PALEOMAGNETISM, STRATIGRAPHY, AND PETROLOGY OF THE UPPER CRETACEOUS ROSKRUGE VOLCANICS AT BELL MOUNTAIN, SOUTHEAST ARIZONA

Reconnaissance geologic mapping and petrologic study of the Upper Cret aceous Roskruge Volcanics at Bell Mountain in the Roskruge Mountains, southeastern Arizona, have identified five compositionally distinct as h flow tuffs, including the basal red Viopuli Tuff, which comprise six or seven separate cooling units. Previous paleomagnetic investigators inferred eleven cooling units at Bell Mountain, but insufficient info rmation was given to determine which tuffs had been sampled. This stud y was undertaken therefore to establish characteristic remanence direc tions for each tuff sheet. The available paleomagnetic data corroborat e the identification of five map units in the Bell Mountain area, but the number of independent observations is too few for the calculation of a reliable paleopole; paleosecular variation of the geomagnetic fie ld would probably not be averaged out. No correlatable tuffs are prese nt at Bell Mountain, so relative vertical axis rotations cannot be det ermined, although they are probably not large. The absence of regional ly correlatable tuffs suggests the presence of additional, potentially mineralized, volcanic centers perhaps farther north in the Roskruge M ountains or buried nearby beneath Cenozoic basin fill.