松辽盆地北部西斜坡姚家组分层特征及其成因分析

根据录井、测井、岩芯等资料确定姚家组划分标志与分布情况,姚家组底界面为区域不整合面,姚一段和姚二、三段地层超覆于青二、三段地层之上,垂向上向西依次尖灭;姚一段分布范围较小,局限于研究区东侧,姚二、三段地层分布范围较大。在构造、湖平面变化、湖岸线位置、古地形和沉积体系物源供应的共同影响下,姚一段和姚二、三段沉积环境不同,所发育的沉积体系发生变化,并最终导致岩性和电性发生变化,形成分区,姚一段地层划分为分区特征明显的3个地层小区,姚二、三段地层划分为分区特征明显的4个地层小区。

THE STRATIGRAPHIC DIVISION AND SEDIMENTARY GENESIS OF THE YAOJIA FORMATION IN THE WESTERN SLOPE REGION OF THE NoRTHERN SONGLIAO BASIN

The general stratigraphic division and distribution of the three members of the Yaojia Formation are clarified on the basis of well log and core data.The basic boundary of the Yaojia Formation is a regional terrestrial unconformity surface.The strata of the Member 1 and those of members 2-3 of the Yaojia Formation overlap above different horizons of the members 2 and 3 of the underlying Qingshankou Formation.They thin and eventually disappear toward the western part of the basin.The geographic distribution of the Member 1 of Yaojia Formation is relatively small and is mainly restricted to the eastern part of the study area.The distribution of the members 2 and 3 of Yaojia Formation is larger than that of the Member 1 of Yaojia Formation.These differences are related to the tectonics,lacustrine level change,the position of lacustrine bank line,paleotopography,and sediment supplies.The sedimentary environments of the Member 1 of Yaojia Formation and the members 2-3 of Yaojia Formation are different,resulting in their different depositional systems,lithostratigraphic features,electric properties,and geographic distribution.The distribution of the Member 1 of Yaojia Formation can be divided into three stratigraphic subareas and that of the members 2-3 of Yaojia Formation into four stratigraphic subareas.