Luiz Alberto Fernandes

Araçatuba Formation: palustrine deposits from the initial sedimentation phase of the Bauru Basin

A Bacia Bauru (Cretaceo Superior), acumulou uma sequencia sedimentar continental essencialmente arenosa. Numa fase inicial desertica, o seu substrato basaltico foi soterrado por extensa e monotona cobertura de areias eolicas com intercalacoes subordinadas de depositos de loesse. O relevo original do substrato favoreceu a formacao de uma drenagem regional endorreica, sob clima semi-arido, propiciando assim condicoes de formacao do Paleopantanal Aracatuba. Os depositos paludiais (Formacao Aracatuba) constituem estratos tabulares de siltitos e arenitos de cor cinza claro esverdeado tipica, eventualmente cimentados por carbonato de calcio. Moldes e pseudomorfos de cristais de gipsita e dolomita foram identificados na unidade. Aparentemente, estao associados com gretas de ressecacao, marcas de raizes e intervalos com laminacao tipo climbing ripple, que indicam ambiente de aguas salinas rasas e relativamente calmas, submetidas a fases de exposicao subaerea e ressecacao. Nos limites da area de ocorrencia da Formacao Aracatuba, as unidades arenosas podem exibir feicoes sigmoides e estratificacao contorcida, comuns em depositos deltaicos marginais. A Formacao Aracatuba e contornada e posteriormente encoberta por depositos eolicos da Formacao Vale do Rio do Peixe.

Calcretes e registros de paleossolos em depósitos continentais neocretáceos (Bacia Bauru, Formação Marília)

The results presented are based on regional research of calcrete and palaeossols records in the Eastern part of the Bauru Basin, in Sao Paulo State and Triângulo Mineiro region. This basin was filled by Upper Cretaceous siliciclastic sandy sequence, in semi-arid climate on the edges, desert in the center. The most significant calcretes occurrences belong to the the Marilia Formation (Bauru Group), whichon a regional scale, are represented by two extreme types, related to the depositional context. The Ponte Alta type was formed in marginal alluvial fan deposits, the Echapora type in inner aeolian sandy deposits, of wide sand sheets and smooth depressions with temporary rivers and lakes. Three genetic contexts are proposed for the Marilia Formation calcretes: pedogenetic peripheral (Pp), pedogenetic interior (Pi) and phreatic (F). In the first two contexts the edaphic vadose and palustrine processes prevailed, as well as soil profiles poorly developed. It was noticed in them a big frequency of the beta microstructure association. They occur in the Triângulo Mineiro (MG), regions of Monte Alto, Agudos and Bauru (SP). In the phreatic context there was intense development of micritic and spar textures, which probably destroyed the original features of the beta association, generated in contexts Pp and Pi. The superimposed phreatic processes determined the predominance of the alpha microstructure association. They were probably more intense and of the last and/or the most important event in the internal calcrete formation of the basin,in Echapora type profiles. They occur in the regions of Echapora and Marilia (SP). The dendritic configuration of the long and narrow plateaux, sustained by calcified sandstones of the Marilia Formation indicates processes of landscape elaboration through the relief invertion.

Silicificação hidrotermal neocretácea na Porção Meridional da Bacia Bauru

Many occurrences of silicified sandstones were found in areas of exposition of the Caiua and Bauru groups (Bauru Basin, Late Cretaceous), in the northwest part of the states of Parana and extreme west of Sao Paulo, Brasil. Silicification occurs sometimes as pore lining, sometimes as partially or totally filling the intergranular space. Four different but often coexistent types of silicification were identified: (a) microcrystal growth in palisades, (b) sintaxial overgrowth (megaquartz), (c) pore filling by silica in mosaic polygonal texture, and (d) pore filling by silica in microcrystalline texture. Silicification developed in two different settings: (a) in a framework without compaction and (b) in mechanical compaction framework. Geological features of the occurrences and petrographic analyses indicate a hydrothermal origin for the silicification. It is very likely that such a hydrothermal event could have been associated with the Late Cretaceous alkaline magmatism. The silicification developed at the end of sedimentation and closing of the Bauru Basin

The inventory of geological heritage of the state of São Paulo, Brazil: Methodological basis, results and perspectives

An inventory of geological sites based on solid and clear criteria is a first step for any geoconservation strategy. This paper describes the method used in the geoheritage inventory of the State of São Paulo, Brazil, and presents its main results. This inventory developed by the geoscientific community aimed to identify geosites with scientific value in the whole state, using a systematic approach. All 142 geosites representative of 11 geological frameworks were characterised and quantitatively evaluated according to their scientific value and risk of degradation, in order to establish priorities for their future management. An online database of the inventory is under construction, which will be available to be easily consulted and updated by the geoscientific community. All data were made available to the State Geological Institute as the backbone for the implementation of a future state geoconservation strategy.

CONCENTRAÇÃO DE SEDIMENTOS EM SUSPENSÃO: Reservatório de Cachoeira Dourada - GO/MG, Brasil

The determination of the sediments in suspension concentration (CSS) in the Cachoeira Dourada Hydreletric Plant’s reservoir, was realized in two periods, the first in June 2003 and the other in February 2005. The humid and dry periods’ referred CSS showed the predominance of values up to 10 mg/l. However, in the Araras and Corgao rivers mounths, the concentration values reached more than 10 mg/l, like those ones between Corgao and Flecha rivers, which values reached 15 mg/l. The water visibility index (SEC) between Corgao dam and its stream presented values with amplitudes between 100-120 cm and 80-100 cm in the humid and dry periods, respectively. The minor values (CSS and SEC) to the stretch located between Candango and Patos streams can be related to the transverse section’s increase, out flowing’s speed reduction and to the existence of accumulations of water macrophytes.

Proveniência de sedimentos da Bacia de Curitiba por estudos de minerais pesados

Sediment provenance of the Curitiba basin by study of heavy minerals. Curitiba Basin is located in the South-central portion of the first plateau of Parana. It includes the city of the same name and some towns of the metropolitan region. It is a neogean basin elongated towards ENE direction, which belongs to the Cenozoic Rift System in Southeast Brazil. Its maintained sedimentary fill extends over 3,000 km2 and includes sludge, arkosic sands, and gravels of Guabirotuba Formation. Among the basins that are part of the Cenozoic Rift System of Southeast Brazil, Curitiba Basin is the least studied in details. Until the present moment, researches on this accessory assembly were not disclosed. We have analyzed transparent, nonmicaceous and nonmagnetic heavy minerals, with fraction of particle size from 3 - 4 φ (0.125 - 0.062 mm), which were separated using bromoform (d = 2.89 g/cm³) and handheld magnet. The determination was done with permanent assemblies of grains and Canada balsam (n = 1.53), analyzed in a petrographic microscope. In the mineralogical assembly, zircon grains, epidote, tourmaline, kyanite, rutile, and traces of sillimanite and garnet were predominantly found. Zircon occurs as euhedral to sub-euhedral grains, colorless to subordinate pink and metamict. The study of heavy minerals in Curitiba Basin suggests that towards the center of the basin, zircon quantities tend to decrease while amounts of epidote increase. Two mineralogical associations were characterized: the first, called High Zircon, has zircon quantities between 51 to 97%; the second one was called High Epidote and has relative epidote amounts between 31 to 53%. Such differences in zircon and epidote values allow to infer the possibility of having more than one source area for these sediments. The main paleocurrents trends indicated the granites of Graciosa Province and metamorphic rocks of the Atuba Complex as potential source rocks. Moreover, one cannot rule out the possibility of hydraulic segregation. Since zircon is denser, it tends not to move so much the basin transport as the epidote, which presents the lowest density. Therefore, it was concluded that the relative proportion between these two minerals would be a good tracer of the dynamics of sediment transportation in the basin.

Faciologia e contexto deposicional da Formação Guabirotuba, Bacia de Curitiba (PR)

A Bacia de Curitiba situa-se na porcao meridional do Sis- tema de Riftes Cenozoicos do Sudeste do Brasil (SRCSB). Possui cerca de 3.000 km2 de sedimentos cenozoicos com espessura preservada de ate 80 m, denominados de Formacao Guabirotuba. As pesquisas realizadas se ocuparam da caracterizacao sedimentologica e evolucao da compar- timentacao tectonica da bacia. Porem, a distribuicao das associacoes de facies sedimentares e seu contexto deposicional nao foram analisados de modo sistematico e, ainda hoje, prevalecem interpretacoes baseadas nos levantamentos das decadas de 1960 e 1980 ou em correlacoes com ou- tras bacias do SRCSB. E nesta circunstância que este estudo investigou o contexto deposicional dos sedimentos da Bacia de Curitiba por meio da analise dos elementos arquitetonicos e sua distribuicao em exposicoes de superficie. A arquitetura deposicional e os rumos medios de paleo- correntes permitem interpretar que as associacoes A, B, C e D sao de- positos de transicao entre as zonas proximais, intermediarias, e distais de sistemas distributarios fluviais. Por outro lado, as associacoes E e F exibem caracteristicas faciologicas e sedimentologicas distintas em rela- cao as demais associacoes de facies. Sua distribuicao restrita sugere que sistemas fluviais contemporâneos aos demais, mas com sutis diferencas se formaram nos setores oeste e nordeste da bacia. Estes setores coincidem com aqueles onde foram descritas as formacoes Tinguis e Piraquara, in- terpretadas como unidades distintas da Formacao Guabirotuba. A abun- dante quantidade relativa de lama e a ausencia de facies eolicas e/ou de feicoes sedimentares de exposicao e ressecacao, sugerem que tais sistemas formaram-se em condicoes de clima razoavelmente umido.

Avaliação do estado de assoreamento do reservatório de Cachoeira Dourada (GO/MG)

This research analyzed the degree of sedimentation in Cachoeira Dourada reservoir Brazil, belonging to the Paranaiba hydrologic catchment basin. Were evaluated bottom sediments of the lake, in an area of 74 km2. Were considered particle and bathymetric parameters. The results, presented on the maps, showed the distribution of the particles chacteristics and allowed to estimate the volume of sediments. The bottom deposits are essentially constituted of silt and clay in the portion near the dike; of fine and very fine sandy material in the middle sector of the reservoir and, in the beginning of the reservoir, we have since silt just large sand. By comparison of topographic data, since the construction of the reservoir, with present measured bathymetric data, the Cachoeira Dourada reservoir lost 38.5 % of its original storing capacity. The expected reservoir useful life, estimated in this research, is of about 145 years, following this deposition rhythm.

Filamentos microbianos em estromatólitos e laminitos da Sequência Balbuena III (Maastrichtiano/Daniano) da Formação Yacoraite na Sub-bacia Metán-Alemania, na região de Salta, Argentina, e seus significados paleoambientais

Salta Basin is located in the northwest of Argentina and its origin is related to an intracontinental rift which was formed during the Cretaceous and early Paleogene. It is subdivided into four sub-basins (Lomas de Olmedo - east; Sey - west; Tres Cruces - north; and Metan-Alemania - south) that were filled by sediments from the Pirgua (synrift phase), Balbuena and Santa Barbara (both in sag phase) Subgroups. The Subgroup or Supersequence Balbuena is divided into four sequences: Balbuena I, II, III and IV, from bottom to top. This research identified microbial filaments in scanning electron microscope images from stromatolites and laminites samples of Balbuena III Sequence (Maastrichtian/Danian), Yacoraite Formation, in the Metan-Alemania Sub-basin, situated in Cabra Corral dam region, district of Coronel Moldes, Argentina. The occurrence of these filaments, identified in limestones formed in dry weather periods and deposited in the closed lake interval of the studied sequence, indicates the influence of biological activity in the formation of these rocks. The identification of microbial filaments, preserved from cyanobacteria structures, supports the palaeoenvironmental interpretation, since the occurrence of these microorganisms is limited to the photic zone and is common to stressful environments. The laminites of the studied area have been interpreted as formed in supralittoral mudflats in the vadose zone, while the stromatolites were formed in sublittoral environment, being constantly submerged. In addition to the microbialites, the Balbuena III Sequence consists of carbonates, siliciclastic and mixed facies which have been deposited in a lacustrine environment.Manuscript ID 30255. Received in: 03/10/2015. Approved in: 08/31/2015. RESUMO: A Bacia de Salta localiza-se no noroeste argentino e sua origem está relacionada a um rifte intracontinental, formado durante o Cretáceo e início do Paleógeno. Subdivide-se em quatro sub-bacias (Lomas de Olmedo a leste; Sey a oeste; Tres Cruces a norte; e Metán-Alemania a sul) que foram preenchidas por sedimentos dos Subgrupos Pirgua (fase sin-rifte), Balbuena e Santa Bárbara (fase sag). O Subgrupo ou Supersequência Balbuena é dividido em quatro sequências: Balbuena I, II, III e IV, da base para o topo. O presente estudo identificou filamentos microbianos em imagens geradas pelo microscópio eletrônico de varredura em amostras de estromatólitos e laminitos da Sequência Balbuena III (Maastrichtiano/Daniano) da Formação Yacoraite, na Sub-bacia Metán-Alemania, região do dique Cabra Corral, distrito de Coronel Moldes, Argentina. A ocorrência desses filamentos, identificados em calcários formados em períodos de clima árido e depositados no intervalo de lago fechado da sequência em estudo, indica a influência de atividade biológica na formação dessas rochas. A identificação dos filamentos microbianos, preservados a partir de estruturas de cianobactérias, auxilia a interpretação paleoambiental, uma vez que a ocorrência desses microorganismos é limitada à zona fótica e é comum a ambientes estressantes. Os laminitos da área de estudo foram interpretados como formados em planícies lamosas supralitoABSTRACT: Salta Basin is located in the northwest of Argentina and its origin is related to an intracontinental rift which was formed during the Cretaceous and early Paleogene. It is subdivided into four sub-basins (Lomas de Olmedo – east; Sey – west; Tres Cruces – north; and Metán-Alemania – south) that were filled by sediments from the Pirgua (synrift phase), Balbuena and Santa Bárbara (both in sag phase) Subgroups. The Subgroup or Supersequence Balbuena is divided into four sequences: Balbuena I, II, III and IV, from bottom to top. This research identified microbial filaments in scanning electron microscope images from stromatolites and laminites samples of Balbuena III Sequence (Maastrichtian/Danian), Yacoraite Formation, in the Metán-Alemania Sub-basin, situated in Cabra Corral dam region, district of Coronel Moldes, Argentina. The occurrence of these filaments, identified in limestones formed in dry weather periods and deposited in the closed lake interval of the studied sequence, indicates the influence of biological activity in the formation of these rocks. The identification of microbial filaments, preserved from cyanobacteria structures, supports the palaeoenvironmental interpretation, since the occurrence of these microorganisms is limited to the photic zone and is common to stressful environments. The laminites of the studied area have been interpreted as formed in supralittoral mudflats in the vadose zone, Microbial filaments in stromatolites and laminites of Balbuena III Sequence (Maastrichtian/Danian) of Yacoraite Formation in Metán-Alemania Sub-basin, Salta region, Argentina, and its palaeoenvironmental significance

Sedimentologia dos depósitos cenozóicos continentais do Baixo Vale do Rio Ribeira do Iguape, SP

Recent studies on continental deposits that occur at the lower Ribeira do Iguape river valley (southern State of Sao Paulo, Brasil), led to the recognition of five different stratigraphic units, namely: the Sete Barras Formation, the Pariquera-Acu Formation, two levels of fluvial terraces, and colluvial-alluvial deposits. All these sediments were formerly attributed to the Pariquera-Acu Formation (with stages I,IIand III), considered to be Pleistocene. This paper presents the stratigraphic and sedimentological data which support the re-definition of the Pariquera-Acu Formation. Field work and grainsize analysis allowed to determine the main sedimentary processes for each unit. Maturity of heavy-minerals and nature of clays support the interpretation of paleoclimates. Both processes and paleoclimates pointed toward probable depositional systems and Cenozoic evolution of the area