【摘要】 通过对青海官亭盆地详细的野外考察,在民和县喇家遗址北部发现了典型的全新世中期风成黄土古土壤剖面。经过详细的野外考察、系统采样和地球化学元素分析、粒度、磁化率等指标测定,从剖面中初步鉴别出两组红粘土质泥流沉积层（RC₁、RC₂）,分别记录了发生在3850 a B.P.至3600 a B.P.期间的两场大型泥流事件。该研究主要对剖面中两层红色粘土质泥流沉积层与古土壤层以及岗沟源区沉积物的地球化学性质进行对比研究。结果表明:（1）两层红粘土层均为喇家遗址后山沟源区域的暴雨山洪泥流堆积物,粘土质细粉沙质地,层次混乱,随古地面地形起伏变化,含沙石、黄土团块、陶片和木炭屑等。（2）单个泥流堆积层中,元素含量变化剧烈且有极值出现,这是多次暴雨泥流间歇性发生的有力证据。（3）两层红色粘土层与岗沟源区第三纪红粘土的理化特征都极为相近,据此,可推断出该剖面中两层红粘土层均源自北侧谷坡大红山（第三纪红色粘土）地区的大规模暴雨山洪泥流。这些研究成果对于深入理解黄河上游地区史前环境变化及其产生的自然灾害、人类活动之间的关系具有重大的科学价值。更多还原

【Abstract】 The Lajia Ruins in the Guanting Basin,is a product of the prehistoric Qijia Culture. Archaeological excavations have exposed extraordinary pictures of natural disasters that destroyed their settlements and claimed the lives of many people. However,the causation of the prehistoric disasters is of great controversy. Many studies focus on the understanding of the disaster,but lack of detailed geochemical characteristics. Field investigations were carried out in the Guanting Basin in the upper Yellow River valley. A Mid-Holocene palaeosol sequence was identified in the northwest part of the Lajia Ruins. After detailed field observations,pedostratigraphic subdivisions and descriptions,samples were collected systematically and the chemical composition,grain-size distribution and magnetic susceptibility were measured in the laboratory. All of these indexes show that there are two layers of conglomerated red clay inserted into the soil of the mid-Holocene. They were dated to around 3850 a BP and aroud 3600 a BP,respectively,using the 14 C method. A comparative study of geochemical features of conglomerated red clay,the eolian soil,and gully deposits at the foot of the Great Red Hills reveals that:( 1) Two layers of conglomerated red clay classified as the deposits of dense mudflows in connection with rainstorms over the gulley heads. Both of which are silty clay with rolling,wavy and conglomerated structure,very firm,with some stones,earth clods and human remains,including pottery shards,burnt earth,ash and charcoal,etc.( 2) In each of the mudflow deposit bed,major elements also exhibit significant change indicative of the multipled mudflows occuring intermittently.( 3) The physico-chemical characteristics of the two red clay layers resemble to those of the Tertiary red clay deposits over the gully heads in the Great Red Hills. Therefore,such a conclusion can be deduced: these two layers of conglomerated red clay were deposited by flash floods and mudflows from the gully heads behind the Lajia Ruins where the high hills consist of the unconsolidated Tertiary red clay formation. These findings are of great importance in understanding prehistorical environmental change,natural disasters and the human impact over the upper Yellow River basin.更多还原