Why does sorting lead to higher porosity

Porosity is expressed as a percentage calculated from the volume of open space in a rock compared with the total volume of rock. The typical ranges in porosity of a number of different geological materials are shown in Figure Unconsolidated sediments tend to have higher porosity than consolidated ones because they have no cement, and most have not been strongly compressed.

Finer-grained materials e. Primary porosity tends to be higher in well-sorted sediments compared to poorly sorted sediments, where there is a range of smaller particles to fill the spaces made by the larger particles. Glacial till, which has a wide range of grain sizes and is typically formed under compression beneath glacial ice, has relatively low porosity. Consolidation and cementation during the process of lithification of unconsolidated sediments into sedimentary rocks reduces primary porosity.

The grain size, sorting, compaction, and degree of cementation of the rocks all influence primary porosity. For example, poorly sorted and well-cemented sandstone and well-compressed mudstone can have very low porosity. Igneous or metamorphic rocks have the lowest primary porosity because they commonly form at depth and have interlocking crystals.

Most of their porosity comes in the form of secondary porosity in fractures. Of the consolidated rocks, well-fractured volcanic rocks and limestone that has cavernous openings produced by dissolution have the highest potential porosity, while intrusive igneous and metamorphic rocks, which formed under great pressure, have the lowest.

Porosity is a measure of how much water can be stored in geological materials. Almost all rocks contain some porosity and therefore contain groundwater. Groundwater is found under your feet and everywhere on the planet. Porosity is a description of how much space there could be to hold water under the ground, and permeability describes how those pores are shaped and interconnected. This determines how easy it is for water to flow from one pore to the next.

Larger pores mean there is less friction between flowing water and the sides of the pores. Smaller pores mean more friction along pore walls, but also more twists and turns for the water to have to flow-through. A permeable material has a greater number of larger, well-connected pores spaces, whereas an impermeable material has fewer, smaller pores that are poorly connected.

User Tools. Sign In. Advanced Search. Skip Nav Destination Article Navigation. Close mobile search navigation Article navigation. Volume 31, Number 3. Previous Article Next Article. Article Navigation. Other September 01, Relationships between porosity, median size, and sorting coefficients of synthetic sands John J.

Rogers ; John J. Google Scholar. William B. Head William B. Journal of Sedimentary Research 31 3 : — Article history first online:. Abstract The relationship between porosity, median size, and sorting coefficients has been investigated by studying synthetic sands with lognormal size distributions and various median sizes and sorting coefficients.

This content is PDF only. The source of sediment , the way sediment was moved and the conditions that sediment was deposited. How are newly formed sediments transported to new locations? They are transported by wind, water or ice. Well-sorted materials have grains of the same size, while poorly sorted mate- rials have grains of many sizes.

Permeability decreases as the degree of sort- ing varies from good to poor because small grains can fill the spaces between large grains.

Permeability is also influenced by grain shape. Biogenous sediments are formed from the remnants of organisms that refused to be dissolved.

In deeper waters, shells of plankton and other microscopic organisms form these kinds of sediments. Hydrogenous sediments are sediments solidified out of ocean water. As such, chemical reactions create these kinds of sediments.

Shale is the most common sedimentary rock, accounting for about 70 percent of the rock in the Earth's crust. Shale is a fine-grained rock made from compacted mud and clay. The defining characteristic of shale is its fissility.

Black and gray shale are common, but the rock can occur in any color. Grains are usually angular through well rounded. Minerals include all the immature minerals like quartz, micas, clays, and rock fragments.

Rock types include Siltstone, Shale , and Quartz Arenite. Rounding, roundness or angularity are terms used to describe the shape of the corners on a particle or clast of sediment. Such a particle may be a grain of sand, a pebble, cobble or boulder.

Deposition is the geological process in which sediments, soil and rocks are added to a landform or land mass. Wind, ice, water, and gravity transport previously weathered surface material, which, at the loss of enough kinetic energy in the fluid, is deposited , building up layers of sediment. Which would have a higher porosity a well sorted sediment or a poorly sorted sediment?

Category: science geology. Porosity refers to the capacity of earth materials to hold water in spaces found within and between sediments and rock. Thus, well sorted sediments have higher porosity while poorly sorted sediments have low porosity. Permeability refers to how easily water passes through sediments and rock. What are 4 examples of sediment that might eventually become sedimentary rock?