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Lower Cretaceous Barranquin Formation of Northeastern Venezuela

1957; American Association of Petroleum Geologists; Volume: 41; Linguagem: Inglês

10.1306/0bda584f-16bd-11d7-8645000102c1865d

1558-9153

Erimar Von Der Osten,

Geological and Tectonic Studies in Latin America

The Barranquin formation represents the oldest sedimentary rocks of northeastern Venezuela. It consists of a thick sequence of clastic rocks that occur over large areas of the Serrania del Interior. Good exposures of the formation on the islands of the Bahia de Santa Fe region permitted a more detailed stratigraphic study than has been possible hitherto. A large collection of well preserved fossils which include 48 species, 18 of which are new, was obtained at the same time, their study providing new information about the age of the Barranquin strata. The sequence of Barranquin rocks is 1,692 meters thick in the Santa Fe region. This is the largest reported section of the formation, but as elsewhere in Venezuela, the base does not appear. The exposed section was divided lithologically into four members, named from bottom to top the Venados, Morro Blanco, Picuda, and Taguarumo members. The Venados member, representing the lowest 377 meters of the section, consists of alternating thick regular units of buff shale and white, coarse-grained, cross-bedded sandstone. The overlying Morro Blanco member consists of 230 meters of thick-bedded blue-gray limestones and dark-colored shales. The recognition of this thick limestone sequence in the lower part of the Barranquin formation is one of the principal contributions of this stratigraphic survey. The Picuda member, 425 meters of sandstones and shales, overlies the Morro Blanco, and is characterized by alternating thin beds of fine-grained sandstones, bright-colored shales, and ferruginous sandy shales. The uppermost member, the Taguarumo, is 660 meters thick and is characterized by the predominance of dark-colored shales wi h gypsum and jarosite, by olive-green fossiliferous limestones, and by alternations like those of the underlying member, but the beds are thicker. The Barranquin formation is conformably overlain by the formation, the contact being defined as the base of the first massive typically El Cantil limestone. The character of the Barranquin formation in the Santa Fe area suggests shallow-water marine deposition of sediments derived from highlands at the south. Contrary to the statement of previous writers, no evidence was found to indicate continental origin for any part of the formation, or to suggest a source of sediments in a hypothetical landmass, the so-called Paria, at the north. Stratigraphically the Barranquin is correlated with the Rio Negro and Tomon formations of Venezuela and with the Cuche and Toco formations of Trinidad. It has been correlated in the past with the Texas Glen Rose formation of Upper Aptian to Lower Albian age, on the basis of coral and mollusk species. While this correlation is also suggested by part of the Santa Fe fauna, an equally strong paleontologic correlation can be made with Neocomian faunas of Europe. It is concluded that the paleontologic correlation with the Glen Rose formation is a facies correlation and that the age of the Barranquin formation is Valanginian to Barremian, as indicated by the affinity of its fauna to faunas of this age in Europe. Such a conclusion is supported by the presence of Lower Aptian ammonites in the overlying formation.