Trujillo Formation (also known as Trujillo Sandstone) is a Late Triassic geologic formation exposed in the states of Texas and New Mexico, United States. It is a unit within the Dockum Group and preserves fossils dating back to the upper Triassic period (Carnian stage, approximately 216–203 million years ago).
Naming and History
The formation was first named in 1907 by C.N. Gould as the upper formation of the Dockum Group. It was named after Trujillo Creek in Oldham County, Texas. No formal type section has been designated.
Geographic Distribution
The Trujillo Formation crops out along Palo Duro Canyon, the Canadian River and its tributaries in the Texas Panhandle, and is also widespread in the Sangre de Cristo Mountains of New Mexico. It extends into the Tucumcari Basin and is recognized in the Anadarko, Palo Duro, and Permian basins.
Lithology and Stratigraphy
The formation consists predominantly of gray to brown or red sandstone, with some conglomerate and mudstone. Key lithological characteristics include:
- Lower beds: Fine-grained, crossbedded sandstone that tends to form prominent cliffs.
- Middle and upper beds: Coarser sandstone with more abundant conglomerate and mudstone.
- Thickness: Ranges from 45 to 210 feet (14–64 m).
The formation overlies the Tecovas Formation and is part of the Dockum Group. The Cuervo Sandstone Member is preempted by the Trujillo Formation.
Depositional Environment
The Trujillo Formation is interpreted as having been deposited in a braided stream system. The lower beds at Palo Duro Canyon contain unusual cone-shaped iron oxide concretions that likely formed in the vadose zone (the unsaturated zone above the water table).
Paleontology
Fossils preserved in the formation include:
- Typothorax scutes — an aetosaur (armored archosaur) from the Late Triassic.
- Sanmiguelia — an unusual fossil plant of controversial affinity, interpreted by some as an early cycad.
See Also
- Dockum Group
- Tecovas Formation
- List of fossiliferous stratigraphic units in Texas
- Paleontology in Texas
References
- Gould, C.N. (1907). "Geology and water resources of the western portion of the Panhandle of Texas". U.S. Geological Survey Water-Supply Paper. 191.
- Lucas, S.G.; Hunt, A.P. (1989). "Revised Triassic stratigraphy in the Tucumcari basin, east-central New Mexico". Dawn of the age of dinosaurs in the American southwest. New Mexico Museum of Natural History and Science. pp. 150–170.
- Lucas, S.G.; Hunt, A.P.; Huber, P. (1990). "Triassic stratigraphy in the Sangre de Cristo Mountains, New Mexico". New Mexico Geological Society Field Conference Guidebook. 41: 305–318.
- Asquith, George B.; Cramer, Scott L. (September 1975). "Transverse Braid Bars in the Upper Triassic Trujillo Sandstone of the Texas Panhandle". The Journal of Geology. 83 (5): 657–661.
- Dinwiddie, C. L.; et al. (February 2011). "Chronicles of vadose zone diagenesis: cone-shaped iron oxide concretions, Triassic Trujillo Formation, Palo Duro Canyon, Texas". Geofluids. 11 (1): 87–96.
