松辽盆地青山口地区嫩江组下部生物地层及环境变化

BIOSTRATIGRAPHY AND PALEOENVIRONMENTAL CHANGE OF THE LOWER NENJIANG FORMATION IN THE QINGSHANKOU AREA,SONGLIAO BASIN

对松辽盆地青山口地区后金沟剖面进行化石的系统采样、鉴定和分析,识别出了介形类Cypridea gunsu-linensis-Cypridea ardua和Ilyocyprimorpha netchaevae-Periacanthella portentosa-Cypridea ordinata组合,孢粉Proteacidites-Cyathidites-Dictyotriteles和Lythraites-Aquilapollenites-Schizaeoisporites组合。根据介形类、孢粉化石组合,结合叶肢介化石和岩性等资料,厘定了该剖面的层位,认为后金沟剖面属于嫩江组一段上部-二段下部。在生物地层研究的基础上,探讨了沉积时期的古生态、古环境、古气候分析。根据介形类化石的保存特征及丰度、分异度,并结合其他资料,推测在嫩江组一段-二段沉积过渡期发生了一次大规模的湖侵。伴随着湖侵,介形类经历了一个衰退、消亡、复苏的过程。根据对孢粉的分析,认为该沉积期总体属于湿润到半湿润的热带、亚热带气候,其中在嫩江组二段底部黑色页岩的沉积期显得气候更加湿热,向上开始逐渐变干凉。

Ostracods and sporopollen samples were collected from the Houjingou section in the Qingshankou area, Songliao basin. The authors have recognized two ostracod assemblages, the Cypridea gunsulinensis-Cypridea ardua assemblage and the Ilyocyprimorpha netchaevae-Periacanthella portentosa-Cypridea ordinate assemblage. They have also identified two sporopollen assemblages： the Proteacidites-Cyathidites-Dictyotriteles assemblage and the Lythraites-Aquilapollenites-Schizaeoisporites assemblage. Based on lithostratigraphic and biostratigraphic features, the Houjingou section has been correlated to the upper part of Member 1 to the lower part of Member 2 of the Nenjiang Formation. Based on ostracod data （such as morphology, abundance, diversity, and preservation）, sporopollen data （such as climate distribution, and humidity type）, concostracan data, and sedimentary and mineralogical features, the paleoeclogy, paleoenvironment, and paleoclimate of the Houjingou section have been constructed. It is inferred that a lake trasgression occurred in the upper part of Member 1 and lower part of Member 2 of the Nenjiang Formation. Ostracods underwent a diversity decline, disappearance, and recovery during this transgression. Statistical analysis of sporopollen fossils indicates that the Houjingou section was deposited in tropical to subtropical and humid to subhumid paleoclimates. The paleoclimate was probably more humid and warmer during the deposition of the black and oil shales in the lowermost Member 2 of the Nenjiang Formation, followed by drier and cooler paleoclimate.