The end of the Ediacaran: Two new exceptionally preserved body fossil assemblages from Mount Dunfee, Nevada, USA

Abstract

Evaluation of hypotheses that relate environmental to evolutionary change across the Ediacaran-Cambrian transition has been hampered by a dearth of sections that preserve both the last appearance of Ediacaran body fossils and the first appearance of Treptichnus pedum within carbonate-rich strata suitable for chemostratigraphic studies. Here, we report two new exceptionally preserved latest Ediacaran fossil assemblages from the Deep Spring Formation at Mount Dunfee, Nevada (USA). Further, we report these occurrences in a high-resolution carbon isotope chemostratigraphic framework, permitting correlation on a regional and global scale. The lower of the two horizons, at the base of the Deep Spring Formation, hosts a body fossil assemblage that includes Gaojiashania, other vermiform body fossils, and possible Wutubus annularis interbedded with Cloudina shell beds. The upper of the two fossil horizons, in the Esmeralda Member of the Deep Spring Formation, contains Conotubus and occurs within the basal Cambrian negative carbon isotope excursion, establishing it as the youngest Ediacaran fossil assemblage discovered to date. This is the first report of Gaojiashania, Conotubus, and Wutubus in Laurentia, extending the known stratigraphic ranges and biogeographic distributions of these taxa to a global scale. These data refine the relative ages of defining characteristics of the Ediacaran-Cambrian boundary and confirm that a large perturbation to the carbon cycle and surface ocean conditions coincided with the extinction of Ediacaran organisms.

Diverse biomineralizing animals in the terminal Ediacaran Period herald the Cambrian explosion

“…1C) (Cui et al, 2016). The BACE has been shown to be slightly below the first appearance datum of Treptichnus pedum (Smith et al, 2016). It is also slightly below the Anabarites trisulcatus-Protohertzina anabarica assemblage zone and the Asteridium-Heliosphaeridium-Comasphaeridium assemblage zone (Ahn and Zhu, 2017).…”

New high‐resolution age data from the Ediacaran–Cambrian boundary indicate rapid, ecologically driven onset of the Cambrian explosion

“…From the boundary sections of the Yangtze/South China sequence, the Ediacaran–Cambrian boundary was dated between 542.6 ± 3.7 Ma and 536.3 ± 5.5 Ma (Chen, Zhou, Fu, Wang, & Yan, ). Ash beds related to this boundary are yet unknown from other relevant sections globally, such as those in the Flinders Ranges (Australia), Siberia, the Ukraine (Brasier et al., ), the White Inyo–Death Valley–Mojave regions (California) (Hagadorn, Fedo, & Waggoner, ) or the Mount Dunfee section (Nevada) (Smith et al., ).…”

“…The new timeframe allows testing of different evolutionary models for the replacement of the Ediacaran‐type biota (ETB) by the Cambrian‐type fauna (CTF) (Darroch et al., ; Laflamme et al., ; ; Muscente et al., ; Smith et al., ). We herein discuss three models, which differ significantly in the time‐scale they predict.…”

Subsidence history of the Ediacaran Johnnie Formation and related strata of southwest Laurentia: Implications for the age and duration of the Shuram isotopic excursion and animal evolution

“…In terms of chemostratigraphic constraints on age, the conspicuous excursions to -6‰ at the base and top of the Ediacaran section are well expressed in the south Laurentian sections (e.g., Petterson et al, 2011;Smith et al, 2016). The presence of the Shuram excursion in the Rainstorm Member, despite its value as a correlation tool, does little to constrain the depositional age, because unlike the tightly constrained boundary excursions, hard chronological constraints are lacking, as noted already.…”