LOS VAGRES, Limestone

See PUNTA CARNERO, Group

PUNTA CARNERO, Group

TERTIARY (Eocene)

State of Nueva Esparta, Venezuela

Author of name: C. González de Juana.

Original reference: C. González de Juana, 1947, p. 693.

Original description: C. González de Juana, 1947, p. 696.

G. P. Wall (1860) (fide Rutten, 1940) mentioned a small basin of sands and shales of unknown age, which outcrop between Porlamar and Pampatar between the limestones of his "Older Parian system" (in this case, the metamorphic rocks of Margarita) and the lower, calcareous part of his "Younger Parian" (here, the Miocene beds). This appears to be the first notice of the beds later recognized as Eocene in Margarita.

C. J. Maury (1925, p. 412) recorded the presence of "Lower Eocene" (i.e. Paleocene), in the following words: "Isla Margarita and Isla Taos" (should be Toas), "beds with Venericardia planicosta, smooth variety exactly like that from the basal Eocene horizon of Soldado Rock, Boca de Serpiente, bed n° 2, with which these beds of the island, from this and other reasons, are considered synchronous. Identification and correlation, Maury, 1912, 1915; Maury and Harris, 1925. The Eocene mapped by Jahn on Isla Tortuga is probably the same age as that on Margarita". Maury in 1912 has not mentioned Margarita; we have not been able to identify the publication she cites as "Maury, 1915" (perhaps her report on Dominican geology and paleontology, 1917?). The presence of Paleocene on Margarita has not been confirmed by later investigators.

Liddle (1928) included the beds between Porlamar and Pampatar in the Cretaceous in his section, (fig. 4).

P. I. Aguerrevere (1936) published a geologic sketch-map of Margarita, in which he showed outcrops of "older Tertiary" in the regions of Punta Ballena, Pampatar and the Morro of Punta Moreno; in the accompanying text, he states that these rocks have been referred to the Eocene principally due to their resemblance to Eocene formations of other regions, and that the rocks are mainly sandstones.

L. Rutten (1940) described numerous samples collected in 1936 by P. W. Hummelinck from localities in Margarita, Cubagua and Coche. The Margarita samples came from localities near Pampatar, Punta Ballena and conglomerates. From the sandstones of Punta Ballena-Pampatar, Rutten identified Globigerina, radiolaria ( ?), and Lepidocyclina (fragment). From a conglomerate near Caigüire, he identified algas (Corallinacea), Globigerinidae, small nummulites. Lepidocyclininae and Discocyclininae, and especially, Discocyclina georgiana Cushman and Lepidocyclina trinitatensis H. Douvillé, which determined the age as Eocene. Rutten called attention to the presence in the conglomerates of types of rocks which could not have been derived from the island itself, such as the cherts and radiolarites of unknown origin, and of porphyrites and quartzdiorites, which Rutten believed might have been derived from similar rocks in the islands of Los Frailes and Los Testigos. (It may be noted here, that the cherts and radiolarites probably also were derived from Los Frailes, since González de Juana has recognized there a Cretaceous formation made up of such rocks, which has been called in unpublished reports, Los Frailes formation.) Rutten considered as probably Eocene also, samples of marl and phosphatized sandy limestone from Isla Blanca south of Pampatar; it seems more probable, however, that these samples came from the Miocene or Pliocene beds. Rutten states that the Eocene rocks in the region of Pampatar appear to form a syncline.

Senn (1940, p. 1565) stated that González de Juana, in a geological meeting in Trinidad in 1939, had reported the occurrence in Margarita of a sandstone with orbitoids. Senn gave an extract from a letter by Hedberg, in which the latter described the Eocene of Margarita as a series, conglomeratic at the base and passing upward into sandstones and shales with some grit beds, the series containing abundant specimens of Discocyclina in the lower part of the sandy-shaly section. Hedberg believed that this Eocene section of Margarita might be the equivalent of a part of the Scotland formation of Barbados (lower and middle Eocene), opinion shared by Senn.

Liddle (1946, p. 77-78) noted the presence of Eocene in Margarita, quoting Senn and giving an extract from a letter by A. A. Olsson, who reports that the Eocene is overlain by Miocene beds, with marked unconformity. Liddle also indicated the presence of Paleocene, based on the earlier report of Maury (his reference, however, is incorrect.) On his geologic map, he shows a small area of upper Eocene in the vicinity of Punta Moreno, to the north of which he indicates a belt of Lower and Upper Cretaceous; he shows Punta Ballena as formed by Miocene rocks, and Punta Mosquito by Recent beds. His geological cross-section of the island (Liddle, 1946, fig. 3, opp. p. 70) is the same as his section of 1928, except that now the legend of the number "3" of the section reads: "Upper Cretaceous, shale and limestone; Upper Eocene, fossiliferous sandstone and shale; unconformably overlain by Miocene."

C. González de Juana (1947, p. 693-697) published the name Punta Carnero group to designate the Eocene of Margarita. He describes the group as composed of shales and sandy shales, coarse conglomerates, fine to medium-grained sandstones, and flaggy orbitoidal limestones, with a total thickness of about 7,500 feet. The lower Eocene is predominantly conglomeratic, although the conglomerates are very lenticular; the pebbles are very heterogeneous in composition, including fragments of all the older rocks on the island in addition to alocthonous vacuolar intrusives. This conglomeratic part grades upward into sandstones, orbitoidal limestones, flaggy calcareous sandstones, and finally, into dark grey or chocolate-colored carbonaceous shales, with which there are intercalated a few thin ferruginous sandstones, this part of the section corresponding to the maximum depth of the seas during the sedimentary cycle. Above, this shaly section grades in turn into sediments of shallower waters, consisting of calcareous sandstones, flaggy orbitoidal limestones, orbitoidal marls, and sandy shales. The results of wave action, which caused fragmentation of the orbitoid reefs and deposition of the fragments in very shallow waters is observed in the section west of the Punta Mosquito lighthouse. González de Juana notes that west of Las Maritas lagoon and near Zanjón Orinoco in the south, sediments of middle to upper Miocene age lie with pronounced unconformity on the Eocene, whereas in the island of Cubagua, there are some 4,000 feet of Oligo-Miocene sediments unconformably above Eocene beds, which appear to correspond to the upper Eocene of Margarita. These relations are known from wells. The basal sediments of this post-Eocene "section of Cubagua are terrestrial mottled clays; generally considered as Oligocene.

Hess and Maxwell (1949), in a geologic sketch-map, indicated the outcrop areas of the Punta Carnero group, but did not describe the beds in detail. They mention the presence of pebbles of volcanic rocks in the conglomerates, and in the "basal limestone of Los Vagres" (correct spelling, Los Bagres). They do not describe this horizon, except to note that it contains angular fragments of volcanic rocks, diorite and perhaps dacite or andesite. They also note the presence of fragments and pebbles of igneous rocks in the conglomeratic part of the Punta Carnero "formation", and believe that these might have been derived from volcanic flows in the northern part of Margarita (of which, however, there is no present evidence).

The rocks of the Punta Carnero group have been studied in considerable detail by students of the Department of Geology and Mines of the Central University of Venezuela, but the results have not been published. The Punta Carnero unit should be considered as a group, since it can be divided into three formations which correspond to the threefold division indicated by González de Juana in 1947. As for the "basal limestone of Los Bagres" mentioned by Hess and Maxwell, Dr. González de Juana informs us that it is merely a local limestone lens, which does not merit the status of a member, nor does it occur in the immediate vicinity of the locality Los Bagres. The "limestone with an abundant fauna of corals... of definitely Cretaceous age" mentioned by Bucher (1952, p. 68) is probably this same lenticular limestone.

In the student theses, the three formations of the Punta Carnero group have been called, in ascending order: the Las Bermúdez formation (name derived from a property of the same name); the El Dátil formation (named for the Quebrada El Dátil); and Punta Mosquito formation. From limestones in the Las Bermúdez formation, the following fossils were identified: Astrocoenia cf. A. trechmanni Wells (a species described originally from the Upper Scotland formation of Barbados, of middle Eocene age); Discocyclina (Discocyclina) anconensis Barker, Operculinoides trinitatensis, Eoconuloides sp. and Athecocyclina sp., which suggest middle Eocene age, or perhaps as old as lower Eocene. In the type section, this formation measured 610 meters in thickness. The El Dátil formation, which consists principally of shales, lies on the Las Bermúdez formation with transitional and conformable contact, and measures 720 meters in thickness. It contains: Eoconuloides sp. aff. E. wellsi Cole and Bermúdez, Discocyclina anconensis, Operculinoides trinitatensis (Nuttall) and Discocyclina (Asterocyclina) cf. D. (A) asterisca (Guppy). This formation is thought to represent a middle to upper Eocene age. The uppermost formation, the Punta Mosquito, takes its name from Punta Mosquito, but the type section was selected in the zone of the Las Bermúdez property, since in this region the formation can be observed lying with conformable and transitional contact above the El Dátil formation. In this type section, 425 meters were measured, the top of the formation being covered by alluvium. The lower 100 meters consist of calcareous shales with some interbedded limestones, many of them entirely made up of large foraminifera. Above these beds, the formation becomes more sandy. The orbitoidal limestones contain the following forms: Lepidocyclina (Pliolepidina) pustulosa H. Douvillé, Operculinoides trinitatensis (Nuttall) and Discocyclina (Asterocyclina) cf. D. (A.) asterisca (Guppy) which indicate an upper Eocene age.

Frances de Rivero