1,806,591 research outputs found
δ³⁷Cl: the geochemistry of chlorine isotopes
No full textIn this thesis the geochemistry of the stable isotopes of chlorine will be examined. Chlorine is one of the halogens, the seventh group in the periodic system of elements. This group consists of five elements, fluorine, chlorine, bromine, iodine, and astatine. This thesis presents the first chlorine isotope measurements on carbonatites. Significant variations in δ³⁷Cl were observed, but since the samples came from different geological settings it is difficult to interpret the results in terms of fractionating processes. A correlation between chlorine, oxygen and carbon isotopes is suggested. If fractionation of chlorine isotopes is caused by the same processes as the fractionation of oxygen and carbon isotopes, then exchange with the country-rocks or Reyleigh fractionation may be important. The data suggest that δ³⁷Cl in primary carbonatites can be between -1 and 0‰. If these data represent mantle values, which is not proven, this is in agreement with data of volcanic water samples from Indonesia which indicate that chloride escaped from the mantle is enriched in ³⁷Cl, resulting in negative δ³⁷Cl values in the mantle. The results invite more research. It is clear that further research must be combined with an effort to understand the chloride geochemistry of carbonatites, since almost nothing is known on this subject. It is also important to obtain good fractionation knowledge of the HCI degassing system. It will be important to measure both the HN0₃-extractable and the total chloride
Practical applications of multivariate statistics in exploration geochemistry
No full textThe search for new economic ore-deposits becomes increasingly difficult. A
sophisticated approach is required to locate new ones. In exploration geochemistry
the use of uni- and multivariate statistics is often advocated. In this series of
studies it is shown how techniques such as factor analysis, discriminant function
analysis, non linear mapping and cluster analysis can be of use to the exploration
geochemist. Applications are presented to geochemical rock, sediment and water
survey
Geochemistry
Full text linkThis book brings together the knowledge from a variety of topics within the field of geochemistry. The audience for this book consists of a multitude of scientists such as physicists, geologists, technologists, petroleum engineers, volcanologists, geochemists and government agencies. The topics represented facilitate as establishing a starting point for new ideas and further contributions. An effective management of geological and environmental issues requires the understanding of recent research in minerals, soil, ores, rocks, water, sediments. The use of geostatistical and geochemical methods relies heavily on the extraction of this book. The research presented was carried out by experts and is therefore highly recommended to scientists, under- and post-graduate students who want to gain knowledge about the recent developments in geochemistry and benefit from an enhanced understanding of the dynamics of the earth's system processes
Spatial heterogeneity of sources of branched tetraethers in shelf systems: The geochemistry of tetraethers in the Berau River delta (Kalimantan, Indonesia)
No full textThe bulk organic matter composition (total organic carbon (TOC) content and d13CTOC) and composition of isoprenoid and branched glycerol dialkyl glycerol tetraethers (GDGT) in surface sediments from 43 stations in the Berau River delta (east Kalimantan, Indonesia), including two coast-shelf transects and stations within the river mouth, were examined to reveal the spatial heterogeneity in these parameters in order to assess the impact of a tropical river loaded with suspended matter on the sedimentary organic matter in the shelf system. The high-resolution study showed that, despite the extensive transport of eroded soil material by the river to the sea, terrestrial organic matter and brGDGTs are only deposited on a relatively small part of the shelf. The concentrations of brGDGTs are highest (up to 120 µg g-1 TOC) in sediments deposited in and close to the mouth of the Berau River and their distribution indicates that they represent a mixture of soil-derived and river in-situ produced brGDGTs. Crenarchaeol concentrations reach 700 µg g-1 TOC in sediments deposited on the outer shelf due to Thaumarchaeotal production in shelf waters. This results in a strong gradient (0.93–0.03) in the BIT index, with high values in the river mouth and low values on the shelf. The decline in the BIT index is caused by both decreasing concentrations of the brGDGTs and increasing concentrations of crenarchaeol. The BIT index shows a highly significant but non-linear relationship with d13CTOC. On the shelf, in the area not under the direct influence of the Berau River, cyclic brGDGTs become relatively dominant, most probably due to in-situ production in the alkaline pore waters of the surface sediments. The spatial heterogeneity of sources of brGDGTs on the Berau shelf complicates the use of brGDGTs as temperature proxies. Application of the global soil calibration to sedimentary mixtures of brGDGTs in the river-influenced area of the shelf results in a severe underestimation of mean annual air temperature (MAT) by 6 °C. This is due to the mixed origin of the brGDGTs, which are not only derived from soil erosion but, likely, also from riverine production, as has been observed for other river systems.Comparison of the Berau shelf other shelf systems indicates that in-situ production of brGDGTs in shelf sediments is a widespread phenomenon that is especially pronounced at water depths of ca. 50–300 m. It is hypothesized that this is so because benthic in-situ production of heterotrophic brGDGT-producing bacteria is fueled by the higher delivery of fresh organic matter to these sediments as the consequence of higher primary productivity in shelf waters and a decreased mineralization due to the relatively short settling times of particles on the shelf. For palaeoclimatic studies of marine shelf sediments the application of brGDGTs as proxies is severely complicated by the heterogeneity of sources of brGDGTs. Comparison of the brGDGT composition of soils with those of shelf sediments may assist in deciding if sedimentary brGDGTs are predominantly derived from soil erosion. Several methods to do so are discussed
Environment and Geochemistry of Sediments
No full textThis reprint considers a vast range of questions devoted to environmental geochemistry. The themes of the research cover different problems of the geochemistry of sediments, such as the reconstruction of the paleoenvironment in the lake basins, climate evolution during the Late Carboniferous–Early Permian period, and the study of the paleoenvironment in the eastern Tethys. Several articles discuss the features of the geochemistry of sedimentation in places of prehistoric anthropogenic activity. Based on the geochronological analysis, the magnetic susceptibility anthropogenic sources of metals in south-eastern Baltic lake sediments from the Neolithic to the Medieval Age were determined. A new approach using the geochemical indication was developed for the determination of the functional zones of prehistoric archaeological sites in Eastern Europe. The application of geochemical multi-element and geochronological analyses of the Iron Age and early Roman cultural layers was considered at the archaeological site in the Netherlands. Some papers are devoted to the pollution hazard problem concerning, for example, the accumulation and distribution of a hazardous contaminant, mercury (Hg), in the basin of Onega Lake, Russia, the second largest lake in Europe, and the distribution of arsenic in the soils of the Verkhnekamskoe potassium salt deposit, Perm Krai, Russia. The ecological state of basins as a result of technogenic processes using a geochemical approach is illuminated in the papers devoted to the mineralogical and geochemical contents of the bottom sediments of Al-Kharrar and Al-Shuaiba Lagoons, Red Sea, Saudi Arabia
Applied Geochemistry with Case Studies on Geological Formations, Exploration Techniques and Environmental Issues
Full text linkGeochemistry has become an essential subject to understand our origins and face the challenges that humanity will meet in the near future. This book presents several studies that have geochemistry as their central theme, from the description of different geological formations, through its use for the characterization of contaminated sites and their possible impact on ecosystems and human health, as well as the importance of geochemical techniques as a complement to other current scientific disciplines. Through the different chapters, the reader will be able to approach the world of geochemistry in several of its subfields (e.g. environmental, isotope, or biogeochemistry) and learn through practical cases
Applied Geochemistry with Case Studies on Geological Formations, Exploration Techniques and Environmental Issues
No full textGeochemistry has become an essential subject to understand our origins and face the challenges that humanity will meet in the near future. This book presents several studies that have geochemistry as their central theme, from the description of different geological formations, through its use for the characterization of contaminated sites and their possible impact on ecosystems and human health, as well as the importance of geochemical techniques as a complement to other current scientific disciplines. Through the different chapters, the reader will be able to approach the world of geochemistry in several of its subfields (e.g. environmental, isotope, or biogeochemistry) and learn through practical cases
Arsenic Environmental Geochemistry, Mineralogy, and Microbiology
No full textEnvironmental Mineralogy and Bio-Geochemistry of Arsenic provides a comprehensive understanding of arsenic geochemistry in the near-surface environmen
Geochemistry of trace metals in the Scheldt estuary
No full textThe distribution of trace metals has been studied in abiotic compartments of the ScheIdt
estuary (water column and sediments). Seasonal surveys, carried out in 1987-1988, indicate
that the geochemistry of dissolved trace metals (Cd, Cu, Zn) is determined by the redox status
of the upper estuary, and by primary production in the lower estuary. During the warmer
period (spring till autumn), the incoming river water is anoxic, leading to very low dissolved
metal concentrations due to precipitation of metal sulphides. During winter, the river water is
usually not completely devoid of oxygen (although highly undersaturated), precluding metal
sulphide precipitation. Therefore, the dissolved metal concentrations in the incoming river
water are much higher during winter
Mineralogy and geochemistry of bauxite and bentonite deposits from Mozambique
No full textResults of mineralogical and geochemical studies of bauxites, kaolinitic clays and
bentoniteS from Mozambique are presented in this thesis. The bauxite and kaolinitic
clay deposits in Penhalonga area (in the central western part of Mozambique) are
associated with Precambrian magmatic rocks and the bentonites resulted from
weathering of volcanic rocks, belonging to the Lebombos Mountain range in the Boane
district (in the south of Mozambique).
The bauxites and kaolinitic clays are the main products resulting from weathering of
rock types with anorthositic, gabbroic composition and metabasalts. These parent rocks
have been subjected to different degrees of weathering witnessed by the presence in the
profiles of the minerals gibbsite, kaolinite, hydroxides and oxides of iron, as well as
illite in variable amounts. The distribution of major and trace elements, including the
Rare Earths, in the weathering profiles provides gives indications for the main
development trends of the bauxitization-Iateritization in Penhalonga area. Bauxite
formation took place over the main rocks of the area mineralogically with feldspars and
pyroxenes and/or amphiboles as the dominant primary components under influences of
processes ofweathering in tropical conditions.
Although most of the weathering sequences are truncated, due to superficial erosion, the
general behaviour of the chemical elements reflects the composition of the source rock
and, to some extent, the dominant conditions for the geochemical mobility and
fractionation of the elements. This guides to the separation of the easily mobile
elements like the alkalis and alkaline earths and the less mobile or immobile elements.
The later group is represented by elements as AI, Fe, Ti, Zr, which are relatively
retained in the weathered profiles, in almost all stages. Remarkable in the weathering
sequences is the behaviour of the Rare Earth elements (REE), specially the elements Ce
and Eu, which display anomalies, due to their chemistry. On the other hand, taking into
consideration the activities ofNa+, K+, ci+ and I4Si04, the composition of the waters
draining the area also provides evidence of the principal mineral assemblages present in
the weathering sequences.
In the Mozambican territory, associated with the volcanics of the Lebombos mountains,
smectite-rich bentonites constitute deposits of economic interest. The principal mineral
is montmorillonite in concentrations ranging up to an average grade of 75-79% and
invariably associated with silica phases, chiefly cristobalite. According to referenced
discrimination diagrams the bentonites have close affinity with parent rocks of rhyolitic
and rhyodactic compositions. However, the mechanisms of the bentonite formation are
still poorly understood, although, from field relationships and the geological setting of
the bentonitic masses, it seems that they have originated from miscellaneous processes
of alteration of the rhyolitic parent rocks.
The bentonites are chemically of the Ca-type with high silica SIOz and generally low
contents in Alz03 and MgO, features, which are strictly related to the parent rocks of
dominantly rhyolitic composition. In some places occurrences of indurated calcium carbonate horizons are observed in a
vertical profile. Geochemically the bentonites show a uniform composition, which is
also reflected in the trace element content. The behaviour of the chemical elements is
consistent with the general effects of an alkaline environment on the mobilization and
fixation of elements propitiating formation of bentonites instead of zeolites
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