Acerca del límite Cretácico-Terciario en México

Abstract

Based on planktonic foraminifera the Cretaceous/Tertiary boundary is established in Mexico. In the Tampico region this boundary lies within the Méndez Formation. The formerly established Cretaceous/Tertiary boundary, i.e., the extintion of Abathomphalus mayaroensis (Bolli) or the first evolutive appearance of Globigerina eugubina Luterbacher and Premoli-Silva is rejected instead, it is proposed that the Cretaceous/Tertiary boundary to be placed at the top of the A. mayaroensis/G. eugubina Interval-Zone. On the other hand it is demonstrated that the Cretaceous/Tertiary boundary represents a transitional change in planktonic foraminiferal fauna. This transition in faunal change already takes place in the highest Maestrichtian.