PRILIMINARY STUDY ON MORPHOLOGY, DEVELOPMENT PROCESS AND PEAT ACCUMULATION RATE OF PALSAS DURING THE HOLOCENE IN THE ALTAI MOUNTAINS, NORTHERN XINJIANG AUTONOMOUS REGION, NORTHWEST CHINA
泥炭丘(palsa)是在多年冻土区泥炭沼泽地形成的冻胀泥炭丘体,它的形成和发育受区域水文条件、植被群落和气候变化等因素影响。新疆阿尔泰山区特殊的地形特征、丰富的水资源及寒冷的气候特点,使得山区泥炭沼泽资源较丰富;同时,为高海拔多年冻土区泥炭丘的形成和发育提供了有利条件。本研究于2014年8月,通过对新疆阿尔泰山区泥炭资源的调查,对山区多年冻土区泥炭丘的分布、形态特征以及发育现状做较详细调查,结果显示,新疆阿尔泰山泥炭丘分布在2500 m a.s.l.左右的亚高山草甸带多年冻土区,位于黑湖和三道海子的泥炭丘受人类干扰较小,保存较完整,而位于哈拉萨孜的泥炭丘受人类活动干扰严重,处于退化阶段。此外,选取黑湖泥炭丘剖面(93 cm)和哈拉萨孜泥炭丘剖面(180 cm)为主要研究对象,结合AMS 14C测年数据建立了年代-深度关系,探讨阿尔泰山区泥炭丘的剖面特征、形成年代、发育过程及泥炭的累积速率。研究结果表明,全新世以来,阿尔泰山区泥炭丘泥炭累积的平均速率为0.015~0.035 cm/a;在约10000a B.P.的早全新世时期,阿尔泰山区气候温暖干旱,是泥炭丘形成的萌芽期,泥炭累积速率较慢;约7000~ 2500 a B.P.,气候温暖湿润,进入中全新世大暖期,有利于泥炭累积,是山区泥炭丘主要发育阶段;约2500 a B.P.以后的晚全新世时期,山区气候进入寒冷干旱阶段,泥炭的累积速率缓慢,此时是泥炭丘的衰退期。由于阿尔泰山区地质地貌、水文条件、局地小气候特征等多重因素的影响,使得山区内不同区域泥炭丘的泥炭累积速率的峰值、发育过程及发育状态在时间上存在着差异。本研究结果不仅揭示了阿尔泰山区泥炭丘发育过程,也为山区冻土的发育及气候演化过程提供重要线索。
英文摘要:
Palsas are perennial frost mounds found in peat bogs in permafrost regions. Their formation and development are strongly influenced by regional hydrology, vegetation communities and climate change factors. Rich peat resources exist in the Altai Mountains in northern Xinjiang Autonomous Region (46°33'35" ~49°10'45"N,85°31'37"~91°01' 15"E),Northwest China, due to its special terrain features, sufficient water resources and cold climate conditions. Meanwhile, the alpine permafrost regions in the Altai Mountains provide conducive geological conditions for the formation and development of palsas. In this study, we provide detailed descriptions and interpretations for the distribution,morphological characteristics and development stages of palsas in the Altai Mountains on the basis of the detailed investigation results on peat resources in the Chinese Altai Mountains in August 2014. The investigation results indicate that these palsas are distributed in the alpine permafrost zones at elevation of ca. 2500 m a.s.l in Xinjiang Altai Mountains. The palsas in the Heihu region and Sandaohaizi region are well preserved with less impacts of human activities, however, the palsas in the Halasazi region are severely affected by human activities and they have degenerated at present stage. Furthermore, we have selected two typical palsa profiles including Heihu palsa profile (48°40'4.2"N,87° 11'32.6"E ; 93 cm) and Halasazi palsa profile (48°06'54"N, 88°21'09"E; 180 cm)as study subjects to establish the age-depth relationship with AMS 14C dating for discussing the profile characteristic,formation time,development processes and peat accumulation rates of palsas in the Chinese Altai Mountains. The results indicate that the average peat accumulation rates of palsas in the Altai Mountains are 0.015 ~0.035 cm/a during the Holocene ; the formation of palsas began in the warm and dry Early Holocene at ca. 10000 a B.P., when the peat accumulation was slow. Then, from 7000 a B.P. to 2500 a B.P., the climate entered a warmer and wetter period in the Megathermal Period of the Middle Holocene, which promoted peat accumulation. This is the major period for palsa development. Since the late Holocene, the Altai Mountains region entered a cold and dry climate period and the peat accumulation rate has decelerated,and the palsas entered a recession period. However, the difference in local environments, including local geomorphology, hydrology and regional climate,might result in some differences in the time of peak values of peat accumulation rates occurrence, the development processes and the development status of the palsas from different areas of Chinese Altai Mountains during the Holocene. Our findings can not only reflect the palsa development processes in the Altai Mountains, but also provide significant clues for reflecting the development of permafrost and climate evolution in the regions.