Late Bajocian bioevents of ammonoid immigration and colonization in the Arequipa Basin (Pumani River area, Ayacucho, southern Peru).

Abstract

Strata of the Socosani Formation in the Pucayacu and
Pumani sections (Ayacucho Department, Peru), along
several kilometres, have yielded Upper Bajocian
ammonoid fossil-assemblages characterized by the
occurrence of juvenile individuals belonging to endemic or
pandemic taxa, such as Megasphaeroceras and
Spiroceras respectively. In addition, certain Bajocian taxa
relatively common in the Mediterranean-Caucasian
Subrealm, but very scarce in the Eastern Pacific
Subrealm, such as the strigoceratid Cadomoceras and the
phylloceratid Adabofoloceras, occur in this area. These
Late Bajocian bioevents of regional appearance of
immigrant ammonoids and even sustained colonization
should be associated with an episode of maximum
deepening, maximum relative sea-level rise and highest
oceanic accessibility of a Bajocian-Bathonian
deepening/shallowing palaeoenvironmental cycle in the
Arequipa Basin, during the Late Bajocian Niortense
Biochron.