Why fossils are only found in sedimentary rocks

Fossils are common in shale because excellent imprints can be formed in fine-grained sediments like mud. However, only some shales contain fossils because many ocean floor areas were not suitable for animal life. In these areas, fossils only occur from a few dead organisms whose bodies drifted into them and were deposited in the mud. Sandstone can contain fossilized crustaceans, bryozoans, trilobites, and brachiopods.

Desert sandstone does not usually contain fossils unless the desert was once a sea. Fossilized wood, plants, or vertebrates can be found in sandstone in old river beds and deltas.

Sandstone formed on beaches contains fossils of arthropods, mollusks, crinoids, and other marine creatures. Find out the article to this question in the article below:. I Have to Disappoint You, But.. Before going fossil hunting, you should explore the geological formations in your area to identify which ones consist of sedimentary rocks.

Keep your eyes open when you pass through the land in which roads have been cut, and take note of the exposed layers in the embankments. You can also use geological maps of the area you want to explore to see where sedimentary rock is located.

If you go on hikes in the wilderness or along beaches, lakes, or rivers, carefully study any exposed rock faces you encounter. Also, be aware of any stretches of rock you find in old riverbeds and deltas. Fossils may be under your feet and not in rock faces. Be mindful of odd shapes in the rock that could be ancient footprints or tracks.

Try walking in streams while gazing at the ground, not looking for anything in particular but watching for flat, sharp-edged rock fragments that have recently broken off of rock faces. They may contain trace fossils. Particularly lumpy rocks could be fossilized feces called coprolites. Sedimentary rocks often occur near water sources because of the erosion that takes place in these places. Just remember that rivers and lakes dry up, leaving only their channels and basins behind.

Organisms that live in topographically low places such as lakes or ocean basins have the best chance of being preserved. This is because they are already in locations where sediment is likely to bury them and shelter them from scavengers and decay. Mudstone, shale, and limestone are examples of sedimentary rock likely to contain fossils.

As the layers of sediment build up on top of one another, they create a physical timeline. The oldest layers, along with the organisms that were fossilized as they formed, are deepest.

The youngest layers are found at the top. Reading the layers is complicated by the fact that as continents move and mountains rise, the layers are often tipped sideways and altered in other ways. Igneous rock is formed by the cooling of molten rock, either at the surface lava , or underground as granite or other similar rocks.

The weathering process is the first step in the formation of sedimentary rock. One of the stages is mechanical weathering. During the mechanical weathering process, rocks are equally broken down into tiny little pieces by root-wedging , frost-wedging , and abrasion. Furthermore, frost-wedging refers to the thawing and freezing of water in cracks. Also, one thing you should know about mechanical weathering is that they can break rocks down into tiny little pieces.

And I mean smaller pieces. However, they do not alter the minerals. That stays the same. The next stage of the weathering process is chemical weathering. It is like the direct opposite of the mechanical weathering of rocks. Chemical weathering changes minerals into something entirely new.

In this case, the outcome will be new minerals, together with mineral byproducts. In this process, keep in mind that some minerals dissolve completely. Examples are the calcite and halite.

But other minerals like silicate are altered via a chemical process known as hydrolysis. The term hydrolysis refers to a reaction that occurs on minerals present in waters, particularly weakly acidic waters. Another process in a sedimentary rock formation is transportation.

And as you know, transport means you are carrying something from one place to another place. There must also be an agent facilitator of this process. The most critical agent of transportation is no other but water. Water moves particles in rivers Be it the smallest of clay particles or bigger-sized boulders. However, the smaller-sized rock fragments and boulders do not remain the same.

The breaking down process continues, and they also experience chemical alteration as they move down the stream. Water is also involved in the transportation of dissolved minerals. These include silica as well as cations found downstream and even in groundwater. But water is not the only agent that transports particles; the wind also does the same thing. The wind blows sand, dust, and glaciers. Skip to main content. K-5 GeoSource. PDF version. Learn More. What is a fossil?

How do fossils form?