402-pp20 - UNIVERSITY OF SOUTH ALABAMA GY 402: Sedimentary...

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Unformatted text preview: UNIVERSITY OF SOUTH ALABAMA GY 402: Sedimentary Petrology Lecture 20: Carbonate Petrography 1: Tidal Flats Last Time Deltas Deltas defined Classification of Deltas Deltaic Sedimentology Deltas Delta: siliciclastic depositional environments formed at the point where rivers meet bodies of water http://www.tulane.edu/~sanelson/images/delta.gif http://www.tulane.edu/~sanelson/images/delta.gif Deltas The balance between the 3 processes is unique for each delta. End member deltas are characterized by distinct morphologies. Delta Morphology River-dominated Wave-dominated Tide-dominated http://www.geology.pitt.edu/ http://www.geology.pitt.edu/ Deltaic Facies Deltas consist of several key facies Prodelta Distributary Mouth Bar Channel Levees Crevasse Splays Flood Plain Walker, R.G., 1979. Facies Models, Geoscience Canada Reprint Series 211 p., Delta Sections End member classifications Walker, R.G., 1979. Facies Models, Geoscience Canada Reprint Series 211 p., Delta Model http://www.geology.pitt.edu/ http://www.geology.pitt.edu/ 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. Prothero, Carbonate Sedimentary Rocks Source: Prothero, D.R. and Schwab, F., 1996. Sedimentary Geology. W.H. Freeman, 575 p. Prothero, Carbonate Sedimentary Rocks Source:Scholle P.A. and James, N.P. 1995. SEPM Photo CD-1. CD- 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. CD- Tidal Flat Environments Source: Scholle P.A. and James, N.P. 1995. SEPM Photo CD-1. CD- Tidal Flat Environments Source: Scholle P.A. and James, N.P. 1995. SEPM Photo CD-1. CD- Tidal Flat Environments Source: Scholle P.A. and James, N.P. 1995. SEPM Photo CD-1. CD- Tidal Flat Environments Source: Scholle P.A. and James, N.P. 1995. SEPM Photo CD-1. CD- Tidal Flat Environments Source: Scholle P.A. and James, N.P. 1995. SEPM Photo CD-1. CD- 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 Aragonite Calcite (nonferroan) Calcite (ferroan) Magnesium calcite Dolomite Ferroan Dolomite Geochemistry CaCO3 CaCO3 Ca(Fe2+)CO3 Ca(Mg2+)CO3 CaMg(CO3)2 CaMg(Fe2+)(CO3)2 Stain color Pink to red (brown highlights) Pink to red Purple to blue Pink to red (yellow with Clayton Yellow) Not stained Turquoise Carbonate Thin sections calcite PPL note 1 mm 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? Calcite ppl 1 mm Tidal Flat Petrography No! Anhydrite & gypsum ppl 1 mm Tidal Flat Petrography ppl xn 1 mm The moral of the story is that you still have to check your thin sections under crossed polars too! Upcoming Stuff Homework 1) Tidal flat thin sections due Thursday 2) Volcaniclastic discussion re-dues due Thursday 3) St Stephens Quarry re-dues due Friday Lab This Week Tidal flat and evaporite thin sections Next Lecture: Non-skeletal Carbonates ...
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