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Importance of minerals and rocks

More than 70% of the crust is formed by oxygen and silicon. As a result, the silicates are the predominant mineral group, constituting more than 90% of the crust volume. Of the more than four thousand known minerals, approximately ten are considered rock-forming minerals, because they are essential constituents of the most abundant rocks in the terrestrial crust. This is due to the fact that the crust is almost composed by only ten chemical elements (Figure 1).
Figure 1.Most abundant chemical elements in the terrestrial crust (Adapted from Andrade et al., 2009).
The minerals are formed by different types of natural processes that mainly involve: the crystallization from magmas or from saturated aqueous solutions, solid state reactions between minerals, and the degradation of pre-existent minerals due to the reaction with fluids. The magmatic crystallization is the product from the cooling of magmas (liquids of normally silica composition). Such crystallization is not homogeneous, and minerals stable at higher temperatures crystallize first. As the temperature decreases, other minerals crystallize according to the crystallization sequence, referenced as the Bowen’s series (Szabo et al., 2009) (Figure 2).
The heterogeneity of rocks is of fundamental importance for the planet evolution, because it is expressed not only in the interior zoning, but also in the difference that exists between the continental and the oceanic terrestrial crust. The continental crust is formed essentially by aluminous silicates (global composition similar to granite), with thickness of 25 to 50 km. The oceanic crust presents thickness of 5 to 10 km and is composed essentially by basalt, formed by magnesium silicates and being denser than the continental crust due to its higher iron contents. The collision between plates is always accompanied by a deformation of the rocks present in the shock area, which results in the formation of new plutonic and volcanic rocks.
The rocks are grouped according to their origin, in igneous or magmatic, sedimentary and metamorphic types. The igneous rocks constitute approximately 80% of the lithosphere volume and result from the crystallization of minerals from the cooling of the magma between 1200 and 400°C. There are two main types of igneous rocks: extrusive or volcanic and intrusive or plutonic. The extrusive igneous rocks are originated by extrusion of magma to the terrestrial crust surface, through volcanoes or cracks in the crust. Intrusive igneous rocks are produced by the crystallization of magmas that did not reach the surface of terrestrial crust. Generally, these rocks undergo a slower cooling as compared to the extrusive igneous rocks that are chemically equivalent, also presenting a higher content in volatile constituents.
Finally, in the study of rocks chemical composition, one of the most important parameters is the silica content (weight percentage of SiO2). The igneous rock may be acidic (silica content above 66%), intermediate (silica content between 52 and 62%), basic (silica content between 45 and 52%) and ultrabasic (silica content lower than 45%) (Szabo et al., 2009) (Figure 2). Among them, the granite, classified as acidic, and the basalt, classified as basic, are the two types of igneous rocks more representative of terrestrial crust, being highlighted due to its abundance.

Geology of Rio Grande do Sul

The origins of the current geomorphological configuration of Rio Grande do Sul State (RS) are related to more than one an approach and separation cycleof continental mass (craton) through the movement of continental plates. The distribution of geomorphological provinces begins to be explained from the Pre-Cambrian period between 450-650 million years ago, when the ancient masses of the planet were aggregated as Pangea.
The geological evolution from the beginnings of the planet Earth until the Carboniferous period is recorded in the rocks of the current province of Escudo Sul-rio-grandense. From this period the process of subsidence begins in the region where RS is currently partforming a wide topographic depression, which is filled by sediments, giving rise the sedimentary Paraná basin. In the current province of Depressão Periférica is possible to observe part of these sediments. Other part of these sediments is covered by volcanic rocks of the current province of Planalto do RS (Figure 3).
The sinking of the sedimentary basin increased slowly as the deposited sedimentary layer mass pressure was intensified, which continued for about 140 million years, reaching a considerable thickness of sedimentary rocks up to 1 km in RS. The movement of tectonic plates separation triggered a volcanism with numerous fissures, with lavas from basaltic to dacitic origin, and many magma extrusions occurred in an interval less than ten million years. The volcanic rocks covered an area of approximately 1.3 million km2, denominated as the province of Planalto do RS.
The continuity of volcanism caused this crevice to widen and allow the entrance of seawater, originating the Atlantic Ocean and the continents of South America and Africa, in a process that persists until this moment through the expansion of the plates. Approximately 65 million year ago, in the beginning of the Cenozoic period, shortly after the fissures volcanism and the separation between South America and Africa, the shoreline was cropped and formed by basaltic, granitic and metamorphic rocks of the Escudo Sul-rio-grandense. Thus, the coast is the geologically younger region of the RS, originated from successive sea level oscillations which began after the end of the Tertiary period and in the Quaternary period, establishing the current province of the Planície Costeira.

Escudo Sul-rio-grandense

The Escudo Sul-rio-grandense (ESRG) represents the basement of RS, located in the center-south region, being the result of the orogeny that promoted the union of Neoproterozoic lands, giving rise to the Western Gondwana Paleocontinent. The ESRG has about 65,000 km2 of area in RS (Chemale Jr., 2000) and is delimited to the North, West and Southwest by the Paraná Basin, and to the East by the Pelotas Basin, also known as Província Costeira of the Rio Grande do Sul. The ESRG’s rocks are distributed in undulate to strong undulate relief, from an altitude lower than 100 to 500 m. The ESRG is also called a crystalline basement, because it forms the base that supports other geological formations, and because of the high degree of consolidation of its rocks.
The ESRG is predominantly formed by igneous and metamorphic rocks, such as granite, gneisses, shales and mafic and ultramafic volcanic rocks.
Developed from granite and gneisses, in reliefs varying from soft to strong undulate, occur soil types from the classes Argissolos Vermelhos/Vermelho-Amarelos (Red and Red-Yellow Ultisols), Cambissolos (Inceptisols) and Luvissolos Háplicos (Alfisols) and Neossolos Litólicos/Regolíticos (Entisols). Also occur soil types of higher chemical fertility, developed from shales, as Neossolos Regolíticos (Entisols) and Luvissolos Crômicos (Alfisols), and from andesits, as the Chernossolos Ebânicos (Molisols) (Brasil, 1973; Streck et al, 2008).

Depressão Periférica

The Depressão Periférica province is characterized by low altitude lands located at the foothills of the Planalto province, presenting flattened relief of smooth hills with few outcrops and fluvial plains. This unity is formed by sedimentary rocks of Paraná Basin (sandstones, siltstones and argillites), which originated from the deposition of sediments with varied composition and granulometry, which were gradually compacted and lithified.
The Depressão Periférica belongs to an extensive corridor that links the RS from West to East. Hills of up to 200 m are common in this area and represent the old escarpment line of Serra Geral. In this way, this geomorphological province presents a complex succession of different sedimentary rock types, eventually exposed as a function of the removal of overlying rocks. In the Southeast segment of this province, soils rich in smectites and with higher chemical fertility occur, as Planossolos (Ultisols or Alfisols) and Luvissolos Háplicos (Alfisols), Chernossolos Argilúvicos (molisols) and Vertissolos Ebânicos (Vertisols). In the South-North and West-East segments, the Planossolos Háplicos (Ultisols or Alfisols) predominate in the flood plains, associated to the Neossolos Flúvicos (Entisols) and Gleissolos Háplicos (Entisols). In other positions of the landscapes, dominated by hills, the Argissolos (Ultisols) predominate, which transition from Argissolos Bruno-Acinzentados (Ultisols) in the lower altitude to Argissolos Vermelhos (Ultisols) in the higher altitude (Brasil, 1973; Streck et al, 2008).


The Planalto province covers the northern half and a portion of Southwest of RS. This province is formed by a succession of levels of volcanic basaltic and rhyolitic rocks from the Serra Geral. These rocks are situated in a practically tabular relief, excavated by rivers in several points, forming deep scarps and valleys, mainly in the Serra Gaúcha region. The northeast region of the RS, named the Campos de Cima da Serra region, is dominated by acidic volcanic rocks and have altitudes of up to 1400 m, gradually falling in a westerly direction to less than 100 m in the Campanha region.
The sequence of basaltic spills in this area is identified in the form of baselines in the slope of the valleys. This expressive volcanic manifestation dating from the Cretaceous period (130 to 140 million years) interrupted the sedimentation of the Paraná Basin. Thus, volcanic lava spills covered much of the sediments of the Paraná Basin, exposing only the portion related to Depressão Periférica region.
The first volcanic spills present, in general, basaltic composition with predominance of elements such as Fe, Ca and Mg; whereas the most recent spills present rhyolitic composition, with higher silica contents and lower Fe, Ca and Mg contents. Intermediary rock types of dacitic composition also occur. Thus, the northeast region of RS presents basaltic spills at lower altitudes, forming the bases and slopes of the hills, while the rhyolitic spills are identified in the higher altitudes, usually above 700 m (Streck et al., 2008). In the intervals between the successive lava spills some sandy eolic sediments are observed and constituted intercalated sandstones, denominated Arenito Botucatu.
In the Campos de Cima da Serra region (Annex 1), located in northeast of RS with smooth to strong wavy relief is considered as the coolest and rainy region predominate acidic soils (gibbsitic/kaolinitic-goethitic) developed from rhyolite, as Cambissolos Húmicos (Inceptisols) and Neossolos Regolíticos/Litólicos Húmicos (Entisols). In the East-West segment of Planalto region with basaltic lithology with smooth wavy to wavy relief, predominate the Latossolos (oxisols), which vary between Latossolos Brunos (kaolinitic-goethitic oxisols) and Latossolos Vermelhos (kaolinitic-hematitic oxisols). In the same sense, the Oxisols vary from clayey (East) in the higher altitudes to the sandy (Center-West) as the altitude decreases, due to the increase of Arenito Botucatu (intercalated sand stone) influence as soil source material. In the Fronteira Oeste and Campanha regions, hotter and less rainy, soils of high chemical fertility occur, as Neossolos Litólicos/Regolíticos Eutróficos (Entisols), generally situated in a smooth wavy relief, with Chernossolos (molisols) and Vertissolos Ebânicos (Vertisols), in flatter areas (Brasil, 1973; Streck et al, 2008).

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Planície Costeira

The Planície Costeira province is located at the East of RS, covering the entire coastal strip of the state and some areas of the Porto Alegre metropolitan region. This region is formed by unconsolidated marine and fluvial-lacustrine sedimentary units, belonging to the Pelotas Basin, and is characterized by a very low relief (below 40 m above sea level), extensive wetlands, lakes and lagoons, being highlighted the Laguna dos Patos, the Lagoa Mirim and the Lagoa Mangueira.
The unconsolidated sand, silt and clay sediments were deposited from the end of the Tertiary Period and during the Quaternary Period (less than 2 million years ago). The sedimentation of this material is a characteristic of coastal environment under the influence of advancement and retreat sea level events, possibly related to interglacial and glacial periods, which formed the beach environment, with lagoons and sandy strips, and shallow water marine environment. The sediments of Planície Costeira region compose the emerged portion of a sedimentary basin denominated Pelotas Basin, deposited from the Period Cretaceous. The soils in the Planície Costeira province are distributed in terraces which correspond to different altitudes above sea level. In the superior terraces, occur Argissolos Vermelhos/Vermelho-Amarelos (Ultisols). In intermediate terraces, occur Plintossolos (Plintosols) and Planossolos Háplicos (Alfisols or Ultisols), followed by Planossolos Háplicos/Nátricos and Gleissolos Melânicos (Entisols) on the lower terraces. In flooded areas, near the lakes and canals, are founded Organossolos Háplicos (Histosols), while in areas near the coast are founded Neossolos Quartzarênicos (Entisols) (Brasil, 1973; Streck et al, 2008).

Climate of Rio Grande do Sul

Of the natural elements, the ones that most influence the formation of a landscape are the climate and the relief, because they interfere and conditionate the other elements and they are also influenced by them. Brazil, a tropical and subtropical country of great territorial extension, presents a geography marked by diversity. According to Ab’Saber (1969), occurs six big natural landscapes in Brazil: the Amazonian Domain; the Caatinga’s Domain; the Cerrado’s Domain; the Mares de Morro’s Domain; the Araucária’s Domain and the Pradaria’s Domain (Pampa Biome) (Figure 4).
Situated in the North of Brazil, the Amazonian Domain is the continental biome of greater extension, with 49.29% of Brazilian territory (IBGE, 2004). This domain is characterized by the existence of innumerous rivers and by an abundant annual precipitation (2,500 mm yr-1). In this domain, the occurred soils are basically the Latossolos (Oxisols), Argissolos (Ultisols) and Plintossolos (Plintosols). The Cerrado’s Domain is the second higher Brazilian domain in territorial extension, where predominate the Latossolos (Oxisols), with color varying from red and yellow.
The Brazilian Southern, differently from the Amazonian region and the rest of the country, is inserted in a subtropical environment, with high annual average precipitation and lower temperatures as compared to the other Brazilian regions. In the South region, two important morphoclimatic domains occur: the Pradaria’s Domain and the Araucária’s Domain, particularly characterized as a function of vegetation type. The Pradaria’s Domain, also known as Pampa Biome or Campanha Gaúcha, is situated in low altitudes with smooth wavy relief and covered by herbaceous vegetation of prairie, where there is the predominance of relatively fertile soils, as Chernossolos (Molisols) and Vertissolos (Vertisols) (Streck et al., 2008). On the other hand, the Araucária forest is a vegetal formation characterized by the presence of Araucaria angustifolia, with altitudes varying from 500 and 1,300 m in the three Southern states (Silva, 1996). The Araucária forest is an ecosystem of Mata Atlântica, which extends through the States of Paraná, Santa Catarina and Rio Grande do Sul and some parts of the States of São Paulo and Minas Gerais.
The soils of such domain (Araucária’s Domain) are composed mainly by Latossolos (Oxisols), Cambissolos (Inseptisols) e Neossolos Litólicos/Regolíticos (Entisols).
The climate factor is a complex conception constituted by a series of climatic variables which can be measured, as temperature, precipitation and evapotranspiration. In this way, the determination of such variables allows the expression of a specific climate condition. Thus, the climate is one of the most important soil formation factors, affecting the leaching, the moisture, the organic matter content and quality and the rates of related processes and reactions. Consequently, climate also has an effect in the depth of soil profiles, as well as in the texture and in the mineralogical composition formed.
Mota (1953) elaborated a study on Rio Grande do Sul’s climate according to the Köppen classification (1936) and concluded that the climate is classified in the fundamental type “Subtropical (or almost Temperate)” of Cf formula, with the Cfa and Cfb variants, being:
Cfa – Humid subtropical climate without drought, where the temperature of the hottest month above 22°C and of the coolest month ranging from 3 to 18°C; Cfb – Temperate climate, where the hottest month presents a temperature below 22°C.
The average annual temperature of RS is 18°C, varying from 16 to 19.4°C, depending on the region (Figure 5). The higher temperatures are observed in the Pampa, in the Missões and in the Depressão Central regions, while the lower ones occur in the Campos de Araucárias, in the Encosta Superior do Nordeste and in the Planalto Médio regions. The average monthly temperature varies from 9.9 to 13.6°C in the coolest month, normally in July, and 22.3 to 26.1°C in the hottest month, January.
More recently, Maluf (2000) suggested a new climate classification for the RS, where three climate classes are distributed in the different regions: Subtropical (ST), Subtemperate (STE) and Temperate (TE). These classes were delimited considering the average annual temperatures (Ta) and the average monthly temperature of the coolest month (Tf). This ordination also presupposes the insertion of dry season to obtain the local climatic type.
A climate variable of expressive importance for understand the pedogenesis is the difference between average precipitation and average evapotranspiration (temperature result) in the different regions of interest (Figure 5). Even considering the climate gradient in the East-West axis of RS, the 1:1 clay mineral kaolinite appears as the predominant mineral in the soils. However, in the West region, the lower leaching becomes the weathering processes less intense, resulting in the formation of 2:1 clay minerals, as smectite and vermiculite. In the East region, the weathering conditions are more intense, promoting a higher soil desilication and reducing the 2:1 clay mineral content, as compared to the kaolinite, and increasing the iron oxides contents, as hematite and goethite. The occurrence of aluminum oxides, as gibbsite, is restricted to soils located in the Araucária’s Domain (Caner et al., 2014), where the leaching causes an intense desilication, similar to that verified in Central Brazil.

Table of contents :

6.1. Importance of minerals and rocks
6.2. Geology of Rio Grande do Sul
6.2.1. Escudo Sul-rio-grandense
6.2.2. Depressão Periférica
6.2.3. Planalto
6.2.4. Planície Costeira
6.3. Climate of Rio Grande do Sul
6.4. Great pedogenetic processes of southern Brazil
6.4.1. Soil weathering and formation
6.4.2. Reactions involved in the weathering of silicate
6.5. Origin and evolution of pedogenic minerals
6.5.1. Study of the weathering profile: geopedological profile Measure of the alteration intensity
6.5.2. Alteration processes of soil clay minerals Mineralogical modifications in the pedoenvironment
6.5.3. Soil response to Integrated Crop-Livestock Systems Soil clay minerals in the ICLS
6.6. Final considerations
7.1. Abstract
7.2. Introduction
7.3. Materials and Methods
7.3.1. Localization and classification of profiles
7.3.2. Characterization and environmental settings of sampled sites Climate and lithology Vegetation in the ecosystem context
7.3.4. Morphological Description and Sampling
7.3.5. Physical analysis
7.3.6. Chemical analysis
7.3.7. Mineralogical analysis
7.3.8. Weathering indexes
7.3.9. Microscopy
7.3.10. Fourier Transform Infrared Spectroscopy (FTIR)
7.4. Results
7.4.1. General properties of the soil
7.4.2. Chemical extractions
7.4.3. Mineralogy of the weathering profiles Diffraction and optical microscopy Diffraction of the clay fraction (< 2 μm) Fourier Transform Infrared Spectroscopy (FTIR)
7.4.4. Total chemical analyses and weathering indices
7.5. Discussion
7.5.1. Evolution of the pedogenic minerals
7.5.2. Alteration intensities and weathering índices
7.5.3. Environmental relevance and soil use
7.6. Conclusions
8.1. Abstract
8.2. Introduction
8.3. Material and methods
8.3.1. Soil selection, sampling and sample preparation
8.3.2. Chemical analyses
8.3.3. Mineralogical analyses
8.3.4. Statistical analysis
8.4. Results
8.4.1. General soil properties
8.4.2. Clay Mineralogy and submicrometric fractionation
8.4.3. No grazing (NG)
8.4.4. Intensive grazing (IG)
8.5. Discussion
8.6. Final Considerations
8.7. Conclusions


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