西周沣镐遗址全新世土壤研究

Holocene Soil Formation at the Fenghao Site of the West Zhou Dynasty near Xi'an City

根据西安西部西周沣镐遗址附近全新世土壤剖面磁化率、全铁、有机碳、Rb和Sr等指标的测定分析 ,揭示了与全新世环境变化相对应的成壤过程 ,阐明西周时代土壤和土地资源状况及人类耕作对成壤过程影响。认为全新世早期气候较温和干燥 ,风尘堆积速率降低 ,有一定生物风化成壤作用 ,土壤发育表现为边沉积边成壤 ;全新世中期气候温暖湿润 ,生物风化成壤作用大于风尘堆积作用 ,随着沉积和成壤继续 ,土壤层深厚 ,形成古土壤层 (S0 ) ;全新世晚期气候恶化 ,沙尘暴频繁发生 ,风尘堆积作用大于风化成壤作用 ,形成现代黄土层 (L0 )覆盖了土壤 (S0 ) ,使之成为埋藏古土壤。西周时期 (30 0 0～ 2 72 0aB .P .)气候干旱使环境资源恶化 ,土壤退化严重 ,当时的耕作层和古地面位于相当于黄土 (L0 )下部、古土壤 (S0 )顶界以上 10cm的层位。

A Holocene soil profile at the Fenghao site of the West Zhou Dynasty to the west of Xi′an City was investigated multi-disciplinarily. The results including magnetic susceptibility, total Fe, TOC Rb and Sr in the soil provide information on the development of the brown soil and the accumulation of eolian dust under the conditions of the monsoonal climatic change. In the early stage of the Holocene, dust deposition was reduced because of the climatic warming, and the biological weathering was beginning. In the mid-stage of the Holocene, climate became warmer and wetter, so the speed of pedogenesis was faster than the dust deposition. The Holocene paleosoil (S 0) was formed. In late period of the Holocene, because the climate became dryer, the dust-fall happened frequently, and then the speed of the dust deposition was faster than the pedogenesis, so that the recent loess (L 0) was accumulated and covered the soil (S 0) and the S 0 became a buried paleosoil. The records of cultivation of the West Zhou Dynasty (3000-2720 a B.P.) was found at the turn from the mid to late Holocene. The change from soil formation to loess accumulation indicates environmental deterioration and soil degeneration. Therefore the cultivated layer is situated in the lower part of the recent loess(L 0) about 10cm above the paleosoil(S 0).