Lana C., Souza Filho C.R., Marangoni Y.R., Yokoyama E., Trindade R.I.F., Tohver E., Reimold W.U.
Department of Geology, University of Stellenbosch, Private Bag XI, Matieland 7620, South Africa; Departamento de Geologia e Recursos Naturais, Instituto de Geociencias, State University of Campina (UNICAMP), Campina 13083-970, Brazil; Instituto de Astronomia, Geofísica e Ciencias Atmosfericas, Universidade de Sao Paulo, Rua do Matao 1226, Sao Paulo, SP 05508-090, Brazil; Museum for Natural History (Mineralogy), Humboldt University, Invalidenstrasse 43, 10115 Berlin, Germany
Lana, C., Department of Geology, University of Stellenbosch, Private Bag XI, Matieland 7620, South Africa; Souza Filho, C.R., Departamento de Geologia e Recursos Naturais, Instituto de Geociencias, State University of Campina (UNICAMP), Campina 13083-970, Brazil; Marangoni, Y.R., Instituto de Astronomia, Geofísica e Ciencias Atmosfericas, Universidade de Sao Paulo, Rua do Matao 1226, Sao Paulo, SP 05508-090, Brazil; Yokoyama, E., Instituto de Astronomia, Geofísica e Ciencias Atmosfericas, Universidade de Sao Paulo, Rua do Matao 1226, Sao Paulo, SP 05508-090, Brazil; Trindade, R.I.F., Instituto de Astronomia, Geofísica e Ciencias Atmosfericas, Universidade de Sao Paulo, Rua do Matao 1226, Sao Paulo, SP 05508-090, Brazil; Tohver, E., Instituto de Astronomia, Geofísica e Ciencias Atmosfericas, Universidade de Sao Paulo, Rua do Matao 1226, Sao Paulo, SP 05508-090, Brazil; Reimold, W.U., Museum for Natural History (Mineralogy), Humboldt University, Invalidenstrasse 43, 10115 Berlin, Germany
The 40-km-wide Araguainha structure is the largest and best-exposed complex impact crater in South America. It was excavated in flat-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 field 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 field 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. © 2007 Geological Society of America.