AGUA CLARA Formation

TERTIARY (upper Oligocene)

State of Falcón, Venezuela

Author of name: R. Arnold, 1911 (private report).

Original reference: A. H. Garner, 1926, p. 681.

Original description: ibid.

Ralph Arnold, during private investigations between 1911 and 1916, seems to have been the first to apply the term Agua Clara to a series of dark shales cropping out near the village of the same name in the State of Falcón. The first published use of the term is believed to have been by A. H. Garner (1926, p. 681); but the same year R. Koch (1926) described a new species of foraminifera, Miogypsina staufferi Koch, stated to be indicative of the Agua Clara formation of western Falcón. It was described more comprehensively by R. A. Liddle, 1928, p. 260-269.

The Agua Clara formation consists predominantly of dark gray shales, intercalated with thinly bedded sandstones and rare fossiliferous limestones. The shales are variably arenaceous, concretionary, gypsiferous and carbonaceous. The relatively thin sandstone beds are commonly firmly cemented, locally glauconitic and fossiliferous; on exposed surfaces the normal greenish to purplish gray color becomes modified by red splotches. At the locality the thickness is about 2,600 feet, according to A. Senn (1935, p. 75). In West Buchivacoa (later the District of Mauroa) Halse (1937, p. 187) states that it is impossible to distinguish the Agua Clara and underlying San Luis except on a paleontologic basis. He reports a thickness of 2000 feet in outcrop and 3,200 feet in Vega Oscura wells. The abundant Agua Clara fauna includes mollusks, corals, algae, and foraminifera. Liddle (1928, p. 261) gave the age of the Agua Clara as upper Oligocene, a conclusion reaffirmed 20 years later by Renz (1948, p. 19, 77). An interim dissenting view is that of Hoffmeister (1938, p. 117) who, in correlating the upper Agua Clara with the La Rosa formation of the Bolívar Coastal Fields, implies a lower Miocene age for at least the upper Agua Clara.

Some local and generally obsolete terms for portions of the Agua Clara formation are: the El Mene de Mauroa oil sands in the area of the El Mene de Mauroa oil field (Liddle, 1946, p. 426); the Hombre Pintado oil sands in the vicinity of the oil fields of the same name (Liddle, 1928, p. 265-266; 1946, p. 426, 430-431); "La Planchada sandstone" and/or "La Planchada oil sand" in the southwestern part of the District of Buchivacoa (Liddle, 1928, p. 261, 266, 268; 1946, p. 429); the Cauderalito limestone (Williston and Nichols, 1928, p. 449-451); the Quiróz beds (Garner, p. 682; Liddle, 1928, p. 261, 266; 1946, p. 425, 426, 434-435) in the southeastern part of the District of Miranda, State of Zulia; and possibly also the lower portion of the Boca de Don Diego beds of eastern Falcón (Liddle, 1928, p. 267; 1946, p 431). These terms are generally regarded as having been applied to portions of the upper Agua Clara formation in separate localities. Although Williston and Nichols (1928, p. 449) agree in essential correlation of the Quiróz, El Mene (de Mauroa), Hombre Pintado, Cauderalito, and La Planchada beds, they consider these units as having affinity with the Socorro rather than the Agua Clara formation.

W. M. Chappell