Triple oxygen isotope composition of chert during the Ediacaran-Cambrian transition and implications for paleotemperature reconstruction

Abstract:

The Ediacaran-Cambrian transition represents a crucial interval of Earth’s history marked by a significant shift in the environmental conditions and rapid diversification of metazoans (well known as the “Cambrian Explosion”). However, the quantitative paleotemperature of this interval, a key factor of marine environment affecting biological activities, remains poorly constrained, partially due to the lack of reliable paleothermometer proxies.

The oxygen isotope composition (δ¹⁸O) of chert has been extensively used to investigate ancient environments and especially useful as a paleothermometer. However, the chert δ¹⁸O record of deep time might be affected by other factors (seawater δ¹⁸O and secondary diagenesis) and whether the δ¹⁸O signal stands for the original paleotemperature information remains controversial (Liljestrand et al., 2020). To address these debates, triple oxygen isotope data provide more useful information than traditional δ¹⁸O analysis only, and various triple isotope mass balance models have been established to trace the origin of the signals (Liljestrand et al., 2020; Sengupta & Pack, 2018), thus affording effective constrains on the mineral histories and temperature reconstruction.

The interval across Ediacaran-Cambrian boundary of South China accumulates abundant nodular and bedded chert. Here, we measure triple oxygen isotope compositions of these chert deposits, which may bear potential archives of seawater temperature and marine conditions and provide insights into the interactions of biological revolution and environmental change during the Cambrian Explosion. Preliminary results will be reported and discussed.

References

Liljestrand, F. L., Knoll, A. H., Tosca, N. J., Cohen, P. A., Macdonald, F. A., Peng, Y., & Johnston, D. T. (2020). The triple oxygen isotope composition of Precambrian chert. Earth and Planetary Science Letters, 537, 116167. https://doi.org/10.1016/j.epsl.2020.116167

Sengupta, S., & Pack, A. (2018). Triple oxygen isotope mass balance for the Earth’s oceans with application to Archean cherts. Chemical Geology, 495, 18–26. https://doi.org/10.1016/j.chemgeo.2018.07.012