163 Impact Cratering Processes Across the Solar System: In Memory of Dr. Bevan M. French

Session focuses on the nature of impact craters and their influence on planetary geologic evolution. We solicit contributions on aspects of impact crater formation, ejecta, shock processes, geochemical and mineralogical signatures, modeling, and geologic implications; comparison among planetary bodies.

Tuesday, 21 October 2025
8:00 AM - 12:00 PM
HBGCC, 214C

Investigating Confirmed and Suspected Impact Structures in West and Central Texas: Observations Made in Preparation for a GSA Field Trip

Paper number: 163-10
Program: Technical Sessions
Time: 10:30 AM – 10:45 AM

Authors

Abstract

The 2025 GSA Annual Meeting features a field trip to investigate the impact record of west and central Texas. We will visit the simple crater (and associated crater field) at Odessa and the complex Sierra Madera impact structure south of Fort Stockton. We also will explore the proposed structure at Hico, southwest of Fort Worth, and the enigmatic Bee Bluff disturbance between La Pryor and Uvalde. We were asked to organize this trip by the Planetary Geology Division prior to the passing of our mentor, colleague, and friend, Dr. Bevan M. French. We now lead it in his memory, which is especially appropriate given that his petrography is important to the Bee Bluff story. 

The purpose here is to report some new field observations from these sites that were made scouting the sites in preparation for the trip.

Bee Bluff is an unusual case of a structure that was accepted and subsequently removed from the crater database, not due to doubts about the veracity of shocked quartz in the disturbed sandstones, but rather because of the supposition that the sandstones contained shocked quartz prior to the disturbance. It is remarkable that no one has pursued documenting the source of those ejecta. We have made new observations of shocked minerals in a nearby polymict breccia that may help understand these relationships. And an unusual siltstone breccia, containing red fine-sandstone clasts, more than 40 km southeast that may also be helpful. 

Structural analyses strongly suggest that the Hico structure is the eroded remains of an impact structure. However, materials evidence has been lacking. We are conducting petrography on an extremely high-flow-regime hummocky siltstone that was identified in the central-uplift area, some possible basement clasts, and some curious spherulitic carbonates that were found on the eastern side of the structure. 

Finally, although the impact origin of Sierra Madera is well-established, there are unresolved questions including its size. The central uplift is approximately 4 km across and possibly suggests a final crater diameter significantly greater than 13 km. We are examining some large limestone blocks 20 km south of the center that contain unusually twinned and kink-banded carbonate rocks. If these are associated with the impact rather than regional tectonism, it may increase the recognized limits of the structure.   

Geological Society of America Abstracts with Programs. Vol. 57, No. 6

doi: 10.1130/abs/2025AM-414492

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