Tunjuelo Formation

The Tunjuelo Formation, Río Tunjuelo or Río Tunjuelito Formation (Spanish: Formación Tunjuelo, Q1tu, Qpt, Qcc) is a geological formation of the Bogotá savanna, Altiplano Cundiboyacense, Eastern Ranges of the Colombian Andes. The formation consists mainly of conglomerates with intercalating shales and sandstones. The Tunjuelo Formation dates to the Quaternary period; covering the complete Pleistocene epoch, and has a maximum thickness of 150 metres (490 ft). It is a formation of the lacustrine and fluvio-glacial sediments of Lake Humboldt.

Tunjuelo Formation
Stratigraphic range: Pleistocene
~2.6–0.01 Ma
↓
TypeGeological formation
UnderliesChía Fm., Sabana Fm.
OverliesMarichuela Formation
Subachoque Formation
Thicknessup to 150 metres (490 ft)
Lithology
PrimaryConglomerate
OtherSandstone, shale
Location
Coordinates4°28′04.0″N 74°08′11.9″W
RegionBogotá savanna, Altiplano Cundiboyacense
Eastern Ranges, Andes
Country Colombia
Type section
Named forTunjuelo River
Named byHelmens & Hammen
LocationTunjuelo River valley
Year defined1995
Coordinates4°28′04.0″N 74°08′11.9″W
RegionCundinamarca
Country Colombia

Paleogeography of the Pleistocene
by Ron Blakey

Etymology

The formation was first defined and named by Helmens and Van der Hammen in 1995 after the Tunjuelo River, also called Tunjuelito River, of southern Bogotá.[1]

Description

Lithologies

The Tunjuelo Formation consists mainly of conglomerates with intercalating shales and sandstones.[1]

Stratigraphy and depositional environment

The Tunjuelo Formation conformably overlies the Marichuela Formation and in other parts the Subachoque Formation. The Tunjuelo Formation is overlain by the thin Chía Formation. The age has been estimated to be Pleistocene based on palynology and radiocarbon dating, covering the Pleistocene from 2.6 to 0.01 Ma.[2] The depositional environment has been interpreted as fluvio-glacial terraces.[1]

Outcrops
Type locality of the Tunjuelo Formation to the south of the Bogotá savanna

The Tunjuelo Formation is found at its type locality in the Tunjuelo River valley, in the synclinal of Guasca, near Cogua, Cundinamarca,[1] and in the basins of the rivers San Cristóbal, San Francisco, Arzobispo and Subachoque, and the creeks (quebradas) Las Delicias, La Vieja, Rosales and Chicó of the Colombian capital.[3] In the Tunjuelo River valley, the formation is crossed by the northeast-southwest oriented Yerbabuena Fault.[4]

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See also
Geology of the Eastern Hills
Geology of the Ocetá Páramo
Geology of the Altiplano Cundiboyacense

References
  1. Montoya & Reyes, 2005, p.71
  2. Montoya & Reyes, 2005, p.72
  3. Lobo Guerrero, 1992, p.6
  4. Geological Map Bogotá, 1997

Bibliography
  • 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.

Maps
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