EL PAO, Sandstone

TERTIARY (Oligocene)

State of Cojedes, Venezuela

Author of name: A. H. Garner, 1926.

Original reference: A. H. Garner, 1926, p. 680.

Original description: ibid.

The "Pao sandstone" (misspelling for El Pao) was named and described by Garner (1926, p 680). The type locality "forms hills four miles south of town of El Pao, State of Cojedes". He describes the unit as "massive, coarse, conglomeratic, hard, brown sandstone" and considers it of Eocene age. In his fig. 1 (p. 678) in the bolumn corresponding to Central Venezuela, Garner indicates an approximate thickness of 1.000 ft. for the "Pao sandstone" and an upper contact conformable with the so called El Guapo shale of Oligocene age. Correlations with the "Aragua sandstone" and "Misoa Hill" formations are also proposed.

Liddle (1928, p. 51, 209) mentions the rocks of Garner's unit and says (p. 209). "South and southeast of Pao, "galeras" or rugged sandstone hills, which trend generally east and west, including the "galeras" del Pao, Corozal, Morrocoyes, Guarumen and others, mark the beginning of surface exposures of the Ortiz sandstone." In a latter publication, Liddle (1946, p. 340) repeats this paragraph but does not include the rocks in the Ortiz sandstone but in the Guarumen group, in consideration of the restriction previously introduced by Kamen-Kaye (1942, p. 126-33) to the name Ortiz.

The name El Pao sandstone refers, really, to a marginal basal formation of the Guarumen group of Kamen-Kaye. J. Evanoff (1951, p. 246-247) described in the section of Quebrada El Baho, affluent of Quebrada Lele, State of Miranda, a unit probably equivalent to El Pao sandstone, which he named Batatal formation. Among the outcrops of the Batatal formation the author mentioned the "galeras" of Cojedes, the type-area of Garner's El Pao and the outcrops located to the east of Sabana de Uchire (State of Anzoátegui) known also as Caho Dulce formation. The type-section of Kamen-Kaye's Guarumen group (Guarumen River) follows regionally along along the strike, horizons which are approximately equivalent to the units above mentioned.

El Pao sandstone (or formation) and its northeastern equivalents constitute clastic facies of the steep northwestern slope of the oligo-miocene basin, the regional trend of which is southwest-northeast. Inside the basin, that is, towards the southeast of the depositional line of the "galeras" of Cojedes and Guârico, the sandy-conglomeratic basal facies, locally shaly, carbonaceous and gypsiferous of the Guarumen group pass rapidly into deeper water sediments, mainly shales. Sandstone developments show-up again at the base of the Guarumen group, on the southeastern flank of the sedimentary basin, where they are known (in the subsurface only) as La Pascua formation. This unit is transgressive and thus younger than the El Pao and Batatal formations.

Liddle (1946) describes sections apparently equivalent to that of the El Pao sandstone: The most conspicuous part of the Guarumen group is a horizon of massive conglomeratic sandstone which breaks down under weathering into enormous boulders. The insides of these boulders are grayish-white, but the outsides, which are often encased with a ferruginous coating more or less a centimeter thick, are deep, reddish brown. The ferruginous matter of the coloring is in general, derived from hollow, clay ironstone concretions, which are disseminated throughout the formation (p. 338). Further down he says that these sandstones are intercalated with silts and clay shales (ibid.).

Liddle describes in particular outcrops that are approximately equivalent to the El Pao sandstone in the "galeras" of Dos Caminos and Morrocoyes (p. 340-341) but considers their stratigraphic position in the Guarumen group section uncertain. At Dos Caminos the sandstone contains "small pebbles of milk-white quartz firmly cemented". At Morrocoyes "though some members of the sandstone are thinly bedded, the shale are practically absent". According to Liddle, the thickness of the section outcropping at Morrocoyes is about 2,000 ft.

The sediments of the El Pao f ormation and its equivalents acted as resistant masses against the pressure exerted from the north that determined the "Llanos" frontal thrust. In the present times, these sediments are tectonically uplifted, locally overturned and almost always overlain by Cretaceous and Paleocene formations dragged from the present mountain front and pushed down to the southeast. The most typical surface exposures of this unit are the "galeras" located to the south of El Pao, Ortiz, Dos Caminos and Morrocoyes; also part of the Guarumen River section. Less prominent outcrops, affected by complex thrusting in association with the main overthrust, form a discontinued and narrow band with a SW-NE regional direction towards the west of San Rafael de Orituco, and from the NE of Altagracia de Orituco to the east of Sabana de Uchire. This outcropping area includes the type-sections of the Batatal and Caño Dulce formations, units of a typical litoral Ethology. The Caño Dulce formation is tectonically uplifted at its type-section 10 kms. to the north of Clarines; the upper and lower contacts are concealed, but according to Hedberg (1950, p. 1198, 1203) the thickness is 1,200 ft.

In the Merecure depositional sequence, the El Pao formation is probably equivalent to the upper part of the Naricual formation of Anzoátegui. Previous to the beginning of the Guarumen transgression, the sequence in the Barcelona basin had had no break since Eocene time.

J. M. Sellier de Civrieux