North Dakota NORTH DAKOTA’S HELL CREEK DELTA Stratigraphy
ROCK ROCK UNIT COLUMN During the Cretaceous, about 65 million years ago, a well drained lowland PERIOD EPOCH AGES MILLIONS OF YEARS AGO Holocene Oahe .01 corridor existed between the rising Rocky Mountains and the Western Interior Seaway to the east. Sediments eroded from the Rocky Mountains Coleharbor were carried to this western North Dakota lowland by rivers and streams Pleistocene QUATERNARY 1.8 Pliocene Unnamed 5 and were deposited in a huge delta, the Hell Creek Delta. These Miocene 25 Arikaree sediments, now turned into sandstone, siltstone, and mudstone, are called the Hell Creek Formation. Woodlands, ponds, and swamps that existed on
Brule this subtropical, deltaic coastal plain provided habitats for many kinds of Oligocene
38 exotic plants and animals including several species of dinosaurs such as South Heart Chadron Chalky Buttes Triceratops and Tyrannosaurus rex. Freshwater fishes, salamanders,
Camels Butte Eocene Golden lizards, turtles, crocodiles, birds, snails, clams and small mammals coexisted 55 Valley Bear Den with the dinosaurs. Fossils of animals, including sharks, rays, and mosasaurs (large marine lizards) that inhabited shallow marine waters Sentinel Butte adjacent to the delta are found in the Fox Hills Formation and Breien TERTIARY Member of the Hell Creek Formation. The species of dinosaurs that existed at this time were the last dinosaurs to ever live.
Bullion
Paleocene Creek
Slope
Cannonball
Ludlow 65
Hell Creek
Fox Hills
ACEOUS Pierre CRET
84 Niobrara
Carlile
Carbonate Calcareous Shale Claystone/Shale Outcrop in Sioux County showing the Fox Hills Formation (Cretaceous) Siltstone Sandstone Sand & Gravel overlain by the Hell Creek Formation (Cretaceous). The marine Breien Mudstone Lignite Glacial Drift Member of the Hell Creek Formation caps the hill. Outcrop is 35 m thick. View is to the northeast.
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