Benefits of bacterial biomineralization

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Bacterial biomineralization: where to from here?

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Depositional timing of Neoarchean turbidites of the Slave craton - recommended nomenclature and type localities

Two temporally distinct Neoarchean turbidite packages are known to occur in the Slave craton. The older is a greywacke-mudstone succession that includes the renowned Burwash Formation (ca. 2661 Ma). In this study, a previously undated tuff bed is demonstrated to have crystallized at ca. 2650.5 Âą 1.0 Ma refining the deposition age of these turbidites between ca. 2661 and 2650 Ma. The younger turbidites are locally distinctive as they contain interstratified banded iron formation (BIF). Previous work demonstrated that the younger turbidites were deposited between ca. 2640 to 2615 Ma, based entirely on maximum depositional ages from detrital zircons. A ~3-cm-thick felsic-to-intermediate tuff bed was discovered interbedded with these BIF-bearing turbidites. The tuff bed contains a single age population of zircon with a crystallization age of 2620 Âą 6 Ma defining the depositional timing of these BIF-bearing turbidites. New U-Pb detrital zircon dates from extensive turbidite sequences in the eastern and central part of the Slave craton are also presented. We use the new and previously published results to recommend nomenclature for these extensive sedimentary rocks in the Slave craton. The ca. 2661 to 2650 Ma turbidites remain part of the previously ascribed Duncan Lake Group. The younger ca. 2620 Ma turbidites are assigned to the new Slemon Group. Where robust age-data exist, we recommend formation names and include type localities for each.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Uranium in iron formations and the rise of atmospheric oxygen

International audienceThe concept of the Great Oxidation Event (GOE), during which atmospheric oxygen rose precipitously and perhaps to near-modern levels around 2.4-2.1 billion years ago (Ga), has become entrenched in our views on secular atmospheric evolution. Multiple proxies confirm a permanent shift towards more oxygenated conditions at some time near the Archean-Proterozoic boundary. However, it remains unclear precisely when this transition occurred, due in part to the likely temporal variability in those early levels and different sensitivities of the proxies utilized to track atmospheric oxygen partial pressures. Here, we provide a new look at the timing and magnitude of early atmospheric oxygenation through the record of uranium (U) concentrations in iron formations (IF). Just as IF are important archives of the redox state of seawater, concentrations of redox-sensitive U in IF are faithful proxies for oxidative continental weathering and associated delivery of dissolved U to seawater. Our dataset suggests that there was an increase in U redox cycling and transport at ca. 2.47 Ga, just before the permanent loss of mass-independent sedimentary sulfur isotope anomalies traditionally used to define the onset of the GOE. Further, there is significant temporal variability in the IF U record that we propose reflects dynamic Precambrian redox conditions. We provide additional support for earlier suggestions that the GOE was a protracted event marked by vacillating oxygen levels

Post-depositional REE mobility in a Paleoarchean banded iron formation revealed by La-Ce geochronology: A cautionary tale for signals of ancient oxygenation

Precambrian banded iron formations (BIF) are chemical sedimentary deposits whose trace element signatures have been widely used to interrogate the chemical composition and redox state of ancient seawater. Here we investigated trace element signatures in BIF of the 3.22 Ga Moodies Group, Barberton Greenstone Belt (South Africa), which are interbedded with near-shore siliciclastic sedimentary rocks and represent one of the oldest known shallow-water occurrences of BIF. Unusual rare earth element (REE) signatures, notably with pronounced negative Ce anomalies in shale-normalized spectra, have been previously reported for chemical sediments of the Moodies Group, which we confirm here through an expanded dataset for Moodies BIF spanning three different localities. We find negative Ce anomalies as low as 0.2 Ce/Ce⁎ that are associated with unusual enrichment of LREE relative to HREE in the sample set. While total REE abundances and certain REE features appear strongly related to the concentration of detrital indicators (e.g., Zr), and are likely primary, other features, notably LREE enrichment, cannot be explained as a primary feature of the sediment. This is better explained by later addition of REE from a LREE-enriched but Ce-depleted fluid that generated the significant negative Ce anomalies observed in surface samples of Moodies Group BIF. This REE addition event influenced both Sm-Nd and La-Ce isotope systematics, the latter yielding an isochron of 60 ± 32 Ma, thus constraining the timing of emplacement of the negative Ce anomalies to the past 100 Ma, possibly upon surface exposure of the Barberton Greenstone Belt to wetter conditions during the Cenozoic. Our findings constitute a cautionary tale in that even the most immobile elemental redox proxies may be more sensitive to post-depositional modification than previously thought, and demonstrate the clear advantage offered by paleoredox proxies coupled to radiometric geochronometers to enable the direct dating of ancient signals of Earth surface oxygenation

Cell surface reactivity of Synechococcus sp. PCC 7002: Implications for metal sorption from seawater

International audienc

A bacterial role in Paleoproterozoic clay formation

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