RIO DE ORO, Beds

See RIO DE ORO, Formation

RIO DE ORO, Formation

CRETACEOUS (Maestrichtian)

Department of Santander del Norte, Colombia

Author of name: A. H. Garner, 1926.

Original reference: A. H. Garner, 1926, p. 681.

Original description: ibid.

In 1926 Garner (p. 681) described brown, sandy shales, fairly soft, with small limestone lenses from the Río de Oro which deposits he called Río de Oro formation. He considered the age as Oligocene or probably lower Miocene.

According to Hedberg and Sass (1937, p. 85) the Río de Oro formation named by Garner is too loosely defined to determine whether its scope is the same as that of the Río de Oro formation as described by Hedberg and Sass. According to these authors, the formation was named by geologists of the Venezuelan Gulf Oil Company and the drainage basin of the Río de Oro and Departamento Norte de Santander, Colombia. The Río de Oro formation consists of thin marine fossiliferous and frequently glauconitic limestones and ironstones, interbedded with shales, silstones, and sandstones such as are typical of the underlying Mito Juan formations and overlying La Sierra sandstone. It contains some coal. The tickness of the formation varies from 90 to about 300 meters.

Molluscan fossils are fairly common in the limestones and ironstones. Ammonites have been found just above the Mito Juan. Spath (in Hedberg and Sass, 1937, p. 86) determined Sphenodiscus and Couahuilites. Foraminifera from the Río de Oro formation are rather scanty according to Hedberg and Sass (1937, p. 86) but include, besides arenaceous forms, species of Gümbelina, Gümbelitria, Gyroidina and Vaginulina. The fauna seems to indicate uppermost Cretaceous age.

Sutton (1946, p. 1654) considers the Río de Oro beds as locally the upper member of the Mito Juan formation. Also Notestein et al. (1944, p. 1185) consider the Río de Oro limestone as a facies development of the Upper Mito Juan. See also González de Juana (1951, p. 209). According to Liddle (1946, p. 274) the sediments which Hedberg and Sass include in their Río de Oro formation along the Sierra de Perijá, are actually parts of two formations, the lower part (Maestrichtian) is part of the Mito Juan and upper portion is part of the Río Guasare formation (Paleocene).

W. A. Mohler