The Bohemo‐Iberian regional chronostratigraphical scale for the Ordovician System and palaeontological correlations within South Gondwana

Abstract

The Bohemo‐Iberian regional scale for South Gondwana, involving the ‘Mediterranean Province’, comprises five regional stages (Arenigian, Oretanian, Dobrotivian, Berounian and Kralodvorian) plus the global Tremadocian and Hirnantian. The predominance of shallow‐water taxa in those high‐latitude faunas imposes serious difficulties for correlating the regional succession with the formal global chronostratigraphy because of the almost total absence of the key graptolites and conodonts defining the base of the standard series, stages and stage slices. Instead, the abundant benthic faunas (trilobites, brachiopods, molluscs, echinoderms) of South Gondwanan origin largely dominated in the area from the middle Darriwilian to the late Katian. The poleward faunal migration of originally Avalonian, Baltic, Laurentian and even Asiatic taxa during the Boda Event of global warming progressively ends with the endemicity in the region, where the ensuing benthic assemblages were severely affected by the Hirnantian glaciation. The regional scale significantly improves the precision of correlations between Ordovician strata from SW and central Europe, North Africa and a large part of the Middle East. An updated record of palaeontological data from areas where Mediterranean faunas remain practically unknown, or are still poorly investigated, is also included. Palaeobiogeographical relationships based on the distribution of faunas across South Gondwana are suggested as an improvement for positioning many territories in modern palaeogeographical reconstructions and offer a constructive approach to problems related to the pre‐Variscan and pre‐Alpine orogenic puzzles.

A Gondwanan perspective on the Ordovician Radiation constrains its temporal duration and suggests first wave of speciation, fuelled by Cambrian clades

“…() for the Cambrian and Gutiérrez‐Marco et al . () for the Ordovician. We have partitioned the locality‐based occurrences of brachiopod species into stage slices.…”

An Upper Ordovician (Katian) trilobite fauna from the Lower Ktaoua Formation, Morocco

“…In profile, the pygidium is convex behind the axis. The deeply curved profile of the pygidium is like that of the type species of Heterocyclopyge from the lower Katian (see Gutiérrez-Marco et al 2017) Vinice Formation of Bohemia (Marek 1961), but that species has a clearly defined pygidial border and a blunt tip to the pygidial axis. H. shelvensis (Whittard 1961, pl.…”

Middle Ordovician acritarchs and problematic organic-walled microfossils from the Saq-Hanadir transitional beds in the QSIM-801 well, Saudi Arabia

“…This stratigraphic interval corresponds to the upper part of the Arenigian, Oretanian to part of the Dobrotivian in the Bohemia-Iberian chronostratigraphic scale of Gutiérrez-Marco et al (2016). This Darriwilian MFS, named O30, is comparable in importance to the S10 in the early Silurian (Haq and AlQhatani, 2005).…”

“…Moreover, some trace fossils are also present at the Saq/Hanadir boundary (ElKhayal and Romano, 1988;Seilacher, 2000). The details of sedimentary facies and faunas have been described in a previous paper (Le Hérissé et al, 2007), and supplementary information on other stratigraphically equivalent localities can be found in Ghavidel-Syooki et al (2014) and Gutiérrez-Marco et al (2016). The age of the Hanadir Member, originally regarded as Early Ordovician (Helal, 1964), was re-assigned on palynological evidence to the Darriwilian, i.e., late Arenig to Llanvirn of the British terminology (Al-Hajri, 1995).…”

“…The difficulty arises because the faunas used for the definition of stratotypes in deep-water facies of Canada and China are hardly recognized in inner-shelf facies of the south polar Gondwana and peri-Gondawanan areas. For this reason, some regional schemes have been recently introduced, such as the Bohemo-Iberian (= "Mediterranean") chronostratigraphic scale in the South Gondwana paleobiogeographical region (Gutiérrez-Marco et al, 2016).…”