Where in the World in Saudi Arabia?
The Arabian Shield Geology
Ancient Landmass - Saudi Arabia
(for more photos of fossils and sandstone geology: http://theadventuresofmenu.shutterfly.com/ )
The geology in Saudi Arabia is quite unique. Many millions of years ago, the eastern half of the country was under water – what is now the Arabian Gulf (see picture above right). Today, you can go anywhere in the desert from Riyadh to the east coast and find fossils everywhere. The fossils range in size from tiny shark’s teeth to larger brain corals or entire coral reefs – all frozen in stone. So we thought that we’d take Flat Stanley with us to see if he was as lucky at finding fossils as we had been…. he was … and he learned a lot about sandstone, fossils and geology that day!
Fossil beds as rich and abundant in Saudi Arabia. There is no need to dig or even search very hard; artifacts of ancient animals litter the ground. Entire hillsides and cliffs there are composed of fossils. The Riyadh Escarpment is especially rich in pre-historic remains of sea life – this was the eastern edge of the ancient sea. There are thousands of acres of the desert floor covered with fossils; these ancient coral beds must have been an astounding site!
Due to the abundance of sandstone (fossilized ancient beaches) and limestone (ancient coral reefs) there are many examples of dahls (dals) to explore. In English these would be the equivalent of sink-holes or caves created by streams of water.
Along the eastern coast of Saudi Arabia, you can find sedimentary limestone rocks deposited in layers by the rising and falling of ancient seas. On the western coast there is an ancient land mass, called the Arabian Shield, made up of igneous & metamorphic rocks. Occasionally you can find sedimentary rocks due to uplifting & erosion processes.
Sedimentary rock forms in water, where the weight of the water presses down on the layers of sand and clay to squash them together into a new rock. Sometimes animals and plants get stuck in between the layers, and then fossils in their shape get molded into the new stone. Because some kinds of grains, like sand, are bigger and heavier than other kinds, like clay, they sink faster when they fall into the lake or the ocean. That’s how you get different kinds of sedimentary rocks. Some kinds are mostly made near shore, and they have mostly sand in them, like sandstone. Other kinds are mostly made farther from shore, and they have mostly clay in them, like shale. The particles that get furthest from shore are the ones that make limestone. All of these rocks still form today, just the same way they formed billions of years ago. http://www.historyforkids.org/scienceforkids/geology/rocks/sedimentary/
This flow of water, slightly acidic from acid rain or from passing through something acidic, is what digs out the caves (sinkholes or dahls in Arabic). It essentially widens cracks in the rock. And the ceiling may also collapse, making a mound of limestone on the floor, and a concave dome above.
Old Widow Hag
Shark's Tooth Fossil
Flat Stanley Finds a Fossil
Heading down a wadi looking for fossils
Flat Stanley and Fossilized Trees
Miles of fossils, Jebel Baloum
Flat Stanley Discovering Geology
Stalactite, Sawh, Saudi Arabia
Sandstone and Limestone Cliffs, Sawh, Saudi Arabia
Sea of Sand
Stalactites and stalagmites occur in limestone caves. The stalactite is above, and hangs downward like an icicle; the stalagmite is below and sticks up. They grow in pairs, the slightly acidic water dissolves some of the limestone, carrying it downward. When the water evaporates, the limestone appears to have flowed downward. Some of the water does not evaporate until it has fallen through the air, and landed on the floor, the remaining limestone building the stalagmite. Sometimes the stalactite is missing, as they sometimes break off and fall; you will often see their pieces on the floor. Or human visitors may break them off, and take them away. Often, the stalactite and stalagmite will connect, and become a column.
Approaching Al Khatla Dahl
Al Khatla Dahl
Fossilized Sea Shell, Tuwaiq Escarpment
More Coral Fossils
Flat Stanley Finds More Sand Balls
Flat Stanley and Sand Balls
Crystals in the Sand
Flat Stanley Finds a Fossil
Moqui Marbles (sand balls) are sedimentary concretions. They form as sediments are laid down at the bottom of bodies of water. The moqui marbles have harder minerals than the normal sediment. The sediment layers then turn to sandstone. When the sandstone erodes away, the marbles are uncovered. Seeing these in the middle of the desert is evidence of ancient rivers and lakes.
Entering Sadus Dahl
Inside a Dahl (Sinkhole)
Flat Stanley's First Dahl (Sinkhole)
Fossilized Brain Coral
Al Khufaisat Dahl
Al Khufaisat Dahl
Pools Carved in Sandstone
Fantastic Sandstone Cliffs
Flat Stanley and Coral Fossils in Limestone
Lava tubes are created when lava flows as a river; the lava at the edges often solidifies into a hollow tube, or it may be open at the top. When the lava quits flowing, sometimes an empty tube is left, perhaps going on for miles.
Liquid rocks shoot up to the surface when volcanoes suddenly erupt. Then tons of liquid rock rockets out of the top of the volcano and lands on the surface. When the liquid rock cools down, it becomes igneous rock. There are a lot of different kinds of igneous rock, depending on what kind of molecules are involved, and how fast the liquid rock cooled down. Some of the better-known kinds of igneous rock that comes from volcanoes are pumice, lava, and obsidian. When lava cools, it often turns into basalt. Other igneous rocks formed slowly, deep in the earth. Some examples are quartz and granite. About a quarter of the rocks on earth are igneous rocks. http://www.historyforkids.org/scienceforkids/geology/rocks/igneous/index.htm
Flat Stanley’s Visit to the Lava Tubes and White Volcanoes: http://gallery.flatstanley.com/?p=4414
For more reading on Saudi geology:
Fossilized Coral (Tuwaiq Escarpment)
Fan Coral Fossil
Coral Fossil, Tuwaiq Escarpment
Tuwaiq Escarpment: A huge ancient coral reef and modern sandstone cliff