The geochemical composition of the terrestrial surface (without soils) and comparison with the upper continental crust (original) (raw)
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Earth surface geochemistry and mineralogy : processes, hazards, soils and resources
2016
Co-Authors (alphabetical): Eyal Ben-Dor, Tel Aviv University, Tel Aviv, Israel Janice Bishop, SETI Institute, Mountain View, CA Joseph Boardman, AIG LLC, Boulder, CO Roger N. Clark, Planetary Science Institute, CO Tom Cudahy, CSIRO, Perth, Australia Bethany L. Ehlmann, California Institute of Technology, Pasadena, CA Robert O. Green, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA Bernard Hubbard, United States Geological Survey, Reston, VA Raymond Kokaly, United States Geological Survey, Denver, CO John Mars, United States Geological Survey, Reston, VA John F. Mustard, Brown University, Providence, RI Greg Okin, University of California, Los Angeles, CA Cindy Ong, CSIRO, Australia Roberto de Souza Filho, University of Campinas, Brazil Freek van der Meer, ITC, Netherlands Gregg Vane, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA
Zenodo (CERN European Organization for Nuclear Research), 2022
International Union of Geological Sciences Manual of Standard Methods for Establishing the Global Geochemical Reference Network Aims The aims of the International Union of Geological Sciences Commission on Global Geochemical Baselines are: • To provide high quality geochemical baseline data for the terrestrial part of our home planet Earth. • To establish a Geochemical Reference Network for levelling data sets of existing regional geochemical projects, and • To provide reference samples and sites for future monitoring of the chemical state of the World's terrestrial surface. Hence, the generated geochemical data must be of high quality, integrity and consistency. Synopsis "Everything in and on the Earth-mineral, animal and vegetable-is made from one, or generally some combination of, the natural chemical elements occurring in the rocks of the Earth's crust and the surficial materials derived from them. Everything that is grown, or made, depends upon the availability of the appropriate elements. The existence, quality and survival of life depends upon the availability of elements in the correct proportions and combinations. Because natural processes and human activities are continuously modifying the chemical composition of our environment, it is important to determine the present abundance and spatial distribution of the elements across the Earth's surface in a much more systematic manner than has been attempted hitherto" (Darnley et al., 1995, p.x). Although such a global database is urgently needed for multipurpose use, the systematic attempt is still in its infancy because of the non-existence of a manual of comprehensive and standardised methods of sampling and other supporting procedures. The current 'International Union of Geological Sciences Manual of Standard Methods for Establishing the Global Geochemical Reference Network' fills this gap. The Manual follows the concept of 7356 Global Terrestrial Network grid cells of 160x160 km, covering the land surface of Earth, with five random sites within each grid cell for the collection of samples. This allows the establishment of the standardised Global Geochemical Reference Network with respect to rock, residual soil, humus, overbank sediment, stream water, stream sediment and floodplain sediment. Apart from the instructions for the collection of samples, the Manual covers sample preparation and storage, development of reference materials, geoanalytical methods, quality control procedures, geodetic and parametric levelling of existing geochemical data sets, data conditioning for the generation of time-independent geochemical data, management of data and map production, and finally project management. The methods described herein, apart from their use for Establishing the Global Geochemical Reference Network, can be used in other geochemical surveys at any mapping scale.
Geochemical background—concept and reality
Science of The Total Environment, 2005
The definitions and use of the term dbackgroundT in exploration and environmental geochemistry are reviewed. Based on data from two subcontinental-scale geochemical mapping projects, it is shown that trying to define da backgroundT for a large area is fraught with problems. It is demonstrated that background may change from area to area within a region and between regions. Although global averages are of general use, no specific global background levels of elements, for example in soils, can be defined, at best regional or local operational estimates can be made, though with caveats. Using background estimates based on concentrations in deeper soil levels to judge element concentrations in upper soil horizons (e.g., the TOP/BOT-ratio) can lead to severe misinterpretations if natural biogeochemical soil formation processes are ignored. Because of large natural variations in element concentrations in, for example soils, even the establishment of maximum admissible concentration based on ecotoxicological investigations is a difficult exercise. Organisms may become adapted to natural differences. Furthermore, there are challenges in converting the concentrations of the soluble substances used in ecotoxicological studies to appropriate levels in solid phase material, for example soils, analysed by commonly employed acid digestion procedures. Toxicological thresholds may thus also need to consider a spatial component that is presently neglected.
The history, progress, and future of global-scale geochemical mapping
Geochimica Brasiliensis, 2018
Pesquisas geoquímicas de escala global ou de escala continental abrangem milhões de quilômetros quadrados da superfície da Terra, geralmente com uma densidade amostral muito baixa (1 ponto por 1.000 a 10.000 km 2). Padrões geoquímicos produzidos a partir desses levantamentos de baixa densidade refletem processos que atuam na ampla escala de amostragem. Esses processos estão relacionados a vários fatores, incluindo a tectônica, clima, intemperismo, composição geoquímica e mineralógica do material original do solo, glaciação em escala continental, topografia, alteração e mineralização em escala regional e, em alguns casos, atividade humana. Um atlas geoquímico de múltiplos elementos da superfície da Terra baseado neste tipo de pesquisa tem sido um tópico de discussão entre os geoquímicos desde os anos 80. Nos últimos 15 anos, vários levantamentos geoquímicos em escala global foram conduzidos (Austrália, China, Europa, Índia, México, Estados Unidos da América) e os dados e mapas estão sendo usados como uma ferramenta para ajudar na gestão ambiental e de recursos. Em 2016, o estabelecimento da International Union of Geological Sciences (IUGS) Commission on Global Geochemical Baselines e da United Nations Educational, Scientific and Cultural Organization (UNESCO) International Centre for Global-Scale Geochemistry proporcionou um futuro promissor para a continuação do mapeamento geoquímico de escala global em outras partes do mundo, com o produto final sendo um banco de dados geoquímico global e um atlas derivado desse conjunto de dados. Palavras-chave: mapeamento geoquímico, escala global, escala continental, levantamento geoquímico ABSTRACT Global-scale, or continental-scale, geochemical surveys cover millions of square kilometers of the Earth's surface generally at a very low sample density (1 site per 1000 to 10,000 km 2). Geochemical patterns produced from these low-density surveys reflect processes that act at the broad scale of sampling. These processes are related to many factors including tectonics, climate, weathering, geochemical and mineralogical composition of the original soil parent material, continental-scale glaciation, topography, regional-scale alteration and mineralization, and in some cases, human activity. A multi-element geochemical atlas of the Earth's land surface based on this type of survey has been a topic of discussion among applied geochemists since the 1980s. Over the past 15 years, several global-scale geochemical surveys have been conducted (Australia, China, Europe, India, Mexico, United States of America) and the data and maps are being used as a tool to aid in environmental and resource management. In 2016, the establishment of both the International Union of Geological Sciences (IUGS) Commission on Global Geochemical Baselines and the United Nations Educational, Scientific and Cultural Organization (UNESCO) International Centre for Global-Scale Geochemistry has provided a hopeful future for continuing global-scale geochemical mapping in other parts of the world, with the ultimate product being a global geochemical database and atlas derived from this dataset.
Geochemistry: Exploration, Environment, Analysis
Forest rings are large circular features common in boreal forests in Ontario, Canada, characterized by ring-shaped topographic depressions in carbonate-rich soil. This paper documents the compositional variation of soil and of the peat that commonly fills the depression, along transects across two representative rings: one centred on an accumulation of CH4 in glacial sediments and the other on H2S in both glacial sediments and bedrock. Clayey mineral soil at the ring edge (annulus) shows low pH, oxidation-reduction potential (ORP), Ca and carbonate, and high Al, Fe and Mn by both aqua regia digestion and a 0.25M hydroxylamine hydrochloride leach (0.25M NH2OH.HCl at 60°C). Antithetic responses occur in the overlying peat, including elevated carbonate and pH over the areas with low pH, ORP and carbonate in the mineral soil. The observed relationships suggest vertical migration of carbonate species from mineral soil into peat at the annulus, and lateral migration from the annulus to adjacent areas in the mineral soil. The geochemical data support the hypothesis that forest rings are the surface expression of reduced chimneys, similar to those observed over metallic mineral deposits, despite both these sites being known to be barren. Strongly negative ORP values in shallow soils in the annulus suggest autotrophic microbiological activity contributes to the sharp change in redox conditions at the ring boundaries. The similar geochemical responses at for-est rings and soils over mineral deposits show that these features can be used to understand the variation in redox, pH, metals and soil hydrocarbons over mineral deposits and to help differentiate ore-related from secondary geochemical features due to the presence of a reduced chimney.
Curation and Analysis of Global Sedimentary Geochemical Data to Inform Earth History
GSA Today
Large datasets increasingly provide critical insights into crustal and surface processes on Earth. These data come in the form of published and contributed observations, which often include associated metadata. Even in the best-case scenario of a carefully curated dataset, it may be nontrivial to extract meaningful analyses from such compilations, and choices made with respect to filtering, resampling, and averaging can affect the resulting trends and any interpretation(s) thereof. As a result, a thorough understanding of how to digest, process, and analyze large data compilations is required. Here, we present a generalizable workflow developed using the Sedimentary Geochemistry and Paleoenvironments Project database. We demonstrate the effects of filtering and weighted resampling on Al 2 O 3 and U contents, two representative geochemical components of interest in sedimentary geochemistry (one major and one trace element, respectively). Through our analyses, we highlight several methodological challenges in a "bigger data" approach to Earth science. We suggest that, with slight modifications to our workflow, researchers can confidently use large collections of observations to gain new insights into processes that have shaped Earth's crustal and surface environments. 1 Supplemental Material: table of valid lithologies; map depicting sample locations; crossplot illustrating analytical uncertainty; flowchart of the proposed workflow; histograms showing the effects of progressive filtering, the distribution of spatial and age scales, and proximity and probability values; and results of sensitivity tests.