The calpionellid crisis - the defining marker for the Jurassic/Cretaceous boundary in all continents

In latest Tithonian times, in the Crassicollaria colomi Subzone, dominant Crassicollaria species suffered a decline. Next, the ultimate calpionellid crisis occurred in the Calpionella alpina Subzone, where practically nothing, but the taxon C. alpina, survived. The same succession of calpionellid associations and the same crisis has been demonstrated in all continents in a large body of literature, as we illustrate it herein. The event, and the base of the Alpina Subzone that it marks, is the outstanding level for definition of the Tithonian/Berriasian (J/K) boundary.
   This level is also close to the original top of the “Portlandian”, d’Orbigny’s topmost Jurassic stage. And, in Tethys, close above the ammonite level (Jacobi Subzone) that was previously used to define the boundary. In the Jacobi Subzone, the appearance of the ammonite genus Delphinella acts as a proxy for the base of the calpionellid Alpina Subzone. In the Caribbean and Mexico, the Alpina Subzone is also proved. In the Andes, the Alpina subzone’s base lies close to the base of the ammonite Substeueroceras koeneni Zone, and it is marked by the last appearance of Calpionella elliptalpina, as it is at sites in Tethys. No other boundary level that has been suggested in the J/K interval has such a strong primary marker, and no other has so many proxies to support it.