| Santa Teresa Formation | |
|---|---|
| Stratigraphic range: Late Oligocene (Deseadan) ~ | |
| Type | Geological formation |
| Underlies | alluvium |
| Overlies | San Juan de Río Seco Formation |
| Thickness | Type section: 118 m (387 ft) Maximum: 150 m (490 ft) |
| Lithology | |
| Primary | Claystone |
| Other | Siltstone, calcareous sandstone |
| Location | |
| Coordinates | 4°50′55″N 74°37′14″W / 4.84861°N 74.62056°W |
| Country |  Colombia |
| Extent | Western Eastern Ranges, Andes Southern Middle Magdalena Valley |
| Type section | |
| Named for | Vereda Santa Teresa |
| Named by | De Porta |
| Location | San Juan de Rioseco |
| Year defined | 1966 |
| Coordinates | 4°50′55″N 74°37′14″W / 4.84861°N 74.62056°W |
| Region | Cundinamarca |
| Country | Colombia |
| Thickness at type section | 118 m (387 ft) |
 Paleogeography of Northern South America 35 Ma, by Ron Blakey | |
The Santa Teresa Formation (Spanish: Formación Santa Teresa, Tist, Pgst) is a geological formation of the western Eastern Ranges of the Colombian Andes, west of the Bituima Fault, and the southern Middle Magdalena Valley. The formation spreads across the western part of Cundinamarca and the northern portion of Tolima. The formation consists of grey claystones intercalated by orange quartz siltstones and sandstones of small to conglomeratic grain size. The thickness at its type section has been measured to be 118 metres (387 ft) and a maximum thickness of 150 metres (490 ft) suggested.
In the formation, dated on the basis of its fossil content to the Late Oligocene, many leaf imprints and mollusks were found, suggesting a lacustrine to deltaic depositional environment with periodical marine incursions.