The crater-infilling successions of the 2.7 km-diameter, Ritland impact structure are classified as: (A) late syn-impact, (B) early post-impact and (C) late post-impact sediments. The late post-impact sediments represent later stages of crater sedimentation during stable crater conditions. The transition between the early post-impact and late post-impact crater sedimentation is marked by a ~6 m-thick succession exposed in the southcentral part of the crater. The lowermost part of this succession consists of fine- to medium-grained sandstone, deposited from turbidity flows during the retreating or abandonment stage of earlier prograding submarine fans. Fine sandstones intercalated with silty shales in the middle part represent alternating episodes of turbiditic and suspension deposition. Upward transition of this facies into thick, dark-grey to black shales suggests establishment of anoxic to hypoxic bottom-water conditions where sediments were deposited during an extensive period of suspension deposition. Local coarse clastics exposed in the easternmost crater wall represent small-scale scree deposits, suggesting that submarine slides and reworking of the sediments were active processes for a long time after the impact.
Late post-impact sedimentation in the Ritland impact structure, western Norway