Metals in Okefenokee peat-forming environments: relation to constituents found in coal

Ba, Ca, Co, Cr, Cu, Fe, Hg, K, Mg, Mn, Na, Ni, Pb and Zn were studied in cores of peat from two major vegetational areas of the Okefenokee Swamp, Georgia; both total peat and organic fractions were investigated. Except for Hg and Pb, metal concentrations were either higher or equal to Clarke values. The sandy bedrock is not an important contributor to metal concentrations found in peat. Levels of metals in a given peat sample were related to plant materials which gave rise to the peat; it does not appear that vegetational environment plays a critical role in determining trace metal distribution, but does play a role in determining the amount of humic or pre-vitrinitic constituents that eventually are found in coal.     

Example of Neogene tectonic indentation in the Eastern Betic Cordilleras: the Arc of Aguilas (Southeastern Spain)

Abstract

Neogene deformations have deeply disturbed the initial architecture of the pile of nappes within the Eastern Betic zone. The Arc of Aguilas, displaying a southeast-facing concavity, is a spectacular example of such a post-nappe structuration. Miocene deposits involved in the torsion of the Arc provide a chronology of the deformation. The Arc of Aguilas is one element within a system of rigid-plastic indentation including the following units, from the inner (SE) to the outer (NW) zones : — A rigid block, little deformed, located in the present day abyssal plain, play the part of the indenter.

— A structural pad corresponding to the Aguilas Arc itself. It was severely folded during Miocene times.

— A large peripheral zone mainly subjected to faulting during the Neogene (essentially strike-slip faults). These faults control the evolution of different types of sedimentary basins during the Late Neogene (Tortonian to Pliocene).

Two large shear zones: N020 sinistral (Palomares and Terreros faults), N100 dextral (Las Moreras faults) guided the deformation of the Aguilas Arc within a compressive stressfield of which major tensor axis oscillated between NW-SE and N-S.     

Continental rift-setting and evolution of Neoproterozoic Sindreth Basin in NW-India

The Neoproterozoic Sindreth Basin, NW India, and its surrounding area represent a half graben structure situated between the undeformed Malani Igneous Suite (MIS) in the west and a corridor of coeval Cryogenian ductile deformation, anatexis and granite intrusion in the east. The main lithologies observed in the basin are conglomerate, fanglomerate, debris flow and lake deposits derived from a nearby continental provenance, intercalated with concurrent mafic and felsic lava flows. Based on geological traverses across the strike of the basin, we propose a three-fold classification comprising Lower Clastic Unit and an Upper Clastic Unit and a Bimodal (basalt–rhyolite) Volcanic Unit separating the two. Tilting due to basin inversion and faulting has been observed; however, the rocks are unmetamorphosed and show undisturbed primary sedimentary features. The stratigraphic record of the basin is characteristic for deposition and magmatism in a fault-related continental setting. Implications of the findings have been discussed in the context of Neoproterozoic crustal dynamics in NW India. This study provides conclusive evidence for a continental setting for Sindreth Basin evolution and contests the recent models of active subduction setting (either back-arc basin or accretionary sediments over a subduction zone).     

Distribution of heavy metals in marine bivalves, fish and coastal sediments in the Gulf and Gulf of Oman

An assessment of marine contamination due to heavy metals was made in the Gulf and Gulf of Oman based on marine biota (fish and various bivalves) and coastal sediment collected in Bahrain, Oman, Qatar, and the United Arab Emirates (UAE) during 2000-2001. Sediment metal loadings were generally not remarkable, although hot spots were noted in Bahrain (Cu, Hg, Pb, Zn) and on the east coast of the UAE (As, Co, Cr, Ni). Concentrations of As and Hg were typically low in sediments and the total Hg levels in top predator fish commonly consumed in the region were < 0.5 microg g(-1) and posed no threat to public health. Very high Cd concentrations (up to 195 microg g(-1)) in the liver of some fish from southern Oman may result from food-chain bioaccumulation of elevated Cd levels brought into the productive surface waters by upwelling in the region. Very high As concentrations (up to 156 microg g(-1)) were measured in certain bivalve species from the region. Although not certain, the As is probably derived from natural origins rather than anthropogenic contamination.     

Some problems of the tectonic framework of the Guiana Shield with special regard for the Roraima Formation

Zusammenfassung Die Arbeit diskutiert Probleme der tektonischen Entwicklung des Guyana-Schildes, eines gro\en kratonischen Gebietes archaischen Alters. Seine Konsolidation fand viel früher statt als die Konsolidation des Brasilianischen Schildes. Guyana stabilisierte sich schon wÄhrend des Älteren Proterozoikums vor 1800 M. J. Vulkanite und Molasse der Roraima-Formation füllten die Depressionen der gefalteten archaischen Gebiete auf. Der Sockel des Guyana-Schildes wird durch die Guyano Eburnéenne Geosynclinal (Choubert, 1969), die Transamazonische Geosynklinale, gebildet, welche sich von Venezuela bis Französisch-Guyana mit gleichem Streichen über eine Entfernung von mehr als 1000 km verfolgen lÄ\t. Eine archaische Geosynklinale von diesem Ausma\ ist bisher aus anderen Schildgebieten der Erde unbekannt.Die archaischen Metasedimente, Metavulkanite und kristallinen Gesteine von Guyana haben allgemein eine E—W-Streichrichtung und unterscheiden sich damit von der vorherrschenden N—S-Streichrichtung der oberprÄkambrischen Gesteine des Brasilianischen Schildes.Jung-prÄkambrische Geosynklinalen und Orogenesen scheinen im Guyana-Schild zu fehlen. Die in Brasilien aktive jung-proterozoische Assynthische (Baikalische oder Brasilianische) Orogenese hat den Guyana-Schild nicht erfa\t. Dort war die letzte Orogenèse die Post-Barama-Mazaruni-Bartica-Orogenese vor 2000 M. J. Zwischen 2000 M. J. und 1800 M. J. entwickelte sich die PrÄ-Roraima-ErosionsflÄche. Dieser Phase folgte die Ablagerung der tafeligen Roraima-Formation vor 1750 M. J. mit dem anorogenen Post-Roraima-Vulkanismus (Dolerite und Gabbro-Intrusionen). Die gro\e Verbreitung der fast nicht verformten Roraima-Sedimente beweist, da\ der grö\te Teil des Guyana-Schildes wÄhrend des Älteren Proterozoikums stabilisiert war.Das Problem der Entstehung des Amazonas-Beckens und die Rolle der Transcurrent-Verwerfungen sowie das VerhÄltnis zwischen den kontinentalen Transcurrent-Verwerfungen und den Bruchzonen des mittelozeanischen Rückens werden dargestellt.

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In this paper some problems of tectonical evolution of the Guiana Shield are discussed that represents a large cratonic area of Archaic age. Its consolidation took much earlier place than the consolidation of the Brazilian Shield. The Guianas were already settled at early Proterozoic time, 1.800 m. y., when molasse and volcanic deposits had been accomplished at depressions of areas folded during the Archaic time 2.000 m. y. The basement of the Guiana Shield is formed by rocks of the vast Guiana-Eburneana Geosyncline (Choubert, 1969), named also Trans-amazonian Geosyncline which has an extension of more than 1.000 km, with the same direction. Such a huge Archaic geosyncline is unknown at an other cratonic area of the world.The predominant trend and structural lineament of the Archaic rocks is quite different than in the Brazilian Shield. The characteristic trend of the early Precambrian rocks of the Guiana Shield is approximately E-W, contrary to the main N-S structural alignement of the Brazilian Shield.Late Precambrian geosynclines and orogeny seem to be absent in the Guiana Shield. The young Proterozoic Assynthic (Baicalian) Orogeny has not more affected the Guiana Shield, where the last orogeny was the Post-Barama-Mazaruni-Bartica Orogeny, which occurred at the Archaic, 2.000 m. y.Between 2.000 m. y. and 1.800 m. y. took place the development of Pre-Roraima erosion surface. It was followed by the deposition of the tabular Roraima Formation, manifesting the stabilisation of the central part of the Shield before 1.750 m. y., when the emplacement of the gabbroic and doleritic volcanites succeeded. The large distribution of the not metamorphosed flat lying Roraima sediments proves that the Guiana Shield was already consolidated during the old Proterozoic time and was never more affected by younger orogenic movements.It is also discussed the problem of origin of the Amazonas Basin, and the important role of the Transcurrent Faults in the tectonic framework of the Guiana Shield and the probable genetic relationship between the transcurrent faults and the fracture zones of the Mid-Atlantic Ridge.

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Resumo O Escudo das Guianas representa uma ampla área cratÔnica da Era Arcaica. Sua consolidaÇÃo já ocorrera muito antes de consolidaÇÃo do Escudo Brasileiro. As Guianas tornaram-se estáveis durante a Era Proterozóica inferior, 1.700 m. a. quando deposiÇÕes vulcânicas e molasse de Roraima foram concluidas em depressÕes de áreas dobradas durante a Era Arcaica, O embasamento do Escudo das Guianas é formado pelo imenso Geossinclínio Guiano-Eburneano (Choubert, 1969) ou Transamazoniano, que representa um geossinclinal de mais de 1.000 km de extensÃo, de mesma direÇÃo. Geossinclinal Arqueano de tamanha amplitude nÃo é conhecido em outra regiÃo cratÔnica de mundo.As rochas metassedimentares, metavulcânicas e cristalinas arcaicas tÊm um alinhamento aproximadamente E-W, diferindo do principal alinhamento estrutural N—S do Escudo Brasileiro.Geossinclínos e orogÊnia do Pré-Cambriana superior parecem estar ausentas no Escudo das Guianas. A orogénia do Proterozóico superior (Assíntica ou Baicaliana) nÃo mais afetou o Escudo das Guianas, onde a Última orogÊnia foi a orogÊnia Barama-Mazaruni-Bartica, que ocorreu há 2000 m. a. Entre 2000 m. a. e 1800 m. a. deu-se o desenvolvimento da superfície de erosÃo Pré-Roraima. Esta fase foi seguida pela deposiÇÃo da FormaÇÃo Roraima tabular, o que revela a estabilizaÇÃo da parte central do Escudo, há 1.750 m. a. quando ocorreu o emplacement dos vulcanitos gabróicos e doleríticos. A grande distribuiÇÃo dos sedimentos Roraima quase horizontals nÃo metamorfizados, prova que o Escudo de Guianas já estava consolidado durante o Proterozóico inferior e nÃo foi mais afetado por movimentos orogÊnicos mais jovens.Foi discutido também o papel importante das falhas transcorrentes na constituiÇÃo tectÔnica do Escudo das Guianas; o problema da origem da Bacia AmazÔnica, e a provável relaÇÃo genética entre as falhas transcorrentes as zonas de fratura da Cadeia Meio-Atlântica.

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— - . , . , . . 1800 . Roraima , . - (Choubert, 1969), , , 1000 . . , E-W N-S .- , , . - — — . Post Barama-Mazaruni-Bartica Orogenese 2000 . 2000 1800 - — . Roraima — 1700 - ( ). - , . Transcurrent, Transcurrent .

     

Design-based versus model-based sampling strategies: Comment on R. J. Barnes' “bounding the required sample size for geologic site characterization”

Two fundamentally different sources of randomness exist on which design and inference in spatial sampling can be based: (a) variation that would occur on resampling the same spatial population with other sampling configurations generated by the same design, and (b) variation occurring on sampling other populations, hypothetically generated by the same spatial model, using the same sampling configuration. The former leads to the design-based approach, which uses classical sampling theory; the latter leads to the model-based approach and uses geostatistical theory. Failure to recognize these two sources of randomness causes misunderstanding about dependence of variables and the role of randomization in sampling, unwarranted narrowing down the choice of sampling strategies to those that are model-based, and abuse in simulation experiments. This is exemplified in Barnes' publication on the required sample size for geologic site characterization by nonparametric tolerance intervals. A basic design-based strategy like Simple Random Sampling is shown to require smaller sample sizes than the model-based strategy advocated by Barnes. In addition, Simple Random Sampling is completely robust against model errors and less complicated.     

Suitability of GNSS for analysis of soil subsidence in Recife in a highly urbanized coastal area

Natural Hazards - Recife Metropolitan Region, in the northeast of Brazil, is formed by a coastal plain bounded by hills and by the Atlantic Ocean. Recife Metropolitan Region has about 4 million...     

On the standardization of measurements of the anisotropy of magnetic susceptibility

The magnetic anisotropy of several artificially constructed samples has been measured with different types of instruments in several laboratories. Susceptibility bridge determinations have given consistent results, but the magnitude of the anisotropy determined by the Digico anisotropy delineator is incorrect. For future measurements with this instrument it is necessary to make either a simple calibration change or to make a minor change in the associated computer program. A set of equations for correcting the old published data is given.