Sedimentary rock deposits in layers like these sandstones.
All kinds of weather along with the freezing and thawing of glaciers wear away the rocks of the earth. Once the Appalachia Mountains of the eastern U.S. were as high and rugged as the Rocky Mountains, but today appear rounded because of weathering. Even though weather or erosion never stops, fragments and grains -- scientifically termed clasts -- carried by wind and water and then deposited, layer-by-layer, help in building the sedimentary rocks seen today.
Water Volume and Speed
Depending on the speed and volume of water in a stream or river, different sized fragments or clasts are broken off, picked up in mountain areas and carried downhill until the water slows enough to drop the clasts. Powerful spring or catastrophic floods when the ice dams broke as the glaciers melted back, scoured the landscape, picking up massive loads of rock, gravel and boulders and carrying them miles away before slowing enough to deposit them. Deposit after deposit of clasts -- clay rock grains -- finally built-up enough layers to compact the lower layers. Combined with the pressure, dissolved minerals migrated to the open spaces between the grains and began to precipitate, or crystallize, effectively "cementing" the fragments together into solid rock.
Clastic Sedimentary Deposits
Conglomerate deposits with differently-sized fragments, many of them quite large, formed where massive floods carried the larger fragments. Quieter times brought in more uniform gravel and clays until enough built-up to compress the lower layers. Sandstone formed along beaches from wave action, in large river deltas and along the sides of streams and rivers where relatively even-sized clasts deposited over the eons. These are the harder grains of silicate minerals like quartz and quartzite. In these locations, the current is strong enough to still carry the finer clays, but slow enough to drop out the sand. Mudstones and shale formed in ancient lake and sea bottoms, wherever the water was still enough for the finer particles to sift down and drop to the bottom.
Chemical Sedimentary Deposits
Several chemical and biochemical processes create mineral fragments that collected, eventually compressed and formed sedimentary rocks. Chemical rocks formed when a body of water became super-saturated with the minerals brought into the basin. Evaporation of the water triggered the increase in mineral content. Some limestone, rock salt and gypsum are the most common sedimentary rocks formed this way.
Biochemical Sedimentary Rocks
Biochemical sedimentary rocks form when living organisms use the available minerals to build their own tissue, notably shellfish use calcium and plants use carbon. When shellfish and similar organisms die, they decay and the mineral fragments drop out, deposit and once again through compression, form limestone. Plant material, when compressed strongly enough, eventually forms coal beds. Other organisms like diatoms leave deposits of chert. Sedimentary rocks form wherever enough fragments accumulate in large layers and can exert pressure on the layers below them.
Related posts
Salt Flats at Death Valley, CaliforniaThe Surface of the EarthChemical sedimentary rocks form at the earth's surface. Sedimentary rocks are rocks that have been placed by weathering or erosion in...
Geologists classify rocks based on the materials from which they are made.Basically, a rock is any naturally occurring consolidated material made up of one or more minerals. Geologists classify ro...
It typically takes millions of years for sedimentary rocks to form.If you've ever visited the Grand Canyon or been by any river or cliff where you observed horizontal stripes in the rocks there, t...
Sedimentary rock forms in layers over time.Sedimentary rocks are formed from small mineral particles called sediment. Natural forces, such as gravity, water or wind, can exert enough pressure on s...
Many famous statues were carved from marble.With the right tools and training, an artist can carve nearly any type of rock to create a sculpture. Marble, which is in the middle of the scale that r...
