Santa Marta
Key facts
- Country
- Brazil
- Diameter
- 10 km
- Age
- between about 66 and 100 million years
- Location
- 10.17° S, 45.25° W
A round pattern of hills and valleys about 10 km across in the cerrado of southern Piauí, Brazil.
Santa Marta is an eroded impact structure about 10 km across in the state of Piauí, in north-eastern Brazil. It is one of the more recently confirmed impact structures in South America.
Discovery. The round structure was noticed on satellite images, and in the 2010s geologists carried out field studies. They found shatter cones, cone-shaped fractures produced only by the shock of an impact, and quartz grains with planar deformation features and other shock effects. These confirmed that Santa Marta is an impact structure, and the results were published in 2015.
What it hit. The impactor struck sedimentary rocks, mainly sandstones and siltstones, of the Sanfranciscana and Parnaíba basins. The structure has a central uplift surrounded by an annular basin and an outer ring of faulted rocks.
Age. The youngest rocks affected are Cretaceous sandstones, so the impact happened less than about 100 million years ago. It is thought to be older than about 66 million years, but the age is not precisely known.
Why it matters. Santa Marta shows that new impact structures are still being found and confirmed, even in well-mapped countries, by combining satellite images with careful fieldwork. The impactor is unknown.
Did you know?
Santa Marta's impact origin was confirmed only in 2015.
It was first noticed on satellite images.
Shatter cones and shocked quartz proved its origin.