MACOITA, Formation

UPPER DEVONIAN ?

State of Zulia, Venezuela

Authors of name: Geologists of the Caribbean Petroleum Company (?).

Original reference: H. D. Hedberg and L. C. Sass, 1937, p. 79.

Original description: none published.

The name Macoíta was probably first used as a formation name by the geologists of the Caribbean Petroleum Company, who pioneered geologic surveys in the Perijá mountain front.

Hedberg and Sass (1937,p. 79) state that the "red shales, siltstones, and sandstones... well exposed on Río Macoíta", and populary referred to as the "Old Red Series", have been called "Macoíta formation". Liddle (1943, p. 19-20) says that the "Old Red Series" is not present on Río Macoíta, and uses the term Río Macoíta formation for the "Thinly-bedded, sandy, micaceous gray shales and dark-gray, evenly bedded, quarzitic, fine-grained sandstones which are well exposed on Río Macoíta", eliminating the application that Hedberg and Sass gave to the term Macoíta (which he erroneously cites as "Macoíta series").

The type section (Richmond Exploration Company private report) begins near the "matera" Alirán on the Río Macoíta and extends northwestward for about three kilometers, to a point about half a kilometer northwest of "hacienda" Puerto Nuevo.

"The Macoíta formation is composed predominantly of interbedded olive gray, calcareous, carbonaceous siltstone and medium-gray to olive tan, minutely cross-bedded, fine, arkosic sandstone. Bedding is regular, with thickness of individual strata varying from a decimeter to a half meter or more. The upper 200 to 300 meters is of brick-red siltstone, sandy siltstone, and red and green conglomerate stringers, in a red, sandy and silty matrix. Conglomerate pebbles are red, calcareous siltstone and pinkish-gray, siliceous porphyry." (W. K. Gealy, Richmond Exploration Company private report.)

The Macoíta formation is underlain by the Tinacoa formation, apparently conformably. From observations in the adjacent area, the upper contact, with the La Quinta formation, is known to be unconformable, although the unconformity is not readily apparent on Río Macoíta.

Structural complexity, particularly in the lower part, makes it difficult to measure the thickness of the Macoíta, but at least, 1000 meters is reported in the type area. The formation is recognized from a few kilometers south of the Río Macoíta to the Totumo area, about forty kilometers to the north. At the area to the south and west, the formation is veiled in structural complexity and there is a lack of geologic investigations.

No fossils have been found in the Macoíta formation, but it is correlated with the Campo Chico formation of the Río Cachirí area farther north, which Liddle (1943, p. 14, 19) assigns to the Upper Devonian on the basis of stratigraphic continuity (Río Cachirí series) with underlying strata carrying Lower and Middle Devonian fauna.

K. L. Edwards