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norskBlar i forfatter "Kirsimäe, Kalle"
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Authigenesis of biomorphic apatite particles from Benguela upwelling zone sediments off Namibia: The role of organic matter in sedimentary apatite nucleation and growth
(Journal article; Tidsskriftartikkel; Peer reviewed, 2018-07-30)Sedimentary phosphorites comprise a major phosphorus (P) ore, yet their formation remains poorly understood. Extant polyphosphate‐metabolizing bacterial communities are known to act as bacterial phosphate‐pumps, leading to episodically high dissolved phosphate concentrations in pore waters of organic‐rich sediment. These conditions can promote the precipitation of amorphous precursor phases that are ... -
Boron concentrations and isotopic compositions in methane-derived authigenic carbonates: Constraints and limitations in reconstructing formation conditions
(Journal article; Tidsskriftartikkel; Peer reviewed, 2021-12-23)The boron content and isotopic composition (δ<sup>11</sup>B), of marine carbonates have the potential to constrain CO<sub>2</sub> chemistry during carbonate growth conditions. However, obtaining and interpreting boron compositions from authigenic carbonates in geological archives present several challenges that may substantially limit their application. In particular, contamination from non-carbonate ... -
Chromium evidence for protracted oxygenation during the Paleoproterozoic
(Journal article; Tidsskriftartikkel; Peer reviewed, 2022-03-24)It has commonly been proposed that the development of complex life is tied to increases in atmospheric oxygenation. However, there is a conspicuous gap in time between the oxygenation of the atmosphere 2.4 billion years ago (Ga) and the first widely-accepted fossil evidence for complex eukaryotic cells . At present the gap could either represent poor sampling, poor preservation, and/or difficulties ... -
Constraining the conditions of phosphogenesis: Stable isotope and trace element systematics of Recent Namibian phosphatic sediments
(Journal article; Tidsskriftartikkel; Peer reviewed, 2021-03-31)Modern phosphogenesis occurs on continental margins influenced by upwelling and high primary productivity. The formation of phosphatic sediments is coupled to global climate fluctuations, biological cycling of phosphorus and local redox conditions. Although the processes involved in phosphogenesis are well described, high-resolution data on the redox and stable isotope systematics in Recent in-situ ... -
Electrospun Amphiphilic Nanofibers as Templates for In Situ Preparation of Chloramphenicol-Loaded Liposomes
(Journal article; Tidsskriftartikkel; Peer reviewed, 2021-10-20)The hydration of phospholipids, electrospun into polymeric nanofibers and used as templates for liposome formation, offers pharmaceutical advantages as it avoids the storage of liposomes as aqueous dispersions. The objective of the present study was to electrospin and characterize amphiphilic nanofibers as templates for the preparation of antibiotic-loaded liposomes and compare this method with ... -
Heterogeneous REE + Y distribution in Early Paleozoic shelly phosphorites: Implications for enrichment mechanisms
(Journal article; Tidsskriftartikkel; Peer reviewed, 2021-10-27)Sedimentary phosphorites are important carriers of Rare Earth Elements and Yttrium (REE + Y). Primary biogenic and sedimentary apatite contain very low amounts of REE + Y and enrichment of these elements occurs during diagenesis. Although the influence of post-depositional processes on REE + Y concentrations in sedimentary phosphorites is well established, the processes controlling the degree of ... -
Hydrothermal dedolomitisation of carbonate rocks of the Paleoproterozoic Zaonega Formation, NW Russia — Implications for the preservation of primary C isotope signals
(Journal article; Tidsskriftartikkel; Peer reviewed, 2019-03-03)The Paleoproterozoic Zaonega Formation in Karelia, NW Russia, has played a key role in understanding the environmental conditions postdating the Great Oxidation and Lomagundi-Jatuli Events. Its carbonate- and organic-rich rocks (shungite) define the postulated Shunga Event representing an accumulation of very organic-rich sediments at c. 2 Ga and are central in ideas about changing ocean-atmosphere ... -
Iron Isotopes Reveal a Benthic Iron Shuttle in the Palaeoproterozoic Zaonega Formation: Basinal Restriction, Euxinia, and the Effect on Global Palaeoredox Proxies
(Journal article; Tidsskriftartikkel; Peer reviewed, 2021-03-31)The Zaonega Formation in northwest Russia (~2.0 billion years old) is amongst the most complete successions that record the middle of the Palaeoproterozoic era. As such, geochemical data from the formation have played a central role in framing the debate over redox dynamics in the aftermath of the Great Oxidation Event (GOE). However, uncertainty over local redox conditions and the degree of ... -
The kaolinite shuttle links the Great Oxidation and Lomagundi events
(Journal article; Tidsskriftartikkel; Peer reviewed, 2021-05-19)The ~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 ... -
Multiple sulphur isotope records tracking basinal and global processes in the 1.98 Ga Zaonega Formation, NW Russia
(Journal article; Tidsskriftartikkel; Peer reviewed, 2018-09-19)The exceptionally organic-rich rocks of the 1.98 Ga Zaonega Formation deposited in the Onega Basin, NW Russia, have refined our understanding of Earth System evolution during the Paleoproterozoic rise in atmospheric oxygen. These rocks were formed in vent- or seep influenced settings contemporaneous with voluminous mafic volcanism and contain strongly <sup>13</sup>C-depleted organic matter. ... -
Palaeoproterozoic oxygenated oceans following the Lomagundi–Jatuli Event
(Journal article; Tidsskriftartikkel; Peer reviewed, 2020-03-16)The approximately 2,220–2,060 million years old Lomagundi–Jatuli Event was the longest positive carbon isotope excursion in Earth history and is traditionally interpreted to reflect an increased organic carbon burial and a transient rise in atmospheric O<sub>2</sub>. However, it is widely held that O<sub>2</sub> levels collapsed for more than a billion years after this. Here we show that black shales ... -
Protracted post-glacial hydrocarbon seepage in the Barents Sea revealed by U–Th dating of seep carbonates
(Journal article; Tidsskriftartikkel; Peer reviewed, 2024-03-01)The hydrocarbon seepage chronology during deglaciation across the formerly glaciated Barents Sea was established using uranium-thorium (U–Th) dating of seep carbonates. Seep carbonates were sampled with remotely operated vehicles (ROV) from the seafloor at three active hydrocarbon seeps (water depth 156–383 m), located in the north-west (Storfjordrenna), north-central (Storbanken High), and south-west ... -
REE+Y uptake and diagenesis in Recent sedimentary apatites
(Journal article; Tidsskriftartikkel; Peer reviewed, 2019-07-30)Rare Earth Elements and Yttrium (REE+Y) distribution in authigenic phases are frequently used as proxies for reconstructing past seawater conditions. Sedimentary apatite precipitates near the sediment-water interface and is therefore capable of recording the REE+Y composition of the overlying water column. While the overprinting of primary REE+Y signal during late stage diagenesis is a widely known ... -
A refined late-Cryogenian – Ediacaran Earth history of South China: phosphorous-rich marbles of the Dabie and Sulu orogens
(Journal article; Tidsskriftartikkel; Peer reviewed, 2017-12-02)The late-Cryogenian – Ediacaran geological framework for South China is constructed principally from sedimentary successions preserved in the central and western regions of the Yangtze Block. New stratigraphic and carbonate-carbon isotope data allow us to extend that framework into the exhumed HP-UHP subduction complexes of the eastern Dabie and Sulu orogens that separate the South and North China ...
