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

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.

Characteristic landforms and geomorphic features associated with impact structures: Observations at the Dhala structure, north‐central India

“…In the Dhala structure, the area occupied by this annular moat (ring syncline) is covered with post-impact sediments of the Dhala Formation. Similar features have been observed at many other impact structures worldwide (e.g., Dypvik et al, 1996;Schmieder et al, 2011;de Oliveira et al, 2017). The dug well sections observed in the annular moat of the Dhala structure comprise various sedimentary units (sandstone, pebbly sandstone, siltstone, sandy shale, and shale) that contain dropstones, convolute bedding, and related soft-sediment deformation structures (Pati, Reimold, et al, 2008;Pati et al, 2010Pati et al, , 2019.…”

“…The annular moat is the area between the crater rim and central uplift/elevation, also termed a ring syncline (Kenkmann et al, 2014;de Oliveira et al, 2017). In the Dhala structure, the area occupied by this annular moat (ring syncline) is covered with post-impact sediments of the Dhala Formation.…”

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

“…), and Santa Marta (Oliveira et al. , ). 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.…”