| Description |
The 403-m thick North Horn Formation at the type section in Emery; County, Utah, is divided into three lithologic units that reflect changing; environmental conditions below, across and above the Cretaceous-Tertiary (K-T); boundary: (1) a lower variegated unit, (2) a middle carbonaceous unit, and (3) an; upper variegated unit. The middle unit lithology suggests an environmental; change from a semi-arid floodplain to a lacustrine-wetland setting that may have; been responsible for the disappearance of part of the lower fossil assemblage,; such as Alamosaurus, above the top of the lower unit. The remaining; Cretaceous taxa, including dinosaurs, that inhabited lacustrine and wetland; environments, disappeared during the deposition of the middle unit below the KT; boundary. |
