海原剖面12.5-7.2kaBP期间化学元素与粒度组成的古环境意义

The grainsize and the chemical elements at the Haiyuan section implicating the paleoenvironment during 12.5 to 7.2 kaBP

宁夏南部海原剖面12.5-7.2 kaBP期间的地球化学元素含量与粒度组成的环境指示意义显著,主要表现为冷干气候条件下植被稀疏,上游及坡面植被水土保持能力低造成粗颗粒物质含量较多,易溶元素如Na氧化物较多被淋失,难溶解的Si、Al、Fe氧化物相对富集;暖湿气候条件下植被发育良好,剖面沉积的细颗粒物质含量较多,土壤中Na元素不易淋失,Si、Al、Fe含量相对减少。但也注意到在温暖湿润环境下,元素活动性相近K2O与Na2O含量出现相反的变化,这可能主要是生物地球化学循化的作用,即植物对钾的吸附作用强于对钠的吸收导致的。

The changes of grainsize and the content of geochemical element of Haiyuan section implicate the environment between 12.5 and 7.2 ka BP.Combined with the recoreds of pollen,we can draw the following conclusion： The coarsegrain is obviously rich,at the same time,SiO2、Al2O3、Fe2O3 are riched and Na2O is poor in the sediments formed under the conditions of cold-dry climate due to low vegetation cover and the water and soil loss.The finegrain is rich,SiO2、Al2O3、Fe2O3 are poor and Na2O is rich in the sediments formed under the conditions of warm-moist climate due to high vegetation cover.It needs motion that the content of Na2O and K2O with similar chemical characterise show opposite,especially in warm-moist environment.It appears opposite which probably was the biogeochemical function,because the plant absorpt K more than Na.