砾石在分析盆地物源区迁移与湖岸线演化中的作用*

中国中西部盆地的盆山结合部位,勘探程度较低、钻井少、地震成像复杂,致使利用传统的地震相、测井相、岩心资料等研究原型盆地岩相古地理特征较为困难。基于露头中巨厚砾岩发育层段对应盆地内储集层平面展布范围最广这一认识,运用“将今论古”方法,建立南天山前现代冲积扇、扇三角洲平原、河流等沉积体系中砾石与搬运距离关系,以及不同沉积相类型中砾石发育产状与湖岸线远近关系,定量计算了准噶尔盆地多条重点剖面侏罗系—白垩系现今位置与沉积物源区和湖岸线演化的距离,恢复了侏罗纪—白垩纪物源区范围与湖岸线演化过程。认为侏罗纪—早白垩世砂砾岩储集体向盆地内延伸范围最大时期的湖岸线,明显与现今盆地边缘线有一向西北方向敞开的夹角,该认识对在编制岩相古地理图过程中以盆地边缘线即为湖岸线的观念提出了不同见解,为恢复准南等低勘探程度区原型盆地的岩相古地理特征、预测有利储集体的展布提供参数依据。建立的刻画物源区变化和湖岸线迁移的定量评价方法与参数,是对传统沉积学研究的有益补充。

Role of gravel in analysis on migration of source area and lake shorelines in lacustrine basin

Low-resolution drilling and seismic imaging in the low-exploration area of the orogenic-basinal regions in the central and western parts of China is complicated. It is difficult to use traditional seismic facies, logging facies or core data to study the palaeogeographic features of the archetypal basin. We established the relationship both between gravel and transport distance, and between gravel development and shoreline migration in the pre-modern alluvial fan, fan delta plain, river and other sedimentary facies. The distance between several outcrops and shorelines from Jurassic to Cretaceous in the Junggar Basin was quantitatively calculated. The evolution process of source area and shorelines of the Junggar Basin in Jurassic to Cretaceous was reconstructed. The palaeogeographic features of the sedimentary archetypes of the basin in the lower-resolution exploration area of the southern and other regions are predicted to provide the basis for predicting the distribution range of the favorable reservoir. The establishment of the delineation of the source area and the quantitative evaluation parameters of the shorelines migration are an important and beneficial supplement for the innovation of traditional sedimentology.