Some index Foraminifera of the Tampico embayment area of Mexico

The Tampico Embayment Area of Mexico is broad and of low relief. It comprises the portion of the Gulf Coastal Plain extending from the Tamaulipas Mountains to a short distance south of the Panuco River. The northern oil fields are in this region. The area may be treated as a unit from a geologic standpoint. Along the coast is a narrow belt of Tertiary sediments. In the remainder of the area Cretaceous sedimentary strata are covered with a thin veneer of alluvium. The Tertiary and Cretaceous rocks contain an abundance of Foraminifera but practically no other fossils. Thus Foraminifera furnish the only available criteria for stratigraphic correlation. Travel is difficult, outcrops are rare and when found are usually deceptive in dip, physiographic expression of the underlying structure is practically absent, and lithologic differences are not sufficiently varied for differentiation of horizons. It is apparent, therefore, that the solution of structural problems related to the oil fields may be greatly aided by correlation based on the study of Foraminifera. Most of the work in correlation involves, only the formations of the Upper Cretaceous, from near the middle of the Velasco to the base of the Upper Cretaceous. These formations of the Upper Cretaceous include, the Velasco, the Mendez, the Papagallos and the San Felipe. These formations overlie the Tamaulipas limestone of Lower Cre-