Magnetostratigraphy of the Cretaceous-Tertiary boundary at Agost (Spain)

Abstract

A detailed magnetostratigraphic investigation of the Agost section (Spain) containing the Cretaceous-Tertiary (K/T) boundary is reported. Thermal demagnetization--contrary to alternating field demagnetization--succeeds in revealing the polarity of the characteristic remanent magnetization, although an overlap in blocking temperature spectrum exists with a normal polarity, secondary magnetization component. The K/T boundary occurs at two-thirds from the base of a reversed polarity zone and by comparison with earlier results [1] this polarity zone is correlated to chron C29r. Linear regression of sedimentation rates in other sections with an established magnetostratigraphy and containing the K/T boundary yields an age of 66.45 Ma for this boundary. On the basis of this age and the magnetic reversal ages of the Berggren et al. [13] polarity time scale, new first appearance (FAD) ages around the K/T boundary are suggested for the planktonic species Morozovella trinidadensis (Bolli) (66.04 Ma), Morozovella pseudobulloides (Plummer) (66.34 Ma), Eoglobigerina taurica (Bang) (66.41 Ma) and "'Globigerina eugubina'" Luterbacher & Premoli Silva (66.43 Ma).