MARCELINA, Formation

TERTIARY (Paleocene? Lower Eocene)

State of Zulia, Venezuela

Author of name: F. A. Sutton, 1946.

Original reference: F. A. Sutton, 1946, p. 1663-1665

Original description: ibid.

The name is taken from Caño Marcelina, a small, southward flowing tributary to the Río Guasare, in Distrito Páez, and was used by Sutton (1946, p. 1663-5) to substitute for Garner's (1927, p. 680) term "La Rosa coal measures", which "must be rejected in order to prevent confusion with the Miocene petroliferous La Rosa formation of the Bolivar Coastal oil field." Actually, "La Rosa coal measures" is the older term; if compared with "La Rosa formation" as to priority, Garner's name warrants preference. However, Sutton further states that Garner's "name La Rosa was evidently an error for Santa Rosa, another tributary of the Río Guasare lying east of the Caño Marcelina." The name Santa Rosa is used by some geologists for the limestone member underlying the Upper Cretaceous Colón shale (Socuy limestone member) in western Zulia. Therefore (although this latter use also postdates Garner's) since the Marcelina name is well established, no change is recommended.

Sutton (1946, p. 1663-5) described the Marcelina as interbedded, lightgray, locally calcareous, micaceous, and carbonaceous sandstones, and darkgray to black, sometimes sandy shales, containing sandstone and sandy-limestone nodules, and numerous coal beds. Critchett (Richmond Exploration Company private report) described the Marcelina of the Río Guasare area as "dark-gray", carbonaceous shale interbedded with gray, fine-grained, micaceous, thin-bedded sandstones and siltstones, thick beds of buff, mediumgrained, micaceous, cross-bedded, locally feldspathic and calcareous sandstone, red, siliceous, porcellanous shale, and, in the upper portion, numerous coal beds. A few thin beds of sandy limestone are present, and calcareous, fossiliferous sandstones occur above the lower contact."

Gealey (Richmond Exploration Company private report) reports about 540 meters of Marcelina formation on the Río Guasare, and about 400 meters on the Río Socuy to the south. In the nearby Mara oil field, the Marcelina is generally not recognized, as there are only rare specks of carbonaceous matter in the samples. At Macoa, some 60 kilometers to the south, about 100 meters of section has been assigned to the Marcelina, but coals are very minor and are interspersed with thin, limey streaks.

The Marcelina is equivalent to the lower part of the Paso Diablo formation of Hedberg and Sass (1937, p. 90), and roughly corresponds to the "Third Coal horizon" of Distrito Colón and elsewhere south and east of Lake Maracaibo. It is conformable with the underlying Guasare formation, and represents a phase of regression at the close of the "Cretaceous cycle" of marine sedimentation (which extends through the Paleocene to a stage of maximum emergence perhaps during the lower Eocene). The Marcelina seems to represent a swamp, geographically restricted to a ring bordering the gradually retreating and diminishing Cretaceous sea. Away from northwest Zulia, it is not easy to distinguish which part of the section represents the Marcelina and which the Guasare, because the limestones of the Guasare and coals of the Marcelina are sporadically developed, depending on local conditions.

From the standpoint of sedimentary facies, the Marcelina roughly correlates with the "Third Coal horizon", some part of the Barco-Los Cuervos sequence of the Barco area, and part of the Trujillo sequence along the Mérida Andes mountain front.

Rare microfossils found in the Marcelina on the Rio Cachirí, northwest Zulia, are reported also from the Guasare interval in Richmond's Zulia 26D-1 well in the Macoa area. Because of its conformable relation with the Guasare, and the unconformity with overlying sandstones of Eocene age, the Marcelina is thought to be of upper Paleocene and possibly lower Eocene age. In the Río Socuy area, the overlying sandstone unit, part of the Paso Diablo sequence of Hedberg and Sass (1937, p. 90), is called "Misoa" by Sutton (1946, p. 1664). In the Macoa area, the sandstone formation overlapping the Marcelina is the La Sierra. The age limits of the Marcelina are not known definitely because age diagnostic fossils are lacking.

K. L. Edwards