Non-Terrigenous Sediments and Rocks

1. Non-Terrigenous Sediments and Rocks Carbonate Sediments and Rocks

2. No “Simple” Classification Scheme

3. Carbonates (>50% primary carbonate minerals) Limestone (CaCO3) Chemical biochemical Dolomite (CaMg(CO3)2) Chemical Most Common non-Terrigenous Sedimentary Rocks

4. Carbonate Rock Classification • Allochems • Carbonate sand • Micrite • Micro Crystalline calcite • Cement (spar)

5. The sand-sized grains that occur in carbonate rocks are called allochemical particles or allochems. Intraclasts Ooliths Peloids Skeletal particles (bioclasts) The interpretation of the depositional setting of carbonates is based on grain types, grain packing or fabric, sedimentary structures, and early diagenetic changes. Carbonate Rocks Constituents

6. Carbonate Rocks Constituents • The sand-sized grains that occur in carbonate rocks are called allochemical particles or allochems. • Intraclasts (rock fragments): • formed, transported and redeposited within the basin • Ooliths: concentrically laminated carbonate structures, including: • oolites -concentrically laminated structures,less than 2mm in diameter, thought to be abiogenic in origin • pisolites - same as oolites, but greater than 2mm in diameter • oncolites - spheroidal stromatolites (> 1-2 cm) • Peloids: • silt to fine grained sand sized carbonate particles with no distinctive internal structure; most thought to be fecal pellets • Skeletal particles (bioclasts): • whole microfossils, whole megafossils, broken shell fragments • algae, forams, corals, bryozoans, brachiopods, gastropods, pelecypods, ostracods, etc.

7. Carbonate Rocks Constituents • Intraclasts (early lithified carbonate fragments): • irregularly-shaped grains that form by syndepositional erosion of partially lithified sediment.

8. Carbonate Rocks Constituents • Ooliths: concentrically laminated carbonate structures, including: • oolites -concentrically laminated structures,less than 2mm in diameter, thought to be abiogenic in origin • pisolites - same as oolites, but greater than 2mm in diameter • oncolites - spheroidal stromatolites (> 1-2 cm)

9. Pelloids: silt to fine grained sand sized carbonate particles with no distinctive internal structure; most thought to be fecal pellets Carbonate Rocks Constituents

10. Skeletal particles (bioclasts): whole microfossils, whole megafossils, broken shell fragments algae, forams, corals, bryozoans, brachiopods, gastropods, pelecypods, ostracods, etc. Standard microfacies (fossil fragment type -> environment) Carbonate Rocks Constituents

11. Carbonate Rocks Constituents • Micrite: • microcrystalline carbonate particles of clay (<1-4 micron) size (subtranslucent matrix) formed by • chemical or biochemical ppt • abrasion of allochems • implies deposition in a low energy environment just like in terrigenous mudstones

12. Carbonate Rocks Constituents • Cement: • sparry (twinkling crystalline) orthochemical material formed in interstitial pore spaces of “grainy” carbonate sediment • cement in pores indicates original void space • also recrystallized allochems or micrite

13. Carbonate Rocks Constituents • Insoluble Residues – • minor amounts of clay minerals and quartz occur in limestones, as insoluble residues, (so called because they do not dissolve in HCl) • Most insoluble material is chert (siliceous) • chert mostly originates from the shells of silica secreting organisms including diatoms, radiolarians, and some sponges.

14. Type I limestone, Sparry Allochemical rocks: allochems > 50%, spar cement > micrite mud [4 rock types] more energetic environment, some sorting Type II limestone, Micritic Allochemical rocks: allochems >10%, micrite mud > spar cement [4 rock types]lower energy environment, more poorly sorted than Type I Type III limestone: Micrite: allochems < 10% very low energy at the site of deposition (carbonate mudrock) “Biolithite”: Reef rock Classification Schemes: Folk Classification

15. Classification Schemes: Dunham Classification • Dunham Classification • Texture and allochem type incorporated into classification • sediment deposited in calm vs agitated waters • mud-bearing vs mud-free sediment • grain vs mud support • bound (biologically) • depositional texture recognizable

16. 5 Principles of Dunham Classification • Presence or absence of lime mud; is there any mud at all. Calm waters allow for the accumulation of lime mud and indicates the absence of current induced agitation • Grain Support: self supporting framework: • fluid circulation, diagenesis • Grain kind: standard microfacies types • Grain size, rounding, and coating: hydrologic interpretations • Biogenically ppt masses bound at time of deposition: • Boundstone • organic framework • laminations not consistent with gravity (stromatolite) • roof over sediment filled cavities

17. Folk Textural Spectrum Classification • Concocted to incorporate textural characteristics comparable to textural maturity in TC sediments • Mud component • Sorting • Rounding

18. Dolomitic Rocks • Typically devoid of primary textures and structures; if primary textures are preserved • <10% dolomite: “dolomitized” (rock name) • >10% dolomite: dolomitic (rock name) • recrystallized carbonate: dolostone • saddle dolomite: “burial” dolomite of hydrothermal origin