论文部分内容阅读
近年来详细的野外区域地质调查发现,道虎沟化石层的分布并非仅仅局限在道虎沟村附近,还断续出露于相邻其他几个地区.道虎沟化石层角度不整合在复杂的基底地层之上,岩石地层层序由三部分组成,其中下部为夹红色页岩沉积,这一地层曾经被误认为是下伏土城子组.野外大规模化石发掘显示,道虎沟层的化石主要富集在上部地层的湖相页岩中;由于后期强烈的构造改造,地层在多处发生褶皱倒转.新发现的地层接触界线清楚地证明,一直被认为是“上覆”地层的髫髻山组中酸性火山熔岩(同位素年龄159~164Ma)实际上为其下伏地层,道虎沟化石层的时代不可能早于这一年龄,也不可能是中侏罗世“九龙山组”.目前的化石发现和研究显示,叶肢介和昆虫组合所反映的时代要早于脊椎动物化石所代表的时代,如辽西螈、热河翼龙和带羽毛的手盗龙类等与义县组同一类群的分子非常相似.虽然目前还没有发现可靠的热河生物群鱼类化石,但是这一地层的脊椎动物化石组合更接近于早白垩世热河群.道虎沟层与热河群无论从沉积地层特征、火山活动和脊椎动物群面貌都很相似,属于相同的火山-沉积旋回,化石动物群可能代表了热河生物群最早的记录.
Detailed field geological survey in recent years shows that the distribution of Donghugou fossil layer is not only confined to the vicinity of Daohugou village but also exposed intermittently to several adjacent areas. Of the basement strata, the rock stratigraphy sequence consists of three parts, of which the lower part of the folder for the red shale deposition, this formation has been mistaken for the underlying Tuchengzi Formation. Large-scale field excavation shows that the Daohugou layer The fossils are mainly concentrated in lacustrine shales in the upper strata, and the strata turn over in many places due to intense post-structural tectonism. The newly discovered stratigraphic contact boundary clearly demonstrates that it has been considered as an overburden The acidic volcanic lava (isotopic age of 159 ~ 164Ma) in the Jixianshan Formation is actually the underlying strata. The age of the Donghugou fossil formation can not be earlier than this age, nor can it be the Middle Jurassic Jiulongshan Formation. The current fossil discoveries and studies show that the combination of leaf-limbs and insects reflects the era earlier than that represented by vertebrate fossils, such as the common lizard, the pygmy dragon and the feathered heron, Same group Although there is no reliable Jehol biota fish fossil, the vertebrate fossil assemblage in this stratum is more similar to the Early Cretaceous Jehol Group.Daohuogou Formation and Rehe Group are not only formed from sedimentary strata Features, volcanic activity, and vertebrate fauna are all similar and belong to the same volcanic-sedimentary cycle. The fossil fauna may represent the earliest record of the Jehol Biota.