OREGANO, Formation

TERTIARY (predominantly Oligocene)

States of Anozátegui and Monagas, Venezuela

Author of name: H. D. Hedberg, 1946 (private report).

Original reference: H. D. Hedberg, 1950, p. 1202-1203.

Original description: ibid.

Hedberg (1946, private report) named the "Orégano formation" from Rio Orégano, District of Libertad, State of Anzoátegui. In 1950 (p. 12021203) the same author published the term "Orégano formation" for a rather ill-defined stratigraphic unit of the Santa Inés group in northeastern Anzoátegui and northwestern Monagas. It is described as "...the shallow-water marine facies into which the Uchirito and Quiamare formations apparently grade in an easterly direction". The formation is partially exposed on Río Orégano, about 1 kilometer south of the Santa Inés-Urica road crossing. Here it is in conformable stratigraphic contact with the underlying Carapita formation, and consists predominantly of bluish-gray shale and massive buff sandstone, but chert pebble conglomerates are also interbedded. The shale contains common echinoids, mollusks and crabs. Hedberg states that well sections farther east suggest an extensive subsurface unit composed of shallow-water marine, fossiliferous shales, sandstones and conglomerates, constituting the transition zone between the non-marine or brackish-water Santa Inés sediments to the west and the moderately deep-water Santa Inés shales to the east. Well sections in uplift areas along the northern mountain front indicate overlapping of Orégano facies on older pre-Santa Inës rocks.

A recent revision of the foraminiferal faunas from Rio Orégano, south of the Santa Inés-Urica road crossing, definitely indicates a predominantly Oligocene age for the formation.

Cecily Petzall