辽东湾坳陷渐新统生物相及湖泊演变

OLIGOCENE BIOFACIES AND LAKE ENVIRONMENT EVOLUTION OF THE LIAODONG BAY DEPRESSION

如何揭示深水湖盆演变过程,是一个困扰地质学家的难题,生物相是一个有效的研究手段。本文利用辽东湾坳陷渐新统特有的渤海花介属Bohaichthere、天津介属Tianjinia等标志化石新建了E相,利用介形类、腹足类、藻类等标志化石有序组合重新厘定了A相、B相、C相和D相,并以之为依据,对沉积环境进行了分析。通过渐新统不同时期的生物相的横纵向变化特征,分析了生物群和湖泊水体环境的演变过程。生物群的出现、繁盛、绝灭与湖泊的扩张、收缩、灭亡具有一致性。湖泊长期深水水体的存在是西营介属Xiyingia能够在渐新世继续生存的主要原因。渐新世湖泊水体中心区始终位于JZ25-2-A至JZ20-2N-A井一线的坳陷中心区域,中期存在一次向北、盆地边缘扩张过程,晚期湖泊水体中心区向坳陷中心收缩直至灭亡。

How to reveal the evolution of deep lake basins is a challenge to the geologists.The biofacies is one of the effective research means.In this paper,the E phase has been newly constructed from the Iconic fossils of Bohaichthere,Tianjinia and so on,which are unique to the Oligocene record in the Liaodong Bay Depression.Meanwhile,the A,B,C and D phases were redefined by the orderly assemblage of ostracoids,gastropods and algae.Then,based on this,the sedimentary environment was analyzed.Through the characteristics of the horizontal and vertical changes of biofacies in the different Oligocene periods,the evolution process of biota and lake water environment was analyzed.The emergence,prosperity and extinction of biota were consistent with the expansion,contraction and extinction of the lake.The long-term existence of deep water in the lake was the main reason for the survival of Xiyingia in the Oligocene.The central area of the Oligocene lake water body was always located in the center of the depression from Well JZ25-2-A to Well JZ20-2N-A.In the middle period,there was a northward basin expansion.And in the late period,the lake water body shrank to the depression center until its disappearance.