PALAEOZOIC/Silurian 193 area today includes the Maritime States of Canada and the USA as far south as Cape Cod, Massachusetts, eastern Newfoundland, southern Ireland, England, Wales, Belgium, Holland, and parts of northwestern Germany North and South China were also independent terranes, as was Sibumasu, which stretched from Burma through Thailand and western Malaysia to Sumatra in Indonesia There were also many smaller terranes, including Perunica (Bohemia, Czech Republic) The oceans were dominated by the vast Panthalassic Ocean, which was comparable in size to today’s Pacific The Iapetus Ocean between Laurentia and Avalonia–Baltica, which had been very substantial in Cambrian and Ordovician times, was steadily closing During the Late Ordovician some of the island arcs within Iapetus collided with and accreted to the eastern margin of Laurentia or the western margin of Avalonia–Baltica The Silurian saw the major continent–continent collision between Laurentia and Avalonia–Baltica, which resulted in the closure of Iapetus and the Caledonian Orogeny (see above) This orogeny caused considerable uplift and formed the land supporting the Old Red Sandstone Continent in the Late Silurian and Devonian (Figure 6) The combined terrane that resulted from the Laurentia– Avalonia–Baltica collision is termed Laurussia To the south of the Avalonian part of Laurussia the widening ocean between it and Gondwana is termed the Rheic Ocean Over a vast area of the continental shelf of Gondwana, today including France, Bohemia, the Iberian Peninsula, Italy, and much of northern Africa, anoxic conditions prevailed, precluding the colonization by benthos The fossils preserved in the black shales deposited there consist largely of plankton, including graptolites and cephalopods It was not until Late Silurian times in some of these areas, for example Bohemia, that the seafloor became oxygenated, enabling its colonization by brachiopods, crinoids, and other benthos The climate of the Silurian started cold The latest Ordovician (Hirnantian) ice-cap was very widespread, but gradually receded in Llandovery times; the latest known Silurian glacial sediments are in the early Wenlock of Brazil, which was near the then south pole It is not until the Late Llandovery (Telychian) that warmer-water carbonate deposits become common, but from then on into the Wenlock, Ludlow, and Pridoli the global temperature was obviously warm to hot This can be deduced from the carbonate build-ups and bioherms present in the Wenlock type area of England and in Gotland and elsewhere and also from the Late Silurian evaporite deposits, which are widespread but best known from New York State, USA See Also Europe: Caledonides of Britain and Ireland; Scandinavian Caledonides (with Greenland) Famous Geologists: Murchison; Sedgwick Fossil Invertebrates: Brachiopods; Graptolites Gondwanaland and Gondwana Palaeozoic: Ordovician; Devonian Time Scale Further Reading Bassett MG, Cocks LRM, Holland CH, Rickards RB, and Warren PT (1975) The type Wenlock Series Institute of Geological Sciences Report 77(13): 33 Cocks LRM and Rickards RB (eds.) (1988) A global analysis of the Ordovician Silurian boundary Bulletin of the British Museum (Natural History) Geology 43: 394 Cocks LRM and Torsvik TH (2002) Earth geography from 500 to 400 million years ago: a faunal and palaeomag netic review Journal of the Geological Society, London 159: 631 644 Cocks LRM, Woodcock NH, Rickards RB, Temple JT, and Lane PD (1984) The Llandovery series of the type area Bulletin of the British Museum (Natural History) Geology 38: 131 182 Cocks LRM, Holland CH, and Rickards RB (1992) A Revised Correlation of Silurian Rocks in the British Isles Special Report 21 London: Geological Society Holland CH and Bassett MG (eds.) (1989) A global stand ard for the Silurian System National Museum of Wales Geological Series 9: 325 Holland CH, Lawson JD, and Walmsley VG (1963) The Silurian rocks of the Ludlow District, Shropshire Bulletin of the British Museum (Natural History) Geology 8: 93 171 Landing E and Johnson ME (eds.) (2003) Silurian lands and seas: paleogeography outside of Laurentia New York State Museum Bulletin 493: 400 Martinsson A (ed.) (1977) The Silurian Devonian Bound ary Stuttgart: Schweizerbart’sche Sengor AMC and Natalin BA (1996) Paleotectonics of Asia: Fragments of a synthesis In: Yin A and Harrison M (eds.) The Tectonic Evolution of Asia, pp 486 640 Cambridge: Cambridge University Press