大兴安岭南段赛罕乌拉石海剖面分析及其与蒙山拦马墙石河结构对比
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A profile analysis of block field in Saihanwula National Natural Reserve,Greater Hinggan Mountains and its comparison to a boulder stream in Mount Mengshan Global Geopark,Shandong
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    摘要:

    石海(石河/冰石河)作为冰缘地貌的重要标志之一,在国内地学界尚未引起足够的重视,以至于缺少介绍石海结构特征的中文文献,更未建立判别标准,在地貌认知阶段就发生很多误判。为了揭示石海的剖面结构特征,笔者等对位于大兴安岭南段的赛罕乌拉国家级自然保护区乌兰坝石海首次进行了开挖解剖,从而归纳了原生石海的基本结构特征:岩块棱角鲜明,呈镂空状堆积,岩块直径总体上上大下小。根据野外调查确认,赛罕乌拉海拔1800 m以上的区域至少还存在着局部现代石海,也就是说,还残存着不连续冻土带,而且保持年平均气温0℃左右的气候环境。根据赛罕乌拉现今气候记录和石海分布,笔者等估算了全新世初期赛罕乌拉石海开始发育时的地表温度在0~-4℃,而今天年平均气温已经升高到2℃,升温幅度2~6℃。根据赛罕乌拉石海剖面结构特征,笔者等对山东蒙山石河进行了结构对比,认为二者剖面结构基本一致,排除了前人近年来争议明显的冰川侧碛堤和泥石流成因说。结构对比揭示山东蒙山境内全新世早期至少局部存在过冰缘气候环境,而这也为山东境内更新世冰川地貌研究提供了重要的信息。此外,本研究也为中国冰缘地貌解剖和资源调查提供了一个可以参考的研究实例。

    Abstract:

    Objectives: Periglacial landforms, including block fields (felsenmeer), rock glacier, stone circles, and patterned ground etc., are the key elements reflecting the past and even recent climatic and environmental conditions. They are often found in the past active glacial landform areas, and easily affected by modern mass wasting events like debris flow and rock fall etc. However, our Earth scientists often misunderstand these landforms due to lack of criteria to recognize the phenomena. To clarify a standard criteria for identifying periglacial landforms, we tried to dissect a block field to reveal its profile.Methods: We selected a large block field, Wulanba block field, in the north of Saihanwula National Natural Reserve, Chifeng, Inner Mongolia, to ditch and reveal the profile structures, and tried to reconstruct the past periglacial environment. Furthermore, we correlated the exhumed profile in Saihanwula to Lanmaqiang block pile in Mount Mengshan, and confirmed the Lanmaqiang block pile as a boulder stream formed in the early Holocene.Results: The profile exhumed at the eastern margin of Wulanba block field shows the following features:(1) The eastern margin of Wulanba block field is composed of angular andesitic porphyrite blocks, building an active layer as thick as 1.8m above the bedrock head.(2) The rock blocks pile up in particle supported texture, leaving the voids without matrix inside. This is called openwork structure.(3) The larger blocks, including some more than 50cm in diameter, are floated in the upper part, while smaller particles and rubbles dropped to the lower part of the profile with the clays and soils filled in the small voids of the rubbles directly above the bedrock head.(4) The exhumed part of the block field belong to inactive block field. However, there are some patches of active block fields above 1800 m a.s.l. in the Natural Reserve, revealing some isolated permafrost remaining in the local periglacial envrironment.Conclusions:(1) We dug a pit at the margin of Wulanba block field in the Saihanwula National Natural Reserve to show the structure of an intact field block. The openwork structure of the large angular blocks and small rubbles can be a unique feature to identify block field (or felsenmeer) or block stream formed in the periglacial condition.(2) According to the block field formation under freezethaw conditions, we estimated that the climate in Saihanwula has warmed up for at least about 2~6°C since early Holocene.(3) We correlated the excavated block field profile in Saihanwula to Lanmaqiang boulder pile in Mount Mengshan, and found the similarity of the two, confirmed that the Lanmaqiang boulder pile was a boulder stream formed in periglacial environment in the early Holocene.(4) Former researchers argued that Lanmaqiang boulder pile was a lateral moraine or debris- flow deposits. We inspected landforms in the vicinity area of Lanmaqiang boulder stream and concluded that there was no evidence or traces for lateral moraine or debris- flow deposits.(5) Block field and other related periglacial landforms are very closely related to former glacial landforms and modern mass wasting events, so we have to investigate these landforms and understand their mechanisms.

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吕洪波,高于,浦津,孟和达来,欧阳江城,巴特尔,刘波,张云喜,李桂林.2020.大兴安岭南段赛罕乌拉石海剖面分析及其与蒙山拦马墙石河结构对比[J].地质论评,66(6):1572-1587,[DOI].
Lv Hongbo, GAO Yu, PU Jin, MENGHE Dalai, OUYANG Jiangcheng, Bater, LIU Bo, ZHANG Yunxi, LI Guilin.2020. A profile analysis of block field in Saihanwula National Natural Reserve, Greater Hinggan Mountains and its comparison to a boulder stream in Mount Mengshan Global Geopark, Shandong[J]. Geological Review,66(6):1572-1587.

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  • 收稿日期:2020-05-28
  • 最后修改日期:2020-07-24
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  • 在线发布日期: 2020-11-17
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