Geology board: Do I live on an ancient beach?

2,367 Views | 8 Replies | Last: 6 yr ago by bobbranco
Gary Johnson
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I stumbled on this construction site while walking my dog the other day. There's a vertical cut showing about 4' of strata.

  • this is half a mile from White Rock Creek in central Dallas county, a Trinity River tributary
  • My research has discovered the Trinity was once much larger with a much greater flood plain



Here's another cross section from a few feet away showing a narrower, more distinctly red band:


  • The top layer is 1-2 feet stiff clay(I'm pretty sure).
  • At 3-4 foot depth, whitish band at the bottom, is "slightly weathered chalk" from the Austin chalk formation(I think), which would be 65 million years old. Formed from coral reefs when Texas was under the ancient North American Seaway.



I'm most interested in the redish/brownish band in the middle. Is this from the shallow sea, or are these river deposits? It's a redish sandy clay with smoothed rounded pebbles, these must have been formed either by beaches/shallow seas(millions of years ago), or by river runoff during glacial melting(10k to 20k years ago)So my question is, are these pebbles just 10s of thousand of years old, river pebbles from ice-age runoff? Or are these ancient beaches with sand and pebbles from 100s of thousands or millions of years ago?

Most pebbles are 0.5 inches to 2 inches. See below:



Anyway it's pretty cool to think DFW used to be on top of a vast mountain range with peaks as high as the contemporary Rockies, and was also a beach and shallow sea at times. I guess I didn't time my property investment properly.

cross posted on DFW board
https://texags.com/forums/37/topics/2867319
FTACo88-FDT24dad
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AG
The Ouchita Mountains once ran from Arkansas to southwest Texas, basically tracking I 35 quite a bit.

Also, the "Hill Country" is not composed of hills. It's eroded, uplifted plateau that has eroded and created valleys that look like hills.
ABATTBQ87
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AG
During the excavation of DFW Airport in 1970-72, a rare Plesiosaur was found where the new Braniff terminal would be built. (This is now Terminal B, Home to American Eagle) With a grant from Braniff Airways and Southern Methodist University, the dinosaur was restored and put on display between gates 10 and 11. Braniff Hostess Pamela Kretlow was pictured with the 70 million-year-old animal.


huisachel
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..........and it will be again someday. Geologic time will do that
BigJim49 AustinNowDallas
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AG
Austin - seashells on family property on 40th street on a bluff above Shoal Creek !
BigJim49AustinnowDallas
MGS
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ABATTBQ87 said:

During the excavation of DFW Airport in 1970-72, a rare Plesiosaur was found where the new Braniff terminal would be built. (This is now Terminal B, Home to American Eagle) With a grant from Braniff Airways and Southern Methodist University, the dinosaur was restored and put on display between gates 10 and 11. Braniff Hostess Pamela Kretlow was pictured with the 70 million-year-old animal.



So where is it now?
'03ag
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XUSCR said:

The Ouchita Mountains once ran from Arkansas to southwest Texas, basically tracking I 35 quite a bit.

Also, the "Hill Country" is not composed of hills. It's eroded, uplifted plateau that has eroded and created valleys that look like hills.
This got me looking around and I found this



I don't understand what happened to the portion that ran through Texas. Just eroded? Was it not as tall as the portion in Arkansas?
p_bubel
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'03ag said:




I don't understand what happened to the portion that ran through Texas. Just eroded? Was it not as tall as the portion in Arkansas?
Quote:

By late Paleozoic (approximately 350 million to 240 million years ago), the Texas Craton was bordered on the east and south by a long, deep marine basin called the Ouachita Trough. Sediments slowly accumulated in this trough until late in the Paleozoic Era. Plate-tectonic theory postulates that the collision of the North American Plate (upon which the Texas Craton is located) with the European and AfricanSouth American plates uplifted the thick sediments that had accumulated in the trough to form the Ouachita Mountains.

At that time, the Ouachitas extended across Texas. Today, the Texas portion of the old mountain range is mostly buried by younger rocks. Ancient remnants can be seen in the Marathon Basin of West Texas due to uplift and erosion of younger sediments. The public can see the remains of this once-majestic Ouachita Mountain range at Post Park, just south of Marathon in Brewster County. Other remnants at the surface are exposed in southeastern Oklahoma and southwestern Arkansas.
During the Pennsylvanian Period, however, the Ouachita Mountains bordered the eastern margin of shallow inland seas that covered most of West Texas. Rivers flowed westward from the mountains to the seas bringing sediment to form deltas along an ever-changing coastline.

The sediments were then reworked by the waves and currents of the inland sea. Today, these fluvial, delta, and shallow marine deposits compose the late Paleozoic rocks that crop out and underlie the surface of North Central Texas.
Texas Almanac
VaultingChemist
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AG
Those look like river deposits. You can find fossils, including shark teeth, less than a mile from the High Five interchange in North Dallas.
bobbranco
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AG
Looks like cut shows: lime stabilized soil, over select fill, over another layer of lime stabilized soil.

Is that paving at the top?

Also, picture #3 is that unfinished concrete at the bottom of the cut where your tennis shoe and red bull can are next to a piece of rebar?
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