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Abstract "Heft 10"

Freiburger Bodenkundliche Abhandlungen

Schriftenreihe des
Institut für Bodenkunde und Waldernährungslehre
der Albert-Ludwigs-Universität Freiburg i.Br.
Schriftleitung: F. Hädrich

Heft 10

Helio Olympio da Rocha

Die Böden und geomorphologischen Einheiten der Region von Curitiba

Freiburg im Breisgau 1981

ISSN 0344-2691


Soils and geomorphological units in the region of Curitiba (Parana -Brazil)

The study presented pursues two main objectives:
a)    morphological and analytical characterization of soils from different parent materials to determine their genesis and their stages of weathering, as well as to place them in a classification system .
b)    investigation of the relationships between geomorphological units, mainly pediplains and pediments, and the occurence or distribution of different soil groups.
The mentioned relationships were investigated in two areas of the sediment basin of Curitiba, Parana, Brazil.
For the pedological characterization of the research areas 21 representative profiles, each showing a different stage in development and each occurring in a different topographic situation, were selected from various soil groups.
In addition to soil samples, rock samples from the Guabirotuba Formation were also collected. These samples represent the typical parent materials comprising the various geomorphological units. The soil and rock samples were analysed for their chemical, physical, and mineralogical properties then the soil were morphologically classified by profile descriptions in accordance with the guidelines of the "Sistema Brazileiro de Classifica-cao de Solos".
The following methods were used to analyse the soil materials: total content (HF/HC1O4); pedogenic oxide.  (Fe, Al, and Mn) extraction using dithionit-citrate, ammonium-oxalate, and sodium-pyrophosphate; exchangeable cations (Ca, Mg, and Al with KC1 and H+Al with calcium-acetate); clay minerals (x-ray diffraction and differential thermoanalysis); heavy minerals (determination in the 0, 2-0, 05 mm fraction using flotation with tetrabromethane and bromoform, identification and counting using a polarization microscope); particle size distribution (clay determination with the pipette method, sand determination with wet sieving, and silt determined as the difference).
The topographic situation or rather the geomorphologicai units were characterized by a description of the properties of the rock components and of the essential geomorphologicai structures such as pediplains, pediments, and erosion surfaces on slopes. These geomorphologicai units were differentiated through a combination of various criteria obtained from aerial photograph interpretations, from field surveys, and from the results of parent material analysis.
In addition topographic and geological maps were evaluated.  The typical geomorphologicai units of the research areas were derived from old pediplains.

6. 1 Geomorphological Units and Soil Formation
The significance of geomorphological units in soil analysis has already been emphasized in several studies, in which the necessity of an integrated investigation into both these areas has also often been stressed as both research branches have many aspects in common.
The investigation of the interrelationships between morphogenesis and pedogenesis can contribute to the use of small scale soil maps to support the the data obtained from areal photo  interpretation.  For Brazil this aspect has an especial significance since general soil maps of varying intensity have already been drawn up for various regions of the country. The optimum utilization of the land use capabilities of such regions is necessarily based upon the evaluation of small scale soil maps.
The research area, i. e. the environs of Curitiba, is part of the first high plateau of Parana, in which several older erosion levels, usually pedi-plain surfaces,  can be demonstrated (Pd 2, Pd 1).  The orographically lowest (and most recent) pediplain surface Pd 1 is the so called 'Curitiba surface'. The investigations here presented were carried out within the boundaries of this pediplain surface and its respective pediment surface or erosion levels.
The origin of the erosion and deposition layers in the region of Curitiba must be traced back to the interplay between two mainly quaternary morphogenetic processes. In semi-arid climatic phases (glacial) morphogenesis was distinguished by mechanical re-deposition processes resulting in a topographical leveling of the region. In warm, humid climatic phases (interglacial) chemical weathering and gully erosion predominated, producing a landscape characterized by erosion processes (BIGARELLA and SALAMUNI, 1959, 1962).
Another factor influencing the surface configuration of this region is the tectonic faults in the rock series there (MARINI, 1967). The recurrent changes in climate and in morphogenetic processes brought about an erosion caused sinking and structuring of the former pediplains, esp. the Pd 1 pediplain which today ocurrs only as a residual pediplain surface.
After erosion of the sediments of the Pd 1 pediplain during humid climatic conditions, two pediment-like surfaces (P 2 and P 1) developed in a lower lying erosion level of the old Pd 1 pediplain. The formation of this pediment ocurred during different semiarid climatic phases. However, the P 2 pediment surface is somewhat older and higher. In some places it reaches the level of the Pd 1 pediplain and can therefore often be confused with this in the field. The pedisediment material of the P 2 pediment can be correlated with that of the residual pediplain. Similarly, the material of the P 1 pediment is related to the components of Pd 1 and P 2.
In recent times under prevailing warm humid climatic conditions, the pediment surfaces were again morphologically re-structured by intense gully erosion. Since the erosion base in the region around Umbara is lower than that of Canguiri, the effect of gully erosion in the former was more pronounced so that only island remnants of the pedisediment material remain The soil forming substrates of the geomorphological units in the areas under investigation are comprised of the following: clays,  clays with arkose, arkose, migmatites, pedisediments,  colluvium and alluvium. The pedisediments (compare chap.  5.1.2) are designate as those which were transported during semi-arid climatic conditions and which contributed to pediment formation. Their development history and material properties enable their differentiation from colluvial material which are usually younger and more intensely mixed and weathered, moreover, the colluvia in the study area are often separated from the underlying relict soil formations in situ or from underlying parent material by stone lines. The above outlined history of the study area is reflected in the distribution and formation of the soils there.
Intensively weathered latosols are characteristic of the remnants of the Pd 1 pediplain surfaces. On the lowest lying pediment surfaces (P 2), however, which were not subjected to such intense erosion in recent times, are found correspondingly less developed latosols especially around the area of Canguiri. Soil development on those landscape structures subjected to erosion in recent times or rather formed by erosion processes (sunken pediment surfaces, erosion slopes) resulted in the formation of soils with a B-textural horizon and cambisols. Here one must distinguish between soils with a B-textural horizon on the pediment surfaces which are further along in their development and those less developed soils of similar type on erosion slopes.  On the other hand, the ocurrence of cambisols is practically limited to erosion slopes, whereby the type of parent material primarily determines whether a cambisol or a soil with a B-textural horizon will develop in comparable topographical positions.

6. 2 Chemical Properties of the Soils
The Titanium content (total analysis) is higher in the soils of the latosol group tha n in the other investigated soils. Marked differences, however, are found within this group. The soil variants developed from clay mixed with arkose contain the most Ti while the latosols from migmulite material contain the least.  The latosols are further characterized by low amounts of SiO2 and bases as well as a residual enrichment of Fe, Mn, and Al oxides. All investigated latosols show a dithionite-soluble iron: total iron (Fed : Fet ) ratio of over 0, 8. These high ratios are not only representative of latosols but also of soils with a B-textural horizon occurring on pediment surfaces.
This means that the supply of silicate bound iron in these soils is very low or rather that the weathering of the primary substance has proceeded very far, which is further expressed in a very low degree of iron oxide activity or in a low ratio (usually less than 0, 03) of amorphic Fe : dithio-nite-soluble Fe. Within the latosol group the soils originating from migma-tite materials have  the lowest Fe and Mn oxide contents. They are also distinguished from the other variants by low Ki values. In comparison to the latosols the soils with a B-textural horizon show higher quantities of bases and SiO2. This is essentially due to their low degree of weathering as compared to the latosols.
In the variants developed from clay with arkose, the contents of bases and SiO  are higher than in those stemming from migmatite material. Hence these differences reflect the typical properties of the respective parent rocks.
The quantities of Ti are lower in the soils with B-textural horizons than in the latosols. The Ti content is not correlated with the amounts of rutile, anatase, or titanite.
The cambisols are found on surfaces rejuventated by erosion. This circumstance is expressed in manifold physical, chemical, and mineralogical findings. In contrast to the latosols and the soils with a B-textural horizon, these soils show a markedly lower Ti content and higher Ki values.
The content of silicate bound iron is much higher in the cambisols than in all other soils studied. Within this group the contents of total iron are much lower for the variants arising from clay-arkose mixtures than for those from pure clay.
The cambisols are further characterized by high Feo : Fed  ratios, which in accordance with the relatively low developmental stages of these soils, demonstrate a low degree of oxide crystallization. Along with other analysis results this shows these soils to be intermediate stages between cambisols and latosols.
The highest manganese (Mn) content were found in the C-horizons of the cambisols. Abnormally high Mnt and Mnd contents appear in profile 16 due to above average higher contents of Mn in the parent materials (clays of the Guabirotuba Formation).
Latosols,  soils with B-textural horizons, and cambisols can also be significantly differentiated in respect to their exchange capacity, and the base saturation of the mineral soil. Both values decrease considerably from cambisols to latosols.
All investigated latosols have an exchange capacity less than 13 mval/ 100 g clay. The soils with B-textural horizons forming from migmatite material show a similarly low exchange capacity (e. g. profile 15). The exchange capacity of the other variants of soils with B-textural horizons average around 24 mval/100 g clay.  Corresponding to their higher content of 3-layered clay minerals, the cambisols have the highest exchange capacity. Although their saturation of bases is low, the majoritiy of the latosols do not possess any "alico" property, i. e. the saturation of the sorption complex with exchangeable Al in the B-horizon is less than 50 %. The amount of bases here is sufficient to produce a considerable saturation of the inherently low exchange capacity. In contrast most of the soils with B-textural horizons and most of the cambisols demonstrate an "alico" character despite higher supplies of bases.

6. 3  Heavy Mineral Spectra and Contents in the Soils
The soils developed from clay and arkose mixtures show a heavy mineral spectrum in which zirkon is dominant and in which tourmaline, anatase and disthene are of lesser importance. The heavy mineral composition of profile deviates from this typical pattern due to the low amounts of arkose in the clay parent material. The soils forming from clay have similar zirkon and tourmaline contents, with disthene appearing in average quantities. Sometimes epidote dominates the heavy mineral spectrum, e. g. in profile 11 and in the C-horizon of profile 6, which also contains considerable amounts of zirkon and tourmaline. Further observations show lower contents of extremely stable heavy minerals in the clays and in alluvial material than in other parent materials. In the soils forming from migma-tites the heavy mineral spectrum is dominated by extremely stable heavy minerals, especially zirkon followed by anatase. Tourmaline and epidote are present in low quantities, the latter appearing more often in regolith (weathered migmatite).
The alluvial material presents the greatest diversity in heavy minerals.
The results of heavy mineral analyses in connection with the total analysis prove to be very useful for the differentiation of the soils according to their parent materials. In many cases seemingly contradictory results of chemical analysis could be explained by the composition of the heavy mineral spectrum.

6. 4  Clay Minerals of the Soils
The clay mineral spectrum of the soils of the pediment surfaces is dominated by kaolinite followed by gibbsite.
Mixed layer minerals and clay minerals of the chlorite-vermiculite type are also present, however are of minor importance. Illite appears in small quantities in the subsoil of the latosols and soils with B-textural horizon forming from clay-arkose material. The soils of the erosion slopes contain lower amounts of kaolinite; gibbsite appears in the surface soil while illite and montmorillionite predominate  at greater dephts.
The appearance of kaolinite and gibbsite type clay minerals in association with mixed layer minerals of the chlorite-vermiculite group in heavily weathered materials can be explained by the erosion caused admixture of younger material.

6. 5  Soil Texture
In general the latosols can be classified as clay in particle size. The variations developed from clay pedisediments in the Canguiri region are deeper and show a greater morphological uniformity than the latosols derived from migmatites in the Umbara region. The soils with arkose admixtures in the parent material present a coarse sand:  fine sand ratio greater than 1, while the soils derived from clay show a corresponding ratio that is always less than 1.  The relationship silt : clay proves very useful for the estimation of the degree of weahtering of the various parent materials.
Hence, the clay pedisediments and the pedisediments from migmatite material, which constitute the parent substrates for the latosols show a silt : clay ratio ranging between 0. 2 3 and 0. 24, while the less weathered substrates demonstrate a higher quotient. This ratio is 1. 98 in regoliths from weathered migmatites, 0. 50 in the colluvia and 0. 33 in the clays.

6. 6  Systematic Classification of the Soils
The systematic classification of the soils (comp. Tab. 14) is in accordance with the criteria of the Brazilian classification system and also with the 7th Approximation or rather FAO classification (comp. Tab. 13 and 14).
Tab. 14: Classification of Soils (comp. also Tab. 13)

Profil Brasilianische Klassifikation " 7 - Aproximation'' FAO/UNESCO
P 3 Latosol Vermelho Escuro Haplohumox Rhodic Ferralsol
P 4-5-8-14
Latosol Vermelho Escuro Sombrihumox Rhodic Ferralsol
P 9 Latosol Vermelho Escuro Haplohumox Humic Ferralsol
P 19 Latosol Vermelho Amarelo Haplohumox Humic Ferralsol
P 18-20 Latosol Vermelho Amarelo Haplohumox Orthic Ferralsol
P 1-2-10-12 Rubrozem Palehumult/ Haplohumult
Humic Acrisol
P 15-17-21 Podzolico Vermelho Amarelo Palehumult Humic Nitosol
P 16 Podzolico Vermelho Amarelo Argiudoll Luvic Phaeozem
P 6-7-11 Cambisol Haplumbrept Humic Cambisol

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