深沪湾末次冰期以来的地层结构及古环境演变

Stratigraphic structure and paleoenvironmental evolutionof Shenhu Bay since the last-glacial period

通过深沪湾高分辨率浅地层剖面声学地层和地质钻孔沉积地层的对比,并结合沉积物的粒度、微体古生物以及AMS14C测年的综合分析,揭示了研究区晚更新世末次冰期以来的地层层序,探讨了深沪湾的古环境演变。深沪湾高分辨率浅地层剖面自上而下划分的5个声学地层单元与钻孔岩芯划分的5个沉积地层单元具有较好的对应关系。8.2 ka BP左右,全新世海侵使得海水进入深沪湾海域,海平面低于现今海平面10~12 m,气候凉爽;7 ka BP左右海水到达现今海平面位置,并于6 ka BP左右到达最高,约比现今海平面高2~3 m,气候温暖湿润,这一时期,近岸大量裸子植物被海水淹没并被沉积物快速掩埋;5 850~5 642 a BP研究区温度降低,该降温活动持续到2 ka BP左右,气候凉爽干燥;2 ka BP以来温度逐渐上升,600 a BP左右有一个相对冷期,之后温度又逐渐上升至现今水平。

Based on the comparison of high-resolution seismic reflection and typical core data,combined with the comprehensive analysis of sediment grain size,clay minerals,micropalaeontology and AMS 14 C dating,we revealed the stratigraphic sequence since the last-glacial period of Late Pleistocene in the study area,and discussed the paleoenvironmental evolution of Shenhu Bay.The high-resolution seismic profiles selected from the study area was subdivided into five seismic units(SU1,SU2,SU3,SU4,SU5)in ascending order,which are correspond well with the five sedimentary stratigraphic units(DU1,DU2,DU3,DU4,DU5).About 8200 years ago,the sea water entered the Shenhu Bay area during the Holocene transgression.Then the sea level was 10-12 m lower than the present level,and the climate was cool.The sea water reached the present sea level at about 7 ka BP and reached the maximum at about 6 ka BP,the highest sea level was about 2-3 m higher than present level.During this period,the climate was warm and humid.Meanwhile,a large number of gymnosperms were inundated by sea water and were quickly buried by marine sediments.The temperature in the study area decreased at about 5850 to 5642 a BP,and the cooling activity lasted until about 2 ka BP,during which the climate was cool and dry.The temperature gradually increased since 2 ka BP and there was a relatively cold period about 600 years ago after which the temperature gradually increased to the present level.