Study On Cycadophytes From The Middle Jurassic Flora Of Sandaoling, Turpan-Hami Basin, Xinjiang, China

The Middle Jurassic flora of Sandaoling in the Xishanyao Formation of the Hami Depression is one of the representative Middle Jurassic floras of Xinjiang,China,and indeed the entire north of China.It can represent the main characteristics of flora during this period.The general characteristics of this flora are made clear,but compared with most other regions in north of China,the systematic palaeobotany of Sandaoling are still at a relatively lower level.The systematic taxonomy of the cycadophytes from the Sandaoling Opencast Coal Mine,Hami is studied in detail in this thesis.Based on leaf macromorphology and cuticular features,we present here a detailed morphological description of these leaf fossils and by comparsion with the known species of the corresponding genera,refer them to 5 new species,Nilssoniopteris hamiensis sp.nov.,N.crassiaxis sp.nov.,Pterophyllum xinjiangensis sp.nov.,Anomozamites spanstomatiger sp.nov.and A.sandaolingensis sp.nov.,3 old species,Anomozamites nilssoni,Anomozamites elegans and Nilssonia tenuicaulis,and 1 conformis species,Anomozamites cf.kirgisicus.The present thesis also briefly summarizes the establishment,the research history,the type species and the diagnosis of these genera.Especially in our Nilssoniopteris species,they possess unique venation patterns that are not only simple and free,but also forked and merged to form closed loops or merge with the adjacent veins.The generic diagnosis of Nilssoniopteris is thus accordingly emended,particularly in the venation pattern.According to the previously published literature,a systematical reexamination of Nilssoniopteris,Pterophyllum and Anomozamites species is recognized,and their stratigraphic and geographic distributions,evolutionary development and their relationships with paleoclimates are analyzed.Some conclusions are as follows:(1)These three genera all migrates mainly from the Euro-Sinian region of the middle and low latitudes to the Siberian-Canadian region of the middle and high latitudes.(2)The diversity of these three genera in their evolutionary development shows certain characteristics.(3)Our paleoclimatic reconstruction of these three genera suggests that their paleoclimatic conditions experience a shift from the subtropical-tropical zone to the warm temperate zone.(4)These three generamight have grown in the humid warm temperate or subtropical-tropical region,especially in the warm climatic zone.Finally,based on sedimentary characteristic and palaeontological features(including plants,non-marine bivalves and sporopollens)the palaeoclimatic analyses of the study area during the early Middle Jurassic period indicate a warm,humid climate.The present thesis represents the first account of cycadophytes plant fossils from Sandaoling of northern Xinjiang,which enrich the diversity of these plants of the Middle Jurassic flora in the north of China and offer new fossil evidence for the investigation of phytogeographical and paleoclimate of Xinjiang,China.It is of scientific significance in Geology,Paleobaotany and Paleoclimatology.