PROJETO RADAM

ABSTRACT
Results of regional geological mapping using radar imagery at 1:250.000 and
1:1.000.000 scales are presented.
The area of work corresponds to about 192.290sq. km., between longitudes
40° 30' to 48° 00' west, and latitude 04° 00' south to the littoral. It
encompasses the coastal parts of the Maranhao and Piaui States, and portions
of the states of Para and Ceara. Geologically it corresponds to the northern
part of the Piaui—Maranhao Sedimentary Basin, and the coastal areas in
which the Barreirinhas and Sao Luis basins are located.
The total area actually mapped comprises 780.000sq. km., covering all of the
sedimentary basin and adjacent Precambrian terrains. However, for uniformity
purposes, the global area was divided into three blocks corresponding ,
likewise, to three different reports.
The objectives of the work were twofold. First, coincident with that of
RADAM PROJECT itself, to furnish, in a short period of time, a
comprehensive panoramic sight of the most important geological aspects of
extensive regions of north and northeast Brazil. Secondly, to verify the
degree of detail that could be obtained with radar imagery, since the area
had already been mapped with the use of other sensors.
Initially, intention was to use data of previous work and merely transpose
the information to the radar imagery. However, the complete failure of this
procedure led to direct field investigation to determine the correspondence
of imagery — geologic features. Based on this, preliminary interpretations
were made, followed by field checking and compilation of the final maps.
The area presents two assemblages of rocks quite distinct. The first is
represented by Undivided Precambrian granitic and metamorphic rocks
making up the Caraiba, Gurupi and Jaibaras groups. The second assemblage
is comprised by sedimentary rocks ranging from Lower Paleozoic (Silurian)
to Quaternary. Paleozoic formations are restricted to the northeastern
margin of the basin, whereas about 80% of the region is covered by the
Itapecuru (Cretaceous) and Barreiras (Tertiary) formations.
I/7