Grain Sizes and Arrangements Flashcards

Questions and Answers

What is the Wentworth Size Scale?

An arrangement of cubic packing

A type of sediment

A method for measuring permeability

A classification system for grain sizes (correct)

What does the term 'argillaceous' refer to?

Sediments with significant mud content.

What is argillite?

Low-grade metamorphic rock that was originally a mudrock.

What are the two meanings of the word 'clay' in sedimentology?

Grain sizes less than 4 µm and a group of layered silicate minerals Signup and view all the answers

What characteristics define clay?

Commonly formed from weathering of silicate minerals, usually small grains, often form in pore spaces during diagenesis. Signup and view all the answers

The method to measure grain size that involves fluid displacement is called ______.

Volume measurement Signup and view all the answers

Name one method of measuring grain size.

Sieving. Signup and view all the answers

What is the definition of immature sediments?

<blockquote> 5% mud, poorly sorted, angular grains </blockquote> Signup and view all the answers

Submature sediments contain more dark minerals compared to immature sediments.

False Signup and view all the answers

How is maturity of sediments defined?

By the amount of weathering, energy, and transport history Signup and view all the answers

What are the two important components of grain shape?

Roundness and Sphericity. Signup and view all the answers

What do striations indicate?

Glacial transport. Signup and view all the answers

What is the definition of porosity?

Percentage of void space relative to total volume. Signup and view all the answers

What defines permeability in geological terms?

The ability of a material to transmit a fluid under a pressure gradient. Signup and view all the answers

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.