HATO VIEJO, Formation

PRE-CRETACEOUS (Triassic-Jurassic ?)

States of Guárico and Anzoátegui, Venezuela

Author of name: M. W. Haas, 1939.

Original reference: H. D. Hedberg, 1942, p. 200-201.

Original description: M. W. Haas, 1939, in Hedberg, 1950, p. 1184.

This formation is a subsurface unit that has been penetrated by wells in the States of Guárico and southwestern Anzoátegui. It was named from the well Hato Viejo N° 1, drilled by Standard Oil Company of Venezuela, in the District of Monagas, State of Anzoátegui.

Although published for the first time by Hedberg (1942, p. 200-201), the formation was named and originally described from the type section by M. W. Haas in 1939 (quoted by Hedberg, 1950, p. 1184) as follows:

In the well Hato Viejo N° 1, "the formation was entirely cored showing its relation to the argillite (Carrizal formation) and the basement. The type section is Hato Viejo N° 1 from 2740' to a depth of 2850'. The formation directly underlies the argillite (Carrizal formation) and overlies the basement. Its contact with the argillite (Carrizal formation) appears to be conformable. Essentially the formation consists of massive hard fine to coarse "rained, friable, gritty, pinkish gray, gray and dark gray sandstone which is slightly calcareous, and in portions is extremely micaceous and pyritic. The grains are rounded and firmly cemented. Quartzite cobbles and conglomerates occur in the sandstone at irregular intervals and jointing is noted in several places. Calcite veins are present along fracture planes. Certain portions of the sandstone show quartzitic characteristics and others are highly feldspathic, green, and glauconitic".

Hedberg (1942, p. 200-201; 1950, p. 1182-1185) follows the original description by Haas, but makes the following observations on the basis of data from other wells; the formation consists largely of medium to coarse-grained arkosic-quartzitic sandstone. It is locally at least 300 feet thick but may be considerably thicker. The lower part of the unit carries a simple zircon-leucoxene mineral suite which grades upward into a garnet-biotite suite like that of the overlying Carrizal formation. Some streaks of green argillite also indicate its close relation to the Carrizal formation. No fossils have been found. Some reason are given for suposing the Carrizal-Hato Viejo formations to be time equivalents of the Jurassic-Triassic (?) La Quinta formation of the Venezuelan Andes. However, the formation may be as old as Paleozoic; such an opinion is also held by Liddle (1946, p. 114).

Liddle (1946, p. 100), Bucher (1952, p. 94) and Feo-Codecido (1953-4, p. 114) consider that, lithologically, the Carrizal-Hato Viejo formations are comparable to the outcropping metamorphic series (slate, argillite and quartzite) of the El Baúl area.

The formation is missing toward the east of southern Anzoátegui where Cretaceous Temblador formation rests unconformably on rocks of the Guayana complex (González de Juana, 1947, p. 694). The Hato Viejo formation appears to be relatively thin in most wells of the State of Guárico.

No outcrops of the Hato Viejo formation have been identified in any portion of Eastern Venezuela (Hedberg, 1950, p. 1185).

Gustavo Feo-Codecido