New Mexico Geological Society Annual Spring Meeting — Abstracts

The Lincoln Fold Belt contains a set of disharmonic, short wavelength folds with a controversial timing and origin. Located just outside the village of Lincoln, New Mexico, folded sedimentary rocks of the Leonardian (Middle Permian) Yeso Formation are exposed in the surrounding hills. The overlying Permian San Andres formation is poorly exposed and contains harmonic folds with long wavelengths. Both of these units are located in an area with a complex geologic history.

Previous stratigraphic and structural studies resulted in several possible mechanisms and ages of fold formation being proposed. Estimates of the age of fold formation range from Permian (syndepositional) to Tertiary. Proposed mechanisms for the formation of the folds include softsediment deformation, gravitational mass wasting and slumping, Laramide deformation, deformation caused by the dikes and sills from either the nearby Capitan Pluton or the Sierra Blanca intrusion, and deformation caused by movement along basement faults.

Mapping of the study area has yielded bedding measurements within the Yeso Formation that strike predominantly northwest/southeast, and fold axes that trend predominantly northeast/southwest. Wavelength measurements in the Yeso folds range from 10-60 m. Fold trends do not vary significantly with distance measured perpendicular to the fold axes. Bedding within the overlying San Andres does not appear to have a consistent strike pattern, but all fold axis measurements trend north to northeast. Wavelengths in San Andres folds range from 300- 400 m. The Yeso-San Andres contact is discordant, possibly due to the presence of an unconformity or fault. U-Pb dating of cross-cutting diabase dikes will be used to better constrain the timing of folding.