Response of mollusk assemblages from the Luochuan loess section to orbital forcing since the last 250 ka

This note presents a new result of terrestrial mollusk study from the Luochuan loesssection since the last 250 ka. A total of 213 samples, taken at intervals of 10 cm in the S0-L3 portion, were analyzed for fossil mollusks. Generally, 150-600 individuals were counted in each sample. According to the distribution of mollusk fossil assemblages in the loess section, 11 mollusk fossil zones have been recognized, representing different climatic and ecological conditions. Three main ecological groups were identified according to the temperature and moisture requirements of each taxon. The cold-aridiphilous group shows maxima at about 240-220, 190-182, 150-140 and 74 -66 ka BP. The thermo-humidiphilous set has high abundances for at least 6 times in the section at about 246-240, 220-216, 170-158, 92-86, 60-44 and 10 kaBP. Our results show that variations in mollusk ecological groups are related with changes in the Earth orbital parameters at the 41 and 20 ka frequencies. Maxima in thermo-humidiphilous taxa

黄土高原35万年来冬、夏季风变化周期的差异——陆生蜗牛化石的证据

通过对黄土高原洛川、长武剖面最近 3 5万年来陆生蜗牛化石的高分辨率研究 ,揭示出喜温湿和喜冷干蜗牛种类分别存在不同的变化周期 :喜温湿类蜗牛化石所揭示的东亚夏季风的变化存在明显的 41 0 0 0a和 2 3 0 0 0a周期 ,与地轴倾角和岁差 (低纬度太阳辐射 )的变化周期有关 ;而反映冬季风变化的喜冷干蜗牛种类则表现出不同的变化特点 ,其主要为 0 .1Ma和 41 0 0 0a的周期。冬、夏季风的变化与地轴倾角 41 0 0 0a周期都存在很好的相关性 ,但与地球轨道的岁差 (1 90 0 0～ 2 3 0 0 0a)及偏心率 (0 .1Ma)的周期没有一致的相关关系。在轨道尺度上冬、夏季风之间不存在此消彼长的简单变化模式。