Early Toarcian Oceanic Anoxic Event Research Articles

00/01494 Renewable energy—the way forward

Deposits with unusually high Mn contents sampled at Monte Mangart in the Julian Alps include organic-rich marlstone and black shale with interbedded manganoan and siliceous limestone, which were deposited during the early Toarcian Oceanic Anoxic Event. Mn enrichment during that period has been related to global sea-level change coincident with increasing subsidence rate. The formation of Fe–Mn nodules, marking a hardground at the base of the Monte Mangart section, seems to be triggered by release of Mn from remote hydrothermal vents into a region of relatively elevated submarine topography where oxidizing conditions prevailed. However, very high Mn contents in carbonate phases above the hardground imply an additional diagenetic source of this element in the lower part of this section. The whole stratigraphic sequence (ca 30 m) displays a transition from Mn-rich (up to 8.8%) sediments, in the lower part, to Mn-poor (less than 1.8%) sediments in the middle and upper parts. The drastic decrease in Mn content's up-section is accompanied by a clear decrease in the mean size of pyrite framboids, indicating more intense anoxia/euxinia in the water column. In the presence of Mn2+, conditions of high alkalinity induced precipitation of Mn carbonates during early diagenetic processes. Negative δ13Ccarb values coincident with high Mn contents indicate involvement of organic matter in the mineralization process. The striking similarity of Ce/Ce* and Mn profiles demonstrates that, consistent with redox-chemistry of Mn and Ce under anoxic conditions, Ce3+ and Mn2+ were mobilized and released into pore water where precipitation of Mn carbonates occurred.

Synchrony between Early Jurassic extinction, oceanic anoxic event, and the Karoo-Ferrar flood basalt volcanism

Research Article| August 01, 2000 Synchrony between Early Jurassic extinction, oceanic anoxic event, and the Karoo-Ferrar flood basalt volcanism József Pálfy; József Pálfy 1Department of Geology and Paleontology, Hungarian Natural History Museum, H-1431 Budapest, Hungary Search for other works by this author on: GSW Google Scholar Paul L. Smith Paul L. Smith 2Department of Earth and Ocean Sciences, University of British Columbia, Vancouver, British Columbia V6T 1Z4, Canada Search for other works by this author on: GSW Google Scholar Author and Article Information József Pálfy 1Department of Geology and Paleontology, Hungarian Natural History Museum, H-1431 Budapest, Hungary Paul L. Smith 2Department of Earth and Ocean Sciences, University of British Columbia, Vancouver, British Columbia V6T 1Z4, Canada Publisher: Geological Society of America Received: 10 Jan 2000 Revision Received: 18 May 2000 Accepted: 23 May 2000 First Online: 02 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (2000) 28 (8): 747–750. https://doi.org/10.1130/0091-7613(2000)28<747:SBEJEO>2.0.CO;2 Article history Received: 10 Jan 2000 Revision Received: 18 May 2000 Accepted: 23 May 2000 First Online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation József Pálfy, Paul L. Smith; Synchrony between Early Jurassic extinction, oceanic anoxic event, and the Karoo-Ferrar flood basalt volcanism. Geology 2000;; 28 (8): 747–750. doi: https://doi.org/10.1130/0091-7613(2000)28<747:SBEJEO>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract A well-known second-order mass extinction took place during the Pliensbachian and Toarcian Stages of the Early Jurassic. First recognized as a minor Pliensbachian peak in the global extinction rate, it has alternatively been interpreted as a regional response to the early Toarcian oceanic anoxic event. Detailed studies established it as a global long-term event spanning five successive ammonoid zones. Here we present a revised time scale based on high-precision U-Pb ages resolved to the zone level, which suggests that elevated extinction rates were sustained for about 4 m.y. and peak extinction occurred at 183 Ma. Recent isotopic dating of flood basalts from the southern Gondwanan Karoo and Ferrar provinces documents a culmination in volcanic activity ca. 183 Ma. The onset of volcanism is recorded as an inflection and start of a rapid rise of the seawater 87Sr/86Sr curve. The synchrony of voluminous flood basalt eruptions and biotic crises, as already noted for three of the major mass extinctions, permits a causal relationship, which in this case may be mediated by widespread oceanic anoxia. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Lower Jurassic epicontinental carbonates and mudstones from England and Wales: chemostratigraphic signals and the early Toarcian anoxic event

ABSTRACTSections through Lower Jurassic epicontinental carbonates from Southern Britain (Junction Bed and equivalent) show a positive carbon‐isotope excursion (δ13Ccarbonate), detectable in bulk rock, in the falciferum Zone of the lower Toarcian. Isotopic data from organic matter in more clay‐rich sections from Wales and north‐east England, together with determinations on belemnite calcite, indicate that highest δ13C values are localized in the upper exaratum Subzone of the falciferum Zone. Levels of particular enrichment in organic carbon were developed in the early to mid‐exaratum Subzone and hence pre‐date this δ13C maximum. These phenomena reflect the impact of the early Toarcian oceanic anoxic event in the British area. Similar isotopic trends have been recorded in other Toarcian sections from Tethyan Europe and are interpreted as reflecting the chemistry of sea water. On the assumption of isotopic correlation between the English and Tethyan sections, the δ13C maximum would be everywhere dated as latest exaratum Subzone in terms of the north European ammonite scheme.Absolute oxygen‐isotope values in carbonates probably reflect both early diagenetic cementation and later temperature‐related burial diagenesis, although a palaeotemperature maximum is tentatively identified as characterizing the early falciferum Zone. Subsequent climatic deterioration may have been triggered by drawdown of CO2, related to regional excess carbon burial during the oceanic anoxic event. Using the positive δ13C excursion as a correlative level in sections from different faunal provinces (Britain, Italy and Spain) implies that lower Toarcian zonal stratigraphy is diachronous between northern and southern Europe. There is evidence for partitioning of water masses between the north European shelf and the Tethyan continental margin during the Early Jurassic.