Cover Image Credits

Top panel shows a field photograph of Wonoka Formation carbonates (yellow strata in foreground) sitting stratigraphically beneath Pound Subgroup siliclastics (red strata in background) in South Australia. The Pound contains soft-bodied, decimeter-scale fossils commonly interpreted as examples of Earth's oldest animals, and the Wonoka hosts the deepest δ¹³C excursion in Earth history, with values evolving from −12 to +5 permil over ∼700 m of stratigraphy. To assess the relative timing of acquisition of carbon isotopic values in the Wonoka, we performed an ‘isotope conglomerate test’ on basal Wonoka canyon-fill strata, where sediments are primarily composed of tabular-clast carbonate breccias sourced from eroded sections of the Wonoka canyon-shoulder, where the δ¹³C excursion is preserved. Bottom panel depicts a ‘positive’ isotope conglomerate test, as the observed clast δ¹³C values in this polished hand sample range between −9.0 and −5.8 permil. Other tests reveal values in clasts ranging from −12 to +5 permil in single, meter-scale breccia units. This result indicates that acquisition of carbon isotopic values was syn-depositional, and pre-dated the deposition of the canyon-fill. Cover image photographs by Christine Y. Chen. (See Stratigraphic expression of Earth's deepest δ¹³C excursion in the Wonoka Formation of South Australia by J. M. Husson, A. C. Maloof, B. Schoene, C. Y. Chen, and J. A. Higgins, this issue, p 1–45).