摘要： 四川盆地侏罗纪大安寨段沉积时期水体富营养化,形成了介壳灰岩—泥页岩的湖相混积层系,为混积岩沉积机制研究提供了“天然实验室”。综合利用岩心、测井、录井等资料,以川北仪陇—营山地区为研究区,对大安寨段的岩性分类与沉积相展布特征进行研究,并讨论了该湖相混积层系的沉积过程与控制因素。结果表明: 大安寨段湖相混积层系以介壳组分与细粒硅质碎屑(包含黏土矿物)的混杂与交替为主,整体上可划分为一个完整的湖侵—湖退沉积旋回,大一亚段与大三亚段沉积时期介壳滩分布面积较大,大二亚段则广泛发育半深湖—深湖亚相,此外浅水介壳灰岩可在重力流驱动下于深水环境中发生搬运与再沉积作用; 混积过程主要为相混合与间断混合模式,混积作用受控于湖平面升降变化、物质来源、地质营力等因素,湖平面的升降变化控制着不同沉积微相的分布,地震、风暴浪等触发机制引起的重力流沉积促使不同微相与物质来源的沉积物(陆源碎屑搬运、生物—化学碳酸盐沉积、远源细粒物质悬浮等)相互混合,增加了混积岩内部的杂乱程度并扩大了混积岩的平面分布范围。本次研究建立了仪陇—营山地区大安寨段湖相混积层系沉积过程模式,可为陆相页岩油气勘探和相似地质背景下混积作用的成因研究提供借鉴和参考。

关键词: 混积层系, 岩性分类, 沉积相展布, 沉积过程, 控制因素, 侏罗系, 川北

Abstract: Water eutrophication occurred during the depositional period of Jurassic Da'anzhai Member in Sichuan Basin,forming lacustrine hybrid sedimentary strata of fossiliferous carbonate and shale. It provides a “natural laboratory”for the study of depositional mechanism of mixed sedimentary strata. In this paper,the lithologic classification and sedimentary facies distribution of Da'anzhai Member in Yilong-Yingshan area located at the northern Sichuan Basin are studied based on core and well logging data,and the depositional process and controlling factors of the mixed sedimentary strata are also discussed. The results show that the lacustrine mixed sedimentary strata was composed of intermixing and alternation of bivalves,ostracods components and fine-grained siliceous debris(including clay minerals). The shell beach was widely distributed in the depositional stage of Da₁ and Da₃ sub-member,while Da₂ sub-member was dominated by semi-deep and deep lacustrine subfacies,which forms a complete lacustrine transgressive-regressive sedimentary cycle. Additionally,shallow-water coquina can be transported and re-deposited in deep-water environment driven by gravity flow. The lacustrine mixed depositional process was mainly facies mixing model and punctuated mixing model. The mixing depositional process was controlled by lake level fluctuation,provenance,geological agent, etc. The fluctuation of lake level controls the distribution of different sedimentary microfacies. Gravity flow caused by triggering mechanisms such as earthquakes,storms and waves,prompted the mixing of sediments from different material source and microfacies(terrigenous detrital transportation,bio-chemical carbonate deposition,suspended deposition of fine particles,etc.),increasing the internal disorder degree and expanding the spatial distribution scope of hybrid sedimentary rocks. Finally,the depositional mechanism model of lacustrine hybrid sedimentary rocks in Da'anzhai Member of Yilong-Yingshan area was established,which can provide theoretical support for the exploration of continental shale oil and gas and can provide reference for the study of hybrid sedimentary rocks under similar geological setting.

Key words: hybrid sedimentary strata, lithologic classification, sedimentary facies distribution, depositional process, controlling factors, Jurassic, northern Sichuan Basin

中图分类号: 

• P588.21