EM - Escola de Minas

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Palaeoecological implications of an Upper Cretaceous tetrapod burrow (Bauru Basin; Peirópolis, Minas Gerais, Brazil).
(2019) Martinelli, Agustin Guillermo; Basilici, Giorgio; Fiorelli, Lucas Ernesto; Klock, Carolina; Karfunkel, Joachim; Diniz, Ariela Costa; Soares, Marcus Vinícius Theodoro; Marconato, André; Silva, João Ismael da; Ribeiro, Luiz Carlos Borges; Marinho, Thiago da Silva
We describe a globally rare example of a tetrapod burrow from the Upper Cretaceous Bauru Group (Bauru Basin) from Peirópolis, Minas Gerais State, Brazil. The sedimentary succession containing the burrow includes a rich vertebrate assemblage comprising fish, podocnemid turtles, mesoeucrocodylians, saurischian dinosaurs, among others. The burrow is composed of an oblique tunnel (~30°), oval in cross-section, with a horizontal and suboval terminal chamber; it is 1.3 m long from the midpoint of its inferred entrance to the midpoint of the bottom of the chamber. It occurs in the upper portion of a sandstone succession, interpreted as a braided channel deposit, and the burrow-fill comprises medium-grained sandstone with mudstone intraclasts derived from fluvial floodplain facies. it is overlain by other fluvial channel deposits. Analyses suggest that the burrow was dug after the filling of the braided channel and during the pedogenesis of its exposed upper surface. Based on burrow morphology and size, the most plausible producer of this burrow is a notosuchian mesoeucrocodylian, such as small to mid-sized notosuchians (e.g., sphagesaurids). The Bauru Group has an extensive fossil record of notosuchians with disparate morphologies, and it is noteworthy that the small-sized notosuchian Labidiosuchus amicum comes from the same unit as the burrow. Moreover, arid to semi-arid conditions have been inferred for fossil-bearing rocks of this unit, and as such the data here presented add to our palaeoecological knowledge of Cretaceous mesoeucrocodylians in Gondwana. Moreover, it constitutes a new Cretaceous record of a tetrapod burrow during a period when such ichnofossils are globally rare.
Interpretation of magnetic data based on euler deconvolution : analysis of the main host gold structure in the northeastern portion of the Quadrilátero Ferrífero, MG, Brazil.
(2016) Madeira, Thiago José Augusto; Barbosa, Maria Sílvia Carvalho; Borges, Antonino Juarez
The study of the geometry and kinematics of deep geological structures, bearing mineralization, has advanced greatly by the aggressive progress of geophysical techniques over the last decades. The gold mineralization located in the Quadrilátero Ferr´ıfero has its genesis controlled by shear zones. The geophysical analysis (aeromagnetic and aero-electromagnetic) by means of two-dimensional magnetic data inversion profiles (Euler deconvolution) and later interpolation, provided the 3D configuration of a tectonic-structural geological model, explaining the spatial configuration of lithostratigraphic and structural units, and kinematics features of the main shear zone mineralized in gold in the northeastern portion of the Quadril´atero Ferr´ıfero. The processing of airborne geophysical magnetic data of the Rio das Velhas Project provided the generation of inversion profiles with outputs up to 5000 m deep, opening new windows for gold prospection at the surroundings of the main gold mineralized structure in the Quadril´atero Ferrífero. The integration of geological, geophysical data and field observations was essential for the final results of this work.
A Late Quaternary palynological record of a palm swamp in the Cerrado of central Brazil interpreted using modern analog data.
(2018) Cassino, Raquel Franco; Martinho, Caroline Thaís; Caminha, Silane Aparecida Ferreira da Silva
The fossil pollen record from a Late Quaternary peat core collected in the São José palm swamp, in the northwest region of Minas Gerais state (Central Brazil), is interpreted using a dataset of modern pollen spectra as modern analogs. Principal component analysis and dissimilarity coefficients were used to compare fossil and modern samples, supporting the interpretation of past environmental dynamics. The results suggest that at ca. 15,700 and ca. 15,400 cal years BP, the buriti (Mauritia flexuosa) palm (that characterizes the palm swamps today) was absent and the climate was colder. Around 15,200 cal years BP, the increasing occurrence of buriti and the development of the Cerrado stricto sensu, a savanna woodland, indicate a warmer climate. At the end of the Late Pleistocene and during the Pleistocene-Holocene transition, the palm swamp central zone expanded and a dense Cerrado stricto sensu developed, suggesting a warm and humid climate. By the end of the Early Holocene, a much drier climate is suggested by the shrinkage of the palm swamp and a more open regional vegetation. Subsequently, and until ca. 4400 cal years BP, a wetter climate is indicated by the extended central zone of the São José palm swamp that reached a maximum expansion at ca. 6500 cal years BP. After 3500 cal years BP, the predominance of the Campo Sujo, a herbaceous-shrubby vegetation, indicates the return of relatively dry conditions. In the last two millennia, a decrease in the extent of the humid zone of the palm swamp suggests an intensification of drier conditions. Lower precipitation inferred at the end of the Holocene, and the predominantly humid conditions in the Middle Holocene, is different from the general pattern observed in southern and western Cerrado sites, but is in agreement with paleoclimate data from Northeastern Brazil.

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