Simulating the Evolution of Fluid Underpressures in the Great Plains, by Incorporation of Tectonic Uplift and Tilting, with a Groundwater Flow Model

Table 2

Stratigraphic column.

Age	Geohydrologic unit name	Lithologic description	Geohydrologic unit type	Model layer	Range of thickness (feet)
Neogene	Ogallala Formation	Terrestrial gravel, sand, and clay	Aquifer	1	0–300
Neogene-Paleogene	Laramide Basin Fill	Terrestrial gravel, sand, and clay	Aquifer	2	0–2,300
Late Cretaceous	Pierre & Niobrara Formations	Marine shales and carbonates, some sand layers	Aquitard	3	0–6,800
Early Cretaceous	Dakota Formation	Sandstone	Aquifer	4	0–500
Jurassic-Triassic-late Permian	Morrison-Leonardian Formations	Terrestrial sand, silt, and clay with upper Permian shale and evaporites	Aquitard	5	0–1,200
Early Permian	Wolfcampian Formation	Clastic marine sediments with carbonate beds	Aquifer	6	0–1,100
Pennsylvanian	Virgilian-Missourian Formation	Clastic marine sediments with carbonate beds	Aquifer	7	400–1,600
Pennsylvanian	Desmoinesian Formation	Marine carbonates in the east, terrestrial sediments in the west	Aquitard in west, aquifer in east	8	100–700
Early Pennsylvanian	Basal Pennsylvanian Unit	Marine shales with some carbonates	Aquitard	9	100
Early Paleozoic	Mississippian-Silurian-Ordovician-Cambrian Units	Limestones and dolomites with karst weathering, & lesser interbedded shales	Aquifer	10	0–1,100
Precambrian	Precambrian Basement	Granite and gneiss	No-flow boundary	Model lower boundary	NA