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Topic: Silurian

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In the News (Sun 18 Mar 18)

  Silurian - LoveToKnow 1911
The Silurian rocks may occur in close continuity with the upper Ordovician, as in S. Europe; or, as in the typical region, the Llandovery beds may rest unconformably upon older rocks; in N. America also there is a marked unconformity on this horizon.
In a general sense the Silurian period was one of comparative quiescence as regards crustal disturbances, and a relative sinking of the land was followed by a relative elevation affecting wide areas in the N. hemisphere.
Volcanic activity was quite subordinate in Silurian times; flows of diabase occurred at the commencement of the period in Bohemia, and evidence of minor basaltic flows and tuffs is found at Tortworth in Gloucestershire and at a few localities in N. America.
www.1911encyclopedia.org /Silurian   (1438 words)

 Palaeos Paleozoic : Silurian : The Silurian Period
A Silurian sea floor, showing numerous tabulate corals of the genus Favosites large Stromatoporoids, the "sunflower coral" (possibly a green alga) Ischadites, and rugose corals of the genera Entelophyllum, Kodonophyllum, Streptelasma and Craterophyllum.
However, evidence from the eurypterid fauna of the Upper Silurian Bertie Waterlime Formation, New York, suggests that two distinct transitional assemblages existed, perhaps caused by a difference in the environmental preferences of juvenile and adult eurypterids (‘ontogenetic segregation’) (Manning 1993).
The eurypterids from the Upper Silurian of the Welsh Borderland may represent a previously undescribed, ontogenetically mixed, eurypterid assemblage, influenced by a series of facies changes; this is supported by sedimentological evidence (Manning, 1993).
www.palaeos.com /Paleozoic/Silurian/Silurian.htm   (1861 words)

 USGS Professional Paper 1151-H: The Geology of Kentucky: Silurian System
The Silurian rocks are of marine origin and are composed of dolomite and shale and minor amounts of limestone and chert, with a total thickness ranging from 0 to 300 ft. The basal contact is a minor erosional unconformity in much of the outcrop area; elsewhere it is probably conformable or paraconformable.
Sometime after deposition of the Silurian sediments, downwarping occurred on both the east and west flanks and the Silurian sediments were eroded off the crest of the arch prior to the deposition of the Devonian sediments, producing a profound unconformity.
Silurian rocks are exposed on the west and south flanks of the Nashville dome in Tennessee but have been removed by pre-Devonian erosion on the east flank.
pubs.usgs.gov /pp/p1151h/silurian.html   (2841 words)

 The Silurian Period of the Paleozoic Era   (Site not responding. Last check: 2007-11-02)
The Silurian Period was a time when the Earth underwent considerable changes that had important repercussions for the environment and life within it.
The Silurian witnessed a relative stabilization of the earth's general climate, ending the previous pattern of erratic climatic fluctuations.
The Silurian was a time for important events in the history of evolution, including many "firsts," that would prove highly consequential for the future of life on earth.
www.science501.com /PTSilurian.html   (822 words)

 Geology of Ohio--The Silurian
Sedimentary rocks of the Silurian System dominate the bedrock surface of the western half of Ohio, although their exposures are limited because thick glacial sediments cover all but the southernmost portion of the outcrop area.
Silurian rocks in Ohio are primarily carbonates--limestones and dolomites--and the many quarries in these rocks in western Ohio indicate their importance.
During the Silurian, Ohio was in tropical latitudes south of the Equator.
www.ohiodnr.com /geosurvey/oh_geol/98_spring/silurian1.htm   (425 words)

 Silurian graptolite biostratigraphy of Portugal
The Silurian succession of the Portalegre syncline (Figure 2, log C) in the southern border of the CIZ, is not clearly defined, though it may be similar to that of the Dornes area (Piçarra and Oliveira, 2002).
The Silurian sequence in the Trás–os–Montes area known from the autochtonous and allochtonous rock units is composed of three lithological members/formations (Meireles, 2000) with a total estimated thickness of 300 m to 1100 m.
This is exemplified by the Silurian succession of the Barrancos area, similar to that of the Valle syncline of the Spanish Ossa Morena Zone (except for the "Scyphocrinoid limestone").
www.unt.edu.ar /fcsnat/INSUGEO/geologia_18/27.htm   (2475 words)

 Silurian period — FactMonster.com
The earth was relatively tectonically inactive during the Silurian.
The transition between the Ordovician and Silurian rocks is not clearly marked in the United States.
Also notable in the Silurian fauna were scorpions, possibly the first animals to live on land and take their oxygen from the air.
www.factmonster.com /ce6/sci/A0845248.html   (470 words)

 Silurian Period
The earliest terrestrial body fossils are known from Silurian sediments: unassignable fragments from the Llandovery (Lower Silurian) age Tuscarora Formation in Pennslyvania, and identifiable arthropod fragments from the Late Silurian.
Of the Silurian Fauna genera present during the Llandovery epoch, 78% also originated in that epoch, which demonstrates that extinctions were followed by a rapid post-extinction "rebound." However, once this Llandovery rebound was completed, standing diversity returned to and was maintained at pre-extinction amounts.
Silurian and Devonian assemblages are superficially similar, dominated by Lichiida and Phacopida, the latter including the well-known Calymenina.
www.peripatus.gen.nz /paleontology/Silurian.html   (2626 words)

 Silurian period - HighBeam Encyclopedia
Silurian period [from the Silures, ancient tribe of S Wales, where the period was first studied; named by the British geologist R. Murchison], third period of the Paleozoic era of geologic time (see Geologic Timescale, table) lasting from 405 to 435 million years ago.
The continents in the Silurian period remained much as they had been in the preceding Ordovician period, with approximately the same areas being subject to flooding by shallow seas.
Also notable in the Silurian fauna were scorpions, possibly the first animals to live on land and take their oxygen from the air.
www.encyclopedia.com /doc/1E1-Silurian.html   (709 words)

 Silurian and Devonian Rocks
The Silurian and Devonian Periods are divisions of the Paleozoic Era.
The Silurian Period, 438 to 408 million years ago, is characterized by the appearance of large coral reefs and the diversification of fish species.
The Silurian was followed by the Devonian Period, from 408 to 360 million years ago.
tapestry.usgs.gov /ages/silurdevon.html   (120 words)

 The Silurian   (Site not responding. Last check: 2007-11-02)
The Silurian (443 to 417 million years ago) was a time when the Earth underwent considerable changes that had important repercussions for the environment and life within it.
The Silurian witnessed a relative stabilization of the earth's general climate, ending the previous pattern of erratic climatic fluctuations.
The Silurian Period is part of the Paleozoic Era.
www.ucmp.berkeley.edu /silurian/silurian.html   (258 words)

South of Lake Winnebago the edge of the Silurian rocks is mantled by thick glacial deposits.
Silurian rocks also occur on the summit of Blue Mound west of Madison.
The Niagara Escarpment, the edge of the Silurian rocks, wraps around the Michigan Basin, It defines the east shore of Lake Winnebago and the Door Peninsula in Wisconsin and the Garden Peninsula in upper Michigan.
www.uwgb.edu /DutchS/geolwisc/geohist/wisilur.htm   (236 words)

 Silurian bibliography
Berry, W. N., and Boucot, A. J., 1970, Correlation of the North American Silurian rocks, 102 of Geological Society of America, Special Paper: 289 p.
Murchison, R. I., 1854, Siluria: The History of the Oldest Known Rocks Containing Organic Remains: London, John Murray.
Ziegler, A. M., 1966, The Silurian brachiopod Eocoelia hemisphaerica(J. de C. Sowerby) and related species: Palaeontology, v.
www.talkorigins.org /origins/biblio/silurian.html   (113 words)

 Silurian Rocks
The Silurian represents the youngest 30 million years of this period and so the actual area of rock dating to the Silurian is much smaller than shown (approx.
Silurian outcrops in Asia are scattered except for the linear feature that follows the Ural Mountains.
China in Silurian times was split into several isolated plates and the complex geology of China and Central Asia account for the patchy distribution.
www.silurian.com /geology/rocks.htm   (284 words)

 The Virtual Siluiran Reef -- Silurian Period
he Silurian can be defined as a period of geologic time between 408 and 438 million years ago that was preceded by the Ordovician Period and followed by the Devonian Period.
"Silurian" was applied to the period of time represented by this fossil assemblage.
Although the Silurian seas were populated by a variety of marine life, the land was inhabited only by a few types of small plants and tiny bugs.
www.mpm.edu /collections/learn/reef/concept-silurian.html   (247 words)

 Silurian Period , Kentucky Geological Survey
Silurian rocks are exposed at the surface in the Knobs Region, which rings the Blue Grass Region.
Silurian rocks are absent in the Blue Grass, but occur below the surface in other parts of Kentucky.
All Silurian rocks found in Kentucky are marine and all the fossils are marine (sea-dwelling) invertebrates.
www.uky.edu /KGS/fossils/silurian.htm   (192 words)

 Geology of Missouri--Silurian/Devonian   (Site not responding. Last check: 2007-11-02)
Silurian and Devonian rocks are lumped together on this map because both are rather scarce in the state.
Silurian strata were deposited during a resurgence of the regressing Tippecanoe Sea--unlike Ordovician age waters, which seemed ubiquitous, these inundations were local in nature, flowing through "seaways", or narrow paths along low lying areas, somewhat like the modern inlets along the Arabian Peninsula.
The early Silurian rocks were deposited from the east, which some say suggest the topographic beginnings of the Mississippi Valley, while the ones in the northwest were laid down much later, and probably due to an adjustment of general sea depth.
members.socket.net /~joschaper/sildev.html   (462 words)

 HA 730-J Silurian-Devonian aquifer text
Although Silurian and Devonian rocks are present throughout the Lower and part of the Upper Peninsula of Michigan, they form the bedrock surface only in the southeastern Upper Peninsula and the northern and the southeastern parts of the Lower Peninsula where they form an aquifer (fig.
In Wisconsin, the aquifer consists largely of Silurian rocks and is unconfined or partially confined by fine-grained sediments in the surficial aquifer system or by shale of the Devonian Kenwood Formation (fig.
The Silurian part of the aquifer crops out and subcrops beneath glacial drift in the southeastern part of the Upper Peninsula of Michigan and in a small area of the southeastern part of the Lower Peninsula (fig.
capp.water.usgs.gov /gwa/ch_j/J-text6.html   (2022 words)

 Silurian Summary
The Silurian is a major division of the geologic timescale that extends from the end of the Ordovician period, about 443.7 Ma (million years ago), to the beginning of the Devonian period, about 416.0 Ma (ICS 2004).
During the Silurian, Gondwana continued a slow southward drift to high southern latitudes, but there is evidence that the Silurian icecaps were less extensive than those of the late Ordovician glaciation.
At the end of the Silurian, sea levels dropped again, leaving telltale basins of evaporites in a basin extending from Michigan to West Virginia, and the new mountain ranges were rapidly eroded.
www.bookrags.com /Silurian   (1780 words)

 Silurian Period - Search Results - MSN Encarta
Silurian Period, third division of the Paleozoic Era of the geologic time scale, spanning an interval of 28 million years, from about 444 million to...
Most of the early complex life forms of the Cambrian explosion lived in the sea.
The most important evolutionary development of the Silurian period (435 million to 410 million years ago) was that of the first air-breathing animal,...
encarta.msn.com /Silurian_Period.html   (143 words)

 Silurian   (Site not responding. Last check: 2007-11-02)
Silurian limestones in the state can be found exposed in the western Wichita uplifts and in the northeastern Ozark uplift near Tulsa.
The Silurian period is the first period in history where fish begin to appear in the fossil record.
Another major occurence during the Silurian is the appearance of the first terrestrial ecosystem.
www.freewebs.com /oklahomarocks/silurian.htm   (295 words)

 Prehistoric Life - Silurian Period in Victoria.   (Site not responding. Last check: 2007-11-02)
In Victoria, rocks of Silurian age occur mostly in the central part of the state, in the Melbourne district and as far North as Heathcote.
Eoactis stachi, from the Upper Silurian in excavations for the Melbourne Underground Rail Loop.
Helicocrinus plumosus, from the Upper Silurian of the Melbourne suburb of West Brunswick.
www.museum.vic.gov.au /prehistoric/fossils/silurian.html   (129 words)

 The Silurian Period: Plants Move Onto Land
Like the periods that have come before, the Silurian is named for an ancient Celtic tribe that lived in Wales where the geologic evidence was found.
The new life in the Silurian Period was the coral reef.
There are a few fossils from the end of the Silurian Period that show us early insects lived among these mosses and made their own colonies.
www.fossils-facts-and-finds.com /silurian_period.html   (600 words)

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