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TitleIsotopic evidence for changes in the mercury and zinc cycles during Oceanic Anoxic Event 2 in the northwestern Tethys, Austria
AuthorYao, H; Chen, X; Wagreich, M; Grasby, S EORCID logo; Liu, S -A; Yin, R; Tostevin, R; Lv, Y; Gu, X; Liu, X; Wang, C
SourceGlobal and Planetary Change vol. 215, 103881, 2022 p. 1-11,
Alt SeriesNatural Resources Canada, Contribution Series 20220217
Mediapaper; digital; on-line
File formatpdf
AreaTethys; Austria
Lat/Long WENS -90.0000 -1.0000 60.0000 -90.0000
SubjectsScience and Technology; Nature and Environment; volcanism; mercury; zinc
Illustrationslocation maps; diagrams; charts
ProgramTargeted Geoscience Initiative (TGI-6) Hydrothermal Ore Systems
Released2022 06 24
AbstractThe Cenomanian-Turonian Oceanic Anoxic Event 2 (OAE 2, ca. 94 Ma) was one of the most extreme carbon cycle and climatic perturbations of the Phanerozoic Eon. Widespread deposition of organic-rich shales during OAE 2 has been attributed to a rapid rise in atmospheric CO2, global heating, and marine anoxia triggered by intense large igneous province (LIP) volcanism. Here, we present new Hg and Zn elemental and isotopic analyses from samples spanning OAE 2 in a hemipelagic section from Rehkogelgraben, Austria, which was part of the north-western Tethys. We compare our data to existing records from a range of sites to constrain the relative timing, magnitude and geographic extent of the perturbation. We find a prominent Hg concentration peak and an overall positive D199Hg excursion, with no correlation between Hg content and organic matter (OM), Mn-Fe-oxyhydroxides, and/or clay minerals. We interpret this to indicate a terrestrial volcanic origin of Hg. The Hg excursion is coincident with an osmium (Os) isotope excursion, and together, this supports a global period of intense LIP volcanism. The d66Zn record from the Rehkogelgraben section decreases abruptly by ~0.5 per mil prior to the onset of OAE 2, a change recorded consistently among all reference sections. Combined with the Hg data, we interpret this to result from isotopically light Zn sourced from LIP activity. However, the second negative excursion in d66Zn during the Plenus Cold Event (PCE), which is recorded in the proto-North Atlantic and adjacent areas and has been attributed to Zn released from OM during re-oxygenation, is not recorded in this section. We suggest that the cool, oxygenated deep water mass did not invade the Penninic Ocean in the northwestern Tethys. Alternatively, this excursion could be missing in our section due to the presence of carbonate-free sediments during the PCE. After the PCE, the positive excursion in d66Zn recorded in all sections reveals a recovery of the atmosphere-ocean system. Our findings highlight the significance of spatial and temporal variations in Hg and Zn isotopes during OAE 2.
Summary(Plain Language Summary, not published)
This paper examines what is known as the Cenomanian-Turonian Oceanic Anoxic Event 2 which occurred 94 million years ago. This represented one of the most extreme carbon cycle and climatic perturbations of the last 500 million years that was characterised by widespread deposition of organic-rich shales that are enriched in many locations with critical minerals. Work is being conducted to understand better what drove formation of these metal rich shales. Results show that a rapid rise in atmospheric CO2, global heating, and marine anoxia triggered by intense large igneous province volcanism, based on novel use of mercury and zinc elemental and isotopic analyses. Results will inform new exploration models for critical mineral resources in Canada and globally.

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