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Topic Review
Geologic Background of Sixtymile Gold District, Yukon, Canada
The Sixtymile gold district, Yukon, Canada has been mined for placer gold since the late 19th century. 
  • 1.4K
  • 14 Apr 2022
Topic Review
Tungsten in Soil
Tungsten (W) occurs naturally in soils and the Earth’s crust is the most important source of this element. Tungsten reserves have been estimated to be approximately 3.1 Mt in ore deposits, where the metal exists mainly as a component of several minerals, such as wolframite (Fe, MnWO4) and scheelite (CaWO4).
  • 1.4K
  • 26 Jul 2021
Topic Review
Amin Beiranvand Pour
My scholarly interests range widely, from mineral exploration to environmental issues such as geo-hazard, structural mapping, geothermal and geomorphic and coastal geology investigations. Subsequently, I have conducted several research projects for geological mapping, disaster management and environmental modeling using a variety of satellite remote sensing data such as the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER), Landsat Enhanced Thematic Mapper+ (ETM+), Landsat-8, Advanced Land Imager (ALI), Hyperion and Phased Array type L-band Synthetic Aperture Radar (PALSAR) satellite data in arid and semi-arid terrains, Antarctic, Arctic and tropical environments. 
  • 1.4K
  • 10 Nov 2020
Topic Review
Bradoriids and the Cambrian Diversification
Bradoriids, among the earliest arthropods to appear in the fossil record, are extinct, ostracod-like bivalved forms that ranged from the early Cambrian to the Middle Ordovician. Bradoriids are notable for having appeared in the Cambrian fossil record before the earliest trilobites, and considering their rapid ascent to high genus-level diversity, provide key data for our understanding of the evolutionary dynamics of the Cambrian Explosion. This paper presents a broad review of bradoriid paleobiology. 
  • 1.4K
  • 29 Oct 2020
Topic Review
Mineralogy and Geochemistry of Ferromanganese Crusts
Late Pleistocene–Holocene rocks from the western part of Cocos-Nazca Spreading Centre (C-NSC) include ferromanganese crusts that elucidate the geochemistry and mineralogy of a deep-sea geological setting. Geochemical, mineralogical and petrological signatures indicate complex formation influenced by mild hydrothermal processes. These crusts consist mostly of mixed birnessite, todorokite-buserite, and Mn-(Fe) vernadite with traces of diagenetic manganates (asbolane), Fe-oxides and oxyhydroxides or hydrothermally associated and relatively pure Mn-oxyhydroxides (manganite). The average Mn/Fe ratio is 2.7, which suggests predominant mixed hydrogenous-early diagenetic crusts with hydrothermal influences. The mean concentrations of three prospective metals (Ni, Cu and Co) are low: 0.17, 0.08 and 0.025 wt %, respectively. The total content of ΣREY is also low, and ranges from 81 to 741 mg/kg (mean 339 mg/kg).
  • 1.4K
  • 27 May 2022
Topic Review
Geodiversity and Geoconservation in Central America
Central America is located in a dynamic region where tectonics and volcanism together with the tropical climate and its diverse vegetation have shaped the landscapes. 
  • 1.4K
  • 06 Jan 2022
Topic Review
Diamond-Bearing Ophiolite
Ophiolites are fragments of ancient oceanic crust and upper mantle, which is created at ocean spreading ridges and then emplaced on land. Ophiolite-hosted diamond discovered in ophiolitic peridotite and chromitite is considered to be a new type that has been named an ophiolite-type by Yang et al., in 2011. 
  • 1.4K
  • 22 Nov 2021
Topic Review
Polar Forests of the Cretaceous
Cretaceous polar forests were temperate forests that grew at polar latitudes during the final period of the Mesozoic Era, known as the Cretaceous Period 145–66 Ma. During this period, global average temperature was about 10 °C (18 °F) higher and carbon dioxide (CO2) levels were approximately 1000 parts per million (ppm), 2.5 times the current concentration in Earth's atmosphere. The abundance of atmospheric carbon dioxide had a very significant impact on global climate and Earth's natural systems as its concentration is considered one of the main factors in the development of a pronounced greenhouse Earth during the Cretaceous with a very low average global temperature gradient. As a consequence, high paleolatitudes in both hemispheres were much warmer than at present. This temperature gradient was partly responsible for the lack of continental ice sheets in polar regions. As a response to elevated global temperatures, the Earth's hydrologic cycle was significantly enhanced due to greater volume of moisture evaporation from the surface of the ocean. In turn, the absolute sea level during this time period stood at elevations much higher than the present level. Continental encroachment of seawater formed widespread shallow seas, including expanses of epeiric seas. An increase in surface area between shallow, warm epeiric seawater and the atmosphere permits higher evaporation rates and more precipitation at various latitudes, producing a more temperate global climate. A widespread temperate climate also had significant effects on high latitude ecosystems.
  • 1.4K
  • 02 Nov 2022
Topic Review
Core-Mantle Differentiation
Core-mantle differentiation is the set of processes that took place during the accretion stage of Earth's evolution (or more generally, of rocky planets) that results in the separation of iron-rich materials that eventually would conform a metal core, surrounded by a rocky mantle. According to the Safronov's model, protoplanets formed as the result of collisions of smaller bodies (planetesimals), which previously condensed from solid debris present in the original nebula. Planetesimals contained iron and silicates either already differentiated or mixed together. Either way, after impacting the Proto-Earth their materials very likely became homogenized. At this stage, the Proto-Earth was probably the size of Mars. Next followed the separation and stratification of the Proto-Earth's constituents, chiefly driven by their density contrasts. Factors such as pressure, temperature, and impact bodies in the primordial magma ocean have been involved in the differentiation process. The differentiation process is driven by the higher density of iron compared to silicate rocks, but the lower melting point of the former constitutes an important factor. In fact, once iron has melted, differentiation can take place whether silicate rocks are completely melted or not. On the premises of these plausible scenarios, several models have been proposed to account for the core-mantle differentiation following the stage of nebular formation of the solar system. They can be summarized into three mechanisms: 1) Percolation of iron alloy through silicate crystals; 2) Separation of metal from rock in a primordial magma ocean; 3) Migration of iron diapirs or dikes through the mantle.
  • 1.4K
  • 08 Nov 2022
Topic Review
Pedro JM Costa
My research focus on the study of coastal processes using geomorphological and sedimentological data coupled with physical and numerical modeling to understand morphological and sediment changes caused by natural hazards (e.g. tsunamis and storms) and their impacts on the environment. I also work on the establishment of provenance relationships in siliciclastic sediments, aspects of aeolian sediment transport, Antarctic soils, Mars geology and geoarchaeological studies.
  • 1.3K
  • 10 Nov 2020
Topic Review
Late Permian Coals
This study reports the mineralogy and geochemistry of the Late Permian C1 Coal from Bole and Laibin mines in eastern Yunnan, Southwestern China (C1 Coal in Laibin mine is composed of three layers termed B1, B2, and B3). The coals are characterized by medium-high ash yields and very low sulfur contents. Compared with average values of trace element concentrations in hard coals worldwide, the Bole and Laibin coals are enriched in V, Co, Cu, Zn, and Se, which were mainly derived from the sediment-source region of the Kangdian Upland. Major minerals in the coal samples and roof and floor strata include quartz, interstratified berthierine/chamosite (B/C), as well as kaolinite, mixed layer illite/smectite, calcite, pyrite, and anatase. Unlike a pure chamosite, the 7 Å peak of interstratified B/C is sharp and narrow, while the 14 Å peak is broad and weak, or absent in some coal samples. Interstratified B/C was largely precipitated from low-temperature Fe-rich and Mg-rich hydrothermal fluids or, in some cases, is an alteration product of kaolinite. Secondary phases of quartz, calcite, pyrite, kaolinite, chalcopyrite, gypsum, and REE-phosphates in the coal samples are the dominant authigenic minerals formed at syngenetic and early diagenetic stages. Four intra-seam partings in C1 Coal, B1, and B3 layers are identified as tonsteins derived from felsic volcanic ashes. These tonsteins consist mainly of cryptocrystalline kaolinite with graupen and vermicular textures, and minor amounts of high-temperature quartz, zircon, apatite, monazite, and anatase. The floor of the C1 Coal in the Bole mine is a tuffaceous claystone and consists of altered high-Ti basalt volcaniclastics, characterized by high concentrations of Zr, Nb, V, Co, Cu, and Zn, low Al2O3/TiO2 ratio (~4.62), high Ti/Y ratio (~900), enrichment of middle rare earth elements, and positive Eu anomalies.
  • 1.3K
  • 19 Jan 2021
Topic Review Peer Reviewed
Physical-Chemical Properties of Nano-Sized Phyllosilicates: Recent Environmental and Industrial Advancements
Phyllosilicates are common minerals that include the most widely known micas and clay minerals. These minerals are found in several natural environments and have unique physical-chemical features, such as cation exchange capacity (CEC) and surface charge properties. When phyllosilicates are nano-sized, their physical-chemical properties are enhanced from those of the micro-sized counterpart. Because of their unique crystal chemical and physical-chemical features, kinetics, and particle size, nano-sized clay minerals (i.e., kaolinite, montmorillonite/illite) and micas (i.e., muscovite) are of great interest in several fields spanning from environmental applications to engineered materials. This paper aims to overview the recent developments of environmental protection and technological applications employing nano-sized natural micas and clay minerals. Emphasis is given to the role that the unique physical-chemical properties of montmorillonite, vermiculite, kaolinite, and muscovite play in nanoparticle formulations, manufacture, and technical performance.
  • 1.3K
  • 06 Dec 2023
Topic Review
Geological Structure and Tectonic Complexity of Northern Thessaly
Knowing the rich presence of active faults in northern Thessaly and the lack of any significant seismic activity since at least the mid-1940s, the 2021 seismic sequence did not surprise people. What did surprise people was the fact that (i) despite the great knowledge of the neotectonic faults in the area, the causative faults were unknown, or almost unknown; (ii) the direction of the 2021 faulting was different than the expected, and given that the focal mechanisms showed almost pure normal dip-slip motion, the extensional main axis was also different than the one known for this area; and (iii) besides the co-seismic ruptures that occurred within the Domeniko-Amouri basin and along the Titarissios River valley, there is evidence of rupturing in the alpine basement of Zarkos mountains. 
  • 1.3K
  • 15 Nov 2022
Topic Review
Geochemical Characteristics of Oceanic Carbonatites
The occurrence of carbonatites in oceanic settings is very rare if compared with their continental counterpart, having been reported only in Cape Verde and Canary Islands. This entry provides an overview of the main geochemical characteristics of oceanic carbonatites, around which many debates still exist regarding their petrogenesis.
  • 1.3K
  • 26 Mar 2021
Topic Review
Microorganisms in the Nucleation of Carbonates
Microbially induced carbonate precipitation (MICP) is an important process in the synthesis of carbonate minerals, and thus, it is widely explored as a novel approach with potential for many technological applications. The processes and mechanisms involved in carbonate mineral formation in the presence of microbes are not yet fully understood. This research covers the current knowledge regarding the role of microbial cells and metabolic products (e.g., extracellular polymeric substances, proteins and amino acids) on the adsorption of divalent metals, adsorption of ionic species and as templates for crystal nucleation. Moreover, they can play a role in the mineral precipitation, size, morphology and lattice. By understanding how microbes and their metabolic products promote suitable physicochemical conditions (pH, Mg/Ca ratio and free carbonate ions) to induce carbonate nucleation and precipitation, the manipulation of the final mineral precipitates could be a reality for (geo)biotechnological approaches. The applications and implications of biogenic carbonates in areas such as geology and engineering are presented and discussed in this research, with a major focus on biotechnology.
  • 1.2K
  • 03 Jan 2023
Topic Review
Adelaide Superbasin
The Adelaide Superbasin is a series of geologically related rift to passive margin sedimentary basins formed during the Neoproterozoic to Cambrian. They are located at the south-eastern margin of Proterozoic Australia.
  • 1.2K
  • 18 Apr 2022
Topic Review
Global Isotopic Hydrograph Separation
Isotopic Hydrograph Separation (IHS) is a novel research field that has shown a great shift in separating runoff into pre-event and event water throughout its production lifetime.
  • 1.2K
  • 24 Sep 2021
Topic Review
Lake-Level Fluctuations
Recent decades of warmer climate have brought drying wetlands and falling lake levels to southern Alaska. These recent changes can be placed into a longer-term context of postglacial lake-level fluctuations that include low stands that were as much as 7 m lower than present at eight lakes on the Kenai Lowland. Closed-basin lakes on the Kenai Lowland are typically ringed with old shorelines, usually as wave-cut scarps, cut several meters above modern lake levels; the scarps formed during deglaciation at 25–19 ka in a kettle moraine topography on the western Kenai Lowland. These high-water stands were followed by millennia of low stands, when closed-basin lake levels were drawn down by 5–10 m or more. Peat cores from satellite fens near or adjoining the eight closed-basin lakes show that a regional lake level rise was underway by at least 13.4 ka. At Jigsaw Lake, a detailed study of 23 pairs of overlapping sediment cores, seismic profiling, macrofossil analysis, and 58 AMS radiocarbon dates reveal rapidly rising water levels at 9–8 ka that caused large slabs of peat to slough off and sink to the lake bottom.
  • 1.2K
  • 25 Apr 2022
Topic Review
Soil in Atsbi Wenberta
The soils of the Atsbi Wenberta woreda (district) in Tigray (Ethiopia) reflect its longstanding agricultural history, highly seasonal rainfall regime and relatively low temperatures. The northern part of the district is on the high uplifted Atsbi Horst (with metamorphic rock and consolidated Palaeozoic fluvio-glacial deposits) , whereas the southern part is dominated by the Des’a forest on Antalo Limestone. In between there is the fluvial landscape of Hayqi Meshal. Particularities in the southern part of the district are soil catenas on intervening plains behind tufa dams and in a polje.
  • 1.2K
  • 30 Sep 2022
Topic Review
Gas Emissions from Arctic Permafrost
The active emission of gas (mainly methane) from terrestrial and subsea permafrost in the Russian Arctic has been confirmed by ample evidence. A generalization and some systematization of gas manifestations recorded in the Russian Arctic is carried out. The published data on most typical gas emission cases have been summarized in a table and illustrated by a map. All events of onshore and shelf gas release are divided into natural and man-caused and the natural ones are further classified as venting from lakes or explosive emissions in dryland conditions that produce craters on the surface. a description of the observed man-caused gas manifestations associated with the drilling of geotechnical and production wells in the Arctic region is given.
  • 1.2K
  • 29 Oct 2020
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