This is a repository copy of Trilobite extinctions, facies changes and the ROECE carbon isotope excursion at the Cambrian Series 2-3 boundary, Great Basin, western USA.

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Globally, the Series 2 – Series 3 boundary of the Cambrian System coincides with a major carbon isotope excursion, sea-level changes and trilobite extinctions. Here we examine the sedimentology, sequence stratigraphy and carbon isotope record of this interval in the Cambrian strata (Durness Group) of NW Scotland. Carbonate carbon isotope data from the lower part of the Durness Group (Ghrudaidh Formation) show that the shallow-marine, Laurentian margin carbonates record two linked sea-level and carbon isotopic events. Whilst the carbon isotope excursions are not as pronounced as those expressed elsewhere, correlation with global records (Sauk I – Sauk II boundary andOlenellusbiostratigraphic constraint) identifies them as representing the local expression of the ROECE and DICE. The upper part of the ROECE is recorded in the basal Ghrudaidh Formation whilst the DICE is seen around 30m above the base of this unit. Both carbon isotope excursions co-occur with surfaces interpreted to record regressive–transgressive events that produced amalgamated sequence boundaries and ravinement/flooding surfaces overlain by conglomerates of reworked intraclasts. The ROECE has been linked with redlichiid and olenellid trilobite extinctions, but in NW Scotland,Olenellusis found after the negative peak of the carbon isotope excursion but before sequence boundary formation.

The Kalkarindji continental flood basalt province of Northern Australia is the oldest basaltic LIP in the Phanerozoic having erupted in the mid-Cambrian. At this time, during the Cambrian Explosion, the global environment suffered a series of mass extinctions and biotic turnover. Kalkarindji had the potential to release 1.65 x 10 6 Tg of CO 2 , approximately 1.72% of the total Cambrian atmospheric carbon reservoir. It has there fore been implicated as a driver of the environmental changes in the Cambrian Series 2. However, temporal discrepancies between Kalkarindji eruptions and biotic turnover may prevent this LIP from being attributed as the sole cause of the Botomian-Toyonian Extinction, which wiped out up to 45% of all genera in the fossil record; while environmental factors such as sea-level change causing ocean anoxia are implicated in the Redlichiid-Olenellid Extinction. It is certainly possible that Kalkarindji could have played a part in forcing these environmental changes, but further advances in geochronology and sedimentary volcanic proxies are needed to confidently define a direct causational link between these events at the dawn of the Phanerozoic.

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