Pirabas Formation Research Articles

Paleontological study of the Oligocene/Miocene boundary in the Ilha de Santana and Pirabas formations, Pará-Maranhão Basin on the Northwest equatorial platform of Brazil

Sedimentary carbonate outcrops of the Pirabas Formation at the Bragantina platform in North Brazil represent the exposed portion of the entire carbonate succession in the marine equatorial platform from the subsurface Ilha de Santana Formation (Cretaceous/Maastrichtian-Miocene/Messinian) in the Pará-Maranhão Basin. The transgressive deposits, flooding, and advance of the carbonate platform were investigated through the study of outcrops of the Pirabas Formation (type locality in the Ilha de Fortaleza, Pará state) and the analogous carbonate from the uppermost section of the Ilha de Santana Formation from the well 1-MAS-16-MA (510–660 m below sea floor). The stratigraphic analyses were based on petrography, microCT, microfossil assemblages (foraminifera, ostracods, and bryozoans) and index species (Amphistegina, Archaias, Pyrgo, Quinqueloculina, Pirabasoporella, Nellia, Skylonia, and Alpheus), and biofacies approach. The Ilha de Santana Formation (Burdigalian/Langhian at 510–660 mbsf section of 1-MAS-16-MA) and the Pirabas Formation (Burdigalian at the Ilha de Fortaleza outcrops) suggest that shallow-water sedimentary facies are similar to those deposited in the marginal basins and mark the start of siliciclastic supplies to the inner platform and the decline of coralline algae carbonate factories.

Brazilian Miocene crabs II. A new genus and species (Crustacea: Decapoda: Brachyura) from Pirabas Formation, northern Brazil

In this study, we describe and illustrate Pirabacarcinus iaran. gen. n. sp., a novel species within the family Pilumnidae, collected from Miocene deposits of the Pirabas Formation, Brazil. Notably, this constitutes the first known fossil Pilumnidae from Brazil and only the second in South America, with the prior record from the Miocene of Chile. Pirabacarcinus iaran. gen. n. sp. is characterized by a series of distinct morphological characters, setting it apart from other known brachyuran species from the Pirabas Formation and other morphologically similar groups. The combination of a carapace with anterolateral margin longer than posterolateral margin, with three blunt spines anteriorly upturned; and a posterior region of carapace, including metabranchial and intestinal regions sloped, metabranchial region without lobes, and intestinal region reduced, faintly delimited set the new species apart from several brachyuran fossil genera. Opportunity is taken to describe and illustrate three cheliped fragments collected from the same locality of the new species.

Miocene tropical storms: Carbonate framework approaches and geochemistry proxies in a reservoir model

The Bragantina Platform is an important sedimentary package that occurs in northwestern Brazil, typically around the equatorial western Atlantic coast. Most of the latest Neogene succession of this carbonate-siliciclastic platform consists of the Pirabas Formation of Miocene age (Burdigalian to Serravalian). High-energy coastal storms and hurricanes as a consequence of trade wind anomalies during the Neogene impacted the shallow-water inner marine heterozoan assemblage deposits of the Pirabas Formation. A chaotic overlap of benthic infauna and epifauna, and of demersal and pelagic species in the same section was analyzed using petrography, petrophysics, micro- and macropaleontology, taphonomy, and geochemistry in order to understand sedimentary and paleoenvironmental processes. The equatorial carbonate platform of Brazil reveals high-energy and multiple Miocene tropical storms. This high-energy wave environment caused severe damage to shallow-water heterozoan assemblages at the seafloor, resulting in chaotic faunal arrangements, and removing fine-grained particles thus improving the petrographic properties of the rock (porosity and permeability).

Brazilian Miocene crabs I. Taxonomic review of Cyclocancer tuberculatus Beurlen, 1958 and Hepatella amazonica Beurlen, 1958 (Pancrustacea, Decapoda, Brachyura)

In describing Cyclocancer to accommodate his new species C. tuberculatus, Beurlen highlighted that his new genus was a cancroid intermediate in form between Atelecyclus and Cancer, but with enough characters to be placed in a new genus. Examination of C. tuberculatus type material revealed that Cyclocancer is a junior synonym of Hepatus. Therefore, C. tuberculatus is herein transferred into Hepatus as H. beurleni nomen novum because H. tuberculatus (Beurlen, 1958) is a junior homonym of H. tuberculatus Saussure (1858), a junior synonym of Hepatus pudibundus (Herbst, 1785). Miohepatus gen. nov., comb. nov. is proposed here to accommodate Hepatella amazonica Beurlen from the Pirabas Formation, Neogene, Pará, Brazil, based on new morphological evidence from the type material.

Scanning holotypes from the Vertebrate Paleontology Collection at the Museu Paraense Emilio Goeldi (Brazil): Tools for research and science outreach

AbstractThe scanning of paleontological collections is increasingly important for morphological studies and science outreach. In addition to ensuring data sharing, digitization contributes to preserving morphological information in case of damage to the original specimens. In this communication, we aim to report digital versions of the holotypes from the Vertebrate Paleontology Collection at the Museu Paraense Emilio Goeldi, Brazil. For this purpose, eighteen holotypes of Early/Middle Miocene Teleostei from Pirabas Formation, northern Brazil, were scanned using microtomography, and cybertypes were proposed. The CT‐Scan data were stored in a virtual repository, can be freely accessed, and are available for future studies on the morphology of these specimens. Furthermore, these specimens are tiny and fragile, and digital versions can be an alternative to safely handling them. Finally, the digitization of important specimens, at least of holotypes, needs to be a standard practice in museum collections over the next years.

Biostratigraphy and Paleoenvironments of the Pirabas Formation (Neogene, Pará State-Brazil)

Biostratigraphy and Paleoenvironments of the Pirabas Formation (Neogene, Pará State-Brazil)

Taphonomic feedback, paleoecology, and ostracod biostratigraphy of the Oligocene-Miocene carbonate deposits in the onshore Pará-Maranhão Basin, Northern Brazil

The Oligocene-Miocene carbonates of the Bragantina Platform are represented by densely fossiliferous rocks, which overlay the basement of the Northern Brazilian coast. Outcrop-based stratigraphy analysis combined with petrography, taphonomy, paleoecology, and ostracod biostratigraphy was carried out in the eight (8) m-thick of the Neogene mixed carbonate-siliciclastic succession exposed mainly in the Atalaia Beach. This outcrop is the classical exposure of the Pirabas Formation, generally overlaid by the siliciclastic deposits of the middle Miocene Barreiras Formation. The taphonomic signature in the last carbonate beds of this sedimentary succession indicates intense storms as autogenic processes succeeded by rapid allogenic burial by Barreiras’ deposits. These processes caused death, disarticulation, and accumulation of the benthic communities in the shallow platform, forming a coquina substrate (Taphofacies 1). During a low-energy period, shell-gravel-dwelling individuals represented mainly by Turbinella tuberculata and Mercenaria prototypa colonized this carbonate hardground (Taphofacies 2). Forced regression of Barreiras’ siliciclastics caused a fast shift of continental facies over coastal carbonate zones. The rapid burial culminated in the death of benthic communities creating a geochemical environment propitious for the pyritization of shells, leaves, and trunks (Taphofacies 3). The ostracod biozonation formed by the Cytherella stainforthi biozone and by the Quadracythere brachypygaia, Jugosocythereis pannosa, and Neocaudites macertus sub-biozones support the paleoenvironmental interpretation, chronocorrelation with the Caribbean units and confirm the Miocene age for this carbonate succession. Although taphonomic, paleoecologic, and biostratigraphic studies were carried out in a unique occurrence of the Pirabas Formation. These high-resolution stratigraphy analysis allowed the discovery of the details of this burial event that led to the shutdown of carbonate fabric on the Eastern Amazon Coast.

Biostratigraphy and paleoenvironment correlation based on benthic foraminifera from the cenozoic Marajó and Pirabas formations, Eastern Amazon Coast, Brazil

The Oligocene-Miocene foraminifera biostratigraphy correlation has been applied successfully as a geological tool for establishing the paleoenvironmental conditions during the deposition of siliciclastic and carbonate strata in the Eastern Amazon coastal basins. In this region, previously interpreted tectonic compartments represented by the Marajó Basin and Bragantina Platform were the main sites of siliciclastic and carbonate sedimentation influenced by Late Paleogene-Neogene transgressive–regressive events. In the subsident Marajó basin, a siliciclastic estuary was developed, supplied by the Cratonic Amazon River. The transcontinental river did not influence the Bragantina region to the East, allowing the implantation of a shallow carbonate platform. These Neogene segments require further sedimentological, stratigraphic, and paleontological studies to define these limits. The use of foraminifera content has been considered an important tool to assist in this differentiation, providing a paleoenvironmental and paleoecological reconstruction model. This work used qualitative and quantitative analyses integrating several diversity indices, complementing the R-mode cluster and the correlation of planktonic and benthic (P/B) ratios. The similarity in faunal diversity indicated that these siliciclastic and carbonate units represented by the Marajó and Pirabas formations are chronocorrelated. Marajó Formation is interpreted as a restricted, suboxic, marginal marine environment (lagoons/mangroves) with variable salinity and abundance of the species as Cribroelphidium williamsoni, Ammonia tepida, and A. beccari. In contrast, the Pirabas Formation was deposited in a brackish, oxic, and carbonate platform characterized by Cibicidoides subhaidingerii, Cibicides pachyderma A. beccarii, and Cassidulina laevigata species. These foraminifera assemblages confirm the previous stratigraphic and paleoenvironmental interpretations providing new insights into understanding the Late Paleogene-Neogene evolution of the Eastern Amazonia Coast.

Palaeoenvironment of the Miocene Pirabas Formation mixed carbonate–siliciclastic deposits, Northern Brazil: Insights from skeletal assemblages

The Bragantina Platform is an onshore basin of the Brazilian equatorial margin, including the Pirabas Formation, the youngest bioclastic-dominated formation in the area (early–middle Miocene), testifying to the final demise of carbonate factories along this margin area and the transition to a siliciclastic-dominated sedimentation. Although the greatest part of the Pirabas Formation is overlain by the Barreiras Formation and the post-Barreiras deposits, the outcrops provide the opportunity to investigate these Neogene successions that are the onshore equivalent of the large offshore basins (e.g. Amapá Formation: Foz do Amazonas and Ilha de Santana Formation: Pará-Maranhão) of the margin. The latter are deemed to represent an important target for reservoir models. Aiming to thoroughly describe the Pirabas Formation deposits and provide a quantitative and simple approach to analysing the outcropping successions, this study examines seven different successions and a quarry using palaeontological and petrographical methods. Similar to the modern Brazilian equatorial margin, the siliciclastic fraction in the Pirabas Formation rocks decreases as the distance from the coast increases, whereas the bioclastic material is found in greater amounts offshore. However, while the carbonate production close to the Amazon River mouth currently occurs hundreds of kilometres offshore, the carbonate factories in coastal along the Pirabas platform are also located in coastal waters. This indicates that the terrigenous input over the carbonate rocks was still lower than that found at present. The combining analysis of the skeletal and foraminiferal assemblages enabled a separation of protected embayments (characterised by seagrass-related assemblages), exposed areas (characterised by bioclastic shoals) and mangrove forests (characterised by dark fine-grained sediments). This accurate approach serves as an unprecedented reference for the northeastern part of the South American equatorial margin and lays the foundation for future research.

Dominance of Miocene echinoderms in the equatorial Neogene marine platform of Brazil and their insights into the paleoenvironment

Echinoderms are one of the most important invertebrates in the early to middle Miocene heterozoan carbonate deposits of the Pirabas Formation of the northern Brazil. The well-preserved echinoid tests were useful for accurate identification, whereas the sediment filling the tests provide significant information regarding the rock matrix. The dominance of disarticulated ophiuroid, crinoid, and asteroid plates, and damage on the echinoderm test provides a basis for taphonomic processes to elucidate a paleoenvironmental interpretation based on the echinoderm assemblages. Nineteen echinoderm taxa (ten valid species and nine species in open nomenclature) were recorded based on well-preserved and/or fragmented tests and/or spines, including Abertellidae †Abertella pirabensis (Santos, 1958), Placatenellidae †Placatenella complanata (Brito, 1981), Clypeasteridae †Clypeaster lamegoi Santos, 1958, †Clypeaster paraensis Brito, 1979, and †Clypeaster paulinoi Santos, 1958, Cassidulidae †Anisopetalus oliveirai (Santos, 1958) and †Rhyncholampas candidoi Fernandes and Morais, 1994, Echinolampadidae †Echinolampas paraense Santos, 1958, Schizasteridae †Agassizia eugeniae Brito and Ramires, 1974 and Schizaster sp., Cidaridae Cidaris sp., †Phyllacanthus priscus Brito and Ramires, 1974, and Prionocidaris sp. The smaller echinoderm fragments were dominated by disarticulated plates of Gorgonocephalidae ophiuroids, Comatulidae crinoid Sievertsella sp., Goniasteridae asteroids, as well as spines and tests fragments of Cidaridae echinoids. The echinoderm assemblages suggest an inshore and shallow water paleoenvironment over a soft sandy carbonate bottom. MicroCT analyses of sediments filling echinoid tests exhibited a microfossil assemblage, including foraminifera, sponges, ahermatypic corals, bryozoans, and mollusks. Broken and disarticulated tests and plates in chaotic orientations suggest high-energy paleoenvironment. Evidence of test damage indicates complex predator-prey interactions. Overall, the microCT analyses of echinoid tests proved to be a high accuracy non-destructive, analytical approach for investigating fossil echinoderms and their paleoenvironment.

Fossil isotopic constraints (C, O and 87Sr/86Sr) on Miocene shallow-marine incursions in Amazonia

Several studies have reported Miocene shallow-marine incursions in the Pebas Megawetland system (Western Amazonia) based on paleontological and sedimentological evidence. Only a few publications restricted to Middle and Late Miocene fossils outcropping in the Iquitos (Peru), Benjamin Constant and Eirunepé (Brazil) areas have provided isotopic evidence to test these incursions. In this study, we present new carbon, oxygen, and strontium (87Sr/86Sr ratios) isotopic data of macrofossils (pacu and ray teeth, crab claws and oysters), and microfossils (ostracods and foraminifera) from reported lower to lower upper Miocene sedimentary rocks of Western and Eastern Amazonian (Peru and Brazil), mainly from shallow-marine deposits. It was also analyzed present-day organisms from distinct environments (beach, sea, riverine, and estuary) and compared these results with Miocene fossils. While C and O isotopic compositions indicate that Western Amazonia fossils display an isotopic composition similar to the present-day continental, limnic and riverine, environments (−17‰ to −5.61‰ for δ13C and − 10.14‰ to −1.92‰ for δ18O), Eastern Amazonia fossils display C and O isotopic compositions comparable to those from seawater environments (−2.53‰ to −0.72‰ for δ13C and − 4.85‰ to −1.76‰ for δ18O). We further used the 87Sr/86Sr isotopic composition of the fossils to estimate paleosalinity conditions. The 87Sr/86Sr isotopic compositions indicates that Eastern Amazonian water bodies of the Pirabas Formation (Marajó Basin) varied from mesohaline to marine conditions. In contrast, Early Miocene Western Amazonian water bodies of the Pebas Megawetland System (PMWS) are characterized by freshwater conditions. Nonetheless, in Middle and Early Late Miocene, oligohaline conditions are found in the Peruvian part of the PMWS. Paleosalinity estimates of the Brazilian part of the PMWS are less constrained and might indicate a salinity range between freshwater or oligohaline conditions. Our isotopic data suggest the PMWS was occasionally submitted to oligohaline conditions during Middle and Early Late Miocene shallow-marine incursions. We suggest that Miocene shallow-marine incursions in Western Amazonia at this time were characterized by transitional paleoenvironments, reconciling isotopic, sedimentological and paleontological evidences.

X-ray micro-computed tomography of burrow-related porosity and permeability in shallow-marine equatorial carbonates: A case study from the Miocene Pirabas Formation, Brazil

The Miocene Pirabas Formation is of strategic importance for the hydrocarbon industry since it represents the onshore portion of larger offshore basins of Northern Brazil, including the Foz de Amazonas, the Pará-Maranhão, Barreirinhas, Ceará, and the Potiguar basins of the equatorial margin of South America. The Pirabas Formation from the Aricuru outcrop (Pará State) is a shallow-water mixed siliciclastic-carbonate deposit, comprising highly bioturbated wackestone and packstone. However, the impact of these biogenic structures on the reservoir quality of this formation has been overlooked. Here, our results show that pervasive Thalassinoides penetrating the rock matrix, result in remarkably improved porosity and permeability, thus, turning the Pirabas Formation in extremely favorable strata for fluid flow and storage. Since these bioturbated layers are likely to be common in the sub-surface counterparts of this formation, the hydrocarbon potential of these deposits is probably higher than previously expected. Also, considering that the offshore basins of Northern Brazil are directly related to the breakup of the African and American plates during Aptian-Albian, the exploratory interest in the correlated Guinea Gulf (Jubilee play) and French Guiana-Suriname Basin (Zaedyus play) need to be reconsidered. Overall, the results of this research highlight the importance of integrating ichnological datasets with reservoir characterization studies for more accurate reservoir quality assessments.

CARLOTTA JOAQUINA MAURY: UMA VIDA DEDICADA À CIÊNCIA

This article is a remote teaching activity within de PET-Geology Group (UFPA) and presents a summary of Carlotta Joaquina Maury’s academic professional career and their scientific contribution to the pioneering studies of the Pirabas Formation. Carlotta Joaquina Maury (1874-1938), who was recognized as the first woman to work with paleontology in Brazil. Despite all adversities she was a consulting paleontologist and stratigrapher to Royal Dutch Shell’s Venezuela Division and one of the official paleontologists the Geological and Mineralogical Service of Brazil. In 1925, she published “Tertiary Fossils from Brazil with Description News Cretacean Forms” where she described numerous species of mollusks from the northeastern coast of Brazil, performing the stratigraphic correlation of these faunas with similar faunas of the Caribbean and Gulf of Mexico. Carlotta Joaquina Maury was fellow of the Geological Society of America, American Geographical Society and of the Brazilian Academy of Sciences. An admirable woman ahead of her time. Keywords: Paleontologist, Scientific women, Pirabas Formation.

Miocene heterozoan carbonate systems from the western Atlantic equatorial margin in South America: The Pirabas formation

Outcrops of Neogene carbonates of the North Brazilian platform occur exclusively along the equatorial coast and represent some of the few existing examples of Neogene carbonate systems of the Atlantic coast of South America. The Pirabas Formation (early-middle Miocene) is the northernmost part of this platform. Although onshore mainly consists of small and scattered outcrops, it considerably extends in the subsurface keeping record of relevant geological and paleontological episodes of tropical South American history. Intending to improve the knowledge of South American carbonate and providing a solid basis for future comparisons between the Pirabas Basin and other, largely subsurface, Cenozoic basins, this research investigates the Aricuru outcrops by combining a standard petrographical and paleontological approach with advanced microCT analyses. The Aricuru area is characterized by mixed siliciclastic-carbonate sand-sized deposits, which probably deposited after the early Miocene according to the palynological assemblage. The bioclastic fraction of the rock is dominated by benthic foraminifera (mostly soritids, amphisteginids, small rotaliids, and small miliolids, typical of marginal marine environments), bryozoans, calcareous algae (Halimeda), echinoderms and mollusks. The abundant siliciclastic fraction together with the taxonomic composition of the foraminiferal, echinodermal, crustacean, ichnofossil and fish assemblages indicates deposition in a tropical coastal environment featuring both protected and more exposed sectors. The carbonate system probably developed under abundant nutrient supply, which fostered heterotroph suspension feeders over hermatypic corals. The demise of this system was most likely caused by a growth in siliciclastic input due to increased rainfall in the coastal area. The sedimentary evolution of the Pirabas Formation is similar to the one of the Foz do Amazonas Basin, and fits well with the general evolutionary trend of Cenozoic carbonate factories of the region, indicating the potential of the Pirabas subsurface record for understanding other Cenozoic basins, their paleoenvironmental significance, and their potential as oil, gas and water reservoirs.

Uca maracoani (Crustacea, Decapoda, Ocypodidae) from a Miocene paleomangrove in Brazil: A case of evolutionary stasis among tropical American fiddler crabs

The Miocene fiddler crab Uca maracoani antiqua Brito, 1972, from the Pirabas Formation (Brazil), has been recurrently claimed to be a valid species and the oldest fossil record of the brachyuran crab family Ocypodidae. However, morphological investigations with the aid of microCT scan images of a large number of topotypic specimens and re-examination of the type material of U. maracoani antiqua revealed that it should actually be merged into the synonymy of Uca (Acanthoplax) maracoani (Latreille, 1802). Therefore, U. maracoani, the morphology and ecological traits of which have persisted essentially unchanged for at least 16 Ma (Burdigalian to present), is actually a long-lived crab species inhabiting an estuarine, sheltered mudflat environment that, likewise, has essentially remained unchanged. Burgeoning evidence suggests that evolutionary stasis may not be uncommon among mangrove crabs, as revealed by Afruca tangeri (Eydoux, 1835) from the middle Miocene in northeastern Spain and U. ornata (Smith, 1870) from the Plio-Pleistocene in Honduras. Uca antiqua is redescribed and illustrated based on 3D volume reconstruction and several topotypic specimens. The microCT analysis revealed a considerable number of fossil concretions of U. maracoani, with both males and females likely sharing the same burrow. This is the first fossil record of a male fiddler crab with a female inside a burrow, where mating usually takes place. This mating style is common to almost all extant American fiddler crabs.

Palaeontological framework from Pirabas Formation (North Brazil) used as potential model for equatorial carbonate platform

Abstract The Pirabas Formation (early to middle Miocene) from the equatorial margin of North Brazil is characterized by a shallow-marine carbonate platform with high fossil diversity and abundant micro- and macrofossil remains. The Pirabas Formation represents a unique carbonate system along the Atlantic margin of South America that developed before the onset of the Amazon delta. We studied the palaeontology and lithofacies of outcrops of the uppermost Pirabas Formation and found that was deposited in a coastal marine environment with marginal lagoons under the influence of a tidal regime and tropical storms. The remains of calcareous algae, molluscs, crustaceans, echinoiderms, bryozoans, solitary corals, fish and marine mammals, together with foraminifera, ostracods and other marine microfossils, shaped a biogenic framework, that together with the post-depositional processes of dissolution of skeletal grains, is responsible for the mean packstone-floatstone porosity of 14.9%. The palaeontological framework and the petrophysical characterization of the carbonate rocks from the uppermost Pirabas Formation outcrop represent a baseline to interpret the entire Pirabas Formation in the subsurface stratigraphic sections (cores) of this important Neogene unit. Considering that carbonate rocks account for ~50% of oil and gas reservoirs around the world, this research provides a model for Neogene tropical carbonate deposits useful for carbonate petroliferous reservoirs in the Brazilian equatorial basins.

The crustaceans burrow Sinusichnus sinuosus from the Oligocene-Miocene carbonate deposits of eastern Amazonia

Sinusichnus Gibert 1996 is recorded for the first time in the Oligocene-Miocene Pirabas Formation of Northern Brazil. In these Oligocene-Miocene carbonate deposits, Sinusichnus sinuosus is characterized by horizontal, highly regular sinusoidal burrow systems with T- and H-shaped branching points. The main difference between the S. sinuosus described herein and other occurrences worldwide is the anomalous diameter of the burrows (4 to 10 cm). These trace fossils occur in organic matter-rich, wackestone/packstone and laminated mudstones interbedded with boundstones deposited in an inner carbonate platform paleoenvironment. The exceptional size of the studied S. sinuosus could have been associated to the producer’s size, which may be attributed to construction by large crustaceans, similar to fossils found within the Pirabas Formation. Also, the sinusoidal morphology and retrusive spreiten could be a result of the fodinichnial/domichnial behavior.

Taxonomy of Ostracods from the Pirabas Formation (Upper Oligocene to Lower Miocene), Eastern Amazonia (Pará State, Brazil).

Ostracods from the Upper Oligocene to Lower Miocene Pirabas Formation, Northeastern Amazonia, Pará State, Brazil were examined from one subsurface and four outcrop sections. A total of 119 species were recognized and are illustrated; another 53 species were left in open nomenclature. Twenty-seven of the species are common to the Neogene of Caribbean, another two species are known from areas other than the Caribbean, and one species was already described from the studied unit. This study provides a robust taxonomic database for paleoenvironmental, biostratigraphic and paleogeographic studies and contributes to the knowledge of the paleodiversity of Neogene Ostracods from the Southwestern Atlantic.

Interpretações paleoclimáticas a partir da tafoflora de Caieira, Formação Pirabas, Oligoceno/Mioceno da Amazônia Oriental, Pará, Brasil

The Caieira taphoflora, which is associated with the Pirabas Formation, is the best documented one for the Oligocene/ Miocene of the eastern Amazonia. The taphoflora represents a predecessor of a phytophysiognomy of the Amazon Forest, specifically of a floodplain forest, which has developed under a warm and humid climate. The main physiognomic characteristics – type of margins and leaf area – of the angiosperm leaves of 19 species of this taphoflora, allowed us to carry out the reconstruction of the mean annual temperature (MAT) and the mean annual precipitation (MAP) for the moment of its deposition. The different equations used to reconstruct the MAT and the MAP are based on univariate methods known as Leaf Margin Analysis and Leaf Area Analysis. These equations indicated that the Caieira taphoflora developed under a MAT between 24.6 and 25.0 °C, and a MAP between 1849 and 2423 mm. The values are similar to the current values for the region where the taphoflora was collected, therefore, it is possible to infer that the current climatic configuration has been firmly established since the Oligocene/Miocene, as well as its vegetation. The values also indicate that the climate was colder, between 1.1 and 1.5 °C, and less humid, between 42 and 619 mm, for the moment of deposition of the Caieira taphoflora, possibly due to the global cooling event known as Mi-1 glaciation, which affected the whole Amazonia during the Oligocene/Miocene transition.

ANÁLISE DA SUBSUPERFÍCIE COM SONDAGEM ELÉTRICA VERTICAL (SEV) NOS MUNICÍPIOS DE CAPANEMA E PRIMAVERA, NORDESTE DO ESTADO DO PARÁ.

Estudos geológicos e geofísicos baseados na técnica de investigação Sondagem Elétrica Vertical (SEV) foram utilizados na identificação de litofácies de origem tectônica dos depósitos neógenos carbonáticos e siliciclásticos, correspondentes as Formações Pirabas e Barreiras, e sedimentos da unidade Pós-Barreiras, que constituem o preenchimento da Plataforma Bragantina, nos municípios de Capanema e Primavera, região continental do nordeste do estado do Pará. Os dados de resistividade aparente das sondagens elétricas foram processadas utilizando o programa IPI2win, que é projetado para realizar inversões 1D automáticas, correlacionando-as sempre que possível com os perfis litológicos de poços, disponíveis na plataforma online do Sistema de Informação de Águas Subterrâneas (SIAGAS), com o intuito de ajustar os valores de espessuras das camadas (fornecidas pelos perfis ) com a solução do modelo geoelétrico e estimando-se as resistividades de cada camada de acordo com a composição mineralógica descrita nos poços. Os resultados das sondagens elétricas realizadas neste trabalho mostraram-se satisfatórias, pois permitiram diferenciar o possível contato entre a Formação Pirabas com o embasamento cristalino a uma profundidade em torno de 50 metros no município de Capanema, devido o forte contraste de resistividade, no município de Primavera diferenciou as Formações Pirabas e Barreiras, em torno de 9 metros de profundidade.
 Palavras-chave: Sondagem Elétrica Vertical (SEV). Neógeno. Nordeste do Estado do Pará.