Francisco Sergio Bernardes Ladeira

Solos do passado: origem e identificação

Soils are a result of the interaction between forming factors and processes in the different landscapes of the Earth´s land surfaces. Long-term processes change landscapes and associated soil profiles. These changes result from gradual or catastrophic processes of eolian, tectonic and climatic or even human impact, and are generally irreversible, destroying the associated soils. Nevertheless, in particular situations soils may remain preserved in a specific area of the ancient landscape, embedded in sedimentary and volcanic sequences, resulting in the so-called paleosols. Paleosols are a source of relevant information for a variety of purposes and are particularly valuable in providing evidence for reconstructing past terrestrial ecosystems and environments, mainly in the case of rare or nonexistent fossils; for the characterization of ancient atmospheres and paleoclimate, stratigraphic correlations, as indicator of old relief surfaces, of mineral concentrations; pedogenetic paleoprocesses and sedimentary processes, and as indicator of continental drift in geoarchaeology. In Brazil, studies of paleosols are still rare and relatively recent, beginning in the 1970s, in contrast to the United States of America and Europe, where such studies are quite advanced and widely reported. This review discusses relevant concepts in paleopedology, with the purpose of arousing some interest, mainly among the pedologic scientific community of Brazil, where little research work on this subject is available yet.

The mineralogy of paleosols in the Marília Formation and their importance in the environmental evolution of the Maastrichtian of the Bauru Basin in southeastern Brazil

Soils and paleosols reflect the complex interplay between sedimentation, erosion and non-deposition. An analysis of the mineralogical components of paleosols is critical for the reconstitution of the factors, processes and environments in which they were formed. The recognition of mineralogical assemblages can reveal the environmental conditions during pedogenesis and through quantitative analysis it is possible to identify a vertical variation in mineral concentration or leaching over the paleosol profiles, indirectly pointing to environmental processes that dominated during the pedogenetic evolution. The objective of this study is to discuss the significance of mineral phases and to quantify the environmental evolution and degree of development of paleosols of the Marilia Formation, Maastrichtian of Bauru Basin. Three sections have been described (A1, A2, A3) in the Marilia Formation. The mineralogy was determined by x-ray diffraction, and mineral quantification was obtained through the Rietveld refinement method. The calcretes of the Marilia Formation are pedogenic, mostly authigenic minerals. The variation of quartz, calcite, palygorskite and smectite, the micromorphology, and the diversity of subsurface horizons (Bkm, Btkm, Bt) indicate that the studied paleosols did develop in semi-arid conditions, with episodes of higher rainfall rates, humidity, leaching and desilication.

Gondwana Paleosurfaces in the State of Rio Grande do Sul, Southern Brazil

Several papers in Brazil have identified the importance of the planation surfaces in the evolution of the landscape, particularly those referring to the Gondwana Surface and the “Sul-Americana” Surface. These works were especially common between the 1950s and 1970s. Starting with the 1980s, such contributions became much scarcer. More recently, several, more appropriate dating techniques stimulated again the publication of papers related with these themes. This study has the aim of reviewing the knowledge about the paleosurfaces of the state of Rio Grande do Sul. The investigation discusses the summit surfaces named by Ab’Saber as the Vacaria Surface and the Cacapava do Sul Surface. The Vacaria Surface is carved into Mesozoic effusive rocks, whereas the Cacapava do Sul Surface has a much more complex evolution, basically eroded on Precambrian rocks. Contrarily to other areas of Brazil, the surface carved in the oldest rocks is located at intermediate elevations. The Vacaria Surface evolved during the Late Cretaceous and the Paleogene, whereas the Cacapava do Sul Surface has an even older development, typically corresponding in this area to the Gondwana Surface, with some particular characteristics which are unique in regional terms, as remnants of Triassic sedimentary rocks on top and evidence of lateritic profiles, which today occur only in the lowest parts of these sections, but which had influence on the development of some landforms until today.