Afonso César Rodrigues Nogueira

Soft-sediment deformation at the base of the Neoproterozoic Puga cap carbonate (southwestern Amazon craton, Brazil): Confirmation of rapid icehouse to greenhouse transition in snowball Earth

Stratigraphic and isotopic data identify the lower 45 m of the Araras Group, on the southwest margin of the Amazon craton, as a Neoproterozoic platform cap carbonate deposited below wave base upon Varanger glacial diamictites of the Puga Formation. The basal beds consist of moderately deep water pinkish dolomudstone with stratiform to wavy fenestral microbialites locally cut by tube-like structures and fenestral nonmicrobial planar laminites with tepee-like features. Above the basal carbonates are deep-water bituminous lime mudstones with alternating thin calcite crusts and lime mudstone laminae commonly disrupted by calcite crystal fans (pseudomorphs after aragonite). The basal contact of the Puga cap exhibits soft-sediment deformational structures (principally load casts) that are here attributed to rebound-induced seismicity acting upon both recently deposited carbonate sediments and underlying unconsolidated diamictite. These features constitute the first clearly recognized sedimentological evidence for the rapid change from icehouse to greenhouse conditions as postulated in the snowball Earth model of Neoproterozoic glaciation.

Mid- and late-Holocene sedimentary process and palaeovegetation changes near the mouth of the Amazon River

The integration of sedimentary facies, pollen, spores, carbon and nitrogen isotopes records, C/N ratio and radiocarbon dates allowed the identification of changes in vegetation and the sources of organic matter accumulated on tidal flats near the mouth of the Amazon River during the mid and late Holocene. Data from the margin of Amazon River indicate marine influence related to mangrove presence over a tidal mud flat between 5560–5470 cal. yr BP and 5290–5150 cal. yr BP. Afterward, the mangrove area shrank following the return of more humid conditions and increase of Amazon River discharge. A common reworking process of the tidal flat through the lateral migration of a meandering creek occurred in the study site, with later development of transitional vegetation under freshwater influence. Following the natural vegetation succession under stable climate and hydrological conditions, the expansion of ‘várzea’ (flooded freshwater vegetation) forests occurred since 600–560 cal. yr BP until the present. Furthermore, regarding the tidal flats located west of the mouth of Amazon River, these stable conditions also allowed the mangrove maintenance over mudflats with deposition of marine organic matter during at least the last 2350–2300 cal. yr BP.

Ariid sea catfishes from the coeval Pirabas (Northeastern Brazil), Cantaure, Castillo (Northwestern Venezuela), and Castilletes (North Colombia) formations (early Miocene), with description of three new species

Ariidae catfish are described from the early Miocene Pirabas Formation in northeastern Brazil, Cantaure and Castillo formations in northwestern Venezuela, and Castilletes Formation in North Colombia. A skull from the Pirabas Formation is described as Cathoropsgoeldii, n. sp. and an otolith is identified as Cathorops sp. The otoliths from Cantaure, Castillo and Castilletes formations are described as Cantarius nolfi n. sp. and Bagreprotocaribbeanus n. sp. These coeval lithostratigraphic units reflect the Proto-Caribbean conditions and the shallow water tropical palaeoenvironment during the Miocene, particularly associated with marine coastal lagoon and estuarine influence.

Evolução de um sistema lacustre árido Permiano, parte superior da Formação Pedra de Fogo, borda oeste da Bacia do Parnaíba

Analise faciologica e estratigrafica realizada na regiao de Filadelfia, TO, borda oeste da Bacia do Parnaiba, permitiu redefinir o paleoambiente da parte superior da Formacao Pedra de Fogo, de idade permiana. Os depositos estudados constituem uma sucessao de aproximadamente 100 m de espessura, predominantemente siliciclastica, com carbonatos e evaporitos subordinados, onde foram definidas 21 facies sedimentares agrupadas em seis associacoes de facies (AF): AF1) Lacustre com rios efemeros; AF2) Lago influenciado por ondas de tempestade; AF3) Sabkha continental; AF4) Lago central; AF5) Dunas eolicas; e AF6) Lago/oasis com inundito. Estas associacoes indicam que durante o Permiano, um extenso sistema lacustre de clima arido, desenvolveu-se adjacente a campos de dunas eolicas e sabkha continental, com contribuicoes de rios efemeros. Incursoes fluviais nos lagos propiciavam a formacao de lobos de suspensao e fluxos em lencol (AF1). Planicies de sabkha (AF3) formaram-se nas porcoes marginais do lago que, eventualmente eram influenciados por ondas de tempestades (AF2), enquanto zonas centrais eram sitios de intensa deposicao pelitica (AF4). O baixo suprimento de areia eolica neste sistema propiciou a formacao de um campo de dunas restrito (AF5), com desenvolvimento de lagos de interdunas (oasis), onde proliferavam nucleos de samambaias gigantes, inundados esporadicamente por rios efemeros (AF6). Os dados faciologicos, corroborados pela paleogeografia da regiao durante o Permiano Superior, indicam que a sedimentacao da parte superior da Formacao Pedra de Fogo ocorreu sob condicoes climaticas quentes e aridas.

PALYNOLOGY OF THE MIDDLE MIOCENE–PLIOCENE NOVO REMANSO FORMATION, CENTRAL AMAZONIA, BRAZIL

Abstract. In order to reassess and amend previously published palynological data drawn from the Novo Remanso Formation, central Amazonia, we revisited the organic-rich samples from their work using systematic and quantitative biostratigraphic analyses, with possible implications in the biodiversity and paleoecological studies of Late Neogene deposits of Amazonia. In the study area, the Novo Remanso Formation is characterized by sandstones and mudstones deposited in a meandering river environment. The palynological assemblage comprises 46 morphotypes, including 21 species of pollen and 25 species of spores. Polypodiisporites usmensis, Retitrescolpites? irregularis and Mauritiidites franciscoi var. franciscoi, typical of lowland freshwater forests and shallow water lakes dominate the assemblage. Also, lower frequencies of Grimsdalea magnaclavata co-occur with Psilatricolporites crassoexinatus, Proteacidites triangulatus, Bombacacidites simpliciriloensis, Pteridaceoisporis gemmatus and Cingulatisporites laevigatus. Based on quantitative biostratigraphic techniques, the Novo Remanso Formation Is assigned a middle Miocene—Pliocene age In our study area. The presence of Elaterosporites klaszii (Albian-Cenomanian) In the Novo Remanso deposits strongly indicates Cretaceous rocks in the source-area, whereas absence of Andine palynomorphs may be indicative of a nearby source area for the deposits during the deposition of the Novo Remanso Formation.

Fossil Fungi from Miocene Sedimentary Rocks of the Central and Coastal Amazon Region, North Brazil

Abstract Samples from outcrops of the Miocene Solimões and Barreiras formations from the central and coastal Amazon regions of Brazil were analyzed palynologically. Assemblages of fossil fungi were identified, and are described herein, and their relevance to paleoenvironmental and paleoclimatic studies in tropical regions discussed. The fungal assemblage comprises four spore groups, 19 species belonging to 12 genera. Additionally, two new species are proposed. The samples from the Solimões Formation contain the following taxa: Mediaverrunites elsikii, Mediaverrunites mulleri, Monoporisporites sp., Fusiformisporites crabbii, and Multicellites cingulatus. The presence of these suggests river channel margins colonized by freshwater vegetation, where seasonal fluctuations of water table and rainfall produce wetter substrates. The samples from the Barreiras Formation showed higher species and generic diversity than those from the Solimões Formation with Hypoxylonites minutus, Hypoxylonsporites ater, Hypoxylonites sp., the new species Inapertisporites multiporus n. sp., Pluricellaesporites regularis, Lacrimasporonites levis, Monoporisporites annulatus, Spirotremesporites simplex, Dyadosporites novus, Dyadosporites sp., and Multicellaesporites attenuates. All of these correspond to parasitic fungi from a range of from tropical wetlands. Spegazzinites sp. and Dicellaesporites aculeolatus, good indicators of marine influence and mangrove presence, were also identified in the samples from the Barreiras Formation. Furthermore, the fungal spore taxa Inapertisporites multiporus, Mediaverrunites elsikii, Mediaverrunites mulleri, Pluricellaesporites regularis, and Spirotremesporites simplex serve as stratigraphic indicators when combined with miospore index taxa such as Crassoretitriletes vanraadshooveni, Grimsdalea magnaclavata and Fenestrites longispinosus indicating a Miocene age for these sediments in the Amazon region.

Reconstituição paleoambiental das formações Motuca e Sambaíba, Permo-Triássico da Bacia do Parnaíba no sudoeste do Estado do Maranhão, Brasil

O intervalo que compreende o final do Paleozoico e inicio do Mesozoico foi marcado por mudancas globais paleogeograficas e paleoclimaticas, em parte atribuidas a eventos catastroficos. A intensa continentalizacao do supercontinente Pangeia, com a implantacao de extensos desertos, sucedeu os ambientes costeiro-plataformais do inicio do Permiano. Os registros desses eventos no norte do Brasil sao encontrados nas bacias intracratonicas, particularmente na sucessao Permotriassica da Bacia do Parnaiba. A analise de facies e estratigrafica de afloramentos desta sucessao permitiu a individualizacao de 14 facies sedimentares agrupadas em 4 associacoes de facies (AF): AF1 e AF2, relacionadas aos depositos da Formacao Motuca, e AF3 e AF4, representativas da base da Formacao Sambaiba. A AF1 - Lacustre raso/Mudflat consiste em pelitos vermelhos laminados com lentes de gipsita, calcita e marga, alem de lobos de arenitos sigmoidais. A AF2 - Saline pan e constituida por corpos lenticulares de gipso laminado, gipso nodular e gipsarenito, sobrepostos por pelitos esverdeados com nodulos de dolomita e palygorskita. A AF3 - Lencol de areia e AF4 - Campo de dunas sao formadas, respectivamente, por arenitos de coloracao creme alaranjada com estratificacao plano-paralela e estratificacao cruzada de medio a grande porte. Destaca-se o registro de intervalos deformados lateralmente continuos por centenas de quilometros na zona de contato entre as formacoes Motuca e Sambaiba. Nestes, ocorrem pelitos com camadas contorcidas e brechadas (Formacao Motuca) e arenitos com falhas/microfalhas sinsedimentares, laminacao convoluta e diques de injecao preenchidos por argilitos (Formacao Sambaiba), interpretados como sismitos induzidos por terremotos de alta magnitude (>; 8 na escala Richter).

Neogene sharks and rays from the Brazilian ‘Blue Amazon’

The lower Miocene Pirabas Formation in the North of Brazil was deposited under influence of the proto-Amazon River and is characterized by large changes in the ecological niches from the early Miocene onwards. To evaluate these ecological changes, the elasmobranch fauna of the fully marine, carbonate-rich beds was investigated. A diverse fauna with 24 taxa of sharks and rays was identified with the dominant groups being carcharhiniforms and myliobatiforms. This faunal composition is similar to other early Miocene assemblages from the proto-Carribbean bioprovince. However, the Pirabas Formation has unique features compared to the other localities; being the only Neogene fossil fish assemblage described from the Atlantic coast of Tropical Americas. Phosphate oxygen isotope composition of elasmobranch teeth served as proxies for paleotemperatures and paleoecology. The data are compatible with a predominantly tropical marine setting with recognized inshore and offshore habitats with some probable depth preferences (e.g., Aetomylaeus groups). Paleohabitat of taxa particularly found in the Neogene of the Americas (†Carcharhinus ackermannii, †Aetomylaeus cubensis) are estimated to have been principally coastal and shallow waters. Larger variation among the few analyzed modern selachians reflects a larger range for the isotopic composition of recent seawater compared to the early Miocene. This probably links to an increased influence of the Amazon River in the coastal regions during the Holocene.

Multiple sulfur isotope evidence for massive oceanic sulfate depletion in the aftermath of Snowball Earth

The terminal Neoproterozoic Era (850–542 Ma) is characterized by the most pronounced positive sulfur isotope (34S/32S) excursions in Earths history, with strong variability and maximum values averaging δ34S∼+38‰. These excursions have been mostly interpreted in the framework of steady-state models, in which ocean sulfate concentrations do not fluctuate (that is, sulfate input equals sulfate output). Such models imply a large pyrite burial increase together with a dramatic fluctuation in the isotope composition of marine sulfate inputs, and/or a change in microbial sulfur metabolisms. Here, using multiple sulfur isotopes (33S/32S, 34S/32S and 36S/32S ratios) of carbonate-associated sulfate, we demonstrate that the steady-state assumption does not hold in the aftermath of the Marinoan Snowball Earth glaciation. The data attest instead to the most impressive event of oceanic sulfate drawdown in Earths history, driven by an increased pyrite burial, which may have contributed to the Neoproterozoic oxygenation of the oceans and atmosphere.

Depósitos flúvio-costeiros da Formação Raizama, Ediacarano-Cambriano da faixa Paraguai Norte, região de Nobres, Mato Grosso, Brasil

The Ediacaran-Cambrian Raizama Formation presents siliciclastic deposits exposed discontinuously along of the southern margin of the Amazon Craton and the Northern Paraguay Belt, Central-Western Brazil. These deposits are interpreted as progradational coastal succession conformably overling the carbonate platform succession of the Upper Araras Group. The facies and stratigraphic analysis of outcrop section were carried out in the Nobres region, State of Mato Grosso, allowed the individualization of seventeen facies, grouped into five facies associations (FA): FA1) lower shoreface, consisting of sandstone with parallel and wave-truncated lamination (microhummocky) parted by laminated mudstones, locally bioturbed by Skolithos; FA2) upper shoreface, composed by parallel and swaley cross bedded sandstone; FA3) subtidal, represented by sandstones with tangential and through cross stratifications drapped by siltstone/very fine sandstone laminae interpreted as channel and bar deposits; FA4) tidal flat is characterized by sandstones with tangential and sigmoidal cross bedding, even parallel stratification, low-angle cross bedding, mud cracks, siltstone/very fine sandstone rhythmites with flaser bedding, organized in shallowing-meter scale cycles; and FA5) distal braid plain consisting of sandstones with through cross-bedding and laterally discontinuous lags, parallel stratification and low-angle cross stratification partially reworked by wave. The sedimentation of the Raizama Formation suggests an increase in the siliciclastic supply linked to uplift regions of the Craton in the northwest of the studied area, succeeding the Araras carbonate platform deposits. Tubular trace fossils in the FA1 indicate, by the first time, the presence of burrowed organisms, what strongly points to an age near of the Ediacaran-Cambrian boundary.