Библиотека

Wimbledon W.A.P., Reháková D., Halásová E., Lintnerová O., et al (2019) Progress with selecting a GSSP for the Berriasian Stage (Cretaceous) - illustrated by sites in France and Italy // XIVth Jurassica & Workshop of the ICS Berriasian Group, 2019, At Bratislava. Pp. 186-187.

Since 2009 the Berriasian Working Group (ISCS, ICS) has been searching for the best sequence globally to represent the Tithonian/Berriasian (Jurassic/Cretaceous) boundary. To take this forward, it has made field assessments of more than sixty localities, documenting their sequences, fossil biotas and magnetostratigraphy. only on such a sound factual basis could the best boundary markers be distinguished, prior to selecting a GSSP. Founded on this substantial study of new localities and reassessment of others, in 2016, the base of the Alpina Subzone was chosen as the most consistent marker for the base of the Berriasian: this horizon showing a well-documented turnover of calpionellid taxa, a turnover that has the widest geographical distribution of any biotic event in the J/K interval. These decisions on a primary marker were shared with, and discussed with, a wider community at the Vienna Cretaceous Symposium in 2017. There the WG agreed, again, to try to select a GSSP site that yielded, at least, results for magnetostratigraphy, calpionellids, ammonites and calcareous nannofossils, so as to give the greatest possibilities for correlation to more distant regions. In 2018, at the Berriasian workshop in Kroměříž, discussion focussed on consideration of a shortlist of seven GSSP candidates: Puerto Escaño (Spain), Brodno (Slovakia), Fiume Bosso (Italy), Torre de´ Busi (Italy), Rio Argos (Spain), Kurovice (Czech Republic), and the Drôme / Haute Alpes ( Vocontian Trough) plexus of sites (Le Chouet, Font de St Bertrand, Haute Beaume, Charens & Tré Maroua)(France). In a debate on the biotic and magnetostratigraphic attributes of each locality, their assets and negative points were assessed. fSome sites were rejected because they lacked a full complement of defining characters or had other specific defects: Puerto Escaño (condensation & aberrant nannofossil distribution), Brodno (lack of ammonites and incomplete M18r), Torre de´ Busi (no ammonites, aberrant calpionellid distribution), Kurovice (tectonised intervals close to the boundary level), and Rio Argos (no magnetostratigraphy). addition, a very extensive profile at Theodosia (Ukraine), for which there had been great hopes, was ruled out, because no coherent calpionellid zonation could be established. The final conclusion was that profiles at Fiume Bosso and in the Vocontian Basin provided the best candidates, and that documentation of these should continue, in preparation for their consideration as GSSPs – to be followed by a formal WG vote. That vote will be concluded in May 2019.

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