Porcona Fm

Period:

Paleogene, Neogene

Age Interval:

Middle Eocene to Late Oligocene - Barat et al. (2014)

Province:
Eastern Panama

Type Locality and Naming

This formation was named by Shelton (1952) the "Corcona" Formation for a tributary of the Chico River. However, since all regional maps spell the name "Porcona" it is assumed that Shelton's name is a misspelling. Coates et al. (2004)

The Porcona Fm crops out mainly on the northeastern flank of the Chucunaque-Tuira Basin. However, Barat et al. (2014) have also observed that Porcona Fm occasionally appears along the southern flank of the Chucunaque–Tuira Basin, marking the beginning of sedimentation in this Basin. The unit was interpreted by Esso Exploration and Production Panama (1970) to be middle-upper Oligocene and deposited at lower bathyal depths.

Synonym: Corcona; Corcona Fm

Lithology and Thickness

It consists mainly of gray and black, calcareous, foraminiferal shale, limestone (Figure 1), and glassy tuff with radiolarians. It also contains probable resedimented blocks of shelly glauconitic sandstone and "orbitoid" sandstone. Barat et al. (2014) could not obtain a complete stratigraphic sequence of the Porcona Fm; however they described several outcrops:
(i) bioclastic limestone that contains larger benthic foraminifera and red algae, which indicates a shallow marine depositional environment, which they dated as Late Oligocene; (ii) marl of the Late Middle Eocene and Late Oligocene, determined by the nannofossil. assemblages (Figure 2). Similar marls also appear in the area between the San Miguel Gulf and the Sanson Hills, overlying the Early Eocene cherts.

Thickness: The earlier works in this area suggested a thickness of between 300 and 700 m for the Porcona Fm, however the Oxoco International Report (1983) revealed a thickness of over 2000 m of Late Middle Eocene to Late Oligocene sediments and the presence of oil circulation in the Chucunaque–Tuira Basin.

[Figure 1. Late Oligocene alternating finely layered limestones and marls in an outcrop of the Pacora river in the Chucunaque Basin. Barat (2013)]

[Figure 2. Marls from the Chucunaque–Tuira Basin, Porcona Fm (9.20737°, −78.88950°, WGS84). Barat (2013) and Barat et al. (2014).]

Lithology Pattern:

Clayey limestone

Relationships and Distribution

Lower contact

The Porcona Fm unconformably overlies the deformed rock of the San Blas Complex Fm.

Upper contact

The Darien Fm and Porcona Fm are regionally overlain by the Clarita Fm.

Regional extent

Eastern Panama

GeoJSON

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Fossils

N/A

Age

Age Span:

Beginning stage:

Rupelian

Fraction up in beginning stage:

0.667

Beginning date (Ma):

29.49

Ending stage:

Aquitanian

Fraction up in the ending stage:

Ending date (Ma):

23.04

Depositional setting

Depositional pattern:

Additional Information

References: Shelton (1952); Esso Exploration and Production Panama (1970); Oxoco International Report (1983); Coates, Anthony G. et al. (2004); Barat et al. (2014).

Compiler:

Jacques LeBlanc (2021), Stratigraphic Lexicon: The Onshore Cenozoic Sedimentary Formations of The Republic of Panama. Biosis: Biological Systems, 2(1), 173 pp. https://doi.org/10.37819/biosis.002.01.0095 (or via https://sites.google.com/site/leblancjacques)