The 600+ million year geologic history of North Central Texas and all of Texas involved several periods of mountain-building, tectonic activity. The “pre-Texas” landmass, attached to the North American continental core, was repeatedly whacked into other landmasses, forcefully pulled apart again, and moved about the globe on mobile crustal plates. (An excellent virtual-reality visual representation of this process can be seen at the Institute for Geophysics, UT Austin website.)
Over millions of years, sediments were pushed up, some collapsed, and others were folded and warped. Volcanoes spewed molten rock and ash. Deeply buried sediments were heated forming magmas that were injected into other sediments. These processes created mountains and inland seas. Continuous erosion flattened mountains to plains and filled in the seas. Vast amounts of sediment washed into the Gulf creating thick, steeply-dipping layers of rock. These events set the stage to form the Texas we know today.
The following is a summary of events by geological era. (Click for a geologic time scale with links to period paleomaps.)
Thick sequences of coarse grading to fine sediments were washed from the continental core into an ancient sea - into the location of what would become Texas. Tectonic collisions and plate movement built mountains, created metamorphic structures, and formed massive granitic bodies. Most of these features were eventually eroded into a flat, rocky tableland. The ancient sea coast stretched from Dallas to Del Rio.
Shallow seas invaded flat, rocky “Pre-Texas” providing a repository for eroded continental sediments arriving from the north and west. During the 250 million years from the Cambrian to the Mississippian, coarse sands and gravels accumulated in the near shore environment while limestones, dolomites, and cherts were deposited in the deeper waters to the south and east. Flora and fauna proliferated. The fossil record shows an abundance of life.
During Pennsylvanian time the North American plate collided with the newly forming Pangea landmass, squeezing and buckling Texas rocks once again. The sweeping, S-shaped feature seen on the Texas geologic map, the
Ouachitas, is a result of this collision. Believe it or not, a huge, sweeping mountain range runs right through North Central Texas. You can’t see it since what remains is buried deep within the earth.
As mountains rose in Dallas, the earth’s crust to the west warped downward forming large basins which eventually filled with water and fine sediment creating brackish seas. Texas rested, tectonically speaking, during the Permian. Erosion continued unabated wearing down the mountains, washing sediment into the western basins from the east and the west. Organically-rich sediments, reef structures, and coastal deposits were covered, buried, and compressed. Abundant plant and animal remains buried within porous, sedimentary rocks, laid the ground work for the future wealth of many a Texas oilman.