PROTEROZOIC—PHANEROZOIC EON TRANSITION δ13CCARB COMPOSITES CONSTRUCTED WITH A REPRODUCIBLE DYNAMIC PROGRAMMING ALGORITHM

Current best estimates of the absolute timeline of skeletal animal appearances from the latest Ediacaran through the early Cambrian are based on visual correlations of δ¹³C_carb excursions (Maloof et al., 2010). However, one of numerous challenges to global δ¹³C_carb correlations stems from limited sampling of repeated excursions that make cycle-to-cycle matches questionable. Applying dynamic programming to the alignment of chemostratigraphic time series data, in principle, offers an objective and reproducible method of aligning records for the purposes of establishing temporal frameworks and evaluating stratigraphic completeness (Lisiecki and Lisiecki, 2002; Haam and Huybers, 2010). More recent implementations seek to provide an ensemble of plausible age models to capture alignment uncertainty, including that associated with changes in sedimentation rates among sections (Hay et al., 2019; Ajayi et al., 2020; Hagen et al., 2020). Development of a complete ensemble of plausible age models is important for evaluating hypotheses of early skeletal animal diversification.

Here we present dynamic programming-derived Cambrian Terreneuvian Series (~539 – 521 Ma) δ¹³C_carb composites for four highly fossiliferous regions: Arrowie and Stansbury Basins, South Australia (cf. Betts et al., 2018); Yangtze Platform, China (cf. Jiang et al., 2012, Li et al., 2013); Zavkhan Terrane, Mongolia (cf. Smith et al., 2016; Topper et al., 2022), and Siberian Platform (cf. Kouchinsky et al., 2007). For each of these four fossiliferous regions, we build three δ¹³C_carb composites by selecting from each dynamic programming ensemble the alignment that best (i) minimizes diachroneity between lithostratigraphic formation boundaries, (ii) minimizes diachroneity of the first appearance datums of select index fossils, and (iii) maximizes the Pearson correlation coefficient. We evaluate which combinations of regional δ¹³C_carb composites generate a stable timeline for early Cambrian fossil first appearances, and which produce timelines that deviate from prior hypotheses.