Covachón Fm

Period:

Paleogene

Age Interval:

Early/Middle Eocene (Figure 051) - Buchs et al. (2011)

Province:
Tonosí & Azuero basin

Type Locality and Naming

It was originally considered to pertain to the lower Tonosí Fm but was eventually defined by Buchs et al. (2011) as a separate formation.

The formation is exposed mostly in the southwest corner of the Azuero Peninsula but may also occur as deformed slices in contact with the Azuero Mélange in the northwest edge of the Azuero Accretionary Complex (Buchs et al. (2011)). Facies 1, Covachón (539765/799275, UTM WGS84); Facies 2, Covachón (540545/799335, UTMWGS84); and Facies 3, close to the mouth of the Río Lajas (531490/796780, UTM WGS84). Covachón is accessible by an unpaved road from Cambutal. The mouth of the Río Lajas is accessible by boat from Cambutal or Búcaro. Exposures are accessible at low tide exclusively.

[Figure 1. 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). The Covachón Fm is near the south.]

Synonym: Covachon Fm; wrongly spelled “Cobachon Fm” in post-2011 literature

Lithology and Thickness

The Covachón Fm is a >300 m thick shallowing-upward, folded and faulted sedimentary succession that unconformably rests on top of the Azuero Arc Gr (Azuero Accretionary Complex) (Figure 2) and is separated by an unconformity from the overlying Tonosí Fm (Buchs et al. (2011)). It represents a package of detrital sediments that, in general, unconformably encroaches on the Azuero Accretionary Complex and is in turn separated by an unconformity from the overlying Tonosí Fm. The Covachón Fm includes three facies: Facies 1: interbeds of volcaniclastic calcareous lutite, siltstone and sandstone (Figure 3 top). The beds are typically 3 to 50 cm thick and define parallel layers that extend over several hundreds of meters. It has been interpreted as turbiditic deposits. Facies 2: is composed of 50 cm to ~50 m (?) thick chaotic deposits, which are interbedded with Facies 1 and 3. The deposits are matrix supported and contain abundant fragments of basalt, shallow marine limestone and soft-deformed sediments. It has been interpreted as mass-flow deposits (Figure 3 center). Facies 3: Is composed of sandstones with abundant rounded and well-rounded pebbles of basalt and shallow marine limestone. The sediments are matrix-supported. It has been interpreted as slope, near littoral deposits (Figure 3 bottom). On the basis of these observations, the Covachón Fm represents a shallowing-upward sequence deposited on top of the Azuero Accretionary Complex (Buchs et al. (2011)).

Thickness: >300 m

[Figre 2 Tectonostratigraphic chart showing the igneous complexes exposed on the Azuero Peninsula and surrounding areas as well as the sedimentary formations overlapping them. The ages of all formations/complexes were measured either by 40 Ar/39 Ar or Paleontologic methods (Barat (2013) and Modified from Buchs et al. (2008)). Note that Buchs et al. (2011) and Barat (2013) now includes the Pesé Fm as part of the Tonosí Fm, and the Macaracas Fm as the equivalent of the Santiago Fm.]

[Figure 3 (top). Lithic sandstones and siltstones from Facies 1 of the Covachón Fm at the mouth of the Lajas River on West Azuero Peninsula at 7°12'49.57"N 80°42'0.86"W. Ramirez (2013); (center). Mass-flow deposit (facies 2) from the Covachón Fm (Covachón, south Azuero Peninsula). Buchs (2008) and Buchs et al. (2011); (bottom). Pebbly sediments (facies 3) of the Covachón Fm (coastal exposure west of Río Lajas, south Azuero Peninsula) (Buchs (2008) and Buchs et al. (2011)). The conglomeratic sandstone of facies 3 can be observed at the mouth of the Lajas River at 7°12'45.07"N 80°42'5.47"W. Ramirez (2013)]

Lithology Pattern:

Clayey sandstone

Relationships and Distribution

Lower contact

Azuero Arc Gr (Azuero Accretionary Complex)

Upper contact

Tonosí Fm

Regional extent

GeoJSON

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Fossils

Larger benthic foraminifera

Age

An Early to Middle Eocene age can be determined from reworked larger benthic foraminifera near the base of the section, whereas a Middle Eocene age, results from the analysis of large benthic foraminifera in the matrix of chaotic deposits (Buchs et al. (2011) and Ramirez (2013)).

Age Span:

Beginning stage:

Lutetian

Fraction up in beginning stage:

Beginning date (Ma):

48.07

Ending stage:

Priabonian

Fraction up in the ending stage:

Ending date (Ma):

37.71

Depositional setting

A shallowing-upward sequence. Facies 1: turbiditic deposits; Facies 2: mass-flow deposits; Facies 3: slope, near littoral deposits.

Depositional pattern:

Additional Information

References: Buchs et al.; (2011) Ramirez (2013); Ramirez et al. (2016)

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)