GY 402: Sedimentary PetrologySedimentary Structures. George Allen and Unwin 194p) Grain size = a...

transcript

GY 402: Sedimentary Petrology

Lecture 3: Fluid Flow and Sediment Entrainment

Instructor: Dr. Douglas W. Haywick

UNIVERSITY OF SOUTH ALABAMA

Last Tuesday

A) Basic sediment grain size B) Ternary plots (grain size classification) C) Interpreting grain size data (case studies)

D) Grain size parameters (statistics)

Udden-Wentworth grain size (Wentworth, 1922)

Gravel: (>2.00 mm)

Sand: (0.063 mm – 2.00 mm)

Silt: (0.004 mm – 0.063mm)

Clay: (< 0.004mm)

Sand-Silt-Clay Scheme 1 Folk (1954)

Symbol Index

C-clay; Z-silt; M-mud; S-sand;

sC-sandy clay; sM-sandy mud; sZ- sandy silt;

cS-clayey sand; mS-muddy sand;

zS-silty sand

Symbol Index

C-clay; Z-silt; S-sand;

sC-sandy clay; zS-silty sand; sZ- sandy silt; zC- silty clay

cS-clayey sand; szc-sand-silt-clay;

cZ-clayey silt

Sand-Silt-Clay Scheme 2

Sheppard (1954)

Symbol Index M-mud; G-gravel; S-sand;

sM –sandy mud; mS-muddy sand;

(g)M-slightly gravelly mud; (g)S-slightly gravelly sand;

(g)sM-slightly gravelly sandy mud; (g)mS-slightly gravelly

muddy sand;

gM-gravelly mud; gms-gravelly muddy sand; gS-gravelly sand;

mG-muddy gravel; MsG-muddy sandy gravel; sG sandy gravel

Gravel-Silt-Fines Scheme

Folk (1954)

Descriptive parameters

Source: Blatt, Middleton and Murray (1980)

Roundness (comparison of determination

techniques)

Today’s Agenda

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)

What is Viscosity?

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

Modes of Viscous Flow

Ideal Fluid Flow

Ideal Fluid Flow (f

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

Ideal Fluid Flow (f

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

Enter Stoke’s Law

Stoke’s Law

Vg = gd2(-)

Stoke’s Law

Vg = gd2(-)

g = gravitational constant (9.8 m/s2)

Stoke’s Law

Vg = gd2(-)

d = particle size diameter (mm)

Stoke’s Law

Vg = gd2(-)

(sigma) = grain density (g/cm3)

Stoke’s Law

Vg = gd2(-)

= grain density (g/cm3)

(rho) = fluid density

Stoke’s Law

Vg = gd2(-)

= fluid density

(mu) = dynamic fluid viscosity

Stoke’s Law

Vg = gd2(-)

= fluid density

= dynamic fluid viscosity

Vg = settling velocity

Stoke’s Law

Vg = gd2(-)

Stoke’s Law

Vg = gd2(-)

18 g is a constant

Stoke’s Law

Vg = gd2(-)

18 g is a constant

= grain density (not a true constant, but…)

Stoke’s Law

Vg = gd2(-)

18 g is a constant

= fluid density (not a true constant, but…)

Stoke’s Law

Vg = gd2(-)

18 g is a constant

= fluid density (not a true constant, but…)

= dynamic fluid viscosity (not a true constant, but…)

Stoke’s Law

Vg kd2

Vg is proportional to grain size

Stoke’s Law

Vg kd2

Vg is proportional to grain size

or, alternatively, grain size is proportional to settling velocity

Stoke’s Law (Graphic Representation)

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

log d (mm)

Actual settling characteristics

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

log d (mm)

Impact Law (Graphic Representation)

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

log d (mm)

Vg = 1.33-

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

log d (mm)

Vg = 1.33-

The result of turbulence and grain interaction as large grains fall through a fluid

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

log d (mm)

Vg = 1.33-

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

log d (mm)

Vg = 1.33-

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

log d (mm)

Composite curves (Stoke’s + Impact)

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

log d (mm)

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

log d (mm)

Laminar flow

Turbulent flow

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

log d (mm)

Settling Curve (Graphic Representation)

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

log d (mm)

Settling Curve

(AKA Rubey’s Curve)

Grain Size Analysis

At 23 oC, all sand and gravel will fall at least 10 cm in 4 minutes, 28 seconds

At 23 oC, all silt, sand and gravel will fall at least 7.5 cm in 5 hours, 43 minutes

Grain Size Analysis

Sand and gravel are determined via sieving

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

gravel fractions: not routinely done

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

0.005.00

10.0015.0020.0025.0030.0035.0040.00

grain size

Real Fluid Flow & “Entrainment”

Sorry, but we have to talk a bit about physics (and about how airplanes fly)

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)

Entrainment

Deposition

Traction

Deposition

Suspension

Grain size = a

Entrainment = ae

Grain size = a

Entrainment = ae

Entrainment velocity = Vae

Grain size = a

Suspension = as

Grain size = a

Suspension = as

Suspension velocity = Vas

Grain size = a

Settling = ad

Settling velocity = Vad

Upcoming Stuff

Homework 1) Write 2 Ass. (Hypothesis write up) Due Thursday 11 AM

2) Write 1 Assignment redo (Paper Structure) Due Thursday 11 AM 3) Peer 1 Assignment Due Friday 5 PM

Today’s Lab

Grain Size Analysis

Online Lecture (watch Wednesday): Bed form Development (5)

Thursday Activity

Activity 2: Hand specimens (bring your hand lens)

Writing Assignment 2

Hypothesis

Writing Assignment 2

Methods

GY 402: Sedimentary Petrology

Lecture 3: Fluid Dynamics

Instructor: Dr. Doug Haywick dhaywick@southalabama.edu

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

GY 402: Sedimentary PetrologySedimentary Structures. George Allen and Unwin 194p) Grain size = a...

Documents