松辽盆地白垩纪沉积特征

SEDIMENTARY CHARACTERISTICS OF THE CRETACEOUS SONGLIAO BASIN

松辽盆地晚侏罗世岩石圈破裂后,玄武岩浆喷溢,在白垩纪,盆地经历了裂前成穹、拉张破裂、断陷、断陷转向坳陷、坳陷和萎缩等6个地质演化阶段(图10),盆地中充填了厚近万米的陆相沉积。各演化阶段具有不同的沉积序列。早白垩世沙河子组至营城组时期,为断陷盆地发育阶段,形成火山岩-冲积扇-扇三角洲-湖泊(夹阵发型浊积岩)-沼泽相的序列;早白垩世登娄库组时期,盆地为从断陷向坳陷转化阶段,形成冲泛平原-湖泊相为主的序列;早白垩世泉头组-晚白垩世嫩江组时期,盆地为坳陷活动阶段,形成了冲泛平原-三角洲-湖泊(夹稳定型浊积岩)相;而晚白垩世四方台组-明水组时期,盆地进入萎缩阶段,再度出现以冲泛平原-冲积扇及小型残存湖泊沉积为主的沉积序列。这一垂向上的沉积序列,充分显示出夭折大陆裂谷的沉积特征。有许多事实说明在盆地发展的坳陷阶段发生过两次大的湖侵,且与全球海平面上升同步,导致湖与海沟通。

The Songliao basin is a Mesozoic continental rift basin. The rupture of the lithosphere in the Late Jurassic brought about the eruption of basaltic magma. The evolution of the basin progressed through 6 stages: pre-rift doming, extensional fractering, fault subsidence, fault downwarping, downwarping and shringkage, rensulting in the deposition of a continental sedimentary column nearly 10000 m thick. There are different depositional sequences in these stages; the at composed mainly of volcanic rocks and alluvial fan—fan delta—lacustrine facies—swamp facies in the fault subsidence stage; mainly of alluvial plain-lacustrine facies in the fault downwarping stage; the mainly of alluvial plain—delta-extensive lacustrine facies in the downwarping stage; and that dominated by alluvial plain deposits with subordinate minor alluvial fan and relict lacustrine facies in the shrinkage stage. These constitute a composite depositional column fully displays the sedimentary characteristic of a failed continental rift basin, Facts indicate that two large-scale lake 'invasions', synchronous with the global relative rise of sea level, which took place in the downwarping stage of the basin development, leading to the connection between lake and sea.