Armuelles Fm

Period:

Quaternary

Age Interval:

Pleistocene (Calabrian to Middle Pleistocene) (Figure 046) - Cortés et al. (2019)

Province:
Burica Peninsula

Type Locality and Naming

Named by Terry (1941). (Figure 5), 382. “Conglomerate that passes upward into sandstones and shales. Overlies Charco Azul Fm. Thickness more than 4000 feet. Pleistocene.”

Burica Peninsula (Figure 046, Figure 047)

[Figure 1. Geological map of the Burica Peninsula showing the location of a Pliocene fossil whale found in the Burica Fm (Cortés et al. (2019)). Note also the dash line delineating the border between Costa Rica and Panama Right - Geologic and geomorphic map of the ESE Burica Peninsula draped on slope map and displaying the Quaternary marine terraces. LH1 and LH2 correspond to the lahar sequences described below. Also, Qt1 to Qt8 represent the Monte Verde Fm. Modified from Morell et al. (2011)]

Synonym: Armuelles Member; See “Charco Azul Gr” for some additional comments on synonymy.

Lithology and Thickness

The Armuelles Fm consists of ∼500 m of sandstones and siltstones with abundant shelly fragments and shelfal facies sediments (Figure 055). The facies within the formation record deposition within sequentially shallower water depths, with middle bathyal foraminifera in the lowermost Armuelles Fm indicating a record of slope to shelf transition since the Early Pleistocene. Corrigan et al. (1990); Olsson (1942a).

Thickness: ~370 to 500. Morell et al. (2011) ; Cortés et al. (2019)

[Figure 2. Stratigraphic section with location of fossil sites. Modified from O'Dea et al. (2012)]

Lithology Pattern:

Siltstone

Relationships and Distribution

Lower contact

Burica Fm (Figure 046, Figure 047)

Upper contact

Monte Verde Fm (Morell et al. (2011)) (Figure 046)

Regional extent

Burica Peninsula

GeoJSON

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Fossils

The Armuelles Fm is a fossil-rich deposit that rests on the Burica Fm. Its fossils show that it was deposited in very shallow marine waters. It is best exposed along the Rabo de Puerco river in Armuelles, where a complete section of different fossil horizons can be crossed by walking a couple of kilometers upstream from where it intersects the road (8º 16.801'N, 82º 51.995'W) . At the base of the section you can find large boulders that still retain abundant oysters, corals and bryozoans (Okamura et al. (2013)). Going up the section, you can find a wide bed of bivalve mollusks of the Pinna genus with exceptionally well-preserved specimens of this large filter mollusk (Figure 055). Today, Pinna inhabits shallow sandy and muddy areas. Above the Pinna bed are a series of clam and snail horizons dominated by oyster shells and gastropods of the Oliva genus (Figure 055) (O’Dea et al. (2007)). Crabs can also be found. Todd & Collins (2005).

[Figure 3: Representative fossils of the Armuelles Fm. Part of a valve from Pinna (left). Gastropod from the genus Oliva (family Olividae) (top right). Ostra (bottom right). All of them are locally abundant. Scale = 2cm. O'Dea et al. (2007).]

Age

Age Span:

Beginning stage:

Calabrian

Fraction up in beginning stage:

Beginning date (Ma):

1.80

Ending stage:

Lt. Pleist.

Fraction up in the ending stage:

Ending date (Ma):

0.13

Depositional setting

Depositional pattern:

Additional Information

References:

Olsson (1942a).
Coryell et al. (1942);
Woodring (1960). The name was used in a brief description of the geology of the Burica Peninsula, southwestern Panama. The Armuelles Fm, made up principally of foraminiferal siltstone and sandstone, crops out on the Burica Peninsula southward from Puerto Armuelles. It has a maximum thickness of about 4,000 feet and unconformably overlies the Pliocene Charco Azul Fm. The molluscan fauna represents a shallow-water assemblage. The mollusks, nearly all of which are Recent species, have been listed by Olsson (1942a, pp. 9-12) and some species were described in the same publication. The high percentage of Recent species indicates that the age is not older than early Pleistocene.
Obando (1986); Jung (1989)
Corrigan et al. (1990), originally named the “Charco Azul Gr” as the “Charco Azul Fm” and included in it its three Members “Peñita”, “Burica” and “Armuelles”. It is only later that it was renamed as a Group, while each of its members were given the designation of “Formation”.
Kolarsky (1992); Coates et al. (1992); Collins et al. (1995) ; Kolarsky et al. (1995a, 1995b); Schlegel (1996); Lattig et al. (2000); Todd & Collins (2005) ; O’Dea et al. (2007) ; Beu (2010); Morell et al. (2011) ; Landau et al. (2012c); Okamura et al. (2013); Cortés et al. (2019).

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)