套子湾沿岸加积型滩脊成因及其环境意义

讨论套子湾沿岸加岸加积型滩积的成因及其环境意义，提出滩脊→加积型滩脊→海岸沙丘的地貌发育模式，加积型滩脊的形成发展与海岸环境变化密切相关。     

气动试验法测定渗透系数的可行性分析

基于竖管法测定沉积物渗透系数的原理,设计一种以空气作为流体测定沉积物渗透率的试验方法—气动试验法,将沉积物的空气渗透率(k_a)转换成用水当做流体时测定的渗透系数(K_w)。利用气动试验法和竖管法分别测定3组沙漠砂样和7组河漫滩砂样的渗透系数。试验结果表明,气动试验法测定沉积物的渗透系数可行,与竖管法相比更加方便、快捷,可以解决竖管法耗水、耗时的局限性,可应用于干旱-半干旱地区野外沉积物渗透系数的测定。     

西南印度洋中脊表层沉积物中存在热液组分的地球化学证据

Hydrothermal materials in deep-sea sediments provide a robust tracer to the localized hydrothermal activity at mid-ocean ridges. Major, trace and rare earth element(REE) data for surface sediments collected from the ultraslow spreading Southwest Indian Ridge are presented to examine the existence of hydrothermal component.Biogenic carbonate oozes dominate all the sediment samples, with CaO content varying from 85.5% to 89.9% on a volatile-free basis. The leaching residue of bulk sediments by ~5% HCl is compositionally comparable to the Upper Continental Crust(UCC) in SiO_2, Al_2O_3, CaO, MgO, alkali elements(Rb, Cs) and high field strength elements(Nb, Ta, Zr, Hf, Ti). These detritus-hosted elements are inferred to be prominently derived from the Australian continent by means of eolian dust, while the contribution of local volcaniclastics is insignificant. In addition, the residual fraction shows a clear enrichment in Fe, Mn, and Ba compared with the UCC. Combining the positive Eu anomaly of residual fraction which is opposed to the UCC but the characteristic of hydrothermal fluids and associated precipitates occurred at mid-ocean ridges, the incorporation of localized hydrothermal component can be constrained. REE mixing calculations indicate that more than half REE within the residual fraction(~55%–60%) are derived from a hydrothermal component, which is inferred to be resulted from a diffuse fluid mineralization. The low-temperature diffuse flow may be widely distributed along the slow-ultraslow spreading ridges where crustal faults and fissures abound, and probably have a great mineralization potential.     

风沙运动理论体系的创建与研究

确定风、沙源、风沙流、下垫面和沙地地表形态是构成风沙运动体系的5个基本要素。确定风速的强弱、沙粒的走停、气流含沙量的盈亏、下垫面的扬抑作用和沙地地表的蚀积变化是这些基本要素各自参与风沙运动的主要表现特征。这些表现特征都能一分为二, 于是10个对立侧面的相互作用构成了风沙运动发展变化的总体。系统地研究这些侧面的组合关系、揭示它们相互促进相互制约的演变机理, 进而依其内在联系进行排序, 将其串联成一体, 并绘出图式, 这样便形成了名之曰"强、弱、扬、抑、走、停、盈、亏、蚀、积十纲辩证"的风沙运动理论体系。其中"强、弱、走、停、盈、亏、蚀、积八纲辩证"是本理论体系的核心。     

Clay mineralogy of a red clay–loess sequence from Lingtai, the Chinese Loess Plateau

The Chinese Loess Plateau (CLP) comprises an extensive record of eolian deposition that contains important information about climate change. The objective of this study is to investigate if mineralogy can provide more insight into the long-term evolution of the East Asian monsoon. Comparisons between mineralogy and other paleoclimatic records (grain size and magnetic susceptibility) from the CLP have been made to evaluate the efficacy of mineralogy as a paleoclimatic tool.Here we present data from a mineralogical study of a red clay–loess sequence at Lingtai, central Chinese Loess Plateau. Changes related to source area(s), transport processes and weathering regime over time are recorded in mineral variation.Higher average concentrations of kaolinite, chlorite and quartz in the red clay, together with abrupt changes in relative mineral abundances across the red clay–loess boundary suggest a change of source area at 2.6 Ma. From 2.6 Ma to about 1.7 Ma the summer monsoon influence increases, destroying chlorite and contributing fine illite particles to the sediment. At around 1.7 Ma the mineralogy becomes relatively constant, suggesting that the monsoon was fairly stable during this period. At 0.7–0.5 Ma an increase of both summer monsoon and winter monsoon activity is inferred from illite, kaolinite, chlorite and plagioclase concentrations. Over the last 0.5 Ma mineralogy suggests an aridification of source area(s) as chlorite and plagioclase concentrations increase where illite concentration decreases. The last major change occurred around 0.07 Ma and indicates reducing summer monsoon influence as chlorite and quartz concentrations increase and illite concentration, as well as the < 2 μm size fraction, decreases. The mineralogical trends and differences between loess and paleosols units suggest different source areas in the last 0.5 Ma.     

A STATISTICAL TEST OF FLORISTIC ZONES AS INFERRED FROM THE POLLEN RECORD: SOUTHERN NEW ENGLAND

This study presents the stratigraphic and floristic interpretations of data collected from a 6.49 m core taken within the Rowley River Marsh, Massachusetts. Twenty-five samples were collected at 28 centimeter intervals from the core in this Holocene coastal marsh. Based on stratigraphic control, the age of the core samples includes a time sequence extending back 4,600 years from the present. Analysis of the core stratigraphic units suggests the environment has essentially been a low energy estuarine system for the past 4,600 years. The 25 samples were also processed for pollen taxa present since 4,600 years B.P. A discriminant function analysis was used to test the floristic zonal similarity of the diagnostic taxa (Picea, Pinus, Carya, Tsuga, Quercus) from the core with those same taxa used to establish the floristic zones for the southern New England region. The results of the analysis demonstrated that 84% of the samples were correctly classified by floristic zone. Although the distribution of diagnostic taxa from this study is generally in agreement with the previously established floristic zones, the Tsuga taxa are present throughout the temporal sequence, suggesting the occurrence of a cooler climate regime for the sampling site since 4,600 years B.P.     

Dependence of Near-Surface Magnetic Susceptibility on Dust Accumulation Rate and Precipitation on the Chinese Loess Plateau

Magnetic susceptibility (MS) of surface sediment varies systematically across the Loess Plateau in central China, decreasing exponentially from >200×10⁻⁸ m³/kg at the northern margin of the Qinling Shan to ≤30×10⁻⁸ m³/kg near the southern margin of the Mu Us Desert. MS correlates highly with loess median grain size (r²=0.79), which decreases south-southeastward across the plateau. It also correlates with mean annual temperature (MAT) and mean annual precipitation (MAP) (r²=0.58 and 0.60, respectively), and with their product MAT×MAP (r²=0.83), which is considered a measure of potential pedogenic activity. Because regional isopleths depicting grain size and the primary meteorological parameters are nearly parallel, it is difficult to determine their relative influence on MS. A simple MS model, based on the observed spatial variation in loess thickness, permits quantitative assessment of the effect of the dust accumulation rate on the MS signal of surface sediment and isolates the likely role of climate in the production of magnetic minerals. The model suggests that 84% of the loess MS variance is dictated by the diluting effect of dust and 10–11% is associated with meteorological factors, primarily precipitation. The observed and modeled relationships support hypotheses that attribute variations in MS in the loess-paleosol succession to varying rates of dust deposition and in situ production of magnetic minerals in the accretionary soils, both of which are controlled by monsoon climate.     

晚新生代黄土高原风尘堆积与粉尘源区干旱化问题

基于黄土高原风尘堆积的岩性和磁性地层研究 ,计算了晚新生代黄土高原风尘堆积速率变化 ,并与深海沉积记录的粉尘通量变化对比 ,初步探讨了海陆风尘沉积记录的晚新生代亚洲内陆粉尘源区的干旱化过程 ,揭示出自 4 5MaB P 以来粉尘源区干燥度的逐级增加 ,尤其是在 3 6 2 6MaB P 时段黄土高原风尘沉积速率和ODP885 / 886孔粉尘通量的显著增加 ,暗示可能由于青藏高原在此时段加速隆升所造成的亚洲内陆粉尘源区干燥度的急剧加强。     

Magnetic properties and their paleoclimatic implications revealed from the last glacial eolian sedimentary sequence in Pengze, Jiangxi

The sand-hill section in Hongguang, Pengze County, Jiangxi Province is composed of eolian sand beds interbedded with 12 weakly-pedogenetic paleosols, and this sedimentary sequence was formed from about 25 to 13 kaBP. A detailed rock-magnetic study demonstrates that the magnetic minerals in the sequence are dominated by multi-domain magnetite grains in addition to small amounts of maghemite and hematite. Compared with the eolian sand beds, the paleosols are characterized by smaller magnetic particles, higher proportion of low-coercivity minerals and markedly increase in the magnetic mineral content. In the section, various magnetic parameters (K, ARM, SIRM and S ratios) display a roughly gradual increase from eolian sand beds to the overlying paleosols but an abrupt decrease from paleosols to the overlying eolian sand beds. The content of low-coercivity magnetic minerals shows the lowest values in the second eolian sand bed from the bottom of the section, and from the bed upwards it gradually increases on the whole in the eolian sand beds. These magnetic properties reflect regional climatic changes during the last glacial maximum.     

Holocene Yellow Silt Layers and the Paleoclimate Event of 8200 a B.P. in Lop Nur, Xinjiang, NW China

Many yellow silt layers have been identified in the Holocene sediments in the last lake of Lop Nur (playa), Xinjiang, northwestern China. Statistics of drill-hole cores have revealed more than one hundred layers, which exhibit regularity in time sequence. Study has further verified that these yellow silt layers were deposited through eolian processes. The time-frequency distribution diagram shows an obvious peak occurring at about 8200 a B.P., which is consistent with the dry, windy and cold climate event occurring at 8200 a in other places around the world. Therefore, this event is regarded as a response to the global climate change.