Re-Os geochronology for the Cambrian SPICE event : Insights into euxinia and enhanced continental weathering from radiogenic isotopes

Summary, in English

The late Cambrian Steptoean positive carbon isotope excursion (SPICE) represents a major perturbation to the global carbon cycle and was associated with trilobite extinctions and expansion of anoxic and/or euxinic water masses during episodes of eustatic sea-level change. We present a new Re-Os age together with Os and Nd isotope stratigraphy and major and trace-element data from the Alum Shale Formation (Scania, Sweden). The Re-Os age of 494.6 ± 2.9 Ma is from the interval of peak δ¹³C_org values, providing the first radiometric age constraint for this Cambrian carbon isotope excursion, interpreted as a possible pre-Mesozoic ocean anoxia event, and the timing of biomere-level extinctions. The Os isotope chemostratigraphic profile can be explained by an increase in terrigenous weathering prior to the SPICE, potentially driven by sea-level fall, and in agreement with enhanced nutrient supply, primary productivity, and organic matter burial as the driver of the SPICE event. Post-SPICE, the Os isotopes become increasingly unradiogenic; however, invariant εNd_(t) values argue against a change in provenance and instead support a decrease in the continental weathering flux, possibly related to eustatic sea-level rise.

• Author: Alan D. Rooney; Alexie E.G. Millikin; Per Ahlberg
• Department/s: Lithosphere and Biosphere Science
• Publishing year: 2022-06
• Language: English
• Pages: 716-720
• Publication/Series: Geology
• Volume: 50
• Issue: 6
• Links: http://dx.doi.org/10.1130/G49833.1
• Document type: Journal article
• Publisher: Geological Society of America
• Topic: Geology
• Status: Published
• ISBN/ISSN/Other: ISSN: 0091-7613