bluuebunny/crossref_metadata_2025 huggingface dataset:
Concept of equilibrium profile in deep-water turbidite system: effects of local physiographic changes on the nature of sedimentary process and the geometries of deposits
Authors: Ferry J-N. , Mulder T. , Parize O. , Raillard S.
Published: April 2008

In the middle slope section of the Lower Congo Basin a late Miocene channel system was tracked on 3D seismic profiles over more than 350 km. Along its course, between shelf and basin, the system encountered four regional tectonic structures that induced local slope modifications, either by uplift or by subsidence. The turbidite deposits of this channel system were influenced strongly by these structures, in terms of both character and morphology. From the proximal to the distal part of this channel system, variations in parameters such as the sinuosity, the width and depth of basal incision, the presence of splay and levee deposits, the location of vertical aggradation zones and channel avulsion, all correlate with changes in longitudinal slope gradient. Thus, along a conventional sigmoidal slope, the convex regions are subjected to erosional processes whereas the concave regions are depositional. The direct relationship observed between sedimentary deposits and changing slope gradient highlights an important control in deep-water turbidite systems. This apparent response to local gradient changes on the slope suggests the existence of a sedimentary equilibrium profile similar to that defined for fluvial systems.
Magnetic fabric and microstructure of a mylonite: example from the Bitterroot shear zone, western Montana
Authors: Sidman D. , Ferré E. C. , Teyssier C. , Jackson M.
Published: April 2008

The Bitterroot shear zone, SW Montana, is a mylonitic detachment that developed by strain localization during the Palaeocene-Eocene orogenic collapse of this part of the North American Cordillera. Anisotropy of magnetic susceptibility (AMS) data from two transects across the shear zone and into the granitic footwall demonstrate the continuity between the low to high-temperature solid-state fabric in the shear zone and the magmatic fabric developed in the footwall granite. This fabric gradually and smoothly rotates from E-dipping in the shear zone to W-dipping in the footwall granites, forming an arch over 10 km wide. Furthermore, the mineral fabric of both paramagnetic and ferrimagnetic minerals is consistent with the AMS fabric, displaying the same arching, which is interpreted to have developed by a rolling-hinge process in the footwall granites during activation of the Bitterroot shear zone. The AMS method thus stands out as a robust indicator of fabric over a wide range of deformation conditions.
Effects of bedding and foliation on mechanical anisotropy, damage evolution and failure mode
Authors: Baud Patrick , Louis Laurent , David Christian , Rawling Geoffrey C. , Wong Teng-Fong
Published: April 2008

In this study we review recent advances in our understanding of anisotropy in rocks, focusing on dilatant and compactant failure in sandstones and in a foliated metamorphic rock. In sandstones, the anisotropy can be associated with bedding, as in the Rothbach sandstone, or it can also be due to shape anisotropy of the grains and/or the pores, as in the Bentheim sandstone. Two scenarios are proposed for the development of anisotropy in these two end members. In a metamorphic rock with strong foliation like the Four-mile gneiss, it has been commonly observed that the brittle strength is minimum at a foliation angle of about 30°–45°. A damage mechanics model is proposed that underscores the dominant role of biotite foliation in the development of microcracking. In contrast it is often observed in sandstones with strong bedding that the strength is minimum in the direction parallel to bedding. New results for the Rothbach sandstone showed that compared to parallel-to-bedding samples: (i) in the brittle faulting regime the perpendicular-to-bedding samples have both a higher strength and dilatancy stress; and (ii) in the cataclastic flow regime the compactive yield envelope for the perpendicular-to-bedding samples expands significantly towards higher stress values.
High-strain deformation tests on natural gypsum aggregates in torsion
Authors: Barberini V. , Burlini L. , Rutter E. H. , Dapiaggi M.
Published: April 2008

Evaporitic minerals, such as gypsum, within sedimentary sequences play an important role in localizing deformation, especially in thrust tectonics, implying that their strength is generally lower than that of other rocks. To study the rheological and microstructural evolution of gypsum with strain, a set of experiments was performed on natural gypsum samples from Volterra (Italy). To reach high shear strain (up to γ = 5), deformation tests were performed in torsion at 300 MPa confining pressure, at temperatures up to 127 °C, and at shear strain rates between 10
−3
and 10
−5
s
−1
. All samples were studied by optical microscopy, to investigate the evolution of the microstructure with strain, and by X-ray diffraction (XRD) analyses, to determine whether and to what extent gypsum dehydrated during deformation. The shear stress increased with shear strain rate and decreased with temperature. A peak stress was usually reached at γ between 0.5 and 1.5. After the peak, 30–40% of weakening occurred but mechanical steady-state conditions were never reached. The microstructure evolved from a plastic deformation microstructure, where grains changed shape according to the bulk strain imposed, into a recrystallization-dominated microstructure, where grains were more equant. The shear stress sensitivity to strain rate increases with progressive strain, thus a meaningful constitutive flow law can only be determined from experiments in which steady-state flow is eventually reached. These results imply that gypsum in nature will flow plastically at shear stress levels lower than those expected from previous experimental studies due to the strain weakening associated with dynamic recrystallization, which can occur at temperatures even lower than gypsum dehydration.
Influence of phyllosilicates on fault strength in the brittle-ductile transition: insights from rock analogue experiments
Authors: Niemeijer A. R. , Spiers C. J.
Published: April 2008

Despite the fact that phyllosilicates are ubiquitous in mature fault and shear zones, little is known about the strength of phyllosilicate-bearing fault rocks under brittle-ductile transitional conditions where cataclasis and solution-transfer processes are active. In this study we explored steady-state strength behaviour of a simulated fault rock, consisting of muscovite and halite, using brine as pore fluid. Samples were deformed in a rotary shear apparatus under conditions where cataclasis and solution transfer are known to dominate the deformation behaviour of the halite. It was found that the steady-state strength of these mixtures is dependent on normal stress and sliding velocity. At low velocities (<0.5 µm s
−1
) the strength increases with velocity and normal stress, and a strong foliation develops. Comparison with previous microphysical models shows that this is a result of the serial operation of pressure solution in the halite grains accommodating frictional sliding over the phyllosilicate foliation. At high velocities (>1 µm s
−1
), velocity-weakening frictional behaviour occurs along with the development of a structureless cataclastic microstructure. Revision of previous models for the low-velocity behaviour results in a physically realistic description that fits our data well. This is extended to include the possibility of plastic flow in the phyllosilicates and applied to predict steady-state strength profiles for continental fault zones containing foliated quartz-mica fault rocks. The results predict a significant reduction of strength at mid-crustal depths and may have important implications for crustal dynamics and seismogenesis.
Water distribution in dynamically recrystallized quartz grains: cathodoluminescence and micro-infrared spectroscopic mapping
Authors: Muto Jun , Nagahama Hiroyuki , Hashimoto Testsuo
Published: April 2008

The distribution of water in dynamically recrystallized quartz aggregates in granitic mylonites was investigated by cathodoluminescence (CL) observations and micro-infrared (IR) spectroscopic mapping. It is clear from CL observations and micro-IR spectroscopic mappings that the CL intensity and contrast depend on the density of defects (e.g. the content of molecular H
2
O and absorbed OH species). Dynamic recrystallization, as a recovery process of intracrystalline strain, decreases the densities of excess carriers originated from defects. The decrease in the densities of excess carriers decreases the CL intensity and contrast within each grain. To investigate the effect of water weakening in the rheological properties of the crust, CL spectroscopy and micro-IR spectroscopic mapping are essential in the determination of concentration and distribution of water in natural high-strain zones.
Application of Geographical Information Systems to shape-fabric analysis
Authors: Fernández F. J. , Menéndez-Duarte R. , Aller J. , Bastida F.
Published: April 2008

A Geographical Information System (GIS) has been applied to shape-fabric analysis and strain measurement. It works in either raster or vectorial format, allows determination of many geometrical features of grains and stores additional descriptive information linked to all these graphic elements. Some new applications for shape characterization and strain measurement have been developed, e.g. the shape parameter
S
, the Fry method installed as a variant that uses only contiguous grains (TFry method) and a new method (ASPAS method), based on the intersection lengths of the lines of a radial network with the grain boundaries. A compilation of finite-strain estimates on a tectonite sample has been used to compare the results obtained by the new methods. As the shape fabric does not register the full strain history, the strain ratios obtained from the shape-fabric analysis are lower in most cases than those obtained using pretectonic markers.
The Appalachian peri-Gondwanan realm: a palaeogeographical perspective from the south
Authors: Hibbard James P. , Miller Brent V. , Tracy Robert J. , Carter Brad T.
Published: April 2008

The Appalachian peri-Gondwanan realm (APGR) is an extensive tract of exotic Neoproterozoic-early Palaeozoic crustal blocks that occupies the eastern flank of the orogen. Traditionally, southern APGR elements have been correlated with those of the northern Appalachians on the basis of gross geological similarities. Most palaeogeographical reconstructions of the APGR are based on data from the northern Appalachians; consequently in these reconstructions, southern APGR elements are viewed commonly either as being affiliated spatially with those of the north or ignored. However, emerging data from two southern Appalachian crustal blocks give new insights into the palaeogeography of the APGR. The Smith River allochthon may be a part of the APGR on the basis of recently obtained U-Pb monazite and staurolite ages that are apparently incompatible with a Laurentian origin. The allochthon and possibly adjacent terranes, appear to have followed a palaeogeographical track independent of other APGR elements. The Carolina zone is recognized as peri-Gondwanan in origin on the basis of its (i) gross geological evolution, (ii) fossil fauna and (iii) tectonic history. Mid-Palaeozoic regional kinematic patterns suggest that Carolina and its commonly held northern counterpart, the Avalon zone, travelled together on the same lithospheric plate, but their contrasting tectonic histories suggest that they formed along different margins of this plate. These interpretations lead to a new model for middle Palaeozoic interactions of the APGR with Laurentia.
Investigating the deep structure of terranes and terrane boundaries: insights from earthquake seismic data
Authors: Reading Anya M.
Published: April 2008

The crust and upper mantle structure beneath a single, three-component broad-band seismic station may be determined using energy from distant earthquakes. Features such as the depth of the seismic Moho, the abruptness of the change in seismic velocity across the Moho, the velocity profile through the crust and the seismic velocity of the upper mantle may be found using receiver function techniques. Waveforms are analysed which contain energy arising from the interaction of incoming signals with the Earth structure beneath the receiving station. Seismic characteristics of the deep crust are often continuous or slowly varying across a single terrane and, moreover, show sudden contrasts across terrane and other major tectonic boundaries. Such techniques are, therefore, appropriate tools in the exploration of deep structure and, hence, in the understanding of large-scale continental assembly. They complement geological and geochronological investigations of surface rocks by providing the third spatial dimension. In regions of no surface basement exposure, seismic and other geophysical methods provide the only means of mapping the lateral extent of a given terrane and/or tracing province boundaries. Receiver function methods are presented here in the context of terrane tectonics with illustrative examples from former Gondwanan provinces and locations on the Pacific margin.
Geochronology of Proterozoic basement inliers in the Colombian Andes: tectonic history of remnants of a fragmented Grenville belt
Authors: Cordani U. G. , Cardona A. , Jimenez D. M. , Liu D. , Nutman A. P.
Published: April 2008

Basement inliers of high-grade metamorphic rocks within the eastern Colombian Andes record a Grenvillian history. Among them, the Garzón Complex and the Dibulla, Bucaramanga and Jojoncito gneisses were studied using different geochronological methods to produce better correlations in the context of the reconstruction of the Grenville belt and of the supercontinent of Rodinia. The dynamic evolution of all of these units includes a final collisional event with exhumation of high-grade rocks. Such a tectonic history bears strong similarities with the Grenville Province in Canada and seems to confirm that these domains took part in the aggregation of Rodinia. Mesoproterozoic U-Pb zircon ages indicate heritage from magmatic protoliths, and the Sm-Nd model ages, as well as the ε
Nd
values, suggest derivation from an evolved continental domain, such as the Amazonian craton, with some mixing with juvenile Neoproterozoic material. When these continental fragments are correlated with similar terrains in Mexico and the Central Andes, a large crustal fragment is implied; very probably it made up the southern portion of the Grenville belt within Rodinia, which was disrupted when Laurentia separated from Gondwana forming the Iapetus Ocean, leaving behind cratonic fragments that were later accreted to the South American Platform.
Economic natural resource deposits at terrestrial impact structures
Authors: Grieve Richard A. F.
Published: April 2008

Economic deposits associated with terrestrial impact structures range from world-class to relatively localized occurrences. The more significant deposits are introduced under the classification: progenetic, syngenetic or epigenetic, with respect to the impact event. However, there is increasing evidence that post-impact hydrothermal systems at large impact structures have remobilized some progenetic deposits, such as some of the Witwatersrand gold deposits at the Vredefort impact structure. Impact-related hydrothermal activity may also have had a significant role in the formation of ores at such syngenetic ‘magmatic’ deposits as the Cu-Ni-platinum-group elements ores associated with the Sudbury impact structure. Although Vredefort and Sudbury contain world-class mineral deposits, in economic terms hydrocarbon production dominates natural resource deposits found at impact structures. The total value of impact-related resources in North America is estimated at US$18 billion per year. Many impact structures remain to be discovered and, as targets for resource exploration, their relatively invariant, but scale-dependent properties, may provide an aid to exploration strategies.
Metallogenic fingerprints of Archaean cratons
Authors: de Wit Maarten , Thiart Christien
Published: April 2008

Archaean cratons are fragments of old continents that are more richly endowed with mineral deposits than younger terrains. The mineral deposits of different cratons are also diversely enriched with useful (to humankind) chemical elements. Cratons are therefore mineral-diversity hotspots that represent regional geochemical heterogeneities in the early Earth, evidence for which remains encoded on each craton as unique metallogenic ‘fingerprints’. Some of the younger cratons (<3.0 Ga, e.g. Superior Province, Yilgarn and Zimbabwe) have strong Au, Cu, Pb and Zn imprints. Older (>3.0 Ga) cratons, however, are remarkably enriched in siderophile elements such as Ni, Cr, PGE, in both their crustal and mantle sections (e.g. Pilbara and Kaapvaal Cratons). Still other Archaean cratons are relatively enriched in Sn, W, U and Th (e.g. Amazonian, Leo-Man, Ntem and South China Cratons). How most of these fragments of old continents inherited their rich and diverse metallogenic characteristics is unresolved. Their dominant metallogenic inventories were formed near the time of their separation from the mantle; thereafter the inherited metals were frequently remobilized and redistributed during subsequent tectono-metamorphic, magmatic and erosion-deposition processes (e.g. tin in South America; platinum and gold in Southern Africa). Because different cratons are likely to represent only small remnants of once much larger and probably varied Archaean continents, part of the total metal inventories of Archaean continents must have been recycled back into the mantle. Using six selected element groups from our extensive in-house GIS database of Gondwana mineral deposits, we derive the metallogenic fingerprints of 11 Archaean cratons of the southern hemisphere, and compare these against metallogenic fingerprints of the same elements in younger crust of three continents (Africa, Australia and South America). We confirm that the mineral deposit density and diversity of Earth’s continental lithosphere has decreased with time. We conclude that metallogenic elements were transferred more efficiently from the mantle to the continental lithosphere in the Archaean and/or that subsequently (<2.5 Ga) recycling of these elements (mineral deposits) back into the mantle became more effective.
Pre-mineralization thermal evolution of the Palaeoproterozoic gold-rich Ashanti belt, Ghana
Authors: Harcouët V. , Guillou-Frottier L. , Bonneville A. , Feybesse J. L.
Published: April 2008

The region of the gold-rich Ashanti belt in southern Ghana was chosen as the subject for a detailed regional thermal modelling study. Geological studies, in addition to laboratory measurements of thermal properties and heat-production rates, allow us to constrain a finite-element thermal modelling. Scenarios intergrating variations of the structure of the crust and various chronological settings were examined. We calculated the thermal regime before and after the thrust tectonism that affected the region during the Eburnean orogeny (2130–2095 Ma), just before ore deposit formation. This gives a new insight into the regional thermal state of the crust before the mineralizing events. To satisfy the thermobarometric observations, the most probable mantle heat flow must be 60 mW m
−2
, which is at least three times greater than the present-day value. At shallow depths, our results also indicate anomalies of lateral heat flow reaching 25 mW m
−2
, focused on the margins of each lithological unit, including the Ashanti belt. These anomalies are related to the distortion of the isotherms in the first few kilometres that can be explained mostly by lateral contrasts in thermal conductivity. Such anomalies could be of importance for the mineralizing events, as they would favour fluid circulation locally.
Geodynamic processes that control the global distribution of giant gold deposits
Authors: Leahy K. , Barnicoat A. C. , Foster R. P. , Lawrence S. R. , Napier R. W.
Published: April 2008

This paper address the question of why giant gold deposits are so unevenly spread over the continents, what processes control their distribution, and how more might be found? Using the source-migration-trap paradigm, it is proposed that the regional distribution of gold deposits is controlled by fluid access to gold sources on a regional scale, and by large-scale migration mechanisms. Local distribution is controlled by migration and trap processes, not discussed in this paper. Our current levels of understanding of gold suggest a strong geodynamic control in the generation of enriched source rocks and the fluids that may carry gold, particularly the influence of subduction and accretion during orogeny. A new six-fold geodynamic classification system that emphasizes subduction and accretion processes has been used here qualitatively to assess the potential for gold-bearing source areas. The resulting classification is compared to the distribution of 181 known giant gold deposits (those with more than 100 t contained gold). The results confirm the proposition that the distribution of giant gold deposits is ultimately a function of the amount of oceanic crust consumed during the orogenic episode that built that part of the crust. Of the six geodynamic classes described, large ocean closure orogens were found to contain the most gold, with nearly half of the world’s gold held in known giant deposits. Implications for understanding ore genesis, exploration for other giant deposits, and for other empirical explanations of the distribution of gold are discussed further.
Properties of fault damage zones in siliclastic rocks: a modelling approach
Authors: Odling N. E. , Harris S. D. , Vaszi A. Z. , Knipe R. J.
Published: April 2008

Major faults are surrounded by damage zones of minor faults that, in siliclastic rocks, can form barriers to flow in their own right. Reservoir flow simulation — now a routine part of reservoir management — requires equivalent hydraulic parameters on the scale of the whole fault, while reservoir geological models, from which flow simulator grids are generated, require information on the 3D characteristics of fault populations. Here, a stochastic model of fault damage zone architecture is generated and used to explore the impact of damage zone architecture on extrapolation from 1D (fault throw) and 2D (fault length) to 3D fault population characteristics. Sampling of the simulated damage zone models shows that clustering of faults causes deviations from simple laws relating particularly 1D samples to 3D population power-law exponents, with differences between expected and observed values of up to 0.25. The stochastic model is used to generate input for a 2D discrete fracture flow model for the case where minor (isotropic) fault permeability is four orders of magnitude lower than that of the host rock and, thus, forms partial barriers to flow. The flow model is used to explore the impact of fault damage zones on bulk fault permeability. The damage zone is shown to be around 50% efficient, i.e. a simple estimate of bulk permeability can be made using the harmonic average of fault rock and host-rock permeability weighted by thickness in 1D traverses (e.g. core, well logs), where only half the observed thickness of fault rock in the fault damage zone is assumed. Considering the contributions of the damage zone and the major slip zone, the fault damage zone is likely to make a significant contribution to the bulk permeability of the fault as a whole when the permeability of minor faults in the damage zone is similar to, or at most, one order of magnitude greater than that of the slip zone fault rocks.
Anomalous diffusion in simulations of pumping tests on fractal lattices
Authors: Sellers Shaun , Barker John A.
Published: April 2008

The recent interest in fractals in the geosciences literature has led to several proposed theoretical models for the hydraulic testing of fractured-rock systems that exhibit a fractal-like geometric structure. There is, however, no agreement on the correct form of the resulting model equations. In order to gain some insight into the range of possible behaviours to be expected from pumping tests on such systems, as well as the type of theoretical models needed, extensive simulations of pressure diffusion for transient groundwater flow, modelled by random walks on both deterministic and random fractal lattices were performed. For simplicity, the focus was on measurements of the random-walk dimension for generalized Sierpinski carpets, a proposed model for porous and fractured media. In addition to the expected anomalous slow down in diffusion in fractals as measured by the random-walk dimension, the simulations show further novel and unexpected anomalous behaviour due to the presence of internal boundaries at all scales. None of the proposed theoretical models for pumping tests on fractals appears consistent with all of the observed anomalous behaviours. The simulations suggest that interpretation of experimental pumping tests in terms of well-defined non-integer dimensions can be difficult, even when finite-size effects are negligible.
Models of tracer breakthrough and permeability in simple fractured porous media
Authors: Johnston P. B. , Atkinson T. C. , Odling N. E. , Barker J. A.
Published: April 2008

Tailing and bimodal behaviour of tracer breakthrough curves from tracer tests conducted in fractured porous media are commonly presented as ‘deviations’ from the Fickian model for homogeneous porous media. Tailing is mainly attributed to: (1) tracer storage brought about by diffusion between mobile and static regions of fluid; (2) a concentration of flow towards the wider (aperture) and, thus, more permeable fracture zones; and (3) the high variance in fracture conductivity and consequent mixing of tracer. Bi- (or multi-) modality has been attributed to solute following a few highly permeable flow paths. Systematic numerical simulations of flow and transport in geometrically simple fractured porous media were conducted using a 2D finite difference flow code and a particle tracking transport model. As a simplification only advective dispersion was considered. The modelling study produced a large variety of tracer breakthrough curves, including two patterns commonly seen in field data — the backward tailed uni-modal type and the Gaussian type. The study demonstrates that different types of breakthrough might be characteristic of particular sets of conceptual models for heterogeneities and, as such, may provide a useful pointer in the application and interpretation of tracer tests.
Mineral resources and their economic significance in national development: Bangladesh perspective
Authors: Akhtar Afia
Published: April 2008

Modern urbanization, industrialization, transportation and communication systems are the achievements of worldwide sustainable mineral resource development and their proper utilization in various sectors. Sustainable mineral resources have played, and are still playing, a vital role in shaping the modern civilized industrial world. This means that the sustainable socio-economic infrastructure of any country is an indication of its richness in natural resources, its technological know how, its ability to explore and exploit mineral resources, and, finally, its wisdom in utilizing those resources properly in the development activities of the nation. In development activities, countries of the developing world are generally far behind compared with countries in the developed world. This is mainly due to a lack of adequate natural resources, properly educated human resources and good socio-economic conditions. Although Bangladesh is a small country, it has a number of mineral resources such as natural gas, oil, coal, hard rock, limestone, white clay, glass sand and mineral sand. At present, natural gas is the only mineral commodity significantly contributing to the national economy. More than 90% of the country’s energy needs are met by gas, total reserves of which are 21.35 trillion cubic feet (TCF) and 12.43 TCF, respectively. Huge reserves of hard rock (granodiorite, quartzdiorite, gneiss) and coal in northwest Bangladesh will help, in the near future, to meet the growing demand for construction materials and energy for the ever-growing population. Total coal reserves are 1753 million tons (MT), the market value of which is more than US$110 billion. Hard rock reserves are 115 million tons, valued at over US$3 billion. Fully fledged extraction of these resources would help to alleviate the country’s poverty through industrialization. It is expected that coal will soon be extracted on a commercial basis, of which 70 to 80% will be used in power generation. The mineral resources so far found in Bangladesh are meagre in comparison to its high population. To meet the growing demand of the population, more mineral resources need to be discovered and developed, otherwise sustainable development cannot be achieved. However, it is difficult for developing countries like Bangladesh to carry out the necessary activities for exploration and exploitation of hidden mineral resources without foreign assistance. This is a major drawback for Bangladesh. To progress towards an endurable sustainable society, a nation such as Bangladesh must give priority to the development of its existing mineral resources, which can play a major role in helping to reshape the country’s socio-economic infrastructure.
Obstacles in the sustainable development of artisanal and small-scale mines in Pakistan and remedial measures
Authors: Husain Viqar
Published: April 2008

Pakistan is a large country with diverse geology and geography. It possesses many industrial rocks and minerals, including precious stones, marble and granite. Some metallic mineral deposits, and large reserves of coal/lignite, oil and natural gas also occur. Pakistan’s mining industry is dominated by thousands of artisanal and small-scale mines, which lack capital, technical know how, modern equipment and trained manpower. Further, local mining practices cause much damage to mineral deposits and are very hazardous to the health of mine workers and the environment. The mining sector is backward due to lack of political will and pragmatic mining laws, and absence of technical and financial support by the government agencies to the small mining units. Moreover, the narrow base of the domestic mineral industry leads to poor demand in the local market and low mineral production. Additionally, the lack of infrastructure and the poor law and order situation adversely affect the mineral industry. Further, mineral-rich districts of the country are socio-economically backward due to hilly terrain or arid climate and, hence, less suitable for agriculture. Sustainable development of artisanal and small-scale mines is possible if the necessary legal, technological, financial, commercial, social and environmental support is provided on a long-term basis.
Mining and environmental problems in the Ib valley coalfield of Orissa, India
Authors: Mishra P. Paramita
Published: April 2008

The exploitation of mineral resources through surface and underground mining has in the past caused a wide range of environmental problems such as health degradation, air, water and noise pollution, decline in agricultural production, deforestation, displacement and other socio-economic impacts. However, over the past number of years, stakeholders in the industry have been striving to avoid and mitigate the potential detrimental effects of mining on fragile ecosystems and local communities. Governments are increasingly formulating and adopting policies to ensure the sustainable development of their country’s mining industry and mining companies are striving to be better environmental citizens. Environmental groups have become increasingly involved in mining disputes. However, a lot has to be achieved to ensure mining in carried out in a sustainable way. This paper concentrates on the environmental effects of coal mining in the Ib valley coalfield of Orissa, India. Background to the increasing awareness of the environmental issues associated with mining is provided in the first section of this paper. The second section discusses the general problems associated with mining, with particular reference to the Ib valley coalfield. In addition, measures undertaken by the companies operating the Ib valley coalfield to deal with environmental problems are presented.
System dynamics modelling: a more effective tool for assessing the impact of sustainable development policies on the mining industry
Authors: O’Regan B. , Moles R.
Published: April 2008

The high mobility of mining investment is frequently cited in the literature. Consequently, the concept of relative attractiveness is particularly important. This paper describes a detailed computer simulation ‘feedback’ model. The model provides a means of examining the effects of varied environmental, fiscal and corporate policies on the flow of investment funds and mineral resources between a number of simulated mining firms and competing countries. Through a quantitative analysis of existing data, the model exposes, within the context of sustainable development, the underlying assumptions used as a basis for corporate decisions. Through the compression of time, the model provides a means of taking these assumptions to their logical conclusions. Exposing assumptions in this way leaves less room for misinterpretation and provides a solid basis for enhancing the understanding of system structure. It is by better understanding system structure that more effective sustainable development policies may be designed and implemented. An outline of the system dynamics method is also presented.
Flow events on a hyper-arid alluvial fan: Quebrada Tambores, Salar de Atacama, northern Chile
Authors: Mather Anne E. , Hartley Adrian
Published: April 2008

The Tambores alluvial fan is located within the hyper-arid Atacama Desert of northern Chile. We examine evidence of the range of flow processes operative in this environment from a combination of Pleistocene-Holocene fan deposits and a recent (2001) flood event (16 m
3
s
−1
) in the fan feeder channel and upper alluvial-fan area. The field evidence suggests that peak flows recorded in the older deposits generated extensive sheetflood events dominated by antidune deposition in the upper fan area. These extreme, supercritical flows were generated by floods with sustained high sediment and water discharges and high stream power. Easily erodable alluvial source materials ensured high sediment discharge could be maintained within flood events. High stream power was ensured as a function of the tectonically exacerbated gradients within the source area. The 2001 event indicates the rapid rheological changes that can occur within an individual flood event, ranging from hyperconcentrated streamflow to mudflow. The flow deposits vary little in maximum clast size either between the varying flood events in the upper fan area, or down the fan gradient. This is due to a limited calibre of sediment being produced from the source area. The study highlights: (1) the range of flow rheologies that can be generated from a hyper-arid catchment both within and between flood events of varying magnitude and the associated difficulties in generating a reliable stratigraphy from the resultant deposits; (2) the high stream power and sediment discharge associated with major flood events and thus the nature of flood hazard in the catchment and on the fan; and (3) the limitations of sedimentological information such as maximum clast size as an indicator of peak flow characteristics in ancient deposits.
Fans with forests: contemporary hydrogeomorphic processes on fans with forests in west central British Columbia, Canada
Authors: Wilford D. J. , Sakals M. E. , Innes J. L. , Sidle R. C.
Published: April 2008

Alluvial and colluvial fans with forest cover are common in the valleys of west central British Columbia, Canada. Given the low population density of the region, most of these fans are uninhabited and the primary land use is forestry. The fans are desirable for timber harvesting due to the combination of the relatively easy access to their valley-bottom locations and their high-quality timber. However, they are also sites influenced by debris flows, debris floods and floods, and the interaction between conventional forest practices and these natural hydrogeomorphic processes has led to substantial financial costs and disturbance to forests and stream channels. Basic watershed morphometrics can be used to predict the dominant hydrogeomorphic process influencing forested fans. The hydrogeomorphically active zones of forested fans have characteristic site and stand features, and are referred to as the hydrogeomorphic riparian zone. Features within these zones can be used to determine the frequency and disturbance extent of hydrogeomorphic events. Appropriate management strategies can be developed to limit the effect of forestry activities on natural hydrogeomorphic processes.
The fluvial megafan of Abarkoh Basin (Central Iran): an example of flash-flood sedimentation in arid lands
Authors: Arzani Nasser
Published: April 2008

The Abarkoh Basin is situated in central part of the NW-SE-trending Gavkhoni-Sirjan depression of Central Iran. The studied fluvial megafan represents a Quaternary fan, which is located in the western part of this intermontane, extensional basin. This fan covers an area of 940 km
2
and with a gentle slope (about 0.5°) over a 45 km-length terminates in a playa lake in the centre of the Abarkoh Basin. Its catchment is the Abadeh Basin (> 2000 km
2
), which is a NW-SE-trending intermontane basin and mainly floored with the Quaternary alluvial-fan sediments. The studied megafan was built by stream-dominated processes, as revealed by the presence of thick-bedded, clast-supported gravels-sandy gravels (gravelly-sandy conglomerates) in the proximal-fan areas that grade into thick marls with sinuous, lenticular channel-filled, grain-supported, imbricated, pebbly conglomerates in the proximal-medial fan regions. Thick calcareous marls and lenticular, single channel-fill sandstone-conglomerate deposits characterize the distal part of the fan and pass laterally into sediments of the playa lake fringe. The aim of this paper is to present an example of a fluvial megafan in an arid-semi-arid setting, to highlight the flash-flood, sheetflood-channelized sedimentation in megafans, and to stress their importance in water resources in arid lands. Fluvial fans are frequently identified in the rock record. The fluvial megafan of the Abarkoh Basin represents one of only a few described, large-scale, stream-dominated, Quaternary megafans in arid-semi-arid settings.
Climate and tectonically controlled river style changes on the Sajó-Hernád alluvial fan (Hungary)
Authors: Gábris Gyula , Nagy Balázs
Published: April 2008

Based on geomorphological field investigations, sediment analysis, radiocarbon and palynological data, changes in fluvial style have been recognized on one of the most important low-angle fluvial-dominant alluvial fans on the margin of the Great Hungarian Plain (Hungary). Late Pleistocene and Holocene climatic and tectonic controls are reflected partly by meandering and anastomosed channel pattern changes, and partly by erosional step features on the cone that mark erosional and accumulational phases. This work has led to the surface mapping of a ‘horizontal stratigraphy’ as part of a larger research project in the Tisza region.
Upper Cretaceous-Palaeocene basin-margin alluvial fans documenting interaction between tectonic and environmental processes (Provence, SE France)
Authors: Leleu S. , Ghienne J.-F. , Manatschal G.
Published: April 2008

Upper Cretaceous-Palaeocene alluvial-fan conglomerates exposed along the northern margin of the Arc Basin (Provence, SE France) preserve a continuum between undeformed basinal deposits and syntectonic alluvial-fan deposits. Based on the distribution of facies associations and growth structures in the alluvial-fan deposits, and using marker levels and erosional surfaces, the tectono-sedimentary evolution of the basin margin is discussed. On a long timescale, the stratigraphic pattern in the alluvial-fan deposits mainly records the tectonic activity in the catchment, and subordinate out-of-syncline thrusts in the basin margin. On an intermediate timescale, evolution in the drainage area controls the spatial evolution of the alluvial fans and some minor changes in depositional facies. High-frequency cycles record aggradation-stabilization sequences, resulting in vertically superimposed alluvial-fan bodies more probably tectonically controlled, whereas alternation between conglomerates-siltstones at the scale of interbedding most probably reflects climatic cycles.
Lower Cretaceous (Berriasian-Aptian) biostratigraphy of the Neuquén Basin
Authors: Aguirre-Urreta M. Beatriz , Rawson Peter F. , Concheyro G. Andrea , Bown Paul R. , Ottone Eduardo G.
Published: April 2008

The Berriasian-Aptian succession in the Neuquén Basin is mainly marine in the lower part and non-marine in the upper portion. A detailed ammonite zonation is presented for the Berriasian-?Early Barremian interval. While some ammonite taxa are endemic, others are widely distributed and there are several levels where correlation can be suggested with the ‘standard’ stages and zones of the Tethyan Mediterranean area. Several nannofossil bioevents are recognized, and these provide evidence for correlation with Tethyan areas. Correlations suggested by both groups are reasonably consistent. Berriasian-Aptian palynomorphs include both terrestrial and marine forms. Several terrestrial assemblages can be recognized, but the marine forms are mainly long-ranging taxa, especially in the Agrio Formation.
Sedimentology of the tide-dominated Jurassic Lajas Formation, Neuquén Basin, Argentina
Authors: McIlroy Duncan , Flint Stephen , Howell John A. , Timms Nick
Published: April 2008

Tidal depositional systems are often interpreted as lowstand/transgressive estuarine deposits within sequences that are either wave or river dominated during highstand times. The Middle Jurassic Lajas Formation of the Neuquén Basin, Argentina, comprises 600 m of well-exposed tide-dominated facies deposited within four unconformitybounded sequences, spanning approximately 4.5 Ma. Facies associations include tidedominated deltas, sandy-heterolithic tidal channel fills and extensive progradational tidal-flat successions, which are locally cut by heterolithic tidal channel fills. Despite the narrow bathymetric depositional range and the complex facies variability, flooding surfaces can be defined and mapped along a 48 km-long outcrop belt. These flooding surfaces allow definition of three distinct types of parasequence that exhibit coarsening-upwards, finingupwards and coarsening- to fining-upwards motifs. Sequence boundaries are marked by widespread, but shallow, incision, and the juxtaposition of stacked fluvial/tidal channel fills on a variety of subtidal and intertidal facies. Unconventional grain-size changes at sequence boundaries can occur where basinward facies shifts are marked by juxtaposition of heterolithic-argillaceous intertidal/supratidal mudflat deposits on subtidal sandflat facies. The maintenance of macrotidal conditions through complete base-level cycles is interpreted as being due to the structural topography inherited from rifting, causing the whole sub-basin to behave as a structurally controlled embayment.
The transgression of an erg — sedimentation and reworking/soft-sediment deformation of aeolian facies: the Cretaceous Troncoso Member, Neuquén Basin, Argentina
Authors: Strömbäck Anna , Howell John A. , Veiga Gonzalo D.
Published: April 2008

The Cretaceous Troncoso Inferior Member of the Huitrín Formation comprises fluvial and aeolian facies that form a drying-upwards succession within the Neuquén Basin. The basal fluvial sandstones were deposited as braided river deposits and lie unconformably on top of either the deep-marine Agrio Formation or, locally, the shallow-marine Chorreado Member (Huitrín Formation.). In places, the fluvial sandstones are interbedded with remnants of aeolian deposits recording an arid environment and ephemeral flows. In the study area the upper section is predominantly aeolian and was controlled by northerly winds with both linear and transverse dune types being deposited. The depositional system was rapidly flooded and dune topography (relief ranging between 2 and 35 m) was preserved on its top surface. In addition to dune topography, the Troncoso dunes also show evidence of reworking and
in situ
soft-sediment deformation related to the flooding. The principal aim of this paper is to document the soft-sediment deformation and preservation of topography associated with the flooding of the dune field.

Within the soft sediment deformed and reworked sediments at the top of the Troncoso Inferior Member spatial and temporal relationships indicate that they formed in a specific sequence. Initially, water-escape processes created convolutedly folded and dish structures that were concentrated in areas of slightly higher preserved dune topography. Secondly, the convolutedly folded and dish facies were eroded and reworked by wave undercutting and migrating three-dimensional dunes in a shallow-marine environment. This subaqueous reworking resulted in an interbedded massive and cross-stratified unit. With further deepening of the water, the topography became stabilized and the uppermost part of the interval (0.1–0.3 m) was reworked by waves across most of the basin. In the topographic lows between dunes, liquefaction-induced sediment gravity flows deposited massive-flatlaminated facies.

The reworked and soft-sediment deformed aeolian dune topography is overlain by the evaporites of the Troncoso Superior Member. The distribution of flood-related facies and the amount of preserved dune topography (2–35 m) indicates that the transgression must have been rapid but of low energy.