Exotic trilobites from the uppermost Cambrian Series 3 and lower Furongian of Sweden

Abstract

ABSTRACT:Żylińska, A., Weidner, T., Ahlgren, J. and Ahlberg, P. 2015. Exotic trilobites from the uppermost Cambrian Series 3 and lower Furongian of Sweden. Acta Geologica Polonica, 65 (1), 21-67. Warszawa.Seventeen taxa of exotic trilobites representing eight families are described from the olenid-and agnostoid-dominated strata of the uppermost Cambrian Series 3 and lower Furongian alum shale facies of Sweden and from glacial erratic boulders of Denmark. Only five taxa are assigned to species level, i.e., Maladioidella abdita (Salter, 1866), Olentella rara (Westergård, 1922), Pedinocephalus peregrinus (Henningsmoen, 1957), Ptychoparia pusilla (Westergård, 1922), and Westergaardella olenorum (Westergård, 1922), whereas the others are left under open nomenclature or remain unrecognized. Most are described for the first time from the Cambrian of Scandinavia. Their affinities point to a strong connection with East Gondwana, Laurentia, Kazakhstania and Siberia. Exotic trilobites appear in the succession directly after periods of very low oxygen concentration in the Alum Shale Sea; their occurrences correspond to the ranges of agnostoid arthropods in the succession and seem to be linked to global transgressive events causing an influx of cool and/or oxygen-depleted waters onto the shelf of the Baltica palaeocontinent.

The Furongian (upper Cambrian) Alum Shale of Scandinavia: revision of zonation

“…Other faunal elements are rare but include a few polymerid and agnostoid taxa (Westergård , ; Henningsmoen ; Ahlberg & Ahlgren ; Żylińska et al . ). Ahlberg () discussed the intercontinental correlation potential of the co‐occurring agnostoid species (see also Rushton ).…”

“…For a comprehensive review of non‐olenid trilobites from the Furongian of Scandinavia, see Żylińska et al . ().…”

“…Rare non‐olenid trilobites occur sporadically (Westergård ; Terfelt & Ahlgren ; Żylińska et al. ). Although they are important for intercontinental correlations, they have not been used for defining bio‐ and chronozones in the Furongian of Scandinavia.…”

Brief oxygenation events in locally anoxic oceans during the Cambrian solves the animal breathing paradox

“…The fauna was therefore adapted to opportunistically take advantage of the short-term re-oxygenation episodes embedded within a long-term de-oxygenated situation. Fossiliferous intervals are dominated by only 1–2 species that occur in immense numbers, whereas trilobite species known from better ventilated environments elsewhere are exceedingly rare in the Alum Shale 23–25 . In this way, frequent bottom-water ventilation in oxygen-restricted Cambrian oceans created intermittent habitats for opportunistic animals.…”

Elviniid trilobites from the Elvinia Zone (late Cambrian, Furongian) of Mendoza, western Argentina

“…While Elvinia Walcott, 1924 is confined to Laurentia, Irvingella has been recorded from diverse paleocontinents at different latitudes (Żylińska et al, 2015). Such a cosmopolitan distribution may have been facilitated by the development of pelagic habits at some point of the life cycle (Rushton, 1967; Fortey, 1985; Żylińska et al, 2015; Chatterton and Gibb, 2016). Most of the Irvingella occurrences lie at or near the base of the Jiangshanian global stage; in Laurentia it ranges from the upper Steptoean to the basal Sunwaptan; in Australia it defines the base of the Iverian stage; in China it comes from the middle and late Changshanian; and in Kazakhstan and Siberia, from the late Sakian (Geyer and Shergold, 2000; Peng et al, 2012).…”