Superposed lateral ramps in the Pell City thrust sheet, Appalachian thrust belt, Alabama

In the Appalachian thrust belt in Alabama, thrust sheets of Paleozoic strata generally strike northeastward and are imbricated northwestward; four transverse zones cross the regional strike of the thrust belt. The large-scale Pell City thrust sheet ends southwestward at an oblique lateral ramp within the Harpersville transverse zone, where the leading edge of the thrust sheet (the Pell City fault) curves abruptly 55° counterclockwise. The northwest-striking segment of the Pell City fault conforms to the geometry of an oblique lateral ramp in the footwall. Furthermore, the Pell City fault cuts up section in the hanging wall southwestward toward the transverse zone, indicating a hanging-wall lateral ramp emplaced over the footwall oblique lateral ramp.In the hanging wall adjacent to the northwest-trending segment of the Pell City fault, a pervasive train of upright, isoclinal folds (with 50% apparent shortening) trends N15°W, oblique to the regional translation direction. The fold train is limited to the southwestern part of the Pell City thrust sheet; farther northeast, the regional northeasterly strike prevails. The isoclinal folds in the hanging wall indicate contractional crowding perpendicular to the footwall oblique lateral ramp.     

China's Urbanization in 1949–2015: Processes and Driving Forces

The pace and scale of China's contemporary urbanization are stunning. This paper reviews process and the underlying driving forces of China's urbanization between 1949–2015. Contemporary China's urbanization has experienced four stages, and each has had different driving forces: 1) economic re-construction and industrialization-led urbanization(1949–1977); 2) economic reform and market-led urbanization(1978–1995); 3) economic globalization and the global-local urbanization(1996–2010); and 4) the land-economyled urbanization(2010–). These urbanization processes and driving forces will undoubtedly provide scientific reference and have significant implications for developing countries, especially African countries, to formulate their urbanization public policies.     

Cyclic characteristics of sediments in the Moon Island Beach Subgroup, Newcastle Coal Measures, New South Wales

Cyclic characteristics of a sequence of Permian coal-measure sediments have been studied using Markov chain analysis on borehole data. Fining-upwards and oscillating sequences can be distinguished, and depositional regimes are proposed to explain the observed sequences. However, there is no clearly defined relationship of sequence type to tectonosedimentary environment. The relationship of the number of coal-defined and fining-upwards cycles to total thickness and mean cycle thickness is examined using linear regression. The relationships for coal-defined and fining-upwards cycles are essentially the same. Significant positive correlations are present between the number of cycles and total thickness and significant inverse relationships are present for the number of cycles and the mean cycle thickness.     

The Argo Abyssal Plain

Eighteen geophysical transects were made in the Argo Abyssal Plain to study the magnetic anomalies, bathymetry and seismic structure. Magnetic anomalies were identified as being the Mesozoic anomalies M-10 to M-25, increasing in age from the Java Trench to the northwest continental shelf of Australia. A new bathymetric map shows that the Argo Abyssal Plain is bounded by the 5600-m contour and reaches a maximum depth of 5730 m against the inshore side of the Exmouth Plateau. Joey Rise was found to limit the Argo Abyssal Plain on the southwest. Continuous seismic profiles, sonobuoy data and seismic data from other cruises permit one to contour the depths to oceanic basement. Numerous diapir-like structures were observed, but their nature and origin is obscure.     

Biogeochemistry and bacteriology of ferrous iron oxidation in geothermal habitats

A survey of hot, acid springs in Yellowstone Park has shown that high concentrations of ferrous and ferric iron are often present. Total ionic iron concentrations in different springs ranged from less than 1 ppm to greater than 200 ppm, and up to 50% of the ionic iron was in the ferrous form. Some of these springs also have high concentrations of reduced sulfur species (S^2? and S⁰). Significant populations of the bacterium Sulfolobus, acidocaldarius, an autotrophic organism able to live and oxidize sulfur compounds at low pH and high temperature, were present in most of these springs. The role of this organism in the oxidation of ferrous iron was investigated by incubating natural samples of water and assaying for disappearance of ferrous iron. Controls in which bacterial activity was inhibited by addition of 10% NaCl were also run. Bacterial oxidation of ferrous iron occurred in most but not all of the spring waters. The temperature optimum for oxidation varied from spring to spring, but significant oxidation occurred at temperatures of 80–85°C, but not at 90°C. Thus, 85–90°C is the upper temperature at which bacterial iron oxidation occurs; a similar upper limit has previously been reported for sulfur oxidation in the same kinds of springs. The steady-state concentrations of ferrous and ferric iron are determined by the rate at which these ions move into the spring pools with the ground water (flow rate), by the rate at which ferric iron is reduced to the ferrous state by sulfide, and by the rate of bacterial oxidation. The bacterial oxidation rate is faster than the flow rate, so that the rate of reduction of ferric iron is probably the rate-controlling reaction. In several springs, no decrease in ferrous iron occurred, even though high bacterial populations were present. It was shown that in these springs, ferrous iron oxidation occurred but the ferric iron formed was reduced back to the ferrous state again. These springs were all high in suspended sediment and the reductant was shown to be present in the sediment. X-ray diffraction revealed that the sediment contained three major ingredients, elemental sulfur, natroalunite, and quartz. Chemical analyses showed a small amount of sulfide, too little to reduce the ferric iron. Elemental sulfur itself did not reduce ferric iron but when elemental sulfur was removed from the sediment by CS₂ extraction, the activity of the sediment was abolished. It is hypothesized that the sulfide present in the sediment (possibly bound to natroalunite) reacts with elemental sulfur to form a reductant for ferric iron. The results show that bacteria can have a profound influence on the ferrous/ferric ratios of geothermal systems, but that temperature and mineral composition of the water may significantly influence the overall result.     

Seismicity associated with mining

The virgin state of stress in the earth's crust is disturbed by mine excavations which result in stress concentrations in the rock. Rock emits seismic pulses when subjected to stresses approaching in value the strength of the rock. Mining gives rise to seismic activity ranging from microseismic events radiating 10⁻⁵ J (M - 6) to rockbursts or tremors radiating 10⁹ J (M5).

Rock failures in mines fall into four main categories: rockfalls, in which loosened rock falls mainly under its own weight; rockbursts which are violent failures of rock and may cause damage to excavations; bumps, which are violent failures, but which do not cause damage to the excavations; and outbursts in which the rapid release of gas causes rock to be ejected into the excavation. Microseismic activity is associated with all these four categories of rock failure.

Rockbursts and bumps occur in deep metalliferous mines in which thin tabular deposits in strong, brittle siliceous rocks of igneous or metamorphic origin are worked. The seismicity associated with mining appears to have many features in common with those natural earthquakes. However, the mechanics and dynamics of mining can be analysed relatively completely and the excavations provide access to the source region of the seismic events.

Comprehensive studies of rock deformation and fractures have been made on several gold mines of the Witwatersrand System. The gold-bearing reefs are mined at depths of down to more than 3 km below surface by stoping. This creates flat voids in the quartzitic strata extending laterally for distances of up to several kilometres with an initial excavated thickness of a metre. Geodetic-type measurements in tunnels and boreholes traversing the rock mass around these excavations have shown that the rock mass responds elastically over long periods of time to the extension of the boundaries of the excavations resulting from advancing the stope faces. Failure of the rock in the regions of maximum stress concentration near the edges of these excavations is an unavoidable concomitant of mining. It gives rise to new fracture planes closely parallel to the stope faces and to continuous seismic activity. The foci of seismic events with magnitudes from less than 0 to greater than 3 are found to occur mainly within tens of metres of the advancing stope faces. Diurnal and weekly distributions of seismic activity and of deformation show that the failure of the rock is time-dependent. The seismic radiation efficiency has been found to be of the order of 0.1%.

The seismicity is related to the spatial rate of energy release associated with the extension of the excavations and the incidence of seismic events and their magnitudes can be predicted statistically from calculated values of this quantity.     

Relation between n-alkane distributions and effective coalification temperatures in some Permian shales

In Permian shales of the Sydney Basin, Australia, n-alkane distributions have been compared with effective coalification temperatures (ECTs) estimated from vitrinite reflectivities. The upper, non-marine part of the section shows evidence of progressive cracking (shift of n-alkane maximum toward shorter chains and tendency to eliminate longer chains) as depth and ECT increase; but this trend is not maintained in the underlying marine section.All samples show lack of a maximum in the longer-chain n-alkane distribution. Possible reasons discussed are (i) a cracking rate of long chains greater than their formation rate; (ii) a need for higher temperatures than the rock has so far undergone to produce a new crop of long chains; or (iii) exhaustion of the straight-chain generating potential of the kerogen. Pyrolysis experiments may be effective in testing these possibilities.The linking of ECTs to alteration stages of sediment hydrocarbons opens the possibility of comparing these stages among formations which differ in age and organic and inorganic composition, and among basins of diverse geological history.     

Using groundwater levels to estimate recharge

Accurate estimation of groundwater recharge is extremely important for proper management of groundwater systems. Many different approaches exist for estimating recharge. This paper presents a review of methods that are based on groundwater-level data. The water-table fluctuation method may be the most widely used technique for estimating recharge; it requires knowledge of specific yield and changes in water levels over time. Advantages of this approach include its simplicity and an insensitivity to the mechanism by which water moves through the unsaturated zone. Uncertainty in estimates generated by this method relate to the limited accuracy with which specific yield can be determined and to the extent to which assumptions inherent in the method are valid. Other methods that use water levels (mostly based on the Darcy equation) are also described. The theory underlying the methods is explained. Examples from the literature are used to illustrate applications of the different methods. Electronic Publication     

Choosing appropriate techniques for quantifying groundwater recharge

Various techniques are available to quantify recharge; however, choosing appropriate techniques is often difficult. Important considerations in choosing a technique include space/time scales, range, and reliability of recharge estimates based on different techniques; other factors may limit the application of particular techniques. The goal of the recharge study is important because it may dictate the required space/time scales of the recharge estimates. Typical study goals include water-resource evaluation, which requires information on recharge over large spatial scales and on decadal time scales; and evaluation of aquifer vulnerability to contamination, which requires detailed information on spatial variability and preferential flow. The range of recharge rates that can be estimated using different approaches should be matched to expected recharge rates at a site. The reliability of recharge estimates using different techniques is variable. Techniques based on surface-water and unsaturated-zone data provide estimates of potential recharge, whereas those based on groundwater data generally provide estimates of actual recharge. Uncertainties in each approach to estimating recharge underscore the need for application of multiple techniques to increase reliability of recharge estimates. Electronic Publication