APON, Formation

CRETACEOUS (Neocomian-Aptian to ?lower or ?middle Albian)

State of Zulia, Venezuela

Author of name: F. A. Sutton, 1946.

Original reference: F. A. Sutton, 1946, p. 1642.

Original description: ibid.

The term Cogollo limestone, or Cogollo formation, was arbitrarily used for the complex of Cretaceous limestones (or part of it) which is intercalated between the basal cretaceous clastics and the La Luna formation.

In view of the comprehensive character of the name Cogollo formation ilimestone), F. A. Sutton replaced it by the term Cogollo group (Sutton, 1946, p. 1641). The name Apón formation was introduced by F. A. Sutton for the lower part (predominantly limestone unit) of the Cogollo group in the Sierra de Perijá, Zulia. The upper Cogollo group was subdivided into the Aguardiente and Capacho formations (Sutton, 1946, p. 1642).

F. A. Sutton reported the Apón formation to be composed of gray and blue-gray, hard, dense, thick-bedded, sometimes fossiliferous limestones with subordinate interbeds of black, calcareous shale, black, shaly limestone, and calcareous sandstone. From Río Negro, F. A. Sutton mentions 50-75 feet of black calcareous shale and platy limestone containing numerous black, fussiliferous limestone concretions (La Luna type) in the middle part of the formation (see middle Apón member, below).

At the type section on Río Apón, Sierra de Perijá, the formation attains about 650 meters in thickness; in Trujillo, where the formation chiefly consists of clastic deposits which contain a few limestone interbeds (Uribante formation, "Tomón" of authors), a thickness of about 600 meters was measured. Toward the Mérida Andes and the Barco Concession, Colombia, it decreases in thickness to approximately 300 meters. The formation was found in a reduced thickness of about 100 meters on Toas Island (E. Rod).

The Apón formation is known from outcrops and well sections in eastern Colombia and Zulia.

The contact between the Apón formation and the underlying Río Negro formation is conformable and transitional; the boundary with the surmounting Aguardiente-Lisure formations appears to mark a disconformity.

The Apón formation corresponds to the lower and to the main part of the middle Cogollo limestone discriminated in the La Paz-Mara Field, Zulia (Smith, 1951, p. 62 etc.); J. E. Smith's "Upper Cogollo" equals the Capacho-Maraca formations and should, therefore, be excluded from the Cogollo unit.

The Apón formation is subdivided into an upper Apón member, a middle Apón member, and a lower Apón member (Rod and Maync, 1954, p. 202 etc.).

The so-called "lower, middle, and upper Cogollo of the Cogollo formation" distinguished in the Barco Concession (Notestein et al., 1944, p. 1174) and in the Tarra Field, Zulia (Staff of Caribbean Petroleum Company, 1947, p. 612) are by no means equivalents of the lower, middle, and upper Apón formation; they succeed the Aguardiente (Lisure) formation which in itself is younger than the Apón formation.

3. Upper Apón member.

Light-colored hard, bedded, often coquinoid limestones; Miliolid limestones; thin-bedded nodular marry limestones; white chalky limestone; blue-gray marls; sandy or detrital limestones may occur near the base.

Thickness: 40-145 meters (Sierra de Perijá).

Type locality: Río Cogollo, Sierra de Perijá, Zulia.

Fossils: Orbitolina concava-texana (Roem.), generally restricted to the upper Apón member.

Choffatella decipiens Schlumberger, in southern Lara (usually confined to the lower Apón member).

2. Middle Apón member.

Black bituminous laminated limestones, marry limestones, and shales carrying black to gray dense fossiliferous limestone concretions.

Thickness: The maximum thickness of the middle Apón member attains 205 meters (Río Negro); from here, the beds show a rapid thinning toward south and north, and the middle Apón member is not developed in its characteristic black limestone-shale facies in the Mérida Andes or on Toas Island.

Type locality: Río Cogollo, Sierra de Perijá, Zulia.

These characteristic sediments have been previously noticed (Liddle, 1928, p. 149; Hedberg, 1931, p. 238; Hedberg and Sass, 1937, p. 82; Sutton, 1946, p. 1642). The "well-defined marl layer of 100 feet thickness at the top of the lower third" of the Cogollo formation in the La Paz Field (Staff of Caribbean Petroleum Company, 1948, p. 599) and J. E. Smith's "middle Cogollo shale break" in the Apón of the Mara-La Paz region (Smith, 1951, p. 64) are the exact equivalent of the middle Apón member. E. Rod restricts his middle Apón member to this conspicuous black shale-limestone interval on top of the lower Apón member; accordingly, the rest of J. E. Smith's "middle Cogollo" is referred to the upper Apón member.

This typical black limestone-shale facies (with limestone concretions) of the middle Apón member is developed again in a regional scale in the Upper Cretaceous La Luna formation. Notwithstanding the fact that both lithotopes are highly fossiliferous and contain diagnostic faunas, they were occasionally confused in the past.

The contacts between the middle and lower Apón members and between the middle and upper Apón members are conformable. Fauna: Different species of the ammonite genera Cheloniceras, Colombiceras, Deshayesites, Duirenoya, Douvilleiceras, Sanmartinoceras, etc. (see faunal lists in Sutton, 1946, p. 1643, etc.; Rod and Maync, 1954, p. 266, etc.).

This cephalopod assemblage proves an upper Aptian (Gargasian, age of the middle Apón member.

1. Lower Apón member.

Variety of cream-colored massive coquinoid, often crystalline limestone; gray nodular limestones and blue-gray marly limestones; gray nodular limestones and blue-gray marly limestones; pellet and detrital limestones; interbeds of shales and dolomite; chert nodules.

Thickness: 360-380 meters (Sierra de Perijá).

Type and reference section: Cafio Santa Rosita, north of Río Apón, Sierra de Perijá, Zulia. The lower Apón member grades into the Río Negro formation below and is in conformable contact with the middle Apón member.

Fauna: Choffatella decipiens Sehlumberger (generally restricted to the lower Apón member).

Pseudocyclammina hedbergi Maync. Orbitolina concava texana (Roem.) (in the Mérida Andes).

Choffatella biozone.

The presence of Choffatella in the Lower Cretaceous of Venezuela (Táchira) was recorded for the first time by L. Kehrer (1937, p. 66-67). It was subsequently reported to occur also in the basal Cretaceous of Trujillo (Tomalin, 1938, p. 20). W. Maync discussed the genus, especially the species Choffatella decipiens Schlumberger, and its stratigraphic value in the Caribbean region (Maync, 1949 (1950)). In Western Venezuela, Choffatella decipiens is usually confined to the lower Apón member (Maync, loc. cit.; Smith, 1951) but locally (Lara) persists into the upper member of the Apón formation. It is also present in limestone beds of the Uribante ("Tomón") formation.

The biostratigraphic term Choffatella zone was introduced by W. Maync (Rod and Maync, 1954, p. 277, 279). It characterizes beds of Aptian age; a Barremian age for the earliest income of Choffatella decipiens is possible, though not proved yet.

Age: The lower Apón member underlies beds catrying diagnostic ammonites of upper Aptian age; the basal Apón formation may, consequently, be of early Aptian age. The upper Apón member on top of the upper Aptian middle Apón member is disconformably overlain by the Lisure formation for which a middle (to upper) Albian age is assumed. The entire Apón formation therefore extends through the Aptian into the ?lower-middle Albian.

The Cachirí limestone of northwestern Zulia and the lower part of the "Cogollo limestone" of authors correlate with part of the Apón formation. The combined Tibú and Mercedes members of the Uribante formation (Barco Concession) correspond to the Río Negro and Apón formations of the Sierra de Perijá. The Borracha formation of Eastern Venezuela is a time-equivalent of the Apón formation.

Wolf Maync