泥河湾地区第四纪下限问题

本文主要根据泥河湾地区红崖剖面资料,着重讨论泥河湾层的时代归属、第四纪下限和泥河湾古湖的演化等问题。笔者认为,泥河湾层不仅包括下更新统,而且还包括部分中更新统和部分上新统,但不包括上更新统;第四纪下限年龄为2.6MaB.P.。本文还提出泥河湾古湖早在第三纪就已经形成,自第四纪以来至少有五次大的湖水涨缩,可能曾经一度干涸的看法。

THE LOWER BOUNDARY OF QUATERNARY IN NIHEWAN AREA

Nihewan is located in Yangyuan county,Hebei Province.Nihewan beds,famous bothin China and the world,was first named by G.B.Barbour in 1924.It was generally consideredthat the lower boundary of Quaternary is located at the bottom of Nihewan beds.We have sys-tematically studied Nihewan beds with various methods since 1963.And in recent years wehave mainly studied the lower boundary of Quaternary.According to the study on Hongyasection,we have found that the boundary where paleoclimatic changed from warm and wet tocold and dry is located at about 21m above the bottom of Nihewan beds and is taken as thelower boundary of Quaternary which is located at 12m (2.6 Ma B.P.) under Matuyama/Gaussboundary.Under the boundary,Nihewan beds are mainly red-brown and black clay,withgypsum.They belong to freshwater fluvio-lacustrain and swamp deposits,containing Hippa-rion cf.houfenense,Zygolophodon sp.,Lynx variablis Tang,Antilospira yuxianensis,Paraca-melus sp.,Axis shansius,Prosiphneus sp.,Mimomys sp.Above the boundary,the deposits aremainly yellow-green silt,clayey silt and grey-brown silty clay,interbedded with many grey-white sandy gravel and calcareous beds.They belong to shallow semi-saltwater fluvio-lacu-strain deposits,containing Coelodonta sp.,Equus sanmeniensis.,Gazlla sinensis,Meles chiar,Canis chihlensis minor.This boundary can be correlated with the lower boundary of the loessin the Loess Plateau and the Middle Villafranchian in EuropeThe Nihewan paleo-lake had formed as early as in Tertiary,and it expanded andshrank and sometimes dried up in Quaternary.It might have experienced at least five largefluctuation of expansion-shrinkage and withered away in the middle or late middle Pleistocene.A charcoal clastic bearing horizon was found near the boundary,it might be a great geo-logical event.The Nihewan beds contain partial Pliocene,lower Pleistocene and partial Middle Plei-stocene,but not including Upper Pleistocene.