Stratigraphy, Paleontology and Depositional Environments of the Lower Permian Robledo Mountains Formation of the Hueco Group, Robledo Mountains, New Mexico

Early Permian fossil localities, including numerous tracksites, in the southern Robledo Mountains of Dona Ana County, New Mexico, cover an area of approximately 20 km2 . Lower Permian strata exposed here belong to four formations of the Hueco Group (ascend ing order): Shalem Colony, Community Pit, Robledo Mountains and Apache Da m Formations. With the exception of the Robledo Mountains Formation, the Hueco Group is dominated by shallow water ma rine facies. The Robledo Mountains Formation is as much as 125 m of ma rine carbona tes and shale, intercalated with siliciclastic red-beds that comprise about one-third of the uni t's thickness. At more than 30 localities, the red beds in the study area contain extensive invertebra te a nd vertebra te (tetrapod-footprint) trace fossils and a megafossil plant assemblage composed mainly of Wnlchin. Marine facies of the upper part of the Robledo Mountains Forma tion contain an extensive late Wolfcampian assemblage of megafossil invertebrates, dominated by brachiopods and bryozoans, with considerable numbers of molluscs (bivalves, gastropods, a few specimens of ammonites), and numerous indeterminate crinoids. on-fusulinid foraminifera ns and ostracods dominate the microfossil assemblages. Conodonts from the lower part of the Robledo Mountains Forma tion, found in stra ta that bracket most of the tracksites, indicate a late Wolfcampia n (= la te Artinskia n) age. Carbonates of the Robledo Mow1tains Formation were deposi ted in relatively quiet shallow­ water shelf environments below active wavebase. They show a trend from restricted circulation (brackish?) wa ters in the lower part of the forma tion to more open normal marine waters in the middle a nd u pper parts of the formation. Most of the 34 red-bed tracksites in the Robledo Mountai ns Formation occur a t one stratigraphic level and th us represent a mega tracksite tha t encompassed a t least 20 km2. Tracksites were formed on siliciclastic tidal flats during early stages of rising base level (transgression). Spencer Lucas, Andrew B Heckert, John Estep, Adrian Hunt, and Orin Anderson(1998) STRATIGRAPHY, PALEONTOLOGY AND DEPOSITIONAL ENVIRONMENTS OF THE LOWER PERMIAN ROBLEDO MOUNTAINS FORMATION OF THE HUECO GROUP, ROBLEDO MOUNTAINS, NEW MEXICO. NMMNH Bulletin (#12) STRATIGRAPHY, PALEONTOLOGY AND DEPOSITIONAL ENVIRONMENTS OF THE LOWER PERMIAN ROBLEDO MOUNTAINS FORMATION OF THE HUECO GROUP, ROBLEDO MOUNTAINS, NEW MEXICO 'New Mexico Museum of Na tural History and Science, 1801 Mountain Road NW, Albuquerque, New Mexico 87104; 'Department of Ea rth and Planeta ry Sciences, University of New Mexico, Albuquerque, New Mexico 87131; Mesa Technical College, 911 S. Tenth St., Tucumcari, New Mexico 88401; 4 New Mexico Bureau of Mines and Mineral Resources, Socorro, New Mexico 87801 ABSTRACT: Early Permian fossil localities, including numerous tracksites, in the southern Robledo Mountains of Dona Ana County, New Mexico, cover an area of approximately 20 km . Lower Permian strata exposed here belong to four formations of the Hueco Group (ascend ing order): Shalem Colony, Community Pit, Robledo Mountains and Apache Da m Formations. With the exception of the Robledo Mountains Formation, the Hueco Group is dominated by shallow water ma rine facies. The Robledo Mountains Formation is as much as 125 m of ma rine carbona tes and shale, intercalated with siliciclastic red-beds that comprise about one-third of the uni t's thickness. At more than 30 localities, the red beds in the study area contain extensive invertebra te a nd vertebra te (tetrapod-footprint) trace fossils and a megafossil plant assemblage composed mainly of Wnlchin. Marine facies of the upper part of the Robledo Mountains Forma tion contain an extensive late Wolfcampian assemblage of megafossil invertebrates, dominated by brachiopods and bryozoans, with considerable numbers of molluscs (bivalves, gastropods, a few specimens of ammonites), and numerous indeterminate crinoids. on-fusulinid foraminifera ns and ostracods dominate the microfossil assemblages. Conodonts from the lower part of the Robledo Mountains Forma tion, found in stra ta that bracket most of the tracksites, indicate a late Wolfcampia n (= la te Artinskia n) age. Carbonates of the Robledo Mow1tains Formation were deposi ted in rel atively quiet shallowwater shelf environments below active wavebase. They show a trend from restricted circulation (brackish?) wa ters in the lower part of the forma tion to more open normal marine waters in the middle a nd u pper parts of the formation. Most of the 34 red-bed tracksites in the Robledo Mountai ns Formation occur a t one stratigraphic level and th us represent a mega tracksite tha t encompassed a t least 20 km. Tracksites were formed on siliciclastic tidal flats during early stages of rising base level (transgression). Early Permian fossil localities, including numerous tracksites, in the southern Robledo Mountains of Dona Ana County, New Mexico, cover an area of approximately 20 km . Lower Permian strata exposed here belong to four formations of the Hueco Group (ascend ing order): Shalem Colony, Community Pit, Robledo Mountains and Apache Da m Formations. With the exception of the Robledo Mountains Formation, the Hueco Group is dominated by shallow water ma rine facies. The Robledo Mountains Formation is as much as 125 m of ma rine carbona tes and shale, intercalated with siliciclastic red-beds that comprise about one-third of the uni t's thickness. At more than 30 localities, the red beds in the study area contain extensive invertebra te a nd vertebra te (tetrapod-footprint) trace fossils and a megafossil plant assemblage composed mainly of Wnlchin. Marine facies of the upper part of the Robledo Mountains Forma tion contain an extensive late Wolfcampian assemblage of megafossil invertebrates, dominated by brachiopods and bryozoans, with considerable numbers of molluscs (bivalves, gastropods, a few specimens of ammonites), and numerous indeterminate crinoids. on-fusulinid foraminifera ns and ostracods dominate the microfossil assemblages. Conodonts from the lower part of the Robledo Mountains Forma tion, found in stra ta that bracket most of the tracksites, indicate a late Wolfcampia n (= la te Artinskia n) age. Carbonates of the Robledo Mow1tains Formation were deposi ted in rel atively quiet shallowwater shelf environments below active wavebase. They show a trend from restricted circulation (brackish?) wa ters in the lower part of the forma tion to more open normal marine waters in the middle a nd u pper parts of the formation. Most of the 34 red-bed tracksites in the Robledo Mountai ns Formation occur a t one stratigraphic level and th us represent a mega tracksite tha t encompassed a t least 20 km. Tracksites were formed on siliciclastic tidal flats during early stages of rising base level (transgression).