Ammonoids From the New Stenopopanoceras Transiens Subzone at the Deşli Caira Section (Middle Triassic, Northern Dobrogea, Romania), Proposed as the Candidate GSSP for the Anisian Stage

We document several ammonoid taxa from the lowermost Aegean (lower Anisian) of the Deşli Caira B section, Dobrogea (Romania), candidate section for the GSSP of the Anisian stage. The specimens were collected from beds 2827 and 822A2, and include the new genus Simionescuites, with three new species, i.e., S. dobrogeanus n. gen. n. sp, S. laevicostatus n. gen. n. sp, and S. nodiumbilicatus n. gen. n. sp; Longobarditoides caucasius Shevyrev, 1961; Pseudosageceras sp. ind.; and Sageceras sp. ind. In addition, seven specimens are assigned to Stenopopanoceras transiens Tozer, 1972.Integration of these new taxa with those described from the same stratigraphic interval by Balini et al. (2024) demonstrates that Stenopopanoceras transiens is the most common, short-ranging species within the interval between sample 822A2 Lower and 822A2 Upper. On this basis, a revision of the Paracrochordiceras–Japonites beds recognized in Chios (Greece) by Assereto (1974) is proposed. The Stenopopanoceras transiens subzone is herein established as a range subzone, representing the lower part of the Paracrochordiceras–Japonites Zone. At Deşli Caira, the latter is defined as the interval zone extending from the first occurrence (FO) of Stenopopanoceras (bed 822A2 Lower) to the last occurrence (LO) of Paracrochordiceras, presently identified in bed 2848.The S. transiens subzone is documented in the Caucasus and Iran. It can be correlated with New Zealand, whereas its occurrence in the Himalaya is uncertain. On a larger scale, the S. transiens subzone can be directly correlated with the ammonoid scale of Siberia (Arctic paleobioprovince), and precisely with the Karangatites arkhipovi subzone, first subzone of the lowermost Anisian Grambergia taymirensis Zone, on the basis of the FO of Stenopopanoceras. In Nevada (Pacific paleobioprovince), the FO of Stenopopanoceras is diachronous, being recorded in the Silberlingites mulleri zone (middle part of the lower Anisian), but the S. transiens subzone can be correlated with the lowermost Anisian Japonites welteri beds, on the basis of the FO of Paracrochordiceras. Based on the data currently available, the FOs of Stenopopanoceras and Paracrochordiceras appear to represent the most readily correlatable biostratigraphic events and are therefore considered the most suitable candidates for the selection of primary and secondary marker events for the Anisian GSSP.