Pennsylvanian coarse-grained fan δs associated with the Uncompahgre uplift, Talpa, New Mexico
— J. Michael Casey and A. J. Scott

Pennsylvanian sedimentary rocks exposed in the Sangre de Cristo Mountains of northern New Mexico represent a series of clastic wedges deposited along the eastern margin of the ancestral Uncompahgre uplift. These wedges record an Atokan to early Desmoinesian episode of uplift that resulted in the east- ward and southeastward progradation of coarse fan-delta lobes into the adjacent Taos trough. Rapid shifting of these small deltas during basin subsidence resulted in a vertical stacking of complex interbedded sequences of coarse elastics alternating with marine limestone and mudstone. Similar facies assemblages are characteristic of the many cratonic basins associated with the ancestral Rocky Mountains.

Exceptional examples of these complex cycles crop out in the vicinity of Rancho de Taos, New Mexico (fig. 1). This study focuses on exposures along the east side of state highway 3 and in adjoining east-trending canyons 4 to 4.5 kilometers south of Talpa, New Mexico. Five progradational sequences were recognized in the lower 105 meters of section measured in the area (fig. 2). Two sequences (3 and 4) were chosen for discussion.

Twenty-six measured sections and several outcrop sketches detail lateral and vertical variations in lithology, stratification type and fossil content. Environmental conditions have been interpreted from these relationships. Inferred processes combined with directional features, lithofacies geometry and strati- graphic successions have been integrated into a depositional model.