浅覆盖区土壤化学成分与基岩化学成分的关系及其意义——以大兴安岭北部地区为例

以大兴安岭北部地区为例，研究了浅覆盖区土壤与基岩化学成分的关系。指出浅覆盖区残积型土壤主要造岩元素组合继承了基岩元素组合特征；在岩石风化成土过程中，元素再分配和迁移使土壤中大多数元素（氧化物）含量产生明显的“均一化”。在此基础上，对土壤地球化学异常的识别与评价问题进行了讨论并提出了建议。     

地质雷达及浅层地震在泥质粉砂岩中断裂带上的曲线特征

探讨了如何利用地质雷达及浅层地震有关原理判释泥质粉砂岩中隐伏断裂带的性质和特征。主要的工作方法是通过现场实测，分析地质雷达反映在张性断裂带和压性断裂带上的曲线特征，分析浅层地震相遇时距曲线在断裂带上的曲线特征。后者的主要特征有：（1）在断裂带上初至时间延长；（2）在断裂带上左右支时距曲线上下跳动的幅度均等；（3）在断裂带上跳动的长度不一；（4）在断裂带左右支时距曲线上下跳动或反相；（5）时距曲线呈喇叭口。阐明了地质雷达和浅层地震的原理及其在泥质粉砂岩中勘查断裂构造的效果     

Temporal patterns of suspended sediment yield following moderate to extreme hydrological events recorded in varved lacustrine sediments

A 487‐year annually laminated (varved) sediment record from Nicolay Lake, Cornwall Island, in the Canadian High Arctic was evaluated to determine the impact that years with high sediment yields had on sediment yields in subsequent years. All of the 40 largest years showed evidence for increased sediment yield in the subsequent 10–30 years. The positive anomalies in lagging years were approximately scaled according to the size of the initiating year, although many intermediate years (25‐ to 100‐year recurrence) showed weak or variable responses. The smallest events considered (10‐ to 25‐year recurrence) showed a consistent, but low‐amplitude response. Additionally the 10‐year events revealed frequent negative sediment yield anomalies in the preceding decade. This behaviour was interpreted as a frequent sediment activation cycle initiated by the modest year, and leading to sediment yield hysteresis lasting 15–25 years. The largest years (greater than 50‐year recurrence) showed consistently above‐average sediment yields in the preceding decade, in part due to the frequent occurrence of moderate (Q₁₀) years. It is hypothesized that temporary storage of sediment and previous initiation of erosion sites resulted in extraordinary sediment yields during intense summer rainfall events. This study demonstrates the potential use of varved lake sediment records to improve our understanding of long‐term sediment dynamics. These records present an opportunity to further develop and test sediment dynamic and routing models to gain insight into the interaction of time and space in fluvial and sediment delivery processes. Copyright © 2002 John Wiley & Sons, Ltd.     

Geochemical stream sediment survey in Winder Valley, Balochistan, Pakistan

A pilot scale geochemical survey of sediments from the Winder Stream (SW Pakistan) and its tributaries was carried out. The Winder Stream mainly receives sediment from the southern extensions of the Mor and Pab Ranges in the District of Lasbela (Balochistan). In these two mountain ranges, rocks from Jurassic to Cretaceous age are exposed. Rocks of the Ferozabad Group comprise of carbonates and siliciclastics of Lower–Middle Jurassic age and occupy the dominant part of the Mor Range. These strata host syngenetic and epigenetic Zn–Pb–Ba mineralizations of Stratiform Sediment-Hosted (SSH) and Mississippi Valley Type (MVT) deposits.Quantitative estimates of mobile and immobile elements were made from active stream sediments of the Winder stream and its tributaries. The samples were analyzed for Ag, Zn, Pb, Cu, Ni, Co, V, Mn, Fe and Ba using atomic absorption spectroscopy. The abundance of these elements is discussed in relation to local geological conditions such as bedrock, climate, weathering, mobility and pH of the dispersing waters. A number of Zn anomalies have been distinguished in the study area. Kharrari (Zn, 360 ppm), Sand (Zn, 340 ppm) and Draber (Zn, 210 ppm) are demarcated as new areas for Zn mineralization. The present study also indicates prospects of Ag, Cu and V in the rocks of the Mor Range.Relationships between various elements have been identified from scattergrams and reflect genetic associations. Whereby the positive correlation between Cu–Zn (0.55, n=18) and Cu–Pb (0.63) is related to possible sulphide mineralization.     

Cenozoic tectonic events at the border of the Paraná Basin, São Paulo, Brazil

In the last decade, even in areas that had been considered tectonically stable, a great amount of Cenozoic, including the Quaternary period, structural data have been collected throughout Brazil. The main goal of this study is to describe the Cenozoic structures and tectonic evolution of an area that is located at the border of the Paraná Basin in the state of São Paulo.The research methods consisted of the analysis of: (1) brittle structure data, mainly conjugate fractures and fault slip data; (2) lineaments traced on air photos and TM Landsat and radar images; and (3) a second-order base surface map.The study area, during the Cenozoic, has been affected by five strike–slip tectonic events, which generated mainly strike–slip faults, and secondarily normal and reverse ones. The events were named, from the oldest to the youngest, E1-NE, E2-EW, E3-NW, E4-NS, and E5-NNE; and the maximum principal stresses σ1 strike approximately NE–SW, E–W, NW–SE, N–S, and NNE–SSW, respectively. Event E2-EW seems to have been contemporaneous with the deposition of the Rio Claro Formation, the most important Cenozoic deposit of probable Neogenic age, and also to have controlled the distribution of its deposits. Event E3-NW was the strongest one in the area, as is pointed out by structural data, and the maximum principal stress σ1 of event E5-NNE is partially concordant with the orientation of σH-max of well break-out data in the Paraná Basin, suggesting a Neotectonic activity for this event. Finally, discontinuities parallel and correlated to the directions of strike–slip faults of the Cenozoic events seem to have actively controlled the sculpturing of the relief in the study area.     

Mineralogy and chemistry of bentonite (?) deposits at Minjingu, Lake Manyara, North Tanzania

Olive green clays likely to be bentonitic in composition have been mineralogically and chemically studied. They occur in association with other lacustrine sediments at Lake Manyara. Radiocarbon dates from four diatom horizons indicate ages ranging from 12 Ka to 135 Ka suggesting a Mid-Holocene age. Middle Pleistocene age have been assigned to the ridged oncolites of Lake Manyara. The olive green coloured clays in the Manyara basin are known to occur in association with other lake beds including phosphorite deposits, stromatolites, bioturbated silty clays, partly silicified marls, conglomerates and olive green coloured opal beds. The results presented herein are from the olive green coloured clays. The olive green clays (bentonite?) are a result of devitrification or alteration of volcanic ashes and/or pyroclasts. The green clays occur in different forms as they are separated from each other by other lacustrine sediments. The alteration might have taken place in slightly different environments in terms of salinity and alkalinity. One of the top layer is friable and shows conchoidal fractures when dry. The other beds below in the lacustrine sequence are cemented with calcite and some dolomite as well as zeolites. The lowermost layer in the sequence is friable and shows cracks filled with coarse crystalline calcite. Mineralogically the bentonite is composed of the clay minerals illite, illite-smectite mixed layer clays, and chlorite. Other authigenic minerals include various zeolites (analcime, clinoptilolite, erionite and some traces of mordenite), opal, and fluorapatite. The clays have magnesium contents varying from 3.01% to 7.43%. The calcium contents vary widely due to presence or absence of one of the two minerals calcite or apatite. Trace elements like Ba, Ce, Sr, Zr are equally attributed to the presence of calcite and apatite. The formation of the illite-smectite mixed layer clays in an alternating manner with other lake sediments depicts different episodes of volcanic eruptions in the area. The mineralogical composition of smectites, zeolites, and opal in the green clays suggests a deposition of pyroclasts and volcanic ashes in a closed lake system with fluctuating levels. Due to evaporation alkalinity and salinity levels were fluctuating. The clays might have been bentonite which have undergone illitisation, a phenomena noted in other neighbouring rift basins.     

Late-Glacial and Early Holocene Environmental and Climatic Change at Lake Tambichozero, Southeastern Russian Karelia

High-resolution lithostratigraphy, mineral magnetic, carbon, pollen, and macrofossil analyses, and accelerator mass spectrometry ¹⁴C measurements were performed in the study of a sediment sequence from Lake Tambichozero, southeastern Russian Karelia, to reconstruct late-glacial and early Holocene aquatic and terrestrial environmental changes. The lake formed ca. 14,000 cal yr B.P. and the area around the lake was subsequently colonized by arctic plants, forming patches of pioneer communities surrounded by areas of exposed soil. A minor rise in lake productivity and the immigration of Betula pubescens occurred ca. 11,500 cal yr B.P. The rise in summer temperatures probably led to increased melting of remnant ice and enhanced erosion. The distinct increase in lake productivity and the development of open Betula-Populus forests, which are reconstructed based on plant macrofossil remains, indicate stable soils from 10,600 cal yr B.P. onward. Pinus and Picea probably became established ca. 9900 cal yr B.P.     

The nature of calcareous deposits along pan margins in eastern central Namibia

In a region along the western margin of the Kalahari in eastern Namibia and western Botswana, many pan basins have mainly calcareous deposits along part of their margins. These are typically lined by low vertical scarps. In Namibia, these pans are mainly located in dry river beds. The petrographical study of these deposits demonstrates that they consist of lacustrine sediments that have to a varying extent been affected by early‐diagenetic processes and by the formation of late‐diagenetic features. The original composition of the deposits ranges from highly calcareous sediments, typically with ostracod, diatom and charophyte remains, to entirely non‐calcareous diatomites. The deposits generally show an upward increase in total carbonate content, which is mainly a synsedimentary feature. The early‐diagenetic processes that affected the deposits include the formation of orthic siliceous nodules. At a later stage, secondary calcite enrichment occurred, leaving only the silica‐impregnated sections unaffected. This enrichment partly accounts for the upward increase in total carbonate content in some profiles and often resulted in the development of a highly calcareous surface horizon. Sepiolite and amorphous silica that are part of the groundmass of the deposits may also partly have formed at this stage. Late‐diagenetic features include various forms of secondary calcite and silica. This study of pan basins in eastern central Namibia indicates that a lacustrine rather than purely pedogenic origin should also be considered for calcareous deposits that commonly occur along pan margins in other parts of southern Africa. Copyright © 2002 John Wiley & Sons, Ltd.     

坝上高原安固里淖粒度年纹层与环境变化

在安固里淖湖心区获取一未扰动沉积物样柱，分析发现了由冬季风搬运物与湖心沉积共同形成的粒度年纹层，建立了纹层年表，恢复了安固里淖湖区8507aB.P，以来的环境变化过程。8507-5429aB.P。冬季风活动较弱，后期的所波动；5429-3244aB.P.冬季风活动较强，3244-2494aB.P。冬季风活动减弱；2494-1165aB.P。冬季风活动略有增强；1165aB.P以来，冬季风活动减弱。安固里小淖粒度年纹层反映的冬季风变化情况与我国北方地区同期的环境变化和海平面变化有很好的对应关系。     

南极菲尔德斯半岛古海蚀龛沉积的古环境记录

在西南极菲尔德斯半岛长城站地区发现有大量古海蚀龛 ,龛内保存有完整沉积剖面 ,通过对其中一个沉积剖面的粒度特征及元素组成的分析 ,确认该剖面是后期的湖相沉积 ,并据此恢复了距今 460 0年以来该地区古环境演化历史。结果表明 ,距今 40 0 0— 30 0 0年长城站区地表岩石化学风化作用较强烈 ,处于一个相对温暖的时期 ,这与湖泊沉积物、海洋沉积物等古环境记录载体的研究结果是一致的 ,证明古海蚀龛沉积可以作为研究南极无冰区和冰缘地区古环境演化历史的一种新的地质载体。