Genesis Of Areas Research Articles

Formation and degradation of textural pedofeatures in soils of ancient tropical coastal plains in southeastern Brazil

Textural features in soils are defined as having a distinct granulometric composition compared to the surrounding groundmass. Among these, clay coatings are found in various pedo-environments, covering a range of climatic conditions, from wetter regions to semiarid areas. This study aimed to understand how textural features in ancient coastal plain soils can reveal mechanisms of their pedogenetic evolution and how this relates to environmental transformations. Three soil profiles were studied at different points in a toposequence, representing the upper, middle, and lower thirds. The study area is located in the municipality of Seropédica, in the state of Rio de Janeiro, southeastern Brazil. Morphological, physical, chemical, mineralogical, and micromorphological analyses were conducted on the selected profiles. Acrisols, formed in free-draining conditions, were later transformed into Planosols due to base level oscillation and the percolation of brackish solutions through the soils. The pedogenetic model proposed in this study involves the following stages: i) Clay formation by in situ mineral weathering, mainly of phyllosilicates, with pseudomorphization of the structures. ii) Destruction of the pseudomorphized structures by pedoplasmation with proximal migration of clay and genesis of textural features of coating and filling. iii) Partial and episodic saturation of the base of the profile with solutions enriched in sodium of a fluvial-marine nature. iv) Dispersion of the clays, leading to the destruction of the textural features and soil micromass, accompanied by relative sand enrichment and E horizon formation. v) Local lowering of the surface and smoothing of the base of the slopes. This transformation model is unprecedented for the southeastern region of Brazil, increasing the evolutionary complexity of soil genesis in areas of ancient fluvial-marine plains.

ATMOSPHERIC SUSPENSIONS OF RUSSKY ISLAND (VLADIVOSTOK) DURING THE 3-YEAR SUPERVISION (2011-2013)

In this paper the results of research of particles of the atmospheric suspensions containing in a snow cover of the Russky Island (Vladivostok) first in the history of supervision, including in the territory of a Campus of Far East Federal University (seasons 2011/2012-2013/2014) are presented. Distribution of the particles of various sizes weighed in air and genesis in areas of the island differing with anthropogenous loading is revealed: campus of Far East Federal University, the bridge through the Eastern Bosphorus Strait and settlement the Channel. It is shown that in connection with increase of anthropogenous press of the Russky Island, its ecological state because of increase in the atmosphere of fractions nano - and microdimensional particles worsens.

Multiple origins of charnockite in the Mesoproterozoic Natal belt, Kwazulu-Natal, South Africa

Four different varieties of charnockitic rocks, with different modes of formation, from the Mesoproterozoic Natal belt are described and new C isotope data presented. Excellent coastal exposures in a number of quarries and river sections make this part of the Natal belt a good location for observing charnockitic field relationships. Whereas there has been much debate on genesis of charnockites and the use of the term charnockite, it is generally recognized that the stabilization of orthopyroxene relative to biotite in granitoid rocks is a function of low aH2O (± high CO2), high temperature, and composition (especially Fe/(Fe +Mg)). From the Natal belt exposures, it is evident that syn-emplacement, magmatic crystallization of charnockite can arise from mantle-derived differentiated melts that are inherently hot and dry (as in the Oribi Gorge granites and Munster enderbite), as well as from wet granitic melts that have been affected through interaction with dry country rock to produce localized charnockitic marginal facies in plutons (as in the Portobello Granite). Two varieties of post-emplacement sub-solidus charnockites are also evident. These include charnockitic aureoles developed in leucocratic, biotite, garnet granite adjacent to cross-cutting enderbitic veins that are attributed to metamorphic-metasomatic processes (as in the Nicholson's Point granite, a part of the Margate Granite Suite), as well as nebulous, patchy charnockitic veins in the Margate Granite that are attributed to anatectic metamorphic processes under low-aH2O fluid conditions during a metamorphic event. These varieties of charnockite show that the required physical conditions of their genesis can be achieved through a number of geological processes, providing some important implications for the classification of charnockites, and for the interpretation of charnockite genesis in areas where poor exposure obscures field relationships.

Towards the quantitative modeling of pedogenesis — a review

The historical development of our pedogenetic model is reviewed, and trends or directions toward the future are discussed. Pedogenetic models are characterized with respect to relative degree of computation, complexity, and level of organization. These three characteristics are used as a framework for classification. Early qualitative models have well served the purpose of soil survey to describe the distribution of soils in landscapes. Further development of qualitative models will contribute to the understanding of soil genesis in areas where soil surveys are not completed. In the developed countries, however, the scientific questions have changed dramatically. Greater interest lies in understanding the physical and chemical processes of soil formation acting within relatively short time frames and assessing the interactions between natural processes and environmental change or anthropogenic impacts. Quantification of pedogenetic processes is a life-line to other environmental disciplines, and a mechanistic understanding would, in an ideal situation, describe and predict the behavior of a system for a limited number of years under changing environmental conditions. A proposed approach to mathematical simulation of the dynamic pedogenetic processes is to integrate soil physical, chemical, and other ecological system models into a quantitative pedogenetic model. Models may be developed as research tools in data-intensive studies at the pedon or horizon level, or for the purpose of simulating a soil system at the catena or soil region level. Specific kinds of pedogenetic models have specific implications with respect to the availability and spatial variability of the data needed for development and testing.

The Precambrian metavolcano-sedimentary sequence east of Ife and Ilesha/SW Nigeria. A Nigerian ‘greenstone belt’?

The metavolcano-sedimentary sequence east of Ife and Ilesha southwest Nigeria has previously been classified as a proterozoic mobile belt. Field observations indicate, however, that this sequence has a typical, for Archaean, granite-greenstone rock succession. Geochemical data could support this opinion. In spite of the lack of age determinations, it is possible to place these rock successions in the early Archaean. This new classification of the metavolcano-sedimentary sequence of the Ife-IIesha area is, therefore, of far-reaching economic importance. The known mineralizations of gold, cassiterite, niobite, tantalite and tungsten in this area and its surroundings call for further prospection, not only in southwest Nigeria, but also in the other mobile belt region of Nigeria. One important result is the fact that geochemical methods are a tool for the stratigraphic classification and rock genesis in areas with strong lateritic weathering or metamorphic overprint.