RANCHERIA, Formation

TERTIARY (Paleocene to middle Eocene)

State of Trujillo, Venezuela

Author of name: A. Salvador, 1949 (private report).

Original reference: A. Salvador, 1950, Ph. D. Thesis, Stanford University.

Original description: ibid.

The name Ranchería was introduced by A. Salvador (1950) to designate the formation exposed just north of the small village of Ranchería, 1.5 kilometers northeast of Chejendé, State of Trujillo. The type locality was designated as outcropping on the hill just north of the village that forms the east flank of the Chejendé anticline. Other good sections are along the Rancheria-Soledad trail and the Chejendé-Río Carache road near El Algarrobo.

The Ranchería formation (Salvador, 1950) consists of thinly bedded, reddish gray and brown, soft, sandy shales and siltstones, irregularly interbedded with gray to yellowish-gray, fine-grained, argillaceous sandstones. Small clay-ironstone concretions are abundant. The thickness varies between 800 and 975 feet in the Chejendé area.

The Ranchería formation is in transitional stratigraphic contact with both the underlying Upper Cretaceous Colón formation and the overlying probably middle Eocene Escuque formation. The formation represents the lateral facies equivalent of the Valle Hondo formation (with reef limestones); their transition is clearly visible between Balambay hill and Ranchería village.

Poorly preserved molluscan faunas occur near the base of the formation and poor but diagnostic foraminiferal assemblages of Eggerella and Haplophragmoides occur throughout the section. From the stratigraphic position of the Ranchería formation between the Colón and Escuque formations and from the lateral relationship with the Valle Hondo formation, a Paleocene, lower and middle Eocene age was assumed for this unit.

The Ranchería formation is equivalent to the Lower Misoa-Trujillo of Tash (1937, p. 168-169), the "Third Coal Horizon" of Liddle (1946, p. 314, 325-326) and the Trujillo formation of González de Juana (1951, p. 273-274, 285).

Gordon A. Young