New Mexico Geological Society Annual Spring Meeting — Abstracts

The Joyita Uplift developed during the Permo-Pennsylvanian Ancestral Rockies Orogeny. It is exposed in the Joyita Hills of central New Mexico. Baars traced the uplift north to the Sierra Nacimiento in the subsurface and marked its southern extent as unknown. Altares also observed a localized uplift southeast of the Joyita Uplift. Permian stratigraphic relationships suggest another, larger uplift may be present east of Socorro.

The Middle Permian San Andres Formation thins abruptly along a north-trending region approximately aligned with Lorna de Las Canas. This unit normally consists of limestone, dolostone and gypsum. Within the region of thinning, the San Andres Formation consists exclusively of carbonate rocks. The evaporites pinch out abruptly from east to west. East of the pinchout, the San Andres is predominantly evaporite; carbonate rocks dominate the lower onequarter of the formation. A narrow zone of karst and terra rossa paleosol occurs at the evaporite pinchout. The Artesia Formation (light reddish brown siltstone and sandstone) rests disconformablyon the San Andres Formation and across the evaporite pinchout.

The abrupt thinning of the San Andres Formation marks the axis of an unrecognized buried uplift; the karst marks the approximate eastern edge of the structure. The western margin of this feature is not apparent but can be approximately located using paleocurrent data from the Bursum Formation and stratigraphic relationships in the Pennsylvanian section as a guide. The same type of thinning and evaporite pinchout in the San Andres is present along the eastern side of the Joyita Uplift although the karst is not exposed. A similar pinchout is also present along the eastern edge of the Pedernal Uplift in Otero County.

This model is consistent with observed stratigraphic relationships in the San Andres across other Paleozoic uplifts in New Mexico. It is now possible to reinterpret several geologic features in the Socorro region including the distribution of depositional facies along the eastern margin of the Permo-Pennsylvanian Lucero-San Mateo Basin.