CoolWater Carbonates Polar carbonates associated with ice sheets

Cool-Water Carbonates

Polar carbonates associated with ice sheets and icebergs Lower Permian, Tasmania Muddy limestone Iceberg rainout Dropstone

Classical carbonate environments are tropical Contain abundant abiotic precipitates (ooids, micrite, etc. ) Contain abundant aragonitic biota of photosynthetic organisms Termed “Photozoan”

Carbonates can also form in cool water where siliciclastic influx is limited Lack abiotic precipitates and contain calcitic biota of heterotrophic animals (rare photosynthetic) Termed “Heterozoan”

Physiology and temperaturesensitivity of carbonate allochems Peloid Micrite Ooid Abiotic Green Algae Minimal control Red Algae Larger Foraminifera Small Foraminifera Solitary Coral Colonial Scleractinian Coral (Mz-Cz) Colonial Rugose Coral (Pz) Hypercalcified Colonial Sponges Some control Brachiopod (Pz) Mollusc (Mz-Cz) Bryozoan (Paleozoic) Bryozoan (Cenozoic) Barnacle (Cenozoic) Strong control HETEROZOAN Cool-water PHOTOZOAN Subtropical Tropical

Temperature is not the only control on photozoan/heterozoan carbonates Nutrients: heterozoan assemblage replaces photozoan in eutrophic settings Photozoan organisms gain energy from sunlight, but cannot compete with faster-growing heterotrophic animals as nutrient levels rise

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)