Magnetic-polarity stratigraphy of the Miocene type Tesuque Formation, Santa Fe Group, in the Espanola Valley, New Mexico.

Several of the type sections of the Tesuque Formation, lower Santa Fe Group, exposed near Espanola, New Mexico, have yielded a composite magnetic-polarity stratigraphy in which the 230m, fine-grained, tuffaceous middle (Skull Ridge) member is characterized by a long zone of uninterrupted reversed polarity; approximately 300m of the coarser-grained, upper (Pojoaque) member is characterized by rocks predominantly of normal polarity. Results from AF demagnetization in fields up to 300 oe and from the acquisition and removal of IRM indicate that the more stable magnetic remanence in these rocks is probably borne by detrital magnetite and therefore can be taken as a record of the geomagnetic field at or near the time of deposition. The stratigraphic utility of the results is confirmed by replication in geographically separate, lithostratigraphically equivalent sections in different fault blocks.-Author