Ordovician Biostratigraphy — Index Fossils, Biozones and Correlation

Figure 2. Middle Ordovician time scale, stages, and graptolite, conodont and chitinozoan zonal schemes. The leftmost column is the chronometric time scale from Goldman et al. (2020, in Gradstein et al. 2020). Zonations and correlations for graptolites are modified from the following (and references therein) — Goldman et al. (2020), Loydell (2012), Maletz (2021), Maletz and Ahlberg (2018), VandenBerg and Cooper (1992), Cooper and Sadler (2012) and Zalasiewicz et al. (2009); for conodonts modified from Goldman et al. (2020), Albanesi and Ortega (2016), Bergström and Wang (1995), Wang et al. (2018), Zhen et al. (2020a, 2020b, 2021); Zhen and Percival (2003), Zhen and Nicoll (2009) and Zhang et al. (2019); and for chitinozoans from Goldman et al. (2020), Nõlvak et al. (2006) and Paris et al. (2004). ¹The South Gondwana graptolite zonation for the Middle Ordovician is adapted from Gutiérrez-Marco et al. (2017).