Sedimentary Rocks and Grain Sizes
What is the correct order of grain sizes from smallest to largest for clastic (detrital) sedimentary rocks?
a) Silt, clay, sand, gravel, cobble
b) Clay, sand, silt, cobble, gravel
c) Gravel, cobble, sand, silt, clay
d) Sand, clay, silt, gravel, cobble.
Final answer:
The correct order of grain sizes from smallest to largest for clastic sedimentary rocks is clay, silt, sand, gravel, and cobble.
Explanation:
The correct order of grain sizes from smallest to largest for clastic (also known as detrital) sedimentary rocks is clay, silt, sand, gravel, and cobble. Sedimentary rocks are formed by the deposition and cementing together of fine grains of material. These materials can range from pieces of igneous rock to the remains of living things. A key characteristic of these rocks is their grain size, which informs us on the environment and condition in which they were formed, as well as their potential uses. Here, the smallest grain size is clay, followed by silt, sand, gravel and the largest being cobble.
The grain size of sedimentary rocks provides valuable information about their formation and composition. Understanding the order of grain sizes in clastic sedimentary rocks can help geologists and scientists interpret the history of a particular rock formation.
Clay, being the smallest grain size, typically forms from the weathering and erosion of rocks with high aluminum content. Silt is slightly larger than clay and is often derived from the breakdown of quartz-rich rocks. Sand grains are coarser than silt and originate from the erosion of larger rocks, such as granite or sandstone. Gravel consists of rounded pebbles and stones that are even larger in size, while cobble represents the largest grain size in clastic sedimentary rocks.
The environment in which these grains were deposited plays a crucial role in determining the final composition of the rock. Clay-rich sedimentary rocks are commonly found in calm, low-energy environments like lakes or deep-sea basins. In contrast, gravel and cobble-sized grains are typically deposited in high-energy environments such as riverbeds or near the base of steep mountain slopes.
By analyzing the grain sizes and textures of sedimentary rocks, scientists can reconstruct past geological events, identify ancient environments, and even predict future geological processes. The study of sedimentary rocks and their grain sizes is essential for understanding Earth's history and the dynamic processes that shape our planet.