西藏南木林乌郁盆地中新世植物化石层位及相关地层问题  

MIOCENE FOSSIL FLORAL HORIZONS IN THE OIYUG BASIN,SOUTHERN CENTRAL TIBET,AND RELATED STRATIGRAPHIC PROBLEMS

作　　者：刘耕武[1] 李建国[1] 

机构地区：[1]中国科学院南京地质古生物研究所,江苏南京210008

出　　处：《地层学杂志》2016年第1期92-99,共8页Journal of Stratigraphy

基　　金：中国科学院战略性先导科技专项(No.XDB03010103);国家自然科学基金(No.41172011)资助

摘　　要：西藏中部的南木林县乌郁盆地属于新生代山间盆地,新近纪沉积发育完整,富含植物和孢粉化石,在研究青藏高原隆升及植被—气候演化中具有重要意义。我们对Spicer等（2003）研究层位进行了孢粉分析,发现这里的孢粉组合总体是以桦科花粉占统治地位、同时又含有大量的松科花粉和丰富的蕨类孢子,明显不同于宋之琛、刘金陵（1982）所报道的以山毛榉科高含量为特征的孢粉植物群。这一发现与李浩敏、郭双兴（1976）指出的芒乡组内存在两个不同的植物化石组合的意见一致。不仅如此,综合已知的植物和孢粉资料,芒乡组甚至可能含有三个植物化石组合（层位）,即下部以桦科含量丰富的组合、中部以高山栎—高山绣线菊高含量为特征的组合、以及上部以单子叶草本植物和松科为主的组合。根据植物和孢粉化石资料以及放射性同位素年代数据,芒乡组时代应属于早中新世到中中新世早期。另一方面,长期以来乌郁盆地的地层命名系统相当繁乱,在实际应用中存在许多同义不同名或同名不同义现象,盆地名称也莫衷一是,给后人的研究带来了种种不便甚至误解。参照地层规范并结合近年来化石和放射性同位素年龄数据等新的研究进展对乌郁盆地新生界地层系统进行了梳理,明确了各地层单元的名称、涵义和时代,自下而上的序列为：日贡拉组（渐新世,上部可能进入中新世）、芒乡组（早中新世晚期至中中新世早期,约18~15 Ma）、来庆组（中中新世晚期至晚中新世早期,主体年龄为15~8 Ma）、乌郁群（晚中新世至上新世,8~2.5 Ma,不排除顶部进入更新世的可能）。The Oiyug Basin is located in the Namling County of southern Central Tibet,China,with an area of about 160 square kilometers and an altitude of 4200~4800m.This basin is important in the research of the evolutionary history of the plateau vegetation,Asian monsoon climate and plateau uplift,because it contains relatively complete the Cenozoic deposits with abundant plant leaf and pollen fossils in the southern plateau area.Among the Cenozoic stratigraphic units in this basin,the Mangxiang Formation contains both leaf and pollen fossils,whereas the upper Rigongla Formation and lower Oiyug Group yield only pollen fossils.Our recent pollen analysis revealed a new fossil pollen assemblage dominated by Betulaceae pollen with abundant Pinaceae pollen and Pteridophyte spores,which is different from that previously reported by Song Zhi-chen and Liu Jin-ling（1982）.In floristic composition this pollen flora highly resembles that of the leaf flora from the correspondent stratigraphic horizon.The Mangxiang Formation therefore probably contains three different fossil levels.The lowest fossil flora is characterized by the dominance of Betulaceae,the middle one contains abundant Fagaceae and the upper one yields rich Pinaceae and monocot plant pollen.It is interesting that the Mangxiang Formation also has three different leaf fossil floras discovered from the correspondent pollen fossil levels.The Oiyug Basin attracts many scientists all over the world in the past decades.In their work different researchers applied different stratigraphic names to the sediments of the basin,which has brought much confusion for subsequent workers.In this paper an attempt has been made to clear this confusion by clearing up superfluous stratigraphic names to meet the Chinese Stratigraphic Codes.It is recommended that the Cenozoic stratigraphic units of the basin include,in ascending order：the Palaeocene to Eocene Linzizong Group,the Oligocene to Early Miocene Rigongla Formation,the Early Miocene to early Middle Miocene Mangxiang Formation,the

关 键 词：生物地层 地层系统 孢粉化石 植物化石 新生界 乌郁盆地 南木林 西藏 

分 类 号：P534.62[天文地球—古生物学与地层学]