6.3.4 Textural Parameters of Clastic Sediments & Sandstone Diagenesis

Grain size (Individual and Bulk/grain size distribution)

Grain shape

Grain Orientation

Porosity

Permeability

5 textural parameters

By volume (Displacement method)

Settling velocity (Stoke's law)

Direct measurement (Sieving)

By Grade Scale (Using chart)

How do we measure grain size

Sphericity

an inherited feature, that is, depends on the shapes of the fragments which formed during weathering.

Roundness

the shape of sediment grains.

Related to the distance sediment has been transported.

Form (Zingg form and Sneed&Folk form indices)

Provides a consistent terminology for describing the overall form of particles

It can be a potential use as guides to provenance and transport histories of siliciclastic sediment.

What is the significance of form and roundness

Lithology and hardness

Factors affecting shapes of sediments

Sorting

a description of the distribution of clast sizes present

well-sorted

it is composed of clasts that mainly fall in one class on the Wentworth scale

poorly sorted

it contains a wide range of clast sizes

Porosity

the volume of void space in a sediment or a sedimentary rock

Packing density, Grain size and shape, Sorting, Post burial

Factors affecting porosity

Packing density

the arrangement of the particles in the deposit. The more densely packed the particles the lower the porosity.

When grains settle through a fluid, the large grains will impact the substrate with larger momentum possibly jostling the grains into tighter packing

How does grain size and shape affect the porosity of a rock

Permeability

related to how easily a fluid will pass through any granular material

Same as the factors affecting porosity

Factors controlling permeability

Maturity

this refers to the extent to which the material has changed when compared with the starting material of the bedrock it was derived from

Through texture and composition

How can we measure maturity

Textural maturity

it can be used to indicate something about the erosion, transport and depositional history.

Mineralogical maturity (compositional maturity)

a measure of the proportion of resistant or stable minerals present in the sediment

Quartz overgrowth

the most common type of silica cement. It commonly gives the grain euhedral crystal faces.

Hematite

typically occurs as a very thin coating around grains (in between the overgrowth and the original grain), but also impregnates authigenic minerals

Diagenetic origin

What indicates the absence of hematite at grain contacts

Semi-arid

A telegenetic environment where oxidation of sulfides and Fe carbonates to Fe oxides may age to hematite

Humid

an environment where leaching of feldspars, carbonates, and heavy minerals can raise porosity significantly