Older Palaeozoic Three geological periods, the Cambrian, Ordovician and Silurian make up the Older Palaeozoic rocks, and together cover a span of some 182 my (Table 2.1). They record a long period of marine sedimentation in the oceans between the continents of Precambrian rock and in the shelf seas along their margins. The number of continents then on the surface of the Earth is not known but four, or more, are believed to have existed, each separated by oceans. One comprised the shield of N. America and Greenland; another the shields of Scandinavia and the Baltic; and a third the shields of Russia and Asia, and a fourth, the shields of S. America, Africa, Antarctica, India and Australasia. Movement of the oceanic plates against these continents and collisions between the continents, as illustrated in Figs 2.3 and 2.4, produced three extensive mountain ranges. Along the edge of the continent formed by the S. American, African, Antarctic, and Australasian plates was raised the Samfrau fold belt, remnants of which can be found extending from N.E. Australia to Tasmania, in the Ellsworth Mountains of Antarctica, in the Cape Fold Belt (Figs 1.10 and 1.12) and the Sierra de Ia Vantana of Buenos Aires. The Baltic and Russian shields collided along the line now occupied by the Urals which is believed to have extended into the Franklin range of N. America. Between N. America and Scandinavia were formed the Caledonides, an ancient range like the others, whose remnants are now found in Scandinavia, the northern part of the British Isles, Newfoundland and the Appalachians. The rocks of the Caledonides were formed in seas at the margins of these converging continents and their stratigraphy records the events of this collision, the period of associated deformation being the Caledonian orogeny. This is described later, because it is an example of mountain building.

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@Zaka231 posted 2 years ago

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