Abstract
ABSTRACT: Santa Marta is a 10 km wide, reasonably well preserved, complex impact structure located in southwestern Piauí state, northeastern Brazil, with a central uplift of 3.2 km diameter. The Santa Marta structure was recently recognized as the sixth confirmed impact structure in Brazil, based on widespread occurrence of shatter cones and the presence of shock deformation features in quartz. The latter includes planar deformation features (PDF), planar fractures (PF), and feather features (FF). The structure was formed in sedimentary strata (conglomerates, sandstones, siltstones and shales) accumulated in two distinct sedimentary basins that overlap in this region: the Paleozoic Parnaíba and the Mesozoic Sanfranciscan basins. Here, we provide an overview of the geology and stratigraphy of the sedimentary successions that occur within the structure, focusing especially on the deformation aspects of the strata from the central area. This study is aimed at advancing the knowledge about Brazilian impact structures and contributing to a better comprehension of impact cratering in sedimentary targets. The deformation in the Santa Marta structure is directly related to variations in the thickness of sedimentary strata and to lithologic diversity in the interior of the structure, which determined the complexity of the deformation, including the formation of inner rings.
Highlights
The Santa Marta structure is a ~10 km wide impact structure centered at 10o10’S/45o14’W (Fig. 1) in the southwestern portion of Piauí state, northeastern Brazil, located ca. 30 km north of Corrente town
Oliveira et al (2014) confirmed the impact origin of the Santa Marta structure by providing the first bona fide impact evidence: shatter cones found at several locations within the structure and different types of shock microdeformation features
The results presented here offer a contribution to the discussion of deformation patterns in complex, medium-sized impact structures formed on previously undeformed sedimentary strata comprising a variety of lithotypes
Summary
The Santa Marta structure is a ~10 km wide impact structure centered at 10o10’S/45o14’W (Fig. 1) in the southwestern portion of Piauí state, northeastern Brazil, located ca. 30 km north of Corrente town. The structure comprises a partially exposed raised rim, as well as a central uplift with the diameter of 3.2 km. It is located in the Parnaíba Province (Almeida 1977), in the southeastern part of the Parnaíba Basin and the northern part of the Sanfranciscan Basin, with the latter overlapping the former in this region (Lima & Leite 1978). The first mention of Santa Marta as a potential impact structure was made by Master and Heymann (2000). Some issues related to the geology of Santa Marta remained unclear, such as the local stratigraphy and deformation aspects
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