Late Eocene Angiosperm Fossils And Paleoenvironmental Significance In Weinan,Shaanxi

Weinan is located in central China at an average altitude of 400 m,with a warm-temperate semi-humid semi-arid monsoon climate.The vegetation type in the area is warm-temperate deciduous broad-leaved forest,and also contains coniferous forest,mixed coniferous and broadleaved forest,broad-leaved forest and shrubs.The Weihe Basin,in which it is located,has accumulated a continuous sedimentary sequence since the Eocene,providing better material for the study of Cenozoic climate evolution and environmental change.A variety of mammalian and sporopollen fossils have been found and reported in the Weihe Basin,but only megafossil plants were found and reported by Tao in the Upper Eocene series Bailuyuan Formation at Weinan.In addition to the many fossilised leaves of Palibinia Korovin,the flora also includes Ulmus Linnaeus,Corylus Linnaeus,Rosa Linnaeus,Campylotropis Bunge,Crataegus Linnaeus and other small trees and shrubs with fossilised leaves,the palaeoclimate has been interpreted as warm and arid.Based on the stratigraphic distribution of the fossil stratum and the mammalian fossils found by previous authors,the current fossil stratum is located in the central part of the Bailuyuan Formation,which is of Late Eocene age.The morphological and anatomical characters were used to describe and identify Trapa Linnaeus,Hemitrapa Miki,Nelumbo Adanson,Eucalyptus L’Héritier,Zelkova Spach,Berberis Linnaeus,Cercidiphyllum Siebold &Zuccarini,Carpinus Linnaeus and other genera.Among them,the leaves and fruits of the Trapa found in the study area are the earliest fossil records of the worldwide,advancing the origin of the modern Trapa from the Miocene to the Late Eocene,and suggesting that the Trapa originated in central China.The fruit of the Hemitrapa,found in the same stratum,indicates that by the late Eocene,the Trapa had diverged significantly from the Hemitrapa,with significant morphological differences.In addition,the discovery of a large number of aquatic plants reflects the presence of large freshwater lakes or other still waters on the southeastern edge of the Weihe Basin during the late Eocene.Temperate-subtropical deciduous trees of Cercidiphyllum,Zelkova and Carpinus and subtropical-tropical evergreen trees of the Eucalyptus indicate that the climate of the Weinan was warmer and wetter during this period than today.This result differs significantly from both the vegetation types and palaeoclimatic interpretations of fossils collected in the Bailuyuan Formation by previous authors,suggesting that the current fossil stratum is not the same as previous authors.At the same time,the combination of other multidisciplinary views suggests that a warm and humid environment existed in central China during the late Eocene,suggesting that the earlier thought Paleogene arid zone of central China may not have existed or persisted.