GUAYANA, Series

PRECAMBRIAN

State of Bolívar, Venezuela

Author of name: R. A. Liddle, 1928.

Original reference: R. A. Liddle, 1928, p. 57.

Original description: ibid.

The name Guayana Series was first used by R. A. Liddle (1928, p. 57) to designate the group of gneissoid rocks, intensely folded, and gneissic granite cut by granitic intrusions which, according to said author, suggests an igneous origin for the whole complex. The sequence would represent the northern border of the ancient continent of Gondwana and the basement of the Venezuelan Guayana region that can be considered as the type-area. The rocks form a slightly convex shield which has been eroded to a peneplain. Later on, the description was modified by Liddle (1946, p. 58-59) in order to include, in the Guayana Series, igneous rocks, younger than those mentioned before but still pre-Cambrian, which form the basements of the Gran Sabana and surrounding areas (Pastora series).

According to Liddle in the northern part of the Guayana shield, the Guayana series lies in uncomformity below the ferruginous quartzites of the Imataca series. In the region of the Gran Sabana, the series is made up of porphyric igneous rocks (quartz porphyre, feldspar porphyre and porphyric andesite) in uncomformity with the overlying Roraima formation, considered tentatively Triassic-Jurassic.

On account of the extreme denudation of the area, it is difficult to estimate the thickness of the series. Liddle (1946, p. 58-59) believes that it exceeds 1000 meters.

The age of the series is uncertain. Liddle (1928, p. 60; 1946, p. 60-61) believes it to be pre-Cambrian and correlates it tentatively with the Archeozoic of the Brazilian shield and the gneissoid pre-Paleozoic rocks of the Venezuelan Andes.

Liddle includes in his Guayana series a complex of units pertaining to the whole pre-Cambrian df the Venezuelan Guayana, today partially subdivided under better defined names and thus more advisable, such as "Archean Camplex", Imataca series, and Pastora formation.

Kugler et al. (1942-1944, p. 22, fig. 1), use the term "Guayana series" in the British Guiana, in the same broad sense as Liddle, 1946, including the pre-Paleozoic basement and the "Volcanic Series' (equivalent to Pastora) as pre-Triassic in age.

G. M. Stockley (1954) in his figure "The Stratigraphy of British Guiana", restricts the term, somewhat modified "Guayana system", to designate only a sequence equivalent to Pastora (see).

Alirio Bellizzia G.