- Geology of Texas
Texas contains a great variety of geologic settings. The state'sstratigraphy has been largely influenced by marine trangressive-regressive cycles during thePhanerozoic , with a lesser but still significant contribution from lateCenozoic tectonic activity, as well as the remnants of aPaleozoic mountain range.General Geology
Texas is approximately bisected by a series of faults that trend southwest to northeast across the state, from the area ofUvalde toTexarkana . South and east of these faults, the surface exposures consist mostly of Cenozoicsandstone andshale strata that grow progressively younger toward the coast, indicative of a regression that has continued from the lateMesozoic to the present. The coastal plain is underlaid bysalt dome s that are responsible for many of the oil traps in the region.North and west of the faults are the Stockton, Edwards, and Comanche plateaux; these define a crustal block that was upthrown during the
Neogene . This large region of central Texas, which extends fromBrewster County east to Bexar, and northeast to the Red River features extensiveCretaceous shale andlimestone outcrops. The limestone in particular is important, both economically for its use incement manufacture and as a building material, as well as practically; a porous limestone formation in theTexas Hill Country is the reservoir of theEdwards Aquifer , a vital water source to millions.Almost in the center of these Cretaceous rocks is the
Llano Uplift , a geologic dome ofPrecambrian gneiss ,schist , andgranite , surrounded byPaleozoic sedimentary rock s. The granite here is quarried for construction, but it is perhaps best known to Texans through its manifestation asEnchanted Rock .From San Saba north to
Childress , and fromWichita Falls in the east toBig Spring in the west, the surface consists of late Paleozoic (Pennsylvanian) to early Mesozoic (Triassic ) marine sediments. These strata grow younger from east to west, until they are overlain unconformably byterrigenous Ogallala sediments ofMiocene andPliocene age. These late Cenozoic deposits dominate theTexas Panhandle .The geology of west Texas is arguably the state's most complex, with a mix of exposed Cretaceous and Pennsylvanian strata, overlain by
Quaternary conglomerates. A series of faults trend southeast to northwest across the region, from Big Bend to El Paso; there are also extensive volcanic deposits. The Marathon Mountains northeast ofBig Bend National Park have long been of special interest to geologists; they are the folded and eroded remains of an ancientmountain range, created in the sameorogeny that formed the Ouachita andAppalachian Mountains . [http://wrgis.wr.usgs.gov/docs/usgsnps/province/inthigh.html USGS]Historical Geology
The Precambrian metamorphic and igneous rocks of the Llano Uplift probably formed during the
Mesoproterozoic Grenville orogeny , which was part of the assembly of thesupercontinent Rodinia . Over time, the mountains of the Grenville orogeny were eroded flat, and later covered by Paleozoic and Mesozoic sediments that were not uplifted and eroded in their present manner until the late Cenozoic.Early to middle Paleozoic rocks in Texas are typically
carbonate deposited in epeiric seas. Exceptions include a significant areaofCambrian sandstone in west Texas, and some shale strata from theDevonian andMississippian periods. TheOuachita Mountains were uplifted across the state during the succeeding Pennsylvanian period; this provided a nearby source of sediment for shale and sandstone, along with more marine limestone deposition. [Spearing, Darwin. "Roadside Geology of Texas." Missoula: Mountain Press Publishing Company, 1991. ISBN 978-0-87842-265-4 pp. 4-7]Permian rocks are the best-known of the Texas Paleozoic. They are widespread in north Texas, where their characteristicred beds are spectacularly exposed inPalo Duro Canyon . The strata are also oil-rich where buried in west Texas, such as in the Midland and Odessa region. Thiscrude oil rich area is known as thePermian Basin . Permian Texas was covered by shallow seas to the west, with evaporation flats to the east and north in the Panhandle. [Spearing, p. 7] Outstanding exposures of Permian strata are located in and aroundGuadalupe Mountains National Park , the geology of which resulted in the definition of several Permian stratotypes; the region is one of the world's best for studies of the period. [http://www.eos.ubc.ca/public/resources/slidesets/guad/slidefiles/guadc0.html] , [http://www.stratigraphy.org/gssp.htm]Early and middle Mesozoic strata are, on the whole, poorly represented in Texas. Triassic rocks are limited to sandstone and shale in the Panhandle, while the Jurassic record is almost nonexistent at the surface. This was far from a monotonous time, though, as it featured the creation of the
Gulf of Mexico , from a rift southeast of the Ouachita Mountains. Deeply-buried salt deposits and marine limestones under the coastal plain date from theJurassic , when the first shallow seas formed. [Spearing, p. 8]The late Mesozoic record is much richer. Cretaceous rocks--particularly those of the lower Cretaceous--are widespread atthe surface, with yet more buried under the coastal plain. The strata consist of massive limestone sequences deposited when theentire region was submerged under the
Western Interior Seaway , during the last great marine transgression. [Spearing, p. 9]The Western Interior Seaway had withdrawn by the beginning of the Cenozoic, the era that put the finishing touch on Texas's currentgeology. The modern coastal plain formed during this time; it comprises increasingly thick sediments (perhaps 15 km deep atthe coastline) deposited southeastward into the downwarping Gulf of Mexico. [Spearing, pp. 10-11]
West Texas was rent by volcanism during the
Eocene andOligocene epochs, activity which formed most of the modern topography of the area. Later crustal extension created a series of alternating horsts andgraben s similar to those in theBasin and Range province of the western U.S. A late Cenozoic uplift of theRocky Mountains led to the deposition of a vast fan of eroded sediment to their east, forming the Ogallala Formation that covers much of the Panhandle. Most of the state's current stream valleys and canyons date from thePleistocene to the present, as the final geologic shaping of the state. [Spearing, pp. 10-11]Economic geology
Texas has been one of the leading states in petroleum production since discovery of the Spindletop oil field in 1901. The state also produces uranium. In past years, the state has also produced mercury, silver, and copper.
ee also
*
Mount Blanco
*Mount Bonnell
*Llano Estacado
*Palo Duro Canyon
* Caprock Canyons
*Basic geologic features of each state
*Geology of North America External links
* [http://geology.about.com/library/bl/maps/bltexasmap.htm Geologic Map of Texas from About.com]
* [http://www.lib.utexas.edu/books/landscapes/ Virtual Landscapes of Texas]Footnotes:
References:
*American Association of Petroleum Geologists. "Geological Highway Map of Texas." Tulsa, 1979.
* [http://wrgis.wr.usgs.gov/docs/usgsnps/province/inthigh.html Geologic Provinces of the United States: Ouachita-Ozark Interior Highlands (Accessed 3/27/06)]*Spearing, Darwin. "Roadside Geology of Texas." Missoula: Mountain Press Publishing Company, 1991. ISBN 978-0-87842-265-4
United States topic
title =Geology of the United States by political division
prefix = Geology of
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