Murca Formation

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 PreꞒ Ꞓ O S D C P T J K Pg N ↓
Type	Geological formation
Unit of	Cáqueza Group
Underlies	La Naveta Fm., Trincheras Fm., Útica Fm.
Overlies	not observed
Thickness	up to 924 m (3,031 ft)
Lithology
Primary	Sandstone
Other	Claystone, siltstone
Location
Coordinates	5°15′27″N 74°21′12″W
Region	Altiplano Cundiboyacense Eastern Ranges, Andes
Country	Colombia
Type section
Named for	Murca River
Named by	Moreno
Location	Pacho, El Peñón
Year defined	1990
Coordinates	5°15′27″N 74°21′12″W
Region	Cundinamarca, Boyacá
Country	Colombia

Etymology

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

Description

Lithologies

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

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

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]

See also

• Colombia portal
• Geology portal

Geology of the Eastern Hills

Geology of the Ocetá Páramo

Geology of the Altiplano Cundiboyacense