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The Cerro do Jarau circular structure forms an outstanding landmark in the lowland plains known as "Pampas" in Rio Grande do Sul state, near the border between Brazil and Uruguay. The name (Jarau Hills) comes from the prominent crests of intensely silicified sandstones which forms a semi-ring of elevated hills in the northern part of the structure. The origin of this conspicuous feature is being debated for decades, having being associated with either endogenous tectonic processes or an impact event. However, no clear evidence to support either hypothesis has been presented so far. The structure was formed in Mesozoic volcano-sedimentary rocks of the Paraná Basin and comprises Jurassic-Cretaceous Guará, Botucatu and Serra Geral formations. The exposure of Guará and Botucatu sandstones in the inner portion of the structure constitutes a stratigraphic/structural window, since the entire western part of Rio Grande do Sul state is covered by basaltic flows of the Serra Geral Fm. Botucatu sandstones are intensely silicified and affected by faulting forming radial and annular patterns. The original bedding of these rocks dips preferentially towards the center of the structure. This paper presents the results of detailed geological mapping conducted at Cerro do Jarau which allowed the identification of several types of impact features, including PDFs and PFs in quartz, feldspar and clinopyroxene, the occurrence of autochtonous lithic breccias and suevite, as well as shatter cones in sandstones and basalts. The set of macroscopic and microscopic features identified at Cerro do Jarau point towards an impact origin for the Cerro do Jarau structure, making it the 6th impact crater known in Brazil.
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