摘要
山东蒙山八字峪(亦有人称为瑶池)砾石堆积堤不连续对称分布于出山沟口,沿流向延伸,具有弧形或舌状沉积的典型特征。2020年10月在蒙山八字峪砾石堆积堤测量了56块砾石组构,并在叠置砾石隙间采集到4个树干14C测年样品。研究结果如下:(1)八字峪堆积垄岗砾石组构、沉积构造、地貌组合等标志,均指向其为山洪泥石流堆积物;(2)缺少扇形地、表泥层与底泥层,具有砂砾透镜体的砾石层,揭示八字峪砾石堤为暴发频率极低、发展周期较长的泥石流堆积;(3)根据已有测年结果和乔木定居期,八字峪砾石堤在距今50年前曾发生山洪灾害,这与文献记载具有一致性;(4)八字峪砾石堤成因属于暴雨直接类特大型历史泥石流,可能是一次性、短历时快速地貌灾害过程,且被后期洪流有所改造;(5)八字峪砾石堤形成原因与冰川作用无关,也不是"典型的石河"。已报道的蒙山"冰川遗迹",不仅缺少可靠的三要素地貌组合证据,而且缺少年代学和沉积学依据。总之,本文从证据链上进一步增强了蒙山山麓碎屑堆积为山洪泥石流成因判别的确定性。
The boulder levee at Baziyu Gully(Yaochi) in Mengshan Mountain, Shandong Province, distributed along the flow direction at the outlet of the valley symmetrically and discontinuously, with typical arc-or tongue-shaped deposition features.. During the field trip in October 2020, we measured the gravel fabric of fifty-six boulders in the Baziyu Levee. We also collected three AMS14C dating samples of dead tree trunks from the crevices of boulders. The results are as follows:(1) the gravel fabric, sedimentary structure and combined geomorphological features of the Baziyu Levee collectively indicate they are debris flow deposits;(2) the absence of fan-shaped deposits, muddy surface and muddy bottom, combining with the presence of gravel layer with sand lens reveal that the levee was formed by intermittent debris flow which has low frequency but high magnitude;(3) according to the AMS14C dating results and tree colonization period, the catastrophic flooding in Baziyu Levee was occurred about 50 years ago, which consistent with the historical records of recent geohazards;(4) the boulder levee at Baziyu Gully was formed by a historical debris flow, which was a rapid geomorphological disaster process induced by heavy rain, and has been modified by the later flood;(5) the formation of Baziyu Levee is irrelevant to any glaciation process and the levee here is not "a typical block stream". The reported "glacial relics" in Mengshan Mountain is unreliable due to the lack of reliable evidence of combined geomorphological features, and the lack of chronological or sedimentological evidence. In conclusion, this study provides more evidence to further strengthens the certainty that the detrital deposits in the foothill of Mengshan Mountain is caused by catastrophic flooding and debris flows.
作者
王乃昂
何青华
孙德浩
刘啸
陆晨遨
刘江
WANG Nai’ang;HE Qinghua;SUN Dehao;LIU Xiao;LU Chen’ao;LIU Jiang(Center for Glacier and Desert Research,College of Earth and Environmental Sciences,Lanzhou University,Lanzhou,730000)
出处
《地质论评》
CAS
CSCD
北大核心
2021年第3期682-694,共13页
Geological Review
基金
国家自然科学基金资助项目(编号:41871021)
兰州大学中央高校基本科研业务费专项(编号:lzujbky-2020-kb53)的成果。
关键词
砾石堆积堤
地貌成因
定居期
历史泥石流
蒙山
boulder levee
geomorphologic origin
ecesis time
historical debris flows
Mengshan Mountain
