Does marine anoxia explain Hg enrichments during the SPICE event? New evidence from the Cambro-Ordovician Durness Group, northern Scotland
Abstract
In recent years, mercury (Hg) concentrations have been used as a fingerprint of large igneous province volcanism, particularly during intervals of mass extinction. All five major mass extinction events, some minor extinctions, and Mesozoic OAE's have been linked to Hg anomalies, and volcanism has been implicated in all of these events. However, much remains unknown about Hg cycling in deep time, and how it is recorded in ancient deposits. Upper Cambrian strata of the Durness Group in northern Scotland preserve a new occurrence of the SPICE event (Steptoean positive isotopic carbon excursion) and a series of Hg enrichments that occur during and immediately after the SPICE. These spikes in Hg concentration likely represent changes in environmental loading, as they persist when normalized for both TOC and clay abundance. In addition, a high abundance of the mineral glauconite, a known redox-sensitive iron-bearing phyllosilicate mineral, co-occurs with the SPICE and the Hg enrichments, but is absent from the rest of the section.
Because there is no known and well-dated LIP coeval with the SPICE, we consider non-volcanic processes that may influence the Hg record. We suggest that the local Hg enrichments and elevated glauconite abundance in the Durness basin were driven by changing redox conditions in the ocean during the SPICE event. These data are consistent with numerous other studies that have invoked low-oxygen conditions during the SPICE interval. While the presence of an unknown LIP cannot be ruled out as a driver for the Hg signal, redox oscillations, a major controller on modern Hg cycling in the oceans, must be considered as a potential driver of Hg enrichments in the Durness Group. These results may be useful for interpreting other Hg enrichments in the geologic record, particularly for intervals that lack known LIPs.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMPP51A..05P
- Keywords:
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- 0473 Paleoclimatology and paleoceanography;
- BIOGEOSCIENCESDE: 1051 Sedimentary geochemistry;
- GEOCHEMISTRYDE: 3675 Sedimentary petrology;
- MINERALOGY AND PETROLOGYDE: 4863 Sedimentation;
- OCEANOGRAPHY: BIOLOGICAL AND CHEMICAL