Early and early Middle Ordovician chitinozoans from the Baldone drill core, central Latvia

Abstract

Early and early Middle Ordovician chitinozoans are relatively poorly known in Baltoscandia, thus the understanding of the early diversification of the group, as well as its biostratigraphic utility, is limited. In this paper, we document the distribution of chitinozoans in the Floian and lower Darriwilian strata of the Baldone drill core from central Latvia, a region from where very limited data on chitinozoans have hitherto been available. The Baldone section hosts one of the thickest upper Lower to lower Middle Ordovician sequences in eastern Baltoscandia and is represented by ca 85 m of red-coloured, mottled and less commonly grey marls and limestones. Chitinozoans were collected from 20 samples, revealing altogether at least 13 genera and 35 species. The lowermost productive sample, attributed to the lower Floian, represents one of the oldest chitinozoan faunas from Baltica. The upper Floian and Dapingian redbeds are barren of chitinozoans, but the lower Darriwilian Šakyna and Baldone formations contain a rich and wellpreserved assemblage with range-through taxonomic diversity reaching up to 19 species per sample. The Baldone section provides new insights into the distribution of the regional biozonal species Cyathochitina regnelli, which is characteristic of the Kunda Regional Stage in Estonia and Sweden. Several other biostratigraphically significant species of Cyathochitina, Conochitina and Lagenochitina that are typical of other regions were also recovered. They suggest links with chitinozoan assemblages of other continents during the early Darriwilian. Based on the rich collection at hand, chitinozoan diversity estimates for early Darriwilian are increased, and four new chitinozoan species are described: Bursachitina baldonia, Conochitina ulsti, Eremochitina? procera and Sphaerochitina? latviensis.

Chitinozoan biostratigraphy of the regional Arenig Series in Wales and correlation with the global Lower–Middle Ordovician series and stages

“…There are no complete specimens of T. granbyensis in the Welsh assemblage, but the largest specimen measures more than 600 μm and the specimens have the typical ovoid apex with a carina that corresponds to the description given by Grahn et al (1996). Conochitina cucumis and Tanuchitina granbyensis highlight increasing affinities between the Welsh and Baltoscandian assemblages during the Dapingian and early Darriwilian, in addition to Cyathochitina calix, although the latter was not found in association with the others in central Latvia (Nõlvak et al 2021).…”

“…The other forms restricted to Assemblage 4b have so far only been recorded lower or higher in the Ordovician succession. Conochitina redouanei and Cyathochitina touggourtensis were both described by Oulebsir and Paris (1993) from the Eremochitina brevis Biozone (upper Floian) of Algeria; Lagenochitina lata has been recorded from the Tremadocian of Baltoscandia (Liang et al 2017;Nõlvak et al 2019), and the Tremadocian and Floian of South China (Wang et al 2005;Chen et al 2009;Liang et al 2018); and Tanuchitina granbyensis has been described and recorded from the Darriwilian Stage of Sweden (Grahn et al 1996) and Latvia (Nõlvak et al 2021). There are no complete specimens of T. granbyensis in the Welsh assemblage, but the largest specimen measures more than 600 μm and the specimens have the typical ovoid apex with a carina that corresponds to the description given by Grahn et al (1996).…”

“…Conochitina cucumis and Tanuchitina granbyensis highlight increasing affinities between the Welsh and Baltoscandian assemblages during the Dapingian and early Darriwilian, in addition to Cyathochitina calix , although the latter was not found in association with the others in central Latvia (Nõlvak et al . 2021).…”

Biostratigraphy and palaeogeographic implications of Ordovician and Silurian chitinozoa from the High Zagros Mountains, Northern Persian Gulf, Iran

“…Paris (1990) stated that five genera such as Armoricochitina, Eremochitina, Velatachitina, Sagenochitina, and Siphonochitina, appear to be restricted to the North Gondwana Domain during the Ordovician when this realm was located in relatively high latitudes. Later on, Aremoricochitina, Eremochitina, and Sagenochitina were also recorded from Baltica (Nõlvak and Grahn 1993;Hints and Nõlvak 2006;Nõlvak et al 2019Nõlvak et al , 2022. Even if many cosmopolitan species are known from equatorial and circumpolar palaeolatitudes (e.g.…”

Latest Ordovician age of the Spinachitina fragilis Chitinozoan Biozone in Baltoscandia

“…We examine the topotypic specimens of S. fragilis and analyse the distribution of coeval chitinozoans in other East Baltic sections in order to provide insights into the taxonomic puzzle and the latest Ordovician chitinozoan biostratigraphy. The studied collection has been obtained using conventional microfossil extraction techniques (Nõlvak et al 2022) and is deposited at the Department of Geology, Tallinn University of Technology (institutional abbreviation GIT).…”