The Las Juntas Formation or Las Juntas Sandstone (, Kiaj, Kialj, K1j) is a geological formation of the Altiplano Cundiboyacense and Tenza Valley, Eastern Ranges of the Colombian Andes. The Las Juntas Formation is found in the departments Cundinamarca, Boyacá and Casanare. The predominantly sandstone formation dates to the Early Cretaceous period; Hauterivian epoch, and has a maximum thickness of .
Etymology The formation was defined and named in 1979 by Rodríguez and Ulloa after Cerro Las Juntas, Guateque, Tenza Valley, Boyacá.Acosta & Ulloa, 2002, p.52Rodríguez & Solano, 2000, p.47
Description Lithologies The Las Juntas Formation has a maximum thickness of and is characterised by a sequence of sandstones with interbedded shales.
Stratigraphy and depositional environment The Las Juntas Formation, the uppermost unit of the Cáqueza Group, overlies the Macanal Formation and is overlain by the Fómeque Formation and the Apón Formation in the Sierra Nevada del Cocuy.Villamil, 2012, p.168 The formation is subdivided into three members, from old to younger; Arenisca de El Volador, Lutitas Intermedias and Arenisca de Almeida. The age has been estimated to be Hauterivian. The formation has been deposited in a near shore deltaic environment, with as provenance areas the Santander High and the Guiana Shield.Villamil, 2012, p.165 The formation represents a regressive sequence in the present-day Eastern Ranges, as the Rosablanca Formation in the Middle Magdalena Valley.Villamil, 2012, p.166
Outcrops
The Las Juntas Formation is apart from its type locality east of Guateque, found in Chingaza National Park, in the El Cochal Synclinal east of the Ocetá Páramo,Plancha 172, 1998 between Lake Tota and Labranzagrande,Plancha 192, 1998 other parts of the Tenza Valley such as close to Macanal and Almeida.Plancha 210, 2010
The Támara Fault thrusts the Las Juntas Formation southeastward on top of the Tertiary San Fernando and Diablo Formations,Plancha 193, 1992 and the Chámeza Fault thrusts the older Macanal Formation on top of the Las Juntas Formation around Chámeza, Casanare.Plancha 211, 2009
Regional correlations
See also
Geology of the Eastern Hills Geology of the Ocetá Páramo Geology of the Altiplano Cundiboyacense
Notes
References
Bibliography
Maps
External links