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Jaffey, A.H.; Flynn, Kian; Glendenin, L.E.; Bentley, W. C.; Essling, A.M.

doi:10.1103/physrevc.4.1889

Cited by 2,214 publications

(993 citation statements)

References 11 publications

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“…Pb mass fractionation was externally corrected using a mass bias factor of 0.14 ± 0.03% per mass unit determined via measurements of 202 We used the ET535 tracer solution 54,55 and U decay constants recommended in ref. 56 . A value of 137.818 ± 0.045 was used for the 238 U/ 235 U zircon based on the work of ref.…”

Section: Nature Ecology and Evolutionmentioning

confidence: 99%

Ichnological evidence for meiofaunal bilaterians from the terminal Ediacaran and earliest Cambrian of Brazil

et al. 2017

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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 ...

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Section: Nature Ecology and Evolutionmentioning

confidence: 99%

Ichnological evidence for meiofaunal bilaterians from the terminal Ediacaran and earliest Cambrian of Brazil

et al. 2017

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“…Details are described in Corfu (2004). The data are calculated with the decay constants of Jaffey et al (1971) and plot with the program of Ludwig (2009). Initial common Pb has been corrected with compositions estimated with the model of Stacey & Kramers (1975).…”

Section: Analytical Proceduresmentioning

confidence: 99%

The U–Pb age of the Finse batholith, a composite bimodal Sveconorwegian intrusion

Jensen¹,

Corfú²

2016

NJG

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The Sveconorwegian autochthonous basement in the Finse area, South Norway, comprises a c. 900 km 2 bimodal batholith, dominated by K-feldspar megacrystic granite. The granite is locally intermingling with gabbroic rocks, and cut by different generations of pegmatite and aplite dykes. Zircon U-Pb geochronological data obtained by ID-TIMS demonstrate that granite, granodiorite and gabbro are coeval, as they define a common upper intercept age of 985.6 ± 1.6 Ma, dating emplacement of the batholith. Titanite is variously disturbed by later Sveconorwegian events. Pegmatites cross-cutting all structures yield zircon and titanite ages of 976 ± 8 Ma, 939 ± 2, and possibly 958 ± 2 Ma, reflecting the latest stages of the evolution of the batholith. The Finse batholith is one of the earliest members of the widespread ferroan hornblende-biotite-granitoid (HBG) suite, in the western part of the Sveconorwegian orogen.

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“…1 V), no tailing corrections on 230 Th were necessary. All ages were calculated with Isoplot v. 3.75 (Ludwig, 2012) using half-lives for 238 U from Jaffey et al (1971) and for 234 U and 230 Th from Cheng et al (2013).…”

Section: Geochronologymentioning

confidence: 99%

Retrograde Accretion of a Caribbean Fringing Reef Controlled by Hurricanes and Sea-level Rise

Blanchon

Richards²,

Bernal

et al. 2017

Front. Earth Sci.

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Predicting the impact of sea-level (SL) rise on coral reefs requires reliable models of reef accretion. Most assume that accretion results from vertical growth of coralgal framework, but recent studies show that reefs exposed to hurricanes consist of layers of coral gravel rather than in-place corals. New models are therefore needed to account for hurricane impact on reef accretion over geological timescales. To investigate this geological impact, we report the configuration and development of a 4-km-long fringing reef at Punta Maroma along the northeast Yucatan Peninsula. Satellite-derived bathymetry (SDB) shows the crest is set-back a uniform distance of 315 ±15 m from a mid-shelf slope break, and the reef-front decreases 50% in width and depth along its length. A 12-core drill transect constrained by multiple 230 Th ages shows the reef is composed of an ∼2-m thick layer of coral clasts that has retrograded 100 m over its back-reef during the last 5.5 ka. These findings are consistent with a hurricane-control model of reef development where large waves trip and break over the mid-shelf slope break, triggering rapid energy dissipation and thus limiting how far upslope individual waves can fragment corals and transport clasts. As SL rises and water depth increases, energy dissipation during wave-breaking is reduced, extending the clast-transport limit, thus leading to reef retrogradation. This hurricane model may be applicable to a large sub-set of fringing reefs in the tropical Western-Atlantic necessitating a reappraisal of their accretion rates and response to future SL rise.

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Precision Measurement of Half-Lives and Specific Activities ofU235andU

Cited by 2,214 publications

References 11 publications

Ichnological evidence for meiofaunal bilaterians from the terminal Ediacaran and earliest Cambrian of Brazil

Ichnological evidence for meiofaunal bilaterians from the terminal Ediacaran and earliest Cambrian of Brazil

The U–Pb age of the Finse batholith, a composite bimodal Sveconorwegian intrusion

Retrograde Accretion of a Caribbean Fringing Reef Controlled by Hurricanes and Sea-level Rise

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