U-Pb zircon date from the Neoproterozoic Ghaub Formation, Namibia: Constraints on Marinoan glaciation

Hoffmann, Karl Heinz; Condon, Daniel J.; Bowring, Samuel A.; Crowley, James L.

doi:10.1130/g20519.1

Cited by 514 publications

(264 citation statements)

References 12 publications

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“…Both pre-Ediacaran-and DPM-type acanthomorphic acritarchs exhibit near-global but mutually exclusive distributions in shallow marine facies, separated by the 635-Ma (29,30) Marinoan glaciation. The oldest DPM-type acritarchs first appear in the lower Doushantuo Fm (55), in association with an ash bed recently dated at 635-627 Ma (30,56,57), and disappear from the record before 580 Ma (48).…”

Section: Discussionmentioning

confidence: 99%

Origin of the Eumetazoa: Testing ecological predictions of molecular clocks against the Proterozoic fossil record

Peterson

Butterfield

2005

Proc. Natl. Acad. Sci. U.S.A.

324

219

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Molecular clocks have the potential to shed light on the timing of early metazoan divergences, but differing algorithms and calibration points yield conspicuously discordant results. We argue here that competing molecular clock hypotheses should be testable in the fossil record, on the principle that fundamentally new grades of animal organization will have ecosystem-wide impacts. Using a set of seven nuclear-encoded protein sequences, we demonstrate the paraphyly of Porifera and calculate sponge͞eumetazoan and cnidarian͞bilaterian divergence times by using both distance [minimum evolution (ME)] and maximum likelihood (ML) molecular clocks; ME brackets the appearance of Eumetazoa between 634 and 604 Ma, whereas ML suggests it was between 867 and 748 Ma. Significantly, the ME, but not the ML, estimate is coincident with a major regime change in the Proterozoic acritarch record, including: (i) disappearance of low-diversity, evolutionarily static, pre-Ediacaran acanthomorphs; (ii) radiation of the high-diversity, short-lived Doushantuo-Pertatataka microbiota; and (iii) an orderof-magnitude increase in evolutionary turnover rate. We interpret this turnover as a consequence of the novel ecological challenges accompanying the evolution of the eumetazoan nervous system and gut. Thus, the more readily preserved microfossil record provides positive evidence for the absence of pre-Ediacaran eumetazoans and strongly supports the veracity, and therefore more general application, of the ME molecular clock.Porifera ͉ acritarchs ͉ Ediacaran ͉ coevolution T he sudden appearance of diverse metazoan fossils Ϸ530 million years ago (Ma) is the focus of ongoing and heated debate: Is this recording a true ''Cambrian explosion'' of early metazoan evolution or merely the onset of extensive burrowing and biomineralization (1)? Certainly the invisibility of microscopic, nonburrowing, and͞or nonbiomineralizing metazoans in the fossil record allows for the possibility of deep Proterozoic origins, so independent lines of evidence must be sought. Molecular clocks offer a potentially powerful approach for testing such evolutionary hypotheses (2), but recent analyses have yielded conspicuously discordant results. Pisani et al. (3), for example, estimate that the protostome-deuterostome ancestor evolved 900-1,100 Ma, whereas Douzery et al. (4) place this node at 642-761 Ma and Peterson et al. (5) at Ϸ570 Ma. With estimated divergence times differing by Ͼ500 million years (myr), there is clearly a need to assess both the methods used and predictions made by individual molecular-clocks analyses.Pisani et al. (3) have argued that their deep estimate for metazoan origins is robust because it agrees with a previous analysis calibrated by using different taxa, i.e., between chick and mouse (6) vs. centipedes and millipedes and spiders and horseshoe crabs (3). However, Peterson et al. (5) demonstrated that a significant rate reduction is associated with the vertebrate sequences, such that a vertebrate-calibrated clock produces a spurious 2-fold ove...

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Section: Discussionmentioning

confidence: 99%

Origin of the Eumetazoa: Testing ecological predictions of molecular clocks against the Proterozoic fossil record

Peterson

Butterfield

2005

Proc. Natl. Acad. Sci. U.S.A.

324

219

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“…The Whyalla Sandstone is thought to have been deposited during the Marinoan glaciation prior to 635 Ma; this date is constrained by radiometric ages associated with cap carbonates in Namibia and China (Bowring et al, 2007;Condon et al, 2005;Hoffmann et al, 2004). Recent detrital zircon (DZ) analysis by Rose et al (2013) demonstrates that the youngest DZ ages within the Elatina Formation approach 635 Ma, consistent with the Elatina Formation being a syn-Marinoan glacial deposit, whereas the youngest DZ ages from the Whyalla Sandstone cluster near 680 Ma.…”

Section: Age and Paleogeographymentioning

confidence: 99%

New constraints on equatorial temperatures during a Late Neoproterozoic snowball Earth glaciation

Ewing

Eisenman

Lamb

et al. 2014

Earth and Planetary Science Letters

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Intense glaciation during the end of Cryogenian time (∼635 million years ago) marks the coldest climate state in Earth history -a time when glacial deposits accumulated at low, tropical paleolatitudes. The leading idea to explain these deposits, the snowball Earth hypothesis, predicts globally frozen surface conditions and subfreezing temperatures, with global climate models placing surface temperatures in the tropics between −20 • C and −60 • C. However, precise paleosurface temperatures based upon geologic constraints have remained elusive and the global severity of the glaciation undetermined. Here we make new geologic observations of tropical periglacial, aeolian and fluvial sedimentary structures formed during the end-Cryogenian, Marinoan glaciation in South Australia; these observations allow us to constrain ancient surface temperatures. We find periglacial sand wedges and associated deformation suggest that ground temperatures were sufficiently warm to allow for ductile deformation of a sandy regolith. The wide range of deformation structures likely indicate the presence of a paleoactive layer that penetrated 2-4 m below the ground surface. These observations, paired with a model of ground temperature forced by solar insolation, constrain the local mean annual surface temperature to within a few degrees of freezing. This temperature constraint matches well with our observations of fluvial deposits, which require temperatures sufficiently warm for surface runoff. Although this estimate coincides with one of the coldest near sea-level tropical temperatures in Earth history, if these structures represent peak Marinaon glacial conditions, they do not support the persistent deep freeze of the snowball Earth hypothesis. Rather, surface temperatures near 0 • C allow for regions of seasonal surface melting, atmosphere-ocean coupling and possible tropical refugia for early metazoans. If instead these structures formed during glacial onset or deglaciation, then they have implications for the timescale and character for the transition into or out of a snowball state.

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“…Likewise, the basal, globally correlated cap carbonate to the Marinoan glaciation, which defines the Cryogenian-Ediacaran boundary, is well-constrained to ca. 635 Ma based on radiometric ages in China (Condon et al, 2005;Zhang et al, 2008), Namibia (Hoffmann et al, 2004), Tasmania (Calver et al, 2013) and NW Canada (Re-Os date; Rooney et al, 2015). Both early and late Cryogenian glaciations, referred to as the Sturtian and Marinoan (based on locations in South Australia), respectively, appear to be globally distributed (Li et al, 2013).…”

Section: Introductionmentioning

confidence: 99%

The Late Cryogenian Warm Interval, NE Svalbard: Chemostratigraphy and genesis

Fairchild

Bonnand²,

Davies

et al. 2016

Precambrian Research

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General rightsThis document is made available in accordance with publisher policies. Please cite only the published version using the reference above. Full terms of use are available: http://www.bristol.ac.uk/pure/about/ebr-terms At the base of E3, interstratification of cap carbonate with ice-rafted and redeposited glacial sediments occurs. Early diagenetic stabilization of carbonate mineralogy from a precursor, possibly ikaite, to calcite or dolomite is inferred. E3 is predominantly dolomitic silt-shale, with sub-millimetre lamination, lacking sand or current-related sedimentary structures. Thin fine laminae are partly pyritized and interpreted as microbial mats. Dolomite content is 25-50%, with δ 13 C values consistently around +4‰, a value attributed to buffering by dissolution of a precursor metastable carbonate phase. Local calcite cement associates with low δ 13 C values. The carbonates form silt-sized, chemically zoned rhombic crystals from an environment with dynamically changing Fe and Mn. Three-dimensional reconstructions of cm-scale disturbance structures indicate that they represent horizontally directed sock-like folds, developed by release of overpressure into thin surficial sediment overlying an early-cemented layer.A shoaling upwards unit near the top of E3 displays calcium sulphate pseudomorphs in dolomite in the north, but storm-dominated limestones in the south, both being overlain by peritidal oolitic dolomites, exposed under the succeeding Wilsonbreen glacial deposits. There is no Trezona δ 13 C anomaly, possibly implying top-truncation of the succession.Regular 0.5 m-scale sedimentary rhythms, reflecting subtle variations in sediment texture or composition occur throughout E3 and are interpreted as allocyclic. They are thought to be mainly primary in origin, locally modified slightly during early diagenetic cementation. Rhythms are proposed to represent ca. 18 kyr precession cycles, implying 6-8 Myr deposition between glaciations.

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U-Pb zircon date from the Neoproterozoic Ghaub Formation, Namibia: Constraints on Marinoan glaciation

Cited by 514 publications

References 12 publications

Origin of the Eumetazoa: Testing ecological predictions of molecular clocks against the Proterozoic fossil record

Origin of the Eumetazoa: Testing ecological predictions of molecular clocks against the Proterozoic fossil record

New constraints on equatorial temperatures during a Late Neoproterozoic snowball Earth glaciation

The Late Cryogenian Warm Interval, NE Svalbard: Chemostratigraphy and genesis

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