Early Permian ichnofossil assemblage from the Fra Cristobal Mountains, southern New Mexico

At Red Gap in the Fra Cristobal Mountains (Sierra County, New Mexico), a ripple-laminated sandstone ~ 24 m above the base of the Abo Formation yields an extensive ichnofossil assemblage. This assemblage is of early Wolfcampian age and derived from a sheetflood sandstone deposited on a broad floodplain with no direct marine influence on sedimentation. Invertebrate ichnofossils are assigned to Arborichnus sp., Monomorphichnus lineatus, Stiaria sp. and cf. Tonganoxichnus robledoensis, and several problematic invertebrate ichnofossils are unassigned. The tetrapod ichnofossils are assigned to Batrachichnus salamandroides, Limnopus sp. and Dimetropus nicolasi. Tonganoxichnus and Batrachichnus are the most common ichnofossils, and this dominanace and relatively low ichnodiversity distinguish the Fra Cristobal ichnoassemblage from the ichnoassemblage of the Robledo Mountains Formation in the Robledo Mountains. The differences between the Fra Cristobal and Robledo Mountains ichnoassemblages are not age related, but most likely reflect paleoenvironmental differences along a north-south transect from tidal flat (Robledo Mountains) to inland floodplain (Fra Cristobal).