- Clastic Sedimentary Rocks are composed of clasts which are
fragments of other rocks, including preexisting igneous, sedimentary and metamorphic
varieties. They are land-derived meaning that particles normally come
from weathered and eroded landforms. They are then transported by running
water, wind or glaciers to their final destination for deposition.
- Clastic, a.k.a. detrital, rocks are formed by the processes of compaction
and cementation.
- As with most sedimentary rocks, the majority of clastic rocks form underwater
and in horizontal layers (bedding planes).
- Compaction is commonly due to the weight and pressure of overlying layers
of sediments.
- Cementation occurs when minerals dissolved in water, pass in and around
rock fragments then either precipitate or evaporate out of solution, cementing
individual fragments together.
- The particles in clastic rocks vary in size, composition and point of origin
both across the classification group as well as within an individual rock
specimen. Rocks are classified as shale, siltstone, sandstone, conglomerate
or breccia based on the size of the fragments that compose the rock rather
than its composition.
Particle size and composition are important to a complete understanding of
this rock classification however the following pages are dedicated to how
Sedimentary Rocks form and in what type of environments.
As you click the subheadings on the left menu, you will read about the roles
of Running Water, Lakes, Wind & Dunes and Glacial Drift and the formation
of clastic rocks.
