VALLE GRANDE, Formation

CRETACEOUS (Aptian-Albian)

State of Sucre, Venezuela

Author of name: E. Rod, 1952 (private report).

Original reference: E. Rod and W. Maync, 1954, p. 239 etc.

Original description: ibid.

A 120-150 meters thick sequence of varicolored marls with thin interlayers of glauconitic limestone and calcareous sandstone, exposed in Valle Grande, east of Cumanacoa, Sucre, was mapped by E. Rod (1952) as Valle Grande formation. The term was introduced into the geological literature in 1954 (Rod and Maync, 1954, p. 239 etc.). The sequence cropping out on the trail from Valle Grande to San Juanillo, 80 meters southeast of Trapiche Valle Grande, was chosen as type locality. Microfauna: Diagnostic upper Aptian ammonite genera like Aconeceras, Cheloniceras, Colombiceras, Dufrenoya, Hypacanthoplites, Megatyloceras, etc., were found at the base of the formation. Neohibolites cf. semicanaliculatus (Blainv.) occurs in the upper part.

The microfauna is similar to that from the García member of the Borracha formation (Cristellaria ex gr gaultina Berth., Textularia rioensis Carsey, Verneuilinoides cf. schizea (Cush. & Alex.); not present in older formations is Patellina subcretacea Cush. & Alex., a form which was found in the middle Albian Placeta member of the Chimana formation.

The Valle Grande formation is held to be a distinctive facies embracing parts of the Borracha and Chimana formations. The upper Aptian ammonite genera at the base of the formation favor a correlation with the upper part of the García marls and the upper Borracha member. In places where the middle Albian Guácharo member of the Chimana formation has wedged out, the Valle Grande formation is unconformably overlain by the Corral Viejo member (Upper Chimana formation).

The numerous greensand horizons within the Valle Grande formation are believed to mark surfaces of disconformities, diastems, etc.

In its lithological character, the Valle Grande formation greatly resembles the Albian Chimana formation.

The Valle Grande formation is recognized between the region of Rio Juanillo-Valle Grande, east of Acarigua (Cumanacoa), and Cariaco-Catuaro, Sucre.

Wolf Maync