Ramgarh, Rajasthan, India: A 10 km diameter complex impact structure

Abstract

The Ramgarh structure is a morphological landmark in southeastern Rajasthan, India. Its 200 m high and 3.5-4 km wide annular collar has provoked many hypotheses regarding its origin, including impact. Here, we document planar deformation features, planar fractures, and feather features in quartz grains of the central part of the Ramgarh structure, which confirm its impact origin. The annular collar does not mark the crater rim but represents the outer part of a central uplift of an approximately 10 km diameter complex impact structure. The apparent crater rim is exposed as a low-angle normal fault and can be traced as lineaments in remote sensing imagery. The central uplift shows a stratigraphic uplift of~1000 m and is rectangular in shape. It is dissected by numerous faults that are co-genetic with the formation of the central uplift. The central uplift has a bilateral symmetry along an SW-NE axis, where a large strike-slip fault documents a strong horizontal shear component. This direction corresponds to the assumed impact trajectory from the SW toward the NE. The uprange sector is characterized by concentric reverse faults, whereas radial faults dominate downrange. Sandstones of the central uplift are infiltrated by Fe-oxides and suggest an impact-induced hydrothermal mineralization overprint. The impact may have occurred into a shallow water environment as indicated by soft-sediment deformation features, observed near the apparent crater rim, and the deposition of a diamictite layer above them. Gastropods embedded in the diamictite have Middle Jurassic age and may indicate the time of the impact. 936

Evidence for shock provides insight into the formation of the central elevated area in the Dhala impact structure, India

“…PDFs are conspicuous indicators of shock metamorphism (French and Koeberl 2010; Kenkmann et al. 2019, 2020). The possible PDFs may, thus, indicate that few grains of the Dhala and Kaimur Formation experienced shock metamorphism.…”

“…Furthermore, {10-13} is the most frequent PDF orientation recorded in the impact melt breccia of the Dhala impact structure (Pati et al 2019). PDFs are conspicuous indicators of shock metamorphism (French and Koeberl 2010;Kenkmann et al 2019Kenkmann et al , 2020. The possible PDFs may, thus, indicate that few grains of the Dhala and Kaimur Formation experienced shock metamorphism.…”