Mississippian Pennsylvanian Permian Tri-Jurassic Cretaceous Tertiary Quaternary Devonian - Silurian Precambrian and Cambrian Rocks Cambrian-Ordovician Rocks

Cambrian-Ordovician Rocks Pennsylvanian Permian Tri-Jurassic Cretaceous Tertiary Quaternary Precambrian and Cambrian Rocks Mississippian Devonian - Silurian


The oldest surface rocks that can be found in Oklahoma occur on the east side of the Arbuckle Mountains. These rocks are Precambrian-aged granites and rhyolites that formed between 1.05-1.35 billion years ago (Johnson, 1996). Little else is known about this period of time in Oklahoma, because very few rocks of this age are exposed at the surface. The only reason these rocks are exposed today is because of a mountain building event, called orogenesis, that occurred over 290 million years ago. The orogeny created the formation of two major fault blocks (called horst blocks). One major fault block is the Arbuckle Mountain block; the other fault block being the Wichita Mountain block. The uplift of these older rocks within the horst block, coupled with subsequent erosion of younger-aged rocks, has exposed these primitive Precambrian rocks along the east flank of the Arbuckle Mountains.
In the Wichita Mountains, a younger episode of igneous activity is recorded by exposure of Lower-Middle Cambrian-aged granites, rhyolites, and gabbros. This igneous activity was short lived, however, because by the Upper Cambrian (about 525 million years ago) Oklahoma sank below sea level, causing shallow seas (called epiric or epicontinental seas) to flood most of the state. This epicontinental sea initially deposited sandstones (the Reagan Sandstone) composed of sediment eroded from the weathered Precambrian and Cambrian igneous rocks. Soon, as the igneous hills were eroded down, sandstone deposition gave way to extensive limestone formation (characterized by the Timbered Hills and lower parts of the Arbuckle Group) across most the state. These limestones mostly formed under quiet-water marine conditions, and contain an abundant assortment of fossil trilobites, brachiopods, and bryozoans (Johnson, 1996).

Click on Paleogeography of the Late Cambrian-Ordovician to get a glimpse as to what Oklahoma was like at this time.

Reference: Johnson, K. S. 1996. Geology of Oklahoma, p. 1-9. In, K. S. Johnson and N. H. Suneson (eds.), Rockhounding and Earth-Science Activities in Oklahoma. Oklahoma Geological Survey Special Publication 96-5.

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