Geology and impact features of Riachão structure, northern Brazil

Maziviero, Mariana V.; Vasconcelos, Marcus Arthur Marçal de; Crósta, Álvaro Penteado; Góes, Ana Maria; Reimold, W. U.; Carneiro, Cleyton de Carvalho

doi:10.1111/maps.12213

Cited by 13 publications

(9 citation statements)

References 25 publications

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“…The youngest deformed strata identified in the crater belong to the Cretaceous Areado and Urucuia groups, which provides stratigraphic constraints to infer a maximum age in the range of 66-100 Ma (Lima and Leite 1978;Dardenne 1997a, 1997b) for the Santa Marta impact event. This also provides a reasonable explanation for the lesser degree of erosion observed at Santa Marta in comparison to the older Serra da Cangalha and Riachão (Maziviero et al 2013) structures, which may be as old as 250 Ma.…”

Section: Discussionmentioning

confidence: 60%

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Shatter cones and planar deformation features confirm Santa Marta in Piauí State, Brazil, as an impact structure

Oliveira

Vasconcelos

Crósta

et al. 2014

Meteorit & Planetary Scien

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A total of 184 confirmed impact structures are known on Earth to date, as registered by the Earth Impact Database. The discovery of new impact structures has progressed in recent years at a rather low rate of about two structures per year. Here, we introduce the discovery of the approximately 10 km diameter Santa Marta impact structure in Piauí State in northeastern Brazil. Santa Marta is a moderately sized complex crater structure, with a raised rim and an off‐center, approximately 3.2 km wide central elevated area interpreted to coincide with the central uplift of the impact structure. The Santa Marta structure was first recognized in remote sensing imagery and, later, by distinct gravity and magnetic anomalies. Here, we provide results obtained during the first detailed ground survey. The Bouguer anomaly map shows a transition from a positive to a negative anomaly within the structure along a NE–SW trend, which may be associated with the basement signature and in parts with the signature developed after the crater was formed. Macroscopic evidence for impact in the form of shatter cones has been found in situ at the base around the central elevated plateau, and also in the interior of fractured conglomerate boulders occurring on the floor of the surrounding annular basin. Planar deformation features (PDFs) are abundant in sandstones of the central elevated plateau and at scattered locations in the inner part of the ring syncline. Together, shatter cones and PDFs provide definitive shock evidence that confirms the impact origin of Santa Marta. Crystallographic orientations of PDFs occurring in multiple sets in quartz grains are indicative of peak shock pressures of 20–25 GPa in the rocks exposed at present in the interior of the crater. In contrast to recent studies that have used additional, and sometimes highly controversial, alleged shock recognition features, Santa Marta was identified based on well‐understood, traditional shock evidence.

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Section: Discussionmentioning

confidence: 60%

“…However, a large number of these structures are still of unknown origin. Until recently, the only confirmed impact structures in this region have been Serra da Cangalha and Riachão, with diameters of 13 and 4.2 km, respectively Maziviero et al 2013;Vasconcelos et al 2013).…”

Section: Introductionmentioning

confidence: 99%

Shatter cones and planar deformation features confirm Santa Marta in Piauí State, Brazil, as an impact structure

Oliveira

Vasconcelos

Crósta

et al. 2014

Meteorit & Planetary Scien

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“…Feather features are widely considered a diagnostic shock deformation phenomenon (Poelchau and Kenkmann 2011), and have been described at several impact structures, including some of the Brazilian ones, such as Serra da Cangalha Vasconcelos et al 2013), Vargeão , Riachão (Maziviero et al 2013), and Santa Marta (Oliveira et al 2014(Oliveira et al , 2017. However, it still has not been completely ascertained whether comparable features may be formed by other tectonic processes although the lack of such reports from both the impact and the tectonic communities strongly speaks out for FFs being characteristic impact deformation.…”

Section: The Search For Shock Deformationmentioning

confidence: 99%

Shock deformation confirms the impact origin for the Cerro do Jarau, Rio Grande do Sul, Brazil, structure

Reimold

Crósta

Hasch

et al. 2018

Meteorit & Planetary Scien

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Cerro do Jarau is a conspicuous, circular morpho‐structural feature in Rio Grande do Sul State (Brazil), with a central elevated core in the otherwise flat “Pampas” terrain typical for the border regions between Brazil and Uruguay. The structure has a diameter of approximately 13.5 km. It is centered at 30o12′S and 56o32′W and was formed on basaltic flows of the Cretaceous Serra Geral Formation, which is part of the Paraná‐Etendeka Large Igneous Province (LIP), and in sandstones of the Botucatu and Guará formations. The structure was first spotted on aerial photographs in the 1960s. Ever since, its origin has been debated, sometimes in terms of an endogenous (igneous) origin, sometimes as the result of an exogenous (meteorite impact) event. In recent years, a number of studies have been conducted in order to investigate its nature and origin. Although the results have indicated a possible impact origin, no conclusive evidence could be produced. The interpretation of an impact origin was mostly based on the morphological characteristics of the structure; geophysical data; as well as the occurrence of different breccia types; extensive deformation/silicification of the rocks within the structure, in particular the sandstones; and also on the widespread occurrence of low‐pressure deformation features, including some planar fractures (PFs). A detailed optical microscopic analysis of samples collected during a number of field campaigns since 2007 resulted in the disclosure of a large number of quartz grains from sandstone and monomict arenite breccia from the central part of the structure with PFs and feather features (FFs), as well as a number of quartz grains exhibiting planar deformation features (PDFs). While most of these latter grains only carry a single set of PDFs, we have observed several with two sets, and one grain with three sets of PDFs. Consequently, we here propose Cerro do Jarau as the seventh confirmed impact structure in Brazil. Cerro do Jarau, together with Vargeão Dome (Santa Catalina state) and Vista Alegre (Paraná State), is one of very few impact structures on Earth formed in basaltic rocks.

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“…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). Two other complex impact structures have, in recent years, been comprehensively investigated in the Parnaíba Province: the 13 km-diameter Serra da Cangalha and the 4.2 km-diameter Riachão structures (Kenkmann et al 2011;Vasconcelos et al 2013;Maziviero et al 2013).…”

Section: Introductionmentioning

confidence: 99%

Geological investigation of the central portion of the Santa Marta impact structure, Piauí State, Brazil

et al. 2017

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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.

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Geology and impact features of Riachão structure, northern Brazil

Cited by 13 publications

References 25 publications

Shatter cones and planar deformation features confirm Santa Marta in Piauí State, Brazil, as an impact structure

Shatter cones and planar deformation features confirm Santa Marta in Piauí State, Brazil, as an impact structure

Shock deformation confirms the impact origin for the Cerro do Jarau, Rio Grande do Sul, Brazil, structure

Geological investigation of the central portion of the Santa Marta impact structure, Piauí State, Brazil

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