William Sallun Filho

Geomorphological map of the Serra da Bodoquena karst, west-central Brazil

Abstract Please click here to download the map associated with this article. The Serra da Bodoquena is a karst area situated on the southern edge of the Pantanal wetland region in the states of Mato Grosso and Mato Grosso do Sul, central-western Brazil. Morphological analysis, on a scale of 1:60,000, made it possible to identify such various karst features as dolines, caves, sinks and springs, as well as karst cones and corridors, among others, compartmentalized into six morphological units. To the west of the Serra, the labyrinth karst that was identified reflects a situation of extreme flattening and diffuse infiltration via vertical fractures, which is gradually limited by polygonal karst, to the extent that there is drawdown of the water level. To the north of the Serra, these features are obscured by a greater degree of uvial incision, which develops in the form of canyons and alluvial plains. To the east, there is a predominance of karst plains with dolines in a thick soil covering, associated with residual hills. There are tufa deposits along the current uvial drainage system, and extensive older deposits occur in Quaternary terraces. Sandstone plains with innumerable dolines occur to the southeast of the Serra, reecting the presence of subjacent karst. Geomorphological mapping of this area will be able to contribute to the Serra da Bodoquena National Park management plan, or assist in the development of anthropic soil use/occupation plans.

A faixa de dobramento Paraguai na Serra da Bodoquena e depressão do Rio Miranda, Mato Grosso do Sul

The Southern Paraguay Belt is a typical fold-and-thrust belt. Its geological evolution began with a continental rifting process, probably at the end of the Cryogenian, evolving into a restricted sea and an extensive marine transgression at the end of the Ediacaran. The final collisional event occurred during the Lower Cambrian, with post-collisional magmatism during the Upper Cambrian. The Corumba Group is divided into five formations (Cadiueus, Cerradinho, Bocaina, Tamengo and Guaicurus). The Puga Formation is correlated to the Cerradinho and Cadiueus formations. This stratigraphy can be seen even in the most deformed parts located in central-eastern area. In the far west of the area, the Corumba Group is deposited above an unconformity in the Rio Apa cratonic block. The name Agachi Schists is suggested for the schists located at the easternmost portion of the area. During the Ediacaran period, whereas, in the east part of the area, the Cuiaba Group was affected by deformation, metamorphism and arc-related granites, in the west part of the area, the Tamengo and Guaicurus formations were deposited, probably in a context of foreland basin. Up to three superimposed coaxial folding events are observed associated with greenschist metamorphism and thrust faults, showing a westward tectonic vergence. WSW - ESE convergence vectors indicate that the collision with the Rio Apa block was slightly oblique. Changes in metamorphism and structural style can be explained by the westward migration of the deformational front. The main thrust faults coincide with important basin boundaries, suggesting that the listric faults of the rift stage were reactived by them.

Quaternary tufa in the Serra da Bodoquena Karst, West-Central Brazil: Evidence of wet period

The Serra da Bodoquena is one of the most extensive continuous karst areas in Brazil, located in the Mato Grosso do Sul State, in the central western part of Brazil, on the southern edge of the Pantanal wetland region. It consists of a north-south plateau that extends for approximately 200 km, which forms an important water divide with an altitude of approximately 800 m. The area has a humid tropical climate with average temperatures between 22 and 24oC and an average annual rainfall of 1,419 mm, with 1-3 dry months. In the Serra da Bodoquena karst occurs the best examples of present-day deposition of tufa, along most of the rivers of the region, in the river beds and along their margins, forming dams (Figure 1).

Estudo comparativo entre estromatólitos do tipo Conophyton das faixas Ribeira e Brasília

The Conophyton stromatolites were described in the Ribeira (C. garganicum) and Brasilia (C. metulum and C. cylindricum) belts, in lithostratigraphic unities attributed to the Mesoproterozoic. Conophyton garganicum occurs in the Ribeira Belt (Itaiacoca Group) in the Itapeva region (Sao Paulo). In the Itaiacoca Group, the Conophyton garganicum forms have also been found at Abapa (Parana). They are similar to the other coniform stromatolites described in Itapeva, but differ from the other forms in the Brasilia belt, including C. cylindricum and C. metulum. In the Brasilia Belt two occurrences of Conophyton are described in the Vazante Group in Minas Gerais, in the Cabeludo (C. cylindricum) and Lagamar (C. metulum) regions and one in the Paranoa Group near Cabeceiras (Goias) (C. cylindricum). Conophyton from Cabeludo differs from the Lagamar´s in laminar thickness, as well as the regularity degree and laminar heritage of the axial zone. Otherwise, the Conophyton from Cabeceiras is similar to the Cabeludo´s in laminar thickness and configuration. The significant differences between the Conophyton from Brasilia and Ribeira belts indicate distinct depositional environments and/or ages. Conophyton shows Late Mesoproterozoic and Early Neoproterozoic ages from Vazante, Paranoa and Itaiacoca groups, which is consistent with available radiometric ages.

O carste no plano de manejo do Parque Estadual Intervales e zona de amortecimento, Estado de São Paulo, Brasil

Located in the valleys of the Ribeira de Iguape and Paranapanema Rivers, where karst features and a large number of caves can be found, the Intervales State Park and its buffer zone lie within an area of Proterozoic carbonate rocks that are of great interest to the mining industry. Based on geomorphological and geological studies, the characterization of the karst was performed in order to develop a management plan for the Intervales State Park and its buffer zone. With this, it was possible to defi ne the degree of vulnerability of the karst aquifer to contamination. The areas of greatest vulnerability are those that facilitate injection of contaminants directly into the aquifer, being characterized by such karst features as caves and sinks. In regions where recharge occurs exclusively via diffuse infi ltration, and runoff convergence with surface watercourses, the degree of vulnerability is lower. Considering this analysis, areas with the greatest impact potential were identifi ed and recommendations made regarding management of the park and its buffer zone.

The Colônia Impact Crater: Geological Heritage and Natural Patrimony in the Southern Metropolitan Region of São Paulo, Brazil

The Parelheiros district, located at the extreme southern end of the São Paulo metropolitan region, is historically famous for the occurrence of an unusual circular depression, denominated in the geological literature as Colônia Crater. This prominent geomorphological structure, with a 3.6-km diameter, formed by impact cratering, represents one of the few records of a violent and devastating geological process that shaped the Earth’s surface in the past. The crater lies within an environmental protection area and displays a remarkable landscape, as well as a rich and singular fauna and flora. With a wide geological and biological diversity, the Colônia impact crater is an extraordinary natural heritage and must be rigorously preserved to: (a) conserve its exceptional natural wealth in order to provide continuity to various scientific researches, (b) implement suitable land use and occupation programmes to maintain the crater as an environmental preservation area and (c) encourage the local community’s participation in the development of sustainable tourism in the region.

Proterozoic Stromatolites of the Itaiacoca Group, Southeast Brazil

The first stromatolites to be described in Latin America were identified in slightly metamorphosed dolostones of the Itaiacoca Group south of Itapeva, state of Sao Paulo (SP), Southeast Brazil (Fig. 1), by Almeida (1944), who named them Collenia itapevensis. Although he did not use the word “stromatolite” anywhere in his text, Almeida correctly interpreted these structures as microbial in origin and recognized both their paleoenvironmental significance and Precambrian age. Few other stromatolites were described in Brazil (see Fairchild and Sallun Filho, 2004) until the decade of 1970, when Precambrian geology and life became an important subject of study worldwide.

Seções de referência de subsuperfície da aloformação Paranavaí

The Paranavai Alloformation is a Quaternary geological formation found in the Upper Parana River Hydrographic Basin (states of Sao Paulo, Parana and Mato Grosso do Sul), composed of colluvial deposits originated from the Cretaceous lithostratigraphic units of the Parana Basin. The sedimentary deposits are reddish brown in color, sandy, non-consolidated, homogeneous, massive, and commonly confused with surface soils and formations. In order to obtain subsurface reference sections for the Paranavai Alloformation, core samples were collected in two regions of the western part of the state of Sao Paulo. The study was conducted involving several parameters (textural, mineralogical, geochemical, isotopic and geochronological) of the sediments of the Paranavai Alloformation and Bauru Group. Two new reference sections were obtained in order to establish the composite-stratotype of its constituent formations: Rancharia reference section (luminescence ages between 71650 ± 9000 and 557000 ± 65000 years BP) and Oriente reference section (luminescence ages between 83000 ± 8500 and 436 ± 53000 years BP). The luminescent ages obtained in this study increase according to the depth of the Paranavai Alloformation, whereas the sediments of the Bauru Group have ages greater than the maximum limit of the geochronological method used. The information obtained from the reference sections shows variability in the patterns of various parameters, proving there were different generations of colluvial deposition throughout the Quaternary period in the western part of the state of Sao Paulo.

Provável significado geológico de idades LOE (luminescência opticamente estimulada) da formação Itaquaquecetuba, SP

The Itaquaquecetuba Formation can be considered as relatively well-known from a paleontological viewpoint. Its fossil content, which is very rich and represented by plants (tree trunks, seeds and leaves) and palynomorphs, has been studied in detail, allowing several authors to suggest different ages and depositional conditions for this unit in terms of paleoclimate and paleoenvironment. At the present state of knowledge, the age assumed of this formation is Paleogene (upper Eocene to lower Oligocene) or Neogene (Miocene), although controversies still remain about the depositional paleoclimate and paleoenvironment. More recently, OSL (Optically Stimulated Luminescence) depositional ages between 47,000 ± 6,000 and 89,000 ± 12,000 years were obtained from samples of sands from the Itaquareia sand pit located in the city of Itaquaquecetuba (Sao Paulo state). These ages correspond to the Pleistocene (Quaternary) and are correlatable with the time of the Wisconsin Glaciation in North America. Considering these new data and some stratigraphic aspects which were unknown before this study, great part of the Itaquaquecetuba Formation, which outcrops in the Itaquareia sand pit, is here interpreted as a Quaternary fluvial channel deposit.