【作者】 郑楠；

【导师】 程捷；

【作者基本信息】 中国地质大学（北京） ， 地理学， 2010， 硕士

【摘要】 内蒙古宁城县毗邻辽西、冀北,是“热河生物群”研究程度比较高的地区。长期以来,地质学家和古生物学者均将这里的古生物化石作为“热河生物群”的一支来研究。直到1998年以后,在五化镇道虎沟村陆续发现了原始哺乳类、爬行类、两栖类、昆虫类的化石。这些新发现的化石在面貌与组合形式上与“热河生物群”的化石大不相同,尤以原始哺乳类和带“毛”翼龙为代表,从而引起了中外学者的特别关注。有的学者因其特殊性将该生物群命名为“道虎沟生物群”,并一直延用下来。但是,研究区的大比例尺地质填图始终没有完成,多年来,一直没有统一的地层划分和命名。同时,学者们对“道虎沟生物群”的时代认识,也存在分歧。目前主要有中侏罗世、晚侏罗世和早白垩世三种不同的观点,本文将主要围绕这个问题展开讨论。笔者根据野外区域地质调查、剖面测量,基本建立起了研究区完整的中生代地层序列,统一了地层命名。借助生物地层学资料和锆石同位素测年数据,探讨了道虎沟地区的时代归属,认为研究区的中生代地层,自下而上为中侏罗统九龙山组、上侏罗统髫髻山组、上侏罗统土城子组和下白垩统义县组。道虎沟含化石层位,应当归属于中侏罗统九龙山组,而不是所谓的义县组。“道虎沟生物群”应当属于中侏罗世的“燕辽生物群”而不是白垩世的“热河生物群”。笔者还根据“道虎沟生物群”动、植物化石的种类和组合面貌,以及沉积学特征,来还原研究区中生代的大地构造环境,气候环境,和沉积环境。认为道虎沟这一喇叭状小盆地的演化历史,要早于周边地区。在中侏罗世就开始接受沉积,形成了一套滨湖、浅湖偶有沼泽相的沉积地层。该区中侏罗世气候温暖湿润,湖边植被茂密,孕育了繁盛的“道虎沟生物群”。这个沉积过程中,始终伴随着间歇性的构造活动和频繁的火山喷发,使生态环境多次恶化,进而直接导致了道虎沟大量生物化石的密集形成和埋藏。更多还原

【Abstract】 Ningcheng is in the southeast of Inner Mongolia, adjoins the west areas of Liaoning province and the north areas of Hebei province, which are famous for the Jehol Biota. There are abundant fossils in the area, which were considered as a part of Jehol Biota by geologists and paleontologists until the year 1998. Since then, many new kind of fossils are discovered, such as primitive mammals, feathered pterosaurs, amblystomas, insects and gymnospermous plants. Their particularities are quite different from Jehol biota. That attracts many scholars, some of them named the fossils Daohugou biota. But for years, detailed regional geology survey had never been preceded. The stratums in the area have not been divided and named congruously. There are three different opinions on the geological age of the biota, middle Jurassic, late Jurassic and early Cretaceous, they will be discussed in this paper.The paper builds the complete stratigraphic sequence of Mesozoic and unifies the names of the stratums based on the survey of region geology and profiles. It includes Jiulongshan Formation, Tiaojishan Formation, Tuchengzi Formation and Yixian Formation from the bottom to the top. And the geology age of the Daohugou Biota is also been discussed. We considered that the biota belongs to middle Jurassic based on biostratigraphy and isotope-dating. It should be a part of Yanliao Biota instead of Jehol Biota.The paper discusses the tectonics environment, climate and sedimentation environment based on the paleobiology characteristic and lithology characteristic. The opinion is that the evolution of Daohugou Basin is earlier than surrounding regions. The sedimentation period began from middle Jurassic and stopped by late Jurassic. At that time, Daohugou was a part of the edge of a lake, the depth of water is less than 1 meter, the lakefront was a forest. The climate was warm and wet. Periodical volcanic activities led to environmental deteriorations, and caused the burying of the fossils.更多还原