EGU22-5955
https://doi.org/10.5194/egusphere-egu22-5955
EGU General Assembly 2022
© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

Degradation of mercury (Hg) signals on incipient weathering refines use of Hg as a volcanic paleoproxy

Junhee Park1, Holly Stein1,2, Svetoslav Georgiev1,3, and Judith Hannah1,2
Junhee Park et al.
  • 1AIRIE Program, Colorado State University, Fort Collins, CO 80523-1482 USA (Juni.Park@colostate.edu)
  • 2Institute for Geosciences, University of Oslo, 0316 Oslo, Norway
  • 3Geological Institute, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria

Perceived mercury (Hg) enrichments and elevated ratios of Hg to total organic carbon (Hg/TOC) in sedimentary rocks have often been linked to volcanism from large igneous provinces (LIPs) and mass extinctions, prompting the hypothesis that elevated Hg concentrations are a proxy for intense volcanism from LIPs.  However, primary Hg and TOC contents of sedimentary rocks can be altered by secondary processes, for example, intense weathering [1].  Before endorsing cause-and-effect between volcanic Hg emissions and biotic crises or mass extinctions, the magnitude of measured Hg and Hg/TOC anomalies in weathered outcrop samples must be compared to equivalent units in core samples, where the outcrop sample provides, in effect, a minimum concentration value.  

Here, we investigate the effects of incipient weathering on Hg contents and Hg/TOC ratios.  We quantify the behavior of Hg during incipient weathering by determining Hg concentrations in visually pristine black shales from outcrops of the Upper Permian Ravnefjeld Formation in East Greenland, comparing these data to equivalent intervals acquired from drill core taken from a plateau 7 km from the outcrop.  Directly correlative Upper Permian shales (drill core) from the mid-Norwegian shelf further enhance our comparison.  Using detailed geochemistry and principal component analysis (PCA), we characterize the main host phases of Hg and relate different Hg contents from pristine samples from East Greenland and the mid-Norwegian shelf to different Hg inputs during shale deposition.  Importantly, we show the vulnerability of Hg contents and Hg/TOC ratios to incipient weathering of fresh-appearing outcrops of organic-rich shale.  

Working with drill core rather than outcrop samples is essential to circumvent the problem, and to provide accurate Hg concentration data for primary events in the paleo-record.

[1] Charbonnier, G., Adatte, T., Föllmi, K.B., and Suan, G. (2020) Effect of intense weathering and postdepositional degradation of organic matter on Hg/TOC proxy in organic-rich sediments and its implications for deep-time investigations. Geochemistry, Geophysics, Geosystems, 21(2).

Funding – HS acknowledges the support of ACS-PRF award #59965-ND2 supporting AIRIE PhD student JP.  Drill cores were acquired from GEUS under Petromaks grant (NFR 180015/S30).  Colorado State University-Geosciences provides no funding for the personnel and operation of the AIRIE Program and its Re-Os laboratories. 

How to cite: Park, J., Stein, H., Georgiev, S., and Hannah, J.: Degradation of mercury (Hg) signals on incipient weathering refines use of Hg as a volcanic paleoproxy, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5955, https://doi.org/10.5194/egusphere-egu22-5955, 2022.

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