渤海湾北岸TZ02孔晚新生代沉积环境演化过程

摘要

渤海湾北岸晚新生代沉积环境和沉积体系不仅是区域水文地质、工程地质的基础,也为古近纪沉积模式提供“将今论古”的依据.本文依据沉积物色度和粒度,以及沉积物岩性、结构和构造等,将渤海湾北岸TZ02孔划分了6个沉积组合、4个沉积阶段:1)2.10～3.22Ma,沉积组合Ⅰ和Ⅱ,湖盆填充期,发育湖相-泛滥平原相或湖相-曲流河相,该时期处于构造稳定期,干冷气候时期发育河流相、泛滥平原相,湿润气候时期发育湖泊相.2) 1.33～2.10Ma,沉积组合Ⅲ,湖盆开始发育期,主要为浅湖相,仅有少量砂体,下部多有机质,上部多钙质淀积结核,指示了盆山之间的构造分异后,湖泊初始发育的特征.3)0.62～1.33Ma,沉积组合Ⅳ,湖盆扩张期,以湖相为主,多砂体,旦有短期湖泊水位变浅和成陆过程;指示了盆山构造分异后,盆地加速沉降,湖盆扩张;山体隆起、河流下切,盆地中湖相砂体增多;此时TZ02孔附近为湖相中心,BG10孔为湖泊边缘. 4)0～ 0.62Ma.沉积组合V和Ⅵ,湖泊填充期,BG10孔为湖相的沉积中心,而TZ02孔为湖泊的边缘,接受滦河迁移摆动后的沉积物;中更新世后,构造沉降形成湖相,而间冰期发育海相,埋深0 ～ 22.5m的海相-河流相更直接地反映了末次冰消期海平面变化过程.%Northern Bohai Bay is located within the northern Huanghua Depression,which has a number of secondary tectonic units.The Cenozoic strata of the Huanghua depression are over 6000m thick:ca.3100m for the Paleogene,ca.2400m for the Neogene,and 330～490m for the Quaternary.Borehole TZ02 (39°19.7′N,119°5.3′E) is located in the southern Laoting County of Tangshan,Hebei Province,and within the Laoting sag of the Huanghua Depression,and located at the natural levee of the abandoned channel for the Luanhe River.Borehole TZ02 has a length of 550m.Based on the luminance values and redness values of sediments,and combining the sedimentary characteristics and grain size characteristics,borehole TZ02 has been divided into six stratigraphic units,and the times of these units have been dated by detail magnetostratigraphic chronology.The bottom age of borehole TZ02 is ca.3.22Ma.From bottom to top,the six stratigraphic units have been identified:(1) The unit Ⅰ,whose age is 2.58～3.22Ma,with the depth of 439.5 ～ 550.0m,has been dominated by lacustrine facies-flood plain and lacustrine facies-meandering river facies.(2) The unit Ⅱ,whose age is 2.10～2.58Ma,with the depth of 357.4～439.5m,has been dominated by lacustrine facies-flood plain facies.(3) The unit Ⅲ,whose age is 1.33 ～ 2.10Ma,with the depth of 241.3～357.4m,has been dominated by lacustrine facies which interbedded a few sand bodies.(4) The unit Ⅳ,whose age is 0.62～ 1.33Ma,with the depth of 120.9～241.3m,has been dominated by lacustrine facies-flood plain and lacustrine facies-lacustrine sand bodies.(5) The unit Ⅴ,whose age is 0.01～0.62Ma,with the depth of 22.5～ 120.9m,has been dominated by lacustrine facies-lacustrine sand bodies and lacustrine facies-braided channel facies,and interbedded the thinner marine bed in the lower of lacustrine facies.(6) The unit Ⅵ,whose age is 0～0.01Ma,with the depth of 0～22.5m,has been dominated by marine facies-fluvial facies.Based on the sedimentary assemblage,there are four depositional phases:(1) The phase of infilling basin,whose age is 2.10～3.22Ma,has been dominated by lacustrine facies-flood plain and lacustrine facies-meandering river facies,and it belongs to the tectonic stable period.During this period,climate change is the main factor controlling sedimentary process,the lacustrine facies had been formed within the warm and humid climate,the flood plain and meandering river facies have been formed within the dry and cold climate.(2) The phase of basin initial development,whose age is 1.33～ 2.10Ma,has been dominated by the shallow lacustrine facies which interbedded a few sand bodies,and organic materials in lower part,and calcareous concretions in upper part,which indicate that the shallower water level is upward and the smaller sedimentation flux are the main characteristics of shallow lacustrine facie after the tectonic differentiation between mountain and basin.(3) The phase of basin expansion,whose age is 0.62～ 1.33Ma,has been dominated by the lacustrine facies with the more sand bodies,which indicate that the basin has expanded with the accelerated tectonic subsidence,and the sedimentation flux has increased by the fluvial erosion with the uplift mountain.While the round TZ02 is the center of the lake,the round BG10 is the edge of the lake with the action of the tectonic movements by NWW-orientated faults.(4) The phase of infilling basin,whose age is 0～0.62Ma,has been dominated by the lacustrine and marine facies.The round BG10 is the center of the lake,while the round TZ02 is the edge of the lake and receive the sediments of Luanhe River.The tectonic subsidence is the main controlling factor to form the lacustrine facies.The marine facies have been formed in the interglacial period,especially in super-interglacial period.The marine facies-fluvial facies of unit Ⅵ directly reflect the sea level changing of the Last Deglaciation.