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Catastrophic flashflood and mudflow events in the pre-historical Lajia Ruins at the northeast margin of the Chinese Tibetan Plateau
Quaternary Science Reviews ( IF 4 ) Pub Date : 2021-01-01 , DOI: 10.1016/j.quascirev.2020.106737
Haiyan Wang , Chun Chang Huang , Jiangli Pang , Yali Zhou , Yuda Cuan , Yongqiang Guo , Yuzhu Zhang , Qiang Zhou , Xiaoqing Rong , Ruiqing Shang

Abstract Global change induced regional environmental variation and related catastrophic surface processes have greatly affected human life and social development during the last decades. These occurrences have also been highlighted by pre-historical catastrophes exposed by archaeological excavation in the Lajia Ruins at the northeast margin of the Tibetan Plateau, which has attracted considerable focus from both geologists and the world media. The cause of the disasters responsible for the destruction of the Lajia Settlement (14C age 4.15–3.85 ka BP) of the Qijia Culture remains controversial due to insufficient investigation of the Holocene sedimentary succession needed to establish a complete pedo-stratigraphic sequence and chronology, and thus to precisely constrain environment variation and related surface processes at that time. During our field investigations, a complete and continuous Holocene soil and sediment profile was identified in the northern part of the Lajia Ruins uniquely. Soil and sediment samples were taken systematically for physical and chemical analysis and optically stimulated luminescence (OSL) dating after detailed field observations and descriptions. The results demonstrate that the pedo-stratigraphic sequence includes Malan loess (L1-1, >11.50 ka BP) and transitional loess (Lt, 11.50–8.50 ka BP) in the bottom, a composite palaeosol (S0, 8.50–3.10 ka BP) in the middle, and recent loess (L0, 3.10–1.50 ka BP) and modern soil (MS, 1.50–0 ka BP) in the top. This pedo-stratigraphic sequence is comparable to those identified in the central part of the Loess Plateau. However, the mid-Holocene palaeosol (S0) is inserted by three layers of red clay (RC1, RC2, and RC3) and flashflood deposit (FFD), and thus subdivided into four sub-layers (S0-upper, S0-upper middle, S0-lower middle, and S0-lower). The red clays and the flashflood deposit are inferred to represent abrupt events of flashflood and mudflow that were dated to 3.96–3.65 ka by OSL and to 3.85–3.60 ka BP by AMS 14C methods. Indeed, the entire settlement, dwellings, pottery artifacts, and human skeletons in the Lajia Ruins are directly packed by these deposits. The Lajia Ruins is thus considered to be destroyed by enormous flashfloods and mudflows coming from the Ganggou and Lujiagou gullies, which submerged the settlement at 14C 3.85 ka BP or OSL 3.96 ka. These disastrous events are related to climatic deterioration since 4.20 ka BP that has resulted in severe convective weather and strong rainstorms affecting the northeast margin of the Tibetan Plateau. With consideration of the badly deformed ground and dwelling floors in the Lajia Ruins by crisscrossing earthquake fissures, that are also infilled and packed by flashflood and mudflow deposits, it is concluded that great earthquakes occurred as the first hitting to the settlement at Lajia. The enormous flashfloods and mudflows may have been induced by multiple earthquakes and rainstorms simultaneously. These results bear important implications for a better understanding of pre-historic environmental change and human-land relationship evolution at the northeast margin of the Tibetan Plateau.

中文翻译:

青藏高原东北缘史前喇家遗址特级山洪泥石流事件

摘要 过去几十年,全球变化引起的区域环境变化和相关的灾难性地表过程极大地影响了人类生活和社会发展。青藏高原东北缘喇家遗址考古发掘揭露的史前灾难也突出了这些事件的发生,引起了地质学家和世界媒体的广泛关注。由于对建立完整的土壤地层序列和年代学所需的全新世沉积序列的调查不足,导致齐家文化喇家聚落(14C年龄4.15-3.85 ka BP)破坏的灾难原因仍然存在争议,从而精确约束当时的环境变化和相关的地表过程。在我们的实地调查中,在喇家遗址北部独特地发现了完整且连续的全新世土壤和沉积物剖面。在详细的实地观察和描述之后,系统地采集土壤和沉积物样品进行物理和化学分析以及光激发光 (OSL) 测年。结果表明,土壤地层层序包括底部的马兰黄土(L1-1,>11.50 ka BP)和过渡性黄土(Lt,11.50-8.50 ka BP),复合古土壤(S0,8.50-3.10 ka BP)中部为近代黄土(L0,3.10-1.50 ka BP),顶部为现代土壤(MS,1.50-0 ka BP)。这种土壤地层序列与在黄土高原中部确定的那些地层序列相当。然而,中全新世古土壤(S0)被三层红粘土(RC1,RC2 和 RC3) 和闪洪沉积层 (FFD),从而细分为 4 个亚层(S0-上层、S0-中上层、S0-中下层和 S0-下层)。红粘土和闪驱矿床被推断为代表闪驱和泥流的突然事件,OSL 测得的年代为 3.96-3.65 ka,AMS 14C 方法测得的年代为 3.85-3.60 ka BP。的确,喇家遗址中的整个聚落、民居、陶器、人骨,都直接被这些沉积物包裹着。因此认为喇家遗址被来自岗沟和陆家沟沟壑的巨大山洪和泥石流摧毁,淹没了14C 3.85 ka BP或OSL 3.96 ka的聚落。这些灾难性事件与4年以来的气候恶化有关。20 ka BP导致青藏高原东北缘强对流天气和强暴雨。考虑到喇家遗址地震裂隙纵横交错的地面和住宅楼面变形严重,并被山洪、泥石流沉积物充填填塞,得出大地震是喇家聚居地的第一次撞击。巨大的山洪和泥石流可能是由多次地震和暴雨同时引发的。这些结果对于更好地理解青藏高原东北缘史前环境变化和人地关系演变具有重要意义。考虑到喇家遗址地震裂隙纵横交错的地面和住宅楼面变形严重,并被山洪、泥石流沉积物充填填塞,得出大地震是喇家聚居地的第一次撞击。巨大的山洪和泥石流可能是由多次地震和暴雨同时引发的。这些结果对于更好地理解青藏高原东北缘史前环境变化和人地关系演变具有重要意义。考虑到喇家遗址地震裂隙纵横交错的地面和住宅楼面变形严重,并被山洪和泥石流沉积物充填,得出大地震是喇家聚落的第一次撞击。巨大的山洪和泥石流可能是由多次地震和暴雨同时引发的。这些结果对于更好地理解青藏高原东北缘史前环境变化和人地关系演变具有重要意义。巨大的山洪和泥石流可能是由多次地震和暴雨同时引发的。这些结果对于更好地理解青藏高原东北缘史前环境变化和人地关系演变具有重要意义。巨大的山洪和泥石流可能是由多次地震和暴雨同时引发的。这些结果对于更好地理解青藏高原东北缘史前环境变化和人地关系演变具有重要意义。
更新日期:2021-01-01
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