Pushing the boundary: A calibrated Ediacaran-Cambrian stratigraphic record from the Nama Group in northwestern Republic of South Africa

New Ediacaran biota from the oldest Nama Group, Namibia (Tsaus Mountains), and re-definition of the Nama Assemblage

“…545 Ma, although the precise timing of this decline remains uncertain (Grazhdankin, 2014; Boag et al 2016; Muscente et al 2019). A distinctive global, cosmopolitan, assemblage consisting of a lower diversity of existing soft-bodied morphogroups (largely erniettomorphs with subordinate rangeomorphs, arboreomorphs and dickinsoniomorphs) persisted, with new diverse skeletal, and non-skeletal tubular fossils, and more complex traces appearing <550 Ma and continuing until at least 539 Ma (Smith et al 2017; Nelson et al 2022). Network analysis has confirmed this to be a statistically significant grouping separate from all other Ediacaran taxa, hence named the Terminal Ediacaran biozone, and further proposed to correspond to the Nama palaeocommunity (Muscente et al 2019).…”

“…Network analysis has confirmed this to be a statistically significant grouping separate from all other Ediacaran taxa, hence named the Terminal Ediacaran biozone, and further proposed to correspond to the Nama palaeocommunity (Muscente et al 2019). The Nama Assemblage was originally named after the biota found in the Nama Group, Namibia (≥550.5 to <538 Ma), where soft-bodied fossils are reported to extend from the Kliphoek Member of the Dabis Formation through the entire overlying succession until the lower Nomtsas Formation (Waggoner, 2003; Nelson et al 2022).…”

“…Calcified taxa are largely limited to carbonate strata, with Cloudina known from ca. 550 to 551 Ma (Bowring et al 2007; Bowyer et al 2023b) and persisting until 538.56 +0.08/−0.09 Ma (Nelson et al 2022). Soft-bodied taxa belong mainly to either the Rangeomorpha or Erniettomorpha, known from the siliciclastic Kliphoek Member of the upper Dabis Formation in the Kuibis Subgroup, and Spitskop Member within the Schwarzrand Subgroup, and are widely distributed throughout the Witputs Sub-basin.…”

A diverse Ediacara assemblage survived under low-oxygen conditions

“…538.8 Ma from Namibia provides a new radiometric marker for this critical transition 31 , and refs. 29 , 32 . further suggested that the Ediacaran-Cambrian boundary may be <538 Ma based on the presence of Ediacara-type fossils up to an ash bed dated to 538.3 ± 0.14 Ma in South Africa and the inference that the base of the Cambrian Period (defined bio- and chemostratigraphically) must be younger than this horizon.…”

“…The negative δ 13 C excursion seen across the Ediacaran-Cambrian boundary (BACE event 37 ) beginning at the top of the Dengying Formation in South China (where values drop to as low as −7‰) may begin in the upper Turkut Formation 25 , 26 , but the sedimentary rocks preserving the negative carbon isotope anomaly are regionally truncated at an unconformity surface below siliciclastics of the Syhargalakh Formation. Alternatively, the shift towards negative δ 13 C values in the upper Turkut Formation could correlate with the A4 anomaly, which is a negative δ 13 C excursion identified as older than the BACE event in Oman 29 , 32 . Higher in the succession, peak δ 13 C values of the Mattaia carbonate platform are potentially equivalent to those in the Zhujiaqiang Formation of South China, which are also biostratigraphically constrained to Cambrian Stage 2 based on the first appearance of N. sunnaginacus assemblage Zone fossils.…”