Subachoque Formation Explained

Subachoque Formation
Period:Pleistocene
Age:Early to Mid Pleistocene
~
Type:Geological formation
Prilithology:Shale, lignite
Otherlithology:Sandstone
Underlies:Sabana Formation
Overlies:Tilatá Formation
Guadalupe Gp.
Guaduas Fm., Cacho Fm., Bogotá Fm., Regadera Fm.
Thickness:up to 150m (490feet)
Map:Blakey Pleist - COL.jpg
Coordinates:4.9548°N -74.2188°W
Region:Bogotá savanna, Altiplano Cundiboyacense
Eastern Ranges, Andes
Namedfor:Subachoque
Namedby:Helmens & Hammen
Year Ts:1995
Location Ts:Subachoque Synclinal
Coordinates Ts:4.9548°N -74.2188°W
Region Ts:Cundinamarca

The Subachoque Formation (Spanish; Castilian: Formación Subachoque, Q1su) is a geological formation of the Bogotá savanna, Altiplano Cundiboyacense, Eastern Ranges of the Colombian Andes. The formation consists mainly of sandy shales and lignite with sandstone beds. The Subachoque Formation dates to the Quaternary period; Early to Middle Pleistocene epoch (from approximately 2.5 to 1 Ma), and has a maximum thickness of 150m (490feet). It is the lowermost formation of the lacustrine and fluvio-glacial sediments of Lake Humboldt.

Etymology

The formation was first defined and named by Helmens and Van der Hammen in 1995 after Subachoque, Cundinamarca.[1]

Description

Lithologies

The Subachoque Formation consists mainly of sandy shales, some organic, with lignite and sandstone beds.[1]

Stratigraphy and depositional environment

The Subachoque Formation is the lowermost of the lagunal and alluvial sequence of the Bogotá savanna. In parts, it conformably overlies the Tilatá Formation and other parts unconformably the Cretaceous Guadalupe Group and the Paleogene Guaduas, Cacho, Bogotá, and Regadera Formations. The Subachoque Formation is overlain by other Quaternary deposits of Lake Humboldt. The age has been estimated to be Early to Middle Pleistocene based on fission track analysis, with reported ages between 2.5 and 1 Ma.[2] The depositional environment has been interpreted as lacustrine and fluvio-glacial with alluvial fans.[1]

Outcrops

The Subachoque Formation is found at its type locality in the western flank of the synclinal of Subachoque and in the western flank of the synclinal of Guasca.[1] The deposition of the Subachoque Formation postdates the main reverse movement of the Bogotá Fault.[3]

See also

Geology of the Eastern Hills

Geology of the Ocetá Páramo

Geology of the Altiplano Cundiboyacense

References

Bibliography

Maps

Notes and References

  1. Montoya & Reyes, 2005, p.69
  2. Montoya & Reyes, 2005, p.71
  3. Geological Map Bogotá, 1997