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
GUARUMEN, Group
State of Guárico, Venezuela
TERTIARY (Oligocene and ? lower Miocene)
Author of name: Kamen Kaye, 1942.
Original reference: Kamen Kaye, 1942, p. 128.
Original description: ibid.
The Guarumen sandstone group was first described by Kamen Kaye (1942, p. 128), and named after the Guarumen River, east-southeast of Ortiz. Kamen Kaye asserts that such river runs, from its headwaters to its mouth, upon 9.000 feet of sediments of this group. This statement is obviously exaggerated.
Kamen Kaye, describing the unit says: "a broad zone of sandstone appears south of the outcrops of the type Ortiz sandstone... not associated with the Cretaceous-Paleocene deposits". According to the same author (p. 130) the outcrops of the Guarumen group form a band that goes from the south of San Carlos into the eastern coast line of Venezuela, west of Piritu, passing through the south of Ortiz and Altagracia de Orituco. In general, the northern border of the sandstone, coincides with the major thrusting in the foothills section of the Cordillera del Interior, which deter mines the outcropping of Cretaceous and Paleocene strata.
According to Kamen Kaye, the sandstone members of the group constitute a fifth of the entire type section. Their texture changes from fine to coarse "rained. Many beds present ripple marks varying beween 5 and 10 ems. in amplitude, which constitute a typical feature of the group. The Ethology is pure quartz with colorless silica cement, in optical continuity with the grains. Upon exposed surface, weathering produces brown colors and locally hematitic reds. Feldspars, commonly altered into kaolin are found: Plant remains, leaves in particular and occasional lignite and woody coal intercalations can be observed in such sandstones. Other facies of the group are limolites, clays and pure shales. The argillaceous facies are red colored due to iron compounds. Gypsum and jarosite are also common.
The Guarumen River valley, chosen by Kamen Kaye, is a poor representative of the thick sedimentary section included by different authors in what can be considered as the modern definition of the name Guarumen. The Guarumen River has a typically subsequent drainage, therefore, it follows the SW strike of the outcrops that seem to be equivalent to the El PaoBatatal-Caño Dulce formations. Such section is tectonically uplifted and dragged down toward the southeast by longitudinal faults associated with the great frontal thrusting, and superposes younger sediments that belong to the same Oligo-miocene depositional cycle, toward the south of the "galeras" de Guarumen. As it is possible to notice, Kamen Kaye's type-area comprises only a minimum section in the lower part of what is generally known today as the Guarumen group. Every attempt to establish a type section in that area, meets with the difficulty of tectonic deformation which conceals part of the sedimentary sequence. In every case, the section should be measured perpendicularly to the strike of the Guarumen River and this would lessen the thickness originally indicated, in the area, by Kamen Kaye.
Near the base of the group, Kamen Kaye also includes, in a provisional way, orbitoidal limestones containing Lepidocyclina, which do not outcrop in the type-section but toward the east-northeast of Altagracia de Orituco and west-northwest of Piritu. Such limestones are considered by the same aúthor as probable upper Eocene, with a probable extension "into Oligocene time". Kamen Kaye (p. 131) is not positive with regard to the relation existing between such limestones and other rocks of the group admitting having examined but briefly the structures in which they are included. He suggests for the group an age comprising from the upper Eocene to the Oligocene, and possibly the lower Miocene. The correlation, according to that author, would be with Hedberg's Merecure, Carapita and Santa Inés "formations".
According to such definition, the Guarumen group would include sediments of two different depositional cycles, since in the Guarumen basin there is no indication of continous sedimentation since Eocene time.
The above mentioned sediments are:
1) The orbitoidal calcareous facies with Lepidocyclina, of the Tememure and Tinajitas formations, predominantly Jacksonian in age, near Altagracia de Orituco and Píritu. (See also LA PEDRERA LIMESTONE and PEÑAS BLANCAS LIMESTONE.)
2) The Oligo-miocene clay-sandy facies, typically developed in the typesection of the group.
Kamen Kaye does not establish the upper or lower limit of his sandstone group of Guarumen, leaving margin therefore, to different interpretations. Later, Liddle (1946, p. 338-45) introduces a considerable confusion in the description of the unit. Liddle does not distinguish clearly, between the Guarumen group and the Ortiz formation, neither between the different Oligomiocene facies, nor between the different levels comprised in the outcrops that he describes and intends to correlate.
In spite of these circumstances, the name Guarumen has survived through recent literature, having been used, in particular, by J. Evanoff (1951) and by J. M. Patterson and J. G. Wilson (1953). This fact obviously proves the need of a name that might include in it, a complex unit of formations, that were deposited in the States of Cojedes and Guárico, during part of the Oligo-miocene. Hedberg's proposal (1950) of including part of the Guarumen formations into the Santa Inés group considerably enlarged geographically toward the west, does not seem to have received general acceptance. The authors, including Liddle (1946) that have recently turned to use Kamen Kaye's name, have taken advantage of the lack of preciseness in the original description, to include in it much more section upwards (Roblecito, Quebradón and Chaguaramas) than what actually outcrops at the type-area. As for J. Evanoff, he has used the name to designate the pre-Cucharo part of the Oligo-miocene sequence only, and so, he excludes from his definition the Eocene as well as the sediments younger than Chaguaramas.
The name Chaguaramas is used by Evanoff to designate the section comprised between the top of Roblecito and the base of Cucharo, this is, a considerably minor section, than what is included under Patterson and Wilson's (p. 2716, fig. 5, p. 2722) definition. In Patterson and Wilson's nomenclature, Evanoff's restricted Chaguaramas, seems to be approximately equivalent to their lower Chaguaramas, considered by them as "equivalent to Periquito", while the overlying Cucharo formation and its lateral equivalents are integrated in the upper part of their Chaguaramas and correlated with Oficina. In the present article, the subscriber gives to the name Chaguaramas the same restricted meaning given by Evanoff.
Based on the reasons already mentioned, for the use of a name to group the different post-Eocene and pre-Cucharo formations and considering that no superficial, non-composed section, might comprise the entire unit of sediments, the subscriber proposes to maintain Kamen Kaye's original name and proceeds to define the unit all over again and to determine its limits with precision:
1) The Guarumen group designates the Oligo-miocene sedimentary sequence that begins with the more or less simultaneous deposition of the E1 Pao, Batatal and Caño Dulce formations, in a narrow depositional belt, located; to the northwest of the present frontal thrust. The next depositional phase coincides with the culmination of the transgression especially noticeable toward the southeast of the original belt, with deposition of the typically shaly, overlying Roblecito formation, including its basal sandstones that are transgressive toward the southeast and known in the subsurface as La Pascua formation. The Roblecito formation was deposited in deeper waters in alternatively lagoonal and marine environments. It is better developed toward the middle of the basin. Toward the northwest, it is partly represented by a typical litoral facies, described by Evanoff as Quebradón formation.
These latter pre-Chaguaramas sediments of the Guarumen group were laid down in a strongly asymmetric basin that goes from Cojedes to Anzoátegui. Its greatest slope is located along a narrow band, inmediately southeast of the borderland and to the northwest of the present frontal thrust. The basin extended in the past toward the southeast, over the gentle slope of a very shallow epicontinental sea located on the "foreland" of the Guayana shield. In its upper part, the Guarumen sequence ends up with a new deposition of a typically estuarine-paludal formation, known as (restricted) Chaguaramas, that lies transgresively above the Roblecito-Quebradõn formations. Marginal conglomeratic facies are noticeable near the base of that formation, in particular, toward the northwest (Peña de Mora conglomerate, in Altagracia de Orituco) indicating there, a probable minor and local discordance, while further southeast into the basin, sedimentation seems to have continued with no gaps in the depositional cycle.
The upper limit of the Guarumen group is provisionally identified with the Chaguaramas-Cucharo contact. When the complex deltaic facies, lagoonal and locally marine, equivalent to the Cucharo formation (considered by González de Juana, 1946, p. 31, as middle Miocene in age), as well as the younger sediments, could be better comprehended that what they seem to be at the present time, it will be possible to include them in the Guarumen group, without injury for its definition. (See ZARAZA GROUP.)
2) According to the available data, the lower contact of the group is determined by a great discordance, noticeable in the subsurface only.
The Guarumen sediments transgress on the Upper Cretaceous, mainly represented by southern litoral facies (Temblador group), approximately equivalent in age, to the Guayuta Group (J. M. Patterson and J. G. Wilson, p. 2712, fig. 3) The Upper Cretaceous was exposed to erosion during the upper Maestrichtian or Danian (as proved right by the occurrence of Querecual blocks in the basal conglomerate of the Ortiz formation laid down to the north of the present thrusting) and most probably during the entire Paleocene, Eocene and lower part of the Oligocene time. The basal Guarumen transgression in Guárico, seems to be contemporary with the deposition of the upper part of the Naricual formation, in Anzoátegui. In the surface, the relations between Guarumen and the underlying units are concealed, either by the main thrust of the mountain front that sets in contact beds of the upper Maestrichtian or Danian with the basal sandstones of the group, or by a series of minor thrusts and reversed faults developed to the southeast of the major thrusting. Along these, the basal sandstones, frequently overturned, cover younger sediments of Guarumen located toward the southeast.
3) The upper Eocene sediments, absent from the type-area originally proposed by Kamen Kaye and deposited to the northeast in another depositional basin, are excluded from the definition of Guarumen.
4) Kamen Kaye's original section in the Guarumen River, being a poor representative of the group, should be substituted by compound sections established in every one of the different depositional provinces of the basin. Such sections should be established on the basis of the type-sections of representative formations of the group.
5) The outcropping of the group is approximately limited in its northern part by the present frontal thrust of the "Llanos" from points located to the south of San Carlos and El Pao (State of Cojedes), going to the northeast, to a point located east of Sabana de Uchire ( State of Anzoátegui). Litoral facies of the basal section of the group, outcrop south of that line, constituting an extensive band. They are tectonically displaced, uplifted and dragged down toward the southeast as faulted blocks. The remaining formations of the Guarumen group (excepting La Pascua) outcrop extensively, owing to the noticeable small regional dips, from central Cojedes toward the greatest part of western Guárico, southern Aragua and from there eastward to the Guárico-Anzoátegui bounding area. These formations outcrop in a generally normal sequence.
The group decreases rapidly in thickness from approximately 5,000 mts., on the axis of the geosyncline located near the borderland, toward the foreland in the southeast. Its age comprises from the middle and predominantly upper Oligocene (Roblecito formation) to perhaps the lower Miocene (Chaguaramas formation).
J. M. Sellier de Civrieux