湖相重力流沉积主控因素与分类方案研究进展

Research progress on main controlling factors and classification schemes of lacustrine gravity flow deposits

深水重力流沉积是当前全球油气的勘探热点。近三十年来,在湖相重力流的沉积特征、主控因素及沉积模式等方面均取得了丰硕成果。然而,由于陆相沉积盆地构造复杂、重力流类型发育多样,湖相重力流分类研究仍存在欠缺。本文通过系统梳理重力流发展历程与研究热点,总结了一套基于沉积成因和主控因素的湖相重力流沉积分类方案,并将湖相重力流的研究热点概括为以下3个方面:1)重力流主控因素研究:不同类型盆地的湖相重力流沉积特征和沉积模式差异性明显,主要受盆内因素和盆外因素控制,盆内因素主要包括盆地类型(如地形坡度)、沉降速率、水体密度等,盆外因素主要包括沉积物的成分和来源。2)“源-汇”系统下的重力流砂体分布:湖相重力流的形成演化和砂体分布样式通常受控于“源-渠-汇”系统,该系统能够将盆内因素与盆外因素很好地联系起来。3)湖相重力流分类:陆相湖盆相较海相盆地具有规模较小、水体较浅、构造活动强烈等特点,导致重力流沉积的控制因素与沉积特征多样、分类复杂。基于不同研究目的,可按沉积成因、发育位置或物源供给进行分类,但湖相重力流的分类方案尚未统一。本文综合考虑重力流成因机制与主控因素,将湖相重力流分为3大类7亚类,具体包括洪水型(缓坡富砂型、缓坡砂泥混合型、缓坡富泥型、陡坡富砂型、陡坡砂泥混合型)、滑塌型(挠曲滑塌型、断控滑塌型)以及洪水-滑塌共存型。目前,湖相重力流的研究成果已十分丰富,但在流体、流态转化和深水水道成因机制上仍存在很大进步空间,综合动力学和沉积学交叉领域探究湖相重力流的形成演化与成因机理研究已成为当前的研究热点和发展趋势。

Deep-water gravity flow sedimentation is topical in global petroleum and natural gas exploration.In the past 30 years,great achievements have been made in the sedimentary characteristics,controlling factors and sedimentary models of lacustrine gravity flow.However,due to the complex structure of continental sedimentary basins and the diverse development of gravity flow types,lacustrine gravity flow classification is still lacking.By systematically sorting out the development history and research into gravity flow,this paper summarizes a sedimentary classification scheme of lacustrine gravity flows based on sedimentary genesis and the main controlling factors,and summarizes the research into lacustrine gravity flows into the following three aspects.1)Research into the main controlling factors of gravity flow:the sedimentary characteristics and models of lacustrine gravity flow in different types of basins are obviously different.These are mainly controlled by intra-basin factors and extra-basin factors.The intra-basin factors mainly include basin types(such as topographic slope),sedimentation rate and water density,while the extra-basin factors mainly include the composition and sources of sediments.2)Gravity flow sand body distribution in source-sink systems:the formation and evolution of lacustrine gravity flow and the distribution pattern of sand bodies are usually controlled by the source-channel-sink system.This system effectively connects internal and external factors within the basin.3)Lacustrine gravity flow classification:Continental lacustrine basins,compared to marine basins,are characterized by smaller scale,shallower water bodies,and intense tectonic activity.These characteristics result in diverse controlling factors and complex sedimentary features of gravity flow deposition.According to different research purposes,it can be classified according to sedimentary origin,development location or provenance supply,but the classification scheme of lacustrine gravity flow has not been unified.In this paper,lacustrine gravity flow depositions are classified into three major types and seven subtypes,by comprehensively considering the causal mechanisms and main controlling factors of gravity flows.Specifically,lacustrine gravity flow depositions are classified into flood-type(gentle slope sand-rich type,gentle slope sand-mud hybrid type,gentle slope mud-rich type,steep slope sand-rich type,steep slope sand-mud hybrid type),slump-type(flexural slump type,fault-controlled slump type),and flood-slump coexisting type.There are plenty of research in the gravity flow of lacustrine facies at present.However,there is still much room for progress in fluid,flow transformation and genetic mechanisms of deep water channels.Therefore,the study of the formation,evolution and genesis mechanism of lacustrine gravity flows by integrating dynamics and sedimentology has become a current research and development trend.