The geology of the Gambia is defined by thick and comparatively recent sequences of sediments and sedimentary rocks, deposited in the last 66 million years. The country is underlain almost entirely by geologically recent

Cenozoic The Cenozoic ( ; ) is Earth's current geological era, representing the last 66million years of Earth's history. It is characterised by the dominance of mammals, birds and flowering plants, a cooling and drying climate, and the current configura ...

sedimentary rocks. Much deeper basement rocks are likely present, although they are not well understood. Most research has focused on oil and groundwater exploration.

Stratigraphy

The oldest rock units recognized in the west of the country, along the Gambia River are sandstones and kaolinitic claystones from the

Oligocene The Oligocene ( ) is a geologic epoch of the Paleogene Period and extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that define the epoch are well identified but the ...

Miocene The Miocene ( ) is the first geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and means "less recen ...

Pliocene The Pliocene ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million to 2.58Pleistocene The Pleistocene ( , often referred to as the ''Ice age'') is the geological Epoch (geology), epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fina ...

are found in the east of the Gambia, while coastal sands, salt, silt and clay are common dating to the

Holocene The Holocene ( ) is the current geological epoch. It began approximately 11,650 cal years Before Present (), after the Last Glacial Period, which concluded with the Holocene glacial retreat. The Holocene and the preceding Pleistocene togethe ...

Hydrogeology

The British Geological Survey reports that the Gambia has extensive surface water which is rarely used for drinking water. At the mouth of river, high salinity is a problem in surface water supplies. The shallow sand aquifer encompasses almost the entire country, made up of Holocene sediments and an underlying, partially confined Pliocene aquifer. The sand aquifer ranges between five and 25 meters thick. The country also has a deep sandstone aquifer, with

fossil water Fossil water or paleowater is an ancient body of water that has been contained in some undisturbed space, typically groundwater in an aquifer, for millennia. Other types of fossil water can include subglacial lakes, such as Antarctica's Lake Vosto ...

as much as 40,000 years confined at depths of 250 to 450 meters. Out of a total storage of 650,000 cubic meters only 80,000 cubic meters is believed to be potable.

Natural resource geology

Petroleum geologists have launched several thousand kilometers of seismic surveys throughout the basin in search of hydrocarbons, but exploration has so far been unsuccessful. In the 1950s, mining began for beach sands rich in titanium, containing large concentrations of

ilmenite Ilmenite is a titanium-iron oxide mineral with the idealized formula . It is a weakly magnetic black or steel-gray solid. Ilmenite is the most important ore of titanium and the main source of titanium dioxide, which is used in paints, printing ...

zircon Zircon () is a mineral belonging to the group of nesosilicates and is a source of the metal zirconium. Its chemical name is zirconium(IV) silicate, and its corresponding chemical formula is Zr SiO4. An empirical formula showing some of the r ...

rutile Rutile is an oxide mineral composed of titanium dioxide (TiO2), the most common natural form of TiO2. Rarer Polymorphism (materials science), polymorphs of TiO2 are known, including anatase, akaogiite, and brookite. Rutile has one of the highest ...

and gangue minerals. The country has large deposits of glass-grade sand that have not been mined.

References

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