Insights into the morphology, geometry, and post-impact erosion of the Araguainha peak-ring structure, central Brazil

Abstract

The 40-km-wide Araguainha structure is the largest and best-exposed complex impact crater in South America. It was excavated in fl at-lying sediments of the intracratonic Paraná Basin, where target rocks are well exposed and have remained undeformed since the impact event ca. 245 Ma. Despite the excellent state of preservation and exposure, information available on the target rock stratigraphy, post-impact erosion, and morphology of the structure is limited. Our combined fi eld observations and remote sensing analysis demonstrate that Araguainha preserves all features of a shallowly eroded peak-ring crater. The interior of the structure exposes a central peak surrounded by a 5-km-wide annular basin and two main ring features 10-12 and 14-18 km from the center. Analysis of the pre-impact stratigraphy, present morphology, and crater dimensions indicates that excavation related to the transient cavity formation was extensive in the annular basin, but minimal to nonexistent beyond the inner ring feature. The formation of the inner ring feature can be reconciled with compressional stresses during outward collapse of the central uplift and inward slumping of the crater walls. Regional stratigraphic data combined with fi eld observations indicate two periods of post-impact erosion associated with exhumation of the Paraná Basin. We estimate that 250-350 m of fallback deposits and target rocks have been removed by erosion. Erosion also accounted for removal of the proximal ejecta immediately outside the rim of the structure. In contrast to previous suggestions that the impact took place in a shallow-marine environment, our observations are more consistent with an extremely shallow, brackish to freshwater lacustrine environment, with little effect on the developing impact crater.

Structural evolution of the 40 km wide Araguainha impact structure, central Brazil

“…The image in the background is a triangular irregular network (TIN) surface converted from ASTER digital elevation. Note that the TIN surface depicts well the outer and inner topographic concentric rings described by Lana et al (2007) (see text for more details). The bars labeled a-a' to f-f' represent structural profiles analyzed for the inner ring feature: the structural data are presented in stereoplots of Fig.…”

“…Remote sensing analysis and stratigraphic correlations indicate that Araguainha preserves a fully exposed central peak, an annular basin and two main concentric ring features ( Fig. 2a) (Lana et al 2007). The crater rim is also well exposed, providing important insights into the mechanics of crater rim collapse (Fig.…”

“…The Araguainha impact structure is the eroded remnant of the largest impact crater in South America (Crósta et al 1981;Theilen-Willige 1981;Engelhardt et al 1992;Lana et al 2006aLana et al , 2007. It is located in the northeastern part of the Paraná Basin (Fig.…”

“…Lana et al (2007) have demonstrated that the present morphology of the crater is largely controlled by the concentric arrangement of the structures and layered sedimentary units. However, while some structural data have been reported for some parts of the impact structure (Lana et al 2006a(Lana et al , 2007, no comprehensive structural analyses have been directed at understanding the geometry of the central uplift and the crater rim. In addition, the structural implications of the concentric ring features for the evolution of the impact crater have not been fully discussed.…”

“…The 40 km wide Araguainha impact structure is a rare example of a shallowly eroded impact structure that provides an unparalleled opportunity to study the kinematics of complex crater formation ( Fig. 1) (Crósta et al 1981;Theilen-Willige 1981;Engelhardt et al 1992;Lana et al 2006aLana et al , 2007. Remote sensing analysis and stratigraphic correlations indicate that Araguainha preserves a fully exposed central peak, an annular basin and two main concentric ring features ( Fig.…”