Foraminifers and Calcispheres from Cuesta del Cura and Lower Agua Nueva(?) Formations (Cretaceous), East-Central Mexico: ABSTRACT

Abstract

This study is based on measured and sampled sections in Peregrina Canyon, Tamaulipas, Santa Rosa Canyon, Nuevo Leon, and at several localities in the Sierra de Catorce, San Luis Potosi. All sections included some covered intervals. The Cuesta del Cura and the Agua Nueva(?) 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 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 averages 150 m in thickness; a maximum of 190 m 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 apenninica, 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 zone (First occurrence). The foraminiferal distribution establishes 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 generally reinforced foraminiferal implications. Microcalamoides diversus (forma C) of unknown affinity occurs in the basalmost few meters of the Cuesta del Cura, suggesting correlation with the middle Albian. End_of_Article - Last_Page 1560------------