Biostratigraphical significance of a new trilobite fauna from the Harkless Formation (upper Stage 4, Series 2, Cambrian), Nevada, USA

Since 1990, it has been proposed that olenelloid and paradoxidid trilobites overlapped in age, even though the former represents the traditional lower Cambrian of Laurentia and the latter represents the traditional middle Cambrian of the `Acadobaltic Realm' (i.e., Baltica, West Gondwana) and Siberia. Subsequent studies on biostratigraphical correlation and radiometric ages have supported this conclusion. The recent discovery of the oryctocephalid trilobites Oryctocephalops frischenfeldi Lermontova, 1940, Ovatoryctocara cf. O. yaxiensis Yuan et al. 2009, and Protoryctocephalus? aff. P.? arcticus Geyer & Peel 2011 from the mid-Dyeran Stage portion of the Harkless Formation, Nevada, not only verifies a direct overlap of olenelloid and paradoxidine trilobites, but also indicates that the upper six olenelloid biochrons of the Cordilleran margin of Laurentia are age equivalent to the range of the oldest paradoxidines. This new fauna from the Harkless Formation also allows for a precise biostratigraphical correlation of this level to age-equivalent strata in Greenland, the Siberian Platform, and South China. This correlation indicates that the upper Dyeran and a portion of the midDyeran Stage are biostratigraphically equivalent to the Bonnia-Pagetides elegans Biozone of Greenland, the Ovatoryctocara Biozone (which contains Paradoxides (s.l.) in its lower part) of the Siberian Platform, and the Protoryctocephalus arcticus to Bathynotus kueichouensis-Ovatoryctocara sinensis biozones of the South China palaeocontinent.

Automated summary

Studies since 1990 have shown that olenelloid and paradoxidid trilobites overlapped in age, contrary to their traditional placement in different Cambrian stages. Recent findings in Nevada provide further evidence of this overlap and allow for precise correlation with equivalent strata in Greenland, Siberia, and South China.