Forth Worth Pin

Forth Worth Pin

This pin I got from Ron Eberhardt formerly with TxDot.

Fort Worth’s motto is: “Where the West Begins”.

The fertile, game-rich land surrounding the banks of the Trinity River had long been a favorite hunting ground for Native Americans in the area, but it soon proved irresistible to settlers as well.

A settlement had been established by Jonathon Bird in the winter of 1840, three miles east of where Birdville is today. In 1843, Sam Houston came to what was then called Fort Bird or Bird’s Fort and remained more than a month, awaiting chiefs from different tribes to discuss a peace parley. Houston departed, leaving Gen. Edward H. Tarrant and George W. Terrell to meet with the chiefs. When the tribes came to the negotiating table, a treaty was made under which the Native Americans were to remain to the west of a line traced passing through the future site of Fort Worth. The line marked “Where the West Begins”—giving Fort Worth its famous slogan.

In an attempt to establish control over North Texas, the Republic of Texas attempted to set up a line of “ranger” (militia) forts on the frontier. When ranger stations proved inadequate, the U.S. Army stepped in and took over the job of watching the frontier. It adopted a “picket line” strategy of establishing forts every 100 miles or so, stretching from the Rio Grande in the south to the Red River in the north.

In the spring of 1849, Fort Graham on the Brazos River represented the northern anchor of that defensive line, leaving a 130-mile gap up the Red River that was a blind spot in the state’s defenses. To extend the line farther north and close that gap, Col. William S. Harney, acting commander of the Department of Texas after the death of Maj. Gen. Williams Jenkins Worth, on May 7 ordered Maj. Ripley Arnold up to the Trinity River.

Arnold took a small party of 2nd Dragoon troopers and proceeded to Johnson’s Station, where he hooked up with Middleton Tate Johnson and four other civilians. They rode west to a spot near the confluence of the Clear and West forks of the Trinity. There, at the end of May, they planted Old Glory on the future site of Fort Worth.

A week later, Arnold was back with his entire command, the 42 men of Company F, 2nd Dragoons. The men set to work building a fort and, by the end of August, they were ready to move in.

A small civilian community grew up in the comforting shadow of the fort. No more than 100 people lived in the vicinity, most of whom were more dependent on the garrison for economic well-being than safety. Farther out from the bluffs, the county created by the state legislature in 1849—Tarrant—also began filling up with homesteaders attracted by the rich soil and the security provided by the U.S. Army. In the next four years, the number of settlers grew to some 350 hardy souls.

On September 17, 1853, the fort was vacated. Troops were redeployed as the line marking the Western frontier made another push toward the Pacific Ocean.

Fort Worth area geological map

Fort Worth area geological map

Dallas–Fort Worth sits above Cretaceous-aged strata, dates ranging from ~145-66 Ma. These Cretaceous-aged sediments lie above the eroded Ouachita Mountains and the Fort Worth Basin, which was formed by the Ouachita Orogeny. Going from west to east in the DFW Metroplex and down towards the Gulf of Mexico, the strata gets progressively younger. The Cretaceous sediments dip very gently (about 1°) to the east.

The Cretaceous rocks in the DFW Metroplex are divided into the older Comanchean Series in the west, and the younger Gulfian Series in the east, as is displayed above.

A simulated-color satellite image of Dallas and Fort Worth, Texas, taken by NASA’s Landsat 7 satellite. Dallas makes up much of the right half of the urbanized area. Red is vegetated area surrounding DFW. Notice also the many reservoirs in the area.

The geology of the DFW Metroplex consists of gently tilted sediments of mostly Cretaceous age, which also obscures a much older geologic record. Sediments older than Cretaceous can be found only at the surface in the extreme western part of the DFW Metroplex, in the area around Weatherford, Texas. Ancient folded mountains formed by the Ouachita orogeny existed in the eastern part of the Metroplex 300 million years ago. These ancient mountains were reduced by erosion and rifting associated with the opening of the Gulf of Mexico in Jurassic time and were buried beneath younger Cretaceous sediments. Although the Ouachita Mountain roots are not visible in the DFW Metroplex since they are buried, they can still be recognized by boreholes and other data. In west Texas near Marathon, the mountain range makes an appearance to the surface, and is known as the Marathon Uplift. To the north of the DFW Metroplex, we can see the roots of these mountains in SE Oklahoma. We know of these today as the Arbuckle mountains, despite the fact that they are far from what the untrained eye would consider a former vast mountain range.

The Marathon-Ouachita-Appalachian-Variscan cordillera, which stretched through central Texas, around Arkansas, up through the Appalachian Mountains and eventually into eastern Europe, occurred when the supercontinents Pangea and Laurussia collided to form Pangea in the late Paleozoic ~300 Ma. The zone of deformation known as the Ouachitas marks a zone of weakness that was exploited when the Gulf of Mexico opened about 165 Ma, in Jurassic time.

The oldest rocks in Texas date from the Precambrian, specifically the Mesoproterozoic and are about 1,600 million years old, and mark the southern limit of the North American craton. These rocks are mostly buried beneath Phanerozoic sediments, but are exposed in the Llano area, where previous Precambrian igneous and metamorphic rocks where uplifted and exposed at the surface. These billion year old rocks can only be seen several thousand feet in the subsurface by boreholes and other data in the DFW Metroplex.

The Fort Worth Basin which lies beneath Cretaceous sediments west of Dallas formed as a foreland basin during the Ouachita orogeny. Horizontal shortening caused flexual isostasy to bend the lithosphere. The bent lithosphere to the west of the Ouachita Mountains caused a bowl shaped depression to form, known as a foreland basin, preserving the Mississippian sediments of the Barnett Shale and other Paleozoic sediments; these sediments mostly formed before the Pangeic collision. Significant deposits of hydrocarbons such as natural gas have economic importance as is seen in formations like the Barnett Shale.

Pangea started to break up during the Triassic ~225Ma. Rifting affected regions which became the central Atlantic (between North America and Africa) and the Gulf of Mexico at about the same time. This rifting created a divergent plate margin that would play an integral role of the future geologic processes to follow. Rifting which involves the stretching of pre-existing crust and mantle lithosphere was initiated by the existence of sufficient horizontal deviatoric tensional stress that broke the lithosphere. Eventually rifting gave way to sea floor spreading in the Atlantic and Gulf of Mexico in the mid Jurassic, around ~165 Ma. Sea floor spreading is where new oceanic lithosphere is being created by upwelling of material, unlike rifting where it only involved the stretching of the crust. Convection currents in the sub-lithospheric mantle are the driving mechanisms that caused sea floor spreading to occur. New lithosphere is made when hot material beneath ocean ridges is brought to the surface by these cells. As the new lithosphere moves horizontally away from the ridges, the new crust added to the Gulf of Mexico and the Atlantic caused the continents of North America and South America to be moved apart. Seafloor spreading in the Gulf of Mexico ceased by the beginning of the Cretaceous and spreading shifted to the proto-Caribbean.

Around 110-85 Ma, there was world-wide oscillatory increases in ocean floor spreading rates. The increase in the amount of basalt being injected into the ocean caused a displacement of water from the ocean basins, which resulted in sea level rise, flooding the coasts of the Texas margin and other bordering continents around the world. The major sea level rise that took place due to an occurrence of an oscillation is known as the Cenomanian transgression, which is the most well known and last major transgression in the Cretaceous. The dispersal of extra magma warmed the water in the ocean, and was a conducive environment for calcareous-shelled organisms, which eventually died and sunk to the bottom of the ocean floor creating thick deposits of limestone. In addition to the displacement of water, an increase in injected magma raised CO₂ levels to around 2-6 times the current level. The increase in CO₂ levels along with the extra production of crust caused global temperatures to rise, which would also play an integral role in the future development of different Cretaceous formations. When the sea floor spreading rates slowed around ~85 Ma, so did the amount of basaltic material being thrown into the ocean which caused the initial water displacement. As seen around the DFW Metroplex, the Cretaceous rocks deposited during this time were directly influenced by increased sea floor spreading rates.

Location: 07-E5

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