鄂尔多斯盆地西缘羊虎沟组孢粉组合特征与古气候意义

Palynological characteristics of Yanghugou Formation at western margin of Ordos Basin, NW China, and paleoclimatic implications

鄂尔多斯盆地西缘羊虎沟组页岩气勘探潜力巨大,但对其孢粉化石的研究较少,此外还存在地层时代厘定不清、古气候古环境特征判识不明等问题。本研究通过对盆地西缘乌达剖面羊虎沟组的孢粉化石展开研究,根据孢粉化石种属及其含量变化,建立了2个孢粉组合带:第Ⅰ孢粉组合(Lycospora noctuina-Stenozonotriletes lycosporoides组合)和第Ⅱ孢粉组合(Dictyotriletes bireticulatus-Ahrensisporites guerickei组合),分别产自羊虎沟组下段、上段。通过与内蒙古白彦套海地区羊虎沟组、宁夏中宁—中卫地区石炭纪—早二叠世孢子带等进行对比,确定了2个孢粉组合的时代,分别为维斯发A—B期和维斯发C—D期,属于巴什基尔晚期和莫斯科期。研究发现羊虎沟组下段较上段的蕨类植物孢子化石含量稍有增加,裸子植物花粉化石含量稍有减少,但总体变化不大,表明羊虎沟组沉积时期气候较为稳定。对孢粉化石与古植物类型的亲缘关系进行推测,羊虎沟组沉积时期生长的古植物多为热带—亚热带型;运用地球化学元素进行验证,研究区应为温暖潮湿的热带—亚热带型气候。

The stratigraphic definition of the Carboniferous Yanghugou Formation in Ordos Basin is not clear and there are few studies on paleoclimate and paleoenvironment.To determine the age of the Yanghugou Formation,this paper studies the pollen fossils of the Yanghugou Formation in the Wuda section of the western Ordos Basin and restores the paleoclimate through the genetic relationship between pollen and paleovegetation.According to the species and content changes of palynofossils,two assemblages are established:Lycospora noctuina-Stenozonotriletes lycosporoides assemblage and Dictyotriletesbireticulatus-Ahrensisporites guerickei assemblage,which divide the Yanghugou Formation into lower and upper sections.By comparing with Yanghugou Formation in the Baiyantaohai area of Inner Mongolia and the Carboniferous-Early Permian fifth spore belts in the Zhongning-Zhongwei area of Ningxia,the ages of these two spore-pollen assemblages are determined,which are A-B stages and C-D stages of Westphalian,respectively,and equivalent to the Late Bashikian and the Moscovian in the International Age Strata.The spore fossil content of ferns in the lower segment of the Yanghugou Formation is slightly higher than that in the upper segment and the pollen fossil content of gymnosperms is slightly lower,but the overall change not significant,indicating a relatively stable climate of the Yanghugou Formation during the deposition period.The relationship between palynological fossils and ancient plant types is speculated.The ancient plants of the Yanghu Formation were mostly tropical-subtropical.Using the earth's chemical elements,this area should be a warm and humid tropical-subtropical climate.