Filamentous microfossils in the early proterozoic transvaal supergroup: their morphology, significance, and paleoenvironmental setting

摘要: Abstract Well preserved filamentous microfossils ( Siphonophycus transvaalensis n. sp.) are described here from the carbonate (Campbellrand Subgroup) to iron-formation (Kuruman Iron Formation) transition of Transvaal Supergroup, South Africa, estimated be 2.5-2.3 Ga years old. The occur in petrographic thin-sections a core sample carbonate-chert. They by permineralization both chert and sparry ferroan dolomite. Stratigraphically fossiliferous occurs as part an upward stromatolitic dolomite limestone sequence (Campbellrand) overlying iron-rich sediments Kuruman-Griquatown Formations. average δ 13 C value kerogen is about - 36.9%. filamentous, unbranched, tubular somewhat flattened, 15–25, μm diameter few many hundred microns length. exhibit coriaceous, finely granular external surface texture resulting presence adhering, randomly distributed, fine mineralic (carbonate) needles. In salient morphological characteristics they comparable tubular, originally polysaccharide, encompassing sheaths extant oscillatoriacean cyanobacteria. comparison with previously Precambrian microfossils, these fossil filaments unusual because their preservation (in addition chert), relatively large diameter, coating precipitated, needles; appear among oldest assured now known Proterozoic-age sediments. interwoven, occurring subparallel aggregates that form mat-like fabric; considered endogenetic situ benthic origin at proximal margin ‘deep shelf’ environment front (distal margin) Campbellrand platform. water depth for this environment, break slope between deep shelf euxinic basin, have been order 40–45 m. Paleomagnetic data support our interpretation micro-organisms inhabited warm marine probably low latitudes.