Geological

Distribution by Scientific Domains
Distribution within Earth and Environmental Science

Terms modified by Geological

  • geological age
  • geological background
  • geological barrier
  • geological change
  • geological characteristic
  • geological constraint
  • geological data
  • geological environment
  • geological event
  • geological evidence
  • geological evolution
  • geological feature
  • geological history
  • geological implication
  • geological information
  • geological investigation
  • geological mapping
  • geological material
  • geological model
  • geological models
  • geological process
  • geological record
  • geological sample
  • geological sciences
  • geological setting
  • geological significance
  • geological structure
  • geological studies
  • geological survey
  • geological time
  • geological time scale
  • geological timescale
  • geological unit

  • Selected Abstracts


    Geological controls on the formation of alluvial meanders and floodplain wetlands: the example of the Klip River, eastern Free State, South Africa

    EARTH SURFACE PROCESSES AND LANDFORMS, Issue 8 2002
    S. Tooth
    Abstract Floodplain wetlands are common features of rivers in southern Africa, but they have been little studied from a geological or geomorphological perspective. Study of the upper Klip River, eastern Free State, South Africa, indicates strong geological controls on the formation of alluvial meanders and associated floodplain wetlands. Along this river, pronounced and abrupt changes in valley width are strongly linked to lithological variations. Where weakly cemented sandstone crops out, the Klip has laterally eroded bedrock and carved valleys up to 1500 m wide. In these valleys, the river meanders (sinuosity up to ,1·75) on moderate gradients (<0·001) within extensive floodplains marked by numerous oxbow lakes, backswamps and abandoned channels, many of which host substantial wetlands. In contrast, where highly resistant dolerite crops out, lateral erosion of bedrock is restricted, with the Klip tending instead to erode vertically along joints or fractures. Here, valleys are narrower (<200 m), channel-bed gradients are steeper (>0·003), the river follows a much straighter course (sinuosity ,1·10,1·34), and floodplains are restricted in width. Long-term landscape development in the Klip and numerous similar catchments depends on the interaction between fluvial processes in the sandstone and dolerite valleys. In the sandstone valleys, vertical erosion rates are controlled by erosion rates of the more resistant dolerites downstream. Hence, in the short- to medium-term (decades to tens of thousands of years), lateral erosion dominates over vertical erosion, with the river concomitantly planing sandstone in the channel floor and reworking floodplain sediments. The thickness of alluvial fill in the sandstone valleys is limited (<4 m), but the resultant meanders are naturally dynamic, with processes such as point bar deposition, cutoff formation and channel avulsion resulting in an assemblage of fluvial landforms. In the longer term (greater than tens of thousands of years), however, vertical erosion will occur in the sandstone valleys as the downstream dolerites are lowered by erosion, resulting in channel incision, floodplain abandonment, and desiccation of the wetlands. Identification of the geological controls on meander and wetland formation provides information vital for the design of effective management guidelines for these ecologically rich habitats, and also contributes to a better understanding of rivers that are intermediate between fully alluvial and fully bedrock. Copyright © 2002 John Wiley & Sons, Ltd. [source]


    Multidisciplinary investigations at Stalag Luft III allied prisoner-of-war camp: The site of the 1944 "great escape," Zagan, Western Poland

    GEOARCHAEOLOGY: AN INTERNATIONAL JOURNAL, Issue 7 2007
    J.K. Pringle
    Stalag Luft III, situated in Zagan, Poland (formerly eastern Germany), was the site of a World War II Allied aviator prisoner of war (POW) camp famous for repeat escape attempts,notably the mass escape of 76 POWs in March 1944, shown in the 1963 film "The Great Escape." The site has had little attention to date because it was within restricted military training grounds until 1992. This paper reports on attempts to locate the undiscovered "Dick" escape tunnel (the "Tom" and "Harry" tunnels from the same escape attempt were discovered and destroyed by camp authorities). Geological and geophysical surveys located hut 122, which contained the "Dick" entrance shaft. Subsequent archaeological investigations included surface artifact collection and inspection of the rubble-filled, tunnel entrance shaft. Excavations to a depth of 10 m through yellow glacio-fluvial sand resulted in the discovery of the refilled "Dick" tunnel with intact bed-board shoring and ventilation system. Our investigation provides valuable insights into POW escape efforts. © 2007 Wiley Periodicals, Inc. [source]


    Recent Developments in Trace Element Analysis by ICP-AES and ICP-MS with Particular Reference to Geological and Environmental Samples

    GEOSTANDARDS & GEOANALYTICAL RESEARCH, Issue 1 2005
    Kathryn L. Linge
    This review describes recent developments in trace element analysis using inductively coupled plasma-atomic emission spectrometry (ICP-AES) and inductively coupled plasma-mass spectrometry (ICP-MS). It aims to focus on the application of ICP techniques to geological and environmental samples. Therefore, fundamental studies in ICP-MS and ICP-AES instrumentation have largely been ignored. Whereas the majority of literature reviewed related to ICP-MS, indicating that ICP-MS is now the preferred technique for all geological analysis, there is still a steady development of ICP-AES to environmental applications. It is clear that true flexibility in elemental analysis can only be achieved by combining the advantages of both ICP-AES and ICP-MS. Two particular groups of elements (long-lived radionuclide and the platinum-group elements) stood out as warranting dedicated sections describing analytical developments these areas. [source]


    Geological and Geochemical Characteristics of the Hydrothermal Clay Alteration in South Korea

    RESOURCE GEOLOGY, Issue 4 2000
    Sang-Mo KOH
    Abstract: Hydrothermally altered areas forming pyrophyllite-kaolin-sericite-alunite deposits are distributed in Chonnam and Kyongsang areas, Cretaceous volcanic field of the Yuchon Group. The Chonnam alteration area is located within depression zone which is composed of volcanic and granitic rocks of late Cretaceous age. The clay deposits of this area show the genetic relationship with silicic lava domes. The Kyongsang alteration area is mainly distributed within Kyongsang Basin comprising volcanic, sedimentary and granitic rocks of Cretaceous and Tertiary age. Most of the clay deposits of this area are closely related to cauldrons. Paleozoic clay deposit occurs in the contact zone between Precambrian Hongjesa granite gneiss and Paleozoic Jangsan quartzite of Choson Supergroup. Cretaceous igneous rocks of the both alteration areas belong to high K calc-alkaline series formed in the volcanic arc of continental margin by subduction-related magmatism. Chonnam igneous rocks show more enrichment of crustal components such as K, La, Ce, Sm, Nd and Ba, higher (La/Yb)cn ratio, and higher initial 87Sr/86Sr ratio (0. 708 to 0. 712) than those of Kyongsang igneous rocks. This might be due to the difference of degree of crustal contamination during Cretaceous magmatism. The most characteristic alteration minerals of Chonnam clay deposits are alunite, kaolin, quartz, pyrophyllite and diaspore which were formed by acidic solution. Those of Kyongsang clay deposits are sericite, quartz and pyrophyllite which were formed by weak acid and neutral solution. The formation ages of the clay deposits of two alteration areas range from 70. 1 to 81. 4 Ma and 39. 7 to 79. 4 Ma, respectively. The Daehyun clay deposit in Ponghwa area of Kyongsang province shows the alteration age range from 290 to 336 Ma. This result shows the different alteration episode from the hydrothermal alteration of Cretaceous to early Tertiary in the Kyongsang and Chonnam alteration areas. These data indicate, at least, three hydrothermal activities of Tertiary (middle to late Eocene), late Cretaceous (Santonian to Maastrichtian) and Paleozoic Carboniferous Periods in South Korea. [source]


    Identification of Five Stages of Dike Swarms in the Shanxi-Hebei-Inner Mongolia Border Area and Its Tectonic Implications

    ACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 1 2004
    SHAO Ji'an
    Abstract Dike swarms are generally ascribed to intrusion of mantle-source magma result from extension. Basic dike swarms around the Shanxi-Hebei-Inner Mogolia borders in the northern peripheral area of the North China Craton can be divided into five age groups according to isotopic dating: 1800,1700 Ma, 800,700 Ma, 230 Ma, 140,120 Ma, and 50,40 Ma. Geological, petrological and isotope geochemical features of the five groups is investigated in order to explore the variation of the mantle material composition in the concerned area with time. And the various extensional activities reflected by the five groups of dike swarms are compared with some important tectonic events within the North China Craton as well as around the world during the same period. [source]


    Quantitative reconstruction of Late Cenozoic landscapes: a case study in the Sierra de Atapuerca (Burgos, Spain)

    EARTH SURFACE PROCESSES AND LANDFORMS, Issue 2 2008
    Alfonso Benito-Calvo
    Abstract We have developed a method to reconstruct palaeorelief by means of detailed geomorphological and geological studies, geostatistical tools, GIS and a DEM. This method has been applied to the Sierra de Atapuerca (NE Duero Basin, Burgos, Spain), allowing us to model a three-dimensional reconstruction of the relief evolution from the Middle Miocene to the present. The modelling procedure is based on geostatistical recovery of the palaeosurfaces characteristic of each geomorphological evolution stage, using polynomial regressions, trend surfaces and kriging. The modelling of morphology trends has been useful in establishing new geological and geomorphological relationships in the geodynamic evolution of this basin, such as uplift quantification, correlation of erosion surfaces and sedimentary units, and the evolution of fluvial base levels. The palaeosurface reconstruction together with an analysis of the slope retreat have allowed us to reconstruct the palaeoreliefs that define the Late Cenozoic landscape evolution of this area, where the Lower and Middle Pleistocene archaeopalaeontological sites of the Sierra de Atapuerca are located. Copyright © 2007 John Wiley & Sons, Ltd. [source]


    The use of GIS-based digital morphometric techniques in the study of cockpit karst

    EARTH SURFACE PROCESSES AND LANDFORMS, Issue 2 2007
    P. Lyew-Ayee
    Abstract Cockpit karst landscapes are among the most distinctive landscapes in the world, and have been the focus of long-standing scientific interest. Early researchers used largely descriptive techniques to categorize the terrain, and subsequent work has not attempted to critically re-evaluate descriptions of landscapes using more sophisticated methods. The distinctive surface topography of cockpit karst areas can be characterized in order to compare them with other karst as well as non-karst areas, and to determine geological and/or climatic conditions that are responsible for the observed terrain. Process models of the rate of karst denudation or evolution can only be accurate if the contemporary morphology of the landscape is quantitatively and unambiguously defined. A detailed analysis of cockpit karst terrain is carried out using the latest GIS-based digital morphometric techniques in order to assess the nature of such terrain and provide further information for subsequent modelling, as well as other non-geomorphological applications, such as environmental management and conservation issues. The paper presents the methodology used for the digital analysis of terrain and landforms in the distinctive Cockpit Country area of Jamaica and its environs. The results indicate that cockpit karst may be categorized based on its vertical, horizontal and shape characteristics, as well as by looking at the semivariogram, slope characteristics, and landscape relief scale, which combine measures of vertical and horizontal scales. Copyright © 2006 John Wiley & Sons, Ltd. [source]


    Controls on modern alluvial fan processes in the central Alps, northern Italy

    EARTH SURFACE PROCESSES AND LANDFORMS, Issue 3 2004
    Giovanni B. Crosta
    Abstract Alluvial fan development in Alpine areas is often affected by catastrophic sedimentary processes associated with extreme ,oods events, causing serious risks for people living on the fans. Hazard assessment in these areas depends on proper identi,cation of the dominant sedimentary processes on the fans. Data from a set of 209 alluvial fans from the central Alps of Italy are presented in this paper and analysed with the help of various statistical techniques (linear regression, principal components analysis, cluster analysis, discriminant analysis and logistic regression). First, we used modern sedimentary facies and historical records (,ood events since 15th century), to distinguish between the two dominant sedimentary processes on alluvial fans: debris ,ows and stream,ows. Then, in order to analyse the main controls on past and present fan processes, 36 morphological, geological and land-use variables were analysed. As with observations for arid-environment fans, catchment morphology is the most in,uential factor in the study area, whereas geology and land use are minor controls. The role of climatic change and landsliding within the catchments also seems to be very important and is discussed. Statistical techniques also help in differentiating groups of alluvial fans by sets of controlling factors, including stage and type of evolution. Finally, by using discriminant analysis and logistic regression, we classi,ed alluvial fans according to the dominant sedimentary process, with a success rate ranging between 75 and 92 per cent. Copyright © 2004 John Wiley & Sons, Ltd. [source]


    Morphometric analysis and tectonic interpretation of digital terrain data: a case study

    EARTH SURFACE PROCESSES AND LANDFORMS, Issue 8 2003
    Gyozo Jordan
    Abstract Tectonic movement along faults is often re,ected by characteristic geomorphological features such as linear valleys, ridgelines and slope-breaks, steep slopes of uniform aspect, regional anisotropy and tilt of terrain. Analysis of digital elevation models, by means of numerical geomorphology, provides a means of recognizing fractures and characterizing the tectonics of an area in a quantitative way. The objective of this study is to investigate the use of numerical geomorphometric methods for tectonic geomorphology through a case study. The methodology is based on general geomorphometry. In this study, the basic geometric attributes (elevation, slope, aspect and curvatures) are complemented with the automatic extraction of ridge and valley lines and surface speci,c points. Evans' univariate and bivariate methodology of general geomorphometry is extended with texture (spatial) analysis methods, such as trend, autocorrelation, spectral, and network analysis. Terrain modelling is implemented with the integrated use of: (1) numerical differential geometry; (2) digital drainage network analysis; (3) digital image processing; and (4) statistical and geostatistical analysis. Application of digital drainage network analysis is emphasized. A simple shear model with principal displacement zone with an NE,SW orientation can account for most of the the morphotectonic features found in the basin by geological and digital tectonic geomorphology analyses. Copyright © 2003 John Wiley & Sons, Ltd. [source]


    Geological controls on the formation of alluvial meanders and floodplain wetlands: the example of the Klip River, eastern Free State, South Africa

    EARTH SURFACE PROCESSES AND LANDFORMS, Issue 8 2002
    S. Tooth
    Abstract Floodplain wetlands are common features of rivers in southern Africa, but they have been little studied from a geological or geomorphological perspective. Study of the upper Klip River, eastern Free State, South Africa, indicates strong geological controls on the formation of alluvial meanders and associated floodplain wetlands. Along this river, pronounced and abrupt changes in valley width are strongly linked to lithological variations. Where weakly cemented sandstone crops out, the Klip has laterally eroded bedrock and carved valleys up to 1500 m wide. In these valleys, the river meanders (sinuosity up to ,1·75) on moderate gradients (<0·001) within extensive floodplains marked by numerous oxbow lakes, backswamps and abandoned channels, many of which host substantial wetlands. In contrast, where highly resistant dolerite crops out, lateral erosion of bedrock is restricted, with the Klip tending instead to erode vertically along joints or fractures. Here, valleys are narrower (<200 m), channel-bed gradients are steeper (>0·003), the river follows a much straighter course (sinuosity ,1·10,1·34), and floodplains are restricted in width. Long-term landscape development in the Klip and numerous similar catchments depends on the interaction between fluvial processes in the sandstone and dolerite valleys. In the sandstone valleys, vertical erosion rates are controlled by erosion rates of the more resistant dolerites downstream. Hence, in the short- to medium-term (decades to tens of thousands of years), lateral erosion dominates over vertical erosion, with the river concomitantly planing sandstone in the channel floor and reworking floodplain sediments. The thickness of alluvial fill in the sandstone valleys is limited (<4 m), but the resultant meanders are naturally dynamic, with processes such as point bar deposition, cutoff formation and channel avulsion resulting in an assemblage of fluvial landforms. In the longer term (greater than tens of thousands of years), however, vertical erosion will occur in the sandstone valleys as the downstream dolerites are lowered by erosion, resulting in channel incision, floodplain abandonment, and desiccation of the wetlands. Identification of the geological controls on meander and wetland formation provides information vital for the design of effective management guidelines for these ecologically rich habitats, and also contributes to a better understanding of rivers that are intermediate between fully alluvial and fully bedrock. Copyright © 2002 John Wiley & Sons, Ltd. [source]


    Assessment of shallow landslide susceptibility by means of multivariate statistical techniques

    EARTH SURFACE PROCESSES AND LANDFORMS, Issue 12 2001
    Cristina Baeza
    Abstract Several multivariate statistical analyses have been performed to identify the most influential geological and geomorphological parameters on shallow landsliding and to quantify their relative contribution. A data set was first prepared including more than 30 attributes of 230 failed and unfailed slopes. The performance of principal component analysis, t-test and one-way test, allowed a preliminary selection of the most significant variables, which were used as input variables for the discriminant analysis. The function obtained has classified successfully 88·5 per cent of the overall slope population and 95·6 per cent of the failed slopes. Slope gradient, watershed area and land-use appeared as the most powerful discriminant factors. A landslide susceptibility map, based on the scores of the discriminant function, has been prepared for Ensija range in the Eastern Pyrenees. An index of relative landslide density shows that the results of the map are consistent. Copyright © 2001 John Wiley & Sons, Ltd. [source]


    The wealth of species: ecological communities, complex systems and the legacy of Frank Preston

    ECOLOGY LETTERS, Issue 3 2007
    Jeffrey C. Nekola
    Abstract General statistical patterns in community ecology have attracted considerable recent debate. Difficulties in discriminating among mathematical models and the ecological mechanisms underlying them are likely related to a phenomenon first described by Frank Preston. He noted that the frequency distribution of abundances among species was uncannily similar to the Boltzmann distribution of kinetic energies among gas molecules and the Pareto distribution of incomes among wage earners. We provide additional examples to show that four different ,distributions of wealth' (species abundance distributions, species,area and species,time relations, and distance decay of compositional similarity) are not unique to ecology, but have analogues in other physical, geological, economic and cultural systems. Because these appear to be general statistical patterns characteristic of many complex dynamical systems they are likely not generated by uniquely ecological mechanistic processes. [source]


    Distribution, zoogeography and biology of the Murchison River hardyhead (Craterocephalus cuneiceps Whitley, 1944), an atherinid endemic to the Indian Ocean (Pilbara) Drainage Division of Western Australia

    ECOLOGY OF FRESHWATER FISH, Issue 3 2005
    M. G. Allen
    Abstract , The Murchison River hardyhead (Craterocephalus cuneiceps) is endemic to the extremely arid Indian Ocean (Pilbara) Drainage Division of Western Australia, where it is found in the Greenough, Hutt, Murchison, Wooramel, Gascoyne and DeGrey rivers, but is absent from numerous rivers within its range. The most likely explanation for the disjunct contemporary distribution is that C. cuneiceps has simply never inhabited the rivers from which it is conspicuously absent (e.g. Ashburton and Fortescue). Biogeographical, geological and palaeoclimatic evidence is presented to support this hypothesis. In the Murchison River, breeding was extremely protracted with recruitment occurring throughout the year. The largest female and male specimens captured were 96 mm total length (TL; 7.73 g) and 86 mm TL (5.57 g), respectively. Sex ratio was 1.09 females:1 male. Batch fecundity ranged from 46 to 454 (mean 167.5 ± 25.7 SE). Estimates for the length at which 50 and 95% of females first spawned were 36.4 and 44.3 mm TL, respectively. Craterocephalus cuneiceps is essentially a detritivore, but also feeds on aquatic invertebrates. Rainfall in the Murchison River catchment is unpredictable and pH, salinity and temperature are variable. A specialised diet, small size and young age at maturity and protracted spawning period, coupled with serial spawning and high fecundity, allows the numerical dominance of this species in competitive, harsh, arid and unpredictable desert environments. Resumen 1. Craterocephalus cuneiceps es una especie endémica de las cuencas del Océano Indico (i.e., Pilbara) de Australia Occidental. Se encuentra en los ríos Greenough, Hutt, Murchison, Wooramel, Gascoyne y DeGrey pero está ausente en numerosos ríos dentro de su área de distribución. La explicación más probable para esta distribución separada en la actualidad es que C. cuneiceps no ha habitado nunca los ríos en los que está ausente tales como los ríos Ashburton y Fortescue. Presentamos evidencia bio-geográfica, geológica y paleo-climática para soportar esta hipótesis. 2. En el río Murchison, la reproducción es extremadamente prolongada con reclutamiento a lo largo de todo el año. Los mayores machos y hembras capturados alcanzaron 96 mm LT (7.73 g) y 86 mm LT (5.57 g), respectivamente. La proporción de sexos fue 1.09 hembras: 1 macho. La fecundidad varió entre 46 y 454 (media 167.5 ± 25.7 SE) y la longitudes a la que el 50 y el 95% de las hembras se reproducen por primera vez alcanzaron 36.4 y 44.3 mm LT, respectivamente. 3. C. cuneiceps es esencialmente detritívoro pero también se alimenta de invertebrados acuáticos. La lluvia sobre la cuenca del río Murchison es impredecible y el pH, la salinidad y la temperatura son variables. Una dieta especializada, pequeño tamaño, una edad joven en la madurez, y un período reproductivo prolongado, ademos de una freza seriada y alta fecundidad, permiten la dominancia numérica de la especie en ambientes competitivos, duros, áridos e impredecibles. [source]


    Determination of refractory organic matter in marine sediments by chemical oxidation, analytical pyrolysis and solid-state 13C nuclear magnetic resonance spectroscopy

    EUROPEAN JOURNAL OF SOIL SCIENCE, Issue 3 2008
    J. M. De La Rosa
    Summary Seeking to quantify the amount of refractory organic matter (ROM), which includes black carbon-like material (BC), in marine sediments, we have applied a two-step procedure that consists of a chemical oxidation with sodium chlorite of the demineralized sediments followed by integration of the aromatic C region in the remaining residues by solid-state 13C nuclear magnetic resonance (NMR) spectroscopy. The efficacy for lignin removal was tested by analytical pyrolysis in the presence of tetramethyl ammonium hydroxide (TMAH). Riverine, estuarine and offshore marine sediment samples were collected from the southwest Atlantic coast of Spain, a site of geological and environmental interest. Measured contents of BC-like material ranged between 3.0 and 45.7% of the total organic carbon. Greater relative BC contents were found in riverine sediments close to urban areas, which show an elevated input of anthropogenic organic material. The contents of BC-like material in offshore marine sediments (5.5,6.1%) were similar to those previously reported for these kinds of samples. However, NMR and pyrolysis-GC/MS of the isolated ROM reveals that abundant refractory aliphatic organic material remains in most of the marine samples after chlorite oxidation. We suggest that this pool of aliphatic carbon may play an important role as a stable carbon pool within the global C cycle. [source]


    Geomorphology, site distribution, and Paleolithic settlement dynamics of the Ma'aloula region, Damascus Province, Syria

    GEOARCHAEOLOGY: AN INTERNATIONAL JOURNAL, Issue 6 2007
    Andrey E. Dodonov
    This survey of the geology, geomorphology, and Paleolithic archaeology of a 300 km2 area in Damascus Province, Syria, focused around the villages of Ma'aloula and Jaba'deen. The study resulted in the definition of seven geomorphological zones that trend northeast,southwest, parallel to the prevailing geological features of the region. The zones span a broad range of elevations, from a dry lake bed in the Jeiroud Basin (ca. 800 m) to the peaks of the Anti-Lebanon Mountains (ca. 2350 m). The research focused on assessing the geological and paleoenvironmental history of the region as a backdrop for 500,000 years of Paleolithic settlement. Among the 618 archaeological sites documented thus far, all major archaeological periods from the Lower Paleolithic through the Epipaleolithic are represented. Most abundant are occurrences of the Levalloisian Middle Paleolithic, with 255 new sites documented. Nine Neolithic sites were also included in the survey. The distribution of sites varies during the Paleolithic and reflects the availability of resources, especially of flint and water, as well as the spatial patterns of erosion and deposition on the ancient land surfaces. © 2007 Wiley Periodicals, Inc. [source]


    Stratigraphic investigations at Los Buchillones, a coastal Taino site in north-central Cuba

    GEOARCHAEOLOGY: AN INTERNATIONAL JOURNAL, Issue 5 2006
    Matthew C. Peros
    The authors present stratigraphic data from Los Buchillones, a now submerged Taino village on the north coast of central Cuba that was occupied from some time prior to A.D. 1220 until 1640 or later. Los Buchillones is one of the best-preserved sites in the Caribbean, with material culture remains that include palm thatch and wooden structural elements from some of the more than 40 collapsed structures. The purpose of this study was to investigate the environment and site-formation processes of the Taino settlement. Sediment cores were sampled from the site and its vicinity to permit integration of the geological and archaeological stratigraphies. The cores were analyzed for color, texture, mollusk content, elemental geochemistry, and mineralogy. The results of the stratigraphic work are consistent with regional sealevel data that shows relative sea level has risen gradually during the late Holocene, but has remained relatively stable since the time the Taino first occupied Los Buchillones. Of the two structures partially cleared, at least one appears to have been built over the water, supported on pilings. Site selection is likely to have resulted from a consideration of environmental factors, such as access to marine, terrestrial, and lagoonal resources, and proximity to freshwater springs. © 2006 Wiley Periodicals, Inc. [source]


    The tectonic regime along the Andes: Present-day and Mesozoic regimes

    GEOLOGICAL JOURNAL, Issue 1 2010
    Victor A. Ramos
    Abstract The analyses of the main parameters controlling the present Chile-type and Marianas-type tectonic settings developed along the eastern Pacific region show four different tectonic regimes: (1) a nearly neutral regime in the Oregon subduction zone; (2) major extensional regimes as the Nicaragua subduction zone developed in continental crust; (3) a Marianas setting in the Sandwich subduction zone with ocean floored back-arc basin with a unique west-dipping subduction zone and (4) the classic and dominant Chile-type under compression. The magmatic, structural and sedimentary behaviours of these four settings are discussed to understand the past tectonic regimes in the Mesozoic Andes based on their present geological and tectonic characteristics. The evaluation of the different parameters that governed the past and present tectonic regimes indicates that absolute motion of the upper plate relative to the hotspot frame and the consequent trench roll-back velocity are the first order parameters that control the deformation. Locally, the influences of the trench fill, linked to the dominant climate in the forearc, and the age of the subducted oceanic crust, have secondary roles. Ridge collisions of seismic and seismic oceanic ridges as well as fracture zone collisions have also a local outcome, and may produce an increase in coupling that reinforces compressional deformation. Local strain variations in the past and present Andes are not related with changes in the relative convergence rate, which is less important than the absolute motion relative to the Pacific hotspot frame, or changes in the thermal state of the upper plate. Changes in the slab dip, mainly those linked to steepening subduction zones, produce significant variations in the thermal state, that are important to generate extreme deformation in the foreland. Copyright © 2009 John Wiley & Sons, Ltd. [source]


    Late-glacial remains of woolly mammoth (Mammuthus primigenius) from Shropshire, UK: stratigraphy, sedimentology and geochronology of the Condover site

    GEOLOGICAL JOURNAL, Issue 4 2009
    J. D. Scourse
    Abstract In 1986 remains of an adult woolly mammoth, Mammuthus primigenius (Blumenbach), were discovered at Norton Farm Pit, Condover, south of Shrewsbury, UK. Preliminary stratigraphical investigations indicated that this individual dated to the Devensian Late-glacial Interstadial, then the first evidence for survival of mammoth in Britain following the Last Glacial Maximum. Initial radiocarbon analysis confirmed this interpretation. Subsequent excavations in 1987/1988 recovered the remains of a further three juvenile mammoth individuals. All of these remains were found in the spoil heaps of overburden (ex situ) and their true stratigraphical context had to be reconstructed from the remnants surviving in the Pit. The 1987/1988 excavations enabled stratigraphical investigation of the site and submission of samples for radiocarbon (14C) dating, including the use of ultrafiltration pretreatment for bone samples, with the aims of reconstructing the geological and palaeoenvironmental evolution of the site and the sedimentary context of the unstratified mammoth remains. These results are presented here. This investigation indicates that the woolly mammoth remains at Condover derive from a dead-ice landscape dominated by eskers, kames and kettle-hole basins, and that the sedimentary sequence in which the mammoth remains were found forms the infilling of a kettle-hole basin. The sedimentary infilling and formation of the kettle-hole basin through ice block melt-induced subsidence were syngenetic. 14C determinations indicate that basin infill was initiated prior to Greenland Interstadial 1, and probably in Greenland Stadial 2 i.e. before 14.7,ka BP and that it continued until the early Holocene, around 8,ka BP. The sedimentological and 14C data indicate that the unstratified mammoth remains can be attributed to a dark grey clayey sandy silt (Unit C1), which accumulated during the earlier part of Greenland Interstadial 1 (14 to 14.5,ka BP) within an actively subsiding slow-flowing, beaded, fluvial network characterized by channels and pools/lakes, and with relatively shallow marginal slopes. The sedimentary architecture indicates survival of the buried ice block into Greenland Interstadial 1 and final melting only towards the end of the Interstadial at ca. 12.65,ka BP. Copyright © 2009 John Wiley & Sons, Ltd. [source]


    The Development of the Observational Method

    GEOMECHANICS AND TUNNELLING, Issue 5 2008
    Wulf Schubert o.Univ.-Prof.
    A continuous observation during construction always has been an important element of geotechnical engineering for minimizing risks. The reasons are the uncertainties in the geological and geotechnical models, as well as the limited capability to sufficiently accurately describe the complex ground behaviour. In the early days design of geotechnical structures thus was mainly based on experience. As usual, experience was used to develop mathematical solutions to the problem. To account for the inherent scatter of parameters and uncertainties in the models, the assumptions made during design had and have to be verified or falsified during construction by observations. For safe and economical construction, the design has to be adjusted during construction to the actual conditions. The term "observational method" was first formally introduced by Peck and Terzaghi. The original ideas behind the method have not always been understood or followed. After a brief historical review of the observational method the current status of the method is critically reviewed, and further developments discussed. Die Beobachtungsmethode einst und jetzt Die Schwierigkeit, den Baugrund ausreichend zu erkunden und dessen Interaktion mit dem Bauwerk zutreffend mathematisch zu modellieren, erfordert die laufende Beobachtung während des Baus, um die Baumaßnahmen an die tatsächlichen Verhältnisse anzupassen und das Risiko vermindern zu können. Mit vermehrter Erfahrung wurden auch Analysemodelle entwickelt. Zur Berücksichtigung der unvermeidlichen Streuung der Baugrundeigenschaften und der Unsicherheiten in den Modellen wurden und werden während des Baus Beobachtungen durchgeführt. Die Bezeichnung "Beobachtungsmethode" wurde formal von Peck und Terzaghi eingeführt. Die damals formulierten Grundsätze wurden nicht immer verstanden und befolgt. Im Beitrag wird nach einem kurzen historischen Rückblick über Entstehung und Entwicklung der Methode der derzeitige Stand kritisch beleuchtet, und weitere Entwicklungen werden diskutiert. [source]


    Shear wave velocity model of the Santiago de Chile basin derived from ambient noise measurements: a comparison of proxies for seismic site conditions and amplification

    GEOPHYSICAL JOURNAL INTERNATIONAL, Issue 1 2010
    Marco Pilz
    SUMMARY We determined a high-resolution 3-D S -wave velocity model for a 26 km × 12 km area in the northern part of the basin of Santiago de Chile. To reach this goal, we used microtremor recordings at 125 sites for deriving the horizontal-to-vertical (H/V) spectral ratios that we inverted to retrieve local S -wave velocity profiles. In the inversion procedure, we used additional geological and geophysical constraints and values of the thickness of the sedimentary cover already determined by gravimetric measurements, which were found to vary substantially over short distances in the investigated area. The resulting model was derived by interpolation with a kriging technique between the single S -wave velocity profiles and shows locally good agreement with the few existing velocity profile data, but allows the entire area, as well as deeper parts of the basin, to be represented in greater detail. The wealth of available data allowed us to check if any correlation between the S -wave velocity in the uppermost 30 m (v30S) and the slope of topography, a new technique recently proposed by Wald and Allen, exists on a local scale. We observed that while one lithology might provide a greater scatter in the velocity values for the investigated area, almost no correlation between topographic gradient and calculated v30S exists, whereas a better link is found between v30S and the local geology. Finally, we compared the v30S distribution with the MSK intensities for the 1985 Valparaiso event, pointing out that high intensities are found where the expected v30S values are low and over a thick sedimentary cover. Although this evidence cannot be generalized for all possible earthquakes, it indicates the influence of site effects modifying the ground motion when earthquakes occur well outside of the Santiago basin. [source]


    Tectonic deformation around the eastern Himalayan syntaxis: constraints from the Cretaceous palaeomagnetic data of the Shan-Thai Block

    GEOPHYSICAL JOURNAL INTERNATIONAL, Issue 2 2008
    Kenji Tanaka
    SUMMARY Lower to Middle Cretaceous red sandstones were sampled at four localities in the Lanpin-Simao fold belt of the Shan-Thai Block to describe its regional deformational features. Most of the samples revealed a characteristic remanent magnetization with unblocking temperatures around 680 °C. Primary natures of magnetization are ascertained through positive fold test. A tilt-corrected formation-mean direction for the Jingdong (24.5°N, 100.8°E) locality, which is located at a distance of 25 km from the Ailaoshan,Red River Fault, revealed northerly declination with steep inclination (Dec./Inc. = 8.3°/48.8°, ,95= 7.7°, N= 13). However, mean directions obtained from the Zhengyuan (24.0°N, 101.1°E), West Zhengyuan (24.0°N, 101.1°E) and South Mengla (21.4°N, 101.6°E) localities indicate an easterly deflection in declination; such as Dec./Inc. = 61.8°/46.1°, ,95= 8.1° (N= 7), Dec./Inc. = 324.2°/,49.4°, ,95= 6.4° (N= 4) and Dec./Inc. = 51.2°/46.4°, ,95= 5.6° (N= 13), respectively. The palaeomagnetic directions obtained from these four localities are incorporated into a palaeomagnetic database for the Shan-Thai Block. When combined with geological, geochronological and GPS data, the processes of deformation in the Shan-Thai Block is described as follows: Subsequent to its rigid block clockwise rotation of about 20° in the early stage of India,Asia collision, the Shan-Thai Block experienced a coherent but southward displacement along the Red River Fault prior to 32 Ma. This block was then subjected to a north,south compressive stresses during the 32,27 Ma period, which played a key role in shaping the structure of Chongshan-Lancang-Chiang Mai Belt. Following this some local clockwise rotational motion has occurred during the Pliocene-Quaternary time in central part of the Shan-Thai Block as a result of internal block movements along the reactivated network of faults. [source]


    A hybrid fast algorithm for first arrivals tomography

    GEOPHYSICAL PROSPECTING, Issue 5 2009
    Manuela Mendes
    ABSTRACT A hybrid algorithm, combining Monte-Carlo optimization with simultaneous iterative reconstructive technique (SIRT) tomography, is used to invert first arrival traveltimes from seismic data for building a velocity model. Stochastic algorithms may localize a point around the global minimum of the misfit function but are not suitable for identifying the precise solution. On the other hand, a tomographic model reconstruction, based on a local linearization, will only be successful if an initial model already close to the best solution is available. To overcome these problems, in the method proposed here, a first model obtained using a classical Monte Carlo-based optimization is used as a good initial guess for starting the local search with the SIRT tomographic reconstruction. In the forward problem, the first-break times are calculated by solving the eikonal equation through a velocity model with a fast finite-difference method instead of the traditional slow ray-tracing technique. In addition, for the SIRT tomography the seismic energy from sources to receivers is propagated by applying a fast Fresnel volume approach which when combined with turning rays can handle models with both positive and negative velocity gradients. The performance of this two-step optimization scheme has been tested on synthetic and field data for building a geologically plausible velocity model. This is an efficient and fast search mechanism, which permits insertion of geophysical, geological and geodynamic a priori constraints into the grid model and ray path is completed avoided. Extension of the technique to 3D data and also to the solution of ,static correction' problems is easily feasible. [source]


    Simple relative space,time scaling of electrical and electromagnetic depth sounding arrays: implications for electrical static shift removal and joint DC-TEM data inversion with the most-squares criterion

    GEOPHYSICAL PROSPECTING, Issue 4 2005
    Max A. Meju
    ABSTRACT A simple scaling relationship is shown to facilitate comparison, correlation and integration of data recorded using the common experimental configurations in electrical and electromagnetic depth sounding. Applications of the scheme to field data from typical geological and landfill environments show that it is robust and, where transient electromagnetic (TEM) data are available, enables easy identification and quantification of electrical static shift (galvanic distortion) in magnetotelluric and direct current (DC) sounding curves. TEM-based procedures are suggested for both the direct removal of static shift in DC sounding curves and effective joint data inversion with the most-squares criterion in the presence of static shift. A case study of aquifer characterization using sounding data from borehole sites in the Vale of York in England shows that static shift is a common problem in this glacial-covered terrain and demonstrates the effectiveness of the proposed joint DC-TEM inversion strategy in handling distorted soundings. [source]


    Salt-water intrusion mapping by geoelectrical imaging surveys

    GEOPHYSICAL PROSPECTING, Issue 4 2000
    S.S. Abdul Nassir
    The geoelectrical imaging method is a tool for mapping the intrusion boundary between fresh water and saline water due to its inherent capability to delineate the lateral changes in pore-water salinity. A new field survey technique that can be used for environmental and geotechnical investigations has been developed. This study evaluates the multiscale survey technique as a tool employed in electrical imaging to detect the salt-water intrusion boundary in Yan, State of Kedah, northwest Malaysia. The technique was incorporated into these surveys, and it has proved to be a robust method for accurately mapping the fresh-water/saline-water boundary. The resulting resistivity sections from these surveys were consistent with both the available geological and borehole information from the area and the previous resistivity surveys conducted by the Geological Survey of Malaysia at those sites. [source]


    Trace Element Determination by ICP-AES and ICP-MS: Developments and Applications Reported During 2004 and 2005

    GEOSTANDARDS & GEOANALYTICAL RESEARCH, Issue 3 2006
    Kathryn L. Linge
    This review describes significant developments in trace element determination using inductively coupled plasma-atomic emission spectrometry (ICP-AES) and inductively coupled plasma-mass spectrometry (ICP-MS) that were reported in 2004 and 2005. It focuses on the application of ICP techniques to geological and environmental samples; fundamental studies in ICP-MS and ICP-AES instrumentation are not included. The literature reviewed indicated that the majority of new publications concerned advances in ICP-MS analysis rather than ICP-AES. However, ICP-AES developments are still being published, particularly in the areas of sample preconcentration and sample introduction. The trend in increasing publication of developments in hyphenated speciation techniques looks set to persist as knowledge of elemental speciation becomes critical for many environmental studies. Collision or reactions cells were the most reported technique for spectral interference removal in ICP-MS, probably reflecting the growing adoption of cell instruments in laboratories during the last few years. [source]


    Recent Developments in Trace Element Analysis by ICP-AES and ICP-MS with Particular Reference to Geological and Environmental Samples

    GEOSTANDARDS & GEOANALYTICAL RESEARCH, Issue 1 2005
    Kathryn L. Linge
    This review describes recent developments in trace element analysis using inductively coupled plasma-atomic emission spectrometry (ICP-AES) and inductively coupled plasma-mass spectrometry (ICP-MS). It aims to focus on the application of ICP techniques to geological and environmental samples. Therefore, fundamental studies in ICP-MS and ICP-AES instrumentation have largely been ignored. Whereas the majority of literature reviewed related to ICP-MS, indicating that ICP-MS is now the preferred technique for all geological analysis, there is still a steady development of ICP-AES to environmental applications. It is clear that true flexibility in elemental analysis can only be achieved by combining the advantages of both ICP-AES and ICP-MS. Two particular groups of elements (long-lived radionuclide and the platinum-group elements) stood out as warranting dedicated sections describing analytical developments these areas. [source]


    Neutron Activation Analysis, Atomic Absorption and X-Ray Fluorescence Spectrometry Review for 2003

    GEOSTANDARDS & GEOANALYTICAL RESEARCH, Issue 1 2005
    L. Paul Bédard
    This review for the year 2003 deals with three relatively well-established, mature, analytical techniques (neutron activation analysis, atomic absorption spectrometry and X-ray fluorescence spectrometry) that nevertheless remain very important for the characterisation of geological and environmental samples. Developments in neutron activation analysis included modification to the technique in relation to the determination of platinum-group elements, as well as consideration of sample size in ore grade estimation. A considerable body of literature was published on the application of atomic absorption spectrometry in the analysis of environmental samples. Many of these proposed technical and methodological improvements, notably in extraction procedures. X-ray fluorescence spectrometry saw developments in in situ analysis, synchrotron micro-XRF (,-SRXRF) and a confocal X-ray set-up for 3D elemental imaging. XRF technologies were used in the analysis of geological samples, reference materials, glasses, solutes and environmental materials. [source]


    Pliocene forest dynamics as a primary driver of African bird speciation

    GLOBAL ECOLOGY, Issue 1 2010
    Gary Voelker
    ABSTRACT Aim, Montane tropics are areas of high endemism, and mechanisms driving this endemism have been receiving increasing attention at a global scale. A general trend is that climatic factors do not explain the species richness of species with small to medium-sized geographic ranges, suggesting that geological and evolutionary processes must be considered. On the African continent, several hypotheses including both refugial and geographic uplift models have been advanced to explain avian speciation and diversity in the lowland forest and montane regions of central and eastern Africa; montane regions in particular are recognized as hotspots of vertebrate endemism. Here, we examine the possible role of these models in driving speciation in a clade of African forest robins. Location, Africa. Methods, We constructed the first robustly supported molecular phylogenetic hypothesis of forest robins. On this phylogeny, we reconstructed habitat-based distributions and geographic distributions relative to the Albertine Rift. We also estimated the timing of lineage divergences via a molecular clock. Results, Robust estimates of phylogenetic relationships and clock-based divergences reject Miocene tectonic uplift and Pleistocene forest refugia as primary drivers of speciation in forest robins. Instead, our data suggest that most forest robin speciation took place in the Late Pliocene, from 3.2 to 2.2 Ma. Distributional patterns are complex, with the Albertine Rift region serving as a general east,west break across the group. Montane distributions are inferred to have evolved four times. Main conclusions, Phylogenetic divergence dates coincide with a single period of lowland forest retraction in the late Pliocene, suggesting that most montane speciation resulted from the rapid isolation of populations in montane areas, rather than montane areas themselves being drivers of speciation. This conclusion provides additional evidence that Pliocene climate change was a major driver of speciation in broadly distributed African animal lineages. We further show that lowland forest robins are no older than their montane relatives, suggesting that lowland areas are not museums which house ,ancient' taxa; rather, for forest robins, montane areas should be viewed as living museums of a late Pliocene diversification event. A forest refugial pattern is operating in Africa, but it is not constrained to the Pleistocene. [source]


    Analysis of the steady-state flow of a compressible viscoplastic medium over a wedge

    INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 6 2006
    Oana Cazacu
    Abstract A new model for calculating the resistance to penetration into geological or geologically derived materials is proposed. We assume steady-state flow of the target material over the penetrator. The target medium is described by a rate dependent constitutive equation that accounts for combined effects of strain rate and compaction on yielding. The wedge-shaped penetrator is considered to be rigid. The influence of the characteristics of the penetrator/target interface, impact velocity, target mechanical properties and nose geometry on the resistance to penetration is investigated. It is found that for low to intermediate impact velocities, accounting for friction results in a blunter optimal wedge geometry for optimal penetration performance. Copyright © 2005 John Wiley & Sons, Ltd. [source]


    Stress behavior from fault data sets within a transtensional zone, South Central Cordillera, Luzon, Philippines: Implications for mineral occurrences

    ISLAND ARC, Issue 1 2009
    Mario A. Aurelio
    Abstract The structural signature in the area between the Baguio mineral district and Ansagan, Tuba, Benguet in the South Central Cordillera, northern Luzon, Philippines, is dominated by northeast- to ENE-trending faults, contained within a NNW,SSE-trending transtensional strip. This 50-km-long, 25-km-wide elongated tectonic zone is bounded to the west by the Pugo Fault and to the east by the Tebbo Fault, both being branches of the Philippine Fault System. Detailed structural geological (particularly microtectonic) analysis of fracture and mineral vein systems indicates strong conformity with the regional structural direction. Computed extensional stress axis ,3 directions are oriented N150° on average, sub-parallel to the strike of the bounding faults. The existence of known mineral deposits and prospects within the tectonic strip implies an intimate relationship between transtension and mineral occurrence. [source]