龙江盆地光华组层型剖面出露完整,沉积连续,含丰富的热河生物群化石,是大兴安岭中段研究热河生物群起源、演化及辐射的重点剖面之一.本文对光华组层型剖面进行了重新精细测制,认为光华组整合于龙江组安山质角砾熔结凝灰岩之上,被甘河组玄武岩局部不整合覆盖,自下而上可识别出下、中、上3个岩性段;对该组所产动植物化石进行了系统的采集和鉴定,丰富了大兴安岭中段热河生物群的生物类别,并依据新采集化石和前人资料,尝试建立了叶肢介、介形虫、植物化石、昆虫等组合,探讨了各生物组合特征.根据对光华组剖面中段顶底岩层进行了LA-ICP-MS U-Pb锆石年代学研究,揭示龙江盆地热河生物生存的时代为125.4±1.4Ma至120.1±1.1Ma,大致跨越500万年,反映龙江盆地热河生物群繁盛于从阿普特期早期至阿普特期中期.结合古生物特点和笔者前期研究成果,认为龙江盆地热河生物群生存的古环境可能是间歇性或季节性的湖泊;古气候应处于温暖湿润的季节性变化的暖温带,并伴有短暂的半干旱气候.%The Guanghua Formation in Longjiang Basin deposited continuously and is exposed in integrity,with abundant fossils of Jehol Biota,making it one of the key sections to probe the origin,evolution and radiation of the Jehol Biota in the middle of Da Hinggan Mountains.This study carried out a precise measurement for the section of Guanghua Formation.It is believed that the Guanghua Formation conformably overlies andesitic welded tuff of the Longjiang Formation,with part covered unconformably by basalt of the Ganhe Formation.Three lithological units have been recognized from bottom to top.Systematic sampling and identification for corresponding biota fossils were carried out,and this has greatly enriched the biota category of Jehol Biota in the middle of Da Hinggan Mountains.Based on newly collected fossils and previously published data,authors established the assemblages of various fossils in the middle of Da Hinggan Mountains,which include limbs,ostracods,plant fossils,insects and others,and further discussed their characteristics.The LA-ICP-MS U-Pb zircon chronology study of the lower to middle sections of Guanghua Formation reveals that the Jehol Biota in the Longjiang Basin occurred at time of 125.4t±1.4Ma to 120.1±1.1Ma,with an span of roughly about 500 million years,reflecting that the Jehol Biota throve from early to middle Apter period.According to paleontological characteristics and our previous studies,it can be concluded that the paleoenvironment of the Jehol Biota in the Longjiang Basin may be the intermittent or seasonal lakes,and the paleoclimate should be in the warm and humid seasonally-changing warm zone,accompanied by the short term arid climate.
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