蒙山峨峪口砾石堆积堤的年代学研究

Study on the chronology of boulder levee in Mengshan Mountain,Shandong

准确界定蒙山峨峪口砾石堆积堤的形成时代,对于探明其成因、澄清山东中低山丘陵第四纪冰川有无之争,是一个需要解决的科学问题。峨峪口堆积垄岗砾石组构、沉积构造、地貌组合等标志,均指向其为山洪泥石流堆积物,且为暴发频率极低、发展周期较长的水石流或稀性泥石流堆积。其下伏第四纪沉积物OSL埋藏年龄和AMS14C年龄可作为砾石堆积堤形成时代的最老约束参考年龄,当地村民迁居此地的历史可作为最小约束参考年代。OSL测年结果为2.1~2.3 ka BP,AMS14C测年结果为951~1522 cal AD,证明砾石堆积堤为数百年前形成的历史泥石流遗迹。

Objectives: To investigate how the boulder levee in Eyukou(located at Mengshan Mountain) was formed and whether Quaternary glaciers exist in the middle and low mountains of Shandong Province, is crucial for us to confirm when the boulder levee was formed. Methods: Based on the evidence of the gravel fabric, the sedimentary structure and the combination of geomorphological features reveal the origin of the Eyukou boulder levee. The age of the boulder levee was speculated by the age of the Quaternary sediments underlying it and the time when local villagers moved here. Because the boulder levee was formed later than the Quaternary sediments underlying it and earlier than villagers moved here. Results: The OSL dating results of sediments underlying the Eyukou boulder levee are 2. 1 to 2. 3 ka BP., indicating that the debris flow accumulation is not earlier than 2. 1 to 2. 3 ka BP. The AMS14C dating results of sediments underlying are 951~1522 cal AD.Conclusions: Based on the dating results, combined with the oral statements of local villagers, it is inferred that the Eyukou boulder levee were debris flow deposits with low outbreak frequency and long duration, formed several hundred years ago. The newly obtained OSL and AMS 14C dating results in this paper could serve as auxiliary evidence to deny the view which considers the boulder levee distributed at the foot of Mengshan Mountain was a " moraine ridge" or a " typical rock stream " in the Early Holocene.