Rualdo Menegat¹, Luís Alberto Dávila Fernandes²

(1) Federal University of Rio Grande do Sul, Brazil, 91.501-970 Porto Alegre, Brazil
(2) Federal University of Rio Grande do Sul/CNPq, Brazil

ABSTRACT: Tectonic and climate control of the late-orogenic Guaritas Basin in Southern Brazil

The Guaritas Basin includes a 1,4 km thick sequence of red-beds cropping out in the central geophysical domain of the Dom Feliciano Belt in southern Brazil. Originated during the large extension that followed colisional and transcurrent tectonic events of this belt, this rift-type basin was filled with alluvial and aeolian depositional systems. From infill to preservation, the evolution of the Guaritas Basin was controlled by extension along NE-trending faults. These faults, mostly a product of reactivation of the neoproterozoic transcurrent shear zones under brittle conditions, have moved as late as 470 Ma years age of the lowest sequence. The Guaritas Basin contains four large depositional sequences bound by unconformities. The moderately dipping lowest sequence is formed by alluvial fans deposits dominated by stream flows with volcanic rocks interlayered. The next sequence is subhorizontal and formed by alluvial fans deposits followed by several cycles of fluvial braided and braidplain superimposed by barcanoid draa facies. A large supersurface marks the boundary with the next sequence, formed by superimposed barcanoid draa with humid interdraa facies associations and interfingered with fluvial braided and flood plain deposits. A disconformity bounds the uppermost sequence which is formed by fluvial braided and flood plain deposits showing axial palaeocurrents. While the basal sequence represent initial stages of the basin infill, the following two sequences result from seasonal of long and dry alternated with short and humid periods responsible for a fast distribution of sediments. The uppermost sequence indicate a decline of arid conditions.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado