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.