Abstract
The present study evaluates the significance of Triassic ostracods from the Romanian Black Sea shelf as part of a project for the understanding of the palaeoceanographical evolution of the offshore extension of the North Dobrogean Orogen. The drill core CM31, sampled from the borehole 817 Lebăda Vest drilled on the western Romanian portion of the Black Sea shelf, contains sediments of Rhaetian, Late Triassic age. The taxonomy of ostracods obtained is discussed and adds to the scientific understanding of marine ostracods during the Rhaetian stage. We document 72 species, of which seven are new: Histriabairdia pontuseuxinusensis Forel gen. et sp. nov., Bairdiacypris argonautaii Forel sp. nov., Ceratobairdia? akhilleusi Forel sp. nov., Isobythocypris atalantella Forel sp. nov., Petasobairdia amazonella Forel sp. nov., Paracypris ovidi Forel sp. nov. and Pseudomacrocypris? kerabani Forel sp. nov. Histriabairdia Forel gen. nov. is introduced to accommodate species of the Triassic–Jurassic interval previously attributed to the modern genus Anchistrocheles. These assemblages point to an outer shelf environmental with relatively normal marine oxygenation. The oldest occurrence of Pokornyopsis, found in this material, indicates that this forerunner of modern troglobitic ostracods may not have been troglobitic in the Triassic.
Highlights
Ostracods are millimetre-size crustaceans that are significant components of the meiofauna
We focus on the Triassic rocks sampled in the borehole 817 Lebăda Vest (817 LV), which provides important data regarding their lithology, microfacies, and especially concerning the outstanding content of microfossils, ostracods, foraminifers (Luka Gale, pers. com.) and conodonts (Tea Kolar-Jurkovsek, pers. com.), relevant for the Rhaetian (Late Triassic) age
An attempt to introduce a phylogeny for Permian and Triassic genera has recently been proposed, describing two lineages (Ceratobairdia lineage and Abrobairdia lineage), both derived from Petasobairdia in the early Permian (Forel & Crasquin 2020)
Summary
Ostracods are millimetre-size crustaceans that are significant components of the meiofauna. Following the high amplitude diversity fluctuations of the Early Triassic, the recovery of ostracods is considered as complete by the Anisian, Middle Triassic (e.g., Crasquin-Soleau et al 2007; Crasquin & Forel 2014) This stage witnessed the acme of a high-diversity plateau that further developed until the brink of the end-Triassic extinction, as well as the radiation of numerous taxa, including Cytheruridae and typically Triassic ornate Bairdiidae (see Forel & Crasquin 2020 for a summary). One of the major future challenges of ostracodology will be to reach a stable consensus on the classification of Bairdiidae, known from the Middle Ordovician (e.g., Becker 2001) up to today in all marine ecosystems, and to complete the ‘morphological phylogeny’ of Permian and Triassic ornate genera proposed by Forel & Crasquin (2020)
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