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Map Earth History Maps of professor Jan Golonka This was the time of maximum dispersion of continents during the Paleozoic. The continents of Gondwana, Baltica, Laurentia and Siberia continued to exist. Baltica, Laurentia and Siberia drifted further northward. Laurentia was situated on equator at this time (Fig. 4).
Convergent Tectonics
Arc-continent collisions occurred along the margins of Iapetus-Tornquist-Pleionic oceanic system in Baltica and in Avalonia causing deformations of the Penobscottian, Grampian, Finnmarkian, and Atholian orogenies (P. Ziegler, 1990; Neuman & Max, 1989). The deformation events in Baltica might have been related to the transformation of a passive margin into a convergent one, due to the development of the subduction zone. Collision between microcontinents (Salairian orogeny) in the Mongolia-Tuwa area (Zonenshain et al., 1990) marked the onset of the formation of the Amuria (Mongolia) microcontinent. The Delamerian-Ross orogeny developed a fold and thrust belt with extensive volcanism along the margin of western Gondwana in southeastern Australia, the Wilson terrane, and from north Victoria Land to the Pensacola Mountains in Antarctica (Cook, 1990; Findlay, 1991; Findlay et al., 1991; Flöttmann et al.; 1993). The Świętokrzyska Phase caused the folding of Cambrian sediments in the northern part of the Holy Cross Mts. in Poland (Lewandowski, 1993).
Subduction zone along the margin of Gondwana between Northwestern South America and the Chinese terranes and the subduction zone located north of western Laurentia, Arctic plates and Siberia continued their development. The subduction along the central margin of Gondwana caused the onset of rifting of the Avalonian terranes (Golonka et al., 1994). The subduction along the northern margin of Baltica was perhaps related to the Ordovician rotation of this plate (see Golonka et al., 1994;Torsvik et al., 1996; McKerrow et al., 1991).
Extensional Tectonics
The rapid northward drift of Laurentia widened the Phoibic or Western Iapetus Ocean (Dalziel, 1997). The distance between Gondwana and Laurentia reached 5000 km (Kent & Van der Voo, 1990). The Iapetus - Tornquist Sea oceanic system also widened significantly (Torsvik et al., 1995, 1996). The estimated width of the ocean between Baltica and Laurentia depends upon the latitudinal position of Laurentia. Rapid northward movement of Laurentia possibly caused separation of Laurentia and East Siberia. The widening of the Paleoasian Ocean could also have happened at this time (Zonenshain et al., 1990). The western part of Paleoasian Ocean evolved into Uralian Ocean (Puchkov, 1997). Rifting activity occurred on the eastern margin of Baltica and in the West Ural Basin between the Pechorian and Pericaspian areas (Nikishin et al., 1996). There is also a possibility of Late Cambrian-Early Ordovician rifting in the Pericaspian Basin (Nikishin et al. 1996). Sauk III was the time of the onset of rifting between Avalonia and Gondwana (McKerrow et al., 1991). Rifting of arcs (Oliverian/Midland Valley terrain), off the eastern coast of Laurentia, occurred in Late Cambrian - earliest Ordovician time (McKerrow et al., 1991).
Sea Level and Climate
The continents were dispersed and in the most advanced drifting stage during the Early Paleozoic time. The global sea level rise was related to drifting of the continents. The significant subsidence and submergence of most of continental margins was a continuation of the Cambrian trend. Sea-level was probably at one of its highest points during the entire Phanerozoic, however, according to Algeo & Seslavinsky (1995) the sea-level estimates could have been exaggerated. Greenhouse conditions prevailed. Likewise the global OAE continued from the previous time slice.
Carbonate Sedimentation
A stable tectonic regime and a hot climate resulted in the deposition of limestones and dolomites on the North America plate, particularly in the southern part of the Mid-continent, as well as on the Barentsia plate and on the eastern Greenland shelf (McKerrow et al., 1991; Mellen, 1977; Chafetz, 1980; Stewart & Pool, 1974). Carbonate and evaporite sedimentation continued on the Siberian craton (Puchkov, 1996, Ronov et al., 1984). Mixed
carbonate/clastic sediments were deposited on Baltica in Poland and Scandinavia (McKerrow et al., 1991; Ronov et al., 1984). Limestones, dolomites and evaporites were deposited in South China. Mixed carbonate/clastic sediments were deposited in North China, South-East Asia, Iran, Iraq (Ronov et al., 1984) and on the northwestern Indian plate (Gupta & Brookfield, 1991).
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