Shale-Facies Microfossils from the Proterozoic Bylot Supergroup, Baffin Island, Canada

Abstract

Organic-walled microfossils are reported from the Borden Rift Basin of northern Baffin Island and Bylot Island. The diverse assemblage, obtained by palynological acid maceration, comprises 39 taxa and occurs in fine-grained siliciclastic and carbonate units from all but the two lowermost formations of the Bylot Supergroup; their age is bracketed between 1,270 and 750 Ma. Of 307 samples analyzed from all parts of the basin, 133 yielded identifiable remains. The microbiota comprises the following taxa: Siphonophycus septatum, S. robustum, S. rugosum n. comb., S. kestron, S. capitaneum, Pellicularia tenera, Polythrichoides lineatus, Obruchevella valdaica, Karamia? sp., opaque filaments, Oscillatoriopsis spp., Palaeolyngbya sp., Arctacellularia tetragonala n. comb., A. ellipsoidea, Chlorogloeaopsis contexta n. comb., C. kanshiensis n. comb., Navifusa bacillaris n. comb., N. majensis, N. actinomorpha n. comb., Leiosphaeridia minutissima, L. tenuissima, L. crassa, L. jacutica, L. ternata, Lophosphaeridium granulatum, Valeria lophostriata, Pterospermopsimorpha insolita, Eomicrocystis elegans, E. malgica, Symplassosphaeridium spp., Synsphaeridium spp., Satka squamifera, Satka spp., Coneosphaera arctica n. sp., Coneosphaera sp., Spumosina rubiginosa, and Fabiformis baffinensis n. sp. The taxon Palaeocalothrix divaricatus, present in some macerates, is possibly a modern fungal contaminant. Abundance and taxonomic diversity varies considerably between formations and environments, with the Arctic Bay Formation exhibiting the greatest productivity and species diversity of the seven formations studied, and the transgressive muddy shelf deposits being the most productive of the 11 environments recognized. This microfossil assemblage of predominantly planktonic species has distinctive taxa in common with Middle to Late Riphean sequences in Siberia (Lakhanda and Miroedikha Groups, ca. 950 to 850 Ma), the lower part of the Thule Group (< 1,270 Ma) in northwest Greenland, the Fury and Hecla Group in western Baffin Island, and taxa reported from the upper part of the Bushimay Supergroup in Zaire. On the other hand, some elements in the Bylot Supergroup are more characteristic of Vendian beds on the Russian Platform, indicating longer stratigraphic ranges for such taxa than previously thought. The compositional similarity between the Borden Basin and Siberian sequences supports palinspastic reconstructions juxtaposing Siberia and Laurentia during the middle to late Proterozoic, and the opening of the Poseidon Ocean.

Microfossils from the Neoproterozoic Gangolihat Formation, Kumaun Lesser Himalaya: Their stratigraphic and evolutionary significance

“…7d, e). Similar forms are reported from the Infra Krol Formation and Bylot Supergroup (Tiwari and Pant, 2004;Hofmann and Jackson, 1994).…”

“…Diameter of the filament ranges from 3 to 8 lm and the maximum length of the filament is 290 lm. These forms are comparable with forms from the Baffin Island Canada and Wernecke Mountains (Hofmann and Jackson, 1994;Hofmann, 1984). Obruchevella parvissima is characterized by spirally coiled tubular filament with a coil diameter of 8-12 lm and filament diameter of 2.5-3.5 lm (Fig.…”

“…Septate filaments, characterized by Nostocomorpha with bead-like appearance, possessing a diameter of 3-8 lm, are present in large numbers mainly in the Utrora section. Comparable structures are reported from various Proterozoic and Cambrian localities (Hofmann, 1984;Hofmann and Jackson, 1994). Characteristic but rare specimens of non-septate filaments, Chlorogloeaopsis contexta are present only in the Jhiroli section.…”

Organic-walled microfossils from the Tonian Gouhou Formation, Huaibei region, North China Craton, and their biostratigraphic implications

“…8A-C), but the cells of Synsphaeridium are relatively larger (36-62 m in diameter), fewer per cluster (3-15), and more irregularly arranged (74-182 m in maximum cluster dimension; n = 7). Although Symplassosphaeridium and Synsphaeridium are morphotaxa with close morphological similarities and perhaps biological affinities, here we follow the practice of Jankauskas et al (1989) and Hofmann and Jackson (1994) to differentiate them on the basis of cell size and number. An elongate aggregate (261 m in length and 39 m in width) consisting of hundreds of tightly arranged spheroidal vesicles (each about 7 m in diameter; Fig.…”

“…Several Proterozoic forms, including Satka Jankauskas, 1979, Spumosina Naumova, 1968, and Culcitulisphaera Riedman and Porter, 2015 are superficially similar to Squamosphaera n. gen. Satka has a spheroidal or elongate vesicle consisting of regularly arranged polygonal plates (Hofmann and Jackson, 1994;Jankauskas et al, 1989;Javaux et al, 2004), which can appear similar to imbricate processes when viewed under transmitted light microscopy. Spumosina is a synaplomorph with a spherical aggregate of cells, which when compressed may have a spongy appearance and may appear similar to spherical processes (Hofmann and Jackson, 1994). Culcitulisphaera differs from Squamosphaera n. gen. in its blister-like outpocktes that are only 1.3-2.7 m in size (Riedman and Porter, 2015).…”