The eolianites between Sanga do Cabral and Botucatu formations in Rio Grande do Sul State, Brazil (original) (raw)
Related papers
Gondwana Research, 2006
The Guará and Botucatu formations comprise an 80 to 120 m thick continental succession that crops out on the western portion of the Rio Grande do Sul State (Southernmost Brazil). The Guará Formation (Upper Jurassic) displays a well-defined facies shift along its outcrop belt. On its northern portion it is characterised by coarse-grained to conglomeratic sandstones with trough and planar cross-bedding, as well as low-angle lamination, which are interpreted to represent braided river deposits. Southwards these fluvial facies thin out and interfinger with fine-to mediumgrained sandstones with large-scale cross-stratification and horizontal lamination, interpreted as eolian dune and eolian sand sheets deposits, respectively. The Botucatu Formation is characterised by large-scale cross-strata formed by successive climbing of eolian dunes, without interdune and/or fluvial accumulation (dry eolian system). The contact between the Guará and the Botucatu formations is delineated by a basin-wide deflation surface (supersurface). The abrupt change in the depositional conditions that took place across this supersurface suggests a major climate change, from semi-arid (Upper Jurassic) to hyper-arid (Lower Cretaceous) conditions. A rearrangement of the Paraná Basin depocenters is contemporaneous to this climate change, which seems to have changed from a more restrict accumulation area in the Guará Formation to a wider sedimentary context in the Botucatu Formation.
The eolianites, distributed along the northwestern part of Ceará State coast, are formed by arenaceous rock deposits of quartz-bioclastic composition, cemented by calcium carbonate. This unit establishes an unique record of aeolian activity with peculiar features, rare on the brazilian littoral, whose particular characteristics, preserved in its structures and composition, highlight a large potentiality to provide relevant informations about coastal environment conditions at the time of its formation. The lithified character of these deposits has provided its preservation along the time; however, more friable parts have facilitated erosive wind action, contributing for the discontinuity of distribution and morphology of eolianites. The eolianite deposits invariably display outcrops with large scale sedimentary inner structures, mainly plane-parallel and planar cross-strata, although cross-braided and festooned forms are also relatively well represented, besides other less common. The deposits display aeolian abrasion “ruin” morphology and have a high rigidity comparatively to other aeolian deposits. The correlation between them and current active dunes has lead to the interpretation that most of eolianites records are representative of an evolution phase represented by the formation of compound dunes, with parabolic dunes accumulation at the final stage. An important aspect of these deposits is also the presence of ancient human occupation records, represented by man fragments of manufactured lithics tools and fires.
Sedimentary provenance in the southern sector of the São Francisco Basin, SE Brazil
Brazilian Journal of Geology
We present new Sm-Nd, U-Pb and Hf isotope geochronological data for the siliciclastic rocks in the southern sector of the São Francisco Basin. An abrupt change in the Sm-Nd data is observed from the Carrancas Formation's oligomitic conglomerates (T DM ages between 2.7 and 3.3 Ga; ε Nd(550 Ma) values between-25.09 and-17.98), its finer facies, and the finer facies of the the Moema Laminite (T DM ages from 1.4 to 2.1 Ga; ε Nd(550 Ma) values between-9.46 and-5.59). No further significant changes in the Sm-Nd data occur farther upwards in the Bambuí Group (Sm-Nd T DM ages within the 1.3-2.0 Ga interval; ε Nd(550 Ma) values from-9.53 to-4.09), showing a lack of reorganization in the source areas throughout the deposition of the basin. This is yet another argument to dismiss an unconformity within the Bambuí Group. The presence of the index fossil Cloudina sp. in the lower Sete Lagoas Formation makes the glaciation probably Late Ediacaran in age. U-Pb ages for detrital zircons of the Bambuí Group range from the Archean to the early Ediacaran, but the current data is insufficient to distinguish between the contribution from sources in the Brasília and Araçuaí belts.
Genesis of sandstone-derived soils in the Cerrado of the Piauí State, Brazil
2019
This study characterized the morphological, physical and chemical attributes of sandstone-derived soils at the Cerrado of the Piauí State, Brazil, in order to identify evolutionary standards. The study was carried out with five representative soil profiles identified as P1-RY (Typical Flavic Psychotic Neosol - Aquents), P2-PA (Typical Dystrophic Yellow Argisol - Alfisol), P3-RL (Fragmentary Litholic Distrophic Neosol - Psammenit), P4-RQ (Typical Ortic Quartzenetic Neosol - Orthents) and P5-PV (Typical Dystrophic Red Argisol - Ultisol). Soil samples were submitted laboratory analysis described morphologically. In general, the soils presented high sand content, low pH, low content of exchangeable bases and low cation exchange capacity (CEC). Organic matter governed the CEC in most cases, suggesting dependence of organic matter in the supply of charges. These soils showed a low degree of weathering, but with iron of high crystallinity. Thus, the relief and the parent material are the major important soil-forming factors at the Cerrado of the Piauí State. Moreover, these soils are young, with the soils from the Piauí Formation being more evolved. However, the sandstones from the Canindé Group apparently are providing lithological secondary minerals for the soil.
Sedimentology, 2020
Mixed carbonate–siliciclastic deposits of the Tamengo Formation (terminal Ediacaran), record the rise of calcifying metazoans and the origin of exoskeletons in animals. To explore the relationships between environmental setting and the first appearance of calcified metazoans and their ecology, this study presents detailed sedimentological and stratigraphic data of eight sections that capture the final stages of the Ediacaran (550 to 543 Ma). This study combines stratigraphic characterization with detailed facies descriptions and evaluates lateral heterogeneity and overall ramp sedimentation integrated with fossil distribution. The Tamengo Formation represents a storm‐dominated ramp. The outer to mid‐ramp is composed of very fine‐grained siliciclastic rocks containing Corumbella body fossils and thin‐bedded mudstone/wackestone containing Cloudina. The mid‐inner ramp is dominated by wackestone/packstone with abundant Cloudina skeletal debris and ooid packstone/grainstone shoal deposit...
Journal of South American Earth Sciences, 2019
The Tamengo and Guaicurus formations, upper units of the Corumba Group, are placed at Ediacaran-Cambrian transition due to biostratigraphy and chemostratigraphy data. The Tamengo Formation is composed mainly of limestones with interbedded mudrocks (siliciclastic, carbonate and mixed siliciclastic-carbonate mudrocks) and record occurrences of macro-fossils Cloudina and Corumbella. The Guaicurus Formation is characterized as an extensive and homogeneous siliciclastic siltstone package. This paper focus in sedimentary, petrographic, mineral (XRD) and chemical (XRF) characterizations of mudrocks and siltstones in order to define stratigraphic positioning of the Tamengo and Guaicurus formations, and indicate depositional environment. To this purpose, three areas were studied in the vicinity of Corumba (MS-Brazil): Laginha and Corcal quarries and an outcrop along MS-243 road. The rocks of the Tamengo Formation, under microscope, present fluid diffusion features as well as irregular lamina...
Lower Cretaceous Sedimentary Sequences in the Basin, Northeastern Brazil: A Revision
Revista Brasileira de Geociências
Th e Araripe Basin in northeastern Brazil contain a 700 m-thi ck succession of Jurassíc-Cretaceous strata. The 200 m-thíck Lower Cretaceous is widely known for lts flsh-bearing concretíons and gypsum depo sits. Detailed field studies and core analyses provided data for revision of the Lower Cretaceou s stratig raphy in the Araripe Basin. A regional disconfonnity within the Lower Cretaceous succession is described here for the flrst time. This surface divides the Aptian-Albian succession into two parts : I. a lower sequence of black shale, laminated carbonate, algal mat carbonates, and evaporites in ascendin g stratlgraphic ord er; and 2. an overlyíng sequence contaíning concretionary shale, limestone , and sandstone. These two stratigrapWc divisions are herein defmed as the Ararípína Formation (new name) and the Santana Formation (revísed), respectively. The expressíon of the disconformity varies across the basin. ln the southwest it is marked by caves fonned in the gypsum and a karstic top ograph y. Toward s the northeast, a 50 cm-thick layer of laminar calcareous and siliceous calcret e crust mark s th e disconformity surface. RESUMO A Bacia do Araripe no norde ste do Brasil apresenta uma sucessão sedimentar de idade jurássico-cretáci ca de apr oximadamente 700 m de espessura. As rochas do Cretá ceo Inferior, com cerca de 200 m de espessura, são bem conhecidas pelos depó sitos de gipsita e concreções contendo peixes. Este artigo apresenta uma revisão da estratigrafia do Cretáceo Inferi or com base em trabalho de campo