Igneous Rocks and Seepages Igneous Rocks
Either commonly, or rarely, igneous rocks occur throughout a large part of the Tampico Embayment. In the oil fields, rocks of Cretaceous and Tertiary age have been intruded by dykes and plugs of basaltic character. More rarely, the igneous rocks have been found in wells in the form of sills. The latter are more commonly found in the Middle Cretaceous and the lower part of the Upper Cretaceous in the Sierra Tamaulipas.
DeGolyer (49, Fig. 1) shows the general distribution of the igneous rocks154 east of the Sierra Madre Oriental, from the latitude of Soto la Marina in the north to a short distance south of Papantla (Fig. 18). Two zones of igneous rocks stand out predominantly: one east of the Sierra Tamaulipas in the north, and the other in the south in the Sierra Tantima155 and in a scattered belt surrounding, or radiating from, the latter. The intervening area, north and south of the Rio Pánuco, and east of the zone of the Middle Cretaceous reef limestones in the Sierra Madre Oriental has relatively few intrusions.