Pelagic Sediments: Types, Distribution, Origins

Geological Oceanography OCN 622 Gary McMurtry Principal Pelagic (Deep-Sea) Sediment Types

1. Carbonate Ooze (mostly CaCO3 – Calcite, Aragonite) a. Foraminiferal (mostly Globigerina) – Calcite b. Nannofossil (Coccolithophorids) – Calcite c. Pteropod (planktonic Mollusks) – Aragonite

2. Siliceous Ooze (mostly X-ray amorphous SiO2) a. Radiolarian b. Diatom

3. Red (Brown) Clay (Mostly everything else!) a. Clay Minerals (Illite, Smectite*, Kaolinite, Chlorite) b. Quartz c. Zeolites* (Phillipsite, Clinoptilolite)

d. Barite* (BaSO4) e. Phosphates* (skeletal Apatite, Francolite) f. Ferromanganese Oxides* (micronodules) g. Volcanic Ash (glass, feldspar, pyroxene phenocrysts) h. Cosmogenic Debris ( tektites, Fe-Ni spherules) i. Refractory Organics

j. Other (e.g., Rutile (TiO2) in the insoluble residue of Mn- nodules)

4. Terrigenous** a. Hemipelagic Muds (blue, green, red, volcanic, coral) b. Glacial-Marine (marine glacial ourwash) * Authigenic (in situ) origin. ** Derived solely from land. Pacific pelagic sediments (highly schematic map!)

Source: Garrels & Mackenzie (1971) Present global aerial distribution (Arrhenius, 1963) Recent Global Distribution (Berger, 1974) Foraminifera

(CaCO3-calcite) modern planktonic morphology Nanofossils

(CaCO3-calcite) Modern Cocolithophorids Pteropods (CaCO3-aragonite) Modern planktonic mollusca Radiolarians (SiO2.nH2O-silica) Modern morphology Diatoms (SiO2.nH2O-silica) Modern morphology Early DSDP Classification (Legs 1-37) Post-Leg 37 DSDP Classification (Simplified) Post-Leg 37 DSDP Classification (Simplified) Production vs. Preservation - CaCO3

Foram. Surface Abundance Surface Sediment Distribution Microfossil Dissolution

Source: W. H. Berger et al. (1975) Generalized Reactions

Carbonates

CH2O + O2 --> CO2 + H2O Benthic respiration

2+ - CO2 + H2O + CaCO3 --> Ca + 2HCO3

Actually,

2- - CO2 + CO3 + H2O --> 2HCO3 Broecker (1974)

2+ 2- CaCO3 --> Ca + CO3

Silica

SiO2 + 2 H2O --> H4SiO4 Lysocline, Calcite Compensation Depth (CCD) Peterson’s Famous Balls Experiment & the Fossil Dissolution Index

Peterson (1966) W. H. Berger (1975) Selective Microfossil Dissolution with water depth

After: Be (1977) Carbonate Ion Profiles & the Lysocline (GEOSECS data)

Broecker & Takahashi (1978) Average Modern Basin Compositions Basin-to-Basin Fractionation (W. H. Berger)

Estuarine - Antiestuarine (Lagoonal) Circulation System Concept

Atlantic forms young, oxygenated waters, Pacific receives older, CO2- rich and hence, acidic waters. Silica-rich sediments reflect upwelling. Global Thermohaline Circulation (W. S. Broecker, 1989) Global Seawater Sources, Sinks & Effects of Particle Rain

Broecker & Peng (1982)

The pelagic particle rain feeds benthic respiration. Global Carbonate Cycle

0.11 g/cm2103 yrs (Edmond et al., 1979)

=> 90% dissolution

After: Ramsay, 1974 Global Carbonate Cycle

Morse & Mackenzie (1990) Global Silica Production

After: Calvert (1974) Global Silica Preservation

After: Calvert (1974) NOTE: Dilution of silica by terrigenous sediments near most coasts, Antarctica is the exception! Global Silica Cycle

After: G. R. Heath (1974)

Global Silica Cycle

Wollast & Mackenzie (1983) Units = 1012 g Si/year Fecal Pellet Fluxes

After S. Honjo (1976) Provides Rapid Particle Transport to Seafloor