鄂尔多斯盆地西缘早中侏罗世延安组孢粉化石特征及其古气候意义

Characteristics and Paleoclimatic Significance of Sporopollen Fossils of Early-Middle Jurassic Yan’an Formation in the Western Margin of Ordos Basin

综合分析鄂尔多斯盆地西缘的银探2井779~1190 m深度段的孢粉化石与测井资料,对其所指示的地层时代和所代表的古气候与古环境特征进行探讨。研究表明:银探2井779~1190 m深度段孢粉化石组合可总结为小桫椤孢-格里斯索普新叉瘤孢-脆弱同心粉-具两气囊花粉组合,时代为早中侏罗世延安期。根据孢粉所体现的植物群特征判断早中侏罗世鄂尔多斯西缘为温带亚热带湿润气候。结合测井风化指数、地层元素测井Mg、Ca元素质量分数的比值、体系域、孢粉分异度与比例变化特征,判断早中侏罗世鄂尔多斯西缘在整体湿润的气候背景下发生干冷湿热的气候变化,为超级季风季节性变化导致气候带摆动所致。

The stratigraphic age of 779~1190 m segment of well Yintan 2 and the characteristics of paleoclimate and paleoenvironment in the western margin of Ordos Basin are discussed based on the comprehensive analysis of sporopollen fossils and logging datas in the segment of well Yintan 2 in the western margin of Ordos Basin.The research shows that the sporopollen assemblage in the 779~1190 m segment of well Yintan 2 can be summarized as CNCD,which is dated in the Yan’an period of Early and Middle Jurassic.According to the characteristics of flora reflected by sporopollen,the western margin of Ordos Basin in Early and Middle Jurassic is temperate-subtropical humid climate.Combined with the logging weathering index,the mass fraction ratio of Mg to Ca in strata element logging,the characteristics of system domain,sporopollen differentiation and proportion,it is judged that the climate change of from dry cold to humid heat occurred under the overall humid climate background in the western margin of Ordos Basin in the Early and Middle Jurassic,which is caused by the swing of the climate zones caused by the seasonal change of the super monsoon.