GEOLOGY OF Bonnie M. SAMPSELL Blanca van Hasselt

When one thinks about Egypt, what Meanwhile the African continent drifted northward and comes to our mind? There are the pyra- bumped into the European continent, connecting both continents mids and the sphinx, obelisks and tem- along present-day Turkey and the Middle East. By this time the ples… There are the ; one big Tethys Ocean was reduced into the intracontinental Mediter- may remember Ramses II, Nefertiti, ranean Sea. Once both landmasses were interlocked the forces Ptolemeus and Cleopatrea. There are readjusted and sometime during the Oligocene (about 40 mil- the tombs with colourful illustrations lion year ago), the split between the Arabian Peninsula and the commented in hieroglyphs. There are African continent started. This soon evolved in the creation of mommies and the treasures of Toutankh- the Red Sea Mountains and of the Red Sea. A depression formed Amon. Among the treasures are vases on the West Side of the Red Sea Mountains, which would much in cream coloured alabaster and heavy later become the Valley. In the late Miocene (6 million golden jewellery inlaid with precious year ago, which is 6 000 000 year ago) the African continent and semi-precious stones: deep blue la- had bumped so much into the European continent that even the pis, vivid green malachite, sky blue turquoise, bright red coral, connection between the Atlantic Ocean and the Mediterranean bottle green emeralds, translucent purple amethyst, … Sea along the Strait of Gibraltar was closed. It happens that with Egyptian civilisation is traced back to 5000 year. It is closely the warm Mediterranean climate, about 10 times more water is followed by the Indian civilisation traced back to probably more evaporated compared to the combined amount of water fl owing than 4000 year. These numbers what do they mean? Roman civi- into the Mediterranean from the European and African rivers. So lisation only dates from 2000 years back. The conquests of Geng- after a while the Mediterranean Sea dried out except for a few his Khan and his hordes date back to barely 1000 year ago. The patches and lakes. With the bottom of the dried out Mediterra- intensive sea trade between the western world and Asia by ocean nean at about 2000 to 3000 m deep, the different rivers fl owing navigation only exists since the last 500 year. And yet more than into this deep dried out basin must fi rst have been some kind of 4000 year ago, during the Old Empire in Egypt [2700-2180 BC] waterfalls, progressively carving deep canyons into their rock the fi rst pyramids were build near present day Cairo. formations. Research indicates that within a few hundred thou- Most of Egypt’s monuments are in pale cream coloured lime- sand years the river that was to become the Nile had carved out stone. Either limestone blocs are used for construction of the a vast canyon into the soft limestone, reaching from the present- temples, sphinx and pyramids; or the limestone is hewn out in day Mediterranean shore up to Aswan or beyond, some 1000 km order to host the graves of the dead. If one looks into the geology or more to the south. Citing B. Sampsell based on research by of Egypt this is no surprise. In most of the country located north Said 1981, comparing the ancient Nile Canyon with today’s the of Aswan and West of the Red-Sea Mountains, the rock is mainly Grand Canyon in Arizona: made up by limestone. But then when one visits the temples and Nile Canyon Grand Canyon the museums, there are beautiful polished statues of pitch-black width 10 to 20 km 10 to 20 km basalt, red granite, and spotted porphyry. While the limestone length 1 300 km 320 km is soft and easily carved (which is convenient for the numerous depth 2 500 m 2 080 m inscription in hieroglyphs), the basalt, granite and porphyry are fl ow gradient 1 : 400 1 : 625 very hard stones, diffi cult to work, but beautiful and impressive once polished. So if most of Ancient Egypt is located in an area At the start of the Pliocene (5 million year ago), the Atlan- with mainly limestone, where did the hard stones come from, and tic breached the Strait of Gibraltar, and the Mediterranean Sea how did they get to the temples and graves? Bonnie M. Sampsell started to refi ll. This process may have required less than a thou- describes this among others in her interesting book “A traveler’s sand years. In consequence sea water invaded the Nile Canyon guide to the geology of Egypt” edited by the American Universi- as far as Aswan, and marine sediments fi lled up the canyon for ty In Cairo Press. But be aware, if the previous time spans (5000 about one third or maybe half of the initial canyon depth. These year of Egyptian civilisation) seem impressive, geological time sediments contain seashells. In Late Pliocene (3.3 million year spans will dazzle you. (Apologies, the following paragraphs con- ago) the Nile River started again to fl ow. Fed by small streams tain some geological terminology, but don’t bother). from the continent, the water in the canyon fi rst became brack- South of Aswan (nearby the tropic of cancer) the rock mainly ish, later to become completely fresh. In the subsequent sedi- consists in igneous and metamorphic rock: the old basement com- ments there are no longer seashells, but instead, there are fossils plex. These rocks are very old, at some locations 2 000 million of terrestrial plants and fresh water fi sh. These continental (ero- year (= 2 billion year), which is almost half the age of the Earth. sion) sediments fi lled the canyon to the rim, but the cliffs on both In late Cretaceous, some 80 to 90 million year ago, this area must sides of the Nile Valley which are still visible today, are the old have been the northern shore of the old African continent which Canyon walls. At Aswan the sediment reaches down to about at that point of time was still far away from Europe. There was 250 m below the modern Nile channel. This had engineering not yet a Mediterranean Sea, but a big Ocean called Tethys. On consequences when building the famous . this northern shore of the old African continent sandstone and Bonnie Sampsell’s book contains plenty of other interesting massive layers of limestone where deposited. Near Aswan, at the chapters describing the deserts, the at Alexandria, the northern shore of this old African continent, these layers are not precious stones of the Red Sea Mountains, the ores and minerals very thick. But towards the North into the Tethys Ocean and near of the and the fascinating history of the Canal present day Cairo, they are several hundreds of meters thick. of Suez.

15 i-News June / July 2010