Sierra Madera Astrobleme -- US 385 S of Fort Stockton, Pecos County TX
Posted by: Groundspeak Premium Member Benchmark Blasterz
N 30° 32.401 W 102° 55.506
13R E 699048 N 3380458
Quick Description: The Sierra Madera Astrobleme is a giant meteor crater in Pecos County Texas south of Fort Stockton TX
Location: Texas, United States
Date Posted: 2/5/2017 3:35:32 PM
Waymark Code: WMV13R
Published By: Groundspeak Premium Member lumbricus
Views: 3

Long Description:
If you're in it, you don't know it. It looks like all the rest of the Chihuahuan desert to the untrained eye. If you're looking down from space, you can't miss it!

Fortunately, there are signs letting travelers know when they are entering the astrobleme.

From The University of Texas Permian basin: (visit link)

"Sierra Madera Astrobleme

Sierra Madera is located ninety miles southwest of UTPB. Seventy years ago the renowned geologist P. B. King recognized that the Sierra Madera structure was a different breed of cat. The circular cluster of hills is 1.5 miles in diameter. Older strata are exposed in the central part and strata generally dip radially away from the center. Permian rocks are uplifted as much as 4000 feet in the central uplift. Cretaceous rocks dip gently away from the central uplift and form the outer rim of the structure. However, it is not a simple, structural dome because the bedding is also highly folded and faulted on the small scale.

Many domal structures to the south have igneous rocks associated with them, but Sierra Madera does not. Oil companies are attracted to structural domes, or 'four ways of dip,' and Sierra Madera was no exception. Drilling revealed an amazing phenomenon-- at deeper levels the dome did not exist!

Robert Dietz suggested that the Sierra Madera structure might be the result of a meteorite impact. Howard Wilshire studied the area and showed that shatter cones and micro-breccias indicated extremely high pressures of 200 kilobars. Wilshire's work convinced most geologists that the impact of an extraterrestrial body created a circular crater 6 miles in diameter and a central uplift caused by impact rebound.

See also: (visit link)

Immediately after impact (figure 37A), the crater grew by low-angle jetting (Gault and others, 1968), while a shock wave passed outward and downward.

Figure 37B shows the central uplift forming during excavation of the crater, in accordance with the Canadian high-explosive cratering experiments and with the sequence inferred at Gosses Bluff (Milton and Brett, 1968). Outward thrusting may have dragged or injected slices of dolomite from the Tessey up around the periphery; the slices were then left isolated by subsequent normal faulting related to crater wall collapse. Withdrawal of material moving into the uplift may have caused collapse of the crater walls, or inward movement of collapsing wall blocks may have been responsible for the uplift. Either way, the adjustments may have continued past the excavation stage. Injection of sandstone and of highly shocked, shattered rock in mixed breccias probably began early in the deformation. If analogous to sand flows around the Snowball TNT crater (Diehl and Jones, 1967), some of the fluidized injections may have continued to flow for days.

The freshly formed crater is shown complete in figure 37C. Figure 37D represents the present eroded form of the structure.

from Wilshire, et al (1972).
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

Visit Instructions:
No specific requirements, just have fun visiting the waymark.
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Recent Visits/Logs:
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Benchmark Blasterz visited Sierra Madera Astrobleme -- US 385 S of Fort Stockton, Pecos County TX 12/26/2016 Benchmark Blasterz visited it
Raven visited Sierra Madera Astrobleme -- US 385 S of Fort Stockton, Pecos County TX 9/20/2016 Raven visited it

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