Morphological analysis of the São Miguel do Tapuio Circular Structure, Piauí – Brazil

Abstract

The São Miguel do Tapuio Circular Structure (SMTCS) is one of the largest recognized in the Phanerozoic sedimentary rocks of the Parnaiba Basin, in Piauí (PI), Brazil. Research works on the genesis of the SMTCS consider either an endogenetic origin or meteoritic impact formation. The present study is based on bibliographic survey, fi eldwork and laboratory analyses (remote sensing). The SMTCS superfi cial morphological features, their organization, total diameter, multi-directional pattern and high density of lineaments inside the structure were characterized by remote sensing. Also, the morphostructural units such as the outer margin, intermediate ring, annular depression and a central topographic high were defi ned. The fi eldwork allowed identifying a variable thermal metamorphism in thesandstones that formed the SMTCS. The metamorphism grade increased clearly from the margin to the center, with the presence of highly recrystallized and consolidated metasandstones around the center of the structure. Finally, the geomorphic characterization and the geometric signature obtained for the SMTCS seem to correspond to those of complex impact structures (presence of a central uplift). Moreover, the identifi cation of macro and microscopic deformation structures in the sandstones (while not typical of shock origin) may be more conclusive of a meteoritic origin, and the lack of evidence of igneous activity might explain the observed thermal metamorphism.