景泰老虎山活动断裂地区的第四纪地层的划分与对比研究

老虎山地区的第四系以山麓洪积与山区河流阶地沉积为主，￣１４Ｃ法、ＴＬ法和扩散方程法测定的近４０个年代样品表明：Ⅰ级阶地为全新统，阶地形成年龄为４０８６±１００ａ—４５７８±６０ａ；Ⅱ级阶地为晚更新世晚期沉积，阶地形成年龄为２３Ｋａ；Ⅲ级阶地为晚更新世早中期沉积，阶地形成年龄为７２Ｋａ；Ⅳ级阶地和Ⅴ级阶地为中更新世沉积，其阶地形成年龄分别为２１７±３５Ｋａ和３７８±６０Ｋａ；早更新统仅在局部出露，可能属早更新世早期的沉积。通过与兰州九洲台黄土剖面对比，发现Ⅰ—Ⅴ级阶地的形成年龄与标准剖面中的Ｓｏ、Ｓ＿２、Ｓ＿４等层古土壤形成年龄相一致。这说明河流层状地貌的形成。除了与构造抬升有关外，还与全球冷暖交替的大气候背景有着十分密切的内在联系     

晚更新世中期以来克里雅河流域黄土沉积特征与环境演化

昆仓山中段克里雅河流域不同海拔黄土样品的物质组成，地球化学成分、孢粉组合表明塔里木盆地的继粒物质是其物源。黄土分布于２３００ｍ的前山地带至４９００ｍ高山带，自低而高，黄土厚度变薄，颗粒由粗变细。＾１４Ｃ年龄测定显示本区黄土物质由晚更新世中期（５００００－６００００ａＢ．Ｐ．）－全新世风力搬运的粉尘堆积而成。     

壤中汞气测量在广东凡口厚层疏松物覆盖地区的应用

在地表疏松物厚20—40m的地区,壤中汞气测量显示了埋深200余m的盲矿体,它对疏松层下断裂带的分布也有清晰地指示。汞在地表疏松层中含量为0.06—0.2PPm,主要以气态、土壤胶体及粘土矿物吸附态形式存在。汞在铅锌矿石中含量为14—320ppm,以类质同象形式分散分布于单矿物中。壤中汞气异常是矿床在氧化过程中,痕量汞从矿石中解脱出来,以气态沿各种裂隙进入地表疏松层。     

Characteristics and genesis of hematite in Chinese loess and paleosol sequences： Mineral genetic restriction for magnetic susceptibility as paleoclimate proxy and iron geochemistry

Hematite is an important iron oxide mineral in loess-paleosol sequences in central China. Investigation of the mineralogical characteristics, genetic mechanism and relationship of hematite with other iron oxides and Fe-bearing minerals will help understand the geochemical process before and after eolian deposit, paleocliamte significance of magnetic susceptibility and reconstruct paleoclimate in central China. So, hematite and related minerals of the loess and paleosol units from Chinese Loess Plateau were investigated using optical microscope, X-ray powder diffraction （XRD）, scanning electron microscopy （SEM）, and high-resolution transmission microscopy （HRTEM）. The results show that there are five genetic types of hematite in loess-paleosol sequences of central China： （1） weathering of Fe-bearing silicate minerals, for instance, chlorite, will release iron that is precipitated as aggregates of hematite nano-crystals on mineral surfaces; （2） hematite combined with eolian magnetite grains that resulted from partial oxidation of magnetite, even though the partial oxidation may occur in the original area; （3） phase transformation from eolian goethite to hematite; （4） hematite formed on the edge and surface of maghemite because of dissolution and hematite recrystallization; and （5） eolian detrial hematite. The hematite formed from chemical weathering of Fe-bearing silicates with nanoporous texture because of dehydration from iron hydroxide is the most important genetic mechanism. It is proposed that the fact that hematite was formed from chemical weathering of Fe-bearing silicates is a main reason for the redness in paleosol units. However, too intense pedogenesis and high amounts of precipitation will promote oxidation of eolian magnetite and maghemite dissolution, which may result in the decreasing of magnetic susceptibility.     

中国北方晚第四纪气候变化的沙漠与黄土记录* ——以光释光年代为基础的直接对比

中国北方有约200×10⁴km²的面积被黄土、沙漠和荒漠戈壁沉积物覆盖,这些地区堆积物的形成变化与第四纪气候变化密切相关。关于中国北方沙漠与黄土记录晚第四纪古气候变化的研究不少,但是,由于受到方法和条件等限制,系统的(高密度的)和独立的年代学工作比较薄弱,从而使诸多已经发表的关于沙漠-黄土记录的亚轨道时间尺度气候变化的结论受到质疑。文章通过对黄土高原代表性的4个末次冰期以来的黄土剖面以及毛乌素、浑善达克和科尔沁沙地的20多个末次冰期-全新世的沙-砂质古土壤剖面的研究,获得了150多个独立的光释光年龄数据。在此基础上,结合200多个样品的粒度、有机质含量和磁化率数据,重建末次冰期以来中国北方气候变化过程,对比分析沙地与黄土古气候记录的联系。结果表明,中国北方古气候在57.5~52.5kaB.P.相对干旱,41.5~37.3kaB.P.相对湿润,26~22kaB.P.逐渐干旱,22~18kaB.P.极端干旱,15~10kaB.P.干旱,10~8kaB.P.为干旱减弱的时期,8.0~2.4kaB.P.相对湿润,而2.4kaB.P.以来气候为相对干旱。其间,在8.0~2.4kaB.P.的湿润时期有几次干旱事件,而2.4kaB.P.以来气候变化频繁。具有独立年代控制的黄土和沙漠记录表明,中国北方的气候变化对轨道时间尺度的太阳辐射变化有大约3~4ka的滞后。     

Carbon isotope ratios of C4 plants in loess areas of North China

Carbon isotope ratios (δ ¹³C) of 89 C₄ plant samples were determined from the loess area in North China. δ ¹³C values vary between −10.5‰ and −14.6‰ with a mean of −12.6‰. Along a precipitation gradient from the semi-moist area to the semiarid area, then to the arid area, the δ ¹³C values of C₄ plants show a slight decreasing trend. The δ ¹³C values of C₄ plants in the dry season are found lower than those in the wet season. These trends are opposite to those observed for C₃ species.     

The role of dust source area and pedogenesis in three loess-palaeosol sections from North Bulgaria: A mineral magnetic study

Rock magnetic studies of three loess-palaeosol sections from Bulgaria (Harletz and Orsoja in the NW and Durankulak in the NE at the Black Sea coast) have been carried out. Thermomagnetic analyses of magnetic susceptibility point to magnetite as the major ferrimagnetic carrier in the loess and palaeosol units. Maghemite gives a significant contribution to the total magnetic signal in the recent soils (S₀), while in one of the sections-Orsoja-hematite may also be present. The effective magnetic grain sizes deduced from the hysteresis measurements and the ratios M_rs/M_s and B_cr/B_c fall in the pseudo single domain (PSD) range, but the data distributions in a Day diagram for the three different sections are shifted. This is suggested to be caused by different detrital input (e.g. different dust source areas) and varying degrees of pedogenic modification. The calculated background susceptibilities χ_bg differ significantly as well. The lowest value is obtained for the Durankulak section-χ_bg = 9.95 × 10⁻⁸ m³/kg, which is in accordance with the data from other studies of loess-palaeosol profiles from the Black Sea area. The corresponding background susceptibilities for the other two sections studied-Harletz and Orsoja-are significantly higher (33.1 and 17.75 × 10⁻⁸ m³/kg, respectively). Both parent material and pedogenesis are found to be responsible for the observed differences in the magnetic characteristics.     

Study on the Microstructure of Loess in Meizoseismal Zone

INTRODUCTIONAn earthquake with magnitude of5.8struck Qishan Townin Yongdeng County,Lanzhou,at06:44,July22,1995.The region affected by the earthquake is located in the loess hills with sparsevegetation cover.The region also lags behind economically.The meizoseismal intensity reachedⅧ.For its shallowsource,the earthquake caused relatively heavy damage,though it was a moderateevent.Ground cracks with a widthlargerthan10cmare a commonsight onthe hills aroundthe town,some looks as if they …     

黄土山区煤田三维地震勘探应用实例

山西黄土山区地形起伏较大，冲沟发育，黄土覆盖层厚，各种干扰波并存，激发困难，在进行三维地震勘探前，根据踏勘情况，选取不同岩性地段有代表性的点做试验工作，以确定野外施工参数。在保证野外资料质量的前提下，重点做好静校正、干扰波去除、叠后偏移等处理工作。并充分利用解释系统多种显示功能和自动拾取功能，从不同角度认识断层、陷落柱等地质现象。晋城某煤矿三维地震勘探实例验证了该项技术在复杂黄土山区的应用效果。