Ocú Fm

Period:

Cretaceous, Paleogene

Age Interval:

Cretaceous-Paleogene(?) (Campanian / Maastrichtian to (?) Paleogene) - Buchs et al. (2011)

Province:
Tonosí & Azuero basin

Type Locality and Naming

Del Giudice & Recchi (1969) named it for the town of Ocú on the Azuero Peninsula (Figure 1).

[Figure 1. Top: Simplified geological map of the Azuero/Sona Peninsulas. Bottom: A zoom-in of the Azuero Accretionary Complex which forms the SW edge of the Azuero Peninsula. It represents an accretionary complex composed of Cretaceous to Eocene accreted seamounts and oceanic islands. Modified from Buchs et al. (2008, 2011). Also in Barat (2013).]

[Figure 2. A zoom-in of the Azuero Accretionary Complex which forms the SW edge of the Azuero Peninsula. It represents an accretionary complex composed of Cretaceous to Eocene accreted seamounts and oceanic islands. Modified from Buchs et al. (2008, 2011). Also in Barat (2013).]

Synonym: Ocu Fm

Lithology and Thickness

The Ocú Fm was initially described as well bedded fine-grained limestones with locally interbedded siltstones, tuffs and intermediate lava flows, deposited on top of basaltic basement rocks (Del Giudice and Recchi (1969)). In more details, it is described as volcanic breccia with andesite basalt clasts overlain by hemipelagic limestone (with Late Campanian foraminifera) and siliceous tuffs cut by basaltic andesite dikes. The formation probably rests upon the Azuero Plateau (Figure 1&2). Paleomagnetic data indicate the Ocú Fm formed at ∼2°N. The Ocú Fm limestones locally contain a tuffaceous component (Figure 3) and volcanic clasts derived from an intermediate‐silicic volcanic source. Locally the Ocú Fm contains interbeds of basaltic lava flows and is crosscut by basaltic dykes of the Azuero Protoarc Gr.

In general, the formation is composed of hemipelagic biomicrite that includes various amounts of clastic and tuffaceous material. The biomicrite is composed of a calcareous matrix that bears planktic foraminifera, radiolaria and sponge spicules. Reworking and breaking of the fossils is locally observed and probably occurred in response to bottom sea currents. Locally the limestones have an abundant siliceous component of biogenic origin (Figure 4). Bioturbation of the sediment is common. (Buchs et al. (2010))

Tuffaceous and detrital components of the Ocú Fm include sandy and silty grains of plagioclase, pyroxene, quartz, Fe oxide/sulfide minerals, amphibole, fragmented larger benthic (shallow water) foraminifera, and pumice. The detrital component is 3–10 cm sized turbiditic layers. An ashy component is recognized in the field by a greenish color of the limestone that results from the alteration of glass into chlorite. Rarely, red shales and rounded basaltic pebbles occur in the limestones, and attest to an increased terrigenous influence. (Buchs et al. (2010))

Thickness: N/A

[Figure 3. Calcareous and siliceous volcanic tuffs of the Portobelo Peninsula, Ocú Fm (9.56263°, −79.55680°, WGS84). Barat et al. (2014).]

[Figure 4. Silicified limestone of the Portobelo Peninsula, Ocú Fm (9.56593°, −79.52145°, WGS84). Barat et al. (2014).]

Lithology Pattern:

Limestone

Relationships and Distribution

Lower contact

The Ocú Fm is underlaid by rocks of the Azuero Plateau in the Azuero Peninsula and the Oceanic Basement in all regions east of the Canal Zone.

Upper contact

When not outcropping, the Ocú Fm is overlaid by rocks of the Azuero Arc Gr in the Azuero Peninsula and the Volcanic arc in all regions east of the Canal Zone.

Regional extent

Sona Peninsulas and Colba area.

GeoJSON

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Fossils

The hemipelagic limestone forming the Ocú Fm (from the active quarries south of the town of Ocú) yielded rich and well-preserved assemblages of planktic foraminifera.

Age

A hemipelagic limestone of the Ocú Fm in NW Coiba Island (lower left corner in Figure 1) is intruded by a mafic dyke of the Azuero Protoarc Gr. The limestone, which shows synvolcanic soft deformation, has been dated as late Campanian (∼75–73 Ma); so it is concluded that this also corresponds to the age of emplacement of the Azuero Protoarc Gr. (Buchs et al. (2010)).

Age Span:

Beginning stage:

Campanian

Fraction up in beginning stage:

0.75

Beginning date (Ma):

75.04

Ending stage:

Maastrichtian

Fraction up in the ending stage:

Ending date (Ma):

72.17

Depositional setting

The Ocú Fm locally contain fragments of larger benthic foraminifera, which are evidence for nearby shallow water environments.

Depositional pattern:

Additional Information

References: Weyl (1980); Bourgois et al. (1982); Kolarsky et al. (1995a, 1995b); Buchs David et al. (2010 & 2011); Corral et al. (2011); Barat F. 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)