Rhaetian (Late Triassic) ostracods (Crustacea, Ostracoda) from the offshore prolongation of the North Dobrogean Orogen into the Romanian Black Sea shelf

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.

Middle Permian ostracods (Crustacea) from the Guadalupe Mountains, West Texas, USA

“…The peak of diversity of ornate Bairdiidae occurred in the Late Triassic but they were already present in the Permian (see Forel & Crasquin 2020 and references therein for a review) as illustrated for instance by the material described herein from the Middle Permian of the Guadalupe Mountains. Specifically, the confusion and instability of the conceptions of Petasobairdia Chen, 1982 and Praelobobairdia Kozur, 1991 have recently been described and discussed in Forel & Grădinaru (2020). Herein, we follow the view that Praelobobairdia is a junior synonym of Petasobairdia, as was first introduced by Becker (2001).…”

“…The classification of ornate Bairdiidae is complex and still disputed mainly because of the difficulty to unravel the taxonomic significance of their lateral ornamentation features. As detailed in Forel & Grădinaru (2020), the revision of their classification requires the addition of new characters to avoid producing another classification system that would only be a new point of view further complicating the current situation. The peak of diversity of ornate Bairdiidae occurred in the Late Triassic but they were already present in the Permian (see Forel & Crasquin 2020 and references therein for a review) as illustrated for instance by the material described herein from the Middle Permian of the Guadalupe Mountains.…”

First Evidence of Palaeo-Tethyan Upper Triassic Calcareous Nannofossils in North Dobrogean Orogen (Romania)

“…The core CM 31 drilled into the Upper Triassic sediments represents a 2 m thick limestones from depths 2623 m to 2625 m (Gale et al 2021). A rich assemblage of ostracod and foraminifera constrained a Rhaetian age for the drill core CM 31 in the borehole 817 LV Forel & Grădinaru 2020;Gale et al 2021). A Rhaetian age is also supported by the brachiopod fauna, which includes Euxinella anatolica (Bittner, 1892), Fissirhynchia fissicostata (Suess, 1854), and Rhaetina pyriformis (Suess, 1854).…”

“…Upper Triassic sediment of borehole 817 LV corresponds to 5 m thick, light grey limestones, encountered at a depth of 2620 m below Middle Jurassic black argillites (Forel & Grădinaru 2020;Gale et al 2021). Within those Jurassic sediments, the base of the drill core CM 30 includes clasts of rhyolites and Triassic limestones ).…”

Use of X-Ray Micro-Computed Tomography on Selected Upper Triassic (Rhaetian) Foraminifera From the Western Black Sea Shelf, Offshore Romania

“…The limestone is homogenous throughout the core's length and does not display any sedimentary structure, implying that it was drilled more or less along bedding. The ostracod assemblage recovered from the limestone contains some typical Rhaetian species (Forel & Grădinaru 2020). Other fossils, such as brachiopods, also constrain the Rhaetian age (Grădinaru et al 1989;Forel & Grădinaru 2020).…”