Borehole magnetics: Magnetostratigraphy: An example from UNAM-7, Chicxulub impact crater

Magnetic reversal boundaries define global chronostratigraphic surfaces. As such, rapid identification of these boundaries is useful for constructing chronologically correct correlations and for defining fault displacements. Borehole deviation surveys which use a tri-axial fluxgate sensor to provide geographic orientation also contain a record of the variation of the vector magnetic field versus depth. When the crustal component of the observed vector magnetic field is dominated by remanence minor fluctuations in the orientation of the observed vector reflect the underlying magnetostratigraphy. UNAM-7 which was drilled on the periphery of the Chixculub impact crater, Yucatan peninsula, Mexico was logged using a standard deviation probe. Processing of this data revealed a magneto-stratigraphic reversal history that is compatible with the limited paleomagnetic database, the petrophysical data, and sedimentation rates as defined by results from other boreholes.