| 词条 | Las Juntas Formation |
| 释义 |
| name = Las Juntas Formation | period = Hauterivian | age = Hauterivian ~{{fossil range|132|130}} | image = | imagesize = | caption = | type = Geological formation | prilithology = Sandstone | otherlithology = Shale | unitof = Cáqueza Group | subunits = Arenisca de Almeida Mb. Lutitas Intermedias Mb. Arenisca de El Volador Mb. | underlies = Fómeque Fm., Apón Fm. | overlies = Macanal Formation | thickness = up to {{convert|910|m|ft|abbr=on}} | area = | map = | location | coordinates = {{coord|5|00|49|N|73|27|27|W|display=inline,title}} | region = Altiplano Cundiboyacense & Tenza Valley Eastern Ranges Andes | country = {{COL}} | extent = | namedfor = Cerro Las Juntas | namedby = Rodríguez & Ulloa | year_ts = 1979 | location_ts = Guateque | coordinates_ts = {{coord|5|00|49|N|73|27|27|W|display=inline}} | paleocoordinates_ts = | region_ts = Boyacá | country_ts = {{COL}} | thickness_ts = }} The Las Juntas Formation or Las Juntas Sandstone ({{lang-es|(Formación) Areniscas de Las Juntas}}, 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 {{convert|910|m|ft}}. EtymologyThe formation was defined and named in 1979 by Rodríguez and Ulloa after Cerro Las Juntas, Guateque, Tenza Valley, Boyacá.[1][2] DescriptionLithologiesThe Las Juntas Formation has a maximum thickness of {{convert|910|m|ft}} and is characterised by a sequence of sandstones with interbedded shales.[1] Stratigraphy and depositional environmentThe 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.[3] 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,[1][2] with as provenance areas the Santander High and the Guiana Shield.[4] The formation represents a regressive sequence in the present-day Eastern Ranges, as the Rosablanca Formation in the Middle Magdalena Valley.[5] Outcrops{{Location map | Altiplano Cundiboyacense| width = 250 | lat_deg = 5.013639 | lon_deg = -73.457391 | label = | float = left | position = right | mark = Green pog.svg | marksize = 12 | caption = Type locality of the Las Juntas Formation in the Tenza Valley east of the Altiplano Cundiboyacense }} The Las Juntas Formation is apart from its type locality east of Guateque, found in Chingaza National Park,[1] in the El Cochal Synclinal east of the Ocetá Páramo,[6] between Lake Tota and Labranzagrande,[7] other parts of the Tenza Valley such as close to Macanal and Almeida.[8] The Támara Fault thrusts the Las Juntas Formation southeastward on top of the Tertiary San Fernando and Diablo Formations,[9] and the Chámeza Fault thrusts the older Macanal Formation on top of the Las Juntas Formation around Chámeza, Casanare.[10] {{clearleft}}Regional correlations{{Cretaceous stratigraphy of the central Colombian Eastern Ranges}}See also{{portal|Colombia|Cretaceous|Geology|Prehistory of South America}}{{icon|FAC}} Geology of the Eastern Hills {{icon|B}} Geology of the Ocetá Páramo {{icon|C}} Geology of the Altiplano Cundiboyacense{{clearboth}} References1. ^1 2 3 Acosta & Ulloa, 2002, p.52 2. ^1 Rodríguez & Solano, 2000, p.47 3. ^Villamil, 2012, p.168 4. ^Villamil, 2012, p.165 5. ^Villamil, 2012, p.166 6. ^Plancha 172, 1998 7. ^Plancha 192, 1998 8. ^Plancha 210, 2010 9. ^Plancha 193, 1992 10. ^Plancha 211, 2009 Bibliography
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External links
11 : Geologic formations of Colombia|Cretaceous Colombia|Lower Cretaceous Series of South America|Hauterivian Stage|Sandstone formations|Deltaic deposits|Colombian emeralds|Altiplano Cundiboyacense|Geography of Cundinamarca Department|Geography of Boyacá Department|Geography of Casanare Department |
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