Early–Middle Jurassic brachiopods from Ponor Mountain, Western Balkan Mountains, Bulgaria; taxonomy, biostratigraphy and occurrence in the context of the early Toarcian Oceanic Anoxic Event

ABSTRACT

An upper Pliensbachian–Aalenian brachiopod succession is reported from Ponor Mountain, Western Balkan Mountains, Bulgaria. This includes nine species (6 rhynchonellides and 3 terebratulides) from eight genera. A new genus Bulgariarhynchia and two new species, Bulgariarhynchia ponorensis and Capillirhynchia brezenensis, are formally described. A single species Homoeorhynchia ? aff. prona was found in the upper Pliensbachian. Most of the brachiopods derived from the Toarcian–Aalenian interval, and comprise: Pseudogibbirhynchia jurensis, Rhynchonelloidea angulata, Globirhynchia subobsoleta, Sphaeroidothyris uretae, Lobothyris? hispanica, and Telothyris jauberti. The brachiopod assemblages were dated using coeval ammonite biostratigraphy. Both ammonites and brachiopods display clear northwest European affinities. The new brachiopod taxa are considered autochthonous for the Balkan Mountains. Three biofacies (BF2, BF3 and BF5) were recognised and implied alternating suboxic to anoxic bottom water conditions. A few geochemical proxies are indicative of the early Toarcian Oceanic Anoxic Event (T-OAE) in the stratigraphic column. The main T-OAE pulse was fixed at the coeval positive δ¹³C and negative δ¹⁸O excursions, as well as increases in Hg/TOC ratios and redox-sensitive elements. The late Pliensbachian–earliest Toarcian time span was found to be the most hostile for the brachiopods. Above it, brachiopods lived in less stagnant environments.urn:lsid:zoobank.org:pub:22EF76B7-6A4B-4E54-A5BC-38C87125253E

KEYWORDS:

• Brachiopods
• taxonomy
• biostratigraphy
• early Toarcian Anoxic Event
• Bulgaria

Acknowledgments

The authors are thankful to the Editor-in-Chief Gareth Dyke, the reviewers José F. Baeza-Carratalá (University of Alicante), Michael Sandy (University of Dayton), and Alfréd Dulai (Hungarian Natural History Museum, Budapest) for their useful comments and remarks that helped to improve the manuscript. We are also grateful to Fernando García Joral (Complutense University, Madrid) and Vladan Radulović (University of Belgrade) for their useful taxonomic comments and remarks that helped to improve the manuscript. The research was supported by the Ministry of Science, Technological Development and Innovatin of the Republic of Serbia, Project No. 451-03-68/2022-14/200126 (grant to B.V.R.). This study was funded by the National Science Program “Environmental Protection and Reduction of Risks of Adverse Events and Natural Disasters”, approved by the Resolution of the Bulgarian Council of Ministers (No. 577/17.08.2018), and supported by the Bulgarian Ministry of Education and Science (Agreement No. DO1-271/09.12.2022) (grant to LM). Shell microstructure studies were supported by Synthesis Project (of the EC Research Infrastructure Action under the FP6), a SE-TAF-3928 Project of NMD (undertaken at the Swedish Museum of Natural History, Stockholm, 2008) and also partially supported by a Paleontological Society Sepkoski Grant to NMD for 2008.

Disclosure statement

The authors have no funding or conflicts of interest to disclose.