松辽盆地北部白垩纪超层序特征

松辽盆地北部白垩系由3个超层序组、8个超层序、28个沉积层序组成。断陷湖盆期发育3个超层序和6个沉积层序,以火山岩与粗碎屑岩组合为特征。断拗转化期形成1个超层序和4个沉积层序,以中粗碎屑岩为特征。典型的大型拗陷湖盆期,可识别出3个超层序和15个沉积层序,以湖泊、三角洲相中细碎屑岩沉积为主,水进体系域和高水位体系域沉积时期半深湖-深湖相暗色泥岩广为发育。湖盆萎缩期,可识别出1个超层序和3个沉积层序,以湖泊、三角洲相中粗碎屑岩沉积为主。超层序组界面包括白垩系基岩顶面、营城组顶界面和嫩江组顶界面,与燕山运动各主要幕次形成的区域不整合面相对应,区域构造运动对其起着重要的控制作用。超层序界面可以是上述超层序组界面,也可由平行不整合面和剥蚀界面构成。超层序界面处沉积间断的时间较长,河道下切、地层缺失、暴露等沉积现象发育,与岩石地层单位界面一致。沉积层序界面处沉积间断的时间相对超层序界面要短,与岩石地层单位界面往往不一致。超层序界面在地震剖面上最明显的特征是出现削截、上超和顶超等反射终止现象,岩性、测井曲线也发生剧烈变化。

Characteristics of Cretaceous supersequences in Northern Songliao Basin

The Cretaceous in northern Songliao Basin can be divided into three supersequence sets,eight supersequences and twenty-eight sequences. Volcanic and coarse clastic successions formed during faulting stage contain three supersequences and six sequences. Medium-coarse grained clastics formed in the interim stage from faulting stage to depression stage contain one supersequence and four sequences. During the depression stage the lithology is dominated by lacustrine and deltaic medium-fine grained clasuics and can be divided into three supersequences and fifteen sequences. During uhe deposition of transgressive systems tract(TST)and highstand systems tract(HST)semi-deep and deep lacustrine dark mudstone were widely deposited. One supersequence and three sequences were identified during the shrinkage phase of lake basin when the lacustrine and deltaic medium-coarse grained clastics were dominant.Supersequence set boundaries that were controlled by tectogenesis, include the top boundaries of Cretaceous bedrock, Yingcheng Formation and Nenjiang Formation, which correspond to regional unconformities formed by major tectonic phases of Yanshan Movement. Supersequence boundaries can be either supersequence set boundaries disconformities or erosional surfaces levels. At the supersequence boundaries, the depositional hiatus is quite long, so that channel downcutting, stratigraphic gap and exposure etc. widely exist. Supersequence boundaries are in accord with lithostratigraphic unit boundaries. Compared to supersequence boundaries, the depositional hiatus at sequence boundaries is shorter and sequence boundaries are not compatible with lithostratigraphic unit boundaries. Supersequence boundaries are characterized by truncation, onlap and toplap etc. on the seismic sections and sudden change of lithology and logging curve.