Archive - Deposition Gap in Badlands National Park

June 30, 2019

Mesozoic_cenozoic-boundary (2)

Each Sunday we present a notable item from our archives. This EPOD was originally published July 5, 2013.

Photographer: Dale Chadwick
Summary Author: Dale Chadwick

The distinct boundary between the yellow and red layers and the gray layers in this photo represents a 30 million year gap in sedimentary deposition. It’s the boundary between Mesozoic and Cenozoic Eras -- located in the Badlands National Park in South Dakota. These yellow and red layers are fossils soils (paleosols) laid down on the Pierre Formation shale that was deposited during the Cretaceous Period. At the bottom of the yellow layer are unaltered concretions in the Pierre. The gray layers above the paleosols were deposited during the Oligocene Epoch.

The Pierre Formation contains fossils such as ammonites and other mollusks that lived in shallow seas. Other Badlands formations, including the Brule Formation, positioned on top of the Pierre contain fossil horses, rhinoceroses, camels and turtles.