摘要：

喷发环境对于火山岩储集层的形成和发育具有重要的影响,不同喷发环境下形成的火山岩储集层在储集空间类型、物性特征等方面均有较大的差异,因此准确识别喷发环境、明确不同喷发环境的特征和岩相组合及建立火山喷发模式,对于准噶尔盆地火山岩成因分析、古环境恢复及有利储集层预测具有重要的理论意义和现实意义。文中以准噶尔盆地东部地区石炭系火山岩为研究对象,综合利用野外露头、岩心、测录井、镜下薄片、元素地球化学和有机地球化学等分析资料,确定喷发环境的识别标志,分析不同喷发环境下的岩相组合特征,最终建立不同喷发环境下火山岩的喷发模式。研究结果表明: (1)准噶尔盆地东部地区火山岩喷发环境分为水下喷发和陆上喷发2种,其中水下环境中的火山岩受水体环境影响,发育珍珠岩、细碧岩、石泡流纹岩等特殊岩性,常与沉积岩互层,并具有枕状构造、石泡构造、冻鱼层构造及晶形不完整、玻璃质含量高等结构构造特征,而陆上喷发环境中的火山岩通常具有气孔发育、晶形完整、氧化系数高等特征。(2)早石炭世准噶尔盆地东部地区以水下喷发环境为主,表现为自西向东水体逐渐加深,Sr/Ba值由0.22增大至1.77,指示其由淡水环境经半咸水环境过渡至咸水环境; 晚石炭世以水上环境为主,表现为氧化系数多大于0.5,在局部地区存在水下环境,且水体较浅。(3)准噶尔盆地东部地区的陆上、水下2种喷发模式又可分别划分为近火山口和远离火山口类型,共组成4种岩相组合类型,其中陆上喷发模式主要表现为爆发相和溢流相,水下喷发模式则主要表现为爆发相、侵出相、溢流相和火山沉积相。

关键词: 准噶尔盆地, 石炭系, 火山岩, 喷发环境, 岩相组合, 喷发模式

Abstract:

As an unconventional reservoir,volcanic rock reservoirs exhibit significant heterogeneity. The eruption environment significantly influences the formation and development of these reservoirs. Therefore,accurately identifying the eruption environment and clarifying the characteristics of various eruption environments,along with their associated lithofacies combinations and the established volcanic eruption pattern,is essential for analyzing the volcanic rock genesis,paleoenvironment restoration and the favorable reservoir prediction in Junggar Basin. This study focuses on Carboniferous volcanic rocks and employs a comprehensive analysis that includes field observations,core samples,well logs,thin sections,geochemical elements,and organic geochemistry. The study is organized into three primary steps: (1)establishing identification criteria for various eruption environments,(2)analyzing the characteristics of lithofacies combinations in various eruption environments,and(3)identifying the eruption modes of volcanic rocks in these environments. The results indicate the following: (1)The Carboniferous volcanic rocks in the eastern Junggar Basin exhibit two types of eruptions: subaqueous and subaerial eruptions. Subaqueous eruptions often give rise to distinctive lithologies such as perlite,obsidian,and sepiolite rhyolite,characterized by structures including pillow structures,sepiolite structures,frozen fish layer structures,incomplete crystal forms,and high glass content. In contrast,subaerial eruptions typically display well-developed vesicular textures,complete crystal shapes,and high oxidation coefficients. (2)During the Early Carboniferous period,it was primarily characterized as the subaqueous eruptions,with water bodies gradually deepening from west to east. The Sr/Ba ratio increased from 0.22 to 1.77,indicating a transition in the freshwater environment from brackish to a more saline condition. In contrast,during the Late Carboniferous,it was mainly marked by subaerial eruptions,with an oxidation coefficient exceeding 0.5. Although some areas maintained an underwater environment,the water body were generally shallow. (3)The subaqueous and subaerial eruption modes in the eastern Junggar Basin can be categorized into four distinct types of lithofacies associations: (i)near-crater subaqueous lithofacies assemblage,(ii)distal subaqueous lithofacies assemblage,(iii)near-crater subaerial lithofacies assemblage,and(iv)distal subaerial lithofacies assemblage. Subaqueous eruption mode is primarily characterized by an explosive phase and an overflow phases,whereas the subaerial eruption mode is characterized by an eruption phase,an intrusion phase,an overflow phase,and a volcanic sedimentation phase.

Key words: Junggar Basin, Carboniferous, volcanic rock, eruptive environment, lithofacies association, eruption pattern