Mercury And Sulfur Isotopic Evidence For The Linkages Between The Ca. 510 Ma Kalkarindji Large Igneous Province And Trilobite Crisis

The first major mass extinction of trilobites occurred at the transition from Cambrian Series 2 (CS2) to Miaolingian (M) and coincided with a large marine transgression and volcanic eruptions of a large igneous province (LIP). Understanding the causal links between these events is important in deciphering environmental changes and life evolution at that time. This paper presents S-Hg-C isotopic and Fe speciation data for calcareous shales from the CS2-M Yangliugang Formation in the Dongjin section, South China. In the lower part of this section (Interval I), calcareous shales have limited S isotopic differences between carbonate-associated sulfates (delta S-34(CAS)) and pyrites (delta S-34(Py)) with Delta S-34 values from -4.2 parts per thousand to +8.3 parts per thousand; they also have high Fe-HR/Fe-T ratios from 0.5 to 0.66, that are indicative of a low SO42- content in anoxic seawater. Calcareous shales from Interval I display at least two Hg/TOC peaks (up to 207 ppb/wt%), coincident with volcanic eruptions associated with the ca. 510 Ma Kalkarindji LIP in Australia. In the middle part of the Dongjin section (Interval II), calcareous shales display negative excursions of Delta Hg-1(99) values, delta S-34(P)y values and Fe-HR/Fe-T ratios, which were likely led by a large terrestrial input into a marginal basin from where Interval II deposited. Calcareous shales in the upper part of the section (Interval III) contain pyrite framboids with a mean diameter of <4 mu m and high ratios of Fe-HR/Fe-T (>0.82) and Fe-Py/Fe-HR (>0.78), indicating an euxinic depositional environment. They also record negative excursions in delta C-13 and delta Hg-202 (with low values down to -3.05 parts per thousand and -1.68 parts per thousand, respectively), providing evidence for ocean upwelling. The negative shift of delta C-13 values in the Dongjin section was temporally comparable to the C isotope excursions that coincided with the Redlichiid-Olenellid Extinction Carbon Isotope Excursion (ROECE). We conclude that volcanic eruptions of the ca. 510 Ma Kalkarindji LIP enhanced the continental erosion rate, leading to a high terrestrial SO42- input and an accumulation of H2S in deep marginal basins at the end of CS2. The subsequent ocean upwelling (>506 Ma) brought anoxic/euxinic seawaters into the continental shelf, contributing to the mass extinction of Redlichiid and Olenellid. (C) 2021 Elsevier B.V. All rights reserved.