The Middle Jurassic Flora From Lianshan, Huludao, Liaoning

Western Liaoning is famous as its unique geological tectonic setting and fossils preserve environment and it is regarded as a fascinating Mesozoic terrestrial fossil locality of world. The Mesozoic continental deposits in this region are so well developed that contained abundant fossils in the formations of different periods. The Shangsanjiao and Xiasanjiao Villages area in Baima Township, Liansan District of Huludao, Western Liaoning, is one of typical fossil localities of Haifanggou Formation which was assigned to the Middle Jurassic. The Haifanggou Formation is basically a set of fluvial, lacustrine and swamp sediments, contained various conglomerates, sandstones, siltstones and mudstones, intercalated with tuffaceous fine clastic rocks and coal layers, yielding abundant fossil plants. The reporting of the suspected angiosperm fossils in this formation attracted the attention of the scientific community, but the systematic survey of Jurassic paleontological resources in this area has not yet been carried out until now. In the present thesis, we carry out a detailed taxonomic studies based upon the abundant fossil plants collected from the study area. The study results help us to summarize the appearance and characteristics of the flora, meanwhile, it also provide us very important evidences on reconstructing the palaeoclimate, palaeoecology and palaeogeography of Middle Jurassic in Shangsanjiao and Xiasanjiao villages area.All the fossil plants were collected from the sandstone or siltstone of the middle to the middle-upper parts of the Haifanggou Formation. Some specimen preserved as compression can be examined for studying the cuticle features. 40 species of 28 genera were identified, including Lycopsida, Sphenopsida, Filicopsida, Cycadopsida, Ginkgopsida, Czekanowskiales, Ginkgopsida incertac sedis, Coniferopsida, fructus et semina, and spermatophyte insertae sedis. The study results show that Gymnosperms and Filicopsida should be regarded as the most important part in the present Middle Jurassic flora. Among the gymnosperms, Ginkgopsida, Czekanowskiales and Coniferopsida are dominant groups, have a high genus diversity; Cladophlebis is regarded as the representative of unknown classification Filicopsida; Cycadopsida has the largest number of species but a lower genus diversity, contains mainly Bennettiales. After comparison of the present flora with the floras in north China, Yorkshire, Siberia and combine with the consideration of the flora composition and distribution, we propose that the age of the present flora should be assigned to the Middle Jurassic. It is one of the typical warm temperate floras which located in northern China, distinguished from the floras in south China, Yorkshire, Siberia by the different composition characteristics and molecular features,In addition, the examination of fossil plants indicates that it is a diverse flora dominated by ferns, ginkgoaleans, cycadaleans and conifers of the Middle Jurassic.After the consideration of the classification on plant fossil, the frequency and abundance of the present specimens, we propose the flora were made up by four types of communities, which are shoreside-wetland(Lycopsida and Sphenopsida), lowland(Filicopsida and Cycadopsida), sloping land(Ginkgopsida and Czekanowskiales) and upland(Coniferopsida).In conclusion, this flora can be compared to the floras distributed in north floristic region and represents a warm temperate flora along the Paleo-Pacific Belt. The composition of the flora also suggests that the regional climate was warm and moderately humid, with seasonal variations in temperature and precipitation of warm temperate zone. We speculate that the flora was in the circum-pacific tectonic active belt. The volcanic eruption events occurred occasionally in this area, together with the influence of the Pacific warm current, the warm and humid climate. The plants and animals were probably buried in such an environment and preserved as fossils.