松辽盆地白垩系非海相沉积层序模式

本文阐述了层序地层学在松辽盆地应用的主要依据,总结了白垩系层序地层的基本特征。归纳出层序边界的识别标志。在岩芯中层序边界附近见古土壤或根土层、河床滞留砾岩、水进滞留砾岩、水下滑塌、钙质结核及相突变现象,层序边界之上覆盖风暴岩、三角洲前缘席状流沉积、冲积扇、鲕粒灰岩、生物屑灰岩、物性良好的砂岩和火山岩。层序边界的测井响应特征为退积/前积渐变型、退积/加积突变型、加积/前积型、前积/前积型等。在地震剖面上,层序边界处见削截、上超、顶超等反射结构。根据地震、测井和岩芯资料的综合解释,重点论述了主要含油层系的体系域特征,由此提炼出松辽盆地白垩系层序地层理想模式。低水位体系域由滞后平衡表面之下的冲积扇、河口砂坝、“下切谷”充填物、滑塌、碎屑流沉积、浊积岩及三角洲前缘席状流沉积组成;水进体系域发育风暴岩、砂滩、砂坝、三角洲前缘席状砂、叠层石和碳酸盐浅滩;典型的密集段形成于海泛期,赋存于水进体系域顶部和高水位体系域底部;高水位体系域主要有三角洲、扇三角洲和曲流河体系组成。经对比,松辽盆地与海相基准面变化的二级旋回趋近,但三级旋回高于后者。

Sequence Stratigraphic Model of Nonmarine Sediments in Cretaceous, Songliao Basin

The main foundations of using the basic concepts of sequence stratigraphy in Songliao Basin and the fundamental characteristics of nonmarine seqences in Cretaceous are dealt with in the present paper. Around the sequence boundaries some erosional or exposure evidences in cores were found such as palaeosol or rootlet bed, fluvial lag conglomerate, transgressive lag conglowerate, subaqueous slumping, caliche nodules as well as geological record of the facies that changed abruptly, and there were tempestite, alluvial fan, deltatic front sheet flow deposit, oolitic limestone, bioclastic limestone, sandstone with excellent porosity and penetrability and volcanics upon the sequence boundaries. The logging responses of sequence boundaries were characteristic of progradation to retrogradation gradually, aggradation to retrogradation abruptly, progradation to aggradation or progradation to progradation and so on. It could be seen that on the seismic sections there were some reflecting configurations of truncation, onlap and downlap near the sequence boundaries. On the basis of the comprehensive interpretations of cores, well logs and seismic lines, the paper principally demonstrated the features of depositional system tracts of the major oil payzones. Based on these studies mentioned above, the authors constructed the idearlized models of sequence stratigraphy for the nonmarine Sonliao Basin. The lowstand system tract was composed of alluvial fan, river mouth bar, "incised valley" guests, sluming, debris flow deposit, turbidite and deltatic front flow deposits. The transgressive system tract consisted of tempesitite, sand bank and sand bar, carbonate shoal, sheet sandstone in deltatic front, stromatolite and so forth. The typical condensed section, which is located on the top of TST and on the bottom of HST, was composed of dark shales with marine nannofossils. The highstand system tract was mainly made up of delta, fan delta and meandering stream systems.