Product Code Database
The Sabana Formation (, Q1sa, QTs) is a geological formation of the Bogotá savanna, Altiplano Cundiboyacense, Eastern Ranges of the Andes. The formation consists mainly of with at the edges of the Bogotá savanna and . The Sabana Formation dates to the Quaternary period; Pleistocene epoch, and has a maximum thickness of , varying greatly across the savanna. It is the uppermost formation of the lacustrine and fluvio-glacial sediments of paleolake Humboldt, that existed at the edge of the Eastern Hills until the latest Pleistocene.
The uppermost sediments of the Sabana Formation were deposited during the Last Glacial Maximum, a time when the first humans populated the Bogotá savanna. These hunter-gatherers used the bones of the still extant Pleistocene megafauna as Notiomastodon, Cuvieronius and Equus neogeus, of which fossils have been found in the Sabana Formation.
Knowledge about the formation has been provided by geologists Alberto Guerrero, Thomas van der Hammen and others.
During the Mesozoic, the central part of Colombia was a rift basin to the west of the Guyana Shield, where series of marine platform deposits were deposited. The proto-Caribbean, the result of the break-up of Pangea, formed a long seaway into the South American Plate, up to Bolivia. During the Late Cretaceous, the Western and Central Ranges of the Colombian Andes began rising, while the Eastern Ranges was still absent. The main phase of tectonic uplift of the Eastern Ranges commenced in the Middle Miocene, marked by a change in paleocurrents of the fluvial deposits of the Honda Group, the most fossiliferous stratigraphic unit of Colombia.
Subduction of the Nazca Plate underneath western South America and the resulting compression in the continent created reversal of former extensional faults of the Mesozoic rift basin in the Eastern Ranges. A series of fold and thrust belts, oriented in a north–south to northeast–southwest sense, were formed in the Eastern Andes, uplifting the former marine strata and creating a high plateau between the western and eastern fronts; the Altiplano Cundiboyacense. The tectonic movements of this Andean orogenic phase are reflected in Upper Miocene units as the Marichuela Formation, underlying the Pliocene and Pleistocene sediments of which the Sabana Formation represents the final chapter.
Present-day, the lakes of Fúquene, Lake Herrera and Lake Suesca are remnants of Lake Humboldt, as well as the many wetlands of Bogotá.
During the last phase of deposition of the Sabana Formation, the Bogotá savanna was surrounded by populations of Pleistocene megafauna. Fossils of the Megatherium and Eremotherium have been uncovered from Quipile,De Porta, 1961, p.52Bürgl, 1956 and Fusagasugá and Tocaima respectively, Notiomastodon platensis from Tocaima and Pubenza, accompanied by shells of Neocyclotus, to the west of the savanna, and Cuvieronius hyodon and Equus neogeus from the Sabana Formation at Tibitó.Correal Urrego, 1990, p.77De Porta, 1960 The migration of fauna was favoured by the existence of a dry corridor from the Magdalena River to the Eastern Ranges.Correal Urrego, 1993, p.4 Analysis of the fluorine in a fossil molar of a gomphothere, found in the Sabana Formation at Mosquera, provided an age between the last interglacial and the first stage of the last glacial of the Last Glacial Maximum.Hammen, 1986, p.29 The fossils of Pubenza and Tibitó were dated at 16,300 ± 150 and 11,740 ± 110 years BP respectively.Hammen, 1986, p.30 Researchers at the Universidade Federal do Estado do Rio de Janeiro, UNIRIO propose that all gomphotheres found in Colombia should be reassigned to a single species; Notiomastodon platensis.Mothé et al., 2016aMothé et al., 2016bMothé & Avilla, 2015Mothé et al., 2012 At the latest age of Tibitó, a páramo ecosystem was dominant.Cooke, 1988, p.180
During the Holocene, the inhabitants of the Bogotá savanna gradually moved away from the rock shelters as permanent settlements in favour of more open area locations, as Checua and Aguazuque. Around 5000 years BP, agriculture became a more dominant phenomenon and the fertile clays mixed with volcanic ash of the Sabana Formation, combined with the bimodal pattern of seasonal precipitation made the Bogotá savanna an ideal area for growing crops. Pottery was used in the Herrera Period, from around 2800 years BP onwards, and the sediments of the Sabana Formation were used for various styles of ceramics, grouped by researchers based on the colour of the original clays. The northern settlement of Suesca was an important ceramic producing centre for the people. An advanced civilisation developed in the first and second millennia CE, leading to the Muisca Confederation, a loose collection of . The southern Muisca area was centered around the Bogotá savanna with as main settlement Bacatá in the middle of the savanna, the namesake of the current capital of Colombia, Bogotá.Gómez Londoño, 2005, p.281
With the expansion in the late colonial and early republican era of the Colombian capital to the west and north of the city, the unconsolidated finer sediments of the Sabana Formation became more and more the foundation for construction, leading to problems due to the differential compaction of the sandy and more clay-rich strata. Por qué se hunde la Sabana de Bogotá - El Tiempo
Paleoecology
The Sabana Formation was deposited during the Pleistocene glaciations and interglacials (""). The fluctuations in climate in the Eastern Colombian Andes have been studied around Lake Fúquene at an altitude of , to the north of the Bogotá savanna. During the Last Glacial Maximum of the Pleistocene, the paleoecology of the region varied drastically, marking movements of the upper tree line and the types of vegetation. Pollen analysis shows that páramo vegetation was abundant from 30 ka to 17,500 years ago, with an increase in Andean forest frequency dated at 15.6 ka. Between 13,000 and 11,000 years BP, a decrease in Andean forest percentage is observed, indicative of a colder climate than before. This period has been named the Fúquene stadial. The stadial is followed by an interstadial (Guantivá), with an increase in lake levels of Lake Fúquene.Urrego et al., 2016, p.703 The wetter periods of the interstadial covered earlier paleotopography with humic sediments.Scott & Meyers, 1994, p.390
Human settlement
The latest sedimentation phase of the Sabana Formation, evidenced by the sites El Abra, Tibitó and Tequendama, was accompanied by the first confirmed human settlement in Colombia. Around 12,500 years BP, groups of the rock shelters surrounding the retreating Lake Humboldt. The people of the area hunted the still extant Pleistocene species, and used their remains for the construction of primitive settlements, as bone tools and the skins as clothing. At this stage, the tree line was lower than today.Zonneveld, 1968, p.205
Outcrops
The Sabana Formation is found at its type locality in the Funza II well, and covering most of the Bogotá savanna. The newer parts of Bogotá, especially the neighbourhoods north of the Avenida Chile (Calle 72) in Chapinero and west of the Autopista Norte (Avenida 30), rest upon the Sabana Formation, where the unconsolidated shales cause frequent fissures in the roads constructed in the Colombian capital. The southeastern part of Bogotá, including the historic centre, rests upon the more competent Tunjuelo Formation.
Regional correlations
See also
Notes
Bibliography
Geology
Paleoecology and history
Proposed reclassification of gomphotheres
Maps
|
|
