摘要
本文利用￣（１０）Ｂｅ测年技术￣＊，测定多金属结核内部各生长世代的起止年龄，并联系当时发生的主要古海洋事件，探讨古海洋环境变化对多金属结核生长的影响。经研究表明：（１）结核三个生长世代的年代分别为：始新世末—早中新世中期，中中新世早期—晚中新世末期，上新世—第四纪；（２）第Ⅱ生长世代是多金属结核的重要成矿期；（３）多金属结核的生长间断与全球性温度升高、南极底层流活动减弱有关。
Polymetallic nodules can be divided into three growth stages interrupted by two hia-tuses.According to the results of ￣(10)Be dating technique and analysis of microfossils inpolymetallic nodules,the geological ages of hiatuses are known to be 5.4-4.7Ma and 16-15Ma. By contrast with the research of paleo-oceanographic events,it can be seenthat the hiatus was the results of global phenomenon related to decrease of AABW. In the sliced sheet,it is clear that there are two conspicuous hiatuses from nucleusto surface.Its characteristics are as follows based on early studies:(1) the hiatus ofgrowth generation is mostly unconformable contact;(2)there is clay filled in hiatus;(3)some litle fissures are terminated to the hiatus;(4)microstructures in the growth gen-erations are different.From nucleus to surface,there are three(Ⅰ,Ⅱ,Ⅲ)growth generations.Microfos-sils in them can be well used to determine growth ages.In growth generation Ⅰ,micro-fossils are as follows:Ericsonia of. robusta,Coccolithus sp. ,Triquetrorhabdulus sp.,Coronocylus sp. and Aclinoptychus undulata f.etc,. representing the geological age fromLate Eocene to the mid of Early Miocene. In growth generation Ⅱ,microfossils areActinocyclus ingens var.nodus Bald.,Nitzschia porteri Freng Discoaster aulakos,andDiscoster ddflandrei etc. ,repesenting geological age from Middle Miocene to the end ofMioccene. In growth generation Ⅲ, microfossils are Gephyrocapsa sp.,Cycloccolithussp.,Gephyrocapsa oceanica,Thalassionema nitischoides Grum.,Nitzschia sp.,and Coscin-odiscus sp. etc.,representing geological age from Pliocene to Quaternary. The intervalsof growth stages are the hiatus stages. The first hiatus is 16-15Ma,the second is 5Maaround. According to ￣(10)Be dating technique,the geological age of the second hiatus is5.4-4. 7Ma,and the first hiatus should be Miocene according to the average growth rate.Results of ￣(10)Be dating technique correspond with the analysis of microfossils.By con-trast with the research of paleo-oceanographic events,the geological ages of hiatuses inpolymetallic nodules are discovered to consist with the time when temperature of bottomwater rised,and we know that temperature of bottom water rised during16-15Ma and5Ma,and it got 3.8℃ higher from the initial stage of Miocene to 16-15Ma. This paleo-oceanographic environment may have changed as follows;(1) sedimentary rate in-creased,(2)Eh reduced;and(3)the decrease of upwelling led the decrease of ocean pale-oproductivity. Such factors influenced the accretion of polymetallic nodules,and the hia-tus occurred.
出处
《海洋地质与第四纪地质》
CAS
CSCD
北大核心
1994年第4期33-41,共9页
Marine Geology & Quaternary Geology
基金
国家自然科学基金
