An unconformity is a buried erosional or non-depositional surface separating two rock masses or strata of different ages, indicating that sediment deposition was not continuous. In general, the older layer was exposed to erosion for an interval of time before deposition of the younger layer, but the term is used to describe any break in the sedimentary geologic record. The significance of angular unconformity was shown by James Hutton, who found examples of Hutton's Unconformity at Jedburgh in 1787 and at Siccar Point in 1788.
The Bluestone Formation is a geologic formation in West Virginia. It is the youngest unit of the Upper Mississippian-age Mauch Chunk Group. A pronounced unconformity separates the upper boundary of the Bluestone Formation from sandstones of the overlying Pennsylvanian-age Pocahontas Formation.
The Lake Valley Limestone is a geologic formation widely exposed in southwestern New Mexico. It preserves fossils dating back to the lower to middle Mississippian.
The Sandia Formation is a geologic formation in New Mexico, United States. Its fossil assemblage is characteristic of the early Pennsylvanian.
The Tererro Formation is a geologic formation in Sangre de Cristo Mountains of New Mexico. It preserves fossils dating back to the early Mississippian.
The Arroyo Penasco Group is a group of geological formations exposed in the Nacimiento, Jemez, Sandia, and Sangre de Cristo Mountains of northern New Mexico. It preserves fossils characteristic of the late Mississippian.
The Flechado Formation is a geologic formation in the northern Sangre de Cristo Mountains of New Mexico. It preserves fossils dating back to the early to middle Pennsylvanian.
The Gray Mesa Formation is a geologic formation in New Mexico. Its fossil assemblage dates the formation to the Moscovian age of the Pennsylvanian.
The Galisteo Formation is a geologic formation in New Mexico. It contains fossils characteristic of the Bartonian stage of the Eocene epoch, Duchesnean in the NALMA classification.
The Yeso Group is a group of geologic formations in New Mexico. It contains fossils characteristic of the Kungurian Age of the early Permian Period.
The Atrasado Formation is a geologic formation in New Mexico. Its fossil assemblage dates the formation to the Kasimovian age of the Pennsylvanian. It was formerly known locally as the Wild Cow Formation or the Guadelupe Box Formation.
The Madera Group is a group of geologic formations in northern New Mexico. Its fossil assemblage dates the formation to the middle to late Pennsylvanian period.
The geology of New Mexico includes bedrock exposures of four physiographic provinces, with ages ranging from almost 1800 million years (Ma) to nearly the present day. Here the Great Plains, southern Rocky Mountains, Colorado Plateau, and Basin and Range Provinces meet, giving the state great geologic diversity.
The Osha Canyon Formation is a geologic formation in the Nacimiento Mountains of New Mexico. It contains fossils characteristic of the Bashkirian stage of the Pennsylvanian period.
The Arroyo del Agua Formation is a geologic formation in New Mexico. It preserves fossils dating back to the early Permian period.
The Porvenir Formation is a geologic formation exposed in the southeastern Sangre de Cristo Mountains of New Mexico. It preserves fossils dating back to the middle Pennsylvanian period.
The La Tuna Formation is a geologic formation in the Franklin Mountains of southern New Mexico and western Texas and the Hueco Mountains of western Texas. It preserves fossils dating back to the Bashkirian Age of the early Pennsylvanian.
The Rancheria Formation is a geologic formation in the Sacramento and San Andres Mountains of New Mexico, the Franklin Mountains of southern New Mexico and western Texas, and the Hueco Mountains of western Texas. It preserves fossils dating back to the Visean Age of the Mississippian.
The Gobbler Formation is a geologic formation in the Sacramento Mountains of New Mexico. It preserves fossils dating back to the Moscovian Age of the Pennsylvanian Period.
The Molas Formation is a geologic formation that is found in the Four Corners region of the United States. Its age is poorly constrained but is thought to be Namurian.
