The geology of the Appalachians dates back to more than 480 million years ago. A look at rocks exposed in today's Appalachian Mountains reveals elongate belts of folded and thrust faulted marine sedimentary rocks, volcanic rocks and slivers of ancient ocean floor – strong evidence that these rocks were deformed during plate collision. The birth of the Appalachian ranges marks the first of several mountain building plate collisions that culminated in the construction of the supercontinent Pangaea with the Appalachians and neighboring Anti-Atlas mountains near the center. These mountain ranges likely once reached elevations similar to those of the Alps and the Rocky Mountains before they were eroded.
The Acadian orogeny is a long-lasting mountain building event which began in the Middle Devonian, reaching a climax in the early Late Devonian. It was active for approximately 50 million years, beginning roughly around 375 million years ago, with deformational, plutonic, and metamorphic events extending into the Early Mississippian. The Acadian orogeny is the third of the four orogenies that created the Appalachian orogen and subsequent basin. The preceding orogenies consisted of the Potomac and Taconic orogeny, which followed a rift/drift stage in the Late Neoproterozoic. The Acadian orogeny involved the collision of a series of Avalonian continental fragments with the Laurasian continent. Geographically, the Acadian orogeny extended from the Canadian Maritime provinces migrating in a southwesterly direction toward Alabama. However, the Northern Appalachian region, from New England northeastward into Gaspé region of Canada, was the most greatly affected region by the collision.
The Antler orogeny was a tectonic event that began in the early Late Devonian with widespread effects continuing into the Mississippian and early Pennsylvanian. Most of the evidence for this event is in Nevada but the limits of its reach are unknown. A great volume of conglomeratic deposits of mainly Mississippian age in Nevada and adjacent areas testifies to the existence of an important tectonic event, and implies nearby areas of uplift and erosion, but the nature and cause of that event are uncertain and in dispute. Although it is known as an orogeny, some of the classic features of orogeny as commonly defined such as metamorphism, and granitic intrusives have not been linked to it. In spite of this, the event is universally designated as an orogeny and that practice is continued here. This article outlines what is known and unknown about the Antler orogeny and describes three current theories regarding its nature and origin.
The Taconic orogeny was a mountain building period that ended 440 million years ago and affected most of modern-day New England. A great mountain chain formed from eastern Canada down through what is now the Piedmont of the East coast of the United States. As the mountain chain eroded in the Silurian and Devonian periods, sediments from the mountain chain spread throughout the present-day Appalachians and midcontinental North America.
Carbonate hardgrounds are surfaces of synsedimentarily cemented carbonate layers that have been exposed on the seafloor. A hardground is essentially, then, a lithified seafloor. Ancient hardgrounds are found in limestone sequences and distinguished from later-lithified sediments by evidence of exposure to normal marine waters. This evidence can consist of encrusting marine organisms, borings of organisms produced through bioerosion, early marine calcite cements, or extensive surfaces mineralized by iron oxides or calcium phosphates. Modern hardgrounds are usually detected by sounding in shallow water or through remote sensing techniques like side-scan sonar.
The Ordovician Reedsville Formation is a mapped surficial bedrock unit in Pennsylvania, Maryland, Virginia, West Virginia, and Tennessee, that extends into the subsurface of Ohio. This rock is a slope-former adjacent to the prominent ridge-forming Bald Eagle sandstone unit in the Appalachian Mountains. It is often abbreviated Or on geologic maps.
The Jordan Formation is a siliciclastic sedimentary rock unit identified in Illinois, Michigan, Wisconsin, Minnesota, and Iowa. Named for distinctive outcrops in the Minnesota River Valley near the town of Jordan, it extends throughout the Iowa Shelf and eastward over the Wisconsin Arch and Lincoln anticline into the Michigan Basin.
The Shady Dolomite is a geologic formation composed of marine sedimentary rocks of early Cambrian age. It outcrops along the eastern margin of the Blue Ridge province in the southeastern United States and can be found in outcrops in the states of Alabama, Georgia, Tennessee, North Carolina, and Virginia. It is also can be found in the subsurface of Kentucky, Ohio, and West Virginia. The Shady is predominantly composed of dolomite and limestone with lesser amounts of mudrock. It contains fossils of trilobites, archaeocyathids, algae, brachiopods, and echinoderms, along with the enigmatic fossil Salterella. The Shady Dolomite was first described by Arthur Keith in 1903 and was named for exposures in the Shady Valley of Johnson County in the state of Tennessee. Near Austinville, Virginia, the Shady hosts ore deposits that have been mined extensively for lead and zinc ore.
The Chepultepec Formation, is an Early Ordovician-age geological formation in the Appalachian regions of Eastern North America. Also known as the Chepultepec Dolomite, it is a unit of the Upper Knox Group, overlying the Copper Ridge Dolomite and underlying the Longview-Kingsport-Mascot sequence. The Chepultepec Formation is a primarily limestone and dolomite formation, the earliest formation of the Ordovician period in its area. Further north, it is equivalent to the Stonehenge Formation of the Beekmantown Group. The formation was first described from Allgood, Alabama, and has also been found in Tennessee and Virginia. Allgood was originally named "Chepultepec", providing its name to the formation as well. In Virginia, the Chepultepec Formation has a habit of forming large natural arches, including Natural Tunnel in Scott County and Natural Bridge in Rockbridge County.
The Helms Formation is a geologic formation in Texas and New Mexico. It preserves fossils dating back to the Chesterian (Serpukhovian) Age of the Carboniferous period.
The Bone Spring Formation is a geologic formation found in the Delaware Basin in Texas and New Mexico. It preserves fossils dating back to the Leonardian Age of the Permian Period.
The Hueco Formation is a geologic formation in west Texas and southern New Mexico. It preserves fossils dating back to the early Permian period.
The McColley Canyon Formation is a geologic formation in Nevada. It preserves fossils dating back to the Devonian period.
The Coils Creek Limestone is a geologic formation in Nevada. It preserves fossils dating back to the Devonian period.
The Vinini Formation is a marine, deep-water, sedimentary deposit of Ordovician to Early Silurian age in Nevada, U.S.A. It is notable for its highly varied, mainly siliceous composition, its mineral deposits, and controversies surrounding both its depositional environment and structural history. The formation was named by Merriam and Anderson for an occurrence along Vinini Creek in the Roberts Mountains of central Nevada and that name is now used extensively in the State.
The Johnson Spring Formation is a geologic formation in California. It preserves fossils dating back to the Ordovician period.
The Deicke and Millbrig bentonite layers, specifically the potassium bentonite layer, K-bentonite, were formed from a volcanic eruption during the Taconic orogeny during the Late Ordovician on Laurentia, the craton of North America. Researchers are very interested in the eruptions that formed these bentonite layers because they are thought to be some of the largest volcanic eruptions in the last 600 million years of Earth history, and the resulting ash layer for each eruption individually was greater in volume than the Toba eruption. Bentonite is a type of clay that is formed from the weathering of volcanic ash deposits. Some researchers suggested that the ashes were from a volcanic arc that was on a convergent crust boundary. Researchers believe this because the trace element geochemistry of the bentonite shows that its source was a felsic calc-alkalic magmatic source, which is characteristic of volcanism from a continental crust destructive plate margin setting.
The Precordillera terrane of western Argentina is a large mountain range located southeast of the main Andes mountain range. The evolution of the Precordillera is noted for its unique formation history compared to the region nearby. The Cambrian-Ordovian sedimentology in the Precordillera terrane has its source neither from old Andes nor nearby country rock, but shares similar characteristics with the Grenville orogeny of eastern North America. This indicates a rift-drift history of the Precordillera in the early Paleozoic. The Precordillera is a moving micro-continent which started from the southeast part of the ancient continent Laurentia. The separation of the Precordillera started around the early Cambrian. The mass collided with Gondwana around Late Ordovician period. Different models and thinking of rift-drift process and the time of occurrence have been proposed. This page focuses on the evidence of drifting found in the stratigraphical record of the Precordillera, as well as exhibiting models of how the Precordillera drifted to Gondwana.
The geology of Peru includes ancient Proterozoic rocks, Paleozoic and Mesozoic volcanic and sedimentary rocks, and numerous basins and the Andes Mountains formed in the Cenozoic.
The Canutillo Formation is a geologic formation that is exposed in the Franklin Mountains near El Paso, Texas. The formation is Middle Devonian in age.
Virginia 
United States 
