The end of the Neoproterozoic in the north of the Paraguay Belt and the south
Amazon Craton have been intensely debated. The colision of the Amazon, São
Fransisco-Congo, and the Paranapanema(?) blocks resulted in the uplift of the
Paraguary-Araguaia Belt. In this context, the Raizama Formation, base of the Alto
Paraguay Group and the gol of this study, is characterized by fine to coarse
siliciclastic deposits, associated with the transitional deposits (fluvial with tidal
influence) and shallow marine(foreshore/shoreface), which overlie the carbonate
sedimentation of the Araras Group. The area of study includes the municipalities of
Gloria d’Oeste, Tangará da Serra, Cáceres, Alto Paraguai and Nobres. The
petrographic study of thin sections came from the north of the Paraguay Belt and the
south of the Amazon Craton, permited the individualization of six lithotypes consisted
as quartz-sandstone, subarkoses, dolomitic-limestone, dolomite, chert, and
sublitharenites. Sandstones from Amazon Craton have late dolomite cementation,
whereas the sandstones from Paraguay belt have intense quartz overgrowth. The
concentration of lithic fragments fluctuate of 0,3% to 11,7% in the samples from
Paraguay Belt , absent in the samples from Amazon Craton. The pattern of the
QmFLt diagrams show that the Raizama Formation sediments are recycled orogen
and stable continental blocks. The diagenetic processes that intergrate the diagenetic
sequence are: 1) authigenic clay minerals; 2) mechanical compaction; 3) quartz
overgrowth; 4) pressure solution; 5) replacement and/or solution of quartz; and 6)
dolomization. The study of the Raizama Formation sandstones enable a better
understanding of the diagenetic processes by which these rocks have been
subjected, contributing to the characterization of the Alto Paraguay Group, which has
not been studied much.
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