本文对泥河湾盆地籍箕滩剖面地表下65~75cm、140~150cm、190~ 200cm和300~ 310cm处的4块泥质样品进行了AMS ~(14)C 测年,校正后的年代分别为2117cal.a B.P.、3081cal.a B.P.、5481cal.a B.P.和6420cal.a B.P.,表明籍箕滩剖面305Cm以上地层形成于全新世中晚期。籍箕滩剖面的孢粉、炭屑和磁化率分析,揭示了研究区中全新世以来的植被演替、气候变化和人类活动的影响。6400~5800cal.a B.P.,气候总体温暖湿润,籍箕滩南面的浅山地带可能有森林生长,孢粉百分比和炭屑含量的变化表明,该阶段植被对气候变化和人类活动影响非常敏感。6000cal.a B.P.前人类活动使籍箕滩剖面南面浅山地带的森林遭到一定破坏;6000~5800cal.a B.P.,籍箕滩周边的人类活动可能有所减弱或迁移他处,籍箕滩剖面南面浅山地带的森林得到一定恢复;5500 cal. a B.P.左右的降温事件和4000 cal. a B.P.左右的干旱事件以及人类活动,使得泥河湾盆地的森林植被破坏后再也没有恢复到之前的景观,草原植被迅速发展;4000~2000cal.a B.P.,气候以冷干为主,区域内森林植被几近消失,只在水分条件较好的地方有小片阔叶灌丛林生长,植被类型表现为草原或干草原。泥河湾盆地中晚全新世以来的气候变化与其他地方的对比表明,东亚季风的衰退具同步性。
英文摘要:
The Jijitan profile (JJT, 40°6'46"N, 114°26'54"E) is located in the middle part of the Nihewan Basin,south bank of the Sanggan River, at an altitude of 850m. The thickness of the whole profile is 670cm, but in this paper, only samples from upper part of 0 ~305cm were analysessed. The section of 0 ~ 164cm is river alluvial deposits, the section of 164 ~ 305cm is an oxbow lake deposits. Four pieces of muddy sample from 65 ~75cm,140 ~ 150cm, 190 ~200cm and 300 ~310cm were chosen for AMS ~(14)C dating, they were 2117 cal.a B.P.,3081 cal.a B.P., 5481 cal.a B.P. and 6420cal.a B.P., respectively. In this paper, we discussed the pollen percentages, charcoal content and magnetic susceptibility to reveal the vegetation succession, climate change and human impact on environment in study area. A total of 52 samples for pollen, 22 samples for charcoal, 69 samples for magnetic susceptibility analyses. The result show that during the period of 6400~5800cal.a B.P.,the climate was warm and humid, there were forest in low mountains, the south of Jijitan profile. But the vegetation in Nihewan basin is very sensitive to climate change and human activity. The change of pollen percentage and charcoal content properly reflect the influences of human activities to the forest. Before 6000cal.a B.P.,human activities reduced, the forest occupation in lower mountains area, as there were less arboreal pollen and plenty of charcoals (> 125mum) . Since then, the ancient residents at the Jijitan area might be reduced or migrated. The arboreal pollen percentage increased and charcoal reduced during the period of 6000~5800cal.a B.P.,hinting the forest got recover on the low mountains area in the south of the Jijitan. The forest was damaged seriously because of the cold event in 5500cal.a B.P. and the dry event in 4000cal.a B.P. ; Meanwhile, as the human impact, the forest coverage in Nihewan basin never restored as before, but the grassland developed rapidly. During 4000 ~ 2000cal.a B.P., the climate became cold and dry, the forest was almost disappeared. Only a small piece of broadleaf brush growth where had better hydrothermal condition. The comparison of climate change between Nihewan basin and other regions during the Middle and Late Holocene shows that the East Asian monsoon recession was synchronous.