古昆仑湖地区183-90kaBP间的微体古生物与环境变迁

Microfossils and environmental change in Paleo-Kunlun Lake area during 183-90kaBP

古昆仑湖位于昆仑山垭口昆仑河谷地,大约在200kaBP前已开始沉积,沉积物为一套灰、灰绿、土黄色粉砂质、砂质粘土,厚约7m.在纳赤台西北剖面5.6-2.4m层段产较多微体化石,介形类有8属12种:Ilyocypris biplicata(Koch),I.bradyi Sars,Eucypris crassa(Mller),E.elliptica(Baird),E.rischtanica Schneider,Candona candida(Mller),Stenocypriscf.major(Baird),Cypridopsis obesa Brady & Robertson,Prionocypris gansenensis Huang,Potamocypris villosa(Jurine),P.cf.wolfi Brehm和Limnocythere dubiosa Daday等.轮藻类有Chara aliensis Z.Wang,Chara gansenensis S.Wang和Charasp.根据U系法测年,含化石地层的年龄大约为168-90kaBP,属于倒数第二次冰期至末次间冰期早期.按生物组合和沉积物特征分析,古昆仑湖区在183-90kaBP的环境气候变化大致有两个大的期次、6个小期次:(1)183-130kaBP冷湿期,湖区环境较冷湿,湖泊水质较淡,水温不高.早期(约183-170kaBP),湖面较宽,水体较深,环境动荡,化石贫乏;中期(约170-151.3kaBP),湖面有一定收缩,水质含盐度有所提升,水温仍不高,湖区环境湿度较大;晚期(约151.3-130kaBP),化石贫乏,生态环境、水质条件可能与早期类同.(2)130-90kaBP凉湿期,湖内生态环境较好,生物门类中除介形类外,出现沉水性植物轮藻类,且介形类生物量较前期有很大增加,属种分异度较好.早期(约130-105kaBP),偏冷湿;中期(约105-98kaBP),凉湿,为生物大发展大繁盛时期;晚期(约98-90kaBP),偏凉湿,在98-93kaBP,环境不宜生物生息,化石贫乏;约93-90kaBP,生态环境有所改善,有介形类3属5种,但生物量较小.

Paleo-Kunlun Lake is located in the Kunlun River valley at the pass of the Kunlun Mountains.Its lacustrine deposits began at-200kaBP and consisted of a sequence of gray,grayish green and earth-yellow silty and sandy clay,with a thickness about 7m.Abundunt ostracods were found from the 5.6-2.4m interval of the Naijtal section.Ostracods included eight genera and 12 species,i.e.：Ilyocypris biplicata （Koch）,I.bradyi Sars,Eucypris crassa （Müller）,E.elliptica （Baird）,E.rischtanica Schneider,Candona candida （Müller）,Stenocypris cf.major （Baird）,Cypridopsis obesa Brady Robertson,Prionocypris gansenensis Huang,Potamocypris villosa （Jurine）,P.cf.wolfi Brehm and Limnocythere dubiosa Daday;and charophytes including Chara aliensis Z.Wang and Chara sp.According to U-series dating,the age of the fossilferous strata was estimated for～168-90 kaBP,corresponding to the period of the last second glacial and last interglacial.Based on microfossils and sediments,two longer epochs and six shorter phases had been recognized for the paleolimnological and paleoclimatic changes in Paleo-Kunlun Lake at 183-90kaBP.（1） The cold-wet epoch （183-130kaBP）：The climate of the lake area was relatively cold and wet,the lake water was relatively fresh and the water temperatures were not high.In the early phase （～183-170kaBP）,the lake surface was wide,the water body was deep,the environment was oscillatory and fossils were scarce.In the middle phase （～170-151.3kaBP）,the lake surface shrank to a certain extent,the salinity of the lake water increased somewhat,the water temperatures were not yet high and the humanity of the lake area was high.In the late phase （～151.3-130kaBP）,fossils were scarce and the eco-environment and water salinity were probably similar to those of the early phase.（2）The cold-wet epoch （～130-90kaBP）：The eco-environment in the lake was better,and besides ostracods,there appeared the submerged plant charophytes and the biomass of ostracods increased as compared with the previous epoch.The diversity of genera and species was relatively high.In the early phase （～130-105kaBP）,it was slightly cold and wet.In the middle phase （～105-98kaBP）,it was cool and wet,and this phase witnessed substantial development and thriving of organisms.In the late phase （～98-90kaBP）,it was slightly cool and wet.In its early part （～98-93kaBP）,the eco-environment was not suitable for the growth of organisms and fossils were scarce.The eco-environment was somewhat improved in its late part （～93-90kaBP）,and five species of ostracods belonging to three genera appeared,however,their biomass was low.