Texas Almanac, 1992-1993 Page: 67
656 p. : ill. (some col.), maps ; 23 cm.View a full description of this book.
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ENVIRONMENT 67
floods of gravel and sand into Texas and formed great
alluvial fans as the braided streams crisscrossed the
area. These fans were deposited on the older Paleozoic
and Mesozoic rocks and occur from northwestern Texas
into Nebraska. Between 1 million and 2 million years
ago, the streams of the Texas Panhandle were isolated
from their Rocky Mountain source, and the eastern edge
of this sheet of alluvial material began to retreat west-
ward, forming the caprock of the modern High Plains of
Texas.
During the latter part of the Cenozoic Era, a great
Ice Age descended upon the northern part of the North
American continent. For more than 2 million years,
there were successive advances and retreats of the thick
sheets of glacial ice. Four periods of extensive glaciation
were separated by warmer interglacial pe-riods.
Although the glaciers never reached as far south as
Texas, the state's climate and sea level underwent major
changes with each period of glacial advance and retreat.
Sea level during times of glacial advance was 300 to 450
feet lower than during the warmer interglacial periods
because so much sea water was captured in the ice
sheets. The climate was both more humid and cooler
than today, and the major Texas rivers carried more wa-
ter and more sand and gravel to the sea. These deposits
underlie the outer 50 miles or more of the Gulf Coastal
Plain.
Approximately 3,000 years ago, sea level reached its
modern position, and the rivers, deltas, lagoons, beaches
and barrier islands that we know as coastal Texas have
formed since that time.
Mineral Wealth
Fuel Minerals
Oil and natural gas are the most valuable minerals
produced in Texas, contributing 28 percent of the oil pro-
duction and 33 percent of the gas production in the Unit-
ed States in 1984. Oil and gas have been produced from
most areas of Texas and from rocks of all geologic eras
except the Precambrian. All of the major sedimentary
basins of Texas, have produced some oil or gas. The
well-known Permian Basin of West Texas has yielded
large quantities of oil since 1921, and it is an area of con-
siderable promise for future production as well.
Although large quantities of petroleum have been pro-
duced from rocks of Permian age, production in the
area also occurs from older Paleozoic rocks. Production
from rocks of Paleozoic age occurs primarily from North
Central Texas westward to New Mexico and southwest-
ward to the Rio Grande (Paleozoic outcrop area and
west on map), but there is also significant Paleozoic pro-
duction in North Texas in Tarrant, Grayson and Cooke
counties.
Mesozoic rocks are the primary hydrocarbon reser-
voirs of the East Texas Basin and the area south and east
of the Balcones Fault Zone. Cenozoic sandstones are the
main reservoirs along the Gulf Coast and offshore state
waters.
Coal and lignite occur in rocks of Pennsylvanian,
Cretaceous and Tertiary ages. Coal was produced in
Texas from about 1850 to the 1940s, when petroleum be-
came the common fuel. Significant production of coal
did not resume until the mid-1970s. Most of the pre-1940
production was bituminous coal from North Central
Texas, an area near Eagle Pass or from near Laredo.
North Central Texas production was from Pennsylva-
nian rocks. Thurber, Newcastle and Bridgeport all had
viable coal industries in the early 1900s. As early as 1850,
soldiers from Fort Duncan near Eagle Pass are reported
to have mined coal from the Cretaceous rocks. Commer-
cial mining of coal from Eocene rocks near Laredo be-
gan in 1881. In addition to the commercial mining, small
amounts of coal occurring in the Trans-Pecos were used
to roast the ore in mercury mining districts in the the
Big Bend.
Small amounts of "brown coal" or lignite have been
produced throughout the history of the state. It was min-
ed by many early settlers for family and small industry
use, and it was used to generate "coal gas" or "producer
gas" for Texas cities around the turn of the century. To-
day, Texas ranks sixth nationally in coal production, and
lignite accounts for most of this. Almost all of the lignite
is consumed by mine-mouth electrical generating plan-
ts. Approximately 20 percent of the electricity generated
in the state in 1986 was from plants fired by Texas lignite.
Uranium occurs in several widely separated Texas
localities, but production has been limited to the Ceno-
zoic sandstones along the coastal plains of south-central
Texas, roughly from Karnes County southwest to Webb
County. The surface mines, active from 1959 to the mid-
1970s, have largely been abandoned and reclaimed, and
production today is all from in-situ leaching. This re-quires the injection of a leaching fluid into the urani-
um-bearing strata, reaction of the fluid with the
uranium ore and return of the fluid to the surface for
stripping of the uranium. The fluid is then re-used.
Non- Fuel Minerals.,
In 1985, the value of non-fuel minerals produced was
more than $1.9 billion dollars, ranking Texas second na-
tionally. The non-fuel minerals found in Texas are sum-
marized below in terms of geologic setting:
Igneous and metamorphic rocks are favorable sites for
mineralization and the outcrops of Precambrian rocks
provide occurrences of many metals and some rare
earths. There is no mining of these at this time. The area
around Llano has occurrences of several metals and is
commonly referred to as the "Central Mineral Region,"
reflecting a history of complex mineralization. In the
past, the Central Mineral Region had commercial pro-
duction of such minerals as graphite and vermiculite,
and it has enough varied mineral occurrences to make it
a hunting ground for gem and mineral collectors. The
Precambrian rocks of the Trans-Pecos also have com-
plex mineralization suites. Copper and other metals
have been produced from this area.
Igneous rocks occur primarily in Llano and adjacent
counties and in the Trans-Pecos area. The Precambrian
granites of the Llano area long have been utilized as di-
mension stones. Our state capitol and capitol-complex
office buildings are built of this stone, which is shipped
nationally. The Cenozoic igneous activity in the Trans-
Pecos provided solutions rich with many metals, and
metals now occur in host rocks of several different geol-
ogic time periods. Most of the gold and silver production
recorded for the state was from this region. Other met-
als, including mercury and some lead and zinc, were
produced from this area.
Most of the value of Texas non-fuel minerals is in the
non-metallics. Crushed stone and sand and gravel are
mixed with cement for all types of construction and, in
addition, provide the roadbed for highways. Stone also is
stacked to provide rip-rap for dams and jetties, and
some is used to face buildings. There are numerous
other uses of crushed stone, such as pigments, fillers,
carriers, ceramics and bricks. Crushed limestone is used
to manufacture cement and to produce lime. It is also
used in agriculture and in the abatement of acidic gases
produced by the burning of some fossil fuels. Limestone
constitutes more than 95 percent of all the crushed stone
produced in Texas and comes primarily from rocks of
Cretaceous age. Outcrops of Paleozoic limestones and
Cenozoic limestones and caliche also provide some
crushed stone.
The rocks deposited in West and North Central Tex-
as by the vanishing Permian seas left vast deposits of
evaporitic rocks, such as gypsum, anhydrite and rock
salt. The gypsum is now an important source material
for the manufacture of wallboard. Gypsum also occurs
in the area around Fredericksburg, in the Finlay Moun-
tains east of El Paso, and overlying many salt domes as
a "caprock."
The Permian salt beds and the salt domes of East
and Gulf Coast Texas are a source of brine, produced
primarily for use in the oil industry, but it also has other
industrial and manufacturing applications. Rock salt is
mined from two salt domes.
The clays of Texas, particularly those of the Pennsyl-
vanian and Tertiary periods, have a number of uses in-
cluding ceramics, bricks and refractory products. Some
clays and shales expand when subjected to heat and are
used as lightweight aggregate.
Texas is one of the few states that produce signifi-
cant quantities of helium. The gas is produced in the
Panhandle from Permian rocks, but the source of the he-
lium is considered to be from Precambrian igneous
rocks.
Native sulfur occurs in caprock over some of the Gulf
Coast salt domes, and in bedded Permian rocks of far
West Texas. Some crude oils and gases contain substan-
tial amounts of sulfur, which is removed during proc-
essing. Texas is an important source of this secondary
sulfur.
Phvsiography of Texas
Mountains, seas, coastal plains, rocky plateaus, high
plains, forests - all this physiographic variety in Texas
is controlled by the varied rocks and structures that un-
derlie and crop out in Texas. State and national parks set
aside glimpses of this variation so that Texans and visi-
tors may enjoy the beauty of our state. Parks and the
physical features of Texas are discussed elsewhere in
this volume.ENVIRONMENT
67
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Kingston, Mike. Texas Almanac, 1992-1993, book, 1991; Dallas, Texas. (https://texashistory.unt.edu/ark:/67531/metapth279642/m1/71/: accessed April 24, 2024), University of North Texas Libraries, The Portal to Texas History, https://texashistory.unt.edu; crediting Texas State Historical Association.