LA PASCUA, Formation

TERTIARY (Oligocene)

State of Guárico, Venezuela

Author of name: Geological staff, S. A. Petrolera Las Mercedes.

Original reference: H. D. Hedberg, 1950, p. 1204.

Original description: ibid.

The term La Pascua formation was established by the geological staff of S. A. Petrolera Las Mercedes during early drilling operations in the Las Mercedes area, state of Guárico. The first published reference to the La Pascua sandstone is by Hedberg (1950, p. 1204) in discussing the overlying Roblecito shale of eastern Guárico. Brief mention of the formation was made by Mencher et al. (1953, p. 712, 771-73), and a rather thorough description of the La Pascua in the Las Mercedes region is given by Patterson and Wilson (1953, p. 2715-2719).

The La Pascua has been reported only as a subsurface formation occurring in the state of Guárico. The standard subsurface section for the formation is the well Guayabo-2 in the Las Mercedes oil field.

In general, the La Pascua formation is made up of about 500 feet of interbedded marine to marginal sandstone and dark shales with a few lignitic beds. In the Mercedes area, the sandstones of the La Pascua average about 300 feet gross thickness, and can be divided into eight principal members labeled, from top to bottom, "A", "B", "BB", "C", "D", "E:", "F" and "G". The sands are grey to gray-brown, very fine, to very coarse-grained, with poor to good sorting. The degree of cementation of the sands is variable, with a calcareous or siliceous cement. Kaolinitic material is com mon, and thin layers of kaolin are interbedded with the sandstones. The shales are gray-black, massive to thinly laminated, calcareous to non-calcareous, here and there with grains of pyrite and thin seams of lignite. The fauna from the shales consists of plant impressions, foraminifera, and mollusks, and indicates a marine to brackish water environment.

The La Pascua formation is overlain by the Roblecito formation, and is separated from the underlying formations by an unconformity in which the Locene and Paleocene are missing. The La Pascua rests on progressively older Cretaceous beds from northeast to southwest, until it lies directly on granitic basement or on the Carrizal southwest of the town of Calabozo.

According to Patterson and Wilson (1953, p. 2715), the La Pascua formation is represented in the Guarumen sandstone group described by Kamen-Kaye (1942, p. 126-33) in northwest Guárico. Hedberg (1950, p. 1204) states that the La Pascua sandstone is probably equivalent to the Capaya formation, and the Merecure group (Hedberg, 1950, p. 1196-1199) of north eastern Anzoátegui.

Patterson and Wilson (1953, p. 2715-19), and Mencher et al. (1953, p. 771-72, Chart I, p. 774,776) indicate that the age of the La Pascua formation is Oligocene.

S. J. Brown