Guyana belongs to the Guiana Shield, a massif extending north of the Amazon, between the Andes Mountains and the Atlantic, made up of Precambrian rocks dated to between 2.7 and 3.5 billion years ago.
To the north, the southern peneplain straddles the Inini synclinorium, mainly composed of the Paramaca series, which corresponds to a series of micaschists, aluminous paragneisses and black quartzites whose total thickness is about 1 km.
The north of French Guiana corresponds to a synclinorium composed of the Paramaca series on which sandstone and fluviatile conglomerates lie unconformably.
Shield rocks in Guyana are all dated between 1.6 and 2.5 billion years ago.
Fluvial alluvia of continental origin are mainly located in the lower reaches of the rivers, they are mainly sandy products.