鄂尔多斯盆地盐池地区延安组孢粉组合的发现及其古气候意义

Discovery of sporopollen assemblages of Yan'an Formation in Yanchi,Ordos basin,and its paleoclimate significances

为恢复鄂尔多斯盆地盐池地区早—中侏罗世古气候,重建古环境,对宁东2井进行孢粉分析和黏土矿物测试,建立孢粉组合、孢粉谱。延安组下部为Inaperturopollenites-Psophosphaera-Protopinus组合,地质年代为早侏罗世托阿尔期晚期;延安组上部为Cyathidites-Deltoidospora-Cycadopites组合,地质年代为中侏罗世早期,下/中侏罗统界线位于钻孔2144.5~2153.0 m之间。据孢粉谱建立的古气候和古植被得出,早侏罗世托阿尔期晚期为暖温带半湿润型气候,植被类型为针叶林,中侏罗世早期总体为亚热带湿润型,植被面貌有早期的针阔叶混交林-草丛型向晚期的针叶林-稀草型转变。两组合总体上反映的早侏罗世托阿尔期晚期至中侏罗世早期湿度由半湿润向湿润转变,温度由低向高转变,孢粉谱所指示的气候变化趋势与黏土矿物指标所反映的气候变化趋势一致。气候的转变对该地区聚煤作用有着明显的促进作用。

For rebuilding the paleoclimate and paleoenvironment during the early-middle Jurassic in the Yanchi area of the Ordos basin,we analysis the palynological characteristics and clay minerals of the core Ningdong-2,sporopollen assemblages and sporopollen spectra were established.The lower part of the Yan'an Formation is the Inaperturopollenites-Psophosphaera-Protopinus assemblage,whose age is the late Toarcian of Early Jurassic.The upper part of this formation is the Cyathidites-Deltoidospora-Cycadopitees assemblage,whose age is early Middle Jurassic.The boundary of lower and middle Jurassic is located between 2144.5~2153.0 m of the core.The paleoclimate and paleovegetation established by pollen spectrum shows that the late Toarcian of early Jurassic period was a warm temperate semi-humid climate whose vegetation type was coniferous forest.The early Middle Jurassic was generally subtropical humid climate,whose vegetation appearance transformed from coniferous broadleaf mixed forest-grass type to the coniferous forest-dilute grass type.From the late Toarcian of Early Jurassic period to the early Middle Jurassic period,the humidity changed from semi-humid to wet while the temperature changed from low to high.This climate change trend was also found in clay minerals analysis.The climate shift has had a clear role in promoting coal gathering in the region.