大凌河河口地区中更新世晚期以来沉积环境演化

Sedimentary environmental evolution of the Dalinghe Estuary area since the Late Middle Pleistocene

大凌河河口地区LZK06孔40m以浅岩心的沉积学、古生物学和年代学等综合研究以及该地区LZK02-04钻孔资料,揭示了研究区中更新世晚期以来经历了两次海侵-海退旋回,依次形成了中更新世晚期湖相/河流相→晚更新世海相-湖相/河流相→全新世海相-河流相地层。全新世早中期由于物源供给很少,研究区处于长达约10ka的饥饿滞留相沉积环境,平均沉积速率仅约0.02~0.05cm/a。全新世晚期约1500a cal BP以来,由于人类活动导致水土流失,河流输砂量增加,研究区开始了快速加积过程,平均沉积速率约0.9~1.2cm/a,下辽河平原被快速充填,开始成陆。与全球海面变化时空分布特征的对比,推断辽东湾的第II海相层发育于MIS 5-MIS 3早期,第I海相层发育于MIS 1阶段高海面时期。晚更新世以来频繁的海面升降是辽东湾泥质海岸带地层和环境演化的主要控制因素。

The comprehensive studies of sedimentology, micropaleontology and chronology of borehole LZK06 at 40 m depth and combined with the data of boreholes LZK02-04 in the Dalinghe estuary area revealed that the study area experienced two transgression-regressions since the Late Middle Pleistocene, and the Late Middle Pleistocene lacustrine/fluvial Late Pleistocene marine lacustrine/fluvial Holocene marine fluvial stratums were sequentially formed. In the Early and Middle Holocene, due to the lower source supply, the study area was in a 10 ka long phase of starving deposition environment with an average sedimentary rate of 0.02~0.05 cm/a. In the Late Holocene, about 1500 years ago, due to the human activities leading to soil erosion and increased sediment transport in the river, the study area began a rapid accretion process with an average sedimentary rate of 0.9~1.2 cm/a, and the lower Liaohe plain was quickly filled. Compared with the tempo-spatial pattern of global sea level change, it is speculated that the marine bed II was formed in MIS 5-early MIS 3 and marine bed I was formed in MIS 1. Frequent sea level change is the main controlling factor for stratigraphic and environmental evolution in the muddy coast of Liaodong Bay since the Late Pleistocene.