The Ritland impact structure, southwestern Norway

Abstract– The Ritland structure is a newly discovered impact structure, which is located in southwestern Norway. The structure is the remnant of a simple crater 2.5 km in diameter and 350 m deep, which was excavated in Precambrian gneissic rocks. The crater was filled by sediments in Cambrian times and covered by thrust nappes of the Caledonian orogen in the Silurian–Devonian. Several succeeding events of uplift, erosion, and finally the Pleistocene glaciations, disclosed this well-preserved structure. The erosion has exposed brecciated rocks of the original crater floor overlain by a thin layer of melt-bearing rocks and postimpact crater-filling breccias, sandstones, and shales. Quartz grains with planar deformation features occur frequently within the melt-bearing unit, confirming the impact origin of the structure. The good exposures of infilling sediments have allowed a detailed reconstruction of the original crater morphology and its infilling history based on geological field mapping.