Towards the definition of the Jurassic/Cretaceous boundary: Report on new advances of the Berriasian Working Group of the Subcommission on Cretaceous Stratigraphy (ICS)

A brief report of the Berriasian Working Group (BWG) activities in 2021–2025 is presented. An updated multi-stratigraphical scheme for the upper Tithonian – lower Berriasian is prepared for the Tethyan domain, with suggestions towards the Boreal, Subboreal, South America (Neuquén Basin) and Russian-Siberian realms and provinces. A voting majority of the BWG recommends that the base of Berriasian should be shifted down, from the current position in the middle of M19n2n magnetosubchron (base of the Calpionella alpina Subzone), to the interval between magneto(sub)chrons M20n1r and M19r. The base of the C. alpina Subzone is an acme-type stratigraphical boundary defined as “a bloom of small spherical forms of C. alpina ”, not accompanied by first appearance datums (FADs) of calpionellid taxa, therefore its exact position is difficult to evaluate without quantitative studies. Although a new primary marker for the Jurassic/Cretaceous boundary has not yet been chosen, the interval between M20n1r and M19r contains several FADs of calpionellid, calcareous dinocyst and calcareous nannofossil taxa, most likely matching also the boundaries of radiolarian zones in the Tethys and the Pacific Realms. The interval is correlatable with the boundary interval between the middle and upper Volgian, therefore it might be applied in the Boreal Realm. An increasing amount of bio-magnetostratigraphic data from South America allows for correlation with the relatively short Corongoceras alternans Ammonite Zone. The solution would be further tested in terrestrial sections, and orbital stratigraphic model would be developed, which would facilitate long-distance correlations.