PROJETO RADAMBRASIL

This report and the geomorphological mapping enclosed
comprise Sheet NA.21. Tumucumaque and part of Sheet
NB.21. It corresponds to the section between parallels
00°00' and 05°00'N and meridians" 54°00' and 60°00'W,
covering an area of about 148.550 sq. km. The section
located above parallel'02°00'N also'belongs to the
mapping of Sheets ! NA.20 Boa Vista and NB.20 Roraima
and part of Sheet NA.21 Tumucumaque (Projeto RADAM-
BRASIL, vol. 8). It presents, discusses, and indicates the
solutions to the problems involved in thematic cartography
for geomorphological mapping obtained by radar imagery.
It summarizes the few scattered researches previous to the
RADAMBRASIL Project.
Taking as a starting point the land forms and the altimetric „
positions, it presents a division .of relief into eight Morphostructural
Units: the Amazon-Orinoco Watershed Plateau,
the Roraima Remnants Plateau, the Northern Amazon
Dissected Plateau, the Amapa Hills, the Southern
Guiana Interplateau Depression, the Rio Branco-Rio Negro
Pediplain, and the Northern Parä Peripheral Depression.
Based on geomorphological mapping and controlled by the
soil and the phytoecological' maps, it divides the area
under study into two morphoclimatic dominions and two
intermixed transition strips.
The Morphostructural Units show an arrangement of the
relief controlled by fissure tectony with intermittent effects
until the Holocene. This tectony opened an extensive
depressed gap, later on made plane — the Southern Guiana
Interplateau Depression — which was reshaped.by erosion
into dissected reliefs whenever the tectony acted. Thé
morphoclimatic processes are reflected in the.relief by
126GEOMORFOLOGIA
ABSTRACT
forms rnherited from paleoclimatic drought oscillations
which occurred during the Quaternary. A plane relief of the
pediplanation type is present in-all the Units, but more
characteristically represented in the Rio Branco-Rio Negro
Pediplain. By Controlling the dissection types it was
possible to diagnose the perseverance of dryer climates for
long periods in some sections of the mapped area. These
conditions in the evolution of the relief permitted to control
the utilization, of the regional relief. Thus, the recent
paleoclimatic oscillations have created maladjustments in
the equilibrium of the slopes. The aggressive climates have
installed processes of laminate flowing with the removal of
soils and alterites in the low pediplained areas. That has
exposed unaltered material which can be useful in civil
construction. The instability of this environment indicates
a need for detailed studies aiming at the occupation of the
areas where the forest has not established yet. The
tectonic movements have created effects of drainage superimposition,
what allows for suitable sites to build dams
with energy purposes. Nevertheless, the same tectony has
acted in these sites until recent times, causing trouble to
an adequate location of those dams and to the stability of
engineering constructions. The geopolitical position of the ,
highways planned for this area is analyzed in function of
their adaptation to the. different types of relief. The
problems caused by rocky sills to the navigation in the river
courses will make an integration in the road-river system
very difficult to be achieved, since the guidelines of the
highway planning suggested an E-W direction for the
highways and the drainage follows a N-S direction. It gives
suggestions for a better location, in order to make the
Perimetral Norte highway and its access roads technically
feasible.