Geophysical investigation of the Santa Marta impact structure—Piauí State, Brazil

Abstract The Santa Marta impact structure in northeastern Brazil, recognized as a partially preserved complex crater, was investigated through an integrated geophysical study employing magnetotelluric (MT) and gravity methods. Our research provides constraints on the crater's subsurface architecture. The study utilized broadband MT data from 17 stations and gravity measurements from 226 stations distributed across the structure. The MT data revealed a distinct three‐layered resistivity profile: (i) a shallow resistive layer (100–1000 Ω·m) interpreted as impact breccias and Cretaceous sandstones, (ii) an intermediate conductive zone (1–50 Ω·m) correlated with Paleozoic shales of the Parnaíba Basin, and (3) most significantly, a deep‐seated conductive anomaly (1–20 Ω·m) beneath the central uplift. This deep conductivity anomaly likely results from impact‐induced fracturing coupled with subsequent fluid infiltration pathways. Gravity data exhibited asymmetric Bouguer anomalies (−41 to −27 mGal) that deviate from the typical circular pattern observed in impact structures. Density contrasts (0.3–1.8 g/cm 3 ) suggest substantial basement uplift and preferential erosional patterns. Dimensionality analysis of the MT data confirmed predominant 3‐D effects, necessitating 3‐D inversion techniques to accurately resolve the structure's complex geometry. The integrated resistivity and density contrast models reveal a subdivision of both the central uplift and the annular basin, and the asymmetric gravity signature may indicate postimpact deformation effects. Our results advance the understanding of the Santa Marta structure, establishing a robust geophysical framework for future investigations of similar structures in Brazil and globally. The study conclusively demonstrates that Santa Marta represents a highly complex impact structure in terms of both electrical resistivity and density distributions, directly reflecting its fundamental geological asymmetry.