Marathon Basin -- Fort Peña Park, Marathon TX - Places of Geologic Significance on Waymarking.com

This waymarked sign is one of two "Big Bend Snapshot" signs at the entrance to Fort Peña Park 5 miles outside of Marathon down Old Post Road. It discusses the complex and fascinating geology of this significant region as follows:

"BIG BEND SNAPSHOT: Geology of the Marathon Basin

[inset]

EONS * ERAS * EPOCHS – HOLOCENE
Remember: Numbers equal MILLIONS of years

EONS
0-550 Phanerozoic
550-4600 Precambrian

ERAS
0-70 Cenozoic
70-260 Mesozoic
260-290
290-600 Paleozoic

EPOCHS
0-2 Pleistocene
4-6 Pliocene
6-24 Miocene
24-35 Oligocene

35-57-Eocene
57-65 Paleocene
<10,000 years Holocene


300-600 million years ago – time period described in this sign

5 [300 million years ago] The irresistible forces of colliding continents push vast sheets of rock hundreds of miles inland, while local sections are repeatedly folded repeatedly over themselves.

4 [300 million years ago] Continued pressure causes softer rock layers to break along fold crests while harder layers began to slide over softer layers and thrust faulting begins.

3 [300 million years ago] Intense pressure he forms the weakest rocks into overturned asymmetrical folds while harder, more resistant rocks are pushed over and under them.

2 [300 million years ago] Lateral compression squeezes sediments into folds as ancestral North and South American continental plates began to collide, three hundred million years ago.

1 [550-300 million years ago] Sediments begin to collect in a geosynclinals Marine trough on a subsiding seafloor along continental margins, starting about 550 million of years ago.

During the Paleozoic era, as vertebrates appeared in life moved in land, the Earth’s tectonic plates converged to form the supercontinent Pangea, surrounded by one single global ocean, Panthalassa. Shortly after the opening of the Atlantic Ocean, during the Cambrian period, and undersea valley known to geologists as the Marathon Trough began to form where the Gulf of Mexico is today. For 300 million years, the sinking basin collected thick layers of sediments that were slowly transformed into limestone, sandstone, shale, novaculite, chert and other minerals.

Beginning in the late Pennsylvanian Period, these compacted, lithified marine sediments were deformed, folded, and thrust north and west, as the South American tectonic plate shoved what is now the Yucatán Peninsula to the north and west, pushing the adjacent seabed ashore onto the North American plate. Spectacular evidence of this process is visible throughout the Marathon Basin.

This active mountain building era is known as the Ouachita Orogeny. The same complex forces simultaneously up lifted the Sierra Madre Oriental of Mexico along with the Ouachita Mountains of Arkansas and Oklahoma. This is among the earliest chapters in the history of how Big Bend came to look the way it does today.

[map]
this map shows the distribution of land and water areas as they may have existed roughly 300 million years ago in this region when North and South America collided. As the continents came together, ancestral versions of the Sierra Nevada, Rocky Mountains and Appalachian chain were formed.

At essentially the same time, the Ouachita Orogeny shoved the Marathon Basin into what is now West Texas. Resistant structures from previous continental uplifts deflected the incoming thrust sheets and caused them to break and slide along the indicated transform faults.

[photo]
In the foreground of this photograph and outcrop of erosionally-resistant Caballos Noviculite shows tight folds and fault lines. The same hard as flint rock layer also forms ridges on the hills in the middle ground, and was a favorite tool making stone of early Indians in this region. Santiago Peak, the exposed remains of a much younger 35 million year old shallow igneous intrusion, rises in the background."

Waymark is confirmed to be publicly accessible: yes Access fee (In local currency): .00 Requires a high clearance vehicle to visit.: no Requires 4x4 vehicle to visit.: no Public Transport available: no Website reference: [Web Link] Parking Coordinates: Not Listed

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