Sedimentary rocks are the most common rock type found on the planets surface comprising nearly 70 percent of all surface rocks. Sedimentary rocks are created from layers of sediments accumulating and being compressed together over time. While all sedimentary rocks form in a similar fashion, the rocks often have very different features. These features are dependent upon the natural forces at work during the depositing of the sediments.
One feature common on sedimentary rocks are ripple marks. These are caused by waves as the sediments were being deposited. Most commonly seen in areas where water once was. As the water shifted the sands it created a ripple effect. Over time these sands would become buried and compressed by the impact of the shifting sands would remain. Ripple marks can be caused near oceans, by streams, or lakes. When coming across a rock with ripple features just remember they could only be caused by water.
Mud cracks are the result of mud that became wet and dried out before it ended up buried. The features end up becoming preserved and in some cases rocks with these features are millions of years old. This feature is similar to what a lake bed that dries out does today. Mud cracks form when clay particles have dried out. Fine particles eventually fill in the area while preserving the crack at the same time.
Cross-bedding in rock occurs when sediments are deposited at that are younger than the original. This can be the result of water and wind adding sediments that eventually harden and add to existing rock. They lack the strength of the original rock and are likely to sheer off much easier than the older rock would. Examples of cross bedding can be found all over the world and are most common on cliffs or near water. Water can deposit sediment layers on old rock leading to cross-bedding.
Wave action occurs at the edges of bodies of water. As the waves pounded up against the water they removed all of the fine particles leaving the hardest part of the rock behind. This can create fine pebbles or leave solid miners void of fine particle features. As the water level recedes in time, these features become well preserved. Large lakes and seas are common places to find them.
Soft sediment deformation occurs is common in areas where there is glaciered activity. As glaciers slowly move over the rock, they can create folds in the rocks and deformities to its structure. This process has also been attributed to tectonic activity and associated pressures that rock undergoes during this process. During this process upper layers of rock get shoved or folded below the under layers. The features in sedimentary rocks are a direct result of the natural forces at work in the area the rock was found.
