Abo Formation

Abo Formation
Name	Abo Formation
Type	Formation
Period	Permian
Lithology	Sandstone, conglomerate, mudstone, shale
Namedfor	Abo Pass
Namedby	H.P. Woodward
Region	New Mexico, Texas
Country	United States

Abo Formation is an Early Permian sedimentary unit exposed in the American Southwest, primarily in central and north-central New Mexico and west-central Texas. It crops out in the Rio Grande Rift region and forms part of the continental stratigraphic succession above the Madera Group and beneath the Yeso Group in many sections. The formation records fluvial, coastal plain, and arid continental depositional systems during a time of tectonic reorganization related to the Ancestral Rocky Mountains and the assembly of Pangea.

Description

The formation consists of red beds dominated by coarse- to fine-grained sandstones, interbedded mudstones, and localized conglomerates that form cliffs and slopes in exposed areas such as the Manzano Mountains, Jemez Mountains, Carrizozo Malpais, and the Guadalupe Mountains. Prominent exposures occur along the Rio Puerco, Capitan Reef, and near towns like Socorro, New Mexico, Alamogordo, and Tularosa. Its outcrops control landscape features in national sites including parts of the Bandelier National Monument vicinity and influence sediment supply to basins associated with the Ancestral Rocky Mountains uplift.

Stratigraphy and Lithology

Stratigraphically, the unit lies disconformably above late Pennsylvanian strata of the Madera Group and is commonly overlain by units assigned to the Yeso Group or equivalent formations such as the San Andres Formation in some areas. The lithologic assemblage includes arkosic sandstones, red mudstones, and pebble to cobble conglomerates with locally derived clasts from Proterozoic and Paleozoic source rocks in the Pedernal Uplift and Sacramento Mountains. Sedimentary structures include planar and trough cross-bedding, ripple lamination, mudcracks, and paleosols reflecting episodic fluvial incision and floodplain stability akin to strata in the Cutler Formation and Garber Sandstone farther north and east.

Age and Correlation

Biostratigraphic and radiometric constraints place the formation in the Cisuralian (Early Permian), broadly correlating with the Artinskian to Kungurian stages used in global chronostratigraphy. Correlations tie the unit to coeval deposits in the Midcontinent Series, such as the Wolfcampian assemblages in Texas Permian Basin and equivalents in the Colorado Plateau region. Magnetostratigraphic, palynologic, and vertebrate biostratigraphic data have been used to refine its age relative to units like the San Angelo Formation and the Cutler Group.

Depositional Environment and Paleogeography

Depositional interpretations emphasize a continental setting dominated by east- and southeast-flowing braided and meandering fluvial systems that graded into broad floodplains and ephemeral playa-lake environments under an arid to semi-arid climate influenced by Pangean continentality. Provenance studies indicate sediment derivation from uplifted blocks associated with the Ancestral Rocky Mountains such as the Sandia Crest region and the Sangre de Cristo Mountains, with dispersal patterns comparable to those reconstructed for the Appalachian Basin and Ouachita Orogeny-influenced systems. Paleogeographic reconstructions place the area near the western interior of Pangea, adjacent to shallow basins that later hosted Permian reef and evaporite deposition.

Fossil Content

Fossil assemblages include terrestrial vertebrates, plant fragments, trace fossils, and sparse invertebrate remains. Notable vertebrate ichnofossils and body fossils have been documented that relate to early synapsids and amphibian-grade tetrapods similar to taxa known from Guadalupian and Cisuralian faunas elsewhere, with taxonomic comparisons to genera reported from the Cisuralian of Europe and Russia. Plant fossils and palynomorphs provide floral evidence comparable to Permian assemblages from the Rotliegendes and Autunian floras, aiding biostratigraphic correlation. Trace fossils include terrestrial trackways and burrows comparable to ichnotaxa found in the Red Beds (Pennsylvanian-Permian) of North America.

Economic Resources and Uses

The formation’s porous sandstones serve as local aquifers and influence groundwater flow in basins and arroyos near Albuquerque and Las Cruces, and its conglomerates have been used as aggregate in regional construction projects in communities like Santa Fe and Roswell. Its red beds have limited potential as hydrocarbon reservoirs relative to deeper Permian basin targets such as the Wolfcamp Formation, but studies of porosity and permeability have informed regional resource assessments. Outcrops are valued for educational geology field trips by institutions like University of New Mexico and New Mexico Institute of Mining and Technology.

Research History and Notable Exposures

The unit was named in early 20th-century regional mapping by geologists working in the Territory of New Mexico and later refined by state surveys and academic studies from institutions including the U.S. Geological Survey and multiple university departments. Classic sections and type exposures are accessible near Abo Pass and along highway cuts on U.S. Route 60 and Interstate 25, with well-studied localities in the Estancia Basin and on mesas adjacent to the Rio Grande. Ongoing research addresses provenance using detrital zircon geochronology, paleoclimatic reconstructions, and vertebrate paleontology contributions from museum collections at the New Mexico Museum of Natural History and Science and comparative studies with collections at the Smithsonian Institution and American Museum of Natural History.

Category:Permian formations of North America