Changes

During Cambrian time ([[:file:M106Ch01Fig02.jpg|Figure 2]]) most of the continents were gathered in the southern hemisphere.<ref name=Cocksandtorsvik_2002 /> <ref name=Torsvikandcocks_2009>Torsvik, T. H., and Cocks, L. R. M., 2009, The Lower Palaeozoic palaeogeographical evolution of the northeastern and eastern peri-Gondwanan margin from Turkey to New Zealand: GSL Special Publications, v. 325, p. 3–21.</ref> Gondwana stretched from the equator (Australia) to the South Pole (North Africa). Tectonic movement was active mainly as a consequence of the relative rotation of the different cratons that built Gondwana.<ref name=Veevers_2004>Veevers, J. J., 2004, Gondwanaland from 650-500 Ma assembly through 320 Ma merger in Pangea to 185-100 Ma breakup: Supercontinental tectonics via stratigraphy and radiometric dating: Earth-Science Reviews, v. 68, p. 1–132.</ref> Extensional tectonics that controlled the deposition of major evaporitic successions in the Arabic peninsula (Hormuz Salt Basin) and surroundings (e.g., Punjab Salt Basin) close to the Precambrian–Cambrian boundary (see dashed faults in [[:file:M106Ch01Fig02.jpg|Figure 2]]) came to an end, and no important tectonic activity is observed in the late Cambrian (500 Ma). [[Laurentia]] lay astride the equator in both hemispheres and was separated from Gondwana by the Iapetus Ocean. Avalonia, Armorica, Perunica, Baltica (180&deg; geographically inverted), North and South China, and all the Cimmerian blocks fringed peripheral Gondwana at moderate to high southern latitudes. Torsvik and Cocks<ref name=Torsvikandcocks_2009 /> show that South China was located close to the Equator. According to von Raumer and Stampfli,<ref name=Vonraumerandstampfli_2008>von Raumer, J. F., and Stampfli, G. M., 2008, The birth of the Rheic Ocean - Early Palaeozoic subsidence patterns and subsequent tectonic plate scenarios: Tectonophysics, v. 461, p. 9–20.</ref> the Proto-Tethys ocean, which separated North China (to the north) from the other blocks along the peripheral Gondwana, was subducting toward the south and backarc extension, which is suggested by oceanic Cambrian seaways between the peripheral Gondwanan blocks. Torsvik and Cocks<ref name=Torsvikandcocks_2009 /> recognized that their concept of the Ran Ocean used for the Cambrian-Ordovician ocean existing between Baltica and Gondwana is comparable to that of the Proto-Tethys (sensu Stampfli and Borel<ref name=Stampfliandborel_2002 />), and herein we prefer to use the latter term. Siberia was positioned at low latitudes and was separated from Laurentia and Baltica by oceanic crust. Avalonia rifted off Gondwana in the Early Ordovician with the opening of the Rheic Ocean,<ref name=Nys&aelig;theretal_2002>Nys&aelig;ther, E., Torvik, T. H., Feist, R., Walderhaug, H. J., and Eide, E.A., 2002, Ordovician palaeogeography with new palaeomagnetic data from the Montagne Noire (Southern France): Earth and Planetary Science Letters, v. 203, p. 329–341.</ref> although some authors suggest even older ages for its opening.<ref name=Torsvikandcocks_2009 />

During Cambrian time ([[:file:M106Ch01Fig02.jpg|Figure 2]]) most of the continents were gathered in the southern hemisphere.<ref name=Cocksandtorsvik_2002 /> <ref name=Torsvikandcocks_2009>Torsvik, T. H., and Cocks, L. R. M., 2009, The Lower Palaeozoic palaeogeographical evolution of the northeastern and eastern peri-Gondwanan margin from Turkey to New Zealand: GSL Special Publications, v. 325, p. 3–21.</ref> Gondwana stretched from the equator (Australia) to the South Pole (North Africa). Tectonic movement was active mainly as a consequence of the relative rotation of the different cratons that built Gondwana.<ref name=Veevers_2004>Veevers, J. J., 2004, Gondwanaland from 650-500 Ma assembly through 320 Ma merger in Pangea to 185-100 Ma breakup: Supercontinental tectonics via stratigraphy and radiometric dating: Earth-Science Reviews, v. 68, p. 1–132.</ref> Extensional tectonics that controlled the deposition of major evaporitic successions in the Arabic peninsula (Hormuz Salt Basin) and surroundings (e.g., Punjab Salt Basin) close to the Precambrian–Cambrian boundary (see dashed faults in [[:file:M106Ch01Fig02.jpg|Figure 2]]) came to an end, and no important tectonic activity is observed in the late Cambrian (500 Ma). [[Laurentia]] lay astride the equator in both hemispheres and was separated from Gondwana by the Iapetus Ocean. Avalonia, Armorica, Perunica, Baltica (180&deg; geographically inverted), North and South China, and all the Cimmerian blocks fringed peripheral Gondwana at moderate to high southern latitudes. Torsvik and Cocks<ref name=Torsvikandcocks_2009 /> show that South China was located close to the Equator. According to von Raumer and Stampfli,<ref name=Vonraumerandstampfli_2008>von Raumer, J. F., and Stampfli, G. M., 2008, The birth of the Rheic Ocean - Early Palaeozoic subsidence patterns and subsequent tectonic plate scenarios: Tectonophysics, v. 461, p. 9–20.</ref> the Proto-Tethys ocean, which separated North China (to the north) from the other blocks along the peripheral Gondwana, was subducting toward the south and backarc extension, which is suggested by oceanic Cambrian seaways between the peripheral Gondwanan blocks. Torsvik and Cocks<ref name=Torsvikandcocks_2009 /> recognized that their concept of the Ran Ocean used for the Cambrian-Ordovician ocean existing between Baltica and Gondwana is comparable to that of the Proto-Tethys (sensu Stampfli and Borel<ref name=Stampfliandborel_2002 />), and herein we prefer to use the latter term. Siberia was positioned at low latitudes and was separated from Laurentia and Baltica by oceanic crust. Avalonia rifted off Gondwana in the Early Ordovician with the opening of the Rheic Ocean,<ref name=Nys&aelig;theretal_2002>Nys&aelig;ther, E., Torvik, T. H., Feist, R., Walderhaug, H. J., and Eide, E.A., 2002, Ordovician palaeogeography with new palaeomagnetic data from the Montagne Noire (Southern France): Earth and Planetary Science Letters, v. 203, p. 329–341.</ref> although some authors suggest even older ages for its opening.<ref name=Torsvikandcocks_2009 />

The scanty fossil record makes reconstruction of Cambrian paleobiogeography difficult. This fauna mostly comprises pelagic trilobites and articulated brachiopods.<ref name=Cocksandtorsvik_2002 /> Cocks and Torsvik<ref name=Cocksandtorsvik_2002 /> recognized Laurentia, Siberia, and peri-Gondwana as distinct faunal provinces. Few data are available on climate, which based on the general character of the sedimentary section was probably temperate warm to temperate cool, but arid at low latitudes. No ice seems to have been present at the poles.

The scanty fossil record makes reconstruction of Cambrian paleobiogeography difficult. This fauna mostly comprises pelagic trilobites and articulated brachiopods.<ref name=Cocksandtorsvik_2002 /> Cocks and Torsvik<ref name=Cocksandtorsvik_2002 /> recognized Laurentia, Siberia, and peri-Gondwana as distinct faunal provinces. Few data are available on climate, which based on the general character of the [[sedimentary]] section was probably temperate warm to temperate cool, but arid at low latitudes. No ice seems to have been present at the poles.

Along North Africa and North Arabia, clastic continental deposits fringed a shallow water platform comprising both shales and mixed siliciclastic and carbonate facies.<ref name=Guiraudandbosworth_1999>Guiraud, R., and Bosworth, W., 1999, Phanerozoic geodynamic evolution of northeastern Africa and the northwestern Arabian platform: Tectonophysics, v. 315, p. 73–108.</ref> <ref name=Konertetal_2001>Konert, G., Abdulkader, M. A., Al-Hajri, A. A., and Droste, H. J., 2001, Paleozoic stratigraphy and hydrocarbon habitat of the Arabian Plate: GeoArabia, v. 6, p. 407–442.</ref>

Along North Africa and North Arabia, clastic continental deposits fringed a shallow water platform comprising both [[shale]]s and mixed [[siliciclastic]] and [[carbonate facies]].<ref name=Guiraudandbosworth_1999>Guiraud, R., and Bosworth, W., 1999, Phanerozoic geodynamic evolution of northeastern Africa and the northwestern Arabian platform: Tectonophysics, v. 315, p. 73–108.</ref> <ref name=Konertetal_2001>Konert, G., Abdulkader, M. A., Al-Hajri, A. A., and Droste, H. J., 2001, Paleozoic stratigraphy and hydrocarbon habitat of the Arabian Plate: GeoArabia, v. 6, p. 407–442.</ref>

[[file:m106Ch01Fig03.jpg|thumb|300px|{{figure number|3}}Global paleogeography (top) and major depositional settings in the southern margin of the Tethys (below) during Late Ordovician time (about 440 Ma), modified after Cocks and Torsvik<ref name=Cocksandtorsvik_2002 />]]

[[file:m106Ch01Fig03.jpg|thumb|300px|{{figure number|3}}Global paleogeography (top) and major depositional settings in the southern margin of the Tethys (below) during Late Ordovician time (about 440 Ma), modified after Cocks and Torsvik<ref name=Cocksandtorsvik_2002 />]]