Abstract The terminal Ediacaran fossil record includes microbial mats and body fossils characterized by simple morphologies, which represents a challenge to understand several aspects related to the paleoecology of the emerging complex life. The marine siliciclastic deposits of the Cerro Negro Formation (~560–550 Ma) contain evidence of different styles of microbially induced sedimentary structures (MISS) and discoidal forms associated with them. Different types of MISS, such as Kinneyia and wrinkle structures, elephant skin, and Arumberia, are reported and related to shallow marine depositional environments. These morphologies are commonly associated with the high quality of preservation of body fossils in Ediacaran deposits. The preservation of Aspidella discoidal holdfast is related to biotic and abiotic processes involving substrate sealing by microbial mats, fluidization, and probably organic matter decay. Both abiotic factors (tidal currents and waves, added to liquefaction and sand injection) and biotic factors (substrate biostabilization by microbial mats favoring sediment cohesion) are considered the main ones responsible for the preservation style in the Cerro Negro Formation. This formation constitutes a remarkable example in SW-Gondwana of how preservation dynamics took place on a seabed sealed by microbial mats and is an important deposit conserving diverse Ediacaran forms of life in South America.

Abstract The influence of microbial communities upon sedimentary dynamics is an issue of increasing significance. Over the last decades, studies have revealed a particular class of sedimentary structures and textures produced by the interaction among distinct flows, marine substrate, and benthic microbial communities. We present evidence of the oldest record of microbially-induced sedimentary structures (MISS) in South America, as recorded in low-grade metasedimentary rocks of the Early Mesoproterozoic (∼1536 ± 33 Ma) Tiradentes Formation, state of Minas Gerais, SW Brazil. Types 1, 2, and 3 correspond to wrinkle, pustular, and dome structures related to flat or rippled bed surfaces, preserved in metasandstone deposited in shallow marine settings. Evidence supporting the microbial origin of these structures includes delicate morphology, degree of alignment, presence of original mat cover, and orientation of quartz grains indicating biostabilization. The presence of distinct MISS associated with well-preserved ripple marks, wrinkled surfaces, and flatbeds suggests deposition under varied energy conditions with different potentials for the preservation of surficial structures. Vertical growth of microbial communities influences sediment cohesion and stability. This reduces substrate roughness and, as a consequence, wave and current shear, thereby increasing the preservation potential of bedforms and delicate features of their bedding surfaces.

Abstract The Aptian Crato Formation is world renowned for its well-preserved fossils in microbially-induced laminated limestones, which are regarded as one of the main Cretaceous Konservat-Lagerstätte of the geological record. Detailed stratigraphic investigation and mapping of the up to 90-m-thick Crato Formation at the eastern border of the Araripe Plateau allowed recognition of a regionally persistent fossil-bearing muddy interval, herein defined as the Caldas Bed. At its type locality, it is defined as an up to 2-m-thick coarsening-upward succession of grey/green mudstone and interbedded sandy siltstone and claystone. The 0.85- to 2-m-thick interval was recognized in several localities along the outcrop belt, and it is bounded by sharp, lower (Konservat-Lagerstätte limestone) and upper (sandstone and heterolithic facies) contacts. Despite previous literature data suggesting the presence of marine mollusks, the bed contains freshwater bivalves, small gastropods, spinicaudatans, plant remains, trace fossils, and rare ostracods. The Caldas Bed records benthic paleocommunities representing a short-term isochronous regional freshening event, marked by abrupt changes in sedimentation pattern, bathymetry, salinity, oxygenation and water chemistry.

Abstract Fracturing analysis of low-permeability rocks as reservoir analogs have increased in recent years. The main mechanism involved in the development of secondary porosity in low-permeability, fine-grained limestones of the Irati Formation is fracturing. In these rocks, oil accumulates along fracture planes, vuggy porosity, microfractures, breccias, as well as bedding discontinuities. Joints represent the central element for oil migration and the connection between accumulation sites. Joints are unevenly distributed across the succession of rock types, where carbonate rocks have a much denser array of joints than shales and siltstones. From a mechanical stratigraphy point of view, limestones have a brittle behavior and constitute mechanical units. Ductile shale and siltstone are mechanical interfaces capable of blocking joint propagation. Joints running NW-SE are more effective in trespassing the mechanical interface and are, therefore, more persistent. Joints running NE-SW are less persistent because the ductile behavior of the first two shale beds above the limestone blocks their propagation. The spatial arrangement of regional NW-SE and NE-SW joints promoted reservoir connection, allowing oil migration and accumulation. The joints and oil migration (at least three phases) developed as a consequence of the Gondwana Breakup and are also associated with local pressure gradients.

Abstract Soft-sediment deformation (SSD) structures are widespread in the sedimentary record, and numerous triggering mechanisms can induce its development, including glaciation, earthquakes, overloading, ground-water fluctuations, and wave movement. The Late Cretaceous Uberaba Formation preserves SSD structures as small- and large-scale load casts and associated flame structures, pseudonodules, and convolute laminations observed in the contact of three well-defined intervals among fine- to coarse-grained lithic and conglomeratic sandstone with fine-grained arkose and mudstone beds. Based on the morphology of the SSD structures, sedimentary facies of the Uberaba Formation, and similarities with previous observations in the geological record and laboratory models, these features are assigned to liquefaction-fluidization processes as the major deformational mechanism triggered by seismic and aseismic agents. We propose that a deformation occurred just after the sedimentation triggered by seismic shock waves and overloading, induced by the sudden deposition of coarse-grained sandy debris on fine-grained sediments. Some of these structures can be classified as seismites, providing evidence of intraplate seismicity within the inner part of the South American Platform during the Late Cretaceous. This seismic activity is likely related to the uplift of the Alto Paranaíba High along reactivations of regional structures inherited from Proterozoic crustal discontinuities and coeval explosive magmatism of the Minas-Goiás Alkaline Province.

Abstract Sedimentologic and stratigraphic studies of paleo-deserts from the Brazilian Cretaceous are of great potential to understand the paleoclimate and paleogeography of Gondwana during its final rifting stage. Herein, we describe and discuss two depositional units characterized by two distinct eolian systems that are bounded by a long-lived unconformity. The Lower Unit (Barremian/Aptian) encompasses a wet eolian system composed of dune, interdunes, and ephemeral alluvial deposits. A continuous paleosol horizon in the upper part of the Lower Unit records dune stabilization and end of eolian accumulation, in a period of climate amelioration possibly in the late Aptian. The stratigraphic gap proposed for the unconformity (Cenomanian to Coniacian) coincides with the Cretaceous Thermal Maximum. The Upper Unit (Santonian?/Campanian) comprises dune fields of a dry eolian system capped by the Mata da Corda volcanic rocks. Cross stratification dip directions from both eolian systems shows transport towards SSW. Paleo-winds coming from the northeast quadrant reveal that the continental breakup and drifting had little influence on the surface winds in this Gondwana sector. The Upper Cretaceous paleo-winds are coherent with global paleo-circulation models, based on a high-pressure cell over the South Atlantic proto-ocean, favoring desertification in the inner portion of the southwestern Gondwana.

RESUMO: Após o aparecimento dos metazoários, o início da bioclasticidade e a competição pelo substrato marinho, a saga das esteiras microbiais é marcada por um progressivo declínio. Pontuais aumentos em sua diversidade e na produção de carbonatos durante o Paleozoico em geral estão associados a eventos globais de extinção em massa. Ao longo do Fanerozoico, as colônias microbiais ocuparam nichos ecológicos específicos e ambientes livres de organismos predadores caracterizados por condições ecológicas extremas, como aqueles encontrados em baías hipersalinas, lagos alcalinos e locais sujeitos a hidrotermalismo. Neste trabalho é reportada uma das mais antigas ocorrências de um campo de exudação de metano no registro geológico associado com microbialitos e estruturas sedimentares induzidas por atividade microbial. Nesse sistema, durante a atividade de exalação de metano, instalaram-se condições de extrema anoxia e alta salinidade, proibitivas para a manutenção da vida animal, permitindo, desse modo, o florescimento de colônias microbiais. Por causa das severas imposições do ambiente, os organismos microbiais tornaram-se altamente adaptáveis às condições adversas então vigentes. Nós sustentamos a hipótese de que aumentos na diversidade e na quantidade de colônias microbiais na história da Terra não estão apenas restritos a períodos que sucedem à extinção em massa de organismos predadores de esteiras, mas ocorrem em resposta a condições ambientais localizadas que proporcionam o crescimento de colônias microbiais. De fato, o registro geológico Fanerozoico é pontuado de exemplos semelhantes ao aqui reportado, simulando uma espécie de jogo de esconde-esconde das condições ambientais vigentes no Éon Pré-cambriano.

ABSTRACT: Following the rise of metazoans, the beginning of bioclasticity and substrate competition, the saga of microbial mats was in a fluctuating decline in the end of the Neoproterozoic era. Increases in diversity during the Phanerozoic and punctual upturns in the microbial carbonate production occured after the events of global mass extinctions. Gradually along the Phanerozoic, the microbial colonies occupied isolated niches and grazers-free environments, characterized by physically and/or geochemically stressful conditions, such as those found in saline bays, alkaline lakes and hydrothermal or cold seep vents. Here we report one of the oldest occurrences of a vent camp coupled with cold seepage of methane in the geologic record, associated with well-preserved microbialites and elephant skin structures. During the seep activity, oxygen depletion and high salinity conditions are prohibitive for complex animal life, clearing the way to microbial colonies to flourish. Due to the co-occurrence of high adaptability and low competitiveness of microbial forms, they became highly specialized in stressful conditions. We argue that the sporadic microbial mat upturns in Earth’s history are not restricted to geological periods, following massive death of metazoan species; they also may occur in response to punctual paleoenvironmental conditions that enable microbial colonies to growth. Indeed, the Phanerozoic geological record is punctuated of these examples, in a kind of hide-and-seek game of Precambrian times.

RESUMO: Bivalves permianos da Bacia do Paraná evoluíram em um imenso mar interior, sob condições de extremo isolamento e estresse ambiental. Embora conhecidos desde 1918, a história evolutiva desses bivalves é ainda obscurecida pelo conhecimento incompleto e enviesado sobre a composição faunística e a distribuição estratigráfica de várias assembleias. Portanto, a descrição da assembleia de Tiaraju, a única conhecida no Grupo Passa Dois do sul do Brasil, contribui com novas informações-chave sobre a composição, biocorrelação e idade dessa fauna de moluscos únicos. Terraia falconeri, Cowperesia emerita, Holdhausiella elongata e Terraia altissima foram registradas e descritas. T. falconeri é a espécie mais comum, seguida por C. emerita, H. elongata e T. altissima. A fauna é maiormente composta por Terrainae, faltando os Pinzonellinae. A assembleia é, desse modo, pobremente diversificada, no que tange à composição faunística e guildas (somente bivalves de infauna, facultativamente móveis, suspensívoros estão presentes). Cowperesia emerita e T. altissima sugerem, fortemente, biocorrelação com assembleias das formações Rio do Rasto e Gai-As, Brasil e Namíbia, indicando idade não mais jovem que o Permiano médio (Wordiano-Capitaniano). À luz dessas informações, o mapa geológico da região de Tiaraju, São Gabriel, e o contato local entre as formações Teresina e Rio do Rasto, requerem, ambos, reavaliação.

ABSTRACT: Permian bivalves of the Paraná Basin evolved in a large inland sea, under conditions of extreme isolation and environmental stress. Although known since 1918, its evolutionary history is still obscure due to the incomplete and biased information on faunal composition and stratigraphic distribution of various assemblages. Hence, the description of the Tiaraju assemblage, the only known bivalve occurrence in the Passa Dois Group from the southernmost Brazil, adds new key information on the composition, biocorrelation and age of this unique molluscan fauna. Terraia falconeri, Cowperesia emerita, Holdhausiella elongata, and Terraia altissima were recorded and described. T. falconeri is the commonest species, followed by C. emerita, H. elongata and T. altissima. The faunule is mainly composed by Terrainae, lacking Pinzonellinae. Assemblage is, thus, poorly diversified, both regarding the faunal composition and guild structure (only infaunal, facultatively motile, unattached, suspension feeders present). Cowperesia emerita and T. altissima strongly indicate biocorrelation with assemblages of the Rio do Rasto and Gai-As formations, Brazil and Namibia, providing an age no younger than the mid-Permian (Wordian-Captianian). On the light of this information, the current geological map of the Tiaraju region, São Gabriel, and the local boundary between the Teresina and Rio do Rasto formations requires reevaluation.

RESUMO: Esta revisão incorpora novos dados isotópicos e químicos para correlação quimioestratigráfica de sucessões, predominantemente carbonáticas, na América do Sul (Argentina, Bolívia, Brasil, Paraguai e Uruguai). Estas sucessões, depositadas durante eventos de extensão, aparecem como espessos estratos carbonáticos/siliciclásticos em bacias epicontinentais ou foram acumulados sobre margens passivas em bordos de cratons (ex.: São Francisco, Amazonas, Bloco Rio Apa, Pampia e Río de La Plata) como três megasequências: glaciogênica, plataforma marinha carbonática (sobre diamictitos glacio-marinhos) e predominantemente continental siliciclástica. Em cinturões circunjacentes a cratons, sucessões carbonáticas contendo material vulcanoclástico/siliciclástico foram, na maioria dos casos, fortemente deformados. A idade precisa de sedimentação destas sucessões permanece em debate, mas recentes dados paleontológicos e geocronológicos têm consideravelmente restringidos os intervalos de deposição. Neste trabalho, reportamos trends isotópicos de alta resolução de C, O, Sr e S medidos em amostras bem preservadas e usamos principalmente isótopos de Sr e C em consonância com observações litostratigráficas/biostratigráficas, para estabelecer correlações detalhadas destas sucessões. Propor uma correlação quimioestratigráfica entre bacias Neoproterozoicas na América do Sul é o principal objetivo deste trabalho.

ABSTRACT: This report reviews and incorporates new elemental and isotope chemostratigraphic data for correlation of Neoproterozoic carbonate-dominated successions in South America (Argentina, Bolivia, Brazil, Paraguay and Uruguay). These thick mixed carbonate/siliciclastic successions were largely deposited in epicontinental basins or accumulated on passive margins on the edges of cratons (e.g. São Francisco, Amazonia, Rio Apa Block, Pampia and Río de la Plata paleocontinents) during extensional events related to the rifting of the Rodinia Supercontinent. From the stratigraphic point of view, these successions occur as three mega-sequences: glaciogenic, marine carbonate platform (above glaciomarine diamictites or rift successions), and dominantly continental to transitional siliciclastics. In the orogenic belts surrounding cratons, carbonate-dominated successions with important volcanoclastic/siliciclastic contribution have been, in most cases, strongly deformed. The precise ages of these successions remain a matter of debate, but recently new paleontological and geochronological data have considerably constrained depositional intervals. Here, we report high-resolution C, O, Sr, and S isotope trends measured in well-preserved sample sets and mainly use Sr and C isotopes in concert with lithostratigraphic/biostratigraphic observations to provide detailed correlations of these successions. The establishing of a high-level and definite chemostratigraphic correlation between Neoproterozoic basins in South America is the main goal of this work.

As rochas carbonáticas do Grupo Macaé (Albiano) representam a sedimentação carbonática relacionada ao início da fase drifte na Bacia de Campos. Discutem-se aqui aspectos deposicionais, diagenéticos e estratigráficos das rochas carbonáticas do Grupo Macaé, englobando a porção superior da Formação Quissamã e a porção basal da Formação Outeiro. Análises macroscópicas em testemunhos e microscópicas utilizando-se lâminas delgadas permitiram o reconhecimento de onze fácies sedimentares - nove delas correspondentes à Formação Quissamã e duas à Formação Outeiro. Estas foram agrupadas em cinco associações de fácies, relacionadas às diferentes posições fisiográficas de uma plataforma carbonática. Os bancos carbonáticos estão relacionados à deposição de grainstonesoolíticos e grainstonesoncolíticos em profundidades rasas, acima do nível de base de ondas de tempo bom (NBTOB). Os baixios oncolíticos ou interbancos foram formados em águas menos agitadas e são caracterizadas pela deposição de packstonespeloidais bioclásticos e wackestones,representativos da sedimentação em águas calmas Packstonesbioclásticos e wackestone/packstonesoolíticos representam depósitos alóctones relacionados ao início do afogamento regional da plataforma que ocorre na porção superior da Formação Quissamã. Wackestonescom pitonelídeos e wackestonesbioclásticos com glauconita são aqui relacionados a depósitos de água profunda, característicos da Formação Outeiro. As feições pós-deposicionais revelaram a atuação de processos diagenéticos de micritização, cimentação, dissolução, compactação, dolomitização e recristalização, ocorridos nas fases eo- e mesodiagenética. A análise da sucessão vertical das fácies indica a presença de diversos ciclos de raseamento ascendente, empilhados com uma tendência retrogradacional da sequência em direção ao topo (passagem da Fm. Quissamã para Fm. Outeiro).

Carbonate rocks from the Macaé Group (Albian) represent an example of carbonate sedimentation related to the drift phase in Campos Basin. This study presents depositional features, integrating them with diagenetic and stratigraphic aspects of the Macaé Group carbonates including the upper part of the Quissamã Formation and the lower part of the Outeiro Formation. Macroscopic analyses in cores and microscopic ones in thin sections allowed the recognition of eleven sedimentary facies - nine of them corresponding to the Quissamã Formation and two of them representing the Outeiro Formation. These facies were grouped into five facies associations. Oolitic grainstones and oncolitic grainstones are interpreted to be deposited in shallow depth probably in shoals above the fair weather wave base. The interbanks between shoals were formed in less agitated waters and characterized by deposition of peloidal bioclastic packstones and wackestones representative of sedimentation in calm waters. Bioclastic packstones and oolitic packstones/wackestones represent allochthonous deposits related to the beginning of the regional drowning that occur in upper Quissamã Formation. Pithonellids wackestones and bioclastic wackestones with glauconite are related to deep water deposits, characteristics of the Outeiro Formation. Post-depositional features revealed the action of diagenetic processes as, micritization, cimentation, dissolution, compaction, dolomitization and recrystallization occurred during the eo- and mesodiagenesis phases. Vertical facies analysis suggests shallowing upward cycles stacked in a sequence progressively deeper towards the top (from the Quissamã Formation to the Outeiro Formation).

A individualização e o mapeamento da Formação Serra Alta no Estado de São Paulo sempre foi motivo de controvérsia na comunidade geológica. Apesar de apresentar extensão comparável à Formação Irati em subsuperfície, a unidade ainda carece de estudos mais acurados acerca de seu posicionamento estratigráfico, conteúdo fossilífero, sistema deposicional e idade. Na região centro-leste do Estado de São Paulo, a Formação Serra Alta sucede estratigraficamente a Formação Irati, sendo constituída por depósitos pelíticos cinza escuros. A unidade é mapeada desde o limite sul do estado até o Domo de Gibóia, no Município de Rio das Pedras. Neste local, as formações Serra Alta e Teresina são substituídas pelos depósitos pelíticos da Formação Corumbataí, que se estende para norte, além do limite do Estado de São Paulo, e pode ser considerada unidade correlata a estas. Neste estudo, são apresentadas seções colunares e caracterizados os contatos da Formação Serra Alta com as formações permianas verticalmente contíguas. É apresentada também detalhada análise de fácies, com a finalidade de caracterizar o sistema deposicional. A análise de perfis de sondagem possibilitou também melhor compreensão dos padrões arquiteturais da Formação Serra Alta, auxiliando na determinação de sua real distribuição e posição estratigráfica na porção centro-sul do estado. A integração das informações obtidas permitiu identificar tendências de empilhamento transgressivo particulares, contribuindo para o detalhamento da sucessão predominantemente regressiva em que se depositaram as unidades permianas da Bacia do Paraná.

The delimitation and mapping of the Serra Alta Formation in the São Paulo State, Brazil, has always been a focus of controversy in the Brazilian geological community. Despite its large extension in subsurface, which may be comparable to the Irati Formation, the Serra Alta Formation still needs more detailed studies on its stratigraphic position, fossil content, depositional systems and age. In the east-central portion of the São Paulo State, the Serra Alta Formation overlies the Irati Formation and is predominantly composed of dark grey pelitic facies. The unit is mapped from the southern boundary of the São Paulo State to the Gibóia Dome, located in the county of Rio das Pedras. In this place, the Serra Alta and Teresina formations are replaced by the red colored pelites of the Corumbataí Formation, unit that extends to north beyond the state boundaries and may be considered correlated to these units. In this work, we present columnar sections and describe the contacts of the Serra Alta Formation with vertically adjacent Permian units. We also present the detailed facies analysis, in order to characterize the depositional system. The investigation of subsurface profiles also enabled a better understanding of the architectural patterns of the succession, helping to determine its real distribution and stratigraphic position in the central-south of São Paulo State. The integration of the data allowed identifying a particular transgressive stacking pattern, contributing to detail the late Permian regressive cycle in the Paraná Basin.