The evidence for macroscopic life during the Palaeoproterozoic era (2.5-1.6 Gyr ago) is controversial. Except for the nearly 2-Gyr-old coil-shaped fossil Grypania spiralis, which may have been eukaryotic, evidence for morphological and taxonomic biodiversification of macroorganisms only occurs towards the beginning of the Mesoproterozoic era (1.6-1.0 Gyr). Here we report the discovery of centimetre-sized structures from the 2.1-Gyr-old black shales of the Palaeoproterozoic Francevillian B Formation in Gabon, which we interpret as highly organized and spatially discrete populations of colonial organisms. The structures are up to 12 cm in size and have characteristic shapes, with a simple but distinct ground pattern of flexible sheets and, usually, a permeating radial fabric. Geochemical analyses suggest that the sediments were deposited under an oxygenated water column. Carbon and sulphur isotopic data indicate that the structures were distinct biogenic objects, fossilized by pyritization early in the formation of the rock. The growth patterns deduced from the fossil morphologies suggest that the organisms showed cell-to-cell signalling and coordinated responses, as is commonly associated with multicellular organization. The Gabon fossils, occurring after the 2.45-2.32-Gyr increase in atmospheric oxygen concentration, may be seen as ancient representatives of multicellular life, which expanded so rapidly 1.5 Gyr later, in the Cambrian explosion.
The Carboniferous succession in Adarouch (Central Morocco, north of the Atlas Transform Fault) contains thick carbonate beds including upper Visean, Serpukhovian and basal Bashkirian rocks. Foraminifers enable precise recognition of the Visean/Serpukhovian (V/S), early/late Serpukhovian (eS/lS) and Serpukhovian/Bashkirian (S/B) boundaries.Insolentitheca horrida, Loeblichia ukrainica, “Millerella”spp. andEndostaffella? sp. 2 are regarded as regionally useful indices to the V/S boundary, whereasEostaffellinaspp.,Eostaffella pseudostruveiand some evolved species ofArchaediscusexhibit greater reliability for worldwide correlation of this level. Similarly, the eS/lS boundary is marked locally byBrenckleina rugosa, Eosigmoilinasp., andMonotaxinoidesspp. and globally byLoeblichia minima, Bradyina cribrostomata, Plectostaffellaspp.,Eostaffellina “protvae”and“Turrispiroides”, and the S/B boundary is marked locally byGlobivalulina bulloidesand globally bySeminovella elegantula, andNovella?. Occurrences of these taxa in Morocco allow correlations with the Moscow Basin, the Urals, the Donetz Basin and North America. The Moroccan assemblages share few taxa in common with Saharan basins south of the Atlas Transform Fault. Correlations with western European basins are difficult because of the paucity in the latter of foraminiferal-bearing carbonate strata.
The focus of this paper is to re-evaluate the age and the paleogeographical significance of the Heraultia Limestone in the light of recent advances in SSF systematic and biostratigraphy. Reassessed assemblage is dominated by molluscs (helcionellids, ?polyplacophors and other problematic taxa), and abundant orthothecid hyoliths, problematic tubes; few problematica are also present. Twenty-eight species and three morphotypes are described. Two species and one genus are new (Obscurania tormoi Devaere, sp. nov.; Alaconcha Devaere, gen. nov. and Alaconcha rugosa Devaere, sp. nov.), seven are reported for the first time. Among previously mentionned species, 13 are reassigned, 7 confirmed, and 9 unrecovered from the studied sampled. The global stratigraphic range of each species is established based on updated inventory of known occurrences. It argues for a Terreneuvian (Nemakit-Daldynian/Tommotian according to the Siberian stratigraphic chart) age of the microfossil assemblage. The Watsonella crosbyi-Oelandiella korobkovi Interval Zone is defined and is correlated with base of Cambrian Stage 2 (Tommotian) of Siberia, China, Mongolia, and Avalonia. The Northern Montagne Noire would accordingly witness for one of the earliest, isolated but consequent Tommotian carbonate-platform on the Western Gondwana margin. As a result, present tectonic and palaeogeographic models have to be emended, and factors that favored such isolated platforms should be further investigated.
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