The local geologist 13: A beginner's guide to the field study of sedimentary rocks

Geology is primarily afield study, and no matter what information is collected from detailed study of hand specimens and thin sections in the laboratory, this must be related to the outcrops in order to develop a geological interpretation of a sequence of rocks. Here we focus on the type of information that should be collected when studying sedimentary rocks in the field, and highlight the main techniques employed.     

On some Silurian and Devonian Stromatoporoids of South-Western China

INTRODUCTION Little work has so far been done on Chinese stromatoporoids, thoughthey occur abundantly in the Silurian and Devonian strata of China, especiallyin the south-western provinces. Field work reveals the fact that the Silurian and     

华南泥盆纪层孔虫生长形态及其环境意义

通过对四川甘溪、贵州独山、广西六景和桂林神湾等泥盆纪剖面中层孔虫"生长形态"的系统研究,识别出层孔虫内部存在2大类7小类年生长条带:密度条带(疏密型、递变型、混杂型、突变型和"生长脊"型)和结构条带(结构差异型、单一结构层式),并发现层孔虫年生长条带广泛发育,在中泥盆世30属203种中均有记录。在层孔虫内部识别出了6类生长间断:含沉积物型、综合型、深色型、突变型、边部型和结构差异型。据此,系统总结了华南泥盆纪层孔虫生长形态及其相带分布规律,发现华南泥盆纪层孔虫主要分布在局限台地、开阔台地和台缘礁等7个相带中,各相带层孔虫生长形态差异明显。同时,发现和总结了与礁单元稳定构建密切相关的5个生长形态参数:总体形态、V/B(高与底宽之比)、基面、生长速率和生长间断。研究表明:层孔虫生长过程多由连续生长和间断二者共同组成,受到周期性环境因素(如冷、暖)和随机环境因素(如沉积速率变化)的共同影响,并以后者为主;提出并验证了层孔虫生长形态是高分辨率沉积环境变化的示踪指标,如利用年生长条带计算沉积速率;同时提出层孔虫生长形态是精细分析珊瑚-层孔虫礁的重要手段,如利用层孔虫生长速率推算礁生长速率等。     

Excursion guide 12: Yellowstone

The National Park at Yellowstone contains more than half the world's active geysers. Lying mostly in Wyoming, its host of geothermal features and fresh volcanic rocks offers an incomparable experience for any visiting geologist.     

Carbonates — a guide to hydrocarbons

Unfrozen samples of pure water and 10% v/v nitric acid, stored in acid-cleaned linear (high-density) polyethylene containers, are used as contamination blank controls for hydrogeochemical samples preserved by deep-freezing in similar vessels. After four years the maximum levels of metal contaminants in these blanks are (in μg/1) Fc 0.4; Cr 0.6; Ni 1.0; TI 0.6; Co 1.5; Mn 0.14; Ag 0.17; Cu 1.5; Cd 0.17; Pb 2.4; Zn 2.4. Values slightly lower than these are found for Co, Mn, Ag, Cu, Zn and Pb in the pure water samples. Approximately 0.5–1.0 μg/l of both Zn and Pb are derived from the nitric acid.     

Geological excursion guide 9: Jamaica

Apart from its obvious attractions for the visiting tourist, Jamaica is geologically significant, with a rock record dating from the Cretaceous and occupying a position at the north–east end of the Nicaraguan Rise, adjacent to the North Caribbean Plate Boundary Zone. During the Cretaceous, Jamaica was part of an island arc, but since the Eocene the rock record has been dominated by limestones.     

Excursion guide 11: Mount St Helens

The 1980 eruption of the Mount St Helens volcano produced a huge crater, massive debris flows and truly remarkable blast effects. All the features are still very visible, and the site offers easy access for an unforgettable visit.     

An approach for assessing soil health: a practical guide for optimal ecological management

How to integrate environmental geographic information and biodiversity data combined with management measures to effectively assess soil health is still an unresolved problem. This paper suggests an approach for systematically estimating soil quality and guiding ecological management. First, canonical correspondence analysis is used to predict the distributions of plant species or microorganism communities, principle pollutants and environmental variables from which spatial and environmental data are extracted by the geographic information system (GIS). Secondly, geostatistical methodologies are then used to estimate and quantify the spatial distribution characteristic of the species and pollutants and to create maps of spatial uncertainty and hazard assessment through ArcGis technology. Finally, redundancy analysis provides a suggestion about better management strategy and environmental factor for improving soil health and biodiversity. The combination of these methods with “3S” techniques as an assessment approach effectively meets the challenges for estimation and management in different soil environments.     

Using urban geology: a field guide to Morpeth Railway Station,northern England

A railway station might not seem an obvious subject as a geological locality. Yet with ease of access (just catch a train), the geology of the building stones of a railway station offers certain advantages in the age of inaccessible quarries, and tiresome health and safety paperwork. Hammers can be left at home, and eyes, hand lenses, cameras and compass‐clinometers may all be applied for non‐destructive investigation.     

Thallium: A potential guide to mineral deposits

Several recent studies have suggested that rocks associated with mineral deposits of hydrothermal origin are generally enriched in Rb. TI is similar in its geochemical characteristics to Rb, but its use as a potential guide to ore deposits has not been suggested. Although TI has the same size and valency as Rb, it is concentrated more in residual melts than Rb and K because the TI-O bond is more covalent and weaker than either the Rb-O or K-O bonds.A new method which is rapid and precise has been developed by one of the authors for the determination of TI in geological materials at the ppb level. About 350 rocks from 4 mineralized areas in northeastern Washington and central Montana were analyzed for TI by this method. Most of these rocks were also analyzed for SiO₂, A1₂O₃,Fe₂O₃, MgO, CaO, Na₂O, K₂O, TiO₂, P₂O₅, MnO, Ag, As, Au, Ba, Co, Cu, F, Li, Mo, Ni, Pb, Sr, Sb, Sn, Sr, Te, U, W, and Zn. The ore deposits of the areas studied include the gold-silver deposits of the Republic district, the uranium deposit of the Midnite mine, the coppermolybdenum deposit of Mount Tolman, and the gold deposits of the North Moccasin mining district.In all the mineralized areas there is significantly more TI in hydrothermally altered rocks than in unaltered rocks. The very high abundance of TI in the altered rocks of the North Moccasin gold district, and the significant positive correlations of TI and K and TI and Rb in the mineralized rocks of the other three areas suggest that TI was concentrated in hydrothermal fluids. In altered rocks the average K/Rb and K/TI ratios are lower, and the Rb/Sr and TI/Sr ratios are higher.Often the abundance of TI and the K/TI and TI/Sr ratios are more useful in delineating mineralized areas than the abundance of Rb and the K/Rb and Rb/Sr ratios. The ternary relationships between TI and several other elements, especially Rb, K, Ba, and Sr, show mineralized rocks to fall near the TI apices or near the TI-Rb or TI-K boundaries.     

A Wealden guide I: the Weald Sub-basin

The Wealden strata of southern England provide a range of evidence for Early Cretaceous non-marine environments and their inhabitants, and a climate of warm to hot, 'Mediterranean' aspect. Because of its exposure, and its range of facies, distinguishing a variety of sedimentary environments, the Wealden has long fascinated geologists intent on providing an environmental model. This article is one of two intended to give an overview of Wealden environments, providing the geological framework of these strata. In this article, the type-succession in the Weald Sub-basin of south-east England is summarized and briefly interpreted.     

A Wealden guide II: the Wessex Sub-basin

Part 1 of 'A Wealden guide' ( Geology Today , 2006, v.22, n.3) provided an introduction to the non-marine Early Cretaceous Wealden strata of southern England, and an account of the succession that outcrops within the Weald Sub-basin. This second article focuses on the Wealden of the Wessex Sub-basin, exposed on the Isle of Wight and Dorset coasts of southern and south-west England.     

Historical felt intensities as a guide to earthquake hazard

Up to 150 years of historical mean felt report data at 32 key Australian towns and cities were tested for completeness and converted to intensity recurrence intervals using extreme‐value analysis. It was found that the backward extrapolation of the mean modelled results of the most recent earthquake hazard study for these same localities fell within the 95% confidence interval derived from the regression of these historical data. Historical maximum felt intensities in the same towns and cities of Australia were used to show that damaging intensities of MM7 (or more) can be expected at susceptible sites at one (or more) of these centres, on average at least once every decade. Hence identification of the susceptible sites in each of these localities should be a priority.     

Radiant flux as a guide to relative seismic efficiency

The parameters “radiant flux” (energy radiated per unit area of an earthquake fault in unit time) and “radiant flux per unit displacement” reflect the power dissipated on a fault during slip. Values for moderate-to-large earthquakes range over two orders of magnitude, implying considerable variations in seismic efficiency, even for events of similar magnitude occurring on faults of the same type.     

槽波波速CT 成像技术及其应用

槽波地震勘探因为具有分辨率高、能量衰减小的特点,在煤矿井下隐伏致灾体的地球物理勘 探中已得到了广泛的应用。但现阶段的槽波探测精度尚无法满足矿山智能化的要求。目前,物理模拟多以二维模型条件下的 Rayleigh型槽波模拟为主,Love型槽波研究较少。为了掌握 Love 型槽波的传播规律,进行了三维槽波物理模拟中的 Love 型槽波研究。首先,通过波动方程和频散曲线分析,研究了Love 型槽波的波动及质点振动特征;然后以相似性原则为基础,通过构建类比于野外采集的激发、接收、同步装置,搭建了槽波物理模拟平台;随后通过硅橡胶和树脂等材料的配比选择,制作了符合实际地层岩层属性的地震物理模型;最后通过设计的3种典型观测系统,进行槽波超声物理模拟,成功观测到了物理模型中的 Love 型槽波。通过对煤层和围岩中2条测线的波场记录和频散曲线的对比分析,特别是理论曲线的符合程度进一步验证了模拟的有效性。同时,通过对横穿断层和正常煤层的2条测线Love型槽波波场的对比发现,断层前后波场频率成分发生了以 Airy 相为分界的明显转换,而且过断层后槽波能量几乎全部被衰减。研究结果将为后续定量、精细化槽波地震勘探提供采集、处理及解释等方法技术的理论支撑。