CHAGUARAMAS, Formation

TERTIARY (Oligo-Miocene)

State of Guárico, Venezuela

Author of name: Geological staff, S. A. Petrolera Las Mercedes.

Original reference: H. D. Hedberg, 1950, p. 1203.

Original description: ibid., p. 1203-1204.

The term Chaguaramas was established originally by the geological staff of S.A. Petrolera Las Mercedes in the Las Mercedes region, state of Guárico. The Chaguaramas formation was first mentioned in publication by Hedberg (1950, p. 1203) wherein he stated that the term had been applied to far western equivalents of portions of the Oficina and Quiamare formations cropping out between Altagracia de Orituco, Chaguaramas and Las Mercedes in the state of Guárico.

In a report by Evanoff (1951, p. 248-250) on the geology of the Altagracia de Orituco region, the Chaguaramas formation is discussed and is described as the uppermost formation of the "Guarumen sandstone group", a term previously introduced by Kamen-Kaye (1924, p. 128-133). Evanoff (1951, p. 246) separated the Guarumen group of the Altagracia de Orituco area into the Batatal, Quebradón and Chaguaramas formations. Here, the Chaguaramas formation conformably overlies the Quebrad6n formation and is overlain disconformably by the Cucharo formation.

As discussed by Evanoff (1951, p. 246-280) and Hedberg (1950, p. 1199-1206), the Chaguaramas formation is equivalent to the lower Santa Inés formation, part of the Carapita formation of northeastern Anzoátegui, the upper portion of the Oficina formation in south-central Anzoátegui, and is, in part, equivalent to the Quiamare formation of northwestern Anzoátegui and northeastern Guárico.

Subsequently, Patterson and Wilson (1953, p. 2722) in discussing the Las Mercedes region in the state of Guárico, defined the Chaguaramas formation as including all beds from the top of the Roblecito formation to the base of the Freites formation. From correlations based on lithological characteristics indicated by electric logs, the top of the Chaguaramas formation is correlated with the top of the Oficina formation of western Anzoátegui and the base is correlated with the base of the Periquito formation.

The above definition of the Chaguaramas formation encompasses a much greater section than the definition of Evanoff and others. The Chaguaramas beds of Evanoff and others are approximately equivalent to the lower Chaguaramas beds of Patterson and equivalents to the upper Guarumen beds and also the overlying Cucharo formation.

In general, the Ethology of the Chaguaramas consists of a brackish water sand-shale-lignite series, with local development of fresh-water clays and distinctive clay-pebble conglomerates similar to those from the Quiamare formation. Two distinctive types of environment have been suggested for the deposition of the Chaguaramas formation (Kamen-Kaye and Mencher, private report). At first, the Chaguaramas was deposited in an environment of broad coastal swamps typified by an abundance of thin lignite seams intercalated with a large amount of micaceous sand with moderate secondary cementation. Later, in the upper Chaguaramas time, the scene of deposition changed to that of open mud flats which were subject to intermittent drying and strong oxidation, causing an accumulation of mottled clays. Some lignites were deposited in the upper Chaguaramas beds during occasional intervals of humid climate. Alternating with the mottled occasional intervals of humid clays and lignites, brackish water and occasional true marine deposits were laid down.

Fossils from the Chaguaramas consist of coarse-shelled mollusk fragments and some vertebrate remains.

In the Mercedes region, the Chaguaramas forms the surface rocks. Subsurface and surface evidence indicates that the entire section of the Chaguaramas is exposed by beveling from west to east across the state of Guárico. No type section has been designated.

The thickness of the Chaguaramas in the various Mercedes fields is as much as 2,900 feet, but it is suspected that it may have attained much greater thicknesses, as much as 10,000 to 14,000 feet in northern Guárico (Patterson and Wilson, 1953, p. 2723).

See also ZARAZA, Group.

S. J. Brown

ZARAZA, Group

TERTIARY (middle Miocene)

State of Guárico, Venezuela

Autor of name: P. Christ (?) et al.

Original reference: H. G. Stehlin, 1938, p. 227.

Original description: ibid.

According to G. G. Simpson (1943, p. 55) the name Zaraza series was introduced in private reports by Christ and other geologists to designate Tertiary strata outcropping in the Zaraza region, State of Guárico. A mammalian jaw was found by P. Christ in a good outcropping area and was originally referred to as Astrapotherium christi Stehlin and later changed (Kraglievich, 1928) to Xenastrapotherium genus.

Stehlin (1928, p. 227-232) first published the name "Zaraza series" pointing-out as type-locality the Pozo Rendivú fossiliferous outcrops in the Quebrada Honda, affluent of the Tamanaco River, approximately 10 kilometers to the northeast of the town of Zaraza. The fossiliferous beds are made up of brownish concretioned sandstone. According to Stehlin (p. 231-232) the Astrapotherium indicates that the outcrops are more or less equivalent in age to those of the Santa Cruz formation of Patagonia; probably not older and perhaps slightly younger, but never post-Miocene.

H. D. Hedberg (1937, p. 2013) refers to Stehlin's "Zaraza series" indicating its equivalence with some part of the Santa Inés "formation" (today group).

In discussing the stratigraphy of the State of Guárico, M. Kamen-Kaye (1942, p. 33) mentions a Zaraza group of possible middle Miocene age which includes "strongly fossiliferous beds", but he did not refer to Stehlin's report.

New vertebrate fossils in a horizon probably almost equal to the Astrapotherium horizon were found by G. G. Simpson (1943, p. 54) who visited Stehlin's type-locality in Pozo Rendivú in 1939. The fossiliferous occurrence was described by the author as a brownish sandstone bed containing "numerous fragments of turtle shells, less frequent crocodile remains and relatively few Astrapotherium remains". he identified a turtle (Podocnemis) pertaining to the Pleurodia group, of scarce diagnostic value. Nevertheless basing himself on the above mentioned presence of Xenastrapotherium, Simpson (p. 55) verifies Stehlin's opinion according to which the Zaraza horizon is "almost certainly, not older than Santacruzian which... (Stehlin) . . . considered lower Miocene and it is most probably younger. The Friasan is more or less lower Miocene". Simpson ends-up by assigning a middle Miocene age to the Rendivú bone horizon, saying that it might be lower or upper Miocene but it is very improbable that it would be as old as Oligocene or as young as Pliocene. According to some information received from Dr. R. Hoffstetter, the Santacruzian of Patagonia (Argentina) is considered of yower Miocene age by all modern paleontologists and geologists like Feruglio.

On the other hand, a glyptodont (Asterostemma venezolensis) was described by Simpson (1947, p. 1-10) who based himself on J. H. Todd's field information. The fossiliferous outcrop is found in the valley of the Güiere River, in the near vicinity of the village of San Francisco, located to the southeast of Clarines, State of Anzoátegui. Simpson points out its probable correlation with the section exposed near Zaraza. According to the same author, the glyptodont found in the Güere River could be middle Miocene (Chasicoanian); there is the possibility that it would be much younger than middle Miocene.

It would be very interesting to determine with more precision the age of the Zaraza beds, a part of the sequence in Guárico where there are scarce faunal guides; it would be desirable to make a careful comparison between their saurian, chelonian and mammalian skeletons and those of the Urumaco bone bed, Distrito Democracia, State of Falcón, which is located almost at the top of the Urumaco formation and is of proved upper middle Miocene age, (molluscan assemblage). The material containing Xenastrapotherium in the Pozo Rendivú might perhaps be compared also with the Prepotherium level, Tucupido River, State of Portuguesa, located in the lower part of the Rio Yuca formation.

The author of the present article believes it possible that the beds studied by Stehlin represent a continental facies included somewhere in the Cucharo formation, (see) considered of approximate middle Miocene age and equivalent to the Yucales formation; another lateral facies generally considered as a northern equivalent of the Cucharo formation is the lower part of the Quiamare formation (see); the Zaraza bone beds could also be compared with beds pertaining to the middle or upper part of the Chaguaramas formation (sensu lato) (see) as it was defined by Patterson and Wilson (1953). If, on the contrary, the restricted definition of the Chaguaramas formation, (proposed by Evanoff (1951) and used by the author of the present article in the redefinition of the Guarumen group (see), is accepted, the Zaraza "group" represents, or is a part of, a post-Chaguaramas unit, and therefore post-Guarumen. On the other hand, the Zaraza "group" is older than the Freites formation of the subsurface, the Punche formation of the surface, the "Aragua", Santa Lucía, Zuata, and middle and upper Quiamare formations (see). According to this, it seems rather improbable that the latter formations include Oligocene beds, as it was suggested by some geologists.

The formational nomenclature of what is considered as probable Miocene in eastern Guárico is not yet firmly established; on the other hand, the published descriptions of the type-sections are somewhat unprecise and the understanding of the stratigraphic relations between the brackish water, paludal, fluvial, deltaic and marshy formations with frequent and rapid lateral variations in the facies, present problems not yet solved. The scarcity, or lack, of fossils, increases the confusion. The disputable redefinition of the Santa Inés group, by Hedberg (1950, p. 1199-1205) suffers from those confusions. For instance, Hedberg places the Peña de Mota conglomerate above the Caño Dulce formation and below the Bruzual formation, and correlates this last one with the Roblecito formation. Today (see GUARUMEN, Group) it seems evident that the Caño Dulce formation is equivalent to the Batatal formation and that the Peña Mota facies constitutes a transgressive marginal conglomerate in the base of the Chaguaramas. Therefore, the normal sequence, from base to top, should be: Caño Dulce, Bruzual, Peña Mota. The latter represents the lowermost Miocene.

In synthesis, it is here believed that only future investigations on this complex of facies that Hedberg proposed to include in his Santa Inés group, considerably enlarged in 1950, would permit to decide the best name for the small part of the section discussed by Stehlin, which certainly does not deserve the rank of a formation and much less of a group, and the Miocene age of which, (probably middle Miocene), has been suggested by Stehlin and by Simpson. (See also CUCHARO and CHAGUARAMAS, Formations).

J. M. Sellier de Civieux