Microorganisms from the Gunflint Chert

Abstract

Although an element of skepticism has traditionally prevailed, on the part of both geologists and biologists, with regard to the existence and nature of Precambrian life, evidence is now rapidly accumulating which supports the view that widespread and abundant biological activity occurred as far back in the geologic record as half the presently accepted age of the earth. Geochemical evidence and evidence from the mineralogical and petrographic characteristics of Precambrian rocks is equivocal regarding the time of origin of life and the physical setting of biogenesis. However, structurally preserved fossils showing well-defined morphology are now known from sediments of an age approaching 2000 million years (1, 2). It is the purpose of this article to discuss the geologic occurrence of these oldest known Precambrian fossils, their morphology, and certain chemical analyses of the extractable organic residues. Detailed study of hundreds of thin sections has demonstrated a complex of biologically variable morphological entities. From the range of structures examined, eight distinct generic categories have been selected for detailed description.Dr. Barghoorn is professor of botany in the department of biology and curator of Paleobotanical Collections, the Botanical Museum, at Harvard University, Cambridge, Mass. The late Dr. Tyler was a professor in the department of geology at the University of Wisconsin, Madison. FEBRUARY 1965Twelve new species are these range from single-celle spheroidal bodies to fi branched and unbranchec Among these forms are rat plex, highly distinctive orga unusual morphology and phylogenetic affinity. With preserved units of the cher ganisms occur in profusion.No attempt is made here the voluminous literature on brian fossils. This has beer and excellently done by Gla and Rutten (4). General GeologyThe term algal cherts has applied to certain facies of flint iron formation of the Lake Superior region of Ca adjacent Minnesota. The Gu: formation is one of two S1 conformable units, of which shale is the overlying men gether the Gunflint and the 1 prise the recognizable Anim in the Thunder Bay District o The termn A nimikie rati Huronian is used here becal lack of direct stratigraphic ( with the classical tripartite sequence in the Lake Georgean Bay area to the absolute age of the Gunflint formation is approximately 2000 million (2.0 X 10?) years (5), and this age places the formation in the lower third of the Middle Precambrian.The Gunflint sediments extend eastward some 175 kilometers from the vicinity of Gunflint Lake, on the U.S.-Canada boundary, to Loon Lake, Ontario (Fig. 1). Isolated remnants of the formation occur on the mainland and upon islands in Lake Superior in the Rossport-Schreiber area some 98 kilometers east of Loon Lake. In the Gunflint sequence of Minnesota four major members may be distinguished: Lower Cherty, Lower Slaty, Upper Cherty, and Upper Slaty (6). In many exposures of the formation, however, described; one or more of the upper members has d isolated been removed by ...

Experimental diagenesis of organo-mineral structures formed by microaerophilic Fe(II)-oxidizing bacteria

“…Filaments or stalks coated with Fe oxyhydroxides have been reported in chert layers of the 1.89 Ga Gunflint IF 3,19,45 , in the 1.88 Ga Frere IF 46 , in the 1.88 Ga Sokoman IF 47 , in the 1.8 Ga Duck Creek IF 48,49 , and in the 1.7 Ga IF of the Jerome District, AZ 50 . The absence of twisted stalks in IF older than 1.89 Ga has been proposed as evidence that stalk-forming communities did not exist at that time 19,51 .…”

“…The preservation of microfossils appears best in cherts, for example, see ref. 3, consequently most microbial fossilization experiments performed so far have consisted in evaluating the preservation of microorganisms in silica solutions at ambient conditions for various periods of time, for example, see refs 4-7. Nonetheless, a few studies have revealed that the presence of Fe in solution improves the preservation of bacterial and archaeal cell walls in silica 8,9 . Also the formation of Fe minerals in the cell wall of the nitrate-dependent Fe(II)-oxidizing bacterium Acidovorax sp.…”

Soft‐Bodied Fossils Are Not Simply Rotten Carcasses – Toward a Holistic Understanding of Exceptional Fossil Preservation

“…The three-dimensional fossils of the Silurian Herefordshire Konservat-Lagerstaẗte, for example, preserve remarkable details in carbonate nodules within a volcanic ash (bentonite) which was deposited on the seafloor. [35] Silica precipitates as chert in other settings, providing a medium for preserving carbonaceous fossils: notable examples include early prokaryotes and eukaryotes of Precambrian age, [36] and one of the oldest terrestrial freshwater ecosystems associated with a hot siliceous spring in the Devonian Rhynie Chert of Scotland. [37] Flattening during and following burial is not equivalent to the squashing that characterizes road-kill, although fossils are often said to look like one.…”

Affinity, life cycle, and intracellular complexity of organic-walled microfossils from the Mesoproterozoic of Shanxi, China

“…Such structures were analyzed by FIB-SEM and FIB-TEM in cell walls of the spheroidal microfossil Huroniospora well preserved by permineralization from c. 1.9 Ga Gunflint chert (Wacey et al, 2012). The structures were recognized as the effects of taphonomy, inducing an artificial wall texture (Wacey et al, 2012), although it was originally identified as a species-diagnostic morphology (Barghoorn and Tyler, 1965;Hofmann, 1971;Schopf, 1992).…”