gy 402: sedimentary petrology - university of south alabama(from collinson, j.d. and thompson, d.b....

GY 402: Sedimentary Petrology

Lecture 4: Sedimentary Rock Classification

Instructor: Dr. Douglas W. Haywick

UNIVERSITY OF SOUTH ALABAMA

Last Time (in class)

1. Six modes of sediment movement 2. Real simple fluid dynamics (ideal conditions)

3. Initiation of sediment movement 4. Nasty mathematical relationships (Shield’s Diagram)

5. Useful empirical relationships (Hjulstrom’s Diagram)

Sediment Motion

• Rest (no movement) • Roll • Slide • Saltation (“bouncing”) • Suspension • Mass flow (viscous flow)

Modes of Viscous Flow

(from Collinson, J.D. and Thompson, D.B. 1982. Sedimentary Structures. George Allen and Unwin 194p)

Ideal Fluid Flow


Ideal Fluid Flow (f

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This cartoon is critical and is the basis for grain size analysis!

Stoke’s Law

Vg = gd2(-)

18

g = gravitational constant (9.8 m/s2)

d = particle size diameter (mm)

= grain density (g/cm3)

= fluid density

= dynamic fluid viscosity

Vg = settling velocity

Stoke’s Law

Vg kd2

Vg is proportional to grain size

Composite curves (Stoke’s + Impact)

10-4 10-3 10-2 10-1 100 101 102 103

103

102

101

100

10-1

10-2

log d (mm)

log

Vg

(cm

/s)

Laminar flow

Turbulent flow

Grain Size Analysis

Sand and gravel are determined via sieving

sand fractions: vc, c, m, f, vf,

gravel fractions: not routinely done

Analysis done using simple excel spread sheet (will be available on departmental computers and/or e-mailed to you)

Grain Size Analysis

Fluid Flow & “entrainment”

(from Blatt, H, Middleton, G. and Murray, R., 1980. Origin of Sedimentary Rocks. Prentice Hill, 782 p)

Entrainment is synonomous with: “initiation of grain movement”

Sediment Entrainment


Shear Velocity

Sediment Entrainment (Shield’s Diagram)


Sediment Entrainment (Hjulstom’s Diagram)


Sediment Entrainment (Hjulstom-Sundborg Diagram)


Today’s Agenda 1. Why bother with sedimentary classification? 2. Siliciclastic sedimentary rock schemes 3. Volcaniclastic sedimentary rock schemes 4. Carbonate rock schemes

1.5 mm FOV, PPL

Siliciclastic Rock Classification

1.5 mm FOV, PPL

Particle size classification = energy of deposition


1.5 mm FOV, PPL


Grain type classification

= origin of sediment

Orthoclase

Porosity

Lithic

Quartz


1.5 mm FOV, PPL


Grain type classification

= origin of sediment

The Problem: Sedimentary rocks come in more “flavors” than any other type of rock.

How do you classify all of them?


Sedimentary Rock Classification

Grain size specific and/or…


Grain size specific and/or… Particle type specific (e.g. need specific schemes for major

sedimentary rocks classes)


Particle type specific 1. Siliciclastic sedimentary rocks (Quartz, Feldspars, Clays,

Lithic Fragments, Micas, etc.)

2. Shales and Mudstones (grain to “matrix” content)

3. Volcaniclastic sedimentary rocks (vitric fragments and ash, phenocrysts, lithics )

4. Carbonate sedimentary rocks (skeletal grains, non-skeletal grains and matrix)

5. Organic sedimentary rocks (kerogen content, coal grade etc.)

Siliciclastic Sedimentary Rocks

Source: Blatt, H., Middleton, G and Murray, R., 1980: Origin of Sedimentary Rocks. Prentice Hill, 782 p.

(Arenites)



(Arenites)

GY 402 seal of approval


>75% mud matrix


Mudstone


15 to 75% mud matrix


Wackes


<15% mud matrix


Arenites


Q = Quartz

F = Feldspars (orthoclase + plagioclase)

R/L = Lithic Fragments


Q = Quartz + chert (sometimes)




Q = Quartz


R/L = Lithic Fragments + chert (usually)


Q = Quartz



Granite mountain


Q = Quartz



Granite mountain

Sediment apron


Q = Quartz



Granite mountain

2 cm


Q = Quartz



Granite mountain

2 cm

an “F” grain

(microcline)


Q = Quartz



Granite mountain

2 cm

an “F” grain (albite)


Q = Quartz



Granite mountain

2 cm

a “Q” grain


Q = Quartz



Granite mountain

2 cm

an “R” grain

Volcaniclastic Sedimentary Rocks

Carbonate Sedimentary Rocks


Folk Classification Scheme


GY 402 seal of approval

Source: Prothero, D.R. and Schwab, F., 1996. Sedimentary Geology. W.H. Freeman, 575 p.


Equivalent to sandstone/mudstone in siliciclastic rock schemes



Equivalent to conglomerates in siliciclastic rock schemes



No equivalents in siliciclastic rock schemes


Upcoming Stuff

Homework 1) Write 2 Ass. (Hypothesis write up) Due Thursday

2) Write 1 Assignment redo (Paper Structure) Due Thursday 3) Peer 1 Assignment Due Tomorrow

Today’s Lab

Grain Size Analysis (First column run starts at 12:30: BE THERE!)

Next Lecture: Bed form Development (5)

Writing Assignment 2 Part 1: Hypothesis and Test

Writing Assignment 2 Part 2: Methods

GY 402: Sedimentary Petrology

Lecture 4: Classification of Sedimentary Rocks

Instructor: Dr. Doug Haywick

[email protected]

This is a free open access lecture, but not for commercial purposed. For personal use only.

gy 402: sedimentary petrology - university of south alabama(from collinson, j.d. and thompson, d.b....

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