Environmental change, trilobite extinction and massive volcanism at the Cambrian Series 2 – Series 3 boundary

The Cambrian Series 2 – Series 3 boundary (~509 Ma) was a dynamic
interval marked by a major perturbation to the global carbon cycle;
widespread sea level fall (Sauk Supersequences); the eruption of the
Kalkarindji large igneous province and the extinction of the dominant
trilobites- the olenellids of Laurentia and the redlichiids of Gondwana. This thesis investigates the relative timing of these phenomena from field sites across the Laurentian and Gondwanan palaeocontinents, assessing the severity of environmental change coinciding with extinction. We report that the Redlichiid-Olenellid Extinction Carbon isotope Excursion (ROECE) coincides with the Series 2 – Series 3 boundary in Laurentian sections (NW Scotland, SW USA), though only in the SW USA does ROECE co-occur with the trilobite extinction. Scottish successions of this age are hindered by a lack of fossils, and as such the exact timing of ROECE relative to the
extinction is unclear. New evidence presented in this thesis shows a
variable record of anoxia at the extinction horizon, the most severe
manifestation indicates euxinic conditions during the extinction at Ruin
Wash, Pioche Formation, Nevada. Elsewhere in the SW USA and NW
Scotland, there is evidence for periodic dysoxia (e.g. basal Ghrudaidh
Formation, Durness Group, Scotland and Carrara Formation, SW USA) at the Series 2 – Series 3 boundary and extinction interval. Facies analysis reveals that on Laurentia, ROECE and the extinction horizon occur during the transgressive phase of the Sauk II supersequence. To investigate the temporal relationship between the Series 2 – Series 3 boundary, ROECE, extinction and Kalkarindji eruptions, this thesis presents new Hg data as a proxy for volcanism. On Laurentia the data show an inconsistent relationship between these phenomena, whilst on Gondwana a new preliminary study shows evidence for Hg enrichments at this interval, establishing it as a site to further investigate the sedimentary trace of volcanism.