Este trabalho analisa o papel das zonas de falha com bandas de deformação na resistência ao intemperismo em rochas sedimentares, trazendo como estudo de caso a Bacia Sedimentar Rio do Peixe (BSRP), localizada no Nordeste do Brasil. Os dados foram obtidos por meio de sensoriamento remoto, trabalhos de campo, análises de resistência e topografia, extração de lineamentos e elaboração de modelos digitais de elevação, perfis topográficos e ortomosaicos de alta resolução. Observa-se que, em escala regional, há uma heterogênea distribuição das feições positivas de relevo, relacionadas com os sistemas de falhas de borda presentes na área (Portalegre e Malta), e estruturas deformando o arcabouço estrutural interno da bacia, sendo o trend NE-SW predominante tanto no embasamento quanto na BSRP. Os perfis topográficos mostraram que existe uma correlação entre os altos topográficos e as ocorrências de bandas de deformação (BDs). Elas estão presentes nas zonas de dano das falhas que afetam a bacia, onde se apresentam como enclaves de resistência ao intemperismo diferencial e modelam cristas estruturais.  Esses relevos mais elevados correspondem à zona de dano interna e, com a diminuição da deformação, o acamamento sedimentar fica exposto. À medida que se afasta do núcleo da deformação, a topografia apresenta-se rebaixada e plana, favorecendo a presença de coberturas eluviais. Essas informações permitiram concluir que o relevo da BSRP, nos casos próximos das zonas de falha, apresenta condicionamento estrutural associado a episódios deformacionais que afetaram a permeabilidade e a resistência dos arenitos, levando, assim, à formação de cristas estruturais.

<p>Geoconservation is an instrument of Geodiversity, and encompasses a set of actions from inventorying and characterization of geosites to their conservation and management, in addition to enabling the appropriate use of its scientific, educational, cultural, touristic, and economic values. The inventory, characterization, and representation of geosites from a geopark is essential for recognition of its scientific importance and collaborates to verification of potential conservation and its different forms of use for geopatrimony. The geomorphological mapping as an instrument of this representation permits the users to visualize the landscape elements and makes them understand why such an area is a site and a geopatrimony. This work aims to describe the geomorphological heritage of an area designated for the creation of the Sertao Monunmental Geopark, in central Ceara, Northeastern Brazil, using geomorphological mapping, to represent the landforms and to discuss landscape dynamics.  In this regard, different cartographic products are necessary, such as geological maps, clinographic and hypsometric, pedological, hydrographic network and sub-basins, and geomorphological maps in detail and semi-detail scales in which the main geographic accidents, residual reliefs, planed surfaces, and slopes will be presented. The methodology of the landform classification will be made in accordance with Ross (1991; 1992), Santos <em>et al</em>. (2006), Dantas (2016), Diniz (2017), and IBGE (2009), among others that categorize the relief in taxonomic units. These are the following morphostructural units (1st taxon), morphosculptural units (2nd taxon), morphological units or similar patterns of forms (3rd taxon), types, and forms of relief (4th taxon). For the representation of relief patterns, it is assumed to consult the technical documents with standards and representations of geomorphological aspects. This work will be based, on geoprocessing techniques with GIS, mostly using QGIS software, and satellite and radar image processing for scales 1/250,000 and 1/100,000, and high-resolution imaging for more detailed scales (1/10,000 and 1/25,000). It is expected that this geomorphological mapping contributes to understanding the spatial setting of landforms in the study area providing an interpretation of the geomorphological facts and supporting different activities in the region, such as the orientation of visits and planning projects.</p>

<p>Coastal cliffs are short-term recession features influenced by various mechanisms, such as wave action, rainfall, groundwater, beach geometry, tectonic, and lithology. In Northeastern Brazil, the coastal morphology is characterized by extensive coastal cliffs with modest altitudes (5-25 m) and variable distances from the sea (40-100 m). Among the most representative morphologies are Morro Branco coastal cliffs, located on the east coast of Ceará state, Brazil. These reliefs are composed of the Tibau Formation (±75 Ma), and semi consolidated sandstones of the Barreiras Formation (22-17 Ma), exposed along Brazil's equatorial and eastern coastal margins. The lithological profile presents four sandy claystone sedimentary facies, recognizable from base to top cliff as gray, red, white, and orange, arranged in different degrees of lithification. The main goal of this study was to identify the influence of mechanisms controlling the morphology of coastal cliffs in tropical environments, having as a case study the Morro Branco, NE Brazil. For this purpose, UAV surveys were carried out, together with analyses of rainfall and wave impaction in relation to geological conditions. The average rainfall of the study area (900-1000 mm) is about 40% higher than of coastal cliffs in temperate climates (500-700 mm), attesting to the importance of increased precipitation in erosive processes. In addition, structural analyses of coastal cliffs rocks indicate a scarcity of failures due to the low degree of sandstone consolidation. Despite their high dip angles (80° to 88°), the orientations of cliff line fractures do not coincide with fault systems, being restricted to the area adjacent to the cliff escarpment. The correlation between rainfall and the degree of sandstone consolidation shows that more significant recessions occur at clifftop and middle, coinciding with the orange and white colorations. In these areas, gullies develop along cliff instabilities, leading to intermittent flow-type mass movements. The resulting debris is transported by rainfall to the shoreline, feeding back the beach areas. A positive repercussion is observed at the base of the cliff, represented by the gray and red-colored facies, due to the high degree of consolidation in this region. While the gray coloration is related to the Tibau Formation, the red coloration may have its degree of consolidation linked to groundwater influence. Wave action is also a critical driving mechanism, contributing to the removal of small rock blocks (< 50 cm) in the most lithified sectors, occasioning the formation of cavities (0.2-2 m high) that widen and finally collapse due to moisture. Hence, retreat rates along the cliff base, middle and top diverged, with greater retreats at the clifftop and middle and positive repercussions at the cliff base. We conclude that wave action, slight variations in lithology, and high rainfall totals can be identified as elements that govern the coastal cliff's escarpment retreat in tropical environments.</p>

Resumo:Os relevos cristalinos presentes no nordeste setentrional brasileiro correspondem comumente às áreas de expressão plutônica da Província Borborema. Estas morfologias estão associadas às zonas de cisalhamento, que serviram de condutos crustais às intrusões. Dessa forma, os maciços, que constituem o objeto de análise, encontram-se localizados dispostos preferencialmente ao longo de zonas de deformação, onde têm exercido infl uência nas direções de fraturamento e dissecação. O presente trabalho propôs a análise da evolução geomorfológica dos maciços costeiros localizados na Região Metropolitana de Fortaleza, Ceará, com enfoque nos relevos de Juá/Conceição, Camará, Maranguape e Aratanha, a partir do sensoriamento remoto. O percurso metodológico contemplou a revisão bibliográfi ca e cartográfi ca, o processamento digital de imagens e os trabalhos de campo. A análise das variáveis litologia/fraturamento/altitude se deu mediante a extração de lineamentos estruturais obtidos pelos dados SRTM 30m. Nesse cenário, foi realizada a análise do contexto tectônico, estrutural e litológico para a disposição dos maciços, destacando a importância da erosão diferencial. Os resultados apresentaram lineamentos de direções NE-SW, N-S e NW-SE nas unidades litoestratigráfi cas da Unidade Canindé do Ceará (CC), do Arco Magmático Santa Quitéria (AMSQ) e dos Granitoides Diversos (GD). Os setores fraturados, com maior densidade, estão localizados no embasamento encaixante e acompanham as regiões com falhas e/ou fraturas, delineando as superfícies de erosão. No caso dos granitoides, a baixa densidade de feições lineares, em consonância com sua resistência litológica, responde pelos altos topográfi cos que estão vinculados às cristas residuais, necks vulcânicos e maciços. Informações sobre o Artigo

<p>Granitic inselbergs rise from a plain 160 km away from the coast in Northeastern Brazil. They are located in the structural Borborema Province, within the area of the Quixadá Pluton, one of the igneous intrusions from the later stages of the Brasiliano Orogeny (640 – 570 Ma). In this area, monzonites, diorites, and granites <em>sensu sctricto</em> constitute the main granitic facies, with the former being the predominant lithology supporting these landforms. The granites <em>s.s</em> occur as dikes that vary from a few centimeters to a few meters in thickness and form swarms seen within the inselbergs. This study aims to investigate the structural control exerted by dikes on inselberg morphology. Therefore, four inselbergs with a high density of dikes were selected to carry out detailed analysis. Three petrographic types of dikes were identified: fine-grained isotropic dikes (FID), coarse-grained isotropic dikes (CID), and fine-grained anisotropic dikes (FAD), different in terms of their texture and fabric. X-ray fluorescence analysis shows high silica content of the dikes; the first two types with a higher average (82.9 wt %) and the FAD with slightly lower content (76.2 wt%). In contrast, the host rock has lower average SiO<sub>2</sub> content (64.5 wt %) and high percentage of Fe<sub>2</sub>O<sub>3</sub> (10.7 wt %), compared with 1.69 wt % in the dikes. The results of Schmidt hammer tests in situ correlate with petrological and geochemical characteristics, attesting to the higher uniaxial compressive strength for finer-grained and more siliceous types. These data suggest higher resistance of dikes to weathering attack in relation to the host rock, which is evident in relief features such as dikes protruding from the main rock mass and dissolution features being obstructed by the presence of felsic dikes. The petrographic, geochemical, and geomechanical characteristics make the dikes significant features contributing to the morphology of inselbergs, especially when combined with the geometry of these parallel dike swarms. In the SW zone of the pluton, the dikes present low to medium dip angles (8 to 34° / NW and SE), which are followed by slope outlines of various inselbergs. In the eastern sector, the trending orientations of dikes (NE-SW) locally coincide with the orientations of linear features such as runnels, which are developed along the dike-host rock contact and therefore mirror their parallel array. We conclude that resistant dike swarms within inselbergs influence final morphological patterns related to slope outline and the location of various minor features resulting from selective weathering, commonly developed next to the dike/host rock contact. Additionally, a 3D sketch model is proposed regarding the relationship between preferential occurrence of inselbergs in areas of gently dipping and parallel dyke arrays, as they act as levels of obstruction of vertical denudation that shapes granite forms in epigenic conditions.</p>