松辽盆地松科2井下白垩统营城组火山-沉积序列精细刻画

Volcanic-sedimentary succession description of the Lower Cretaceous Yingcheng Formation based on the ICDP scientific drilling borehole in the Songliao Basin (SK-2)

中国白垩纪大陆科学钻探松科2井连续获取营城组岩心365.32m,岩心直径为214mm,岩心收获率达98.47%,是迄今直径最大,收获率最高且保存最为完整的营城组岩心,这些宝贵资料为营城组研究提供了前所未有的机遇。营城组时期与Aptian-Albian对应。通过对松科2井营城组岩心的精细描述,揭示了营城组火山-沉积序列及其建造过程。营城组主要包括沉积岩与火山岩两大岩类,共计17种岩石类型,其中沉积岩9种(砾岩、粗砂岩、中砂岩、细砂岩、粉砂岩、粉砂质泥岩、泥岩,含角砾凝灰质砂岩、凝灰质砂岩)、火山岩类8种(流纹岩、流纹质角砾集块岩、流纹质角砾集块熔岩、流纹质熔结凝灰熔岩、流纹质含角砾熔结凝灰熔岩、隐爆角砾岩、安山质集块熔岩与凝灰岩)。沉积相为扇三角洲相,具体分为扇三角洲平原亚相、扇三角洲前缘亚相与前扇三角洲亚相,分流河道微相、扇间沼泽微相,水下分流河道微相、河口砂坝微相与静水泥质沉积微相。火山岩相包括爆发相和喷溢相,具体分为空落亚相、热碎屑流亚相、喷溢相中部亚相和上部亚相。沉积岩与火山岩交替出现于营城组中,主要发育3期沉积岩与3期火山岩,自下而上形成3个完整的沉积-火山旋回,即沉积岩Ⅰ-火山岩Ⅰ、沉积岩Ⅱ-火山岩Ⅱ和沉积岩Ⅲ-火山岩Ⅲ。这一发现对于重新认识营城组时期构造-火山-盆地充填规律,可能具有重要启示。文中精细的描述资料为今后相关的深入研究提供了迄今最精准的基本地质素材。

China Cretaceous Continental Scientific Drilling in the Songliao Basin,called SK2 project,has collected 365.32 mof the lower Cretaceous Yingcheng Formation whose age is estimated as Aptian-Albian.The borehole got a highly continuous core section with recovery of 98.47%,which is the most complete and precise geological records up to now for the stratum of continental non-marine Cretaceous in the world.The diameter of core is 214 mm which is among the largest diameter concerning coring engineering.We first described the volcanic-sedimentary succession in centimeter scale and studied the volcanic and sedimentary facies.Considering the sedimentary and volcanic rocks as a whole sequence,we recognized seventeen rock types from drilling core of the Yingcheng Formation.There are nine types of sedimentary rocks,including conglomerate,coarse sandstone,medium sandstone,fine sandstone,siltstone,silty mudstone,mudstone,breccia tuffaceous sandstone,and breccia-bearing tuffaceous sandstone.There are eight types of volcanic rocks including rhyolite,rhyolitic tuff/pyroclastics/agglomerate,rhyolitic welded tuff,crypto-explosive breccia,andesitic tuff,and tuffite.Sedimentary facies is fan delta dominant which includes five sedimentary microfacies of distributary channels,back swamp between delta,subaqueous distributary channels,subaqueous mouth bar and mudstone of still water.Volcanic facies are explosive facies and effusive facies dominant,which include four volcanic subfacies of air-fall,pyroclastic flow deposits,middle and upper flow subfacies of the effusive one.According to detailed description of the Yingcheng sequence, we first recognized three periodic sedimentary and volcanic cycles in the Yingcheng Formation,which have been numbered sedimentaryⅠ-volcanicⅠ,sedimentaryⅡ-volcanicⅡ,and sedimentaryⅢ-volcanicⅢin ascending order.This is a new discovery concerning the vertical features of of the Yingcheng Formation.The centimeter scale description on the core sections from the SK2 may provide some other useful information for related researches in the future.