Stratigraphic and Ecologic Implications of Late Precambrian Microfossils from Utah

Abundant and well preserved microfossils have been discovered in black shales and siltstones of the glaciogenic upper Precambrian Mineral Fork Formation near Salt Lake City, Utah. The rocks are interpreted to have been deposited close to an ice margin in a shallow, restricted marine embayment during glacial retreat. Several distinct morphotypes are discernible, but following Moorman (1974), we interpret most of these as stages in the life cycle of a single planktonic, endosporulating alga, Bavlinella faveolata (Shepeleva) Vidal. The low taxonomic diversity of this assemblage, coupled with the large population size and almost complete dominance by Bavlinella, suggests an ecologically stressed environment. The source of this stress was probably the melting glacier. On the basis of stratigraphic position and lithological correlation with a radiometrically dated sequence in Washington, the Mineral Fork Formation has been considered to be about 800 m.y. old; however, most well dated occurrences of Bavlinella are in rocks of Vendian (650-570 m.y.) age. The presence of Bavlinella faveolata in Mineral Fork strata raises significant questions concerning both the stratigraphic range of this presumed Vendian index fossil and the timing of Late Precambrian glaciation in the North American Cordillera

Life on a Mesoarchean marine shelf – insights from the world’s oldest known granular iron formation

Abstract: The Nconga Formation of the Mesoarchean (~2.96–2.84 Ga) Mozaan Group of the Pongola Supergroup of southern Africa contains the world’s oldest known granular iron formation. Three dimensional reconstructions of the granules using micro-focus X-ray computed tomography reveal that these granules are microstromatolites coated by magnetite and calcite, and can therefore be classified as oncoids. The reconstructions also show damage to the granule coatings caused by sedimentary transport during formation of the granules and eventual deposition as density currents. The detailed, three dimensional morphology of the granules in conjunction with previously published geochemical and isotope data indicate a biogenic origin for iron precipitation around chert granules on the shallow shelf of one of the oldest supracratonic environments on Earth almost three billion years ago. It broadens our understanding of biologically-mediated iron precipitation during the Archean by illustrating that it took place on the shallow marine shelf coevally with deeper water, below-wave base iron precipitation in micritic iron formations

New Microorganisms from the Aphebian Gunflint Iron Formation, Ontario

Two new algal taxa are described from the approximately 2,000 m.y. old Gunflint Iron Formation, Ontario. Leptoteichos golubicii, n. gen. et sp., were relatively large (5-31 mu m) spherical plankters living in the water column above the central portions of the Gunflint basin. Post-mortem degradation processes have acted on this taxon to produce a "spot cell" organization similar to that exhibited by younger putatively eukaryotic cells; however, L. golubicii is here placed among the Algae incertae sedis and considered to be a probable cyanophyte. Megalytrum diacenum, n. gen. et sp., is the preserved sheath of a colonial chroococcalean blue-green alga. It constitutes an allochthonous element of the algal chert facies microbiota of the Gunflint Iron Formation.Earth and Planetary SciencesOrganismic and Evolutionary Biolog

Living Dendrolitic Microbial Mats in Hamelin Pool, Shark Bay, Western Australia

Hamelin Pool, Shark Bay, Western Australia, is home to the largest and most diverse assemblage of living marine stromatolites, with shapes and sizes comparable to ancient structures. A recent field-intensive program revealed seasonally ephemeral occurrences of modern dendrolitic microbial mats forming in intertidal, low energy settings. Dominated by filamentous cyanobacteria, dendrolitic microbial mats are formed when filaments provide a supporting framework as a result of gliding mobility, to build a shrubby morphology. Dendrolites, known throughout the rock record, refer to macroscopic microbialites with mesostuctures composed of unlaminated arborescent structures called shrubs. In these modern examples, thick filaments of Lyngbya aestuarii form the “trunk” of the bush, with finer filaments of Lyngbya fragilis, Phormidium sp. and Schizothrix sp. forming the “branches” These biologically-influenced dendrolitic structures provide insight into the complex interplay of microbial communities and the environment, broadening our understanding of shrub and dendrolite formation throughout the rock record

Evidence for benthic oxygen production in Neoarchean lacustrine stromatolites

The evolution of oxygenic photosynthesis fundamentally altered the global environment, but the history of this metabolism prior to the Great Oxidation Event (GOE) at ca. 2.4 Ga remains unclear. Increasing evidence suggests that non-marine microbial mats served as localized ¡°oxygen oases¡± for hundreds of millions of years before the GOE, though direct examination of redox proxies in Archean lacustrine microbial deposits remains relatively limited. We report spatially distinct patterns of positive and negative cerium (Ce) anomalies in lacustrine stromatolites from the 2.74 Ga Ventersdorp Supergroup (Hartbeesfontein Basin, South Africa), which indicate that dynamic redox conditions within ancient microbial communities were driven by oxygenic photosynthesis. Petrographic analyses and rare earth element signatures support a primary origin for Ce anomalies in stromatolite oxides. Oxides surrounding former bubbles entrained in mats (preserved as fenestrae) exhibit positive Ce anomalies, while oxides in stromatolite laminae typically contain strong negative Ce anomalies. The spatial patterns of Ce anomalies in Ventersdorp stromatolites are most parsimoniously explained by localized Ce oxidation and scavenging around oxygen bubbles produced by photosynthesis in microbial mats. Our new data from Ventersdorp stromatolites supports the presence of oxygenic photosynthesis ¡«300 m.y. before the GOE, and add to the growing evidence for early oxygen oases in Archean non-marine deposit

Impacto orcamentario da utilizacao do Metodo Canguru no cuidado neonatal

OBJETIVO Estimar o impacto orçamentário da utilização do Método Canguru na rede municipal de saúde. MÉTODOS Um modelo de decisão analítico foi desenvolvido para simular os custos do Método Canguru e Unidade Intermediária Neonatal no Rio de Janeiro, RJ, em 2011. A população de referência foi constituída pelos recém-nascidos estáveis clinicamente, que podem receber assistência nas duas modalidades de cuidado. O impacto orçamentário foi estimado para uma coorte hipotética de 1.000 recém-nascidos elegíveis em um ano. A proporção de recém-nascidos elegíveis que recebem assistência nas duas modalidades foi obtida por coleta de dados nas maternidades incluídas no estudo. As probabilidades dos eventos e o consumo de recursos de saúde, no período da assistência, foram incorporados ao modelo. Cenários foram desenvolvidos para refletir a adoção do método Canguru em maior ou menor escala. RESULTADOS A utilização do Método Canguru significou redução de gastos equivalente a 16% em um ano, se todos os recém-nascidos elegíveis fossem assistidos por esse método. CONCLUSÕES A opção Método Canguru é de menor custo comparado com a da Unidade Intermediária Neonatal. A análise de impacto orçamentário da utilização desse método no Sistema Único de Saúde indicou economia importante para o período de um ano