The Silurian is a geologic period and system spanning 24.6 million years from the end of the Ordovician Period, at 443.8 million years ago (Mya), to the beginning of the Devonian Period, 419.2 Mya. The Silurian is the shortest period of the Paleozoic Era. As with other geologic periods, the rock beds that define the period's start and end are well identified, but the exact dates are uncertain by a few million years. The base of the Silurian is set at a series of major Ordovician–Silurian extinction events when up to 60% of marine genera were wiped out.
The Old Red Sandstone is an assemblage of rocks in the North Atlantic region largely of Devonian age. It extends in the east across Great Britain, Ireland and Norway, and in the west along the eastern seaboard of North America. It also extends northwards into Greenland and Svalbard. These areas were a part of the ancient continent of Euramerica/Laurussia. In Britain it is a lithostratigraphic unit to which stratigraphers accord supergroup status and which is of considerable importance to early paleontology. For convenience the short version of the term, ORS is often used in literature on the subject. The term was coined to distinguish the sequence from the younger New Red Sandstone which also occurs widely throughout Britain.
The geology of Shropshire is very diverse with a large number of periods being represented at outcrop. The bedrock consists principally of sedimentary rocks of Palaeozoic and Mesozoic age, surrounding restricted areas of Precambrian metasedimentary and metavolcanic rocks. The county hosts in its Quaternary deposits and landforms, a significant record of recent glaciation. The exploitation of the Coal Measures and other Carboniferous age strata in the Ironbridge area made it one of the birthplaces of the Industrial Revolution. There is also a large amount of mineral wealth in the county, including lead and baryte. Quarrying is still active, with limestone for cement manufacture and concrete aggregate, sandstone, greywacke and dolerite for road aggregate, and sand and gravel for aggregate and drainage filters. Groundwater is an equally important economic resource.
The Chinle Formation is an Upper Triassic continental geological formation of fluvial, lacustrine, and palustrine to eolian deposits spread across the U.S. states of Nevada, Utah, northern Arizona, western New Mexico, and western Colorado. In New Mexico, it is often raised to the status of a geological group, the Chinle Group. Some authors have controversially considered the Chinle to be synonymous to the Dockum Group of eastern Colorado and New Mexico, western Texas, the Oklahoma panhandle, and southwestern Kansas. The Chinle Formation is part of the Colorado Plateau, Basin and Range, and the southern section of the Interior Plains. A probable separate depositional basin within the Chinle is found in northwestern Colorado and northeastern Utah. The southern portion of the Chinle reaches a maximum thickness of a little over 520 meters (1,710 ft). Typically, the Chinle rests unconformably on the Moenkopi Formation.
Pneumodesmus newmani is a species of myriapod that lived during the late Wenlock epoch of the Silurian period around 428 million years ago. Although a 2017 study dates its occurrence based on zircon data analysis as the Early Devonian (Lochkovian), the 2023 study confirmed the age identification of the 2004 study through palynological, palaeobotanical and ziron analyses incorporating newly discovered additional data. It is one of the first myriapods, and among the oldest creatures to have lived on land. It was discovered in 2004, and is known from a single specimen from Stonehaven, Aberdeenshire, Scotland.
The Fröjel Formation is a ten-metre thick siliciclastic unit lying in the carbonate sequence of Gotland, Sweden. Deposited some 424 million years ago during the mid Homerian, the sediments represent an unusually high supply of terrigenous sediment into the shallow carbonate platform that was to become the island of Gotland. Their deposition is coincident with a δ13C excursion of +3‰.
Archipolypoda is an extinct group of millipedes known from fossils in Europe and North America and containing the earliest known land animals. The Archipolypoda was erected by Scudder (1882) but redefined in 2005 with the description of several new species from Scotland. Distinguishing characteristics include relatively large eyes with densely packed ocelli, and modified leg pairs on the 8th body ring. Some species had prominent spines while others had a flattened appearance.
The Four Mile Dam Formation, also called the Four Mile Dam Limestone, is a geologic formation in Michigan. It preserves fossils dating back to the middle Devonian period.
The Norway Point Formation is a geologic formation in Michigan. It preserves fossils dating back to the middle Devonian period.
The Escuminac Formation is a geologic formation in Quebec. It preserves fossils dating back to the Frasnian, in the Devonian period.
The Merrimack Formation is a geologic formation in Quebec. It preserves fossils dating back to the Silurian period.
The Gun River Formation is a geologic formation in Quebec. It preserves fossils dating back to the early Silurian period.
Cowiedesmus is an extinct millipede genus originally described from the middle Silurian of Scotland, and is considered as earliest known land animals alongside Pneumodesmus from same formation. Although a 2017 study suggested that the geological formation it contains actually appears to be from the Early Devonian (Lochkovian) instead, a 2023 study confirmed the age identification of the 2004 study through palynological, palaeobotanical and ziron analyses incorporating newly discovered additional data. Cowiedesmus was about 4 cm (1.6 in) long and characterized by a greatly enlarged pair of legs on the 8th segment which may have been used in clasping females or functioned as gonopods. Coweiedesmus is distinct enough from other living and fossil millipedes to be placed in its own order, Cowiedesmida. The only known species, C. eroticopodus, was described in 2004.
The Patrick Burn Formation is a Silurian aged geologic formation outcropping near Lesmahagow in Lanarkshire in the Scottish Lowlands. Fossils are known from the formation, including from the Birk Knowes locality.
The Solvik Formation is a geologic formation in the central Oslo Region of Norway. It preserves fossils dating back to the early Silurian period.
Cowielepis is an extinct genus of jawless fish in the class Anaspida. It is from the Cowie Harbour fish bed of Stonehaven, Scotland, which age was originally considered as the Silurian, one study reassigned to Early Devonian (Lochkovian), and 2023 study suggested Wenlock age again.
The Waukesha Biota is an important fossil site located in Waukesha County and Franklin, Milwaukee County within the state of Wisconsin. This biota is preserved in certain strata within the Brandon Bridge Formation, which dates to the early Silurian period. It is known for the exceptional preservation of soft-bodied organisms, including many species found nowhere else in rocks of similar age. The site's discovery was announced in 1985, leading to a plethora of discoveries. This biota is one of the few well studied Lagerstätten from the Silurian, making it important in our understanding of the period's biodiversity. Some of the species are not easily classified into known animal groups, showing that much research remains to be done on this site. Other taxa that are normally common in Silurian deposits are rare here, but trilobites are quite common.
Kampecaris is an extinct genus comprising the Kampecarida, an enigmatic group of millipede-like arthropods, from the Silurian and early Devonian periods of Scotland and England. They are among the oldest known land-dwelling animals. They were small, short-bodied animals with three recognizable sections: an oval head divided along the midline, ten limb-bearing segments forming a cylindrical trunk that tapered slightly towards the front, and a characteristic swollen tail formed by a modified segment that tapers at its rear into an "anal segment". The cuticle forming their exoskeletons was thick, heavily calcified, and composed of two layers.
Coalbrookdale Formation, earlier known as Wenlock Shale or Wenlock Shale Formation and also referred to as Herefordshire Lagerstätte in palaeontology, is a fossil-rich deposit (Konservat-Lagerstätte) in Powys and Herefordshire at the England–Wales border in UK. It belongs to the Wenlock Series of the Silurian Period within the Homerian Age. It is known for its well-preserved fossils of various invertebrate animals many of which are in their three-dimensional structures. Some of the fossils are regarded as earliest evidences and evolutionary origin of some of the major groups of modern animals.
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