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 platensis, Cuvieronius hyodon 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.
Etymology
The formation was first defined and named after the
Bogotá savanna (Sabana de Bogotá) by Hubach in 1957, further described by Van der Hammen in 1973,[1] Guerrero (1992, 1993, 1996) and by Helmens and
Van der Hammen in 1995.[2][3][4][5]
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.
Description
Lithologies
The Sabana Formation consists mainly of horizontally bedded little consolidated grey and greenish
shales with
lignite and
diatomites,[3] and fine to coarse
sandstones at the edges of the Bogotá savanna.[6] Numerous
volcanic ash deposits are noted in the Sabana Formation.[2] Organic material is preserved in black soils and silts form the terraces of the central part of the savanna.[5] The volcanic ash had as provenance area the
Central Ranges of the Colombian Andes, with probably minor influences from the volcanic areas of
Boyacá (
Paipa–Iza volcanic complex). The diatomites are associated with the ash layers, a common feature in the geological record.[7]
The
depositional environment has been interpreted as
lacustrine (
Lake Humboldt) and fluvio-deltaic,[2] with a near-continuous deposition since the
Late Pliocene. The Sabana Formation represents the uppermost unit of the lacustrine deposition of Lake Humboldt.[5] At the edges of the lake, numerous deltas of fluvio-glacial origin were present, reflected in the coarser sediments. During periods of stormy climate around the lake, coarser sediments were transported to the interior of the lake. The depositional cycles were geologically speaking fast and the water level of the lake fluctuated greatly during its history. Furthermore, the local tectonic activity of the Bogotá savanna, related to movements of the
Bogotá Fault, influenced the depositional cycles. The middle unit of the formation shows a drying out of the lake and subaerial erosional surfaces.[10] The upper part of the Sabana sequence is characterised by fluvial deposits around a retreating Lake Humboldt, estimated at an age of around 30,000 years
BP. The glacial origin was predominantly the
Sumapaz Páramo to the south of the Bogotá savanna, with minor snow-capped peaks in the
Eastern Hills of Bogotá.[11]
The Sabana Formation was deposited during the Pleistocene glaciations and interglacials ("
ice ages"). The fluctuations in climate in the Eastern Colombian Andes have been studied around Lake Fúquene at an altitude of 2,540 metres (8,330 ft), 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.[12] The wetter periods of the interstadial covered earlier paleotopography with humic sediments.[13]
The latest sedimentation phase of the Sabana Formation, evidenced by the
sitesEl Abra,
Tibitó and
Tequendama, was accompanied by the first confirmed human settlement in Colombia. Around 12,500 years BP, groups of
hunter-gathererspopulated 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
timber line was 1,000 metres (3,300 ft) lower than today.[26]
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 caciques. 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.[27]
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.[28]
Type locality of the Sabana Formation on the Bogotá savanna
The Sabana Formation is found at its
type locality in the Funza II well, and covering most of the Bogotá savanna.[2] 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.[3]
Regional correlations
Stratigraphy of the
Llanos Basin and surrounding provinces
Guerrero Uscátegui, Alberto Lobo. 1996. Estratigrafía del material no-consolidado en el subsuelo del nororiente de Santafé de Bogotá (Colombia) con algunas notas sobre historia geológica, 1–23. VII Congreso Colombiano de Geología - I Seminario sobre el Cuaternario.
Guerrero Uscátegui, Alberto Lobo. 1993. Informe sobre la Cuenca Petrolífera de la Sabana de Bogotá, Colombia, 1–29. Sociedad Colombiana de Ingenieros.
Guerrero Uscátegui, Alberto Lobo. 1992. Geología e Hidrogeología de Santafé de Bogotá y su Sabana, 1–20. Sociedad Colombiana de Ingenieros.
Montoya Arenas, Diana María, and Germán Alfonso Reyes Torres. 2005. Geología de la Sabana de Bogotá, 1–104.
INGEOMINAS.
Gómez Londoño, Ana María. 2005. Lo muisca: el diseño de una cartografía de centro. Chigys Mie: el mundo de los muiscas recreado por la condesa alemana Gertrud von Podewils Dürniz in "Muiscas: representaciones, cartografías y etnopolíticas de la memoria", 248–291.
Universidad La Javeriana.
Van der Hammen, Thomas. 1986. Cambios medioambientales y la extinción del mastodonte en el norte de los Andes. Revista de Antropología,
Universidad de los Andes II. 27–34. .
Montes, Natalia; O. Monsalve; G.W. Berger; J.L. Antinao; H. Giraldo; C. Silva; G. Ojeda; G. Bayona, and J. Escobar. 2015. A climatic trigger for catastrophic Pleistocene–Holocene debris flows in the Eastern Andean Cordillera of Colombia. Journal of Quaternary Science 30(3). 258–270. .
Rutter, N.; A. Coronato; K. Helmens; J. Rabassa, and M. Zárate. 2012. Glaciations in North and South America from the Miocene to the Last Glacial Maximum, 1–67.
Springer.
Scott, David A., and Pieter Meyers. 1994. Archaeometry of Pre-Columbian sites and artifacts, 1–437. The
Getty Conservation Institute.
Torres, Vladimir; Jeff Vandenberghe, and Henry Hooghiemstra. 2005. An environmental reconstruction of the sediment infill of the Bogotá basin (Colombia) during the last 3 million years from abiotic and biotic proxies. Palaeogeography, Palaeoclimatology, Palaeoecology 226. 127–148. .
Urrego, Dunia H.; Henry Hooghiemstra; Oscar Rama Corredor; Belén Martrat; Joan O. Grimalt; Lonnie Thompson; Mark B. Bush; Zaire González Carranza, and Jennifer Hanselman, Bryan Valencia and César Velásquez Ruiz. 2016. Millennial-scale vegetation changes in the tropical Andes using ecological grouping and ordination methods. Climate of the Past 12. 697–711. .
Villarroel, Carlos; Ana Elena Concha, and Carlos Macía. 2001. El Lago Pleistoceno de Soatá (Boyacá, Colombia): Consideraciones estratigráficas, paleontológicas y paleoecológicas. Geología Colombiana 26. 79–93. .
Zonneveld, Jan Isaak Samuel. 1968. Quaternary climatic changes in the Caribbean and N. South America, 203–208.