Stratigraphy, sedimentology and evolution of a vertebrate-bearing, braided to anastomosed fluvial system, Cutler Formation (Permian-Pennsylvanian), north-central New Mexico

Abstract

Cutler Formation redbeds, exposed in north-central New Mexico, contain portions of three megasequences, each with different architectural element and lithofacies compositions. Eight architectural elements are recognized including major sandstone sheets and ribbons of braided and anastomosed fluvial origin, respectively. The remaining six elements are of overbank origin and include crevasse channel and splay deposits, and floodplain sand-, silt- and claystones. The megasequence stratigraphy provides a framework in which to assess the evolution of depositional style through approximately 15 million years.Cutler Formation rivers flowed south-southwest from the San Luis-Uncompahgre Uplift from Late Pennsylvanian to Early Permian. During megasequence 1 ‘time’, the climate was semi-arid, major channels were broad and shallow, interfluve areas were frequently inundated by sheet floods and splays, and floodbasin ponds were common. During megasequence 2 ‘tim’, channels became narrower. Laterally extensive floodplains and basins developed between stable channel belts and were sites of mature caliche development. Locally, anastomosed channel reaches developed and associated crevasse channels were a locus for the preservation of macroplant and vertebrate fossils. The climate, though still semi-arid, was more arid than during megasequence 1 ‘time’. Renewed uplift in the highlands during megasequence 3 ‘time’ flooded the region with coarse clastics and reestablished a style of poorly confined shallow, braided flow. Throughout this time, aridity continued to increase. In the San Diego Canyon area, flow was deflected toward the southeast due to minor uplift in the Nacimiento highland.