LOS BAÑOS, Shale

See PAUJI, Formation

PAUJI, Formation

TERTIARY (upper middle Eocene-upper Eocene)

State of Zulia, Venezuela

Author of name: R. Arnold, 1912-1916 (private reports) (?).

Original reference: R. A. Liddle, 1928, p. 242.

Original description: ibid.

Liddle (1928, p. 242) who first published the name Paují shale stated that probably the name was first applied by Arnold in private reports.

The type section is on the Río Paují in the district of Baralt, State of Zulia, where the stream emerges from the Serranía Trujillo. According to Tash (1938, p. 164-167), the term Paují shale was used by Dagenais as early as 1914, possibly before Arnold. The Paují formation consists essentially of a thick shale series. The strata vary from practically pure black, massive shales, with very little sand content, to thin-bedded sandy shales, platy sandstones and thin limestone layers. The laminated sandy shales, platy sandstones and limestone lenses are chiefly confined to the upper portion of the formation. The shaly part of the original formation is the Paují shale of present definition, the sandy and limy beds the Mene Grande series (see Mene Grande formation). According to Tash (1938, p. 166), the Paují shale consists of an essentially massive, dark-gray to black, slightly sandy and pyritic shale with frequent nodules of limy, siliceous, or pyritic material. In general, there are no sandstones in the true Paují formation until the basal transition zone is reached, just above the Misoa-Trujillo formation. Drilling however, has shown the presence of a hard, rather quarzitic sandstone, 62 feet thick, in the upper portion of the middle part of the Paují formation. This sandstone appears to have only a very limited lateral extent.

Sutton (1946, p. 1670) states that the Paují formation originally included all upper Eocene sediments lying above the Misoa formation in the general area of the Mene Grande oil field. Later, observers noted that a three-fold division could be established to comprise a basal transition zone composed almost entirely of shale, and an upper zone of interbedded sandstones, reef limestones, and shale. Still later, according to Sutton the upper zone was removed from the Paují formation and named Mene Grande formation. Sutton called the lower zone, lower Paují; the middle zone, upper Paují, and the upper zone, Mene Grande formation.

The Paují formation is conformable with the Misoa formation below, and apparently conformable but probably disconformable with the Mene Grande formation above.

According to the Staff of the Caribbean Petroleum Co. (1948, p. 567) the Paují formation (without the Mene Grande formation) in the Mene Grande field, has a thickness of about 2,000 feet; the total thickness is difficult to determine because of the Miocene unconformity and structural complications. Sutton (1946, p. 1670) gives a thickness for the Upper Paují of 5,395 feet being the interval between the top of the Potreritos and the surface in the well Pica-Pica-1 in the Bolívar district. At least 400 feet of Lower Paují has been penetrated in the Mene Grande field without reaching the base of the formation and the Upper Paují in this field has a thickness of 2500 feet according to Tash (1938, p. 167). On the Río Caús in southwestern Trujillo, the Lower Paují measures 246 feet and near El Marfil on the Los Baños anticline the Upper Paují is at least 3641 feet thick.

The Paují formation crops out along the western flank of the Serranía de Trujillo and Cerro Misoa, and is found in wells in the southern Bachaquero field and in the Mene Grande field. In Trujillo, the Paují formation is prominent on the Escuque and Los Baños anticlines and extends along the front of the Mérida Andes southwest past the Río Caús into the northern corner of the State of Mérida.

The age, according to Sutton (1946, p. 1671), is upper Eocene. A prolific marine fauna of smaller foraminifera is described by Nuttall (1935, p. 121-131). The reef limestones of the Paují on the Río San Pedro and Río Caús contain larger foraminifera. According to Van Raadshooven (1951, p. 482) these faunas show distinct differences from the typical upper Eocene faunas and contain species, which point strongly to an upper middle Eocene age.

The Río Raya shale of Garner (1926, p. 681) and the Los Baños shale of Garner (1926, p. 681) are obsolete names for the Paují, considered to be Oligocene by Garner. According to Sutton (1946 p. 1672) the Río Caús formation of Liddle (1928, p. 238-239) is the equivalent of the somewhat thicker orbitoidal limestone in the upper part of the Lower Paují in the section along the Río Caús in southwest Trujillo. Both the San Pedro "formation" and the Río Caús "formation" should rank as local reef limestone members of the Paují formation. For other correlatives, see Sutton (1946, p. 1672). The "Upper Micaceous Sandstone" of the Bolívar coastfields corresponds approximately to the Paují formation of the Mene Grande area, according to the Staff of Caribbean Petroleum Co. (1948, p. 537).

W. A. Mohler