Sediments

1. Sediments

2. Sediments • 4 Main Concepts to Discuss • Sediments as historical records • 2 dominating types of sediment • Marine sediments on land • Sediments ages

3. Sediment Cycle • Over geological time, mountains rise as lithospheric (crustal) plates collide, fuse, and subduct. • Water and wind erode the mountains and transport resulting sediment to the sea. • The sediments are deposited on the seafloor, where they travel with the plate and are either uplifted or subducted. Thus, the material is made into mountains again.

4. Sedimentary Environments: Continental Margins Sedimentary conditions vary according to: Tectonic Status: Active or passive Climate: Glacial: Scour & moraine dumped sed. Large River Flux: Large sediment source & delivery (river systems) Low Sed. & Warm: Carbonates

5. Margin Comparison • Passive Margins • Tend to be dominated by depositional processes • Shelf surface sediments are the result of present day depositional processes (rivers), but also reflect depositional conditions of the recent lower sea level (~15,000 years ago). Known as relict sediments. At that time in higher latitudes, glaciers scoured shelves & deposited sediments (moraines). In lower latitudes rivers flowed farther across the shelves & soils formed on the shelves. • Active Margins • Tend to be dominated by erosional processes • Erosional products are often attached to the overriding plate & may include those from the subduction ocean crust, as well as terrigenous sediments transported by gravitational movements down the slope.

6. Terrigenous Sediments are transported to the ocean via: Deep-sea sediments: sedimentation rates: 1-20 mm/1000 yr Slope sediments: accumulate at rate: 100 mm/1000 yr • Rivers in their particulate loads Ions are also transported to the oceans via rivers & contribute to the salt mass balance.

7. Terrigenous sediments are generally distributed across the shelf based on their grain size Grain Size: Gravel, sand, silt & clay In general there is a gradation of grain sizes from source to place of deposition (i.e bigger heavier grains remain nearer source). Clay Sized Characteristic of continental slope, rise, and deep sea. Found on shelf where energy is low (away from waves & currents) Silt Sized Characteristic of continental slope & rise. Found on shelf where energy is low (away from waves & currents) Sand Sized Characteristic of beach & shelf

8. Marine sedimentologists describe sediment by its grain size, shape, mineralogy, & sorting in order to interpret the source area & transportation process. Quartz: Is the most resistant mineral to abrasion & leaching so dominant mineral in most sands. Gulf of Mexico heavy mineral provinces are used to interpret sediment distribution processes and transportation routes.

9. Where water is quiet (little energy) silt & clay settle to the floor. Silt-Sized: Characteristic of continental slope & rise. Found on shelf where energy is low (away from waves and currents).

10. Clay-Sized – ubiquitous on shelves, slopes, & deep-sea deposits. • Indicates low energy environments when abundant • Have high surface area (flat), so they readily absorb substances & can also form aggregates. • Clays are commonly associated with organic matter, organics cling to the clay. • Also deposited together in fecal pellets (matter). Falls as Marine Snow Larvacean fecal pellets and marine snow from a sediment trap sample in the North Pacific Ocean.

11. Terrigenous Sediments also transported to the ocean via: 2. Glaciers: Glacial marine sediments – around Antarctica are deposited in a belt about 300-1000 km wide. During glacial times the ice shelf advances toward the ocean; during warmer times, glaciers retreat & the sediments are reworked by ocean processes (waves and currents)

12. Terrigenous Sediments also transported to the ocean via: 3. Wind: Dust falls into the ocean, especially in large dust storms • Sediments known as eolian • Small component of sediment delivered to the ocean: North Pacific accumulation 1 mm/1000 years & Atlantic accumulation rates ~2.5 mm/1000 years • Accumulation probably vary through time, depending on changes in global climate

13. Significant amounts of dust are transported to the Caribbean from Africa via dust storms • N. Hemisphere winter greatest concentration of dust settles over Caribbean and equatorial S. America • N. Hemisphere summer the greatest concentration moves north over Florida • Changes caused by seasonally shifting ITCZ

14. Millions of tons of dust are transported from Africa, across the Atlantic to N. America & the Caribbean, via dust storms each year Dust storms deposit more than African soil when they settle. Iron & phosphate from the soil is thought to promote phytoplankton growth in the marine environments of the Caribbean & eastern Atlantic. (Live insects as well)

15. Millions of tons of dust are transported from Africa, across the Atlantic to N. America & the Caribbean, via dust storms each year • Viable live microbes (bacteria, fungi & viruses) are bring found in the dust. Estimates suggest there may be as many as 10 quadrillion microbes in the dust each year. • Of the identified microbes 30% are known pathogens! • Description: Microbes isolated from African dust aerosols grow on a filter placed on agar medium. The dark, fuzzy colonies are fungi and the colored, shiny colonies are bacteria. Photographed December 13, 2001. Air sample collected in Mali, Africa. • USGS Publication

16. Terrigenous Sediments also transported to the ocean via: 4. Volcanic Eruptions: Volcanic sediments, such as tephra and ash-fall from air • Used to correlate and absolute age date • Ash can be injected into the stratosphere, >10-15 km, causing tephra transport from 3000-6000 km.

17. Down slope transportation of Terrigenous Sediments Turbidity currents - mass movement of water Sand & mud are dislodged from continental shelf & slope by a disturbance, such as an earthquake or landslide.

18. Turbidity Current • The material is thrown into suspension, creating a mixture that is denser than water. • The dense mixture flows down the slope, eroding at the flows head. • The flow generally continues across the continental rise, coming to rest as the slope decreases, causing flow to loose momentum. • Head moving past erodes pelagic mud • Coarse sediment is deposited first, followed by successively finer deposits • Distinct deposits called turbidites are formed. • They are characterized by graded bedding.

19. The bulk of terrigenous sediments are deposited on the continental shelf, slope and rise. Thickness is a reflection of supply (elevation coupled with water availability (climate) & distance from land.

20. Beyond the Continental Shelf: • Most sediments found in the deep ocean are deposited from the pelagic environment (upper water column of the open ocean). • Pelagic sediments are very fine grained (clays), the median grain size is <5µm (1mm=1000µm) with <25% of the >5µm fraction being terrigenous • Sediments on older abyssal plains, are typically 1000 m thick.

21. Some pelagic sediments contain biogenic grains: grains that are biological in origin. These include calcareous, siliceous, & phosphatic biological hard parts (shells). • Small floating (planktonic) organisms live in the upper water column & fall to the ocean floor after death. These biogenic grains are especially common on the slope & deep-sea. Biogenic oozes- >50% by weight of the grains are < 5µm & >30% of the grains are composed of skeletal remains (shells).

22. Biogenic ooze can be classified more specifically by shell mineralogy & then by majority type of the organism making the shells • Calcareous Ooze– microfossils made of CaCO3 shells Types of Calcareous (carbonate, CaCO3) Ooze Foraminiferal ooze – dominated by tests of planktonic foraminifera (forams-animal like Protist, most 50-500 µm) Nannofossil ooze – dominated by calcareous fossils (plant-like Protist, 5-50µm)-More resistant to dissolution thank planktonicforams Pteropod Ooze – dominated by planktonic gastropod molluscs with argonite shells (animals) – Easily destroyed by dissolution, so generally occur above 3000 m

23. 2. Siliceous Ooze – microfossils made of SiO2 (silica) opaline shells (amorphous, hydrated form) comprise >30% of Sediment Types of Siliceous Ooze Diatom Ooze(plant like protist, 5-50µm): >30% diatoms, typical of high latitudes & some cont. margins Radiolarian Ooze(animal like protist, 40-150µm) >30% radiolarians – typical of equatorial divergence (upwelling) areas of high biologic fertility

24. How do such small objects sink to the deep sea floor (1000s of m depth)? • Tiny particles should sink very slowly or not at all due to turbulence within the water. • Particles of 5-10 nanometers (nm - 109), would require 100 years to sink to ocean floor. • Sinking rate is accelerated by fine particles combining into small bundles (zooplankton fecal pellets, 50-250 nm size • A single pellet may contain 105coccoliths • Sinking rate of pellets = 40 to 400 meters/day

25. Calcite Compensation Depth (CCD) Depth in ocean that marks where rate of dissolution of carbonate balances (=) rate of accumulation (supply) -marked by a transition from carbonate ooze to red clay CO2 in water makes carbonic acid which dissolves CaCO3 • CO2 is produced by respiration of organisms • Increased pressure increases the solubility of gases in liquids, so deeper water can hold more gas. • CO2 remains close to source (respiration or where organic matter is oxidized

26. CCD – mean depth of 4.5 km About half distance between crests of mid ocean ridge & deepest (non-trench) part of ocean Pacific –CCD typically at shallower depths, 4200-4500 m -Because water is older which causes it to collect more decaying matter and respiration N. Atlantic – CCD typically ≥ 5000 m

27. Red or brown clay may contain: Cosmogenic grains Extraterrestrial Sources: Insignificant fraction of deep sea sediments are micrometeorites called: Microtektites – small glassy bodies, 1 mm to 30 µm in diameter. Several different shapes: ovoid, teardrop, dumbbell – usually yellow brown in color Accumulation rates - .00002 mm/1000 yrs Tecktites – 2-4 cm, found in strewn fields, high velocity impacts

28. Classification of sediment formed “in place”: Authigenic • Authigenic or Hydrogenous source – ions solution in seawater from river input and hydrothermal or volcanic input. • Sediments from in-situ on the ocean floor through inorganic precipitation • Most form from slow precipitation of minerals from seawater

29. More specific types of authigenic or hydrogenous sediments • Metal Rich Sediments & iron oxides – associated with spreading centers (hydrothermal vents) • Manganese Nodules – rich in nickel, copper, cobalt, iron, & traces of others • Evaporites – sediments which form from evaporation of seawater - Restriction from main body of the ocean is required to raise the concentration of salts to the point of precipitation. Generally takes place in an arid area or area of consistent wind.

30. How do we study ocean sediments? • Tools • Clamshell Sampler • Takes shallow water samples • Piston Corer • Used to take deeper samples. Can punch through 25 m of sediment • JOIDES Resolution drilling ship • Returned cores over 1000 m

31. Why do we study ocean sediments? • The sediments give us a glimpse into recent (≤ 180 106 yrs) ocean history • Stratigraphy – Analysis of layered sedimentary deposits, ocean or land. • Deep-Sea Stratigraphy – utilizes variations in rock composition, microfossils, depositional patterns, geochemical and physical characteristics to trace or correlate distinctive sedimentary layers from place to place, establish the age of the deposits, and interpret changes in ocean and atmospheric circulation, productivity, and other aspects of past ocean behavior • This has led to an emerging new field in oceanography – PALEOCEANOGRAPHY!!! • The study of the ocean’s past by interpreting data from cores and by other means, (ice cores, rock outcrops, fossil records, etc.)

32. Conclusions • Sediments are loose accumulations of particulate material. Their depth and composition tell us of relatively recent events in the ocean basin above. • The most abundant sediments are terrigenous (land) and biogenous (living organisms). The volume of terrigenous sediment exceeds that of biogenous sediment, but biogenous material covers a greater area of seabed. • Marine sediments have been uplifted and exposed on land. Arizona’s Grand Canyon is made of marine sediment. • Because marine sediments are usually subducted along with the seabed onwhich they lie, the oldest sediments are relatively young – rarely older than 180 million years.