ravine
A ravine is a landform that is narrower than a canyon and is often the product of streambank erosion.Wonga-Wongue Presidential Reserve in western
Gabon
Gabon (; ; snq, Ngabu), officially the Gabonese Republic (french: République gabonaise), is a country on the west coast of Central Africa. Located on the equator, it is bordered by Equatorial Guinea to the northwest, Cameroon to the north ...
.
Although they are referred to as "
cirque
A (; from the Latin word ') is an amphitheatre-like valley formed by glacial erosion. Alternative names for this landform are corrie (from Scottish Gaelic , meaning a pot or cauldron) and (; ). A cirque may also be a similarly shaped landform ...
s," they are unrelated to the glacial cirques of high latitudes and mountains. In Gabon, they are east-facing slopes cut into the
Upper Cretaceous
The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''creta'', the ...
to
Paleocene
The Paleocene, ( ) or Palaeocene, is a geological epoch (geology), epoch that lasted from about 66 to 56 mya (unit), million years ago (mya). It is the first epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), E ...
sandstone
Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks.
Most sandstone is composed of quartz or feldspar (both silicates) ...
s that dip westward beneath the Atlantic Ocean. Because the sandstones are higher and drier than the surrounding coastal plain, they are covered with grasslands rather than the prevailing
tropical rain forest
Tropical rainforests are rainforests that occur in areas of tropical rainforest climate in which there is no dry season – all months have an average precipitation of at least 60 mm – and may also be referred to as ''lowland equatori ...
. As the sandstones are locally intensely colored, and because the steep slopes tend to be barren, the "cirques" locally appear to be "
badlands
Badlands are a type of dry terrain where softer sedimentary rocks and clay-rich soils have been extensively eroded."Badlands" in ''Chambers's Encyclopædia''. London: George Newnes, 1961, Vol. 2, p. 47. They are characterized by steep slopes, m ...
" similar to those of the American West.Horner, R. H., 1985, The Gabon Basin: its regional setting with respect to onshore basement tectonic elements as interpreted from side-looking airborne radar imagery: Remote Sensing for Exploration Geology, 4th Thematic Conference, Proceedings, Environmental Research Institute of Michigan, p. 31-47.