长江三角洲DY03孔颗石藻及沉积环境浅析

LATE QUATERNARY CALCAREOUS NANNOFOSSILS OF CORE DY03 IN THE YANGTZE RIVER DELTA AND THEIR SEDIMENTARY ENVIRONMENTAL SIGNIFICANCE

本文研究了上海奉贤DY03孔的颗石藻化石。钻孔60.8-2m深度产颗石藻化石,涵盖上更新统的川沙组、南汇组,全新统的娄塘组、上海组和青浦组。颗石藻化石赋存于灰色泥、泥质粉砂或粉细砂中,但化石种类贫乏。群落面貌以Gephyrocapsa oceanica占绝对数量,Braarudosphaera bigelowii,Helicosphaera hyalina和Heli-cosphaera wallichii等偶现,属典型的单种类组合。研究依据颗石藻定量统计,划分出两个海相层:第一海相层,孔深61-40m,属上更新统川沙组和南汇组,颗石藻丰度低,属种单一,代表了海侵过程中的潮上带环境;第二海相层,孔深24.8-2.0m,属全新统娄塘组、上海组和青浦组,颗石藻化石丰度较高,并有数个属种共生,反映当时的滨岸潮上带-河口滨海-浅海近岸海湾的环境演化过程。综合前人的研究成果,认为长江三角洲全新世海侵之强度和范围都超过晚更新世发生的海侵。此外,本文仔细讨论了Gephyrocapsa oceanica的生态特征,显示其为一个盐度适应能力较强、分布广泛的暖水种。

Calcareous nannofossil analyses were performed on a -250 m core （DY03, Fengxian, Shanghai） to recon- struct the paleo-environment conditions. The nannofossils exist only from the core depth of 60.8--2 m,in the Chuan- sha and Nanhui Formations of the Upper Pleistocene, and in the Loutang, Shanghai and Qingpu Formations of the Holocene. Calcareous nannofossils occur in grey mud, muddy silt or muddy fine sand, but in a lower diversity;Gephy- rocapsa oceanica is the predominant species in the core, while Braarudosphaera bigelowii, Helicosphaera hyalina and Helicosphaera wallichii occasionaly occur in some samples,suggesting a mono-species assemblage. Based on the distribution of calcareous nannofossils, two intervals of marine strata were recognized. First inter- val, 61 40 m, belongs to the Chuansha and Nanhui Formations o{ the Upper Pleistocene. Here, the calcareous nan- nofossils has a lower abundance and diversity, which indicates an environment of super tidal zone. Second interval, 24.8--2.0 m, helongs to the Loutang,Shanghai and Qingpu Formations of the Holocene. The calcareous nannofos sils has a higher abundance and several species co-existed, which suggests an intertidal- estuary- shallow marine envi- ronment. The calcareous nannofossil record also implies a stronger Holocene transgression than during the Late Pleis tocene in the Yangtze River delta.