The Wood Fossil Record Of The Miocene Paleoenvironment In The Middle And Lower Reaches Of The Yangtze River

The strata are well-developed in Nanjing and Wuhan,ranging from Precambrian to Quaternary.The Cenozoic strata are rich in gastropods,ostracods,chara,sporopollen,fruits,leaves,foraminifera,fish,mammals and other fossils,which are an important treasure for studying the diversity of Cenozoic ecosystem in this area.However,compared with other large plant fossils like leaves and fruits,wood fossils are rare in the Cenozoic deposits in the middle and lower reaches of the Yangtze River.In the 1980 s,a large number of fossil wood specimens were discovered in Yangluo of Wuhan city.As the first Cenozoic angiosperm wood fossil flora,they are important to reconstruct the Miocene vegetation and paleoclimate in Wuhan and even the middle and lower reaches of the Yangtze River.In recent years,some well-preserved fossil woods has been discovered in the Miocene Yuhuatai Formation of Nanjing.Based on the previous work,this study firstly describe and identify the fossil woods from the Miocene Yuhuatai formation and the Neogene Yangluo paleogravel bed in Luhe of Nanjing and Yangluo of Wuhan.In total,14 species of 12 genera are identified,including 1 similar species and 6 unidentified species.The main results are as follows: Angiosperm fossil woods are of eight types,namely Careyoxylon sp.,Bischofia sp.,Bridelia wuhanensis Yang,Bischofia polycarpa Airy-Shaw,Laurinoxylon wuhanensis Yang,Laurinoxylon sp.,Ormosia pinnata Merr.,and Acrocarpus fraxinifolius Arn ex Wight.Among gymnosperm fossil woods,Agathoxylon sp.is assigned to Araucaria,Chamaecyparioxylon sp.,Juniperoxylon sp.,Cupressus hubeiensis Yang and Cunninghamia sp.are assigned to Cypress while Keteleeria sp.is assigned to Pinaceae.The fossil wood flora,combined with the leaf,stem,fruit,seed and other plant fossils in the surrounding area,shows that the mixed forest vegetation of broad-leaved and conifers developed during the Miocene period.At this time,the climate was slightly humid and warm.To obtain the quantitative data of tree ring,we selected two wood fossil specimens from two localties and calculated annual sensitivity,average annual sensitivity,and the ratio of early wood and late wood respectively.In combination with false rings,tree ring distortions and traumatic resin channels,the climate in this region shows significant seasonal changes,and under the general background of warm and humid climate,there are environmental mutation events such as strong winds and low temperatures.