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Geology of Texas The geologic history of Texas is recorded the site of broad evaporite basins where deeply buried lower Mesozoic salt moved in the rock strata that fill the many subsur- salt, gypsum, and red muds were deposited upward to form domes and anticlinal struc- face sedimentary basins and crop out across in a hot, arid climate. The strata originally tures. Now, Cenozoic strata are exposed the state. The origin of these strata docu- deposited in the Permian Basin are exposed throughout East Texas and in broad belts ments a changing geography that began in the Rolling Plains of West and Northwest in the coastal plain that become younger several billion years ago in the Precambrian Texas and in Trans-Pecos Texas. toward the Gulf of Mexico. Era. Mountains, seas, rivers, volcanoes, The Mesozoic Era in Texas began about In Trans-Pecos Texas, extensive Cenozoic and earthquakes are part of the geologic 245 million years ago when the European volcanoes erupted, thick lava flows were de- story of Texas, and the resources produced and African plates began to break away posited over older Mesozoic and Paleozoic by geologic phenomena (petroleum, coal, from the North American plate, producing strata, and rift basins were formed. Ceno- lignite, metals, groundwater, salt, lime- a belt of elongate rift (fault-bounded) zoic volcanic rocks are now well exposed stone, ceramic clays, and various soils) basins that extended from Mexico to Nova in the arid region of Trans-Pecos Texas. are the legacy of the state’s changing face. Scotia. Sediment from adjacent uplifts was In northwestern Texas, late Cenozoic Texas is underlain by Precambrian deposited in these basins by streams. While streams deposited gravel and sand trans- rocks more than 600 million years old. The Europe and Africa drifted farther away, ported from the Rocky Mountains of south- deformed ancient volcanic and intrusive the basins were buried beneath marine ern Colorado and northern New Mexico. igneous rocks and sedimentary rocks were salt as the East Texas and Gulf Coast During the Ice Age (Pleistocene Epoch, formed early in the Earth’s history. They Basins were created. During the rest of the beginning about 2 million years ago) the are now exposed in the Llano Uplift and in Mesozoic Era, broad limestone shelves Pecos River eroded northward into east- a few small areas in Trans-Pecos Texas. were periodically buried by coastal plains ern New Mexico and isolated the alluvial During the early Paleozoic, broad inland and deltaic deposits as the Texas continental eolian deposits of the Texas High Plains seas inundated the stable West Texas region margin gradually shifted southeastward from their Rocky Mountain source. The (Texas Craton), depositing widespread into the Gulf of Mexico. In the East Texas isolated High Plains were eroded by several limestones and shales. Lower Paleozoic Basin, deeply buried salt deposits moved Texas rivers during and since the Ice Age, rocks are now exposed around the Llano upward forming salt ridges and domes, causing the eastern margin (caprock) to Uplift and in the mountains of Trans-Pecos providing a variety of folded structures and retreat westward to its present position. Texas. The Texas Craton was bordered on traps for oil and gas. While the northern part of the continent the east and south by the Ouachita Trough, In West Texas, during the early Mesozoic was covered by thick Pleistocene ice caps, a deep-marine basin extending along Era, a large shallow lake occupied the streams meandered southeastward across a the Paleozoic continental margin from abandoned site of the Permian Basin, cool, humid Texas carrying great volumes Arkansas and Oklahoma to Mexico. but eventually waters from the Gulf of of water to the Gulf of Mexico. Those Sediments accumulated in the Ouachita Mexico encroached and flooded West Texas rivers, the Colorado, Brazos, Red, and Trough until late in the Paleozoic Era beneath a shallow sea. Dinosaurs roamed Canadian, slowly entrenched their mean- when the European and African continental the land and shallow waters, and marine ders as gradual uplift occurred across Texas plates collided with the North American reptiles dominated the Mesozoic seas until during the last 1 million years. Sea-level plate. Convergence of the North and South the waters withdrew from West Texas, near changes during the Ice Age alternately ex- American plates in this area produced the end of the era. Mesozoic strata are ex- posed and inundated the continental shelf. fault-bounded mountainous uplifts posed along the western and northern River, delta, and coastal sediments deposited (Ouachita Mountains) and small basins margin of the Gulf Coast and East Texas during interglacial (high-sea-level) stages filled by shallow inland seas that consti- Basins and extensively across West Texas. are exposed along the outer 80 kilometers tuted the West Texas Basin. When the Cenozoic Era dawned in of the coastal plain. Since sea level reached Broad limestone shelves and barrier Texas, about 66 million years ago, the its approximate present position about reefs surrounded the deeper parts of the East Texas Basin was filling with lignite- 3,000 years ago, thin coastal-barrier, marine subbasins. Rivers flowed to the bearing deposits of river and delta origin. lagoon, and delta sediments have been landward edges of the basins, forming The early Cenozoic Mississippi River deposited along the Gulf Coast. deltas, and coastlines shifted repeatedly flowed across East Texas, and a large delta Texas is a composite of nature’s pro- as nearshore sediments were deposited occupied the region north of Houston. cesses. Texas today is but one frame in and then eroded by marine processes. Smaller deltas and barrier islands extended a dynamic geological kaleidoscope of Pennsylvanian strata that are products southwestward into Mexico, very much changing rivers, subsiding basins, shifting of these processes are exposed today in like the present Texas coast. Delta and beaches, uplifting mountains, and eroding North-Central Texas. Near the end of the river sands were transported southeastward plateaus. The face of modern Texas is Paleozoic Era, the inland seas retreated into progressively deeper waters of the the link that connects its geologic past to southwestward, and West Texas became Gulf of Mexico. In the Gulf Coast Basin, its inevitable future. Bureau of Economic Geology The Bureau of Economic Geology, established in 1909, is the oldest research unit at The University of Texas at Austin. The Bureau functions as the state geological survey of Texas, and Director Scott W. Tinker is the State Geologist. The Bureau conducts basic and applied research programs in energy resources and economics, coastal and environmental studies, land resources and use, geologic and mineral mapping, hydrogeology, geochemistry, and subsurface nanotechnology. The University of Texas at Austin • University Station, Box X • Austin, Texas 78713-8924 • 512-471-1534 http://www.beg.utexas.edu • Bookstore: 512-471-7144; order online at http://begstore.beg.utexas.edu/store/.

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