的细粒重力流沉积物,是深湖环境的重要搬运和沉积作用之一。柴达木盆地英雄岭地区西部下干柴沟组上段(E3~2)为咸水的半深湖—深湖环境,发育了湖底扇—深湖化学沉淀碳酸盐岩沉积体系。研究表明下干柴沟组上段发育有7大类岩相:云/灰质泥岩、粉砂质泥岩、白云岩、泥质白云岩、泥质粉砂岩、细粉砂岩以及粗粉砂岩岩相,形成了7类细粒沉积岩相组合:(1)泥流—泥质湍流—安静水体沉积岩相组合(LA1);(2)半深湖化学沉淀与事件沉积互层岩相组合(LA2);(3)滑塌—细粒碎屑流—泥流沉积岩相组合(LA3);(4)细粒异重流沉积岩相组合(LA4);(5)细粒浓缩密度流沉积岩相组合(LA5);(6)细粒碎屑流—细粒过渡流—细粒浊流沉积岩相组合(LA6);(7)细粒浓缩密度流—细粒湍流—细粒过渡流—泥流沉积岩相组合(LA7)。细粒重力流作用及其相互转化,形成了多样的岩相组合,反映了复杂的沉积作用过程。湖盆细粒沉积物的形成和分布受古气候、盆地构造及湖平面变化的影响。在整体干旱的气候背景下,气候湿润湖平面上升有利于优质烃源岩和细粒异重流的发育;气候干热湖平面下降则有利于发育化学沉积的碳酸盐岩层和滑塌引起的细粒重力流沉积。咸水湖盆半深湖—深湖环境发育的代表泥流—泥质湍流—安静水体沉积的岩相组合(LA1)和化学沉淀碳酸盐岩与事件沉积碳酸盐岩互层的岩相组合(LA2)是优质的“甜点段”。Fine-grained gravity flows can transport clastic sediments and particulate organic matter from shallow water to deep lakes,forming distinctive sediments finer than 0.0625 mm.During the depositional period of the upper section of the Lower Ganchaigou Formation(E23),a sub-lacustrine fan system and chemically precipitated carbonates developed in a saline semi-deep to deep lake in the Yingxiongling area of the Qaidam Basin.Seven types of lithofacies associations(LA)are identified in the fan fringe sub-environment on the basis of core observations:LA1:association of mud flow,mud turbulent flow,and suspension fallout deposits in quiet water;LA2:association of chemical deposits interbedded with event deposits in semi-deep lake;LA3:association of slump,fine-grained debris flow,and mud flow deposits;LA4:fine-grained hyperpycnal flow deposits;LA5:fine-grained concentrated density flow deposits;LA6:association of fine-grained debris flow,fine-grained transitional flow,and fine-grained turbidity current deposits;LA7:association of fine-grained concentrated density flow,fine-grained turbulent flow,fine-grained transitional flow,and mud flow deposits.These lithofacies associations are attributed to various fine-grained gravity flows and their transformations which are suggestive of complex flow processes.Our study also shows that the fine-grained deposits are influenced by paleoclimate,tectonic activity,and lake-level fluctuations.In an arid environment and during humid periods,lake-level rise promotes the formation of favorable source rocks and fine-grained gravity flow deposits.Conversely,in times of drought,lake-level decrease is more conducive to the development of chemically precipitated carbonates and slump-derived fine-grained gravity flow deposits.Mud flow,mud turbulent flow,and fallout deposits in quiet water(LA1)and chemical deposits interbedded with event deposits(LA2)are the most favorable“sweet sections”in the saline semi-deep to deep lake.

关 键 词：细粒重力流沉积 咸化湖泊 页岩油 下干柴沟组上段 英雄岭地区 柴达木盆地 

分 类 号：P512.32[天文地球—地质学]