The Devonian is a geologic period and system of the Paleozoic, spanning 60 million years from the end of the Silurian, 419.2 million years ago, to the beginning of the Carboniferous, 358.9 Mya. It is named after Devon, where rocks from this period were first studied; the first significant adaptive radiation of life on dry land occurred during the Devonian. Free-sporing vascular plants began to spread across dry land, forming extensive forests which covered the continents. By the middle of the Devonian, several groups of plants had evolved leaves and true roots, by the end of the period the first seed-bearing plants appeared. Various terrestrial arthropods became well-established. Fish reached substantial diversity during this time, leading the Devonian to be dubbed the "Age of Fishes." The first ray-finned and lobe-finned bony fish appeared, while the placoderms began dominating every known aquatic environment. The ancestors of all four-limbed vertebrates began adapting to walking on land, as their strong pectoral and pelvic fins evolved into legs.
In the oceans, primitive sharks became more numerous than in the Late Ordovician. The first ammonites, species of molluscs, appeared. Trilobites, the mollusc-like brachiopods and the great coral reefs, were still common; the Late Devonian extinction which started about 375 million years ago affected marine life, killing off all placodermi, all trilobites, save for a few species of the order Proetida. The palaeogeography was dominated by the supercontinent of Gondwana to the south, the continent of Siberia to the north, the early formation of the small continent of Euramerica in between; the period is named after Devon, a county in southwestern England, where a controversial argument in the 1830s over the age and structure of the rocks found distributed throughout the county was resolved by the definition of the Devonian period in the geological timescale. The Great Devonian Controversy was a long period of vigorous argument and counter-argument between the main protagonists of Roderick Murchison with Adam Sedgwick against Henry De la Beche supported by George Bellas Greenough.
Murchison and Sedgwick named the period they proposed as the Devonian System. While the rock beds that define the start and end of the Devonian period are well identified, the exact dates are uncertain. According to the International Commission on Stratigraphy, the Devonian extends from the end of the Silurian 419.2 Mya, to the beginning of the Carboniferous 358.9 Mya. In nineteenth-century texts the Devonian has been called the "Old Red Age", after the red and brown terrestrial deposits known in the United Kingdom as the Old Red Sandstone in which early fossil discoveries were found. Another common term is "Age of the Fishes", referring to the evolution of several major groups of fish that took place during the period. Older literature on the Anglo-Welsh basin divides it into the Downtonian, Dittonian and Farlovian stages, the latter three of which are placed in the Devonian; the Devonian has erroneously been characterised as a "greenhouse age", due to sampling bias: most of the early Devonian-age discoveries came from the strata of western Europe and eastern North America, which at the time straddled the Equator as part of the supercontinent of Euramerica where fossil signatures of widespread reefs indicate tropical climates that were warm and moderately humid but in fact the climate in the Devonian differed during its epochs and between geographic regions.
For example, during the Early Devonian, arid conditions were prevalent through much of the world including Siberia, North America, China, but Africa and South America had a warm temperate climate. In the Late Devonian, by contrast, arid conditions were less prevalent across the world and temperate climates were more common; the Devonian Period is formally broken into Early and Late subdivisions. The rocks corresponding to those epochs are referred to as belonging to the Lower and Upper parts of the Devonian System. Early DevonianThe Early Devonian lasted from 419.2 ± 2.8 to 393.3 ± 2.5 and began with the Lochkovian stage, which lasted until the Pragian. It spanned from 410.8 ± 2.8 to 407.6 ± 2.5, was followed by the Emsian, which lasted until the Middle Devonian began, 393.3± 2.7 million years ago. During this time, the first ammonoids appeared. Ammonoids during this time period differed little from their nautiloid counterparts; these ammonoids belong to the order Agoniatitida, which in epochs evolved to new ammonoid orders, for example Goniatitida and Clymeniida.
This class of cephalopod molluscs would dominate the marine fauna until the beginning of the Mesozoic era. Middle DevonianThe Middle Devonian comprised two subdivisions: first the Eifelian, which gave way to the Givetian 387.7± 2.7 million years ago. During this time the jawless agnathan fishes began to decline in diversity in freshwater and marine environments due to drastic environmental changes and due to the increasing competition and diversity of jawed fishes; the shallow, oxygen-depleted waters of Devonian inland lakes, surrounded by primitive plants, provided the environment necessary for certain early fish to develop such essential characteristics as well developed lungs, the ability to crawl out of the water and onto the land for short periods of time. Late DevonianFinally, the Late Devonian started with the Frasnian, 382.7 ± 2.8 to 372.2 ± 2.5, during which the first forests took shape on land. The first tetrapods appeared in the fossil record in the ensuing Famennian subdivisi
The Logan Formation is the name given to a Lower Carboniferous siltstone and conglomeratic unit exposed in east-central Ohio and parts of western West Virginia, USA. The Logan Formation was named by Andrews and described as a "buff-colored, fine-grained sandstone" above the Waverly Formation and below the Maxville Limestone. Bork and Malcuit concluded that the Logan Formation was deposited on a shallow marine shelf in a transgressing sea; the age of the Logan Formation has been established as early Osagean by the occurrences of brachiopods, ammonoids and miospores. Andrews, E. B.. "Report of progress in the second district, Part II, IN Report of progress in 1869". Ohio Division of Geological Survey Report of Progress, 2nd series: 1091–1094. Bork, K. B.. J.. "Paleoenvironments of the Cuyahoga and Logan Formations of central Ohio". Geological Society of America Bulletin. 90: 89–113. Doi:10.1130/0016-760690<1091:potcal>2.0.co. Clayton, G.. L.. "Mississippian miospores from the Cuyahoga and Logan Formations of northeastern Ohio, USA".
Journal of Micropalaeontology. 17: 183–191. Doi:10.1144/jm.17.2.183. Matchen, D. L.. W.. "Incised valley fill interpretation for Mississippian Black Hand Sandstone, Appalachian Basin, USA: Implications for glacial eustacy at Kinderhookian-Osagean boundary". Sedimentary Geology. 191: 89–113. Bibcode:2006SedG..191...89M. Doi:10.1016/j.sedgeo.2006.02.002
The Cuyahoga Formation is a geologic formation in Ohio. The age of the formation is difficult to determine, because of a lack of diagnostic fossils; the formation dates from the Late Kinderhookian to the Middle Osagean. Eight members are recognized, among them the Orangeville Shale, Sharpsville Sandstone, Meadville Shale, it preserves fossils dating to the Mississippian subperiod of the Carboniferous period. List of fossiliferous stratigraphic units in Ohio
The Marcellus Formation is a Middle Devonian age unit of sedimentary rock found in eastern North America. Named for a distinctive outcrop near the village of Marcellus, New York, in the United States, it extends throughout much of the Appalachian Basin; the unit name usage by the U. S. Geological Survey includes Marcellus Formation; the term "Marcellus Shale" is the preferred name throughout most of the Appalachian region, although the term "Marcellus Formation" is acceptable within the State of Pennsylvania. The unit was first described and named as the "Marcellus shales" by J. Hall in 1839. Although black shale is the dominant lithology, it contains lighter shales and interbedded limestone layers; the Marcellus Formation is a black shale that may contain limestone beds and concentrations of iron pyrite and siderite. Its sedimentary structure, or bedding, is moderately well developed. Like most shales, it tends to split along the bedding plane, a property known as fissility. Lighter colored shales in the upper portion of the formation tend to split into small thin-edged fragments after exposure.
These fragments may have rust stains from exposure of pyrite to air, tiny gypsum crystals from the reaction between pyrite and limestone particles. Fresh exposures of the pyriteiferous shale may develop the secondary mineralization of orange limonite, the pale yellow efflorescence or bloom of sulfur, associated with acid rock drainage. Pyrite is abundant near the base, the upper contacts of limestones, but framboidal microcrystals and euhedral crystals of pyrite occur throughout the organic-rich deposits; the Marcellus contains uranium, the radioactive decay of the uranium-238 makes it a source rock for radioactive radon gas. Measured total organic content of the Marcellus Formation ranges from less than 1% in eastern New York, to over 11% in the central part of the state, the shale may contain enough carbon to support combustion; the more organic-rich black shales can be bituminous, but are too old to contain bituminous coal formed from land plants. In petroleum geology, these black shales are an important source rock that filled conventional petroleum reservoirs in overlying formations, are an unconventional shale gas reservoir, are an impermeable seal that traps underlying conventional natural gas reservoirs.
To the west the formation may produce liquid petroleum. The Marcellus is found throughout the Allegheny Plateau region of the northern Appalachian Basin of North America. In the United States, the Marcellus shale runs across the Southern Tier and Finger Lakes regions of New York, in northern and western Pennsylvania, eastern Ohio, through western Maryland, throughout most of West Virginia extending across the state line into extreme western Virginia; the Marcellus bedrock in eastern Pennsylvania extends across the Delaware River into extreme western New Jersey. It exists in the subsurface of a small portion of Kentucky and Tennessee. Below Lake Erie, it can be found crossing the border into Canada, where it stretches between Port Stanley and Long Point to St. Thomas in southern Ontario; the Marcellus appears in outcrops along the northern margin of the formation in central New York. There, the two joint planes in the Marcellus are nearly at right angles, each making cracks in the formation that run perpendicular to the bedding plane, which lies level.
These joints form smooth nearly vertical cliffs, the intersecting joint planes form projecting corners in the rock faces. Once exposed, the weathered faces lose most of their organic carbon, turning from black or dark gray to a lighter shade of gray. Outcrops of the Marcellus can contain small beds that resemble coal; the New York outcrops, others further south in Pennsylvania and New Jersey, were extensively excavated in the early 19th century, sometimes at great expense, in the false hope of finding minable coal seams. In Perry County, Pennsylvania along the Juniata River the false coal beds become up to.3 m thick, but they did not produce a valuable fuel, despite the considerable effort expended to mine it from the surrounding hills. Seaweed and marine plants formed the false coal. True coal is formed from terrestrial plants, which only began to appear in Marcellus and fossils. Close proximity to the surface of Marcellus bedrock south of the New York outcrops makes an east-west band running through the city of Syracuse a high-risk area for radon as an indoor air pollutant.
From the surface exposures along the northern and eastern margins, the formation descends to depths of over 2,700 m below the surface in southern Pennsylvania. Upturned beds are exposed in sections of the folded Ridge-and-Valley Appalachians, including exposures on the flanks and axis of the Broad Top Synclinorium in south central Pennsylvania. Exposed beds are nearly horizontal on the Allegheny Plateau, but upturned to form overturned beds found along the Allegheny Front. From Wind Gap, Pennsylvania heading south, the dip of the beds steepens, becoming vertical at Bowmanstown on the Lehigh River. Nearby, in the Lehigh Gap area of Pennsylvania, the Marcellus is extensively faulted, the beds are steeply overturned, with a reverse dip angle of up to 40° south; the Marcellus Shale and the fine-grained shales near the middle of the Mahantango Formation are classified by geologists as slope-formers. Marcellus and Mahantango shale beds dipping at 60° to 75° to the west form the west facing slopes of Tonoloway Ridge on the wes
The Clinton Group is a mapped unit of sedimentary rock found throughout eastern North America. The interval was first defined by the geologist Lardner Vanuxem, who derived the name from the village of Clinton in Oneida County, New York where several well exposed outcrops of these strata can be found; the Clinton Group and its lateral equivalents extend throughout much of the Appalachian Foreland Basin, a major structural and depositional province extending from New York to Alabama. The term has been employed in Kentucky, Michigan, New York, Pennsylvania, Tennessee and West Virginia, though in many of these areas the same interval is referred to as the Rose Hill, Rockwood, or Red Mountain Formations; the term "Clinton" has been assigned to several lower Silurian stratigraphic units in Ohio and Kentucky which are now known to be older than the Clinton Group as it was defined. Many parts of this succession are richly fossiliferous, making the Clinton Group an important record of marine life during the early Silurian.
Several economically valuable rock-types are found within this interval, though it is best known as a significant source of iron ore Stratigraphically, the Clinton Group overlies the coarse siliciclastics of the Medina Group in New York, The Albion Group in the Subsurface of Ohio, the Clinch Sandstone in Virginia and West Virginia, the Tuscarora Sandstone in Pennsylvania. It is overlain by the shales and carbonates of the Lockport Group in New York, the McKenzie Formation in Pennsylvania, the Sneedville Limestone in Tennessee. Owing to the great difference in resistivity between the soft weathering Clinton Group and the massive dolostones of the overlying Lockport, the former tends to erode preferentially out from underneath the latter; this has resulted in the formation of numerous cateracts such as Niagara Falls and the High Falls of Rochester, New York which are but local manifestations of a regional geographic feature called the Niagara Escarpment. The Clinton Group is a traceable, lower Silurian lithostratigraphic unit composed of shale and mudstone, though it encompasses a heterogeneous assemblage of sedimentary rock types, including conglomerate, limestone and ironstone.
In its designated type area in Clinton, Oneida County, New York the unit is 50 meters thick, composed of blue-grey mudstone and sandstone with several discrete ferruginous horizons, known colloquially as "Clinton Ironstones". The lateral equivalent of these beds to the south is the Rose Hill Formation of Pennsylvania, olive-gray to drab, thin-bedded sandstone. In Maryland, the Rose Hill Formation contained the Cresaptown Iron Sandstone. Relative age dating of the Clinton Group places it in the Lower Silurian period, it rests conformably atop the Tuscarora Formation and conformably below the Lower and Upper Silurian Lockport Group and Bloomsburg Formation. Geology of Pennsylvania
The Columbus Limestone is a mapped bedrock unit consisting of fossiliferous limestone, it occurs in Ohio and Virginia in the United States, in Ontario, Canada. The depositional environment was most shallow marine; the Columbus conformably overlies the Lucas Dolomite in northeastern Ohio, unconformably overlies other dolomite elsewhere. It unconformably underlies the Ohio Shale in northwestern Ohio and the Delaware Limestone in eastern Ohio, its members include: Bellepoint, Tioga Ash Bed, Delhi and East Liberty. The type section is located in Ohio; the glacial grooves on Kelleys Island are cut into the Columbus Limestone. It is quarried there. An exposure in Ontario is located at Ontario; the Columbus Limestone contains brachiopods, bryozoans, corals and echinoderms. Due to their mid-continent depositional environment, the fossils are free of deformation caused by tectonic activity common in the Appalachian Mountains. Tabulate corals include Syringopora tabulata, Favosites hemispherica minuta, Emmonsia polymorpha, Thamnoptychia alternans, Pleurodictyum sp. and Coenites dublinensis.
Rugose corals include Prismatophyllum rugosum, Hexagonaria anna, Eridophyllum seriale, Synaptophyllum simcoense, Amplexus yandelli, Zaphrenthis perovalis, Heterophrentis nitida, Cystiphylloides americanum, Odontophyllum convergens, Siphonophrentis gigantea. Brachiopods include Brevispirifer gregarius; the gastropod Laevidentalhum martinei is present, as well as the crinoid Nucleocrinus verneulli. Fish fossils have been found in the East Liberty Member. Goniatites have been found including Werneroceras staufferi and Tornoceras eberlei. Another cephalopod species is Goldringia cyclops. Relative age dating of the Columbus Limestone places it in the Early to Middle Devonian period; the Columbus has been mined for aggregate. Its Calcium carbonate content is higher. List of types of limestone
The Phanerozoic Eon is the current geologic eon in the geologic time scale, the one during which abundant animal and plant life has existed. It covers 541 million years to the present, began with the Cambrian Period when animals first developed hard shells preserved in the fossil record, its name was derived from the Ancient Greek words φανερός and ζωή, meaning visible life, since it was once believed that life began in the Cambrian, the first period of this eon. The term "Phanerozoic" was coined in 1930 by the American geologist George Halcott Chadwick; the time before the Phanerozoic, called the Precambrian, is now divided into the Hadean and Proterozoic eons. The time span of the Phanerozoic starts with the sudden appearance of fossilized evidence of a number of animal phyla. Plant life on land appeared in the early Phanerozoic eon. During this time span, tectonic forces caused the continents to move and collect into a single landmass known as Pangaea, which separated into the current continental landmasses.
The Proterozoic-Phanerozoic boundary is at 541 million years ago. In the 19th century, the boundary was set at time of appearance of the first abundant animal fossils but several hundred groups of metazoa of the earlier Proterozoic era have been identified since the systematic study of those forms started in the 1950s. Most geologists and paleontologists would set the Proterozoic-Phanerozoic boundary either at the classic point where the first trilobites and reef-building animals such as corals and others appear; the three different dividing points are within a few million years of each other. In the older literature, the term Phanerozoic is used as a label for the time period of interest to paleontologists, but that use of the term seems to be falling into disuse in more modern literature; the Phanerozoic is divided into three eras: the Paleozoic and Cenozoic, which are further subdivided into 12 periods. The Paleozoic features the rise of fish and reptiles; the Mesozoic is ruled by the reptiles, features the evolution of mammals and more famously, dinosaurs.
The Cenozoic is the time of the mammals, more humans. The Paleozoic is a time in Earth's history when complex life forms evolved, took their first breath of oxygen on dry land, when the forerunners of all life on Earth began to diversify. There are six periods in the Paleozoic era: Cambrian, Silurian, Devonian and Permian; the Cambrian starts from 541 to 485 million years ago. The Cambrian sparked a rapid expansion in evolution in an event known as the Cambrian Explosion during which the greatest number of creatures evolved in a single period in the history of Earth. Plants like algae evolved, the fauna was dominated by armored arthropods, such as trilobites. All marine phyla evolved in this period. During this time, the super-continent Pannotia began to break up, most of which recombined into the super-continent Gondwana; the Ordovician spans from 485 million years to 444 million years ago. The Ordovician was a time in Earth's history in which many species still prevalent today evolved, such as primitive fish and coral.
The most common forms of life, were trilobites and shellfish. More the first arthropods crept ashore to colonize Gondwana, a continent empty of animal life. By the end of the Ordovician, Gondwana had moved from the equator to the South Pole, Laurentia had collided with Baltica, closing the Iapetus Ocean; the glaciation of Gondwana resulted in a major drop in sea level, killing off all life that had established along its coast. Glaciation caused a snowball Earth, leading to the Ordovician-Silurian extinction, during which 60% of marine invertebrates and 25% of families became extinct; this is considered the second deadliest in the history of Earth. The Silurian spans from 444 million years to 419 million years ago, which saw a warming from Snowball Earth; this period saw the mass evolution of fish, as jaw-less fish became more numerous, jawed fish evolved, the first freshwater fish evolved, though arthropods, such as sea scorpions, remained the apex predators. Terrestrial life evolved, which included early arachnids and centipedes.
The evolution of vascular plants allowed plants to gain a foothold on land. These early terrestrial plants are the forerunners of all plant life on land. During this time, there were four continents: Gondwana, Laurentia and Siberia; the recent rise in sea levels provided new habitats for many new species. The Devonian spans from 419 million years to 359 million years ago. Informally known as the "Age of the Fish", the Devonian features a huge diversification in fish, including armored fish like Dunkleosteus and lobe-finned fish which evolved into the first tetrapods. On land, plant groups diversified. By the Middle Devonian, shrub-like forests of primitive plants existed: lycophytes, horsetails and progymnosperm; this event allowed the diversification of arthropod life as they took advantage of the new