新疆乌恰中侏罗世孢粉植物群及其环境意义

Palynoflora and its environmental significance of the Middle Jurassic in Wuqia,Xinjiang Autonomous Region

基于对新疆乌恰地区中侏罗统塔尔尕组33属48种孢子花粉化石的研究,建立了该区中侏罗世晚期孢粉植物群。塔尔尕组孢粉植物群以包括掌鳞杉科、松科、罗汉松科、南美杉科和杉科的松杉目的优势和包括桫椤科、蚌壳蕨科、紫萁科、海金砂科和双扇蕨科的真蕨目的次优势为特征。根据孢粉植物群的特征,探讨了该区中侏罗世晚期古生态、古气候和古地理特征以及古环境与油源的关系。研究结果表明,乌恰地区中侏罗世晚期气候属于亚热带半湿润—半干旱型,巴通期气候相对湿润,卡洛夫期气候变干,开始趋于干旱。孢粉植物群的生物多样性和植物地理分布的分带性反映,该区中侏罗世晚期具有山峦、河流、湖泊、沼泽、三角洲等多样古地理景观。孢粉学资料显示,乌恰地区在巴通期暖热和相对湿润气候条件下的湖泊和沼泽沉积有利于石油和天然气的形成。

Based on the investigation of 48 species of fossil spores and pollen belonging to 33 genera found in the Middle Jurassic Taerga Formation in the Wuqia area of Xinjiang Autonomous Region, the late Middle Jurassic palynoflora in the area has been established. The palynoflora of the Taerga Formation is characterized by the dominance of Coniferales including Cheirolepidiaceae, Pinaceae, Podocarpaceae, Araucariaceae and Taxodiaceae, and the subdominance of Filicales including Cyatheaceae, Dicksoniaceae, Osmundaceae, Lygodiaceae and Dipteridaceae. In accordance with the character of the palynoflora, the late Middle Jurassic paleoecological, paleoclimatic and paleogeographic character as well as the relationship between paleoenvironment and petroleum source rocks in the area have been discussed. The results of this study indicate that the late Middle Jurassic paleoclimate in Wuqia area should belong to the semi-humid to semi-arid type of subtropic zone. It is suggested that the climate should be relatively humid during the Bathonian Stage. By the Callovian Stage, the climate began to dry out and had a tendency towards drought. The biodiversity of the palynoflora and the zonation of the plant geographic distribution reflect that the late Middle Jurassic palaeogeography in the area should possess various landscapes, including multipeaked mountains, rivers, lakes, marshes, deltas, etc. The patynologicat data show that the lacustrine and marsh deposits under the hot or warm and relatively humid climate conditions in the Bathonian Stage in Wuqia area might be favorable source rocks for the formation of oil and gas.