José Pereira de Queiroz Neto

Geochemistry of water and ground water in the Nhecolândia, Pantanal of Mato Grosso, Brazil: variability and associated processes

A distinctive feature of the Nhecolândia, a sub-region of the Pantanal wetland in Brazil, is the presence of both saline and freshwater lakes. Saline lakes used to be attributed to a past arid phase during the Pleistocene. However, recent studies have shown that saline and fresh water lakes are linked by a continuous water table, indicating that saline water could come from a contemporary concentration process. This concentration process could also be responsible for the large chemical variability of the waters observed in the area. A regional water sampling has been conducted in surface and sub-surface water and the water table, and the results of the geochemical and statistical analysis are presented. Based on sodium contents, the concentration shows a 1: 4443 ratio. All the samples belong to the same chemical family and evolve in a sodic alkaline manner. Calcite or magnesian calcite precipitates very early in the process of concentration, probably followed by the precipitation of magnesian silicates. The most concentrated solutions remain under-saturated with respect to the sodium carbonate salt, even if this equilibrium is likely reached around the saline lakes. Apparently, significant amounts of sulfate and chloride are lost simultaneously from the solutions, and this cannot be explained solely by evaporative concentration. This could be attributed to the sorption on reduced minerals in a green sub-surface horizon in the “cordilhieria” areas. In the saline lakes, low potassium, phosphate, magnesium, and sulfate are attributed to algal blooms. Under the influence of evaporation, the concentration of solutions and associated chemical precipitations are identified as the main factors responsible for the geochemical variability in this environment (about 92% of the variance). Therefore, the saline lakes of Nhecolândia have to be managed as landscape units in equilibrium with the present water flows and not inherited from a past arid phase. In order to elaborate hydrochemical tracers for a quantitative estimation of water flows, three points have to be investigated more precisely: (1) the quantification of magnesium involved in the Mg-calcite precipitation; (2) the identification of the precise stoichiometry of the Mg-silicate; and (3) the verification of the loss of chloride and sulfate by sorption onto labile iron minerals.

MINERALOGY AND GENESIS OF SMECTITES IN AN ALKALINE-SALINE ENVIRONMENT OF PANTANAL WETLAND, BRAZIL

Smectite formation in alkaline-saline environments has been attributed to direct precipitation from solution and/or transformation from precursor minerals, but these mechanisms are not universally agreed upon in the literature. The objective of this work was to investigate the mineralogy of smectites in the soils surrounding a representative alkaline-saline lake of Nhecolândia, a sub-region of the Pantanal wetland, Brazil, and then to identify the mechanisms of their formation.Soils were sampled along a toposequence and analyzed by X-ray diffraction, transmission electron microscopy-energy dispersive X-ray analysis, and inductively coupled plasma-mass spectrometry. Water was collected along a transect involving the studied toposequence and equilibrium diagrams were calculated using the databases PHREEQC and AQUA.The fine-clay fraction is dominated by smectite, mica, and kaolinite. Smectites are concentrated at two places in the toposequence: an upper zone, which includes the soil horizons rarely reached by the lake-level variation; and a lower zone, which includes the surface horizon within the area of seasonal lake-level variation. Within the upper zone, the smectite is dioctahedral, rich in Al and Fe, and is classified as ferribeidellite. This phase is interstratified with mica and vermiculite and has an Fe content similar to that of the mica identified. These characteristics suggest that the ferribeidellite originates from transformation of micas and that vermiculite is an intermediate phase in this transformation. Within the lower zone, smectites are dominantly trioctahedral, Mg-rich, and are saponitic and stevensitic minerals. In addition, samples enriched in these minerals have much smaller rare-earth element (REE) contents than other soil samples. The water chemistry shows a geochemical control of Mg and saturation with respect to Mg-smectites in the more saline waters. The REE contents, water chemistry, and the presence of Mg-smectite where maximum evaporation is expected, suggest that saponitic and stevensitic minerals originate by chemical precipitation from the water column of the alkaline-saline lake.

Soil Erosion in Brazil from Coffee to the Present-day Soy Bean Production

Throughout the twentieth century, Brazilian agriculture was responsible for rapid occupation of territory, especially because of two major crops that were characteristic of the most important agricultural frontiers. The coffee culture was predominant in Brazil during the first half of the century. This crop greatly influenced the country’s national and international economic standing. That period was called the Brazilian coffee cycle, most notably in the south and southeast, where pedoclimatic and geomorphological conditions were more appropriate. However, during the second half of the century, soy and cattle-raising became major factors influencing the expansion of Brazilian agriculture and the incorporation of new areas to the territory, specifically in the savanna region. This expansion was the result of prevailing morphopedological conditions and the new technologies brought about by advances in agronomic research linked to soil correction, fertilization, and irrigation. Subsequent hydropedological imbalances have accelerated erosive water dissection of the relief and the consequent production of sediments, responsible for silting valley floors, reservoirs, and drainage channels. These problems are frequently caused or promoted by the intense and indiscriminate deforestation taking place, in the case of coffee, on large expanses of the Mata Atlântica (Atlantic Forest), and in the case of soy, in the savanna.

Reflexões sobre a gênese da serra geral e da depressão periférica paulista: o exemplo da região da Serra de São Pedro e do baixo Piracicaba, SP

The genesis of the Serra Geral Ridge and Paulista Peripheral Depression has been a fundamental problem regarding the landforms of the State of Sao Paulo since the 1920s, and a final solution is still far from any consensus. Previous studies highlight erosional and tectonic factors related to the formation of these areas; however current research has shown that several hypotheses are only feebly supported. In this sense, this study presents an hypothesis on the genesis of the Sao Pedro Ridge, regional name of Serra Geral, and tests the validity of this proposition in the context of the formation of the Serra Geral Ridge as a whole. The results point to the hypothesis of an origin for the Sao Pedro Ridge by erosion as a consequence of the excavation process of the Paulista Peripheral Depression. This process took place with the establishment of large drainage patterns upon old structural lines that were reactivated during fragmentation of Gondwana. This excavation process and the formation of the proto-escarpment of the Sao Pedro Ridge must have begun between the Paleocene and Eocene, under a wet climate, after deposition of the Itaqueri Formation and establishment of the Cristas Medias Surface, having the geomorphological configuration of these areas transformed by neotectonic activity. Thus, this research confirms Margarida Penteados proposition that the Sao Pedro Ridge had a hybrid erosional/tectonic genesis, which qualifies it as a complex cuesta.

O estudo de formações superficiais no Brasil

Two main tendencies have been expressed in our country in the study of surficial deposits, not always convergent but searching first to define their autochthony or allochthony: for soils because they represent the original materiais, for reliefs because they are related to testimonies of the processes responsible for their genesis and evolution. We shall present here a synthesis of ideas on the origin and directions explored by such tendencies, showing their principal results and ending with the perspectives opened by the use of structural analysis of pedological cover procedure in two ways: the possibility to defime more correctly the autochthony or the allochthony of these materiais and, at the same time, to evaluate the significance of the biogeodynamic processes to the relief features.

Geomorphology of the São Pedro ridge and Lower Piracicaba River region, southeastern Brazil

ABSTRACT This work presents a new geomorphological map (1:50,000) of the São Pedro region in southeastern Brazil. It incorporates new information about landform development and updates the classical legend of the Recherche Coopérative Sur Programme 77 that supported the previous map drawn in 1978. According to the new map and associated papers, tectonic structures have controlled the orientation of the streams that have dissected the regional landforms, especially during wetter periods. Under dry conditions, the planing process caused faster escarpment retreat of the São Pedro ridge and gave rise to a glacis and its Pleistocene colluvial sandy cover. The escarpment, glacis, and other regions were dissected during subsequent wet periods, forming the upper Quaternary main fluvial terraced levels of the Piracicaba and Tietê rivers. Finally, this geomorphological arrangement was disturbed by the reactivation of old structures in the current tectonic environment.

CARACTERIZAÇÃO MORFOLÓGICA E PEDOLÓGICA DE UMA DEPRESSÃO (SERRA-ES-BRASIL)

This study aims to characterize the morphology of the soil cover and a depression and hypotheses of its origin. The methodological basis was a Structural Coverage Analysis Pedologic integrating the recognition of soil cover from four (4) steps: i) topographic survey; ii) auger; iii) elaboration of toposequency; iv) opening trench. Based on the recognition of realized and pedological cover the preparation of a map of landforms in the area, from photointerpretation techniques in aerial photography, it was possible to identify the existence of small depressed areas aligned in the bottom of the depression. The elaborate toposequency showed that soil cover features eight (8) soil horizons and a vertical drop of approximately 9 m from the top of the slope to the onset of depression. The advancement of gley horizon and merge depressed areas with higher elevations, from depression, following upstream in shed may be a sign of a remontant evolution (from downstream to upstream) of depression. The origin of depression may be related to loss of material due to geochemical dissolution. It was possible to establish six (6) stages of evolution of depression.