The Murca Formation (Spanish: Formación Murca, Kim) is a geological formation of the Altiplano Cundiboyacense, Eastern Ranges of the Colombian Andes. The predominantly subarkose sandstone with claystones and siltstones formation dates to the Early Cretaceous period; Valanginian epoch and has a maximum thickness of 924 metres (3,031 ft).

Murca Formation
Stratigraphic range: Late Valanginian
~135–133 Ma
TypeGeological formation
Unit ofCáqueza Group
UnderliesLa Naveta Fm., Trincheras Fm., Útica Fm.
Overliesnot observed
Thicknessup to 924 m (3,031 ft)
Lithology
PrimarySandstone
OtherClaystone, siltstone
Location
Coordinates5°15′27″N 74°21′12″W / 5.25750°N 74.35333°W / 5.25750; -74.35333
RegionAltiplano Cundiboyacense
Eastern Ranges, Andes
Country Colombia
Type section
Named forMurca River
Named byMoreno
LocationPacho, El Peñón
Year defined1990
Coordinates5°15′27″N 74°21′12″W / 5.25750°N 74.35333°W / 5.25750; -74.35333
RegionCundinamarca, Boyacá
Country Colombia

Etymology

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The formation was defined and named in 1990 by Moreno after the Murca River, Cundinamarca.[1][2]

Description

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Lithologies

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The Murca Formation has a maximum thickness of 924 metres (3,031 ft), and is characterised by a sequence of subarkose coarse-grained, locally cross-bedded sandstones with intercalating siltstones and claystones. The basal part of the black and grey feldspar bearing sandstone beds contains large pyrite crystals. The matrix is formed by cements of calcite, iron oxide, sericite and chlorite.[3]

Fossils of Berriasella colombiana and Pseudoosterella ubalaensis have been found in the Murca Formation.[4][5][6][7][8]

Stratigraphy and depositional environment

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The Murca Formation, belonging to the Cáqueza Group, underlies the Trincheras Formation, lowermost unit of the Villeta Group. The contact with the underlying unit has not been observed.[3] The age has been estimated to be Valanginian. Stratigraphically, the formation is time equivalent with the Cumbre, Rosablanca and Útica Formations. The formation has been deposited in a marine environment characterised by turbidites.[4] A mid submarine fan and outer fan setting have been observed in the Murca Formation.[9] A possible source for the sandstones were Precambrian sandstones, gneisses and granites, belonging to the Guiana Shield.[3][10]

Outcrops

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Type locality of the Murca Formation to the northwest of the Bogotá savanna

The Murca Formation is apart from its type locality, found near Nimaima and Guayabal in the western flank and Ubalá and Labranzagrande in the eastern flank of the Eastern Ranges.[1][5][6][7]

Regional correlations

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See also

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  Geology of the Eastern Hills
  Geology of the Ocetá Páramo
  Geology of the Altiplano Cundiboyacense

References

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  1. ^ a b Acosta & Ulloa, 2002, p.37
  2. ^ Moreno, 1990, p.66
  3. ^ a b c Moreno, 1990, p.72
  4. ^ a b Acosta & Ulloa, 2002, p.38
  5. ^ a b Dorado Galindo, 1990, p.23
  6. ^ a b Moreno, 1990, p.76
  7. ^ a b Piraquive et al., 2011, p.207
  8. ^ Pseudoosterella ubalaensis
  9. ^ Acosta & Ulloa, 2001, p.19
  10. ^ Villamil, 2012, p.165

Bibliography

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Maps

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