关键词: 洛川剖面, S₄, 磁化率, 孢粉

Abstract: This article is mainly to analyze the climate change during paleosol period of S₄ through data of spore-pollen and susceptibility，and restore the transition process of vegetation. After the experimental analysis，the maximum value of susceptibility is 200.58×10^-8 m³/kg，and minimum value is 38.20×10^-8 m³/kg on the whole profile. According to the volatility characteristics of the entire curve，it can be divided into three stages，shown as a single peak，and sub-fluctuation existing in each stage. And then calculated the annual average temperature of interglacial period of S₄，which was about 14.94 ℃，and the annual rainfall was about 744 mm; the maximum of annual average temperature reached about 22.55 ℃，and minimum of annual average temperature was 4.41 ℃，with the greatest range of temperatures being 18.14 ℃; the maximum of annual rainfall reached 850 mm，and minimum of annual rainfall was 417 mm，with the greatest range of rainfall being 432 mm. Through the laboratory analysis on the spore-pollen samples，75 samples provided rich spore-pollen，with each sample containing more than 100 spore-pollens，which is required statistically. Generally，in the 75 samples，the spore-pollen of woody plants is identified to genus，and one of herbaceous plant is identified to family，with 126 genus and family identified in total. Comparing the curve of susceptibility and diagram of spore-pollen concentration，the spore-pollen of sub-tropical plants appears at the higher place of susceptibility value，where the change tendencies of the curve of susceptibility and the diagram of spore-pollen concentration are similar. At the lower place of susceptibility value，the spore-pollen of xerophytes appears，with the curve of susceptibility and the diagram of spore-pollen concentration showing negative correlation. The climate change sequence during interglacial period of S₄ in Luochuan area was established through analysis on the vertical variations of magnetic susceptibility and spore-pollen in strata. High resolution analysis on spore-pollen can more meticulously reflect climate change in small scale and more in-depth study of climate change than that on magnetic susceptibility; it is attributed to the vegetation directly reflecting the temperature and precipitation，while magnetic susceptibility could be influenced by various factors. The climate in interglacial period of S₄ is mild and moist; the semi-tropical borderline was in higher latitudes than nowadays，and can be reached the middle area of the loess plateau. The climate variation of interglacial period of S₄ in Luochuan can be divided into five stages，showing the transition of climate from “dry and cold” one，to “warm and moist” one，to “moist and hot” one，to “warm and moist” one and finally to “dry and cold” one，which correspond to the following vegetation: xeromorphism grassland，forest and grassland，forest，forest and grassland and xeromorphism grassland.

Key words: the Luochuan loess profile, S₄, susceptibility, spore-pollen