Chapter 5: Marine Sediments Fig. 5-23

Marine sediments Eroded rock particles and fragments Transported to ocean Deposit by settling through water column Oceanographers decipher Earth history through studying sediments

Marine Sediments Fig. CO-4

Sediments reveal Earth history Sediments lithified Mineral composition Sedimentary texture Past climate Plate motions Age of seafloor Fossil evolution and extinction

Sediments classified by origin Lithogenous Biogenous Hydrogenous Cosmogenous

Lithogenous sediments Rock fragments from land Transported to oceans by Rivers Wind Ice Gravity flows (e.g. turbidity currents)

Lithogenous sediments Fig. 4.5

Rivers transport much sediment Fig. 5-5

Most accumulate near continental margins Wind-blown dust in deep ocean makes abyssal clay (red clay) Mostly quartz (SiO 2 ) Chemically stable Abrasion resistant Lithogenous sediments

Relationship of fine-grained quartz and prevailing winds Fig. 4.6b

Sediment Texture  Grain size indicates energy of transportation and deposition Fig. 5-8

Sediment texture Grain size sorting Indication of selectivity of transportation and deposition processes Textural maturity Increasing maturity if Clay content decreases Sorting increases Non-quartz minerals decrease Grains are more rounded (abraded)

Textural maturity Fig. 5-9

Distribution of sediments Neritic Shallow water deposits Close to land Dominantly lithogenous Typically deposited quickly Pelagic Deeper water deposits Finer-grained sediments Deposited slowly

Neritic lithogenous sediments Beach deposits Mainly wave-deposited quartz-rich sands Continental shelf deposits Turbidite deposits Glacial deposits High latitude continental shelf

Pelagic lithogenous sediments Sources of fine material: Volcanic ash (volcanic eruptions) Wind-blown dust Fine-grained material transported by deep ocean currents Abyssal clay (red clay) Oxidized iron Abundant if other sediments absent

Biogenous sediments Hard parts of once-living organisms Shells, teeth, bones Fig. 5-10

Biogenous marine sediments Commonly either calcium carbonate (CaCO 3 ) or silica (SiO 2 or SiO 2 ·nH 2 O - opal) Usually planktonic (free-floating)

Calcareous ooze (CaCO 3 ) Microscopic protozoans, foraminifera Microscopic algae, coccolithophores Siliceous ooze (SiO 2 ) Microscopic protozoans, Radiolaria Microscopic algae, diatoms Biogenous sediments

Calcium carbonate in biogenous sediments Coccolithopho res (algae) Photosynth etic Coccoliths (nano- plankton) Rock chalk Fig. 4.8a

Calcium carbonate in biogenous sediments Foraminifera (protozoans) Use external food Calcareous ooze Fig. 4.8c

Carbonate deposits Stromatolites Warm, shallow- ocean, high salinity Cyanobacteria Limestone (lithified carbonate sediments) Fig. 4.10a

Calcareous ooze and the CCD Warm, shallow ocean saturated with calcium carbonate Cool, deep ocean undersaturated with calcium carbonate Calcite compensation depth CCD--depth where CaCO 3 readily dissolves Rate of supply = rate at which the shells dissolve

Calcareous ooze and the CCD Scarce calcareous ooze below 5000 m in modern ocean Ancient calcareous oozes at greater depths if moved by sea floor spreading Fig. 4.13

Distribution of calcareous oozes in surface sediments of modern sea floor Fig. 4.14

Silica in biogenic sediments Diatoms (algae) Photosynthetic Diatomaceous earth Radiolarians (protozoans) Use external food Siliceous ooze Fig. 4.7a Fig. 4.7b

Seawater undersaturated with silica Siliceous ooze commonly associated with high biologic productivity in surface ocean Siliceous ooze Fig. 4.11

Neritic biogenic seds Modern carbonates shallow, warm ocean Coral reefs Ooid shoals Beach sands Stromatolites hypersaline Biogenous marine sediments

Pelagic biogenic seds Siliceous ooze beneath areas of surface ocean upwelling (high biologic productivity) Calcareous ooze on seafloor less than about 4500 m CaCO 3 dissolves in cold seawater Biogenous marine sediments

Distribution of biogenic seds Ooze is 30% or more biogenic material (by weight) Biologic productivity Dissolution as shells settle through ocean Dilution by non-biogenic material

Shells and silt-clay fall through seawater column to seafloor

Hydrogenous marine sediments Minerals precipitate directly from seawater Manganese nodules Evaporites Inorganic Carbonates Metal sulfides Small proportion of marine sediments Distributed in diverse environments

Very low rate of accumulation Larger nodules grow larger faster Origin is unknown Fig. 4.15a Manganese nodules

Cosmogenous sediments Extraterrestrial fragments Glassy tektites Fe-Ni micrometeorites Found in deep ocean where other sediments accumulate very slowly

Meteorite impact K-T meteorite crater off Yucatan peninsula Tektites and spherules found in marine seds Shocked quartz in marine seds Fig. 5D

Mixtures of marine sediments Usually mixture of different sediment types For example, biogenic oozes can contain up to 70% non-biogenic components Typically one sediment type dominates in different areas of the sea floor

Distribution of neritic and pelagic marine sediments Neritic sediments cover about ¼ of sea floor Pelagic sediments cover about ¾ Distribution controlled by Proximity to sources of lithogenous sediments Productivity of microscopic marine organisms Depth of water Sea floor features

Fig Distribution of neritic and pelagic marine sediments

Marine sediments often represent ocean surface conditions Temperature Nutrient supply Abundance of marine life Atmospheric winds Ocean current patterns Volcanic eruptions Major extinction events Changes in climate Movement of tectonic plates

Retrieving sediments Dredge Gravity corer Rotary drilling Deep Sea Drilling Program Ocean Drilling Program Integrated Ocean Drilling Program Studies reveal support for plate tectonics and global climate change.

Resources from marine sediments Energy resources Petroleum Mainly from continental shelves Gas hydrates Sand and gravel (including tin, gold, and so on) Evaporative salts Phosphorite Manganese nodules and crusts

Manganese nodules Fig. 4.27

End of Chapter 5: Marine Sediments Fig. 5E