Sul Formation Research Articles

Deciphering the origin of dubiofossils from the Pennsylvanian of the Paraná Basin, Brazil

Abstract. Minerals are the fundamental record of abiotic processes over time, while biominerals are one of the most common records of life due to their easy preservation and abundance. However, distinguishing between biominerals and abiotic minerals is challenging due to the superimposition and repetition of geologic processes and the interference of ubiquitous and diverse life on Earth's surface and crust. Mineral dubiofossils, being potential outcomes of both abiotic and biotic environments, emerge as valuable entities that can contribute significantly to the understanding of this issue, facilitating the testing and refinement of biogenicity criteria. The aim of this contribution is to decipher the origin and history of branched mineralized structures that were previously considered mineral dubiofossils from the Pennsylvanian of the Paraná Basin, Brazil. While this material has different forms and refers to biological aspects, it is challenging to associate it with any known fossil group due to the overlapping geological processes occurring in a transitional deposit of Rio do Sul Formation (Itararé Group of the Paraná Basin), particularly in close proximity to a sill from the Serra Geral Group (Lower Cretaceous), which has undergone thermal effects. Given the absence of attributes essential for supporting the initial hypotheses proposing the material as a potential set of sponge spicules or a result of contact metamorphism in Pennsylvanian turbidites, the objects are now investigated as mineral dubiofossils. To address this challenge, we have developed a descriptive protocol for dubiofossils, building upon prior research in the field. This protocol evaluates the following aspects: (1) morphology, texture, and structure; (2) relationship with the matrix; (3) composition; and (4) context. This is done by assessing indigeneity and syngenicity and comparing the specimens with abiotic and biotic products. Applying this protocol to our samples revealed a wide range of morphologies with internal organization, predominantly composed of calcite with impurities such as iron, magnesium, aluminum, and oxygen. The inferred indigeneity suggests the presence of these minerals concurrently with or prior to the intrusion of the sill. Extensive comparisons were made between the studied samples and a broad spectrum of abiotic minerals, as well as controlled, induced, and influenced biominerals from similar contexts. These comparative analyses encompassed sponge spicules; sea urchin and algae skeletons; minerals induced or influenced by fungi, bacteria, and microbial mats; and inorganic pre- and synsedimentary–eodiagenetic minerals like evaporites, springs, and other precipitates, and mesodiagenetic–metamorphic crystals. Despite this comprehensive analysis, no hypothesis emerged as significantly more likely than others. The comparative analysis did allow us to exclude the possibility of the samples being controlled biominerals due to their patternless diversity of morphologies, as well as purely thermometamorphic in origin due to their branched elongated forms. The occurrence of these structures suggests a complex history: a syn-depositional or eodiagenetic origin of some carbonate or sulfate (gypsum, ikaite, dolomite, calcite, aragonite, siderite), potentially associated with the presence of microbial mats, which may have served as templates for mineralization and mediated mineral growth. Mesodiagenesis could have further modified the occurrence through processes such as mineral stabilization, agglutination, aging, and growth. However, the primary agent responsible for the formation of the dubiofossil was the Cretaceous intrusion, which dissolved and replaced the initial minerals, resulting in the precipitation of calcite. Throughout these steps, a combination of physical–chemical and biological reactions, influenced by intrinsic matrix characteristics, organic matter content, and distance from the intrusive body, may have contributed to the heightened morphological complexity observed, thus corroborating the origin of the material becomes even more challenging. Consequently, both the hypotheses pertaining to the formation of biotic and abiotic sulfates and carbonates remain plausible explanations, hence sustaining the classification of the material as a dubiofossil. This material illustrates how dubiofossils can be a result of a complex history and overlapping geological processes. It also highlights the difficulty in differentiating biominerals from abiotic minerals due to the scarcity of biogenicity arguments.

Late Paleozoic glacial to postglacial stratigraphic evolution of the Rio do Sul depocenter, Itararé and Guatá groups, Pennsylvanian-Cisuralian, southern Brazil

The transition from the Late Paleozoic Ice Age (LPIA) to fully postglacial conditions in SW Gondwana is under increasing discussion due to either the radiometric ages of its boundary or the stratigraphic nature of this transition. The record of this transition in the Paraná Basin is found in the glacial and glacially influenced deposits of the upper Mafra and Rio do Sul Formations (upper Itararé Group) and postglacial strata of the Rio Bonito Formation (Guatá Group). Here we address the depositional architecture and stratigraphic evolution of these deposits in the Rio do Sul depocenter, eastern Paraná Basin, Brazil, the main area of subsidence in the basin during this transition in Pennsylvanian-Cisuralian time, bringing an opportunity to examine the characteristics of glacial to postglacial transition. Analyses of facies, stratigraphic logs, stratigraphic correlations, and paleocurrent dispersal trends allowed us to define three evolutionary stages. The first stage registers glacial advance from the south-southwest represented by an erosive surface and subglacial tillites. Gravitational deposits covered the tillites in response to ice retreat (upper Mafra Formation), and the Lontras Shales (lower Rio do Sul Formation) correspond to the marine maximum flooding. The second stage comprises co-genetic deepwater (Rio do Sul Formation) to shallow (Rio Bonito Formation, Triunfo Member) progradational deposits after the Lontras Shale maximum flooding. Paleocurrent data and glacially related features point to glaciated source areas located to the NE, E, and SE for the Rio do Sul depocenter during this stage. The third stage corresponds to retrogradational stacking pattern upon a fluvial subaerial unconformity (incised valley), starting with fluvio-deltaic beds (Triunfo Member), followed by fine-grained deposits of the Paraguaçu Member of Rio Bonito Formation. No features related to glacial influence characterize this third stage. As previously suggested, tectonic uplift likely drove the additional NE source and created the space that allowed the transitional contact between Rio do Sul and Rio Bonito formations in the Rio do Sul depocenter.

Deepwater to fluvio-deltaic stratigraphic evolution of a deglaciated depocenter: The early Permian Rio do Sul and Rio Bonito formations, southern Brazil

This paper describes facies relationships and stratigraphic architecture of early Permian deglacial deepwater to fluvio-deltaic deposits exposed in the eastern border of the Paraná Basin, southern Brazil. The studied succession is located in the Rio do Sul depocenter and comprises an upward transition between the topmost interval of the Itararé Group (Rio do Sul Formation) and the lowermost unit of the Rio Bonito Formation (Triunfo Member). Geological mapping and facies analysis allowed the recognition of the following facies associations, vertically stacked: thin and thick-bedded turbidites, hyperconcentrated and concentrated density-flow deposits (hyperpycnites), mass-transport deposits, fine-grained heterolithic beds of prodelta, delta-front, shoreface and delta-plain deposits, as well as fluvial beds resting on incised valleys. The stratigraphic analysis through the interpretation of the facies associations, stacking pattern and paleocurrent dispersal trends were enough to define the clinoform stratigraphic architecture, composing a progradational-aggradational pattern. The paleoflows for all facies associations show a main trend towards the south-southwest. In this context, hyperpycnal beds can represent a glacial source from the northeast, because of striated and faceted clasts immersed in the conglomeratic facies, whereas turbidites have been understood as the products of their dilution. Likewise, mass-transport deposits are related to the collapse of the shelf-margin delta, represented by allochthonous blocks composed of deltaic beds within the mass-flow diamictites. Thus, these mass-transport deposits do not evolve downslope to turbidity currents. This configuration was likely for building the relief of the slope system, probably a shelf-edge delta susceptible to mass failure. Paleo-ice flows towards SW recorded in the Rio do Sul Formation, genetic related to fluvio-deltaic deposits of Rio Bonito Formation, highlight the scenario of final stages of the Late Paleozoic Ice Age in the SW of Gondwana and support the previous researches which point to the presence of diachronous ice-spreading centers from paleohighs.

Microbially induced sedimentary structures in late Pennsylvanian glacial settings: A case study from the Gondwanan Paraná Basin

This paper explores microbially induced sedimentary structures (MISS) preserved in Late Paleozoic Ice Age deposits to evaluate the potential microbe-substrate physical interactions in ancient glacial settings. MISS have been recorded worldwide in different modern and ancient settings, mostly in tidal flats. However, their record in ancient glacial settings is still underrepresented. The reported MISS are preserved in the siltstone-claystone glacigenic rhythmites in Trombudo Central region of the Rio do Sul Formation (Paraná Basin, Pennsylvanian, southern Brazil). The recorded structures in these deposits are composed of wrinkle structures, dome structures, mat fragments, mat microfabrics, sinoidal structures, laminated leveling structures, oriented grains and mat-layer bound small grains, kinneyia structure, discoidal microbial colony, elongated filaments, and drab-haloed filaments. They represent the development of endobenthic and epibenthic microbial mats, as well as microbial earths. Endobenthic mat structures predominate in the siltstone beds, suggesting less time for development of microbial mat during deglaciation events and meltwater input. Epibenthic mat structures preserved in the claystone layers indicate episodic quiescence periods that allowed the mat achieve maturity and that cyanobacteria and sulfate-reducing bacteria composed a significant part of the microbial community. The set of MISS observed in the studied rhythmites have been commonly reported in tidal settings, and the presence of microbial earths structures indicate periods of drainage of the water bodies, at least partially. Thus, the microbial communities played an important role in ancient glacial settings during climatic amelioration periods, opening the colonization window for macroorganisms in outwash plains and marginal marine settings. This paper provides a characterization of different sorts of preserved MISS, and evaluate the physical interactions between microbial mats and the substrate, in the ancient glacigenic deposits from the Itararé Group.

Insights from functional morphology and neoichnology for determining tracemakers: a case study of the reconstruction of an ancient glacial arthropod-dominated fauna

Apportioning trace fossils to producers is significant for palaeoecological and palaeoenvironmental studies. A tracemaker is usually attributed through the comparison of the morphology of the trace to the body plans of modern and extinct animals. However, hypotheses of tracemaker identifications may be tested with the use of further methods. This contribution aims to evaluate the potential tracemakers of a trackway-dominated ichnofauna preserved in the siltstone–claystone rhythmites of the Pennsylvanian Rio do Sul Formation in the southern Brazil. These deposits are typical of the deglaciation phase of the Late Palaeozoic Ice Age of Gondwana in the Parana Basin. Thus, the parameters applied in this work are as follows: (1) functional analyses of the traces to infer the biomechanics of the locomotion of the producer; and (2) neoichnology, whereby modern traces whose producers are known are compared to those of the ichnofauna in question. The conclusions obtained with these methods strongly support millipedes as the producers of Diplichnites gouldi and Diplopodichnus biformis. The malacostracan crustacean-related ichnogenera are Umfolozia sinuosa and Gluckstadtella elongata, produced by syncarids or peracarids, while isopods are suggested as the tracemakers of Glaciichnium isp. and Protovirgularia dichotoma. In terms of branchiopod crustaceans, Cruziana problematica is attributed to notostracans. Helminthoidichnites tenuis, Mermia carickensis and Treptichnus pollardi are considered traces produced by insect larvae. The palaeobiology of the tracemakers that produced the ichnofauna preserved in the rhythmites of the Rio do Sul Formation permits inferences that terrestrial (millipedes) and aquatic (crustaceans and insect larvae) animals colonized the sediments. This conclusion points to a dynamic depositional environment, with changing physical and chemical parameters conditioning the biota.

On the origin of the Itararé Group basal nonconformity and its implications for the Late Paleozoic glaciation in the Paraná Basin, Brazil

Outcrop studies of the Itararé Group in the Alfredo Wagner area, along the eastern margin of the Paraná Basin in Brazil, reveal a partially exhumed, NNW-SSE oriented glacial paleovalley. The Carboniferous Rio do Sul Formation represents the basal interval of the glacially influenced Itararé Group, and rests directly on Precambrian basement rocks. This nonconformity is thought to represent an areal scouring surface, as indicated by the series of glacially-carved linear depressions that were incised into the glaciated bedrock during glacial advances. These large-scale erosional landforms differ in their extent by orders of magnitude, and include wide, deep troughs as well as narrower, shallower gouges. Glacial troughs and gouges usually display smaller-scale, subglacial erosion landforms, such as polished and grooved striations on their walls and floors. These indicate the NNW motion of a warm-based, grounded glacier. In addition, large-scale erosional features represent local topographic lows within the major glacial paleovalley. These local lows are large enough to contain part of the succeeding deglacial deposits, which thin toward and onlap the wall of these depressions. We grouped these deglacial deposits into six genetic facies associations (FA-1 to -6) within three fining-upward glacial cycles. FA-1 is composed of black shale, and represents an initial marine flooding event. It can be correlated with the regionally widespread Lontras Shale. FA-2 is composed of sandstones and mudstones associated with flood-derived hyperpycnal flows, and occasionally with surge-type turbidites. FA-3 is represented by plastered or injected, matrix-supported conglomerates emplaced as lodgment tills. FA-4 comprises matrix- and clast-supported conglomerates, sandstones, and mudstones, attributed to ice-rafting and concentrated flows in grounding-line fan facies. This unit also contains ice-keel dragging features, carved into soft substrate. FA-5 is composed of dropstone-bearing black shale, related to a second major marine flooding event within the paleovalley. FA-6 comprises sandstones associated with channelized, surge-type turbidites, forming the second turbidite system in the succession. As these deposits are confined to a paleovalley, we infer that sedimentation was influenced by topographically controlled ice streams, instead of non-confined, widespread ice lobes as previously suggested. Reconstructing South America and southern Africa in their positions during the LPIA suggests that the glacial valleys then present in the Namibia area may have extended further, into the eastern margin of the Paraná Basin. In this scenario, confined outlet glaciers would have flowed out from the Namibian Windhoek ice cap, and terminated along the eastern margin of the Paraná Basin.

Evolution of the Carboniferous-Early Cretaceous units of Paraná Basin from provenance studies based on U-Pb, Hf and O isotopes from detrital zircons

U-Pb, Lu-Hf and O isotope data were obtained on detrital zircons from late Paleozoic-early Mesozoic units from White Column, Paraná Basin, southeastern Brazil, in order to characterize the provenance of the sediments, as well as to contribute to the understanding of the evolution of the basin. The studied section includes rocks from 11 stratigraphical units (from base to top), including the Rio do Sul Formation, Rio Bonito Formation (Triunfo, Paraguaçu and Siderópolis members), Palermo, Irati, Serra Alta and Teresina formations, Rio do Rasto Formation (Serrinha and Morro Pelado members) and Botucatu Formation.U-Pb ages of zircons in these units range from 242Ma to 3.4Ga. All units show four main detrital age-groups, Neoarchean, mid-Paleoproterozoic, Grenvillian and Brasiliano-Pan African reflecting the importance of the Precambrian basement bordering the east side of the section such as Dom Feliciano, Kaoko and Namaqua-Natal Belts as source areas. However, the isotopic signatures show that a portion of the mid-Paleoproterozoic zircons (1.9–2.0Ga) are probably from rocks of the presently covered basement, which was exposed until the deposition of the Rio Bonito Formation. The isotopes also show some Grenvillian aged zircons from Argentinian rocks, which implies a long transport distance.The Siderópolis Member is the unit that shows an important change on the sources of the sediments, since it contains a Permian age peak that was not present on the lower units and that persist on the upper units. The isotopic signatures of these Permian grains link them to the Choiyoi igneous province and North Patagonia Massif, sources from Argentina, reaching the basin by long distance travel on subaquatic environmental and not only from the air (ash falls) as is in common acceptance. Other younger age peaks (Ordovician to Carboniferous) found from Palermo Formation to up section are also linked to Argentinian sources, showing the importance of the long travel distance during the filling of the basin.

Ichnology of deglaciation deposits from the Upper Carboniferous Rio do Sul Formation (Itararé Group, Paraná Basin) at central-east Santa Catarina State (southern Brazil)

Trace fossil assemblages dominated by arthropod trackways are common in sediments deposited during the Late Paleozoic Ice Age. Ichnofaunas preserved in glacially-influenced sedimentary successions were previously reported from Paraná Basin in southern Brazil. The ichnofauna of the Rio do Sul Formation preserved in the rhythmites exposed in Trombudo Central quarries (Santa Catarina State, southern Brazil) is revised in this paper. Cruziana problematica, Diplichnites gouldi, Diplopodichnus biformis, Glaciichnium liebegastensis, Gluckstadtella elongata isp. nov., Helminthoidichnites tenuis, Mermia carickensis, Protovirgularia dichotoma, Treptichnus pollardi and Umfolozia sinuosa were recorded. Two trace fossil suites were recognized. The undermat miners suite is dominated by H. tenuis, indicating the presence of surface grazers (insect larvae, isopods and amphipods). C. problematica, D. gouldi and U. sinuosa dominate the overmat grazers suite, as result of displacement of terrestrial and aquatic arthropods. The integrated sedimentological and ichnological data from Trombudo Central region suggests colonization of ephemeral, shallow water bodies filled by freshwater from glacier melting. The deposition of the rhythmites took place in a glaciolacustrine context represented by shallow ponds in marginal marine settings.

Lowstand Turbidites and Delta Systems of the Itararé Group in the Vidal Ramos region (SC), southern Brazil

Turbidites have captioned the attention of sedimentologists during the last decades due their importance as hydrocarbon reservoirs. However, their relationship to delta systems still deserves further studies. This paper presents examples from a late deglacial to early post-glacial deltaic and turbidite strata exposed in the surroundings of Vidal Ramos (Santa Catarina State, Brazil), southern portion of the Parana Basin. There, the uppermost part of the Mafra Formation and the Rio do Sul Formation onlap the Proterozoic basement and comprises an up to 360 m thick package. It includes (base to top) black shales, mass transport deposits (MTD) and sandy turbidites (Mafra Formation) as well as thin bedded turbidites (tbt), including one interval of black shales and sandy turbidites, overlain by proximal delta front sandstones (Rio do Sul Formation). The analysis of the succession shows two more than 150 m thick coarsening-upwards deltaic successions composed of turbidite sand sheets at their base (prodelta), followed by partially collapsed thin bedded turbidites (delta slope wedge) and delta front sandstones. Both turbidite sand-sheets abruptly overlay black shale intervals related to maximum flooding surfaces and therefore record correlative conformities. A detailed stratigraphic section elaborated from the correlation of four logs (1/100) suggests that distal delta front sands includes both thin bedded turbidites and wave reworked sands whereas the proximal delta front was dominated by long-lived underflows (hyperpycnal flows). The succession suggests that the most expressive turbidite beds (base of the delta systems) have resulted from relative sea-level falls (early lowstand) whereas the thin-bedded turbidites were related to the development of the late lowstand wedge. Black shales represent the transgressive systems tract and HST were not deposited or preserved in the area. High sediment supply associated with lowstand tracts could explain the occasional (Vidal Ramos) to common occurrence of slope failures (slumps and diamictites) involving thin bedded turbidites and delta front sandstones. This situation is quite logical in terms of deglacial periods, and resulting high sediment supply, within a long-term icehouse context, with prevalence of lowstand to transgressive settings.

First articulated sponge from the Paleozoic of Brazil, and a new organization of the order Hemidiscosa

The first-described articulated Permian sponge from Brazil, representing Hexactinellida, has been recovered from the Lontras Shale in the Campáleo outcrop (Permian, Asselian–Sakmarian), Rio do Sul Formation, Mafra, in southern Brazil. It is assigned to the Hemidiscellidae and identified asMicrohemidiscia greinertin. sp. This fossil represents the first record of articulated sponges in Brazil from the Paleozoic Era, as well as the second species known from this genus. Moreover, it increases knowledge of the order Hemidiscosa, a monotypic group mostly defined by simple characters, which is here considered to comprise one family, Hemidiscellidae (Pennsylvanian-Cretaceous), and two genera,HemidiscellaandMicrohemidiscia.

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.

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.

A new lower actinopterygian from the Early Permian of the Paraná Basin, Brazil

ABSTRACT A new actinopterygian, Roslerichthys riomafrensis gen. et sp. nov., is described from the Rio do Sul Formation (Early Permian) of Mafra, State of Santa Catarina, Brazil. This fusiform ray-finned fish is the smallest so far described for the “Lontras Shales.” R. riomafrensis, gen. et sp nov., is placed into the Amblypterus Group of Gardiner and Schaeffer. Discussion is also offered about the taphonomic processes that led to the exceptional preservation of the fossils of these shales.

Anisotropy of magnetic susceptibility applied to diamictites of the Rio do Sul formation, Paraná basin: initial results

Anisotropy of magnetic susceptibility applied to diamictites of the Rio do Sul formation, Paraná basin: initial results

Magmatism and Metallogeny in the Crustal Evolution of Rio Grande do Sul Shield, Brazil

The State of Rio Grande do Sul has a complex Precambrian/Cambrian shield, which has been investigated for four decades. This complexity involves ages ranging from 2.55 Ga (possibly 3.3 Ga) to 550 Ma (and even 470 Ma). The three major juvenile accretionary episodes occurred at 2.55 Ga, 2.26-2.02 Ga and 900-700 Ma, while a continental-scale crustal reworking (collisional) orogeny occurred from 780 to 550 Ma. The three accretionary orogenies are known as the Jequié, Transamazonian and Brasiliano Cycles, respectively. The Brasiliano Cycle includes the collisional orogeny. Magmatism was tholeiitic low-K bimodal basic-acid in the Archean (Santa Maria Chico granulites), and evolved to tonalitic-trondhjemitic-granodioritic in the Paleoproterozoic (Encantadas Complex). During the Paleoproterozoic/Archean transition, komatiites and basalts were formed in greenstone belts (Passo Feio Sul Formation). The end of the Transamazonian Cycle was the beginning of a long period of tectonic quiescence, and the region remained in the interior of the Atlantica Supercontinent until the beginning of the Brasiliano Cycle at ca. 900 Ma (Passinho Diorite). This Neoproterozoic cycle displays two classical orogenic types, namely the São Gabriel accretionary orogeny in the western part of the State and Dom Feliciano collisional orogeny in its eastern part. Accretion generated juvenile tonalite-trondhjemite-granodiorite associations with related ophiolites (Cerro Mantiqueiras Ophiolite), while the collision formed the voluminous and mostly peraluminous and high-K calcalkaline granites of the Dom Feliciano orogeny. The waning stages of the orogeny were responsible for the outpouring of a very expressive silica-saturated volcanism and eventually finished with the Rodeio Velho basalts at 470 Ma. Comparable Paleoproterozoic/Neoproterozoic Precambrian terranes surround the shield in Uruguay, in Santa Catarina and in western Africa. Comparable Neoproterozoic juvenile and reworked terranes occur in NE Africa. Widespread indications of metals are a good sign of possible deposits, but the two major types of deposits are the orogenic epizonal Bossoroca gold deposit and the distal magmatichydrothermal Lavras/Camaquã copper-gold deposits.

FÁCIES, ANÁLISE ESTRATIGRÁFICA E EVOLUÇÃO PÓS-GLACIAL DO MEMBRO TRIUNFO/FORMAÇÃO RIO BONITO, NA FAIXA SUBAFLORANTE DO NORTE CATARINENSE

The Triunfo Member, the unit of Rio Bonito Formation, is the post-glacial deltaic system of the glaciomarine and marine sedimentation of the Rio do Sul Formation (Itarare Group). The wells drilled by CPRM in the eastern margin of Parana Basin are continuously and constitute an important documentation of the Rio Bonito Formation. The sequential analysis of seven wells in northern Santa Catarina State allows the characterization of the following facies successions/associations: glaciomarine, deglaciation, fluvial, deltaic, and marine offshore to shoreface. A stratigraphic section through the studied wells reveals the lateral distribution of the facies associations and the mapping of erosional regressive (corresponding to sequence boundaries) and transgressive surfaces. The investigated area is compartmentalized into three sedimentation domains: the northern one, PP9 to PP 11 wells, where six depositional sequences (four in the Rio do Sul-Triunfo transition and two in the Triunfo Member) overlie the marine substrate of the Rio do Sul Formation. Each sequence is formed by fluvial, deltaic and deglaciation associations (lower part of the sequence), and by glaciomarine and marine associations (upper part). Despite little sampling in the Rio do Sul Formation, the central domain reveals distinctive characteristics (PP6 to PP8 wells): thick glaciomarine deposits in the Rio do Sul substrate, thin transition zone and the predominance of fluvial associations in the Triunfo Member. The southern domain, PP4 and PP5 wells, has thick marine shelf deposits in the underlying Rio do Sul Formation, which partially corresponds to the Rio do Sul-Triunfo transition from the northern domain. Five depositional sequences are identified in the southern domain, and they are correlated with the central and northern domains. In addition, the marine shelf association of the southern domain changes laterally to deltaic deposits toward south (the basal Triunfo delta of the Rio do Sul area).

FÁCIES, ANÁLISE ESTRATIGRÁFICA E EVOLUÇÃO PÓS-GLACIAL DO MEMBRO TRIUNFO/FORMAÇÃO RIO BONITO, NA FAIXA SUBAFLORANTE DO NORTE CATARINENSE

The Triunfo Member, the basal unit of Rio Bonito Formation, is the post-glacial deltaic system of the glaciomarine and marine sedimentation of the Rio do Sul Formation (Itararé Group). The wells drilled by CPRM in the eastern margin of Paraná Basin are continuously and constitute an important documentation of the Rio Bonito Formation. The sequential analysis of seven wells in northern Santa Catarina State allows the characterization of the following fácies successions/associations: glaciomarine, deglaciation, fluvial, deltaic, and marine offshore to shoreface. A stratigraphic section through the studied wells reveals the lateral distribution of the fácies associations and the mapping of erosional regressive (corresponding to sequence boundaries) and transgressive surfaces. The investigated area is compartmentalized into three sedimentation domains: the northern one, PP9 to PP 11 wells, where six depositional sequences (four in the Rio do Sul-Triunfo "transition" and two in the Triunfo Member) overlie the marine substrate of the Rio do Sul Formation. Each sequence is formed by fluvial, deltaic and deglaciation associations (lower part of the sequence), and by glaciomarine and marine associations (upper part). Despite little sampling in the Rio do Sul Formation, the central domain reveals distinctive characteristics (PP6 to PP8 wells): thick glaciomarine deposits in the Rio do Sul substrate, thin "transition" zone and the predominance of fluvial associations in the Triunfo Member. The southern domain, PP4 and PP5 wells, has thick marine shelf deposits in the underlying Rio do Sul Formation, which partially corresponds to the Rio do Sul-Triunfo "transition" from the northern domain. Five depositional sequences are identified in the southern domain, and they are correlated with the central and northern domains. In addition, the marine shelf association of the southern domain changes laterally to deltaic deposits toward south (the "basal Triunfo delta" of the Rio do Sul área).

Mapeamento geotécnico da Formação Rosário do Sul na região metropolitana de Porto Alegre

The objective of the mapping of Rosário do Sul Formation, typical of the Great Porto Alegre region, is to characterize geotechnically soils and rocks of these sedimentary beds. This study refers to the lithology, spacial distribution, presence of residual soils, laboratory testing and behaviour relative to geotechnical applications. These latter consist of geotechnical information necessary to urban planning, particularly with regard to city expansion.

A new genus and species of stem group actinopteran fish from the Lower Permian of Santa Catarina State, Brazil

This work deals with the description of a new genus and species of fossil fish: Santosichthys mafrensis gen. et sp. nov. (Elonichthyidae: Actinopteri). The new fish is represented by a single specimen preserved in a siliceous concretion from marine shales of the Rio do Sul Formation (Lower Permian) of Santa Catarina State, Brazil. Differences between the new form and other Elonichthyidae can be accounted for by the morphology of the cranial bones such as the maxilla and dermopterotic. Besides the description, a brief discussion on the classification and interrelationship of other ‘palaeonisciformes’ is attempted. Santosichthys mafrensis seems to belong to one of the stem-group neopterygians.

Conglomerado Bom Retiro do Sul

A descoberta de um conglomerado basáltico na área de Bom Retiro do Sul constitui-se em mais uma evidência da grande fase erosiva que teve lugar na região central do Estado do Rio Grande do Sul, e que se processou entre o final da sedimentação Botucatu e o início dos derrames basálticos. Trata-se de uma rocha com um significado genético diferente daquelas associadas aos derrames basálticos da Serra Geral e aos arenitos intertrapeanos. Além do caráter genético, elucida o tempo de duração do evento erosivo.