辽东湾晚第四纪层序地层

Sequence stratigraphy of the Late Quaternary in Liaodong Bay

通过对辽东湾高分辨率浅地层剖面声学地层与典型钻孔沉积地层的对比分析,揭示了研究区晚第四纪MIS5以来的地层层序。辽东湾高分辨率浅地层剖面自下而上划定的6个声学地层单元(SU5、SU4、SU3、SU2、SU12、SU11)与钻孔岩芯划分的6个沉积地层单元(DU5、DU4、DU3、DU2、DU12、DU11)具有良好的对应关系。分别与MIS4期、MIS2期低海面时期的沉积间断密切相关的两个层序界面R5、R3,将辽东湾识别出的地层单元自下而上划分为3个层序(SQ3、SQ2、SQ1)。其中SQ3仅识别出上部的海侵体系域与高水位体系域,对应MIS5期海平面相对较高时期的滨浅海相沉积(DU5);SQ2自下而上由低水位体系域(MIS4期的河流相与河道充填相沉积(DU4))与海侵体系域(MIS3期早中期滨海相沉积(DU3))组成;SQ1自下而上包括低水位体系域(MIS2期的河流相与河道充填相沉积(DU2))、海侵体系域(全新世早中期滨海相沉积(DU12))高水位体系域(全新世高海面以来的浅海相沉积(DU11))。研究区的海侵体系域厚度较薄且变化较小,分布广泛,而低水位体系域厚度与横向分布均变化较大。

High-resolution seismic reflection data are studied in details together with core data in order to determine the stratigraphic sequence of Liaodong Bay since the MIS5 of Late Quaternary.The high-resolution seismic profiles selected from the study area may be subdivided into six seismic units,i.e.SU5,SU4,SU3,SU2,SU12,SU11 in descending order,which could be clearly correlated with the six depositional units,DU5,DU4,DU3,DU2,DU12,DU11 respectively based on lithology,microfossil assemblages and geochronology of the cores.These units may be grouped into three distinctive sequences,SQ3,SQ2,SQ1 in descending order by two sequence boundaries of R5 and R3 with obvious hiatus,which correspond to the low sea-levels of MIS4 and MIS2,respectively.The SQ3 is the remained upper part of transgressive systems tract(TST)and highstand systems tract(HST),corresponding to DU5,the littoral and neritic facies of MIS5.SQ2 is composed of lowstand systems tract(LST),fluvial deposits and incised-channel filling facies(DU4)formed in MIS4 plus the TST littoral facies(DU 3)deposited during Early-Middle MIS3.And the SQ1 is comprised of the LST,DU2 fluvial deposits to incised-channel filling facies formed in MIS2,TST,DU12 deposits of littoral facies formed during Early-Middle Holocene,and the HST,DU11 deposits of neritic facies since the highstand sea-level of Holocene.The TSTs is relatively continuous and widely distributed,while LSTs vary considerably in thickness and lateral distribution since MIS5 in Liaodong Bay.