摘要:
通过对黄土—沙漠交接带的定边县、黄土高原中部偏南的灵台县表土样品及甘肃灵台剖面不同层位的黄土—古土壤—红粘土样品中石英颗粒的形态特征及表面微结构的观察测试,结果表明红粘土、古土壤及灵台表土原样中石英颗粒表面具有较丰富的次生硅质沉淀和明显的溶蚀痕迹,指示了碎屑石英在沉积之后,由于适宜的温湿气候条件而经历了较强烈的风化成壤改造作用;而定边县表土样及上粉沙层(L9)土样中的石英颗粒表面干净,具有较多的撞击浅坑等风力搬运痕迹。经过双氧水和盐酸清洗过后的石英颗粒的形态特征及表面微结构非常清晰,多为次棱角至次圆状,均具有较丰富的撞击麻点和浅坑,少数样品可见裂纹分布,说明红粘土和上覆的黄土和古土壤一样,主要为风力搬运堆积;但红粘土样中石英颗粒表面所具有的丰富硅质沉淀和明显的溶蚀痕迹,似乎暗示了晚第三纪沉积气候环境显著不同于第四纪的冷干、暖湿气候组合演化格局。
Abstract:
Based on the analysis of the surface textures of Quartz grains from surface soil, last interglacial paleosol (S1), upper silt layer (L9), upper and middle red clay (RC1 and RC2) samples by Scanning Electronic Microscope, this paper show us that there exist much more silica precipitation and clearly solution evidences on the surface of the primary quartz in Lingtai surface soil, last interglacial paleosol and upper red clay samples, which reveal that eolian deposit has been modified to some degree by pedogenesis procedure after deposition because of suitable climate conditions. However, the quartz surface in the upper silt layer and middle red clay layer is very clean, and shows clearly subangular to subrounded shape and collision pits which are typical eolian evidence. All the quartz pretreated by hydrogen peroxide and hydrochloric acid are characterized by clearly subangular to subrounded shape and abundant collision pits or pocks, which prove that the red clay has the similar sedimentary origin as the overlapped loesspaleosol sequences; but the solution and precipitation evidences on the primary quartz surface may indicate the climate condition during the late Tertiary is different from the Quaternary periods' warmer-wetter and colder-dryer climatic condition.
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