Northern Midcontinent Digital Petroleum Atlas Geologic Systems, Sequences, and Plays Select a Geologic System. You will be shown a page describing the distribution of that system in the Northern Midcontinent. The plays in that system will also be listed.

Geologic System	Sequence	Time Begin (MYA)	Time End (MYA)
Tertiary	Tejas	60	2
Upper Cretaceous	Zuni III	96	65
Lower Cretaceous	Zuni II	138	97
Jurassic	Zuni I & Upper Absaroka	206	144
Triassic	Upper Absaroka	243	213
Permian	Middle Absaroka	268	245
Pennsylvanian	Lower Absaroka	330	286
Mississippian	Upper Kaskaskia	362	330
Devonian	Lower Kaskaskia & Upper Tippecanoe	401	362
Silurian	Upper Tippecanoe	438	408
Ordovician	Lower Tippecanoe & Upper Sauk	488	438
Cambrian	Sauk	548	505
Pre-Cambrian		?	590