松辽盆地北部青山口组四级层序划分及界面特征

Fourth-order sequence division and boundary characters of Qingshankou Formation in the northern Songliao Basin

根据单井沉积旋回对比,结合地震反射特征分析,本文将青山口组划分为3个三级层序,8个四级层序。四级层序界面主要有:1)河道冲蚀底界,表现为砾石层或砂砾岩层、内碎屑泥砾、钙砾或生物成因的灰质河道滞留物,测井曲线多为钟形;2)地表暴露面,表现为根土岩、古土壤层、紫红色泥岩或杂色泥岩、岩相突变带以及钙质结核层,测井曲线多为漏斗形;3)沉积物卸载区和滨岸带,出现钙质砂岩层、介形虫层等特殊沉积,测井曲线多具指形特征。层序界面的地震响应特征有:1)近物源的上坡折区,地震波组表现为削截或冲刷充填;2)坡折带发育区,地震波组表现为上超,亦见下超和顶超;3)强振幅反射同相轴所示的上、下地层的截然差异;4)地震波阻抗反演剖面波组上、下的截然差异等。松辽盆地北部青山口组的四级层序的划分及界面识别,为进一步建立四级层序格架奠定了基础。

Based on sedimentary cycle correlation of single well and analysis of seismic reflection characters, Qingshankou Formation in the northern Songliao Basin was divided into three thirdorder sequences and eight fourth-order sequences. The main fourth-order sequence boundaries were as follow ： 1 ） channel erosion bottom, showing as gravel beds, glutinite beds, intraclast mud pebble, calcigravel or biogenesis limy channel lag deposit, with campaniform logging curve, 2） surface exposure,showing as seat stone, ancient soil beds, mauve-varicoloured mudstone, lithofacies abrupt change and calcareous concretion beds,with logging curve being infundibuliform- shaped,and 3）sediments download area and lake-board, having particular sediments such as calcareous sandstone and ostracoda beds,with dactyline logging curve. The seismic response features of sequence boundary were as follow ： 1 ） near provenance and upper slope break, seismic train of waves showing as truncated or washing-filling reflectors,2）slope break area, seismic train of waves showing as onlap,sometimes downlap or toplap,3 ）sharp difference between upper and lower stratum shown by high amplitude reflection event, and 4）sharp difference be- tween upper and lower train of waves on seismic wave impedance section. The dividing and boundary recognizing of the fourth-order sequence laid the foundation to further establish the fourth-order sequence framework for Qingshankou Formation in the northern Songliao Basin.