Trilobites and biostratigraphy of the Kuonamka Formation, northern Siberian Platform (Olenek River)

Abstract

A study of triobite distribution allowed a biostratigraphic subdivision of the Kuonamka Formation section exposed in the middle reaches of the Olenek River (18 km downstream of the village of Olenek). Through detailed description of the section, a biostratigraphic subdivision down to the level of biozones and faunal beds was performed. These are beds with Calodiscus–Triangulaspis annio, Delgadella ultima–Bergeroniellus expansus Zone, Lermontovia dzevanovskii–Neopagetina orbiculata Zone, Anabaraspis Zone, Cheiruroides arcticus– Pagetia horrida Zone, Kounamkites Zone, Triplagnostus gibbus Zone, and beds with Tomagnostus fissus–Paradoxides sacheri. These biostratigraphic subdivisions were correlated with regional zones of the Siberian Platform. The study also provides analysis of trilobite assemblages from the Lower/Middle Cambrian boundary interval, which was identified in the studied section and other previously described sections (Nekekit, Molodo, Boroulakh Rivers). In the studied section, the base of the Middle Cambrian is defined by the FAD of Cheiruroides arcticus, i.e., at the base of the Cheiruroides arcticus–Pagetia horrida Zone. This level correlates with a presumed lower boundary of Stage 5 of a new International Stratigraphic Chart for the Cambrian System.

Biostratigraphy and taxonomy of Drumian (middle Cambrian) agnostid trilobites of the Manuels River Formation, Avalonian Newfoundland, Canada

“…1990; Høyberget & Bruton 2008) and the T. fissus Zone of Wales and Siberia (Rees et al . 2014; Korovnikov & Shabanov 2016). The species was also reported from New Brunswick, Japan and Australia (Howell 1935; Kobayashi 1939; Shergold et al .…”

New trilobite assemblage from the lower Cambrian (upper Stage 4) of the Lake Zone, western Mongolia

“…Among fossils only assigned to genus level ( Dinesus , Eoptychoparia , Kootenia , Ogygopsis , Olenoides , Pagetides , Proerbia ), only Proerbia has a range within Stage 4, with the other genera abundant in both Wuliuan and the Stage 4. Among fossils assigned to species level, Chondragraulos minussensis Lermontova, 1940, has a range entirely restricted to the upper Stage 4, and Amecephalus laticaudum (Resser, 1939a) can be extended to the Wuliuan (Chernysheva 1961; Egorova and Savitsky, 1969; Egorova et al, 1976; Korovnikov and Shabanov, 2016; Pegel et al, 2016, and other references in systematic paleontology). Therefore, all these taxa are known to range into the upper Stage 4 ( Lermontovia grandis Zone to Ovatoryctocara - Schistocephalus [= Enixus ] Zone), and it would seem more reasonable on the balance of evidence to suggest a Stage 4 age assignment.…”