"SECOND ORBITOID LEVEL"

See TRUJILLO, Formation.

TRUJILLO, Formation

TERTIARY (Paleocene to middle Eocene)

State of Zulia, Venezuela

Author of name: R. Arnold, 1915 (private report).

Original reference: G. E. Tash, 1937, p. 175-176.

Original description: ibid.

Tash (1937, p. 167) pointed out that "Arnold (1915) gives the following description for this formation: "The name "Trujillo" has been suggested for the series of dark shales and shaly sandstones, interbedded with gray and pink quartzitic sandstones, underlying the Paují Shale formation. From the fossils found in the Trujillo formation it is definitely determined to be of Tertiary age, probably Oligocene. The best section of the formation is to be found in Quebrada Arenosa, where it is estimated to have a thickness of 2,214 feet. . . " Tash stated that Dagenais, as early as 1914, used the name "Misoa-Trujillo" for this same series of beds. Tash commented that Dagenais's "Misoa-Trujillo" had undoubted priority over Arnold's "Trujillo", and that Liddle (1928) had adopted Dagenais's name in his work on the geology of Venezuela and Trinidad.

Sutton (1946, p. 1660-1662) pointed out that in his paper he had separated the hyphenated term "Misoa-Trujillo" and that the names Trujillo and Misoa have been assigned to the two distinct lithologic units which constitute the sequence. Thus, Sutton simultaneously had restricted Arnold's "Trujillo" to the lower part of this unit as well as to the lower part of the "Misoa-Trujillo" of other workers. Sutton stated that the type exposure of the Trujillo formation is along Río Misoa, where this stream cuts the western flank of the Serranía de Trujillo and forms the boundary between the Districts of Sucre and Bolivar in eastern Zulia. At the base, the formation is in contact with the Guasare formation near the crest of the El Bafio anticline. It extends downstream from this point for a distance of approximately 23 kilometers (14 miles) to its contact with the overlying Misoa formation. Sutton described the formation as composed largely of dark blue-gray to dark gray and black, locally micaceous and carbonaceous shale, with subordinate amounts of gray and brown sandstone. The sandstones are more pronounced in the upper half of the formation and are gray and brown, fine to medium-grained, micaceous, and locally carbonaceous. The thickness of the formation in the type section has been estimated at 4,876 meters (16,000 feet). This may be excessive in view of probable repetition by faulting and sharp folding in the shale. Sutton claimed that the contact with the overlying Misoa formation is unconformable and that the contact with the underlying Guasare formation is not clearly defined but believed to be conformable. Sutton stated that the known outcrop occurrence of the Trujillo formation extends from the Zulia-Lara-Falcón state boundary junction to the Caracas River valley in the northeastern part of the State of Trujillo. On the basis of its stratigraphic position and faunal content, Sutton considered the formation to be lower and middle Eocene in age. He gave a detailed fossil list (p. 1661). Sutton pointed out that Liddle (1928, p. 181-198) included the Trujillo formation in his "Third Coal horizon" along with the Angostura, Catatumbo Barco, Tabla, Los Cuervos, Guasare and Marcelina formations. G. E. Tash (1937, p. 168) included the Trujillo and the "second orbitoid horizon" in his lower Misoa-Trujillo member. Sutton pointed out that "the orbitoids of the 'second orbitoid horizon' are of upper Eocene age and, in the Río Carache section, occur between the unconformity at the top of the Trujillo and the base of the lowermost quartzites of the Misoa formation".

De Cizancourt and Frizzell (1949, p. 496-497) reported Ferayina coralliformis Frizzell among other larger foraminifera such as Nummulites (Operculinoides) jennyi (Barker), Nummulites (Operculinoides) oliveri (Cushman), Lepidocyclina (Polylepidina) antillea Cushman, etc, from the "Cuicas formation", considered by Sutton (1946, p. 1668) to be the equivalent of the "second orbitoid level", which they placed in the middle Eocene based on this faunal evidence.

González de Juana (1951, p. 273-274) stated that according to his acceptance, the Trujillo formation has its base where the first sandstones which are typical of this sedimentary interval start on top of Paleocene beds, where these can be identified, or on top of the Colón-Mito Juan shales. He placed the top of the Trujillo formation at the point where the thin-bedded sandstones end and the thick banks of sandstones start, which are typical of the Misoa formation. González de Juana pointed out that according to his definition the Trujillo formation is essentially the same as the lower member of Tash's Misoa-Trujillo including a great part of the orbitoidal limestones of the Carache area. González de Juana pointed out that beds of typical Trujillo lihology, i. e., shales and sandstones, interfinger with reefal facies of the Paleocene, and that the sandy and orbitoidal limestones continue higher stratigraphically to the middle Eocene. He cited the La Paz, El Cumbe and Cuicas limestones of Cizancourt (1951) and the San Juan and Quebrada Grande limestones of van Raadshoven (1951). González de Juana emphasized that the Trujillo formation represents beds of Paleocene to middle Eocene age in its typical development but can be separated locally from the Guasare formation and thus restricted to the lower and middle Eocene whenever the reefal limestone fauna necessary for this separation is present.

Information taken from private reports indicates that the unconformity postulated by Sutton at the top of the Trujillo formation does not exist but represented a fault contact. The Trujillo formation of González de Juana usage is accepted by a great number of geologists and, as such, is equivalent to the Ranchería formation.

Leo Weingeist