scholarly journals The kaolinite shuttle links the Great Oxidation and Lomagundi events

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Weiduo Hao ◽  
Kaarel Mänd ◽  
Yuhao Li ◽  
Daniel S. Alessi ◽  
Peeter Somelar ◽  
...  
Keyword(s):  
Carbon Isotope ◽  
Chemical Weathering ◽  
Experimental Results ◽  
Marine Environments ◽  
Great Oxidation Event ◽  
Carbon Isotope Excursion ◽  
Weathering Intensity ◽  
Continental Weathering

AbstractThe ~2.22–2.06 Ga Lomagundi Event was the longest positive carbon isotope excursion in Earth’s history and is commonly interpreted to reflect perturbations in continental weathering and the phosphorous cycle. Previous models have focused on mechanisms of increasing phosphorous solubilization during weathering without focusing on transport to the oceans and its dispersion in seawater. Building from new experimental results, here we report kaolinite readily absorbs phosphorous under acidic freshwater conditions, but quantitatively releases phosphorous under seawater conditions where it becomes bioavailable to phytoplankton. The strong likelihood of high weathering intensities and associated high kaolinite content in post-Great-Oxidation-Event paleosols suggests there would have been enhanced phosphorus shuttling from the continents into marine environments. A kaolinite phosphorous shuttle introduces the potential for nonlinearity in the fluxes of phosphorous to the oceans with increases in chemical weathering intensity.

Climate control of silicate weathering intensity through the Smithian/Spathian boundary in the western USA basin

2020 ◽  
Author(s):  
Nicolas Freslon ◽  
Emmanuelle Pucéat ◽  
Arnaud Brayard ◽  
Germain Bayon
Keyword(s):  
Organic Matter ◽  
Chemical Weathering ◽  
Local Scale ◽  
Early Triassic ◽  
Data Set ◽  
Triassic Boundary ◽  
Anoxic Conditions ◽  
Western Usa ◽  
Weathering Intensity ◽  
Continental Weathering

<p>The aftermath of the end-Permian mass extinction is marked by large and recurrent perturbations of the environment and of the biosphere, which are thought to have delayed the recovery of marine ecosystems. A potential widespread loss of vegetation cover linked to destabilization of terrestrial ecosystems along with the climate warming that persisted for several million years after the Permian-Triassic boundary likely contributed to the markedly enhanced soil erosion and intensified continental chemical weathering recorded in the Early Triassic (Algeo and Twitchett, 2010). As continental weathering delivers nutrients to the oceans, this process could have played a major role in the repeated development of anoxic conditions by sustaining primary productivity and export of organic matter to the seafloor (Algeo and Twitchett, 2010; Sun et al., 2018). Yet our knowledge of the importance of this process in triggering anoxic conditions is currently hampered by the lack of proxies providing chemical weathering records at a local scale. In this study, we tested a novel proxy of chemical weathering intensity at the local scale, based on the coupled isotopic composition of hafnium and neodymium in clay minerals, to explore the links between chemical weathering, climate fluctuations, and anoxia in the western USA basin during the Early Triassic. This proxy has been recently calibrated in modern environments (Bayon et al., 2016) but has only been scarcely applied to deep-time environments.</p><p>We analyzed clay sediments for their Hf and Nd isotope composition from 5 sections within the western USA basin (that encompasses the Smithian-Spathian boundary (SSB). The well -stablished bio-chemo-stratigraphical frame of this basin allows the exploration of the respective timing of anoxia establishment and variations in chemical weathering of the continental masses adjacent to the basin at a high temporal resolution. Our new dataset highlights the existence of a decrease in chemical weathering of the continents surrounding the Basin at the Smithian-Spathian boundary, during the development of anoxic conditions marked by enhanced organic matter burial in the sediments. Our new data therefore bring new light on the links between nutrient inputs linked to modifications in continental weathering and the establishment of anoxic conditions in the western USA basin. The decrease in continental chemical weathering depicted in our data set occurs during the global cooling event identified by conodont  d<sup>18</sup>O records in other regions of the word (Goudemand et al., 2019). This cooling may have promoted a decrease in the intensity of the hydrological cycle and the establishment of more arid conditions in the western USA basin, impeding chemical weathering in the studied area.  </p><p>Algeo, T. J. & Twitchett, R. J. (2010). Geology, 38(11), 1023-1026.</p><p>Bayon, G. et al. (2016). Earth and Planetary Science Letters, 438, 25-36.</p><p>Goudemand, N. et al. (2019). Earth-Science Reviews.</p><p>Sun, H. et al. (2018). Proceedings Nation. Academy of Sciences, 115(15), 3782-3787.</p>

scholarly journals K isotopes as a tracer for continental weathering and geological K cycling

2019 ◽  
Vol 116 (18) ◽  
pp. 8740-8745 ◽  
Author(s):  
Shilei Li ◽  
Weiqiang Li ◽  
Brian L. Beard ◽  
Maureen E. Raymo ◽  
Xiaomin Wang ◽  
...  
Keyword(s):  
Mass Balance ◽  
Chemical Weathering ◽  
Drainage Basin ◽  
Isotope Composition ◽  
Systematic Investigation ◽  
K Value ◽  
Weathering Intensity ◽  
Intensity Changes ◽  
Continental Weathering ◽  
Dissolved Load

The causal effects among uplift, climate, and continental weathering cannot be fully addressed using presently available geochemical proxies. However, stable potassium (K) isotopes can potentially overcome the limitations of existing isotopic proxies. Here we report on a systematic investigation of K isotopes in dissolved load and sediments from major rivers and their tributaries in China, which have drainage basins with varied climate, lithology, and topography. Our results show that during silicate weathering, heavy K isotopes are preferentially partitioned into aqueous solutions. Moreover, δ41K values of riverine dissolved load vary remarkably and correlate negatively with the chemical weathering intensity of the drainage basin. This correlation allows an estimate of the average K isotope composition of global riverine runoff (δ41K = −0.22‰), as well as modeling of the global K cycle based on mass balance calculations. Modeling incorporating K isotope mass balance better constrains estimated K fluxes for modern global K cycling, and the results show that the δ41K value of seawater is sensitive to continental weathering intensity changes. Thus, it is possible to use the δ41K record of paleo-seawater to infer continental weathering intensity through Earth’s history.

Increase in ecosystem complexity aided organic carbon sequestration during the c. 2.22-2.06 Ga Lomagundi carbon isotope excursion

2021 ◽  
Author(s):  
Frantz Ossa Ossa ◽  
Stephan König ◽  
Axel Hofmann ◽  
Andrey Bekker ◽  
Jorge E. Spangenberg ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Sulfate Reduction ◽  
Water Column ◽  
Carbon Isotope ◽  
Chemical Weathering ◽  
Atmospheric Oxygen ◽  
Black Shales ◽  
Electron Acceptors ◽  
Microbial Sulfate Reduction ◽  
Carbon Isotope Excursion

<p>The first dramatic rise in atmospheric oxygen to concentrations above 10<sup>-5</sup> present atmospheric level (PAL), known as the Great Oxidation Event (GOE), was initiated during the early Proterozoic Eon c. 2.43-2.32 billion years (Gyrs) ago [1,2].  Although atmospheric O<sub>2</sub> concentrations are generally accepted to have remained below 1% PAL for at least 1.5 Gyrs following the GOE [3], high atmospheric O<sub>2</sub> build up occurred during the Lomagundi carbon isotope excursion (LE) at the latest stage of the GOE [4]. The LE is the most pronounced and longest-lived carbon isotope excursion in Earth’s history that took place c. 2.22-2.06 Gyrs ago [4,5]. It reflects increased organic carbon (C<sub>org</sub>) burial resulting from high primary productivity at the time of high phosphorous flux to the ocean associated with intense acidic chemical weathering of landmasses. However, mechanisms responsible for such high C<sub>org</sub> sequestration are not yet fully resolved, nor has it been possible to precisely quantify the magnitude and expansion of oxygenation within the coeval atmosphere-ocean system.</p><p>Here, we studied diagenetic concretions of pyrite and carbonate and their host black shales of the Francevillian Group, southeast Gabon, deposited during the LE. Light sulfur (δ<sup>34</sup>S ‰, VCDT) and carbon (δ<sup>13</sup>C<sub>carb</sub> ‰, VPDB) isotope ratios indicate that both pyrite and carbonate formed in sediments through microbial sulfate reduction and C<sub>org</sub> remineralization, respectively. Selenium isotopic ratios (δ<sup>82/76</sup>Se ‰, NIST3149) of the pyrite concretions and their host shales are dominated by highly negative values as low as –3‰, which is strong evidence for partial reduction of selenium oxyanions (SeO<sub>x</sub><sup>2-</sup>) in the sediment below an oxygenated seawater column. Collectively, the data suggests an oxygenated water column in the Francevillian Basin with a large SeO<sub>x</sub><sup>2-</sup> reservoir that continuously resupplied these electron acceptors to the sediment and prevented their quantitative reduction. The studied black shales host putative, fossilized large colonial multicellular organisms that had the ability to laterally and vertically migrate within the sediments [6]. We propose that bioturbation by these organisms allowed an increased flux of electron acceptors (e.g., O<sub>2</sub>, NO<sub>3</sub><sup>–</sup>, SeO<sub>x</sub><sup>2-</sup>, SO<sub>4</sub><sup>-</sup>) into the sediments and pushed the microbial sulfate reduction and methanogenesis zones downward. As a consequence, CH<sub>4</sub> and H<sub>2</sub>S generated in these zones were re-oxidized in more oxic upper levels of the sediments, which prevented them from escaping to the water column. An increase in ecosystem complexity thus likely aided C<sub>org</sub> sequestration to the sediments and O<sub>2</sub> accumulation in the atmosphere-ocean system during the LE.</p><p> </p><p><em>[1] Bekker et al. (2004), Nature, 427, 117–120. [2] Holland (2006), Philos. Trans. R. Soc. B 361, 903–91. [3] Colwyn et al. (2014), Geobiology, DOI: 10.1111/gbi.12360. [4] Karhu and Holland (1996), Geology, 24, 867–870. [5] Bekker (2014), Encyclopedia of Astrobiology, Springer-Verlag, 1–6. [6] El Albani et al. (2019), Proc. Natl. Acad. Sci. USA, 116, 3431–3436.</em></p>

CERIUM ANOMALY ACROSS THE EARLY MISSISSIPPIAN KINDERHOOKIAN–OSAGEAN CARBON ISOTOPE EXCURSION

2019 ◽  
Author(s):  
Deborah C. Morales ◽  
◽  
Ganqing Jiang ◽  
Shichun Huang ◽  
Audrey Warren ◽  
...  
Keyword(s):  
Carbon Isotope ◽  
Carbon Isotope Excursion ◽  
Cerium Anomaly

Field evidence for coal combustion links the 252 My-old Siberian Traps with global carbon disruption

2021 ◽  
Author(s):  
Linda Elkins-Tanton ◽  
Steven Grasby ◽  
Benjamin Black ◽  
Roman Veselovskiy ◽  
Omid Ardakani ◽  
...  
Keyword(s):  
Organic Matter ◽  
Carbon Isotope ◽  
Flood Basalts ◽  
Siberian Traps ◽  
Field Evidence ◽  
Carbon Isotope Excursion ◽  
Show Evidence ◽  
Volcaniclastic Rocks ◽  
Atmospheric Changes ◽  
Global Carbon

<p>The Permo-Triassic Extinction was the most severe in Earth history. The Siberian Traps eruptions are strongly implicated in the global atmospheric changes that likely drove the extinction. A sharp negative carbon isotope excursion coincides within geochronological uncertainty with the oldest dated rocks from the Norilsk section of the Siberian flood basalts. The source of this light carbon has been debated for decades.</p><p>We focused on the voluminous volcaniclastic rocks of the Siberian Traps, relatively unstudied as potential carriers of carbon-bearing gases. Over six field seasons we collected rocks from across the Siberian platform and show the first direct evidence that the earliest eruptions particularly in the southern part of the province burned large volumes of a combination of vegetation and coal. Samples from the Maymecha-Kotuy region, from the Nizhnyaya Tunguska, Podkamennaya Tunguska, and Angara Rivers all show evidence of high-temperature organic matter carbonization and combustion.</p><p>Field evidence indicates a process in which ascending magmas entrain xenoliths of coal and carbonaceous sediments that are carbonized in the subsurface and also combusted either through reduction of magmas or when exposed to the atmosphere. We demonstrate that the volume and composition of organic matter interactions with magmas may explain the global carbon isotope signal, and have significantly driven the extinction.</p>

The recovery of early vertebrates and reef ecosystems following the late Silurian carbon isotope excursion: the Burgen outlier, Gotland, Sweden

2021 ◽  
Author(s):  
Emilia Jarochowska ◽  
Oskar Bremer ◽  
Alexandra Yiu ◽  
Tiiu Märss ◽  
Henning Blom ◽  
...  
Keyword(s):  
Carbon Isotope ◽  
Carbonate Platform ◽  
Fish Diversity ◽  
Global Environmental ◽  
Carbon Isotope Excursion ◽  
Low Diversity ◽  
Early Vertebrates ◽  
Carbonate Factory ◽  
Faunal Distribution ◽  
Rapid Regression

<p>The Ludfordian Carbon Isotope Excursion (LCIE) reached the highest known δ<sup>13</sup>C values in the Phanerozoic. It was a global environmental perturbation manifested in a rapid regression attributed to glacial eustasy. Previous studies suggested that it has also heavily affected the diversity of conodonts, early vertebrates and reef ecosystems, but the timing of the crisis and recovery remained complicated owing to the lateral variability of δ<sup>13</sup>C values in epeiric platforms and rapid facies shifts, which drove faunal distribution. One of the best records of this interval is available in the Swedish island of Gotland, which preserves tectonically undisturbed strata deposited in a Silurian tropical carbonate platform. We revisited the world-renowned collection of the late Lennart Jeppsson, hosted at the Swedish Museum of Natural History, Stockholm, which holds the key to reconstruct the dynamics of faunal immigration and diversification following the LCIE. Here we focus on the Burgen erosional outlier, which remained a mystery, as it had been correlated with the excursion strata, but preserved a high diversity of conodonts and reefal ecosystems. We re-examined key outcrops and characterized macro- and microfacies, as well as chemostratigraphy and unpublished fauna in the collection. Strata in the Burgen outlier represent back-shoal facies of the Burgsvik Oolite Member and correspond to the Ozarkodina snajdri Conodont Biozone. The shallow-marine position compared to the more continental setting of coeval strata in southern Gotland, is reflected in the higher δ<sup>13</sup>C<sub>carb</sub> values, reaching +9.2‰. The back-shoal succession in this outcrop includes reefs, which contain a large proportion of microbial carbonates and have therefore been previously compared with low-diversity buildups developed in a stressed ecosystem. However, the framework of these reefs is built by a diverse coral-stromatoporoid-bryozoan fauna, indicating that a high microbial contribution might be a characteristic of the local carbonate factory rather than a reflection of restricted conditions. In the case of conodonts, impoverishment following the LCIE might be a product of facies preferences, as the diverse environments in the outlier yielded at least 20 of the 21 species known from the Burgsvik Formation in Gotland. Fish diversity also returned to normal levels following the LCIE with an estimated minimum of 9 species. Thelodont scales appear to dominate samples from the Burgen outlier, which is in line with previous reports. Our observations highlight how palaeoenvironmental reconstructions inform fossil niche and diversity analyses, but also how fossil museum collections continuously contribute new data on past biodiversity.</p>

Late Paleocene-Early Eocene Foraminiferal Assemblage and Carbon Isotope Excursion Indicating Hyperthermal Events in Paleotropical Succession of Northwestern India

2021 ◽  
Vol 51 (1) ◽  
pp. 4-13
Author(s):  
Sonal Khanolkar ◽  
Tathagata Roy Choudhury ◽  
Pratul Kumar Saraswati ◽  
Santanu Banerjee
Keyword(s):  
Carbon Isotope ◽  
Detrended Correspondence Analysis ◽  
Western India ◽  
Early Eocene ◽  
Foraminiferal Assemblage ◽  
Trophic Conditions ◽  
Jaisalmer Basin ◽  
Early Eocene Climatic Optimum ◽  
Late Paleocene ◽  
Carbon Isotope Excursion

ABSTRACT This study focuses on marine sediments of the late Paleocene-early Eocene (∼55.5–49 Ma) interval from the Jaisalmer Basin of western India. It demarcates the Paleocene Eocene Thermal Maximum (PETM) using foraminiferal biostratigraphy and carbon isotope stratigraphy. A negative carbon isotope excursion of 4.5‰ delineates the PETM within the basin. We demarcate five foraminiferal biofacies using the detrended correspondence analysis. These reflect characteristics of ecology, bathymetry, relative age, and environment of deposition of the foraminifera. They record the response of foraminifera to the warmth of the PETM. Biofacies A was deposited within an inner neritic setting ∼55.5 Ma and includes benthic foraminifera Haplophragmoides spp., Ammobaculites spp., and Lenticulina spp. The presence of Pulsiphonina prima and Valvulineria scorbiculata in Biofacies B suggests an increase in runoff conditions in the basin. Fluctuating trophic conditions prevailed between ∼54–50 Ma. It is evidenced by alternating Biofacies C (endobenthic and chiloguembelinids of eutrophic conditions) and Biofacies D (epibenthic and acarininids of oligotrophic conditions). Biofacies E is dominated by deep-dwelling parasubbotinids, indicating an increase in bathymetry, possibly corresponding to the Early Eocene Climatic Optimum (∼49 Ma).

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