The Las Juntas Formation or Las Juntas Sandstone ( es, (Formación) Areniscas de Las Juntas, Kiaj, Kialj, K1j) is a

geological formation A geological formation, or simply formation, is a body of rock having a consistent set of physical characteristics (lithology) that distinguishes it from adjacent bodies of rock, and which occupies a particular position in the layers of rock expo ...

of the

Altiplano Cundiboyacense The Altiplano Cundiboyacense () is a high plateau located in the Eastern Cordillera of the Colombian Andes covering parts of the departments of Cundinamarca and Boyacá. The altiplano corresponds to the ancient territory of the Muisca. The Alt ...

and Tenza Valley,

Eastern Ranges The Eastern Ranges is an Australian rules football team in the NAB League, the Victorian statewide under-18s competition. The club is a founding member of the competition (1992) and has produced several players for the Australian Football Le ...

of the Colombian

Andes The Andes, Andes Mountains or Andean Mountains (; ) are the longest continental mountain range in the world, forming a continuous highland along the western edge of South America. The range is long, wide (widest between 18°S – 20°S ...

. The Las Juntas Formation is found in the

departments Department may refer to: * Departmentalization, division of a larger organization into parts with specific responsibility Government and military *Department (administrative division), a geographical and administrative division within a country, ...

Cundinamarca, Boyacá and Casanare. The predominantly

sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates ...

formation dates to the

Early Cretaceous The Early Cretaceous (geochronological name) or the Lower Cretaceous ( chronostratigraphic name), is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 145 Ma to 100.5 Ma. Geology Pr ...

period;

Hauterivian The Hauterivian is, in the geologic timescale, an age in the Early Cretaceous Epoch or a stage in the Lower Cretaceous Series. It spans the time between 132.9 ± 2 Ma and 129.4 ± 1.5 Ma (million years ago). The Hauterivian is preceded by t ...

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 Guateque is a town and municipality in the Colombian Department of Boyacá, part of the subregion of the Eastern Boyacá Province. Guateque's urban center is located at an altitude of on the Altiplano Cundiboyacense at distances of from the dep ...

, 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

s 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 The Fómeque Formation ( es, Formación Fómeque, Kif) is a geological formation of the Altiplano Cundiboyacense, Eastern Ranges of the Colombian Andes. The predominantly organic shale formation dates to the Early Cretaceous period; Barremian to ...

and the

Apón Formation The Apón Formation is a geological formation in northwestern Venezuela ( Maracaibo Basin) and northern Colombia ( La Guajira),García González et al., 2010 whose thick-bedded limestone interbedded with subordinate amounts of dark gray calcareous ...

in the

Sierra Nevada del Cocuy The Sierra Nevada del Cocuy Chita or Guican National Natural Park (or Sierra Nevada de Chita or Sierra Nevada de Güicán, es, Parque Natural Sierra Nevada del Cocuy Chita o Guican is a national park and a series of highlands and glaciated peaks l ...

.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

. The formation has been deposited in a near shore deltaic

environment Environment most often refers to: __NOTOC__ * Natural environment, all living and non-living things occurring naturally * Biophysical environment, the physical and biological factors along with their chemical interactions that affect an organism or ...

, with as provenance areas the Santander High and the

Guiana Shield The Guiana Shield (french: Plateau des Guyanes, Bouclier guyanais; nl, Hoogland van Guyana, Guianaschild; pt, Planalto das Guianas, Escudo das Guianas; es, Escudo guayanés) is one of the three cratons of the South American Plate. It is a ...

.Villamil, 2012, p.165 The formation represents a regressive sequence in the present-day Eastern Ranges, as the

Rosablanca Formation The Rosablanca Formation ( es, Formación Rosablanca, Kir) is a geological formation of the Altiplano Cundiboyacense, Eastern Ranges of the Colombian Andes and the Middle Magdalena Basin. The formation consists of grey limestones, dolomites and ...

in the Middle Magdalena Valley.Villamil, 2012, p.166

Outcrops

The Las Juntas Formation is apart from its

type locality Type locality may refer to: * Type locality (biology) * Type locality (geology) See also * Local (disambiguation) * Locality (disambiguation) {{disambiguation ...

east of

, 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

Notes

References

Bibliography

* * *

Maps

* * * * * *

External links

* {{Colombian emeralds, state=expanded Geologic formations of Colombia Cretaceous Colombia Lower Cretaceous Series of South America Hauterivian Stage Sandstone formations Deltaic deposits Formations Formations Geography of Cundinamarca Department Geography of Boyacá Department Geography of Casanare Department