The area is part of the geological framework of the Tocantins Province, within the southernmost portion of the eastern Amazon. It is comprised between the parallels 08° 00' 00'' and 08° 30' 00'' and the meridians 48° 30' 00'' and 49° 30' 00''. The researched region encompasses a geological section that has insertion in the city of Colinas do Tocantins, continuing through the state highway TO-280 and ending in the vicinity of the city of Couto Magalhães/TO, making up about 107 km in profile. The chronostratigraphic division for the Baixo Araguaia Supergroup is adopted in this work, which includes, from base to top, the Estrondo and Pequizeiro groups. It was decided to include in the Estrondo Group the lithotypes attributed to the Xambioá Formation (in addition to the inclusion, in this group, of the Couto Magalhães Formation). This unit, in its eastern portion, is predominantly constituted by schists and quartzites, being more common biotite schists, feldspathic schists (gneissoids) and pure quartzites; in its western portion, outcrops the unit called, by some authors, the Couto Magalhães Formation, whose main lithology is represented by metasediments, predominantly phyllites. The Pequizeiro Group, in some works called the Pequizeiro Formation (included in the former Tocantins Group), is located in the central-west part of the area and requires rocks fundamentally formed by mica schists, with more frequent chlorite schists and interspersed biotite schists. The Parnaíba basin is represented at its western edge (eastern portion of the work area) by pelitic sediments from the Pimenteira Formation and sandstones from the Cabeças Formation. Essentially conglomeratic units attributed to the Rio das Barreiras Formation and to the Cipó Conglomerate unit were also observed, which, by some authors, have been considered as depositional variations of the Cabeças Formation, or the Piauí Formation or even the Pedra de Fogo Formation. These conglomerates are considered here to be of Eopaleozoic age. The sedimentological characteristics of the Rio das Barreiras Formation do not allow to correlate it with any unit of the Parnaíba basin; the Cipó Conglomerates may be related to the Serra Grande Formation of this basin. The structural features identified within the Baixo Araguaia Supergroup segregate not only two lithostratigraphic groups bundled in the Estrondo and Pequizeiro groups, but also two classes of structures: one originated by a purely ductile and non-coaxial tectonic system; and another coming from a predominantly brittle and coaxial tectonic, implanted later. They are marked by the constant presence of three most important types of tectogenous structures: [a] mylonitic foliation and schistosity; [b] stretch lineation; in addition to a third structure identified punctually; [c] compositional banding. Other not less important features are described as folds, crenulation cleavage, veins and lenses. Within the domain of brittle structures, failures of different types, joints or fractures are recognized, in addition to the lineament of various orientations that can represent different types of structures. The structures identified within the Parnaíba basin are fundamentally characterized through the action of processes originated by faults of a normal nature. They are structures originating from a fragile tectonic regime that generated important normal faults, both on a regional scale and on an outcrop scale. Of equal importance are the discontinuities described as joints that constitute striking impressions recorded in the two sedimentary units mapped within this portion of the basin. The correlation between the features displayed on the outcrop scale (faults, fractures, striations) with the regional scale lineaments shows the main direction according to a preferential north-south direction. This orientation can be visualized through the records (diagrams) of statistical treatments based on field measurements. The glaciotectonic structures studied refer to the deformed and chaotic geometries existing in the Devonian conglomeratic sand deposits belonging to the Cabeças Formation of the Parnaíba basin. They occur in much of the work area, along the easternmost portion of the region. They are mainly tillites that exhibit exuberant shear features, attributed to the tectonism of paleoglaciers at the end of the marine sedimentation of the Cabeças sandstones, in the Famenian. Deformed and slightly deformed tillites originated in a progressive deformation regime through tangential movements in simple and heterogeneous shear zones, generated in distal subglacial and glacial contact environments, are described. Two main relief compartments are exposed within the work area: [1] the one attributed to the Araguaia belt and [2] the one correlated to the sedimentary cover of the Parnaíba basin. Within the scope of the Araguaia belt, which is part of the Planalto do Interfluvio Araguaia-Tocantins, the following differentiated relief units were identified: [a] relief of aligned mountain ranges with sharp tops; [b] relief of hills with tabular tops; [c] relief of isolated hills with domed tops; [d] hilly relief with rounded tops; [and] tertiary plan; [f] fluvial plain of the Araguaia River; [g] Holocene alluvium. The last two sub-units are located in the Araguaia Depression. In the area belonging to the Parnaíba basin, included in the Depression of Tocantins, only two morphological units were identified; [h] relief of flat-topped hills; [i] relief of broad hills with flat and rounded tops. The evolution of the area in the context of the Araguaia belt is understood through the lithospheric distension-compression model, where the distensive phase promoted the formation of hemigraben dominated by normal faults inclined to the east; the compressive phase was characterized by the reactivation of normal thrust faults. The accommodation of these tensors took place through the formation of an imbricated system with associated nappes. The Baixo Araguaia Supergroup has transgressive marine sequence characteristics. The installation of the Parnaíba basin occurred through a NW-SE extension axis during the early Paleozoic, in the Ordoviciian-Silurian. The effects of this opening led to the formation of extensional faults that were concentrated on the W, E and SE edges that were controlled by ancient Precambrian lineaments. The clastic deposits of the Canindé Group, records of the Devonian of the basin, represent the alternation of regressive cycles (pelites of the Pimenteira and Longá formations) and transgressive (sandstones of the Itaim and Cabeças formations) and are characterized by deposition in temperate to cold climates near glaciers.
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