师范类专业学生四位一体实践教学模式的探究

提升目前师范类学生的理论和实践能力,是现阶段综合院校师范教育改革的客观要求,是建构人才培养模式的新课题。从实际出发,针对当前师范生培养模式中的问题,提出了四位一体的师范生培养模式,并指出了在提升师范生理论知识、实践能力和教学实习等方面的创新之处。     

Characteristics and formation mechanism of pedogenic hematite in Quaternary Chinese loess and paleosols

Hematite is an important iron oxide mineral in loess–paleosol sequences in northwest China. Samples containing hematite and related minerals in the loess and paleosol units from Chinese Loess Plateau were investigated using powder X-ray diffraction (XRD), scanning electron microscopy (SEM), and high resolution transmission microscopy (HRTEM). The results show that there are at least three genetic types of hematite in Quaternary loess–paleosol sequences of northern China: (1) Weathering products of Fe-bearing silicate minerals, such as chlorite and biotite, that precipitated as aggregates of hematite nano-crystals on mineral surfaces; (2) oxidation products of eolian magnetite grains with hematite nano-crystals closely associated with magnetite; (3) coarse (silt-sized) hematite grains present in the fresh loess. Hematite with a nanoporous texture indicates that dehydration of iron hydroxide ferrihydrite is the main mechanism for the formation of hematite coating during chemical weathering of Fe-bearing silicates. It is proposed that nano-phase hematite is primarily responsible for the red color of the paleosol units. Paleosol layers are also characterized by higher magnetic susceptibility and increased oxidation of eolian magnetite. It is proposed that the major contribution to magnetic susceptibility is from the nano-phase magnetite that may be related to microbial activity. This research demonstrates that the study of mineral characteristics, formation mechanisms and the relationship between hematite, other iron oxides, and Fe-bearing silicate minerals helps to understand better the geochemical process in loess, both before and after dust deposition. In addition our study helps to explain the correlation between magnetic susceptibility and paleoclimate in northern China during the Quaternary.     

松香基季铵盐双子表面活性剂的合成及分析

松香（酸值170．54mgKOH／g）与环氧氯丙烷反应,合成中间产物3-松香酰氧基-2-羟丙基氯,再与四甲基乙二胺反应,制备了松香基季铵盐双子表面活性剂（GSRP）;用FT—IR对产物结构进行了鉴定,并对其性能进行分析。研究结果表明：中间产物3-松香酰氧基-2-羟丙基氯的酯化率为99．18％;GSRP的合成反应条件为：摩尔比2.2：1（n中间产物：n-四甲基乙二胺）,温度85℃,时间20h,产物得率为76．70％,纯度为96．10％;GSRP的分水时间为16min;临界胶束浓度为1．42×10^-4mol／L,表面张力为36．69mN／m：发泡力为200mm。泡沫稳定性好。     

Paleosols in the moraine-mantle loam sequence of northeastern Europe: The memory of pedogenesis rates and evolution of the environment during OIS3

Morpho-analytical features of the paleocatena (a complexly organized heterochronous sequence), which contains 2 pedostratigraphical units: formed on the Holocene mantle loams Umbric Albeluvisol and the underlain Middle Valday (Wűrmian) paleopedocomplex developed on Moscowian (Riss II) moraine deposits, are described. The buried pedocomplex consisted of: 1) the paleohumus and paleogley (2Atgb–2Gtb–3Atgb) and 2) paleohumus (3Atgb–3AtGb) horizons. Thus, these pedostratigraphic units reflect two studies of pedogenesis marked by two paleohumus horizons. The horizons of the paleopedocomplex are separate parts of the profile classified as the Umbric Gley soil formed during OIS3. The ¹⁴C age of the three paleosol horizons varied between 24,350–30,900 yr BP. The studied paleopedocomplex is the only one known containing the Middle-Valday paleosol formed on moraine deposits, which is a clear sign of the northernmost occurrence of the Bryansk fossil soil in Europe. A detailed hierarchical morphological study of the paleopedocomplex, including meso- and submicromorphological and magnetic susceptibility analyses, allowed us to identify the Late Quaternary pedogenic processes under severe extra-continental climate, including gleyzation, aggregation, cracking and humus formation. Good preservation of these individual pedogenic processes is shown to be a soil memory under the overlapping press of Holocene pedogenesis. It was shown that the clay coating in the Middle Valday of the pedocomplex is a part of the Holocene soil formation. Based on the palynological data, it is possible to subdivide the development of paleovegetation of the area into four stages during which the paleosol horizons had being formed. At the beginning and the final stage of the Middle Valday, the forest–tundra landscapes with inclusions of tundra–steppe associations predominated. During the optimum of Bryansk Interstade, the periglacial pine-birch formations were widespread.     

Stratigraphy of near-valley head quaternary deposits and evidence of climate-driven slope-channel processes in southern Brazilian highlands

During the past 40 years colluvial and alluvial deposits have been used in Brazil as good indicators of regional landscape sensitivity to Quaternary environmental changes. In spite of the low resolution of most of the continental sedimentary record, geomorphology and sedimentology may favor palaeoenvironmental interpretation when supported by independent proxy data. This paper presents results obtained from pedostratigraphic sequences, in near-valley head sites of southern Brazilian highlands, based on geomorphologic, sedimentologic, micromorphologic, isotopic and palynologic data. Results point to environmental changes, with ages that coincide with Marine Isotopic Stages (MIS) 5b; 3; 2 and 1. During the late Pleistocene, although under temperatures and precipitation lower than today, the local record points to relatively wet local environments, where shallow soil-water saturated zones contributed to erosion and sedimentation during periods of climatic change, as during the transition between MIS 2 and MIS 1. Late Pleistocene events with ages that coincide with the Northern Hemisphere Younger Dryas are also depicted. During the mid Holocene, slope-wash deposits suggest a climate drier than today, probably under the influence of seasonally contrasted precipitation regimes. The predominance of overland flow-related sedimentary deposits suggests an excess of precipitation over evaporation that influenced local palaeohydrology. This environmental condition seems to be recurrent and explains how slope morphology had influenced pedogenesis and sedimentation in the study area. Due to relative sensitiveness, resilience and short source-to-sink sedimentary pathways, near-valley head sites deserve further attention in Quaternary studies in the humid tropics.     

Formation and movement of groundwater in the thick loess-palaeosol sequences of the Chinese Loess Plateau

Permeability and water-bearing space are important hydrological characteristics of the loess strata. In this study a systematic experiment was conducted to measure the magnetic susceptibility, grain size, porosity, and infiltration rate of the loess and palaeosol layers on a loess tableland of the central Chinese Loess Plateau, in order to investigate the differences in hydrological conditions between the loess and palaeosol layers. The magnetic susceptibility of the loess layer was lower than that of the palaeosol layer, but the average quasi-steady infiltration rate was about 0.31 mm min~(-1) higher, the coarse silt and very fine sand contents were about7.1% greater, and the porosity was about 5.7% higher. These differences were mainly due to pedogenesis, which was affected by the Quaternary climate. The pedogenesis differences between the loess and palaeosol layers resulted in hydrological property differences in terms of permeability and water-bearing space. The loess layer had a higher permeability and more water-bearing space than the palaeosol layer, which meant that the loess layer is more likely to form aquifers and the palaeosol layer is more prone to form aquitards.The groundwater in the loess strata had a multilayered characteristic, which depended on the relative impermeability of palaeosol layer and the alternate deposition of loess-palaeosol layers. The hydrological characteristics of the loess strata demonstrated that the Quaternary climate had an important control function on the formation and movement of groundwater. This knowledge provides a reliable theoretical basis for water resource development and utilization on the Chinese Loess Plateau, and this study extends the application of Quaternary climate change theory to hydrological systems in loess deposits.     

江西九江泰和第四纪红土成因的比较研究

通过对江西九江和泰和第四纪红土的形成环境、粒度组成、稀土元素地球化学特性和石英微形态特征的研究，探讨两地第四纪红土的成因。结果表明：地处红黄土交接带的九江地区的第四纪红土，具有与下蜀黄土相似的风成特性，系风积成因；而位于吉泰古盆地的泰和地区的第四纪红土，具明显的冲积相特征，应为河流冲积成因。