GUANARE "Outwash Apron"

TERTIARY ? (Pliocene ?) QUATERNARY ? (Pleistocene ?)

State of Portuguesa, Venezuela

Author of name: W. G. Argabrite, 1924.

Original reference: Liddle, 1928, p. 355.

Original description: ibid.

According to Liddle (1928, p. 355), extensive alluvial fans deposited by tributaries of the Orinoco River system on the southern flank of the Venezuelan Andes in the States of Barinas, Portuguesa and Apure, were named and described by W. G. Argabrite. They were named Barinas (or Guanapa) and Guanare "outwash aprons".

Liddle (1946, p. 546) states: "From Río Guanare to Río Chú there is a great outwash apron of roughly stratified material, composed of boulders, principally from the Mirador sandstone, together with clays and shales". "These fans comprise the Guanare apron which is younger than the Barinas (or Guanapa) apron".

With respect to the age of these units, recent studies seem to indicate that the "Barinas apron" is younger than the Guanare apron and that the latter might be upper Pliocene or lower Pleistocene.

The name Guanare formation of Garner, 1926, might have been used also for the Guanare "outwash apron", but there are certain doubts about it.

(See also GUANAPA, Formation)

G. Rivero N.

GUANAPA, Formation

QUATERNARY (Pleistocene)

State of Barinas, Venezuela

Author of name: W. G. Argabrite, 1924.

Original reference: R. A. Liddle, 1946, p. 546.

Original description: R. A. Liddle, 1928, p. 355.

The Guanapa formation was first named the "Guanapa outwash apron" by Argabrite in 1924 (see Liddle, 1946, p. 546) after a locality northwest of the town of Barinas, State of Barinas. The name was used as a synonym for the "Barinas outwash apron" under which term the stratigraphic unit was first described by Liddle (1928, p. 355). Mackenzie (1937, p. 266) was the first to refer to this stratigraphic unit as a formation.

As described by Liddle (1928, p. 355) the Guanapa formation (Barinas outwash apron) is composed of material derived from igneous and metamorphic rocks. Only remnants in the form of mesas and terraces exist today of the once extensive outwash apron deposited by melt waters originating from the Alpine glaciers of the Venezuelan Andes during the Pleistocene. The remnants occur over a distance of 15 kilometers along the major rivers which are the southeastern Andean foothill belt.

Liddle (ibid., p. 355) compared the Guanapa formation (Barinas outwash apron) with the Guanare outwash apron and stated that the Guanapa (Barinas) formation is older than the Guanare outwash apron. The writer disagrees with Liddle's age comparison because the Guanare outwash apron is composed mostly of boulders of Misoa quartzitic sandstone which had to be stripped off their Andean source area before the igneous and metamorphic constituents of the Guanapa (Barinas) formation were exposed. Furthermore, the Guanare outwash apron has been folded lo dip as much as 65° along the frontal foothill cuesta which it forms from the Río Morador northeast of Guanare, to the Río Paguey, southwest of Barinas, whereas the Guanapa (Barinas) formation has only initial depositional attitudes. The age of the Guanare outwash apron is therefore, assumed to be late pliocene or early pleistocene, whereas the age of the Guanapa (Barinas) formation is known to be later pleistocene.

(See also Guanare Outwash Apron).

H. Alberding