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The Phanerozoic Parnaíba sedimentary basin in the north-northeastern region of Brazil covers an area of ~400,000 km2 and contains a number of circular structures, four of which are of possible impact origin: Serra da Cangalha, Santa Marta, Riachão, and São Miguel do Tapuio. All four exhibit a central morphological feature resembling a central uplift, characteristic of complex impact structures. A recently acquired regional aerogeophysical survey provided magnetic and gravity data for the entire basin. The magnetic and gravity characteristics of the four possible impact structures of the Parnaíba Basin were analyzed in comparison with impact structures elsewhere in the world. The analysis shows that, except for the São Miguel do Tapuio structure, three of the structures exhibit geophysical characteristics similar to the signatures found in some known impact structures of comparable sizes that have formed in clastic sedimentary rocks. Serra da Cangalha structure exhibits magnetic highs and gravimetric lows, Santa Marta structure exhibits magnetic lows and gravimetric highs, Riachão structure depicts subdued gravimetric and magnetic highs, and the São Miguel do Tapuio structure shows a magnetic high and a complex gravimetric signature. Based on the observed geophysical signatures presented here, Serra da Cangalha, Santa Marta, and Riachão could be regarded as potential impact structures, whereas São Miguel do Tapuio is the least likely of these four structures to have been formed by an impact event.

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