MACAIRA, Group

UPPER CRETACEOUS-? TERTIARY (? Paleocene)

State of Guárico, Venezuela

Author of name: H. D. Hedberg, 1950.

Original reference: H. D. Hedberg, 1950, p. 1183.

Original description: J. Evanoff, 1951, p. 244-245.

Hedberg (1950, p. 1183 and 1196) used for the first time the name Macaira, in his Table of Correlation, to describe part of the lower Santa Anita, in the columns corresponding to the northeastern part of Guárico and the northwestern part of Anzoátegui. Here, the lower Santa Anita is called Vidoño. In the same table, the term Macaira appears to be the lateral equivalent of the upper Vidoño and of the lower Caratas, in the column corresponding to the northern (Barcelona) and northeastern (Santa Inés) Anzoátegui. However, in the text (op. cit., p. 1196), Hedberg, mentions that the Morros de San Francisco de Macaira, as well as the larger Morros de San Juan, are intimately associated with rudistes and Exogyra or are exposed near shales which contain a fauna of Vidoño foraminifera and these morros could possibly be as old as Middle Cretaceous. Hedberg does not assign a definite place in the geologic section, but apparently he associates the shales to the reef limestones.

The term Macaira was defined as a group by Evanoff (1951, p. 244), to describe a shale section exposed along the Fila Maestra. In the original description, Evanoff includes in the same group the morros forming limestones of San Francisco de Macaira, considering both these the limestones and the shales, as Paleocene in age, and equivalent to the Paleocene San Juan de los Morros. However, numerous samples collected from the morros de Macaira, have been subjected to paleontological investigation showing absence of nummulitic, orbitoidal fauna or algal flora. De Civrieux (private information), indicates that the fauna of these "morros", which contains species of Textularia and Gyroidina, fragments of echinoderms and pelecypods, although not-diagnostic, resemble in general aspect, the limestones of the Lower Cretaceous. For these reasons, and because the paleontology suggests a possible pre-Paleocene age of the limestones, the group is here redefined to include only the shales and sandstones and considering the limestones as possibly older.

No type-section could be established. The group contains strata which could represent more than one formation. It is because of the variableness of the strata, that the sediments have been considered as group. Good exposures occur along the highway between San Francisco de Macaira and Altagracia de Orituco, to the south of Portachuelo, as well as in the immediate vicinity of Morro Grande, south of El Valle. Commercial gypsum deposits are associated with the shales of this formation as well as the limestones that form the morros, but the relation between said deposits and the shales and limestones, is not clear.

The group consists of shales interbedded with sandstones. The shales are gray, light gray and brown and, on weathering, produce red colors. Locally, the lamination is rather poor, but generally speaking, bedding is well developed and they resemble, to a certain extent, the Guayuta, but are lighter in color and do not contain limestone beds. The sandstones are brown and gray, thin bedded, fine "rained and hard.

The beds that make this group are intensely deformed, which renders very difficult the proper determination of its thickness. However, the thickness is probably not greater than 600 meters.

The formation is rather very poor in fossils, but the following foraminifera have been found (D. W. Gravell, private information, 1947): Nodellum velascoensis, Rzehakina epigona, var. lata, wich suggest an equivalence with part of the Vidoño and Caratas formations (Rzehakina-"Spiroplectammina" zone) of Anzoátegui.

According to De Civrieux, the Macaira group probably includes the Ortiz formation (present description) (see) or perhaps represents its exact equivalent.

J. Evanoff