Mariana V. Maziviero^1,*, Marcos A. R. Vasconcelos¹, Alvaro P. Crosta¹, Ana M. Góes², Wolf U. Reimold^3,4, Cleyton de C. Carneiro¹

¹Department of Geology and Natural Resources, Institute of Geosciences, University of Campinas, Campinas, São Paulo, Brazil
²Department of Sedimentary and Environmental Geology, Institute of Geosciences, University of São Paulo, São Paulo, Brazil
³Museum für Naturkunde, Leibniz Institute for Research on Evolution and Biodiversity, Berlin, Germany
⁴Humboldt-Universität zu Berlin, Berlin, Germany

Riachão, located at S7°42′/W46°38′ in Maranhão State, northeastern Brazil, is a complex impact structure of about 4.1 km diameter, formed in Pennsylvanian to Permian sedimentary rocks of the Parnaíba Basin sequence. Although its impact origin was already proposed in the 1970s, information on its geology and shock features is still scarce in the literature. We present here the main geomorphological and geological characteristics of the Riachão impact structure obtained by integrated geophysical and remote sensing analysis, as well as geological field work and petrographic analysis. The identified lithostratigraphic units consist of different levels of the Pedra de Fogo Formation and, possibly, the Piauí Formation. Our petrographic analysis confirms the presence of shock-diagnostic planar microdeformation structures in quartz grains of sandstone from the central uplift as evidence for an impact origin of the Riachão structure. The absence of crater-filling impact breccias and melt rocks, shatter cones, as well as the restricted occurrence of microscopic shock effects, suggests that intense and relatively deep erosion has occurred since crater formation.

Reference
Maziviero MV, Vasconcelos MAR, Crosta A., Góes AM, Reimold WU and de C Carneiro C (in press) Geology and impact features of Riachão structure, northern Brazil. Meteoritics & Planetary Science
[doi:10.1111/maps.12213]
Published by arrangement with John Wiley & Sons

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