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The end of the Neoproterozoic is punctuated by glacial deposition, but the chronology of these deposits is hindered presently by the paucity of geochronological data. Here, we present new radiometric dating for the basal Sete Lagoas cap carbonate deposits that overlie glacial units in the São Francisco craton. Six samples from aragonite‐pseudomorph crystal‐rich facies, showing pristine textures and constant 87Sr/86Sr ratios around 0.7075, yielded a Pb–Pb isochron age of 740 ± 22 Ma, which is interpreted as the depositional age for these remarkably preserved rocks. This age can be used to infer a low‐to‐moderate palaeolatitude of 20–30° for carbonate (and glacial) deposition. In addition, as it overlaps the ages obtained for the oldest Neoproterozoic glacial successions, our result reinforces the idea of a long‐standing ‘Sturtian’ interval, suggesting that this event represents either different discrete glaciations or a protracted event encompassing almost 80 Ma.

The South American Monsoon System (SAMS) is generally considered to be highly sensitive to Northern Hemisphere (NH) temperature variations on multi-centennial timescales. The direct influence of solar forcing on moisture convergence in global monsoon systems on the other hand, while well explored in modeling studies, has hitherto not been documented in proxy data from the SAMS region. Hence little is known about the sensitivity of the SAMS to solar forcing over the past millennium and how it might compete or constructively interfere with NH temperature variations that occurred primarily in response to volcanic forcing. Here we present a new annually-resolved oxygen isotope record from a 1500-year long stalagmite recording past changes in precipitation in the hitherto unsampled core region of the SAMS. This record details how solar variability consistently modulated the strength of the SAMS on centennial time scales during the past 1500 years. Solar forcing, besides the previously recognized influence from NH temperature changes and associated Intertropical Convergence Zone (ITCZ) shifts, appears as a major driver affecting SAMS intensity at centennial time scales.

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International audienceThe end of the Neoproterozoic Era (1000 to 541 Ma) is widely believed to have seen the transition from a dominantly anoxic to an oxygenated deep ocean. This purported redox transition appears to be closely linked temporally with metazoan radiation and extraordinary perturbations to the global carbon cycle. However, the geochemical record of this transition is not straightforward, and individual data sets have been variably interpreted to indicate full oxygenation by the early Ediacaran Period (635 to 541 Ma) and deep ocean anoxia persevering as late as the early Cambrian. Because any change in marine redox structure would have profoundly impacted nitrogen nutrient cycling in the global ocean, the N isotope signature of sedimentary rocks (δ15Nsed) should reflect the Neoproterozoic deep-ocean redox transition. We present new N isotope data from Amazonia, northwest Canada, northeast Svalbard, and South China that span the Cryogenian glaciations (∼750 to 580 Ma). These and previously published data reveal a Nisotope distribution that closely resembles modern marine sediments, with a mode in δ15N close to +4 and range from −4 to +11. No apparent change is seen between the Cryogenian and Ediacarian. Data from earlier Proterozoic samples show a similar distribution, but shifted slightly towards more negative δ15N values and with a wider range. The most parsimonious explanation for the similarity of these Nisotopedistribution is that as in the modern ocean, nitrate (and hence O2) was stable in most of the middle–late Neoproterozoic ocean, and possibly much of Proterozoic Eon. However, nitrate would likely have been depleted in partially restricted basins and oxygen minimum zones (OMZs), which may have been more widespread than in the modern ocean

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The evolutionary events during the Ediacaran-Cambrian transition (~541 Myr ago) are unparalleled in Earth history. The fossil record suggests that most extant animal phyla appeared in a geologically brief interval, with the oldest unequivocal bilaterian body fossils found in the Early Cambrian. Molecular clocks and biomarkers provide independent estimates for the timing of animal origins, and both suggest a cryptic Neoproterozoic history for Metazoa that extends considerably beyond the Cambrian fossil record. We report an assemblage of ichnofossils from Ediacaran-Cambrian siltstones in Brazil, alongside U-Pb radioisotopic dates that constrain the age of the oldest specimens to 555-542 Myr. X-ray microtomography reveals three-dimensionally preserved traces ranging from 50 to 600 μ m in diameter, indicative of small-bodied, meiofaunal tracemakers. Burrow morphologies suggest they were created by a nematoid-like organism that used undulating locomotion to move through the sediment. This assemblage demonstrates animal-sediment interactions in the latest Ediacaran period, and provides the oldest known fossil evidence for meiofaunal bilaterians. Our discovery highlights meiofaunal ichnofossils as a hitherto unexplored window for tracking animal evolution in deep time, and reveals that both meiofaunal and macrofaunal bilaterians began to explore infaunal niches during the late Ediacaran. NATuRE ECoLoGy & EvoLuTIoN Articles Nature ecology & evolutioNsupport for these suggestions is limited to purported body fossils of sponges 19 and demosponge biomarkers 20 . A considerable gap therefore remains between the fossil record of the late Ediacaran and molecular clock estimates for deep splits in the animal tree, for example the origin of Metazoa and Eumetazoa 3 . Assuming that contemporary molecular clock analyses yield accurate, if imprecise 18 , node ages for animal divergences, a small body size and concomitant limited fossilization potential 21 could reconcile these discordant records of animal evolution (but see ref. 22 ).The small body size of the ancestral bilaterian is supported by recent phylogenomic analyses of deep animal relationships, with acoel flatworms and xenoturbellids (Xenacoelomorpha) being a sister group to all remaining bilaterians (Nephrozoa) 23 , and smallbodied spiralian taxa (the 'Platyzoa') recognized as a paraphyletic grade with respect to macroscopic trochozoans 24 . This suggests that early bilaterians and spiralians were small bodied, possibly meiofaunal, and moved using ciliary gliding.Meiofauna comprises all organisms between 32 and 1,000 μ m in size that inhabit pore-water-rich sediments in freshwater to deepmarine environments 25 . Modern meiofaunal communities include animals, foraminifera and some ciliates, and contribute significantly to sediment bioturbation and bioirrigation 26,27 . The meiofauna can be divided into permanent members (that is, animals with organisms of a small size adapted and restricted to the meiofaunal, interstitial realm) and temporary meiofauna (for example, the ...