Biogeographic shifts in a transgressive succession: the Cambrian (Furongian, Jiangshanian; Latest Steptoean–earliest Sunwaptan) agnostoid arthropodsKormagnostellaRomanenko andBiciragnostusErgaliev in North America

Abstract

The first records of the upper Cambrian agnostoid genera Kormagnostella, E. Romanenko, in Romanenko and Romanenko, 1967, and Biciragnostus F. Ergaliev, in Eraliev and Ergaliev, 2001, in Laurentian North America are from a narrow stratigraphic interval in the Steptoean–Sunwaptan boundary interval (Furongian, Jiangshanian) of Nevada and Utah. In Nevada, both genera occur in a condensed bioclastic lag below a major flooding surface, and Kormagnostella also appears in a transgressive interval in Utah. Immigration of these genera is associated with sea level rise, and also with faunal turnover. Biciragnostus is confined to the latest Elvinia Zone, immediately below the onset of a trilobite and agnostoid extinction event at the base of the Irvingella major Zone (basal Sunwaptan). Kormagnostella is present in the latest Elvinia Zone, and has its highest occurrence in the I. major Zone. Stratigraphic data from the Karatau-Naryn Terrane, Kazakhstan indicate that both genera disappear near the local extinction of Irvingella, suggesting that faunal turnover in that region may have been broadly correlative with the more profound extinction in Laurentia. New species are Kormagnostella advena, K. insolita and Biciragnostus viator.

Persistent oceanic anoxia and elevated extinction rates separate the Cambrian and Ordovician radiations

“…The basal Paibian (base Steptoean) extinction has been identified worldwide (Palmer, 1984;Saltzman et al, 2000), and it is becoming apparent that younger events are also global in scope (Westrop and Adrain, 2013 Taylor et al, 2012). The trilobite extinction begins at the base of this zone in Utah, Oklahoma, and western Texas (Stitt, 1983;Ethington et al, 1987;Miller et al, 2003;Taylor et al, 2004Taylor et al, , 2012Adrain et al, 2014), and is nearly coincident (within 5 m of section) with a conodont extinction at the transition from the Rossodus manitouensis zone to the so-called Low Diversity Interval (Ethington et al, 1987;Ji and Barnes, 1993).…”

Trilobites from theCedaria prolificaZone (Cambrian, upper Guzhangian) of the Precordillera of Mendoza, western Argentina

“…), elongate, parallel-sided or posteriorly expanded pygidial axis reaching posterior border furrow, weak to effaced transaxial furrows, and broad cephalic and pygidial marginal furrows. As stated by Westrop and Adrain (2013) (Walcott, 1884, pl. 9, fig.…”

“…Remarks. -Palmer (1954a), Robison (1988), Shergold et al (1990), Peng and Robison (2000), and Westrop and Adrain (2013) discussed in detail the scope of Kormagnostus Resser, 1938. This genus is characterized mainly by having an effaced anteroglabella, a well-defined to partially effaced pygidial axial furrow, a wide (tr. ), elongate, parallel-sided or posteriorly expanded pygidial axis reaching posterior border furrow, weak to effaced transaxial furrows, and broad cephalic and pygidial marginal furrows.…”

Late Cambrian (middle Furongian) shallow-marine dysoxic mudstone with calcrete and brachiopod–olenid–Lotagnostusfaunas in Avalonian Cape Breton Island, Nova Scotia

“…The disappearance of Olenus along with such non-olenid genera as Proceratopyge Wallerius, 1895 may well record the same extinction interval as in Laurentia, followed by the immigration of brachiopods. That is, the end-Steptoean extinction event (or the end of the ‘Pterocephaliid Biomere’; Westrop & Cuggy, 1999) is best expressed in Laurentia but can also be identified in other continents and terranes (see also Westrop & Adrain, 2013 for evidence that this extinction can be recognized in the Karatau–Naryn Terrane of Kazakhstan).…”