Redox conditions and marine microbial community changes during the end-Ordovician mass extinction event
PBN-AR
Instytucja
Wydział Budownictwa i Architektury (Politechnika Świętokrzyska)
Informacje podstawowe
Główny język publikacji
en
Czasopismo
Global and Planetary Change (45pkt w roku publikacji)
ISSN
0921-8181
EISSN
Wydawca
DOI
URL
Rok publikacji
2017
Numer zeszytu
Strony od-do
105-122
Numer tomu
149
Link do pełnego tekstu
Liczba arkuszy
Słowa kluczowe
en
Black shales
Paleoenvironment
Redox conditions
Biomarkers
Microbial communities
Zbrza Basin
Streszczenia
Język
en
Treść
The end-Ordovician (Hirnantian) crisis is the first globally distinct extinction during the Phanerozoic, but its causes are still not fully known. Here, we present an integrated geochemical and petrographic analysis to understand the sedimentary conditions taking place before, during and after the Late Ordovician ice age. Newdata from the Zbrza (Holy CrossMountains) and Gołdap (Baltic Depression) boreholes shows that, like in other worldwide sections, the total organic carbon (TOC) content is elevated in the upper Katian and uppermost Hirnantian to Rhudannian black shales, but depleted (below 1%) during most of the Hirnantian. Euxinic conditions occurred in the photic zone in both TOC-rich intervals. This is based on the maleimide distribution, occurrence of aryl isoprenoids and isorenieratane, as well as a dominance of tiny pyrite framboids. Euxinic conditions were interrupted by the Hirnantian regression caused by glaciation. Sedimentation on the deep shelf changed to aerobic probably due to intense thermohaline circulation. Euxinia in the water column occurred directly during the time associatedwith the second pulse of the mass extinctionwith a termination of the end-Ordovician glaciation and sea level rise just at the Ordovician/Silurian (O/S) boundary. In contrast,we suggest based on inorganic proxies that bottom water conditions were generally oxic to dysoxic due to upwelling in the Rheic Ocean. The only episode of seafloor anoxia in the Zbrza basin was found at the O/S boundary, where all inorganic indicators showed elevated values typical for anoxia (U/Th N 1.25; V/Cr N 4.25; V/(V + Ni): 0.54–0.82 and Mo N 10–25 ppm). Significant differences in hopanes to steranes ratio and in C27–C29 sterane distribution between the Katian, Rhudannian and Hirnantian deposits indicate changes in marine microbial communities triggered by sharp climate change and Gondwana glaciation. The increase from biomarkers of cyanobacteria (2α-methylhopanes) after the O/S boundary implied enhanced microbial activity following the mass extinction event.
Cechy publikacji
peer-reviewed
Inne
System-identifier
60380
CrossrefMetadata from Crossref logo
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