Itarare Group Research Articles

Grupo Itararé na região de Itu, estado de São Paulo: intensos processos glaciais erosivos e deposicionais

O Grupo Itararé, Neopaleozoico (Mississippiano-Pennsylvaniano) da Bacia do Paraná, está exposto em grande parte da faixa leste do Estado de São Paulo, predominantemente sobre rochas pré-cambrianas. As áreas aqui designadas Itu e Salto são notáveis pela abundância de registros glaciais, embora de natureza distinta. Este trabalho discute as feições glaciais presentes nessas áreas como subsídio para reconstruções paleoambientais, partindo-se de estudos prévios, e traz observações inéditas de uma frente sedimentar exposta por escavação na Pedreira Colonial. Na área-Salto, o destaque são as evidências de forte ação erosiva glacial, tais como, rochas moutonnées, só encontradas no Brasil nessa região, e pavimentos estriados, associados a tilitos, diamictitos e depósitos aquoso-glaciais que atingem até 8 m de espessura. Na área-Itu, destacam-se os espessos depósitos aquoso-glaciais e, subordinadamente, diamictitos e tilitos que podem alcançar até 300 m de espessura.

Facies, petrophysical and geochemical properties of gravity-flow deposits in reservoir analogs from the Itararé Group (late Carboniferous), Paraná Basin, Brazil

Abstract Since many reservoirs do not allow direct observation due to their depth and/or difficulty of sampling, studies of analogs have been commonly used as a tool to understand the spatial distribution of reservoir properties. The Parana Basin is 1.6 million km2 large and has two known petroleum systems. However, there are only 124 irregularly distributed wells drilled in the basin, among which 22 contain gas or oil shows and 10 have sub commercial accumulations. The Permo-Carboniferous Itarare Group, due to the exploration history, is the best exploratory target in the basin because it has thick intervals of sandstones with moderate to good reservoir quality and also because it often lies directly on gas-prone source rocks of the Devonian Ponta Grossa Formation. In order to increase knowledge about Itarare Group reservoirs, as well as to better understand its heterogeneities, this study aims to integrate petrophysical data with facies and facies associations using both outcrop and cores from shallow wells in southeastern Parana Basin. By doing this it is expected to fill a gap of quantitative data in previous studies on reservoir analogs in the Itarare Group. Cores and outcrops were analyzed in sandstones in order to integrate surface and subsurface data, and to understand the lateral continuity according to stratigraphic correlations. Equipment such as gamma-ray spectrometer, portable x-ray fluorescence, and a minipermeameter were used for the acquisition of quantitative data. Sedimentological description of cores and outcrops as well as thin section description were also carried out. The facies with the greatest reservoir potential are medium to fine-grained, massive (Sm) and normally-graded (Sg) sandstones. In one outcrop locality (Rio dos Cedros), the Sg facies presents the best reservoir properties such as secondary porosity of 32% and average permeability of 1439 mD. The geochemical data allowed evaluating the gamma-ray variation in relation to chemical elements, such as iron oxide. In outcrop, API radiation is higher in relation to the cores, as well as Al2O3 and Fe2O3. These values are related to the large amount of intraclasts and cementation by iron oxides-hydroxides. Despite in the great amount of iron presents in the Rio dos Cedros samples, the porosity is mainly secondary, generated by the feldspars dissolution. The correlation between the cores and outcrops allowed the evaluation of the influences of mass transport deposits in the petrophysical properties of sandstones. In cores, sandstones interbedded with these deposits have high permeability, but it is not possible to evaluate its lateral continuity. In outcrops it was possible to observe that these deposits affect lateral continuity, permeability and porosity. We conclude that the best reservoir facies in the Itarare Group will be associated with sites within the basin that are away from the slope region and the influence of mass-transport processes.

Evidence for Widespread Remagnetizations in South America, Case Study of the Itararé Group Rocks From the State of São Paulo, Brazil

Paleomagnetism of South American Jurassic/ Cretaceous rocks has been troubled by elongated distributions of poles which has led to contrasting interpretations. Moreover, many discordant paleomagnetic poles from the Carboniferous to the Triassic have also been recognized and systematically explained by a variety of processes, but this portion of the South American apparent polar wonder path (APWP) still remains problematic. To this end, we have conducted a paleomagnetic study of the sedimentary Permo-Carboniferous Itarare Group rocks and three intruding mafic sills of likely Cretaceous age within the state of Sao Paulo, Brazil. The site-mean VGP distributions obtained from the sedimentary rocks define elongations that include the VGPs of the mafic intrusions. We interpret these distributions as remagnetization paths towards the directions characteristic of the sills. Furthermore, we show that the remanence directions of the sills are partially overprinted by the present time-averaged and current Earth's magnetic field. Our interpretations are supported by extensive rock-magnetic data that provides a viable mechanism for the secondary magnetizations. The current study focuses on the paleomagnetism and rock-magnetism of the mafic intrusions and how they affected the paleomagnetic recording of the sedimentary rocks, however, careful analysis of the paleomagnetic data of the Itarare sedimentary rocks enables isolation of a primary VGP distribution that is consistent with the reference Carboniferous pole position. Extending our study to other Carboniferous to Triassic South American paleomagnetic records reveals that the majority of these data are elongated, similarly to the Itarare Group rocks. Regardless of the age of the rocks, the elongations systematically intersect at the location of the Late Cretaceous reference pole, and at a long- recognized problematic location observed in some Jurassic and Cretaceous rock formations. Based on multiple lines of evidence, we interpret the elongations to reflect remagnetizations from the primary VGP positions towards Jurassic-Cretaceous pole locations that occurred as a result of the widespread magmatic events associated with the opening of the South Atlantic. We suggest that the extent of the remagnetizations is formation-specific, and that other rock-formations should be carefully re-evaluated.

CONTEXTO ESTRUTURAL DA ÁREA DA FOLHA TOPOGRÁFICA GUAPIARA

A Folha Topográfica de Guapiara 1: 50.000, localiza-se no extremo sul do estado de São Paulo e compreende a porção norte do Terreno Apiaí, de idade meso- a neoproterozoicas, inserido na faixa centro-sul do Cinturão Ribeira da Província Mantiqueira Central. A região caracteriza-se pelas rochas da sequência metavulcanossedimentar do Supergrupo Açungui, definidas pela Formação Água Clara e os grupos Votuverava e Itaiacoca, além de corpos graníticos do Granito Três Córregos e do Granito Capão Bonito, rochas sedimentares do Grupo Itararé, intrusivas básicas associadas ao Magmatismo Serra Geral e sedimentos quaternários. O quadro estrutural é determinado dominantemente pelo arranjo tectônico neoproterozoico. As rochas apresentam uma evolução estrutural do tipo polifásica, evidenciada pela superposição de eventos de principalmente quatro fases deformacionais Dn, Dn+1, Dn+2 e Dn+3. Os dois eventos iniciais são relacionados a uma tectônica de cavalgamento, de direção NE/SW e NW/SE, respectivamente, acompanhado de estruturas geneticamente associadas, tais como falhas de cavalgamentos, dobras e as foliações Sn e Sn+1. Superpondo-se a estas estruturas, ocorrem dois eventos Dn+2 e Dn+3, ligados a fase colisional final e uma tectônica transcorrente/transpressiva. Esse evento é responsável pelo dobramento das estruturas pré-formadas, com plano axial de direção NE/SW e NW/SE, respectivamente.

O Folhelho Lontras (Permiano, Bacia do Paraná) e seus Fósseis: Descoberta, Identificação e Conhecimento Atual

The Shaler Memorial Fund created in 1907 by students and admirers of the geologist Nathaniel Southgate Shaler, professor from Harvard University, allowed in its first contribution to fostering research, the organization of an expedition to the South and Southeast of Brazil. The expedition had the purpose to confirm Nathaniel`s ideas about the existence of glacial layers older then the Pleistocene. Led by the North American geologist Jay Backus Woodworthy and counting with participation of the Brazilian geologist Euzebio de Oliveira, the expedition not only proved the presence of glacial evidence but also discovered an intercalated fossiliferous marine shale, later known as Lontras Shale, Itarare Group. The fossils, initially studied by the American paleontologist Rudolf Ruedemann and by Euzebio de Oliveira, had its studies intensified from the 1980s with the identification of new outcrops and due the new data of the geological evolution of the carboniferous and permian sedimentary sucessions of the Parana Basin. Economic disputes and discussion about the preservation of Lontras Shale outcrops, besides the discovered of new site namely as CAMPALEO, have reactivated the scientific interest about this unit and its paleontological content, increasing its studies. Poorly known by the Brazilian academic community, the historical context of the Lontras Shale is here reported, highlighting the importance of the Shale Memorial Fund as responsible for the geological and paleontological discoveries that have followed, for more than a century.

GEOLOGIA DA FOLHA TOPOGRÁFICA GUAPIARA NA ESCALA 1:50.000

A região da Folha Topográfica de Guapiara situa-se no extremo sul do estado de São Paulo e compreende na porção central da Província Mantiqueira a faixa centro-sul do Cinturão Ribeira. O arcabouço geológico local envolve rochas da sequência metavulcanossedimentar do Supergrupo Açunguí, de idade meso- a neoproterozoicas deformadas e metamorfizadas no neoproterozoico, associadas a rochas granitoides geradas durante os episódios colisionais ligados ao Ciclo Brasiliano e à formação do Supercontinente Gondwana. As principais unidades litoestratigráficas são constituídas pelos metassedimentos da Formação Água Clara e dos grupos Votuverava e Itaiacoca de idade meso- a neoproterozoica, corpos graníticos neoproterozoicos representantes do Complexo Granito Três Córregos e do Maciço Granito Capão Bonito, rochas sedimentares do Grupo Itararé, efusivas básicas associadas ao Magmatismo Serra Geral e sedimentos recentes quaternários. O quadro estrutural-metamórfico é determinado pelo arranjo tectônico final neoproterozóico, evidenciado nas rochas epimetamórficas por uma evolução estrutural do tipo polifásica, com quatro fases de deformação (Sn, Sn+1, Sn+2 e Sn+3) e três eventos metamórficos (M1, M2 e M3), de caráter regional progressivo, contato e regional a localmente dinâmico de natureza retrometamórfica.
 Palavras-chave: geologia, estrutural, mapeamento, Guapiara.

Palinomorfos e associações de fácies da Formação Lagoa Azul (Grupo Itararé, Pennsilvaniano da Bacia do Paraná) no sudeste do Estado do Paraná, Brasil

No sudeste do Estado do Paraná, o Grupo Itararé assenta-se por meio de discordância angular sobre o substrato pré-glacial, que é composto de unidades precambrianas a devonianas, cada vez mais velhas para o sudeste. Devido a esta configuração estratigráfica, tem-se interpretado que os estratos aflorantes na região de Porto Amazonas representam os níveis mais inferiores do Grupo Itararé, enquanto aqueles da região de Campo do Tenente, localizados mais ao sul da área, representam seções mais jovens. Este artigo apresenta o resultado da análise palinológica e faciológica realizada em sete afloramentos da porção basal do Grupo Itararé (Formação Lagoa Azul), nas regiões de Porto Amazonas, Lapa e Campo do Tenente, visando ao posicionamento palinoestratigráfico. Nove fácies sedimentares foram identificadas compondo, na maior parte, depósitos de transporte de massa e turbiditos, acumulados em ambiente marinho relativamente profundo sob influência glacial. Associações palinológicas foram registradas em todas as três regiões, incluindo escassos elementos indígenas, compreendendo esporos e grãos de pólen monossacados, com grau de preservação variado. As características palinológicas gerais das associações e a presença de determinadas espécies de esporos e grãos de pólen sugerem posicionamento na Zona Ahrensisporites cristatus, correspondente à porção inferior do Grupo Itararé (Formação Lagoa Azul), de idade pennsilvaniana (Neobashkiriano a Kasimoviano). Os resultados obtidos confirmam a ocorrência de estratos glaciais da parte inferior do Grupo Itararé na faixa de afloramentos. Além disso, demonstram a importância do estudo dos processos de retrabalhamento e ressedimentação de palinofósseis pré-pennsilvanianos.

Pennsylvanian conifers from interglacial taphoflora of Monte Mor, Itararé Group, State of São Paulo, Brazil: the earliest of the Paraná Basin

The pre-glossopterid macroflora from the Volpe Ranch, in Monte Mor (State of São Paulo), was deposited during an interglacial context of the Itararé Group. It is characterized by the Paranocladus-Ginkgophyllum-Brasilodendron Association and is included in the middle-basal part of the Itararé Group outcrop, in the NE of the Paraná Basin. It is similar to the Argentine macrofloristic association Krauselcladus-Asterotheca Phytozone (ex-Interval Zone) and its palynofloristic contents belong to the Crucisaccites monoletus Palynozone (Kasimovian to Gzhelian). The conifers in this assemblage are represented by macro and microfossils and record the first level of occurrence of conifers in the basin. They are documented by leafy branches impressions and compressions of Paranocladus dusenii Florin and Buriadia heterophylla (Feistmantel) Seward and Sahni emend. Singh, and platyspermic seeds of the genus Paranospermum. Cuticular studies allowed to correlate the presence of Paranocladus dusenii with the platyspermic seeds Paranospermum cambuiense Ricardi-Branco and to identify a new species of Paranospermum as well. Previous palynological studies in this level led to the recognition of some pollen grains affinis to the gymnosperms (conifers, ginkgoaleans and pteridospermales) comprising monosaccate and bisaccate forms allocated to the genera Cannanoropollis, Plicatipollenites, Potonieisporites and Caheniasaccites indicating certain diversity of conifers as early as in Pennsylvanian. The association of conifers and Ginkgophyllum represents a mesoxerophytic tree community. The abundance of their fragmented material in the taphofloral assemblage suggests allochthonous origin transported toward a deltaic plain which were associated to a parautochthonous origin material. Their fossiliferous sandy matrix overlying the coal also suggests a higher energy agent of transport.

Revaluation of the Samaropsis mendesii Rigby, 1972 from Paraná Basin lower Permian

This paper suggests an emendation to the diagnosis of Samaropsis mendesii Rigby, 1972 (Rio Bonito Formation, Santa Catarina State, Paraná Basin) on the basis of which the Samaropsis gigas Marques-de-Souza et Iannuzzi 2007 comes to be considered a junior synonym of this species. Adding the specimens previously considered as S. gigas from the Rio Grande do Sul State, the stratigraphic range of S. mendesii is extended to the uppermost portion of the Itararé Group. Also, we provide a comparative analysis with the closest Indian species Otofeista milleri (Feistmantel) Pant et al. (1985) (Karharbari beds). The comparison of the S. mendesii with the Indian material pointed to a strong morphometric correspondence between both, highlighting the potentiality of the use of this seed form in stratigraphic correlations due to the peculiarity of the morphology and the abundance of these seeds in Cisuralian (Sakmarian-Artinskian) strata of Gondwana.

Associações naturais de conodontes Mesogondolella spp., Grupo Itararé, Cisuraliano da Bacia do Paraná

Conodonts are primitive chordates which lived during the Paleozoic up to their complete extinction at the Triassic. Exclusively marine, they are widely used in biostratigraphic studies and in studies about vertebrates’ evolution, nowadays, in a new bias, with the discoveries of natural associations of multi-element that helps to better understand the evolutionary mechanisms of the first vertebrates and the paleobiology of this group. Researchers from the Earth and Life Museum of the Paleontological Center in the Contestado University (CENPALEO) found tens of ramiform elements near Mafra, southern Brazil, which macroscopically were similar with porifera spicule, common in the outcrops of the region. After a more detailed analysis, these elements were identified as conodonts feeding apparatuses, in general complete and well-preserved. This article describes the feeding apparatuses of conodonts of the first occurrence of conodonts in the Parana Basin. They represent gondolelids conodonts belonging to the Mesogondolella genus, a well-known Cisuralian marker. It is also discussed the faunas of these primitive chordate, according to the natural associations found in the Lontras Shale, Itarare Group, Parana Basin. Keywords: Mesogondolella, Cisuralian, Lontras Shale, Permocarboniferous.

PALEOENVIRONMENTAL EVOLUTION OF THE ITARARÉ GROUP (PARANÁ BASIN) IN THE REGIONS OF SALTO AND ITU, EAST OF SÃO PAULO STATE, BRAZIL

Itarare Group represents the glacial record of Gondwana Continent in the intracratonic Parana Basin, encompassing regions of Southern Brazil, Eastern Paraguay, Northeast Argentina and Northern Paraguay. Itarare Group is the thickest sedimentary package of Parana Basin, and was deposited over 36 million years during the end of the Carboniferous and the beginning of the Permian. However, in relation to its paleoenvironmental evolution, it is generally understood that more research is necessary, in order to better understand the genesis of the Itarare Group in different places. The present work entailed mapping facies associations for the Itarare Group in the city of Salto, in Sao Paulo State, by identifying and classifying sedimentary facies that, in turn, were utilized to develop a paleoenvironmental evolution model. This model was based on geological mapping carried out over 125 km². Petrological and petrographic descriptions of 32 outcrops of Itarare Group also were studied. These results were compared with subsurface data obtained by Sistema de Informacoes de Aguas Subterrâneas, Servicos Geologicos do Brasil (SIAGAS-CPRM; System Water Information Groundwater, Geological Survey of Brazil). Through lithofacies and petrographic analyses and making a comparison between five column sections, surface and subsurface data, a stratigraphic correlation model was established for the region. Through this model was possible to identify four facies associations, which, together, indicate how the paleoenvironmental evolution of the region occurred. The first three associations (A, B, C) were interpreted as being formed in subaqueous environment, being related to sandy lobe systems, followed by the last association (D), pertaining to a fluvial system. doi: 10.12957/jse.2016.21956

New approach for the study of paleofloras using geographical information systems applied to Glossopteris Flora

This paper introduces a methodology which makes possible the visualization of the spatial distribution of plant fossils and applies it to the occurrences of the Gondwana Floristic Province present on the eastern border of the Brazilian portion of the Parana Basin during the Neopaleozoic. This province was chosen due to the existence of a large number of publications referring to their occurrence, so that a meta-analysis of their distribution could be based on ample information. The first step was the construction of a composite database including geographical location, geology, and the botanical systematics of each relevant fossil. The geographical locations were then georeferenced for translation into various maps showing various aspects of the distribution of the fossils. The spatial distribution of the fossil-housing outcrops shows that these are distributed along the area of deposition studied. Although some genera persisted for long periods of time, others lasted for only short intervals. As time passed, the fossil composition underwent a gradual change from the Late Carboniferous (Itarare Group) to the Late Permian (Rio do Rasto Formation), with the number of genera represented decreasing from 45 in the Itarare Group to 11 in the Rio do Rasto Formation.

Ice-Keel Scour Marks In the Geological Record: Evidence From Carboniferous Soft-Sediment Striated Surfaces In the Parana Basin, Southern Brazil

Abstract Soft-sediment glacially striated surfaces are common structures in ancient glacial successions, such as the Gondwanic Paleozoic record, and document ice erosion on non lithified beds. In most cases, they have been interpreted as the product of subglacial erosion beneath advancing marine or terrestrial glaciers, although direct evidence for glacial sedimentation in associated strata is infrequent. In this paper we document soft-sediment striated surfaces of Carboniferous age occurring in cross-laminated sandstones of the lower Itarare Group, southern Parana Basin, Brazil, and interpret them as scour marks generated by keels of floating ice. Striated surfaces occur in closely spaced, multiple stratigraphic horizons in the lower half of a deglacial sequence, whose facies characteristics indicate sedimentation in subaqueous outwash and deltaic settings. Surfaces are laterally discontinuous, commonly bordered by marginal berms, and in some cases capped by mudstones with dropstones; they have orientations that deviate from the regional paleo-ice flow indicated by glacial grooves carved on the pre-glacial basement. The characteristics observed are consistent with modern and Pleistocene ice-keel scour marks. In addition, soft-sediment striated surfaces from other Gondwanic localities have similar attributes, suggesting that ice-keel scour marks may be more common in the geological record than previously considered and that vertically repeated striated surfaces do not necessarily indicate multiple ice-sheet advances. Therefore, paleo-ice flow reconstructions based on soft-sediment striated surfaces need to be revaluated considering that the movement of free-floating ice masses is controlled by phenomena other than glacier advance.

Mapa Geológico de parte da Folha Arroio América - SH-22-Y-A-IV-1 (MI 2995/1) - Nota explicativa

Esta nota explicativa se refere ao mapa geológico de parte da Folha Arroio América (SH.22-Y-A-IV-1 / MI 2995/1) e tem por base os resultados obtidos durante o Projeto Arroio América, executado em 2003 por professores e alunos do Curso de Geologia da Universidade Federal do Rio Grande do Sul. Diversas unidades litoestratigráficas foram reconhecidas, algumas das quais são inéditas e formalmente designadas. A principal estrutura regional reconhecida é denominada Zona de Cisalhamento Arroio América (ZCAA), composta por diversas zonas miloníticas subverticais de direção NE e cinemática transcorrente esquerda dada por lineação de estiramento de baixo caimento. Significativas reativações de antigos lineamentos em condições rúpteis são encontradas, bem como estruturas rúpteis de direção NW que afetam o embasamento e as rochas sedimentares de idade neoproterozoica a permiana. As sequências de embasamento mais antigas são ortognaisses do Complexo Cambaí, e as rochas supracrustais do Complexo Metamórfico Arroio Marmeleiro (CMAM). Os Dioritos Arroio Branquilho formam uma unidade inédita de biotita-hornblenda dioritos e quartzo-dioritos foliados, que compreendem duas subunidades cogenéticas – a fácies equigranular média e a fácies fina. As relações estruturais observadas indicam que seu posicionamento é anterior à ZCAA. O Tonalito Arroio dos Carros (TAC) e os Granitoides Rincão dos Encerrados (GRE) são também unidades inéditas, correlacionadas à Suíte Lagoa da Meia Lua. O TAC compreende hornblenda tonalitos foliados, de granulação média a grossa, e sua foliação magmática grada para uma foliação milonítica devido a seu caráter sintectônico à ZCAA. Os GRE são biotita tonalitos a granodioritos equigranulares finos a médios, tardi-tectônicos em relação à mesma zona de cisalhamento. O Granito Passo da Chácara, igualmente inédito, é a unidade granítica mais jovem, compreendendo biotita leucossienogranitos fracamente foliados a maciços. A Formação Maricá é composta por arenitos arcóseo-líticos com intercalação subordinada de conglomerados e folhelhos. Evidências localizadas de condições anquimetamórficas são constatadas, bem como clivagem ardosiana em composições pelíticas. É subdividida em duas fácies, uma resultante de sistema fluvial anastomosado e outra formada em condições marinhas rasas. O Monzonito Tapera, bem como as formações Hilário, Cerro da Pedra e Acampamento Velho, são subunidades do Grupo Bom Jardim. No Monzonito Tapera são reconhecidas quatro fácies com base em características texturais e composicionais: monzonítica plutônica, leucodiorítica plutônica, diorítica plutônica e hipoabissal monzonítica. Nas rochas encaixantes do CMAM, são descritos efeitos de metamorfismo de contato em condições de fácies hornblenda cornubianito. A Formação Hilário compreende derrames andesíticos e diques de andesitos e lamprófiros. A Formação Cerro da Pedra é definida neste trabalho como um pacote de conglomerados formados em sistemas de leques aluviais. A fácies proximal é reconhecida na forma de para- e ortoconglomerados oligomíticos, enquanto a fácies distal é representada por ortoconglomerados polimíticos. A Formação Acampamento Velho é representada por um domo de lava e diques riolíticos associados. A Formação Rio do Sul, de idade permiana, pertencente ao Grupo Itararé, é restrita ao extremo norte da área mapeada, onde ocorrem camadas de arenito fino intercaladas com siltitos.

Magnetostratigraphy and mid-palaeolatitude VGP dispersion during the Permo-Carboniferous Superchron: results from Paraná Basin (Southern Brazil) rhythmites

SUMMARY A detailed magnetostratigraphic and rock-magnetism study of two Late Palaeozoic rhythmite exposures (Itu and Rio do Sul) from the Itarare Group (Parana Basin, Brazil) is presented in this paper. After stepwise alterning-field procedures and thermal cleaning were performed, samples from both collections show reversed characteristic magnetization components, which is expected for Late Palaeozoic rocks. However, the Itu rocks presented an odd, flat inclination pattern that could not be corrected with mathematical methods based on the virtual geomagnetic pole (VGP) distributions. Correlation tests between the maximum anisotropy of the magnetic susceptibility axis (K1) and the magnetic declination indicated a possible mechanical influence on the remanence acquisition. The Rio do Sul sequence displayed medium to high inclinations and provided a high-quality palaeomagnetic pole (after shallowing corrections of f = 0.8) of 347.5°E 63.2°S (N = 119; A95 = 3.3; K = 31), which is in accordance with the Palaeozoic apparent wander pole path of South America. The angular dispersion (Sb) for the distribution of the VGPs calculated on the basis of both the 45° cut-off angle and Vandamme method was compared to the best-fit Model G for mid-latitudes. Both of the Sb results are in reasonable agreement with the predicted (palaeo) latitudinal S-λ relationship during the Cretaceous Normal Superchron (CNS), although the Sb value after the Vandamme cut-off has been applied is a little lower than expected. This result, in addition to those for low palaeolatitudes during the Permo-Carboniferous Reversed Superchron (PCRS) previously reported, indicates that the low secular variation regime for the geodynamo that has already been discovered in the CNS might have also been predominant during the PCRS.

Análise Palinoestratigráfica dos Depósitos Permianos (Poços HN-05-RS E HN-25-RS) do sul da Bacia do Paraná

Abstract. PALYNOSTRATIGRAPHIC ANALYSIS OF PERMIAN DEPOSITS (HN-05-RS AND HN-25-RS BOREHOLES) FROM SOUTHERN PARANA BASIN. This paper presents the palynological results obtained from 133 levels of the HN-05-RS and HN-25-RS wells, drilled in Hulha Negra, southern portion of Rio Grande do Sul State. The sampled levels included the Permian units of the Gondwana I Supersequence (Itarare Group and Rio Bonito, Palermo, Irati, Serra Alta, Teresina and Rio do Rasto formations) from Parana Basin, Brazil. A total of 133 palynomorph species were recorded, corresponding to spores (57), pollen grains (65), besides microplanktonic elements and fungi (11). The stratigraphic distribution of all taxa is presented, as well as the relative frequency of selected levels. The analysis allowed the recovery of palynological associations relatively diverse and abundant from the overlying levels of the Irati Formation, which were generally considered sterile. The associations are related to Vittatina costabilis (Asselian to middle A...

Permian bivalves of the Taciba Formation, Itararé Group, Paraná Basin, and their biostratigraphic significance

A small and poorly diversified bivalve fauna from Taciba Formation, Itarare Group, Parana Basin (State of Santa Catarina, Mafra Municipality), is described in this paper for the first time, based on new findings. The fauna is recorded in a 30 cm thick interval of fine sandstone locally at the top of Taciba Formation, in the Butia quarry. The studied fossil-bearing sandstone bed is a marine intercalation recording a brief eustatic rise in sea-level, probably following glacier retreat and climate amelioration at the end of a broad glacial scenario. The fauna is mainly dominated by productid brachiopods, which are not described here, and rare mollusk shells (bivalves and gastropods). Two bivalve species were identified: Myonia argentinensis (Harrington, 1955), and Aviculopecten multiscalptus (Thomas, 1928). The presence of Myonia argentinensis is noteworthy since this species is also present in the Baitaca assemblage found in marine siltstones (Baitaca assemblage) of the Rio do Sul Formation, cropping out at the Teixeira Soares region, Parana State. This species is also recorded in the bivalve fauna from the Bonete Formation, Pillahinco Group, Sauce Grande Basin, Buenos Aires Province, in Argentina. Hence, the marine bivalves of the Taciba Formation are associated with the transgressive event that characterizes the Eurydesma fauna, indicating a Late Asselian-Sakmarian age for the bivalve fauna. Presence of the Myonia argentinensis megadesmid species reinforces the Gondwanic nature of the studied fauna.

Millennial-scale climate cycles in Permian–Carboniferous rhythmites: Permanent feature throughout geologic time?

Two late Paleozoic glacial rhythmite successions from the Itarare Group (Parana Basin, Brazil) were examined for paleoclimate variations. Paleomagnetic (characteristic remanent magnetization, ChRM) and magnetic susceptibility (K z ) measurements taken from the rhythmites are interpreted as paleoclimatic proxies. Ratios of low-frequency components in the K z variations suggest Milankovitch periodicities; this leads to recognition of other, millennial-scale variations reminiscent of abrupt climate changes during late Quaternary time, and are suggestive of Bond cycles and the 2.4 k.y. solar cycle. We infer from these patterns that millennial-scale climate change is not restricted to the Quaternary Period, and that millennial forcing mechanisms may have been prevalent throughout geologic time.

Sarcopterygii do Eopermiano da Bacia do Paraná, Estado de São Paulo

Esta contribuição constitui uma revisão dos Sarcopterygii (Coelacanthimorpha - celacantos; Tetrapodomorpha - Osteolepimorpha e tetrápodes) do Eopermiano da Bacia do Paraná no Estado de São Paulo. O outro grupo importante de sarcopterígeos - Dipnoi (peixes pulmonados) - ainda não foi registrado nesse estado no Eopermiano. Os Coelacanthimorpha foram observados no Grupo Itararé e nas formações Tatuí e Irati. Os arenitos e conglomerados da base do Membro Taquaral da Formação Irati são ricos em ictiofósseis, incluindo dentes labirintodontes atribuídos a Tetrapodomorpha, que variam de poucos milímetros a alguns centímetros, sendo, portanto, os maiores dentes já encontrados no Permiano em São Paulo. A fácies folhelho síltico do Membro Taquaral é a que apresenta maior abundância em número de escamas de Coelacanthimorpha, com espécimes de alguns centímetros de comprimento porém, até agora, nenhum outro Sarcopterygii foi identificado. Apesar dos celacantídeos atualmente serem indicadores de ambiente marinho profundo, no Paleozoico eles podem ser encontrados em rochas depositadas em ambientes de salinidades variadas e na água doce. Os Tetrapodomorpha também possuíam espécies que habitavam ambientes de salinidade variada e continentais. Para análise paleoambiental destes grupos é necessário o conhecimento do contexto sedimentar e da paleobiota associada.

Spectral analysis and modeling of microcyclostratigraphy in late Paleozoic glaciogenic rhythmites, Paraná Basin, Brazil

We investigate the depositional time scale of lithological couplets (fine sandstone/siltstone–siltstone/mudstone) from two distinctive outcrops of Permo-Carboniferous glacial rhythmites in the Itarare Group (Parana Basin, Brazil). Resolving the fundamental issue of time scale for these rhythmites is important in light of recent evidence for paleosecular variation measured in these sequences. Spectral analysis and tuning of high-resolution gray scale scans of sediment core microstratigraphy, which comprises pervasive laminations, reveal a comparable spectral content at both localities, with a frequency suite interpreted as that of short-term climate variability of Recent and modern times. This evidence for decadal- to centennial-scale deposition of these lithological couplets is discussed in light of the ‘varvic’ character, i.e., annual time scale that was previously assumed for the rhythmites.