The Pennsylvanian sedimentary fill of the Taos trough of New Mexico contains a variety of coarse-grained deltaic systems typical of tectonically active, cratonic basins. This delta spectrum reflects the interaction of a large number of variables including: water depth, substrate stability, basin energy, fluvial feeder system variations, and tectonic activity. The deltas evolve from small, coarse-grained fan-deltas into more extensive wave-modified, river-dominated, lobate deltas. This evolutionary trend results from an increase in water depth and basin energy.

During Early Pennsylvanian time, vertical movements west of the Taos trough elevated the Uncompahgre uplift and coarse-grained fan-deltas prograded eastward into the basin. When these deltas prograded into water deeper than 4 m, frontal splays spread bedload sediment on the delta slope. Continued progradation gave rise to coarsening upward sequences 4 to 15 m thick capped by coarse channel deposits. When deltas built into very shallow water (<4 m), steep delta foresets developed. If the fan deltas advanced over thick mud sequences, syndepositional deformation occurred.

As the delta complexes extended into the basin, a broad coastal plain was constructed, and the braided streams evolved into low-sinuosity, bed-load rivers. Water depth in the basin increased, and channel-mouth sand was reworked into extensive delta-front sheet sand bodies by the higher wave energy. On delta abandonment, delta-front sand was reworked into barrier islands with associated washovers, and inlets. In contrast, fan-delta abandonment is only represented by thin, bioturbated calcareous sandstone or limestone beds capping the progradational sequence.

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