Propiedades magnéticas en varias secciones del límite Cretacico-Terciario

Resumen

A characterization of the magnetic properties of the sediments spanning the Cretaceous-Tertiary (K-T) boundary has been carried out in different sections in Spain and northeastern Mexico. The aimof this study is to check the possibility that rock magnetic properties can serve as a macroscopictracer of the well known geochemical, mineralogical and petrologic anomalies associated with theK-T boundary layer, anomalies that are widely view as world-wide distributed consequences of theimpact of a large (~10 km) extraterrestrial body. Several magnetic parameters have been measured:bulk magnetic susceptibility, hysteresis cycles and parameters, IRM acquisition curves, thermaldemagnetization of an IRM imparted along three orthogonal axis, thermomagnetic curves and magnetic behavior at low temperatures. A clear magnetic signature has been found in association withthe reddish iridium-rich layer that defines the K-T boundary in well preserved distal sections (Agostand Caravaca), consisting mainly in an abrupt increase in magnetic susceptibility and a decreasein remanence coercivity. Its association with the diagenetically altered extraterrestrial fraction ot theimpact ejecta is strongly suggested by the behavior observed in El Mimbral proximal section, inwhich the magnetic anomaly is associated uniquely to the finer fraction of the ejecta.