Report on the 6th International Meeting of the IUGS Lower Cretaceous Ammonite Working Group, the Kilian Group (Vienna, Austria, 20th August 2017)
Résumé
The 6th Kilian Group meeting of the IUGS Lower Cretaceous Ammonite Working Group (the Kilian Group) was held in Vienna, Austria, 20th August 2017. The Group mainly discussed the standard zonation that is suitable for and based mainly on ammonite data of the Mediterranean Province of the Mediterranean Caucasian Subrealm (Tethyan Realm). Some changes have been made on three stages. The uppermost part of the Berriasian is now characterised by the Tirnovella alpillensis Zone, that is subdivided into a lower T. alpillensis Subzone and an upper \textquotedblleftThurmanniceras\textquotedblright otopeta Subzone; the T alpillensis (Sub-)Zone is here defined by the first appearance datum (FAD) of the index-species. For the Valanginian, the Neocomites premolicus Subzone is introduced in the lower part of the \textquotedblleftThurmanniceras\textquotedblright pertransiens Zone. The FAD of N. premolicus occurs at the base of the \textquotedblleftT.\textquotedblright pertransiens Zone. So this subzone starts at the base of the \textquotedblleftT.\textquotedblright pertransiens Zone and provisionally ends at the last occurrence of N. premolicus as the upper part of the zone is not characterised by a subzone for the moment. For the Barremian, the former Holcodiscus fallax, Nicklesia didayana, Heinzia communis, Subtorcapella defayae, Coronites darsi, Heinzia caicedi and Anglesites puzosianum horizons have been abandoned. In agreement with systematic positions, the term \textquotedblleftauctorum\textquotedblright is deleted for Taveraidiscus hugii, the index-species of the first zone of this stage. The Kotetishvilia compressissima Zone is subdivided into a lower Holcodiscus fallax Subzone and an upper Holcodiscus caillaudianus Subzone. The Barrancyloceras barremense Subzone (upper subzone of the Toxancyloceras vandenheckii Zone) is replaced by the Gassendiceras alpinum Subzone. The Imerites giraudi Zone is kept but its base should be now defined by the FAD of 1. dichotomus, which marks the inception of the genus Imerites. For certain stratigraphic intervals the Group discussed and in some cases strengthened the previous correlations between the standard Mediterranean zonation with the different ammonite zonal schemes of other provinces and realms. Some members of the Group presented the possibility of using regional stages as secondary standards, in accordance with the recommendations of the International Commission on Stratigraphy. The report concludes with an appreciation of the French ammonitologist Jean-Pierre Thieuloy deceased in 2017, the nomination of a vice chair, membership, future work and next meeting of the Kilian Group. (C) 2018 Elsevier Ltd. All rights reserved.