ABSTRACT

The Cuesta del Cura and the Agua Nueva(?) in Peregrina Canyon, Tamaulipas, Santa Rosa Canyon, Nuevo Leon, and Sierra de Catorce, San Luis Potosi are composed of gray to black, well indurated, laminated, microcrystalline, cherty limestones and dark fissile limestones and calcareous shales. The fissile limestones and shales are voluminous in the Agua Nueva(?), giving it a more clastic aspect which is the basis for its separation. Typically the Cuesta del Cura grades over a short interval into the underlying lighter gray, thicker bedded, unlaminated limestones of the Tamaulipas to form a distinct change in lithic properties, but the upper contact is, obscure and necessarily arbitrary. The Cuesta del Cura varies about a typical 150 m in thickness; a maximum of 190 meters of Agua Nueva(?) was measured and sampled.

Foraminifers and calcispheres are common to abundant in most samples. Along with radiolarians, they form the grains of wackestones and packstones. Planktonic forms dominate, giving faunules a strongly pelagic aspect. Induration allowed study by thin section only. Recrystallization and two dimensional specimens made identification difficult. However, many critical species of the middle Cretaceous fauna were recognized, including: Favusella washitensis, Ticinella roberti, Globigerinelloides breggiensis, Thalmanninella subticinensis, T. ticinensis, Planomalina buxtorfi, Rotalipora appenninica, Praeglobotruncana stephani, P. delrioensis, Globigerinelloides bentonensis, Rotalipora gandolfi, R. greenhornensis, R. cushmani, and Globotruncana helvetica.

The distribution of the foregoing forms permitted division of the succession into eight informal biostratigraphic zones:

Globotruncana helvetica zone               (First occurrence)
Grandes globigerines zone                  (Interval)
Rotalipora cushmani zone                   (Total Range)
Rotalipora greenhornensis zone             (First occurrence)
Rotalipora gandolfi zone                   (Partial Range)
Planomalina buxtorfi zone                  (Total Range)
Thalmanninella ticinensis zone             (First occurrence)
Thalmanninella subticinensis               (First occurrence)

The foraminiferal distribution established a range of Middle Albian to Middle Cenomanian for the Cuesta del Cura and Middle Cenomanian to middle Turonian for the lower Agua Nueva(?).

Calcispheres present include: Calcisphaerula innominata, Pithonella ovalis, P. trejoi, Stomiosphaera conoidea, and S. sphaerica. The ranges reported for these forms are long. Their distribution reinforced foraminiferal implications in a general way.

Microcalamoides diversus, (forma C) of unknown affinity occurs in the basalmost few meters of the Cuesta del Cura, suggesting correlation with the Middle Albian.