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

Ratification of the base of the ICS Geological Time Scale : the Global Standard Stratigraphic Age (GSSA) for the Hadean lower boundary

Peer reviewe

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