辽河三角洲晚更新世以来的地层层序及沉积环境变迁

DEPOSITION AND ENVIRONMENTAL EVOLUTION OF LIAOHE RIVER DELTA SINCE LATE PLEISTOCENE

通过分析辽河三角洲获取的长41.4m的ZK2孔岩心的岩性、粒度、有孔虫丰度及分子标志物等资料的基础上,结合精确的测年数据、海面变化等资料,并与其他钻孔资料分析对比,构建了辽河三角洲晚更新世33ka BP以来的年代地层框架,将ZK2孔自下而上划分为U1-U4这4个沉积相段:U1为河道相,U2为河漫滩相,U3为海相(全新世海侵)和U4为上三角洲平原相。U3段的海相沉积自下而上又可进一步分为U3~1、U3~2、U3~3、U3~4、U3~5 5个沉积层,分别对应了河口湾相、浅海相、前三角洲相、三角洲前缘相、下三角洲平原相(潮坪相)。沉积物的粒度、有孔虫及生物标志物BIT等指标在不同沉积环境中出现了较为明显的变化,且变化趋势相似,揭示了辽河三角洲晚更新世33ka BP以来的海平面变化的沉积历史,其中U3段沉积物(15.75~2.65m)沉积连续,地层完整,测年数据可靠,较完整地反映了辽河三角洲9 100cal.a BP以来全新世海侵期的沉积历史。

The 41.4 mdeep coring hole of ZK2 was drilled at the Liaohe River Delta for the purpose to reveal the evolution of sedimentary environment.According to the depositional proxies,such as lithology,grain size,foraminifera and BIT,and the AMS14 C dating data,the ZK2 core is divided into four depositional units.From bottom to top,the U1 is a river channel facies,the U2 aflood plain facies,the U3 amarine facies（Holocene transgression）and the U4 is an upper delta plain facies.Furthermore,the Unit U3,i.e.the marine segment of the sequence,could be divided into five layers,namely U3~1,U3~2,U3~3,U3~4,U3~5 from bottom to top,corresponding to a sequence of estuarine facies-neritic facies-predelta facies-delta front facies-lower delta plain facies（tidal flat）.All the indices of grain size,foraminifera and BIT indicate an obvious vertical change in depositional environments,resulted from the sea level change around the delta since 33 kyr BP.As a continuous sequence without interruption calibrated by reliable dating data,the U3（15.75~2.65 m）may well reflect the Holocene transgression history of the Liaohe River Delta since 9 100 calyr BP.