Detailed conodont data from the Olenekian–Anisian boundary interval of the GSSP candidate section at Deşli Caira, Romania

Abstract. The Olenekian–Anisian boundary (OAB) interval is an important time in Earth's history, reflecting the last phase of marine ecosystem recovery in the aftermath of the end-Permian mass extinction. Despite this, the Global Boundary Stratotype Section and Point (GSSP) for the base of the Anisian remains undefined. The first appearance of the conodont Chiosella timorensis has been proposed as a potential index for the boundary; however, the discovery of this conodont with ammonoids traditionally considered to be Spathian (late Olenekian) has generated doubts about its suitability as a proxy. At the GSSP candidate section at Deşli Caira, Romania, the OAB was previously drawn at the base of bed GR7, which contained the first occurrence of Ch. timorensis; however, additional collecting has shown that Spathian ammonoids persist higher in the section, and recent studies have instead placed the OAB at the base of bed 822A, approximately 3 m above the previous placement. The conodont faunas from this higher interval are less well studied than those from the lower level; furthermore, the beds in this part of the section have now been subdivided in more detail than they were previously, with bed 822 alone now being split into six sub-beds. Existing conodont faunas are only recorded as coming from bed 822, so their position relative to the new subdivision is not certain. In order to improve the precision of conodont correlation around the potential higher position for the OAB, 10 new samples were collected from bed 821 to bed 824. In addition to characterizing the fauna throughout the OAB interval, these new collections also enable the evolution of late Spathian and early Anisian conodont species to be understood in more detail.