摘要
干旱区晚第四纪已有较多高湖而与湖泊演化的报道和研究,对于认识区域环境变化有重要意义,但高湖面出现的时间尚存争议,高分辨率的气候环境记录仍相对缺乏。本文通过青海共和盆地达连海湖岸地貌考察和AMS ^(14)C年代学研究,讨论达连海古湖晚第四纪高湖面出现的可能时间;并通过达连海DLH99孔岩芯年代和高分辨率代用指标,讨沦高原东北缘末次冰消期以来的气候环境变化。达连海周围存在6级高湖面岸线或台地,^(14)C测年结果显示,最低的两级湖岸堤形成于全新世,其余湖岸台地年代均老于44cal.kaB.P.,当时在达连海地区形成一个较大的古湖泊。DLH99孔显示达连海近15cal.kaB.P.沉积了40.92m的湖相沉积物,平均沉积速率高达2.7mm/a。孢粉资料揭示出,现代干旱的共和盆地在末次冰消期以来存在两个山地针叶林发育阶段,分别位于末次冰消期和全新世早中期。全新世早中期是适合山地针叶林植被发育的气候最宜期,而晚全新世山地森林植被整体衰退。粒度分析结果显示,达连海全新世低水位时期对应于岩芯中部山地森林植被发育的晚期,出现较强烈干旱事件(岩芯深13～15m段),这种湖泊水位与植被所指示的气候变化不一致现象(即低水位时期盆地内耐旱植物和山地乔木花粉同时增加),可能揭示出干旱区山地与盆地环境对区域气候不同响应。达连海存在的系列高湖面和冰消期以来的完整气候记录,为理解晚第四纪季风边缘区气候变化过程及其机制提供了条件。
There have been reports on large paleolakes with high lake levels in the arid region of NW China during Late Quaternary ,which are important for understanding the regional environmental changes. However, the precise age of these high lake levels are still under debates and high-resolution sedimentary records in such regions are relatively rare. Here we report the dating results of high lake levels of a paleolake, Dalianhai Lake,in Gonghe Basin, Qinghai Province,NW China, and a sedimentary proxy record from a core, DLH99, drilled from this lake （36~14＇50＂N, 100~24＇25＂E） since last deglacial. Plant remains, bulk organic matter and mollusk shells from the paleoshores, terraces and the core are dated with conventional and AMS ~4C methods. There are 2 paleoshores and 4 terraces higher than the present desiccated lake surface. Radiocarbon dating results suggested that the 2 paleoshores at elevations lower than 2870m above sea level（m a. s. 1. ） were formed during the Holocene period and the terraces higher than 2870 m a. s. 1. were the evidence of a large paleolake probably older than 44cal. kaB. P., which had been shrinking during Late Quaternary. The 40. 92m-long DLH99 core covers the sediments since 15cal. kaB. P. with an averaged sedimentary rate as high as 2.7mm/a. Pollen assemblages indicated that there were two stages during which mountainous coniferous forests developed around the modem dry Gonghe Basin since the last deglacial. One was in the last deglacial and the other in early-Mid Holocene. The later stage indicated an early-Mid I-Iolocene optimum. The regional vegetation degraded since Late Holocene. Mean grain size and coarse grain components of the sediments suggested a dry period with low lake level in Mid-Holocene（ 13 -15m in depth of the DLH99 core）, corresponding to the late stage of the mountainous coniferous forests. This inconsistent climate situation indicated by lake level and pollen data from the sediment may be attributed to the different responses of basin and mountains to
出处
《第四纪研究》
CAS
CSCD
北大核心
2012年第1期122-131,共10页
Quaternary Sciences
基金
国家自然科学基金项目(批准号:41130102和41021091)
国家学科创新引智计划项月(批准号:B06026)共同资助
