UNIVERSITY OF SOUTH ALABAMA

GY 402: Sedimentary Petrology Lecture 19: Carbonate Petrography 1: Tidal Flats

Instructor: Dr. Douglas W. Haywick

Today’s Agenda Carbonate Petrography Begins •Carbonate classification scheme (with revisions) •Tidal flats (carbonate variety) • Carbonate staining scheme • Carbonate thin section petrography

Carbonate Sedimentary Rocks Come in many different “flavors”: •Originally unconsolidated “bioclastic” (gravel to mud-sized grains) •Cemented frameworks (e.g., reef structures) •Chemically precipitated materials (incl. evaporites) •“diagenetically” altered rocks

Carbonate Sedimentary Rocks

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

Carbonate Sedimentary Rocks

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

Carbonate Sedimentary Rocks

Source:Scholle P.A. and James, N.P. 1995. SEPM Photo CD-1.

Biogenic Carbonate Rocks Reefs & bioherms

Source:Walker, R.G., 1984. Facies Models. Second Edition. Geoscience Canada, 317p.

Biogenic Carbonate Rocks

Fore reefs & biostromes

Source:Walker, R.G., 1984. Facies Models. Second Edition. Geoscience Canada, 317p.

Biogenic Carbonate Rocks Algal bindstones (typical for algal flats)

Source:Walker, R.G., 1984. Facies Models. Second Edition. Geoscience Canada, 317p.

Tidal Flat Environments

Source:Scholle P.A. and James, N.P. 1995. SEPM Photo CD-1.

Tidal Flat Environments

Source: Scholle P.A. and James, N.P. 1995. SEPM Photo CD-1.

Tidal Flat Environments

Source: Scholle P.A. and James, N.P. 1995. SEPM Photo CD-1.

Tidal Flat Environments

Source: Scholle P.A. and James, N.P. 1995. SEPM Photo CD-1.

Tidal Flat Environments

Source: Scholle P.A. and James, N.P. 1995. SEPM Photo CD-1.

Tidal Flat Environments

Source: Scholle P.A. and James, N.P. 1995. SEPM Photo CD-1.

Carbonate Staining Combination of potassium ferricyanide and Alizarin red-S …

… it’s a surface stain.

Done because carbonate rocks are “monominerallic” (mostly composed of CaCO3 albeit in different polymorphs), and staining provides additional geochemical information.

Carbonate Staining Combination of potassium ferricyanide and Alizarin red-S …

… it’s a surface stain.

Done because carbonate rocks are “monominerallic” (mostly composed of CaCO3 albeit in different polymorphs), and staining provides additional geochemical information.

Carbonate Staining Combination of potassium ferricyanide and Alizarin red-S Blue: resolves Fe2+ content of phases

Carbonate Staining Combination of potassium ferricyanide and Alizarin red-S Red/Pink: distinguishes CaCO3 from other minerals

PPL

5 mm

Carbonate Staining Mineral

Geochemistry

Stain color

Aragonite

CaCO3

Pink to red (brown highlights)

Calcite (nonferroan)

CaCO3

Pink to red

Calcite (ferroan)

Ca(Fe2+)CO3

Purple to blue

Magnesium calcite

Ca(Mg2+)CO3

Pink to red (yellow with Clayton Yellow)

Dolomite

CaMg(CO3)2

Not stained

Ferroan Dolomite

CaMg(Fe2+)(CO3)2

Turquoise

Carbonate Thin sections

calcite

PPL

1 mm note

Carbonate Thin sections calcite Ferroancalcite

porosity ppl

2 mm

Carbonate Thin sections

zoned cement! ppl

0.5 mm

Tidal Flat Petrography

ppl

3 mm

Tidal Flat Petrography

Cryptalgal laminations

ppl

3 mm

Tidal Flat Petrography

Calcite (in fenestrae)

Dolomite ppl

1.5 mm

Tidal Flat Petrography

Calcite

Coarse “saddle” dolomite Fine dolomite ppl

0.5 mm

Tidal Flat Petrography

Primary (depositional) laminations

ppl

3 mm

Tidal Flat Petrography

mudcrack

ppl

3 mm

Tidal Flat Petrography

ppl

oncoids

2 mm

Tidal Flat Petrography

Dolomite?

ppl

Calcite

1 mm

Tidal Flat Petrography No! Anhydrite & gypsum

ppl

1 mm

Tidal Flat Petrography

ppl

xn

The moral of the story is that you still have to check your thin sections under crossed polars too!

1 mm

Upcoming Stuff Homework 1) Reading Assignment (cancelled) 2) Tidal flat thin sections due Thursday 3) Moscow Landing background (Write 6) due Thursday* 4) Grain Size Redos due Friday

Lab This Week Tidal flat and evaporite thin sections

On Line Lecture: Non-skeletal Carbonates (Lecture 21)

Thursday Open discussion

This Weekend: Moscow Landing Field Trip

GY 402: Sedimentary Petrology Lecture 19: Tidal Flats Instructor: Dr. Doug Haywick [email protected]

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