The map clearly illustrates connection between the Rio Blanco to
the south and the Berbice, Demerara and Corantijn Rivers to the
north. These lineaments marks the Central Atlantic Rift extension
onshore Suriname, Guyana and Brazil.
The drainage of the northern part of South-America probably took
place by a proto-Amazone through the Takutu depression. During the
Miocene the Pacific Plate started to under-thrust the South
American continent causing it to tilt to the east. This caused the
Amazone to shift its lower tributaries to the south basically
beheading the big rivers that were draining in the Guyana Basin.
This meant for the Guyana basin a change from a sand dominated
system to a clay dominated system. It also ended the carbonate
growth on the shelf due to the mud carried from the present
Amazone river mouth along the coast of the Guyanas.