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Transcript
How did Alfred find fossilised sea creatures high up in the Alps? There were long periods of quiet between earth movements during which sedimentary rocks, thousands of metres thick, formed huge depressions called geosynclines. In some places, the folds were pushed over on one side to give overfolds, while in some of the highest fold mountains, such as the Alps, the rocks have been severely folded and faulted into nappes. Sometimes the folds were simple upfolds (anticlines) and down folds (synclines). Geosynclines are huge depressions which often contain seas. Over millions of years the sediments were compressed into sedimentary rocks such as sandstone and limestone. Rivers carried sediment and deposited them into depressions known as geosynclines. The sedimentary rocks were forced upwards into a series of folds by the movement of tectonic plates. Recent mountain building movements have created the Alps, Himalayas, Rockies and Andes., some of which are still rising. They are called “young fold mountains”. Tectonic plates are sections of the earth’s crust. Alfred is a keen geologist. Tectonic plates float on the mantle – molten rock beneath the earth’s surface Alfred is also a keen climber and is preparing to climb Mt Blanc. He enjoys the amazing scenery created by overfolds and nappes. The mantle is continually moving due to convection currents. The Alps reach great heights – the highest peak is Mt Blanc in France at 4810 m Fold mountains occur where two tectonic plates are moving towards each other. A compressional margin occurs when two tectonic plates are moving towards each other. The Alps are known as “young fold mountains” The Alps lie at a compressional margin. Fold mountains have been formed at times in the earth’s geological history called mountain-building periods. Early geologists suggested that the fossils of sea creatures were deposited on mountains by Noah’s flood. When sea animals die, their remains may fall to the bottom of the sea and they become covered in sediment. When limestone is exposed to wind, rain and chemical weathering, fossils may become exposed.