MERCEDES, Member

CRETACEOUS (Aptian to ?lower Albian)

Barco Concession, Colombia

Author of name: F. B. Notestein, et al., 1944.

Original reference: F. B. Notestein, et al., 1944, p. 1177.

See URIBANTE, Formation.

URIBANTE, Formation

CRETACEOUS (?Neocomian-Aptian to early Albian)

State of Táchira, Venezuela

Author of name: W. Seivers, 1888.

Original reference: W. Seivers, 1888, p. 19.

Original description: ibid.

The name Uribante sandstone was introduced into the literature by W. Sievers (1888, p. 19; see Sievers, 1896, p. 249) for the bulk of Lower Cretaceous deposits that underlie the "blue limestone of Táchira and Barbacoas" (Capacho formation of present-day usage). The Uribante sandstone, reported by W. Sievers to be composed of red, yellow, and white, sometimes saccharoidal quartz sandstones, which are often micaceous and coarse-grained saccharoidal quartz sandstones, which are often micaceous and coarse-grained, is assigned to the Neocomian. W. Sievers correlates it with his Carora sandstone of Lara (see Aguardiente formation).

The name is derived from Río Uribante, Táchira.

The Uribante sandstone embraces all the Lower Cretaceous sediments from their base up to the Capacho formation ("Cogollo limestone" of authors).

The mainly clastic deposits which occupy the same stratigraphic interval in Táchira, Mérida, Trujillo, and Lara, were subsequently placed by L. Kehrer in his Tomón sandstones (group, series, formation) (Kehrer, 1937, p. 54). The local name Playa Grande sandstone was likewise used by L. Kehrer (1937, Fig. 4, p. 56) for the Tomón equivalent in northern Mérida. The white micaceous sandstones of the Tomón contain some very coarsegrained and conglomeratic portions in the middle part. In the Mérida section, the Tomón beds attain a thickness of 350 meters; in southern Táchira, they are developed in a very coarse clastic facies and reach at least 800 meters in thickness (Kehrer, 1937, p. 56, 69).

The basal Tomón is usually represented by conglomerates and sandstones (25-50 meters). Intercalated in the lower part of the clastic Tomón beds are bluish-black limestones, sandy limestones, shales, etc., but the main part up to the Capacho formation ("Cogollo limestone" of authors) is composed of whitish-gray micaceous, often conglomeratic sandstones. C. González de Juana uses the term Tomón facies to denote the initial clastic phase of the Urgonian cycle (González de Juana, 1951, p. 197).

Since both the names Uribante and Tomón sandstones denote the same stratigraphic interval and the beds at the type locality Alto de Tomón partly are referable to the Eocene, the term Tomón is discarded in favor of the name Uribante which has priority (see Rod and Maync, 1954, p. 219).

W. Sievers' name Uribante sandstone was subsequently applied to the Lower Cretaceous sequence in the Barco Concession, Colombia (Notestein et al., 1944, p. 1173) where the Uribante formation was subdivided into the following three members (from top to bottom):

3. Aguardiente Member.

See Aguardiente formation.

2. Mercedes Member.

Alternation of limestones, black carbonaceous and mica-bearing, partly calcareous shales and gray fine to medium-grained glauconitic, often calcareous sandstones; limestones and shales at the top.

Thickness: 149-201 meters.

Type locality: Mercedes Valley, west of the Barco Concession, Colombia.

1. Tibú Member.

Gray dense, crystalline, fossiliferous limestone with some shale intervals, especially near the top; shales and fine-grained calcareous sandstones in the lower part, grading into basal coarse-grained, sometimes carbonaceous sandstones with quartz and feldspar pebbles.

Thickness: Basal sandstone 5-12 meters; limestone unit 95-160 meters.

Type locality: Río Tibú, west of the Barco Concession, Colombia.

In the Barco Concession, the Uribante formation attains a thickness of 418-503 meters which increases to 825 meters in southward direction (Notestein et al., 1944, p. 1177).

The Uribante formation includes the entire Lower Cretaceous from its base up to the Capacho formation, viz. the Río Negro, Apón, and Aguardiente-Lisure formations of the adjacent Sierra de Perijá, Zulia. Consequently, the name Uribante might rather be used as a group term. However, a marked boundary of a depositional cycle was recognized by F. A Sutton at the base of the Aguardiente member, i. e., within the Uribante formation. On this account, the Aguardiente was given formation rank (Sutton, 1946, p. 1645) and considered to represent the base of the Upper Cogollo group. Accordingly, the Mercedes and Tibú Members of the modified Uribante formation represent the combined Apón and Río Negro formations of western Zulia.

In the Mara-La Paz region the Uribante formation is not absent (interpretation by the Staff of Caribbean Petroleum Company, 1948, p. 599; Mencher et al., 1953, p. 723); the "Cogollo limestone" occurring here between the basement and the Upper Cretaceous La Luna formation, includes much more than the "Cogollo limestone" of the Venezuelan Andes, of the Barco Concession, etc. (misusage of the term "Cogollo formation" or "Cogollo limestone"; see Cogollo formation). In the Maracaibo Basin, this so-called "Cogollo" (Cogollo facies of C. González de Juana, 1951) represents the Uribante formation in the predominantly limestone facies (see Apdn-Aguardiente-Lisure formations), known from the Sierra de Perijá, where only the lower part of the Cretaceous exhibits a clastic facies (see Río Negro formation).

The Uribante formation is widely distributed in the Barco Concession and in western Venezuela (Zulia, Táchira, Mérida, Trujillo, Lara). In general, it is chiefly composed of clastics which often contain some intercalated limestones. In direction of the Sierra de Perijá and the Maracaibo Basin, however, the section becomes continuously marine-neritic, the limestone-marl deposition predominates (Apón), and clastics are only developed in a very variable thickness at the base (Río Negro formation).

A few species of Exagyra of Valanginian to Aptian age are listed from the Uribante (Tomón) formation. Microfauna: Choffatella decipiens Schlumberger and Pseudocyclammina hedbergi Maync occur in the Apón equivalent of the formation, and Orbitolina concava-texana (Roem.) is found in marry levels, from the basal part of the Uribante up to the middle portion of the Aguardiente formation (Kehrer, 1937, p. 69; Tomalin, 1938, p. 18, 20; Maync, 1949 (1950), p. 530; Maync, 1953, p. 101). This foraminiferal assemblage characterizes the Apón formation of Zulia with which the main limestone beds of the Uribante formation are correlated.

Age: The biostratigraphic term Choffatella zone including the Aptian beds of the section in Venezuela was applied by W. Maync (Rod and Maync, 1954, p. 227, 229); the earliest income of Choffatella decipiens in Venezuela might antedate the lower Aptian but there is, as yet, no evidence at hand to prove or disprove this concept.

The Uribante formation includes the strata between the pre-Cretaceous unconformity and the base of the Aguardiente formation. An upper Aptian age is assigned to the middle Apón Member, and the Aguardiente (=Lisure) formation is middle (to upper) Albian. Accordingly, the main part of the Uribante formation represents the Aptian stage; the upper portion possibly extends into the Albian.

As yet, there is no incontestable paleontologic evidence available to prove the presence of pre-Aptian levels in the Uribante formation. The find of Astieria (if correctly determined), reported from Uribante (Tomón) beds north of Michelena, Táchira (Kehrer, 1939, p. 700), would, however, suggest a Hauterivian horizon.

Beds of both Barremian and Hauterivian age are known to occur in Colombia, and fossiliferous Barremian was recently recorded from Trinidad, B. W. I. (Kugler, 1953, p. 32-33).

Wolf Maync