San Blas Fm

Period:

Cretaceous, Paleogene

Age Interval:

Cretaceous (Base), top Middle Eocene (Top) - Coates et al. (2004)

Province:
Eastern Panama

Type Locality and Naming

Named by Bandy (1970); Bandy and Casey (1973).

The San Blas Fm crops out in the Massifs of San Blas–Darien, Majé, Bagre and Sapo, as well as in the San Miguel Gulf. Barat et al. (2014)

Synonym: San Blas Complex

Lithology and Thickness

The oldest reliably dated rocks in the Darien belong to a Campanian accretionary volcanic arc complex. Together with their magmatic arc equivalents, they form the basement complex of the Darien, herein described as the San Blas Fm (San Blas Complex) (Figure 011). The San Blas Fm is composed of a Pre-Middle Eocene magmatic basement (Terry (1956); Case (1974)) overlain by volcano-clastic rocks (the Punta Sabana Fm and Caobanera Fm; Esso Exploration and Production Panama (1970, 1971a, 1971b); Bandy and Casey (1973)) and Mesozoic sedimentary formations of the Changuinola Gr, such as Morti Tuffs (Bandy and Casey (1973)) and the Ocú Fm (Ministerio de Comercio e Industrias (1991)).

On the northeastern flank of the Chucunaque-Tuira Basin, in the San Blas and Darien Massifs, the San Blas Fm is a magmatic arc suite consisting of granodiorite, quartz diorite, basaltic andesite, dacite, and rhyolite. On the southwestern flank, in the region around the Gulf of San Miguel, it is represented by an accretionary lithofacies consisting of diabase and pillow basalt associated with radiolarian chert, named the Punta Sabana Volcanics.

Thickness: Very thick but not yet defined (Figure1)

[Figure1: Synthetic chronostratigraphic chart of the different areas of Jacques (2021). The Canal Zone area shows a comparison with the eastern Panama data. Colors are identical to the associated cross sections (Barat (2013) and Barat et al. (2014)). 1) San Blas Fm (San Blas Complex); 2) Darien Fm; 3) Porcona Fm; 4) Bas Obispo Fm; 5) Gatuncillo Fm; 6) Las Cascadas Fm, La Culebra Fm and Cucaracha Fm; 7) Clarita Fm; 8) Pedro Miguel Fm; 9) Late Basalts Fm; 10) Tapaliza Fm; 11) Gatún Fm; 12) Tuira Fm; 13) Chagres Fm; 14) Chucunaque Fm.]

Lithology Pattern:

Volcanics

Relationships and Distribution

Lower contact

N/A (Figure 1).

Upper contact

The San Blas Fm is unconformably overlain by the Eocene-Oligocene Darien Fm and Porcona Fm (Figure 1).

Regional extent

Eastern Panama

GeoJSON

{"type":"Feature","geometry":{"type":"MultiPolygon","coordinates":[[[[-79.61,9.61],[-79.48,9.64],[-79.23,9.6],[-78.99,9.56],[-78.49,9.45],[-78.08,9.29],[-77.84,9.09],[-77.4,8.7],[-77.35,8.59],[-77.3,8.42],[-77.18,8.02],[-77.26,7.82],[-77.39,7.66],[-77.56,7.46],[-77.73,7.31],[-77.83,7.24],[-77.89,7.24],[-78.01,7.33],[-78.25,7.61],[-78.38,7.9],[-78.43,8.14],[-78.4,8.31],[-78.51,8.49],[-78.64,8.67],[-78.88,8.86],[-79.18,8.99],[-79.35,9.03],[-79.37,9.04],[-79.42,9.09],[-79.52,9.13],[-79.52,9.17],[-79.54,9.21],[-79.54,9.3],[-79.54,9.35],[-79.62,9.34],[-79.7,9.33],[-79.8,9.41],[-79.75,9.49],[-79.61,9.61]]]]}}

Fossils

Nannofossils and foraminifera

Age

Age Span:

Beginning stage:

Campanian

Fraction up in beginning stage:

Beginning date (Ma):

83.65

Ending stage:

Maastrichtian

Fraction up in the ending stage:

Ending date (Ma):

72.17

Depositional setting

An assemblage of radiolarians was recovered from the interbedded chert that indicates deposition at abyssal depths during the Campanian. Coates et al. (2004). More recently, several studies have analyzed the geochemical and geochronological characteristics of the magmatic rocks (Lissina (2005); Wegner et al. (2011); Buchs et al. (2010, 2011); Montes et al. (2012b)), and these studies reported three distinctive volcanic–volcano-clastic groups: an oceanic plateau, and a proto-arc to a mature-arc.

Depositional pattern:

Additional Information

References: Terry (1956); Esso Exploration and Production Panama (1970, 1971a, 1971b); Case (1974); Coates et al. (2004); Lissina (2005); Wegner et al. (2011); Buchs et al. (2010, 2011); Montes et al. (2012b); 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)