Nitrogen isotope compositions in sedimentary rocks (d15Nsed) are routinely used for reconstructing Cenozoic N-biogeochemical cycling and are also being increasingly applied to understanding the ...evolution of ancient environments. Here we review the existing knowledge and rationale behind the use of d15Nsed as a proxy for the Precambrian N-biogeochemical cycle with the aims of (i) identifying the major uncertainties that affect analyses and interpretation of nitrogen isotopes in ancient sedimentary rocks, (ii) developing a framework for interpreting the Precambrian d15Nsed record, (iii) testing this framework against a database of Precambrian d15Nsed values compiled from the literature, and (iv) identifying avenues of focused research that should increase confidence in interpreting Precambrian d15Nsed data. This review highlights the intrinsic complexity of the d15Nsed proxy and the significant effort that remains to realize its potential. Specifically, it is crucial to gain a better understanding of how and when diagenesis and metamorphism affect the d15N of bulk and kerogen-bound nitrogen. Ultimately, more data are required to apply statistics to interpreting d15Nsed variability within given geological time intervals. Finally, numerical modeling of the d15Nsed variability expected in different environments under varying redox scenarios is necessary to establish a predictive template for interpreting the ancient nitrogen isotope record. In spite of the challenges facing the application of this proxy to the Precambrian, the existing d15Nsed record shows several features possibly related to the stepwise oxygenation of the surface environment, underlining the potential for nitrogen isotopes to reveal clues about the evolution of early Earth.
After permanent atmospheric oxygenation, anomalous sulfur isotope compositions were lost from sedimentary rocks, demonstrating that atmospheric chemistry ceded its control of Earth's surficial sulfur ...cycle to weathering. However, mixed signals of anoxia and oxygenation in the sulfur isotope record between 2.5 to 2.3 billion years (Ga) ago require independent clarification, for example via oxygen isotopes in sulfate. Here we show <2.31 Ga sedimentary barium sulfates (barites) from the Turee Creek Basin, W. Australia with positive sulfur isotope anomalies of ∆
S up to + 1.55‰ and low δ
O down to -19.5‰. The unequivocal origin of this combination of signals is sulfide oxidation in meteoric water. Geochemical and sedimentary evidence suggests that these S-isotope anomalies were transferred from the paleo-continent under an oxygenated atmosphere. Our findings indicate that incipient oxidative continental weathering, ca. 2.8-2.5 Ga or earlier, may be diagnosed with such a combination of low δ
O and high ∆
S in sulfates.
Although nitrogen is a key element in organic molecules such as nucleic acids and proteins, the timing of the emergence of its modern biogeochemical cycle is poorly known. Recent studies on the ...antiquity of the nitrogen cycle and its interaction with free oxygen suggests the establishment of a complete aerobic N biogeochemical cycle with nitrification, denitrification, and nitrogen fixation at about 2.68 Gyr. Here, we report new bulk nitrogen isotope data for the 2.72 billion-year-old sedimentary succession of the Tumbiana Formation (Pilbara Craton, Western Australia). The nitrogen isotopic compositions vary widely from +8.6‰ up to +50.4‰ and are inversely correlated with the very low δ¹³C values of associated organic matter defining the Fortescue excursion (down to about −56‰). We propose that this ¹⁵N-enrichment records the onset of nitrification coupled to the continuous removal of its derivatives (nitrite and nitrate) by denitrification. This finding implies an increase in the availability of electron acceptors and probably oxygen in the Tumbiana depositional environment, 300 million years before the oxygenation of the Earth's atmosphere.
In the aftermath of the end‐Permian mass extinction, Early Triassic sediments record some of the largest Phanerozoic carbon isotopic excursions. Among them, a global Smithian‐negative carbonate ...carbon isotope excursion has been identified, followed by an abrupt increase across the Smithian–Spathian boundary (SSB; ~250.8 Myr ago). This chemostratigraphic evolution is associated with palaeontological evidence that indicate a major collapse of terrestrial and marine ecosystems during the Late Smithian. It is commonly assumed that Smithian and Spathian isotopic variations are intimately linked to major perturbations in the exogenic carbon reservoir. We present paired carbon isotopes measurements from the Thaynes Group (Utah, USA) to evaluate the extent to which the Early Triassic isotopic perturbations reflect changes in the exogenic carbon cycle. The δ13Ccarb variations obtained here reproduce the known Smithian δ13Ccarb‐negative excursion. However, the δ13C signal of the bulk organic matter is invariant across the SSB and variations in the δ34S signal of sedimentary sulphides are interpreted here to reflect the intensity of sediment remobilization. We argue that Middle to Late Smithian δ13Ccarb signal in the shallow marine environments of the Thaynes Group does not reflect secular evolution of the exogenic carbon cycle but rather physicochemical conditions at the sediment–water interface leading to authigenic carbonate formation during early diagenetic processes.
Microbial sulfate reduction (MSR) is thought to have operated very early on Earth and is often invoked to explain the occurrence of sedimentary sulfides in the rock record. Sedimentary sulfides can ...also form from sulfides produced abiotically during late diagenesis or metamorphism. As both biotic and abiotic processes contribute to the bulk of sedimentary sulfides, tracing back the original microbial signature from the earliest Earth record is challenging. We present in situ sulfur isotope data from nanopyrites occurring in carbonaceous remains lining the domical shape of stromatolite knobs of the 2.7‐Gyr‐old Tumbiana Formation (Western Australia). The analyzed nanopyrites show a large range of δ34S values of about 84‰ (from −33.7‰ to +50.4‰). The recognition that a large δ34S range of 80‰ is found in individual carbonaceous‐rich layers support the interpretation that the nanopyrites were formed in microbial mats through MSR by a Rayleigh distillation process during early diagenesis. An active microbial cycling of sulfur during formation of the stromatolite may have facilitated the mixing of different sulfur pools (atmospheric and hydrothermal) and explain the weak mass independent signature (MIF‐S) recorded in the Tumbiana Formation. These results confirm that MSR participated actively to the biogeochemical cycling of sulfur during the Neoarchean and support previous models suggesting anaerobic oxidation of methane using sulfate in the Tumbiana environment.
Cet article propose une revue de littérature sur les groupes de parole à l’attention des frères et sœurs d’enfants porteurs de handicap et/ou maladie. Il s’inscrit dans la continuité des travaux de ...Dayan, Picon, Scelles et Bouteyre (2006), avec un état des lieux des publications en langue anglophone et francophone parues entre 2006 et 2020. Compte tenu de l’accroissement des études visant les troubles du spectre de l’autisme (TSA), un focus est proposé sur les groupes menés dans ce contexte spécifique. Après avoir décrit la diversité des cadres et approches méthodologiques/théoriques des groupes fratries, leur mode de fonctionnement et objectifs, une analyse comparative des bénéfices qu’ils apportent est réalisée selon qu’ils concernent tout type de handicap/maladie ou se centrent sur les TSA. Les limites de ces études sont analysées et des perspectives pour des travaux futurs sont énoncées.
This paper is aiming to a literature review on support groups for siblings of children with disability or illness. It is in line with the work of Dayan, Picon, Scelles and Bouteyre (2006), with an inventory of publications in English and French published between 2006 and 2020. Given the increase in studies targeting autism spectrum disorders (ASD), a focus is proposed on groups conducted in this specific context. After describing the diversity of the sibling groups’ methodological/theoretical frameworks and approaches, their functioning and objectives, a comparative analysis of the benefits they provide is carried out according to whether they concern any type of disability/disease or focus on ASDs. The limitations of these studies are analyzed and perspectives for future work are outlined.
This study evaluates the potentialities of a lab-made pLIBS (portable Laser-Induced Breakdown Spectroscopy) to sort volcanic rocks belonging to various magmatic series. An in-situ chemical analysis ...of 19 atomic lines, including Al, Ba, Ca, Cr, Cu, Fe, Mg, Mn, Na, Si, Sr and Ti, from 21 sampled rocks was performed during a field exploration in Iceland. Iceland was chosen both for the various typologies of volcanic rocks and the rugged conditions in the field in order to test the sturdiness of the pLIPS. Elemental compositions were also measured using laboratory ICP-AES measurements on the same samples. Based on these latter results, which can be used to identify three different groups of volcanic rocks, a classification model was built in order to sort pLIBS data and to categorize unknown samples. Using a reliable statistical scheme applied to LIBS compositional data, the classification capability of the pLIBS system is clearly demonstrated (90–100% success rate). Although this prototype does not provide quantitative measurements, its use should be of particular interest for future geological field investigations.
•Portable LIBS applied to field geology•Fast semi-quantitative geochemical analysis of volcanic rocks and magmatic series•Discriminant analysis and statistical treatments for LIBS compositional data
Evidence of several major unconformities in the Lower Palaeozoic succession in Iran lead to question the role of tectonic/eustatism/climate in terms of their formation. The studied Palaeozoic ...succession in the Kuh-e Surmeh Anticline is characterized by the preservation of two thin Ordovician and Lower Permian Formations separated by a large hiatus encompassing the Upper Ordovician up to the lowermost Permian. The Ordovician sequences were deposited in shallow shoreface to lower offshore environments and the Lower Permian corresponds to a wave-dominated estuarine system evolving to a delta system. These mainly clastic successions represent good reservoirs in the regional Palaeozoic petroleum system of the Iranian plate separated by a major unconformity. The local erosion of the Zakeen Fm., observed in the neighbouring areas close to the Kuh-e Surmeh anticline, can be used to specify the role of the different controlling factors. We show that the influence of regional tectonics (Hercynian Orogeny/extensional deformation) and climate (Hirnantian and Carboniferous glaciations) related to the late Ordovician and Late Carboniferous/Early Permian succession cannot be ruled out from the possible candidates participating in erosion, but local diapir doming seems to better explain part of this local intense erosion.
Triple oxygen isotope (∆17O with δ18O) signals of H2O and O2 found in sulfate of oxidative weathering origin offer promising constraints on modern and ancient weathering, hydrology, atmospheric gas ...concentrations, and bioproductivity. However, interpretations of the sulfate-water-O2 system rely on assuming fixed oxygen-isotope fractionations between sulfate and water, which, contrastingly, are shown to vary widely in sign and amplitude. Instead, here we anchor sulfate-water-O2 triple oxygen isotope systematics on the homogeneous composition of atmospheric O2 with empirical constraints and modeling. Our resulting framework does not require a priori assumptions of the O2- versus H2O‑oxygen ratio in sulfate and accounts for the signals of mass-dependent and mass-independent fractionation in the ∆17O and δ18O of sulfate's O2‑oxygen source. Within this framework, new ∆17O measurements of sulfate constrain ~2.3 Ga Paleoproterozoic gross primary productivity to between 6 and 160 times present-day levels, with important implications for the biological carbon cycle response to high CO2 concentrations prevalent on the early Earth.
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