CHURUGUARA, Beds

See CHURUGUARA, Formation

CHURUGUARA, Formation

TERTIARY (lower? or middle Oligocene)

State af Falcón, Venezuela

Author of name: H. G. Kugler.

Original reference: N. E. Gorter and I. M. Van Der Vlerk, 1932, p. 100 115, 116.

Original description: A. Senn, 1935, p. 63-65. According to A. Senn (1935, p. 63) the name "Churuguara series" was originally used by H. G. Kugler in private reports. The name first appears in print, in N. E. Gorter and I. M. Van Der Vlerk (1932, p. 100, 115, 116), who listed larger foraminifera from forty different lacalities in Falcón, identified only by numbers. In their Table N° 1, these authors indicate that the "Churuguara-series" occurs below the "San Luis-series" and above the "Paloma alta-series", and that it is 1.700 meters thick; in their table N° 2 they correlate it with the Glendon formation of Alabama, the Moneague of Jamaica, and the Antigua formation of Antigua, which would indicate a middle Oligocene age. They did not describe any af these units. Gravell (1933, p. 8) also mentions the "Churuguara series" as representing the lower Oligocene in central Falcón, but without describing it; he cites from it only three species foraminifera.

The first description was given by Senn (1935, p. 63-65) who calls the unit, the Churuguara beds (Churuguara-Schichten) and considers it a subdivision (essentially a member, though he does not use the term) of his Agua Negra formation (proposed in the same publication), the other members being the underlying Jarillal shales and the basal Santa Rita conglomerate. The name comes from the town of Churuguara, in the Dis- trito Federación, state of Lara. The type section, however, (in accordance with Senn's designation of the type section of his Agua Negra "formation") was given as the flanks of the Buena Vista anticline, along the old road between Piedra Grande and Baragua. The lacalitites of Churuguara and Cerro de los Indios were mentioned as presenting good exposures of the beds. In a restored geologic section, Senn (1935, p. 61) indicates that south of Churuguara, the Churuguara beds finally lie directly on the Santa Rita conglomerate, due to disappearance of the Jarillal shales. He also represents the Churuguara beds as being replaced in eastern Falcón by the Tacamire sands. (See the articles TACAMIRE, GUAYAVAL and GUACHARACA, for the present interpretation of the geological relations in eastern Falcón).

In the same section, Senn used the term "Churuguara facies", to designate a facies of his Agua Negra formation (now considered a group) in the region of Churuguara, this "facies" being characterized by the development of three distinguishable "members" (now considered formations) -Churuguara, Jarillal and Santa Rita- as well as by the abundance of reef limestones in the Oligocene part of the Agua Negra. Senn discussed in some detail the paleontolagy of the Churuguara beds (see below), which he referred to the lower Oligocene.

Liddle (1946, p. 406-409) describes the Churuguara as a "formation", basing his description on Senn, but omitting the paleontological data.

Renz (1948, p. 43) presented arguments for referring the Churuguara to the middle Oligocene. Bucher (1952, p. 32-33), accepting this correlation, observes that the orogeny which folded the Churuguara beds and resulted in the unconformity between these and the San Luis, must have taken place during the middle Oligocene.

As noted in the article on the Agua Negra, it appears better to treat that unit as a group, elevating the Churuguara, Jarillal and Santa Rita to the rank of formations. Aside from this, we have no changes or additions to make to Senn's original description.

The areal distribution of the Churuguara, according to Liddle (1946, p. 406-409) is approximately the same as that of the overlying San Luis; in other words, it should be found in south central Falcón, but not in the eastern Falcón basin, where litoral and reef facies are not developed. Regarding the paleontology and age of the Churuguara, Senn gave a revised list of the larger foraminifera, as identified by Gorter and Van Der Vlerk (1932) and by Gravell (1933); he pointed out, that some changes had to be made in the assignments of the different samples to the respective formations, in Gravell's lists. The most important species are: the large lepidocyclines (Lepidocyclina gigas, L. undosa); an unidentified species of Nummulites ("Camerina sp. a" of Gravell); with thin walls; Heterostegina cf. H. antillea Cushman; and the first appearance of Miogypsina (cf. M. complanata Schlumberger, and M. hawkinsi Hodson). Senn mentions also that there is a marked change in the molluscan fauna of the Churuguara, as compared with that of the Santa Rita conglomerate and Raetomya shales (basal 50 meters of the Jarillal shales). He recognized various different zones based an mollusks (these zones identified only by numbers), his zone with the "VIb fauna" corresponding to the Churuguara formation plus the upper part of the Jarillal. He mentions that Churuguara beds contain the first clypeastrids.

Senn compared the foraminiferal fauna with that of other formations of the tropical Americas, and concluded that, although the presence of the large lepidocyclines (gigas-undosa) has been generally considered to indicate middle Oligocene, he believed that they might have made their appearance in Venezuela somewhat earlier, in the lower Oligocene. He considered this the more probable, since the relation between the Churuguara and the underlying Jarillal beds is transitional. In addition, he believed that the presence of Nummulites suggested a correlation with the Chira formation of Perú (which was then considered lower Oligocene, although it is now considered upper Eocene).

Renz (1948, p. 43) put forward the following arguments in favor of referring the Churuguara beds to the middle Oligocene; (1) there is considerable evidence to indicate that the Miogypsinidae do not appear in the western hemisphere before the middle Oligocene; (2) in any case, the evidence for the presence of Miogypsina in the Churuguara beds must rest on Senn's claim to have found M. cf. complanata in an unspecified lacality, since the citation of the genus by Gorter and Van Der Vlerk and by Gravell, were based, respectively, on a lacality within the San Luis formation, and from a loose block (3) the large Lepidocyclines suggest rather a middle Oligocene age; and; (4) field evidence suggests that the Churuguara beds are in part, a lateral equivalent of the San Luis.

Frances de Rivero