31-1 Geologic Mapping of the 7.5-Minute San Jose Quadrangle, New Mexico with Emphasis on Ancestral Rocky Mountains (ARM) Deformation

Session: Best Student Geologic Map Competition (Posters)

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Abstract:

The tectonics of the late Paleozoic ancestral Rocky Mountain (ARM) orogeny remain unresolved in part due to the pervasive overprinting of ARM-related structures by the subsequent Laramide Orogeny. The Taos Trough represents one of several Pennsylvanian to early Permian sedimentary basins that formed in response to ARM deformation, situated between high-angle, basement-cored uplifts.  Detailed geologic mapping of the San Jose 7.5-minute quadrangle in San Miguel County, north-central New Mexico, documents late Paleozoic structures and stratigraphic relationships that can be differentiated from younger Laramide-aged deformational features. The quadrangle exposes a Pennsylvanian–Permian clastic sequence with minor carbonate, overlying Mississippian strata, which in turn rests nonconformably on Precambrian crystalline basement rocks. Paleozoic succession includes, from oldest to youngest, the Arroyo Peñasco Group (Mississippian undivided), the Sandia Formation, the Porvenir Formation, the Alamitos Formation, the Sangre de Cristo Formation, and the Yeso Formation. A relatively thin Arroyo Peñasco Group consists of varied limestone. The Sandia Formation is dominated by cross-stratified feldspathic sandstone and pebble conglomerate with northwest-directed paleocurrents. It is conformably overlain by the Porvenir Formation, a fossiliferous limestone-shale-sandstone unit, with abundant conodonts. Both Sandia and Porvenir formations exhibit broad north-south folding associated with regional northeast-southwest shortening. The Alamitos Formation lies above an angular unconformity and post dates that folding event. The basin exhibited a change in sediment direction in Alamitos time switching to southerly and then easterly for the Sangre de Cristo Formation. These data indicate that Precambrian basement in the map area was uplifted in the Early Pennsylvanian along a south–north trending, high-angle intrabasinal reverse faults. Granite clasts in the sandstone and conglomerate of the Sandia Formation and folding below the Alamitos Formation suggest synorogenic sedimentation. The latest Pennsylvanian to early Permian record, represented by the Alamitos and Sangre de Cristo formations, reflects waning tectonism and a shift in sediment supply from distal western sources. Collectively, these findings contribute to resolving the late Paleozoic basin evolution in the southern part of Taos Trough.

Keywords: ancestral Rocky Mountains, late Paleozoic, Pennsylvanian, Permian, paleocurrent, uplift, arkosic

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

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