03058nas a2200229 4500008004100000245015100041210006900192300001200261490000800273520230000281653001602581653002302597653002002620653002302640653001902663653002202682100001602704700001402720700002002734700002002754856005402774 2013 eng d00aCambrian Evolutionary Radiation: Context, Correlation, and Chronostratigraphy--Overcoming Deficiencies of the First Appearance Datum (FAD) Concept0 aCambrian Evolutionary Radiation Context Correlation and Chronost a133-1720 v1233 a

Use of the first appearance datum (FAD) of a fossil to define a global chronostratigraphic unit's base can lead to intractable correlation and stability problems. FADs are diachronous—they reflect species' evolutionary history, dispersal, biofacies, preservation, collection, and taxonomy. The Cambrian Evolutionary Radiation is characterised by diachronous FADs, biofacies controls, and provincialism of taxa and ecological communities that confound a stable Lower Cambrian chronostratigraphy. Cambrian series and stage definitions require greater attention to assemblage zone successions and non-biostratigraphic, particularly carbon isotope, correlation techniques such as those that define the Ediacaran System base. A redefined, basal Cambrian Trichophycus pedum Assemblage Zone lies above the highest Ediacaran-type biotas (vendobionts, putative metazoans, and calcareous problematica such as Cloudina) and the basal Asteridium tornatum–Comasphaeridium velvetum Zone (acritarchs). This definition and the likely close correspondence of evolutionary origin and local FAD of T. pedum preserves the Fortune Head, Newfoundland, GSSP of the Cambrian base and allows the presence of sub-Cambrian, branched ichnofossils. The sub-Tommotian-equivalent base of Stage 2 (a suggested “Laolinian Stage”) should be defined by the I′/L4/ZHUCE δ13C positive peak, bracketed by the lower ranges of Watsonella crosbyi and Aldanella attleborensis (molluscs) and the Skiagia ornata–Fimbrioglomerella membranacea Zone (acritarchs). The W. crosbyi and A. attleborensis FADs cannot define a Stage 2 base as they are diachronous even in the Newfoundland “type” W. crosbyi Zone. The Series 2 base cannot be based on a species' FAD owing to the provincialism of skeletalised metazoans in the Terreneuvian–Series 2 boundary interval and global heterochrony of the oldest trilobites. A Series 2 and Stage 3 (a suggested “Lenaldanian Series” and “Zhurinskyan Stage,” new) GSSP base is proposed at the Siberian lower Atdabanian δ13C IV peak—which correlates into South China, Avalonia, and Morocco and assigns the oldest trilobites to the terminal Terreneuvian Series.

10aFAD concept10aGlobal correlation10aLaolinian Stage10aLenaldanian Series10aLower Cambrian10aZhurinskyan Stage1 aLanding, E.1 aGeyer, G.1 aBrasier, M., D.1 aBowring, S., A. uhttp://dx.doi.org/10.1016/j.earscirev.2013.03.008