Reconstrução paleogeográfica com o uso da estratigrafia de sequências: aplicação nas formações Sanga do Cabral e Santa Maria (Triássico da Bacia do Paraná) na região de São Pedro do Sul, RS

Abstract

The Sanga do Cabral and Santa Maria formations comprises the triassic package of the Paraná Basin, occurring restricted to the state of Rio Grande do Sul. The Sanga do Cabral Formation occurs in the central and western depression region of the state, and the Santa Maria Formation occurs only in central depression. These two formations correspond to the sequences of second order, being called Sanga do Cabral Supersequence and Santa Maria Supersequence. The Santa Maria Supersequence is subdivided into three sequences of third order: Santa Maria I, Santa Maria II and Santa Maria III. The proposal of this work is to apply the stratigraphy of sequences in high resolution in the aforementioned formations, considering non-marine factors in sedimentation. This proposal takes into account variations in the stratigraphic base level, controlled by climatic and tectonic changes. For this, stratigraphic profiles in outcrops along roads of the BR-287 and RS-532 highways were surveyed, covering the municipalities of São Vicente do Sul, Mata and São Pedro do Sul. This work used the principle of facies analysis and facies associations, occurring (i) facies association of distal gravel rivers; (ii) association of sandy braided rivers; and (iii) facies association of deltaic lacustrine. The interpretation of the depositional environments, from the faceis associations, suggests two main systems: fluvial and lacustrine. Analysis of the main stratal stacking patterns (degradation, retrogradation and gratification) made it possible to demarcate stratigraphic surfaces, such as flood and regression surfaces and sequence boundaries. The defined of systems tracts represented the breaking of the registry in sequences of high resolution (4th and 5th orders), which aided in the final paleogeographic reconstruction. With this work, an in-depth understanding of the sedimentation during the Triassic period of the Paraná Basin was reached, being able to reconstruct the approximate configuration of the depositional environments of the time and to understand the events of filling of the basin.