Grain Sizes and Arrangements Flashcards

Study Notes

Grain Sizes and Shapes

Wentworth Size Scale categorizes grain sizes in sediments.
Argillaceous sediments contain significant amounts of mud.
Argillite is a low-grade metamorphic rock formed from mudrock.
The term "clay" has dual meanings in sedimentology: grain sizes less than 4 µm and a group of layered silicate minerals.

Measurement Techniques

Grain size can be measured through fluid displacement (volume), weight, linear measurement, visual estimation, and sieving.
Hydraulic settling is effective for fine-grained sediment analysis.
Electrical or optical properties assess suspended fine particles in fluids.

Grain Transport Dynamics

Two types of sediment transport: bedload (traction and saltation) and suspended load (particles transported within the fluid).

Maturity of Sediments

Immature sediments have >5% mud, poorly sorted, and angular grains.
Submature sediments contain less dark minerals and less than 5% mud, with angular to subangular grains.
Mature sediments are quartz-dominant with <5% mud, sorted, and subangular to subrounded grains.
Supermature sediments consist almost entirely of quartz, <5% mud, well sorted, and rounded grains.
Sediment maturity relates to weathering, transport energy, and duration, not geological age.

Sediment Characteristics

Textural inversion involves mixing sediments of different maturities.
Grain shape is defined by roundness (smoothness of corners) and sphericity (shape similarity to a sphere).

Surface Features and Support Types

Striations are linear scratches indicating glacial transport.
Chatter marks are crescent-shaped grooves from rock impacts.
Frosting on quartz sand grains results from wind transport creating tiny pits.
Grain-supported sediments have framework grains in contact, while matrix-supported sediments are surrounded by finer matrix particles.

Packing Arrangements

Cubic packing has a loose arrangement with 48% pore space.
Rhombohedral packing is more space-efficient, with only 26% pore space.
Tabular grains can be randomly oriented, parallel to bedding, or imbricated (angled overlapping).

Biogenic Fabrics

Sediments can display biogenic fabrics formed through organism activity.
Examples include algal or bacterial mats and coral reefs.

Porosity and Permeability

Porosity measures void space as a percentage of total volume, affecting fluid capacity in rock (oil, gas, water).
Permeability indicates how easily a material transmits fluids under pressure.

Description

Explore essential terms related to grain sizes, shapes, and their arrangements in sedimentology. This set of flashcards covers key concepts such as the Wentworth Size Scale and different types of sediments and rocks. Perfect for geology students looking to reinforce their knowledge.