A Late Namurian (318Ma) 40Ar/39Ar Age For Kaersutite Megacrysts from the Black Ball Head Diatreme: an Age Limit for the Variscan Deformation in South-West Ireland

Pracht, Markus; Timmerman, Martin J.

doi:10.3318/ijes.2004.22.1.33

Cited by 6 publications

(2 citation statements)

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“…Recent studies on deep water sediments have shown higher Hg anomalies and the presence of pyroclastic material, indicating that local magmatic activity might have initiated before the deposition of HBS (Pisarzowska et al, 2020). Coeval ash/tuff deposits in Hangenberg Crisis sediments from the deep ocean, such as Poland (Marynowski et al, 2012), Spain (Menor‐Salván et al, 2010) and Ireland (Pracht & Batchelor, 1998) also provide evidence for local and potentially intensified volcanic activity. However, in this global D–C‐type section from South China, we did not find any direct sedimentary or geochemical evidence for volcanism.…”

Section: Discussionmentioning

confidence: 99%

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Isotopic evidence of environmental changes during the Devonian–Carboniferous transition in South China and its implications for the biotic crisis

Cao

Wang

et al. 2023

Geobiology

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The Devonian–Carboniferous (D–C) transition coincides with the Hangenberg Crisis, carbon isotope anomalies, and the enhanced preservation of organic matter associated with marine redox fluctuations. The proposed driving factors for the biotic extinction include variations in the eustatic sea level, paleoclimate fluctuation, climatic conditions, redox conditions, and the configuration of ocean basins. To investigate this phenomenon and obtain information on the paleo‐ocean environment of different depositional facies, we studied a shallow‐water carbonate section developed in the periplatform slope facies on the southern margin of South China, which includes a well‐preserved succession spanning the D–C boundary. The integrated chemostratigraphic trends reveal distinct excursions in the isotopic compositions of bulk nitrogen, carbonate carbon, organic carbon, and total sulfur. A distinct negative δ15N excursion (~−3.1‰) is recorded throughout the Middle Si. praesulcata Zone and the Upper Si. praesulcata Zone, when the Hangenberg mass extinction occurred. We attribute the nitrogen cycle anomaly to enhanced microbial nitrogen fixation, which was likely a consequence of intensified seawater anoxia associated with increased denitrification, as well as upwelling of anoxic ammonium‐bearing waters. Negative excursions in the δ13Ccarb and δ13Corg values were identified in the Middle Si. praesulcata Zone and likely resulted from intense deep ocean upwelling that amplified nutrient fluxes and delivered 13C‐depleted anoxic water masses. Decreased δ34S values during the Middle Si. praesulcata Zone suggests an increasing contribution of water‐column sulfate reduction under euxinic conditions. Contributions of organic matter produced by anaerobic metabolisms to the deposition of shallow carbonate in the Upper Si. praesulcata Zone is recorded by the nadir of δ13Corg values associated with maximal △13C. The integrated δ15N‐δ13C‐δ34S data suggest that significant ocean‐redox variation was recorded in South China during the D–C transition; and that this prominent fluctuation was likely associated with intense upwelling of deep anoxic waters. The temporal synchrony between the development of euxinia/anoxia and the Hangenberg Event indicates that the redox oscillation was a key factor triggering manifestations of the biodiversity crisis.

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Section: Discussionmentioning

confidence: 99%

“…Coeval ash/tuff deposits in Hangenberg Crisis sediments from the deep ocean, such as Poland (Marynowski et al, 2012), Spain (Menor-Salván et al, 2010) and Ireland (Pracht & Batchelor, 1998) also provide evidence for local and potentially intensified volcanic activity.…”

Section: Evaluation Of the δ 13 C Signal Of The D-c Transitionmentioning

confidence: 99%