| 渭南黄土沉积中十五万年来的古土壤及其形成时的古环境 |
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| 引用本文： | 郭正堂,刘东生,安芷生.渭南黄土沉积中十五万年来的古土壤及其形成时的古环境[J].第四纪研究,1994,14(3):256-269. |
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| 作者姓名： | 郭正堂 刘东生 安芷生 |
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| 作者单位： | 中国科学院西安黄土与第四纪地质研究室 |
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| 基金项目： | 国家自然科学基金,中国科学院地质研究所所长基金 |
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| 摘 要： | 关中盆地渭南地区十五万年来的黄土剖面记载了６个大的成壤期。本文对古土壤形成时的古环境进行了解译，并对它们在不同分类系统中的位置进行评价。全新世土壤Ｓ０是联合国土壤分类中的淋溶湿草原土。马兰黄土中包含两层古土壤，属典型黑钙土。Ｓ１古土壤由三层土壤复合组成，从上到下依次为典型黑钙土、淋溶湿草原土和深色淋溶土。成壤期与全球冰量较小的时期相对应，但古土壤的类型及发育程度与深海氧同位素所推测的全球冰量的变化有很大的不一致性，相反许多方面与北半球夏季太阳辐射的变化有较大的可比性。
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| 关 键 词： | 黄土－古土壤序列 古土壤 微形态 古环境 古季风 |
PALEOSOLS OF THE LAST 0.15Ma IN THE WEINAN LOESS SECTION AND THEIR PALEOCLIMATIC SIGNIFICANCE |
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| Institution: | Institute of Geology, Chinese Academy of Sciences,Xi'an Laboratory of Loess and Quaternary Geology, Chinese Academy of Sciences |
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| Abstract: | Abstract:The Weinan loess section at the southern-most part of the Loess Plateau is sensitive to both depositional and pedogenic processes. The sequence of the last 0.15Ma are studied in using micromorphological, soil chemical and clay mineralogicalmethods to identify the soil-forming intervals, interpret the environmental implication of the paleosols and assess their positions in; different soil classification systems.Six paleosols have been identified. The Malan Loess L1, overlain by the Holocene soil S0, contains two clearly separated paleosols named as L(1-2), and L(1-4) Theinterglacial soil S1 is polygenetic consisting of three superposed soil units (S(1-1),S(1-2)and S(1-3)). The morphological features and chemical properties allow us to distinguish the studied soils into three groups.(1) S0 and S(1-2) soils: The upper part of the Holocene soil S0 was strongly reworked by human activity as indicated by the abundant charcoals and brick pieces.An argillic horizon (Bi) is well preserved at the lower part, morphologically similar to that of the S(1-2) soil (dark brown, 7.5-5YR 4/6). They have dense incomplete excremental infilling microstructure with abundant biopores (12-15 % ), typical of steppe dominant soil with mollic epipedon. The dense excremental infillingsimply that the soil profile can be temporarily water-saturated. This is in agreementwith' the Fe-Mn hypocoatings (1-2%) around the biopores. The fine fraction (M5μm) is dark reddish brown and humus-riched, containing some reddish brown ironparticles, indicating brunification and weak rubification of the fine fraction. Theclay coating (about 5%) are dark brown (humus-riched), slightly dusty and non-la'minated with moderate birefringence. This type of humus-riched clay coatings areusually associated with Vegetations containing some species providing fulvic acid inrelative, abundance (e. g. resinous). The above features suggest a ustic soil waterregime and a mesic temperature regime. The vegetation was dominated by densesteppe containing probably some resinous species.(2)L(1-2), L(1-1) and S(1-1) soils: The AC horizon of the soils are dark brown (10-7.5)YR 4/6) with fine granular structure, underlain by a Ck horizon with abundant calcitic pseudomycelia. The fine fraction is humus-riched, containing a greatamount of dark charcoal particles. These soils have typical spongy microstructure,characteristic of steppe soils with mollic epipedon. The well preserved Spongy microstructure, consistent with the absence of Fe-Mn and textural features, indicates thatthe water regime has been ustic and the profiles have rarely been water-saturated.The lack of rubification and the significant humus accumulation suggest a temperatureregime ranging from mesic to frigid type. These soils can be classified as Vermustollsin U. S. A. system and Haplic Chernozems in FAO system with steppe vegetation.(3) S(1-3) soil: It differs from others in three aspects: (1) weak humus accumulation and strong rubification (reddish brown, SYR 4/6-8), indicating that thesoil temperature regime is significantly hotter. A thermic regime can be suggestedas high summer temperature and strong seasonal contrast are the necessary conditionsfor rubification, (2) the moderate Fe-Mn features (3-4%) and clay coatings (5-6%) and the presence of calcareous horizon imply that the water regime is still ustic, but significantly wetter than in the younger soils. The same inference can bemade from the fissure microstructure observed; and (3) a well developed Bt horizonwith prismatic structure. The clay coatings are reddish brown, limpid and microlaminated with high birefringence. Such texture features are commonly interpretedas typical of broadleaf forest soils. This soil was formed under subtropical semihumid conditions with a steppe-forest cover and can be classified as Rhodustalf inU. S. A. system and Chromic' Luvisol in FAO system. The forest may have beendominant during the climatic optimum.As the Loess Plateau is located within the Eastern Asian monsoon zone, thissuccession of paleopedogenesis depicts the variabil |
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