THE DISCOVERY OF THE EOCENE GENUS PALIBINIA FROM XIZANG,CHINA AND ITS GEOLOGICAL AND BIOLOGICAL SIGNIFICANCES
The genus Palibinia Korovin is an extinct group of angiosperms that was widely distributed across China during the Paleogene,with records also found in center Asia,Europe and America from the Middle Eocene to the Late Oligocene.It was initially recognized as an indicator of arid environments based on its morphological traits and geographical distribution,but recent studies have challenged this assumption.This research analyzed leaf fossil specimens previously identified as"cf.Banksia leaf"from the Jianglang flora in the Niubao Formation,Bangor Basin,Xizang.The study applied the HadCM3 climate model,developed by the University of Bristol,to simulate paleoclimates over five periods from the Paleocene to the Oligocene.The paleoclimate for the 24 Palibinia fossil sites were extracted from these simulations.Additionally,paleoclimates for the Jianglang flora in the Niubao Formation and the Relu flora in the Relu Formation(Middle Eocene)were reconstructed using existing data.The Jianglang flora(31.63° N,90.03°E;4850 m a.s.l.)is located in the Bangor Basin,near the Bangong-Nujiang Suture Zone of e central Tibetan Plateau.The Niubao Formation is preliminarily dated to the Late Paleocene-Early Eocene,with fossils embedded in lacustrine mudstones and siltstones.In an approximately 32m thick outcrop,five layers of well-preserved fossils,including plants,mammals,fishes,and insects,have been discovered.Detrital zircon U-Pb dating,along with floristic comparison,placed the age of Jianglang flora within the Middle Eocene,around 47 Ma.The results revealed that the leaf shape,size,and venation pattern of"cf.Banksia leaf"specimens closely resemble Palibinia laxifolia Korovin,leading to their reclassification.Despite thorough the detailed morphological analysis,the phylogenetic relationship of Palibinia to modern groups remains undetermined.According to fossil records,Palibinia initially appeared in the Paleocene strata of Sanshui(Guangdong Province),Hengyang(Hunan Province),and Yizheng(Jiangsu Province).During the Middle Eocene,its distribution expanded to the Qinghai-Tibetan Plateau,Central Asia,Europe,and North America.However,by the Late Eocene,its range contracted,eventually culminating in its extinction during the Late Oligocene.Palibinia played a crucial role in the terrestrial ecosystems of Southeast China during the Paleogene.Although previous studies linked that Palibinia to arid conditions based on its morphological features,our simulations of paleoclimate data from 24 global fossil sites suggest that Palibinia occupied a broad ecological niche.Paleoclimate reconstructions of the Middle Eocene fossil assemblages from the Jianglang flora(Xizang)and the Relu flora(Sichuan)demonstrate that Palibinia also thrived in humid environments,challenging its classification as an arid indicator.Furthermore,paleoclimate stimulations show that regions inhabited by Palibinia typically experienced high average annual temperatures,signifying its adaptation to hothouse climates.As the global climate shifted towards cooler conditions since the Late Eocene,the distribution of Palibinia declined,culminating in its worldwide extinction globally during the Late Oligocene.Based on the research conducted,the following conclusions can be drawn:(1)Palibinia laxifolia Korovin was a crucial component of terrestrial ecosystems in eastern Asia during the Paleogene and was well-adapted to a hothouse climate;(2)Palibinia laxifolia likely originated in southeastern China and subsequently spread to other regions of the Northern Hemisphere;(3)The discovery of Palibinia laxifolia in the Middle Eocene strata of the Bangor Basin in Tibet indicates that there was floristic exchange between the Qinghai-Tibet Plateau and southeastern China during the Paleogene;(4)Palibinia laxifolia exhibited a broad ecological niche and thrived in various environments,suggesting that it cannot be considered an indicator of arid conditions.
万方数据
维普
