Late Triassic Flora Of Guangdong Province And Adjacent Areas,Southern China And Its Palaeoenvironmental Significance

The Triassic-Jurassic(T-J)Boundary marks one of the largest mass extinctions which occurred 201.3 Ma.Recent studies demonstrate that during the T-J transition,great geological events happened,such as floral and faunal turnovers,global transgression and wildfire events which resulted from the strong greenhouse effect by a marked increase in atmospheric carbon dioxide levels and massive volcanism in the Central Atlantic Magmatic Province(CAMP).Compared with great contributions of international research,the correlative studies in China are relatively lacking.The deposits of the T-J transition are well developed in China,such as the Junggar Basin in Xinjiang,the Ordos Basin in Shaanxi and Inner Mongolia,the Sichuan Basin in southwestern China and the Guangdong region in south China.In the central area of Guangdong Province,the coal-bearing series of marine and terrestrial alternating deposits are well developed,in particular,the Upper Triassic Xiaoping Formation.In northern Guangdong are the Hongweikeng Formation,Xiaoshui Formation and Toumuchong Formation series,which yield a variety of terrestrial and marine fossils,such as ammonites,bivalves,ostracods,insects,and plenty of plants.These formations show potential research prospect for biodiversity variation and great geological events during Late Triassic and the later T-J Boundary.Previous researchers have looked at the palaeobotany from northern Guangdong Province.Our new collections from Gouyadong,Chenzhou and Huadu,Guangzhou add to our past knowledge on diverse and rich plant fossil records from the Late Triassic.These Late Triassic records show a high taxonomic diversity including 106 species belonging to 47 genera.Among them,there are 9 species belonging to 4 genera of horsetails,32 species belonging to 13 genera of ferns,9 species belonging to 5 genera of seed ferns,33 species belonging to 11 genera of bennettitales,8 species belonging to 4 genera of cycads,6 species belonging to 4 genera of ginkgos,5 species belonging to 3 genera of conifers and 4 species belonging to 3 genera of incertae sedis.Based on the new cuticle evidence from Gouyadong,new species and new combinations have been proposed:Williamsonia trifasciatis Zhang et Wang sp.nov.,Ptilophyllum lechangense Wang emend.Zhang,Pachypteris xiaoshuiensis(Feng)Zhang comb.nov..This thesis moves Anthrophyopsis from cycads to bennettitales.Based on the comparison with the Late Triassic species and floras of China and abroad,it can be concluded that the geological age of the Xiaoping formation is Late Triassic.With the comparison of plant assemblages from different fossil sites in central and northern Guangdong and the evidence of marine fauna fossils,such as ammonites and bivalves,the age of each fossil site and horizon has been further determined.Among them,four plant zones have been established from bottom to top:Pachypteris-Lindleycaldus zone,Pterophyllum peak zone,Clathropteris-Otozamites zone and Danaeopsis first occurrence zone,which represent an upland plant community,lowland-wetland plant community,wetland bounded by mountains to the east,and lowland-wetland plant community from both delta and peat mire environments.The community changes showing a coordinated variation of the ocean level changes.The whole flora from Guangdong Province represents a warm and humid climate.Research of coal petrology from Guangzhou shows that there is only sporadic wildfire activity during early Carnian age.In addition,this paper explores the response of the flora to the Carnian Pluvial Event(CPE)during the early Late Triassic.And,we've compared the organic carbon isotopic curve with the well-studied area.