海拉尔盆地侏罗系火山-沉积岩地震识别和岩相古地理重建

Seismic Identification of the Jurassic Volcano-Sedimentary series in the Hailar Basin and Lithofacies Palaeogeography Reconstruction

海拉尔盆地侏罗系塔木兰沟组火山岩显示有巨大油气勘探潜力.海拉尔盆地内侏罗系“塔木兰沟组”火山喷发期次和岩相分布尚不清楚,制约了盆内火山岩型油气藏勘探部署.针对海拉尔盆地火山岩相复杂且相变快,火山机构类型多样等特点,通过野外露头调查、年代学资料和单井和连井地震对比,利用地震剖面、时间切片、三维可视化和均方根振幅属性提取等技术,对盆内各个凹陷开展火山-沉积岩识别、旋回划分和岩相古地理恢复.野外露头、测井、地震反射、火山岩U-Pb年代学等证据都表明海拉尔盆地侏罗系发育2期火山-沉积旋回.火山喷发沉静期于火山机构外围发育沉积岩夹层,在地震剖面上形成的连续反射且可区域追踪对比,可以作为旋回划分依据.利用均方根振幅属性对岩性敏感特性来勾勒火山机构和外围的沉积岩.盆内第1期火山-沉积旋回岩以中基性火山岩、酸性火山岩和沉积岩为特征,对应于盆地外围的塔木兰沟组.第2期火山-沉积旋回岩以酸性火山岩和沉积岩为主,对应于盆地外围的玛尼吐组.盆内西部凹陷带主要发育火山机构和裙边砂砾岩体,中部和东部凹陷带主要发育湖相砂岩和泥岩.各个凹陷内火山机构主要集中在盆地或斜坡带,侏罗系火山-沉积发育具有明显的火山-断陷湖盆特征,与区域上额尔古纳和德尔布干断裂空间展布关系密切.

Jurassic volcanic rocks of the Tamulangou Formation show great potential for oil and gas exploration, but it is not clear that the volcanic eruption cycles and paleogeography of the Tamulangou Formation, which restricts the exploration for volcanic reservoirs in the basin. Considering the complicated volcanic facies that are often fast changed and various volcanic edifices, this paper comprehensively analyzes outcrop investigation, volcanic U-Pb geochronology, drilling and logging, and seismic data, and uses the technology of seismic reflection features, time slice, three-dimensional visualization and Mean Square Root Amplitude property to identify volcano-sedimentary series, volcanic eruption cycles and lithological paleogeography of each sag in Hailaer Basin. These lines of evidence suggest that Jurassic rocks in Hailaer Basin developed two sets of volcanic-sedimentary cycles.Sedimentary beds that deposited outside volcanic edifices during the intermittent period of volcanic eruptions are used as mark beds to regionally recognize eruption cycles due to the continuous reflections formed on the corresponding seismic profile. The Mean Square Root Amplitude that is sensitive to lithology is used to outline volcanic edifices and their surrounding sedimentary beds.The first volcanic-sedimentary cycle is characterized by mafic to acidic volcanic rocks and sedimentary intervals that correspond to the Tamulangou Formation outside of the basin. The second volcanic-sedimentary cycle is characterized by acidic volcanic rocks and sedimentary intervals, corresponding to the Manitu Formation outside of the basin. The western depression zone mainly develops volcanic edifices and volcanic-sedimentary aprons at the edges of the volcanic edifices. The central and eastern depression zones mainly develop lacustrine sandstone and mudstone. The volcanic edifices inside sags are mainly concentrated in the basin floor or slope zone. The Jurassic volcanic-sedimentary rocks in the Hailar Basin shows typical characteristics of fault-control lake basins, and the Erguna and Deerbugan fault zones in the region greatly influence the distribution of volcanic-sedimentary rocks.