DescriptionLarge concretion (Sentinel Butte Formation, Upper Paleocene; Little Missouri Badlands, North Dakota, USA) 1.jpg English: Concretions are post-depositional...
bioerosion; Bellevue Formation, Upper Ordovician (Katian), northern Kentucky. Ammonite interiors, Pierre Shale, Upper Cretaceous, South Dakota. Cross-section...
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