Alto Garcas Research Articles

Paleoenvironments of a regressive Devonian section from Paraná Basin (Mato Grosso do Sul state) by integration of ichnologic, taphonomic and sedimentologic analyses

Studies that integrate ichnologic, taphonomic and sedimentologic data result in more accurate paleoenvironmental inferences than isolated approaches. Most of paleontological studies regarding Devonian from Parana Basin were conducted in the southern part of the basin (Parana state), precluding taphonomic or ichnologic studies to the northern part, and even its macrofossils content is understudied. This study analyzes paleoecologic and depositional conditions represented by trace fossils, macrofossils and sedimentary facies in a regressive Devonian section from Parana Basin, Mato Grosso do Sul state, Brazil. Seven ichnofabrics (Macaronichnus, Psammichnites, Arenicolites-Skolithos, Cylindrichnus-Skolithos, Zoophycos, Rhizocorallium- Palaeophycus, and Chondrites ichnofabrics) and three taphofacies (T1: parautochthonous to allochthonous preservation; T2: Autochthonous preservation; and T3: time-averaged autochthonous to allochthonous association) were diagnosed. The studied sections are positioned in a highstand systems tract (HST) exhibiting dominance of sandy facies, and four sub-environments were defined: foreshore; shoreface; storm-dominated shoreface to transitional offshore; and offshore. The dominance of foreshore to shoreface settings in a HST corroborates a shallower context in relation to the southern part. However, similarities in the facies and ichnofacies stacking, as well in the macrofossil content suggest that the hypothetical division between two sub-basins (Apucarana and Alto Garcas Sub-basins) was not complete until early Emsian.

Metacryphaeus Tuberculatus andMetacryphaeus australis(Trilobita, Phacopida) from the Devonian of the Paraná Basin: Taxonomy and Paleobiogeography

Calmoniid trilobites of the genus Metacryphaeus Reed include M. tuberculatus (Kozlowski), M. kegeli Carvalho, Edgecombe and Lieberman, M. meloi Carvalho, Edgecombe and Lieberman, M. rotundatus (Kozlowski), M. giganteus (Ulrich), M. convexus (Ulrich), M. curvigena Lieberman, M. branisai Lieberman, M. caffer (Salter), M. australis (Clarke), and M. allardyceae (Clarke). The geographic distribution of this genus comprises areas of Gondwana, including Bolivia, Peru, Brazil, the Falkland Islands, and South Africa. This study reports a new occurrence of M. tuberculatus in the Parana Basin (Goias and Parana states, Brazil), in both the Alto Garcas and the Apucarana sub-basins. Metacryphaeus tuberculatus was compared with all Metacryphaeus species and, especially, with M. australis, which also represents a new record for the Parana Basin. These new records of M. tuberculatus imply a different dispersion interpretation from that which is known through the literature. Metacryphaeus tuberculatus seems to have originated during the Early Devonian and lived in areas such as Bolivia, Peru, and the Apucarana Sub-basin (Parana Basin, Brazil). The dispersion between these areas is probably related to the Emsian transgression. During the Givetian, the species presumably migrated towards the Alto Garcas Sub-basin (Parana Basin, Brazil) and the Parnaiba Basin. These facts provide an alternative paleogeographic interpretation to that presented by Tropidoleptus Hall and Exaesiodiscus Moore and Jeffords in Gondwana and suggest a different pattern of migration during the Devonian of Brazil.

Dinâmica da matéria orgânica de um neossolo quartzarênico de cerrado convertido para cultivo em sucessão de soja e milheto

O uso e o manejo de Neossolos Quartzarênicos podem influenciar a matéria orgânica do solo (MOS), mas a magnitude dessas alterações ainda é pouco pesquisada nas condições de Cerrado. O objetivo deste trabalho foi estudar as variações que ocorrem na MOS em um Neossolo Quartzarênico, por consequência da conversão da vegetação original para o uso agrícola e cultivo sequencial de soja e milheto em sucessão. Em uma área de cultivo comercial em Alto Garças, MT, foram coletadas amostras de solo nas profundidades de 0-5, 0-10, 0-20 e 0-40 cm, em talhões que estavam sob sucessão soja-milheto durante 1, 2, 6, 8 e 10 anos e, como referência da vegetação original, amostras foram tomadas em área adjacente sob Cerrado nativo. Foram determinados os teores de carbono orgânico total (COT), carbono e nitrogênio total e o teor de carbono nas frações ácidos húmicos, ácidos fúlvicos e na matéria orgânica leve (MOL), além da relação isotópica do carbono na MOS. A conversão do Cerrado para cultivo agrícola elevou o teor de COT do solo, sobretudo em razão do aporte de MOL e fragmentos de carvão. O manejo desse solo com a sucessão soja-milheto, mesmo com o uso de gradagens pesadas, não causou reduções nos teores de COT, ao longo do tempo. Contudo, observou-se variação na distribuição do carbono nas diferentes frações da MOS ao longo do tempo de cultivo, indicando alterações significativas na qualidade da MOS. Notou-se aumento no percentual de carbono na forma de MOL e redução dos teores de carbono na forma de ácidos fúlvicos ao longo do tempo de cultivo, sugerindo a perda seletiva dos compostos mais solúveis. A relação isotópica do carbono do solo aumentou com o tempo de cultivo, indicando maior contribuição do carbono derivado do milheto para a manutenção dos teores de MOS. Os atributos da MOS relativos à camada de 0-20 cm foram mais sensíveis às variações em razão do tempo de cultivo do que os mesmos atributos avaliados nas demais camadas estudadas. As variáveis relacionadas ao fracionamento da MOS evidenciaram-se mais sensíveis às variações por causa do tempo de cultivo do que simplesmente do teor de COT do solo, apresentando o potencial de uso dessas variáveis como indicadores de qualidade do solo.

The Furnas/Ponta Grossa contact and the age of the lowermost Ponta Grossa Formation in the Apucarana Sub-Basin (Paraná Basin, Brazil): integrated palynological age determination

The Furnas/Ponta Grossa Formation contact was until recently considered gradational or abrupt and of a Lochkovian to Pragian age in the Apucarana Sub-basin (Parana Basin, south Brazil). Based on sedimentology and palynomorph evidence a hiatus has been revealed between the Furnas Formation and the overlying Ponta Grossa Formation. The boundary between the topmost Furnas sandstones and the lowermost Ponta Grossa fine-grained sandstones constitutes a transgressive ravinement surface generated during a latest Pragian - early Emsian transgression. The hiatus corresponds to a maximum of ca. 4 Ma. A similar gap is also present in the Alto Garcas Sub-basin.

Othonella araguaiana (Bivalvia, Megadesmidae) from the Corumbataí Formation (Midlle Permian), Eastern Margin of the Paraná Basin: systematic, evolutionary and biostratigraphic significances

In this study, the occurrence of Othonella araguaiana Mendes, a rare bivalve species is reported for the first time in the Pinzonella illusa biozone, Middle Permian Corumbatai Formation, in the State of Sao Paulo. This species was originally described in coeval rocks of the Estrada Nova Formation (= Corumbatai) from the Alto Araguaia and Alto Garcas regions, State of Mato Grosso. The specimens of O. araguaiana were found in the base of a bioclastic sandstone bed, a proximal tempestite, in the middle of the Corumbatai Formation, in the city of Rio Claro, Sao Paulo State. The silicified shells and internal molds are well preserved, showing impressions of muscle scars and other internal anatomic characters (e.g., hinge), never illustrated by previous authors. In his original description, Mendes (1963) called attention to the similarity between O. araguaiana and Terraia aequilateralis, a common veneroid of the Corumbatai Formation. Conversely, Runnegar and Newell (1971) suggested that O. araguaiana belongs to Megadesmidae, being a junior synonym of Plesiocyprinella carinata (the commonest megadesmid of the Passa Dois Group). Our study indicates that O. araguaiana is indeed a megadesmid, but is distinct from the P. carinata. The new occurrence of O. araguaiana demonstrates that a) the paleobiogeographic distribution of this species is wider than previously thought (that it was restricted to the northern part of Parana Basin, Mato Grosso State); b) the molluscan fauna of the Corumbatai Formation (P. illusa biozone) in the State of Sao Paulo is more diverse and dominated by megadesmids; and c) the composition of the molluscan fauna of the Corumbatai Formation in Alto Garcas, State of Mato Grosso, is essentially the same as that of the P. illusa biozone of the eastern margin of the Parana Basin.

Aplicação de dessecantes em pré-colheita: efeito na qualidade fisiológica de sementes de soja

Oscilações de temperatura acompanhadas de altos índices pluviais e flutuação de umidade relativa do ar, nas fases de maturação e pré-colheita, podem provocar perdas na qualidade física, fisiológica e na sanidade de sementes. A aplicação de dessecantes em pré-colheita contribui para a redução da exposição das sementes a condições climáticas desfavoráveis e para diminuir a possibilidade de prejuízos à germinação e vigor. Nesta pesquisa o objetivo foi avaliar o efeito da época de aplicação de dessecantes e da antecipação da colheita sobre a qualidade fisiológica de sementes de soja. Os experimentos foram conduzidos com as cultivares MG/BR-46 Conquista e FMT Tucunaré, na safra 2005/2006, e BRS MT Pintado e FMT Tucunaré, na safra 2006/2007, em Alto Garças, MT. Utilizou-se delineamento experimental blocos casualizado, em esquema fatorial 6x2x2x2 (5 tratamentos dessecantes + 1 testemunha, 2 épocas de dessecação, 2 épocas de colheita e 2 períodos de armazenamento). Os tratamentos dessecantes (paraquat, diquat, paraquat+diquat, paraquat+diuron e glifosato) foram aplicados nos estádios reprodutivos R6.5 e R7 e as sementes colhidas quando atingiram grau de umidade entre 17% e 20% (colheita antecipada) e entre 12% e 13% (colheita normal). As sementes obtidas em colheitas antecipadas foram submetidas à secagem em estufa com circulação forçada de ar, a 38 ºC - 40 ºC, até atingirem graus de umidade entre 12% e 12,5%. O desempenho das sementes foi avaliado em testes de germinação, classificação do vigor de plântulas, tetrazólio, emergência de plântulas em campo e comprimento de plântulas. Os dessecantes paraquat, diquat, paraquat+diquat e paraquat+diuron não influenciam a qualidade fisiológica das sementes, enquanto o glifosato provoca danos por fitotoxicidade no sistema radicular de plântulas de soja, afetando negativamente o desempenho da semente. A dessecação realizada nos estádios R6.5 ou R7, com exceção do uso do glifosato, possibilita a produção de sementes com desempenho semelhante. A colheita antecipada proporciona sementes de soja com melhor qualidade fisiológica.

Palynostratigraphy of the Chapada Group and its significance in the Devonian stratigraphy of the Paraná Basin, south Brazil

The Alto Garcas Sub-basin in the northern part of the Parana Basin evolved differently from the Apucarana Sub-basin in the south. The marine environment was shallower in the Alto Garcas Sub-basin, which contains proportionately more silty and arenaceous rocks. The formations and members defined in the Apucarana Sub-basin are therefore difficult to apply in the Alto Garcas Sub-basin, where the Chapada Group (units 1–4) is more applicable. An integrated miospore and chitinozoan biozonation of the Chapada Group facilitates direct correlation between the Chapada Group’s units and the classical formations of the Parana Basin as defined in the Apucarana Sub-basin. The Furnas Formation and Chapada unit 1 constitute the same lithostratigraphic unit. Beds with rhyniophytes in the uppermost part of the Furnas Formation contain palynomorphs representative of the Si phylozone within the MN spore Zone (late Lochkovian), and the rhyniophyte beds occupy the same stratigraphic interval within Chapada unit 1 (the Lochkovian of the Parana Basin lacks chitinozoans). The lower part of Chapada unit 2 contains spores of the PoW Su spore Zone and chitinozoans of the Ramochitina magnifica and Ancyrochitina pachycerata zones, together indicating a late Pragian–early Emsian age-span. The upper part of Chapada unit 2 corresponds to the GS (AP) and Per (AD pre-Lem) spore Zones, and chitinozoans of the Ancyrochitina parisi, the informal Ancyrochitina varispinosa and Alpenachitina eisenacki chitinozoan zones, thus suggestive of a late Emsian – earliest Givetian age-span. Unit 3 is a proximal and lateral facies equivalent of the upper part of unit 2. The lower part of unit 4 includes spores typical of the early Givetian Lli (AD Lem) spore Zone and chitinozoans of the Ramochitina stiphrospinata chitinozoan Zone; the uppermost (early late Frasnian) part contains spores of the lower BMu (IV) spore Zone and chitinozoans of the Lagenochitina avelinoi chitinozoan Zone. The sandstones of unit 3 were inundated during the earliest Givetian, and the resultant flooding surface marks the base of unit 4 basin-wide. Clearly, the two sub-basins were distinct depositional centers during the Devonian.

MIDDLE AND UPPER DEVONIAN CHITINOZOAN BIOSTRATIGRAPHY OF THE PARANA BASIN IN BRAZIL AND PARAGUAY

Abstract Chitinozoans from Middle and Upper Devonian strata have been investigated from the Parana Basin in southern Brazil and eastern Paraguay. These sequences are present in the Alto Garcas (north) and Apucarana (south) sub‐basins in Brazil, and the “East Paraguay Sub‐basin”; in eastern Paraguay. Marine communication between the sub‐basins was established during the early Givetian. Of the 49 chitinozoan species encountered, 28 species are retained in open nomenclature, and Ancyrochitina simplex is newly described. A chitinozoan biozonation, with five zones, is proposed for the investigated interval. The zones are from oldest to youngest: concurrent range zone of Alpenachitina eisenacki and Spinachitina biconstricta (late Eifelian?‐early Givetian); the interval range zone of Ancyrochitina taouratinensis (latest early‐middle Givetian); concurrent range zone of Fungochitina pilosa and Ancyrochitina langei (late Givetian); concurrent range zone of Hoegisphaera glabra and Ramochitina derbyi (early Frasnian)...

SILURIAN AND LOWER DEVONIAN CHITINOZOAN BIOSTRATIGRAPHY OF THE PARANA BASIN IN BRAZIL AND PARAGUAY

Abstract The taxonomy and distribution of Chitinozoa from Silurian (Llandovery) and Lower Devonian strata are reported from the Parana Basin in southern Brazil and eastern Paraguay. The pre‐Carboniferous sequences of the Parana Basin in this area are present in three sub‐basins viz., the Alto Garcas (north) and Apucarana (south) sub‐basins in Brazil, and the “East Paraguay Sub‐basin”; in east Paraguay. There is more similarity in the lithology between the Alto Garcas and “East Paraguay”; sub‐basins, than between the former and the Apucarana sub‐basin. Llandoverian and Lochkovian to Pragian beds are present in all sub‐basins. So far, no Emsian beds have been found in outcrops from the north‐northwest margin of the Alto Garcas Sub‐basin, and no early Emsian beds in the outcrops on the northeast margin. Furthermore, Emsian beds could not be identified from the “East Paraguay Sub‐basin”; in the present study. The Early Devonian sequence is more complete in the Apucarana Sub‐basin. It seems that the Apucarana ...

FÁCIES SEDIMENTARES E SISTEMAS DEPOSICIONAIS DAS FORMAÇÕES ALTO GARÇAS E VILA MARIA NA REGIÃO DE CHAPADA DOS GUIMARÃES (MT), BORDA NOROESTE DA BACIA DO PARANÁ

The Ordovician-Silurian interval of the Parana Basin, outcropping in the Chapada dos Guimaraes, Campo Verde and Santo Antonio do Leverger counties (MT), is represented by the Alto Garcas and Vila Maria formations. This interval is characterized by sixteen lithofacies and two ichnofacies. Among these lithofacies, nine ruditics, six arenitics and one lutitic are identified. The ruditics lithofacies are named massive conglomerate (Cm), conglomerate in tabular beds (Ct), conglomerates and sandstones interbedded in tabular beds (Ct(H)), conglomerate with cross-stratification (Cc), massive diamictite (Dmm), massive diamictite with evidence ofressedimentation (Dmm(r)), stratified diamictite (Dms), stratifieddiamictite with evidence of current reworking (Dms(c)) and stratified diamictite with evidence of ressedimentation (Dms(r)); the arenitics ones are named massive sandstone (Am), sandstone in tabular beds (At), sandstone with climbing-ripple cross-lamination (Acl), sandstone with cross-stratification (Ac2), sandstone with ripple cross-lamination (Ao) and sandstones and shales interbedded inflaser, wavy and linsen bedding (Ao(H)); and finally the lutitic lithofacies is named shale with dropstone (Fid). The identified ichnofacies are Skolithos (Sko), by the presence of Skolithos linearis, Arenicolites ichnosp. and Diplocraterion ichnosp., and Cruziana (Crz), by the presence of Arthrophycus alleghaniensis, Palaeophycus tubularis, Aulichnites ichnosp., Lockeia ichnosp., Chondrites ichnosp. and Teichichnus ichnosp. Those facies were related in four depositional systems: Fluvial System (SF-facies Cc), Rudaceous Shallow Marine System (SMRrud-facies Ct, Ct(H), Cm, At, Ac2, Crz), Arenaceous Shallow Marine System (SMRarn-facies Am, At, Ac2, Ao, Ao(H), Sko) and Glaciomarine System (SG-facies Dmm, Dmm(r), Dms, Dms(r), Dms(c), Acl, Fid, Crz). The Alto Garcas Formation, based on the association of the facies At, Am and Sko, is interpreted as the SMRarn system. The Vila Maria Formation is characterized by a succession of (i) beds of the Cc facies, interpreted as the SF system; (ii) beds of the Ct(H) facies, interpreted as deposits of a beach-face of the SMRrud system; (iii) beds of the Ct and At facies, interpreted as proximal shoreface deposits dominated by storms of the SMRrud system; (iv) beds of the At, Ct and Crz facies, interpreted as distal shoreface deposits dominated by storms of the SMRrud system; (v) beds of the diamictite facies, and Fid, Crz and Acl facies, all together interpreted as SG system; (vi) beds of the At, Crz, Ct and Ac2 facies, interpreted as proximal and distal shoreface deposits dominated by storms of the SMRrud system; (vii) and beds of the At, Sko, Ao and Ao(H) facies, interpreted as lagoonal and proximal shoreface deposits dominated by storms of the SMRarn system.

FÁCIES SEDIMENTARES E SISTEMAS DEPOSICIONAIS DAS FORMAÇÕES ALTO GARÇAS E VILA MARIA NA REGIÃO DE CHAPADA DOS GUIMARÃES (MT), BORDA NOROESTE DA BACIA DO PARANÁ

The Ordovician-Silurian interval of the Paraná Basin, outcropping in the Chapada dos Guimarães, Campo Verde and Santo Antonio do Leverger counties (MT), is represented by the Alto Garças and Vila Maria formations. This interval is characterized by sixteen lithofacies and two ichnofacies. Among these lithofacies, nine ruditics, six arenitics and one lutitic are identified. The ruditics lithofacies are named massive conglomerate (Cm), conglomerate in tabular beds (Ct), conglomerates and sandstones interbedded in tabular beds (Ct(H)), conglomerate with cross-stratification (Cc), massive diamictite (Dmm), massive diamictite with evidence ofressedimentation (Dmm(r)), stratified diamictite (Dms), stratifieddiamictite with evidence of current reworking (Dms(c)) and stratified diamictite with evidence of ressedimentation (Dms(r)); the arenitics ones are named massive sandstone (Am), sandstone in tabular beds (At), sandstone with climbing-ripple cross-lamination (Acl), sandstone with cross-stratification (Ac2), sandstone with ripple cross-lamination (Ao) and sandstones and shales interbedded inflaser, wavy and linsen bedding (Ao(H)); and finally the lutitic lithofacies is named shale with dropstone (Fid). The identified ichnofacies are Skolithos (Sko), by the presence of Skolithos linearis, Arenicolites ichnosp. and Diplocraterion ichnosp., and Cruziana (Crz), by the presence of Arthrophycus alleghaniensis, Palaeophycus tubularis, Aulichnites ichnosp., Lockeia ichnosp., Chondrites ichnosp. and Teichichnus ichnosp. Those facies were related in four depositional systems: Fluvial System (SF-facies Cc), Rudaceous Shallow Marine System (SMRrud-facies Ct, Ct(H), Cm, At, Ac2, Crz), Arenaceous Shallow Marine System (SMRarn-facies Am, At, Ac2, Ao, Ao(H), Sko) and Glaciomarine System (SG-facies Dmm, Dmm(r), Dms, Dms(r), Dms(c), Acl, Fid, Crz). The Alto Garcas Formation, based on the association of the facies At, Am and Sko, is interpreted as the SMRarn system. The Vila Maria Formation is characterized by a succession of (i) beds of the Cc facies, interpreted as the SF system; (ii) beds of the Ct(H) facies, interpreted as deposits of a beach-face of the SMRrud system; (iii) beds of the Ct and At facies, interpreted as proximal shoreface deposits dominated by storms of the SMRrud system; (iv) beds of the At, Ct and Crz facies, interpreted as distal shoreface deposits dominated by storms of the SMRrud system; (v) beds of the diamictite facies, and Fid, Crz and Acl facies, all together interpreted as SG system; (vi) beds of the At, Crz, Ct and Ac2 facies, interpreted as proximal and distal shoreface deposits dominated by storms of the SMRrud system; (vii) and beds of the At, Sko, Ao and Ao(H) facies, interpreted as lagoonal and proximal shoreface deposits dominated by storms of the SMRarn system.

SEQUÊNCIAS TECTONO-SEDIMENTARES MESOPALEOZÓICAS DA BACIA DO PARANÁ, SUL DO BRASIL

This work presents a basinwide analysis on the Precarboniferous sequences of the Parana basin. Sufarce and well data have been used to update geological interpretation and to suggest a new stratigraphic proposal for the Ordovician-Silurian of the Parana basin. The diamictites, present in the Iapo, Vila Maria, and Rio Ivai Formations, play important role in the new proposal, for they are interpreted as time correlate horizons related to Neo-Ordovician Gondwanan glaciations. It is herein proposed a gradational contact between the Furnas and Ponta Grossa Formations, as well as, the existence of a conspicuous unconformity in the Upper Silurian. The Precarboniferous of the Parana basin is divided into two tectosedimentary sequences: 1. an Ordovician-Silurian sequence (Rio Ivai Group) composed of basal conglomerates and fluvial sandstones, overlain by coastal and marine sandstones (Alto Garcas Formation). This sandy unit is covered by diamictites (Iapo Formation), and transgressive marine shales/coastal sandstones (Vila Maria Formation). The Rio Ivai Group correlates with the Caacupe and Itacurubi Groups in Paraguay; 2. a Devonian sequence (Parana Group) composed of a sandy unit (Furnas Formation) deposited by braid deltas, ending in a marine shaly unit (Ponta Grossa Formation). The Ponta Grossa Formation has two maximum flooding surfaces bounded by prograding deltaic sandstones originating in East and Northeast sources.