Muddy limestone Dropstone Polar carbonates associated with ice sheets and icebergs Lower Permian Tasmania Classical carbonate environments are tropical Contain abundant abiotic precipitates ID: 1026897
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1. Cool-Water Carbonates
2. Iceberg rainoutMuddy limestoneDropstonePolar carbonates associated with ice sheets and icebergsLower Permian, Tasmania
3. Classical carbonate environments are tropicalContain abundant abiotic precipitates (ooids, micrite, etc.)Contain abundant aragonitic biota of photosynthetic organismsTermed “Photozoan”
4. Carbonates can also form in cool water where siliciclastic influx is limitedLack abiotic precipitates and contain calcitic biota of heterotrophic animals (rare photosynthetic)Termed “Heterozoan”
5. HETEROZOANPHOTOZOANCool-waterTropicalSubtropicalBryozoan (Cenozoic)OoidPeloidGreen AlgaeLarger ForaminiferaBryozoan (Paleozoic)Colonial Scleractinian Coral (Mz-Cz)Colonial Rugose Coral (Pz)Small ForaminiferaBrachiopod (Pz)Mollusc (Mz-Cz)MicriteAbioticMinimal controlHypercalcified Colonial SpongesSome controlSolitary CoralStrong controlBarnacle (Cenozoic)Red AlgaePhysiology and temperature-sensitivity of carbonate allochems
6. Temperature is not the only control on photozoan/heterozoan carbonatesNutrients: heterozoan assemblage replaces photozoan in eutrophic settingsPhotozoan organisms gain energy from sunlight, but cannot compete with faster-growing heterotrophic animals as nutrient levels rise
7. Cool-water carbonates lack early cement because aragonitic grains are not present (which normally dissolve and raise saturation during early diagenesis, leading to cement formation)Mechanical grain compaction and suturing (pressure solution)