The Guiana Shield forms the northern part of the Amazonian Craton, the core of the South American continent.
Most of the geology of northern Guyana consists of Palaeoproterozoic Orosirian greenstone belts (Barama-Mazaruni Supergroup) intruded by granites.
[1] Major mafic sills and dykes of the Avanavero Suite intrude all of the older rocks, and are part of a Large Igneous Province (LIP).
[2] Numerous mafic dykes intruded the basement in the late Permian and Early Jurassic, associated with the start of the separation of Africa from South America.
One locality with a possible dinosaur or bird footprint is known near Lethem; List of fossiliferous stratigraphic units in Guyana.