Sediments

1. Sediments

2. What to Watch for? • You will see the true face of the ocean floor • Covered by sediments, gravel, silt and mud • Sediment particles from land, from biological activity, and even from space • Sediments can help us define what occurred in recent history in the ocean basin • Sediment thickest at continental margins • Thinnest over active oceanic ridges • Sedimentary “memory” of ocean basin is short • Think about • Movement, transport, how did the sediment arrive, where did it come from, and how can we tell the story of the ocean basin • Think about daily contact with marine sediment • Building materials, pool filters, toothpaste, oil, natural gas, paint

3. Sediment • Particles of organic or inorganic matter that accumulates in a loose, unconsolidated form.

4. Major Sediment Input to the Oceans Source Estimated Amount (109 tons/yr) Rivers 18.3 Glaciers and ice sheets 2.0 Wind blown dust 0.6 Coastal erosion 0.25 Volcanic debris 0.15 Groundwater <0.48

5. What do sediments look like? • Depends where you are • Atlantic ridge • Sponges and corals may be growing over the dusting of sediment • Smooth ocean floor • Brittle stars feed off surface bacteria and fallen particles of organic sediment • May see ripples if the bottom has swift currents • Colors differ • Biological • Often white or cream colored • Silica deposits • Often gray • Clays on the ocean floor • Red due to oxidation • Chocolate brown

6. Sediment Classifications • Origin • Size • Gravel - Bigger than 2 mm • Sand – .062 – 2 mm, Big in Ocean Terms • Silt – .004 - .062 mm, Gritty on Teeth • Clay - <.004 mm • Use Size to Determine the Energy of the Environment • Well sorted sediments • Sediments mixture that contains sediments of one size • Poorly sorted sediments • Sediments mixtures that contains a variety of of sizes

8. Deep Sea Sedimentation • The Deep sea has two main sources of sediment: • External- terrigenous material transported to oceans via rivers and wind • Internal-biogenic and authigenic from the sea.

9. Origin of the Particles (Genetic) • Proposed by Sir John Murray and A.F. Renard while studying sediments during the Challenger expedition • Terrigenous/Lithogenous – terra = Earth, generare = to produce • From Earth • Biogenous – Bio = life, generare = to produce • From life • Zebra Muscles • Diatoms • Hydrogenous/ Authigenic – Hydro = life, generare = to produce • Precipitates chemically from sea water • Iron Stains in Sink in regular water • Cosmosgenous – cosmos = universe, generare = to produce • Comes from Outer Space • Micro meteorites

10. Origin Classification • Terrigenous: Sands and mud produced by weathering and erosion of rocks on land. • Biogenic: CaCO3 (calcium carbonate) and SiO2 (silica) muds and oozes composed of hard parts of organisms. • Authigenic: formed by precipitation of minerals in seawater (Manganese (Mn) and Phosphorus (P) nodules). • Volcanogenic: ejected from volcanoes (ash). • Cosmogenous: pieces of meteorites that survive trip thru atmosphere.

11. Terrigenous Particles • Coming from islands or nearby continents • Most abundant = Granite • Sources of quartz and clay in the oceans • Earth’s crust is made of minerals • Inorganic crystalline materials that have a specific chemical composition • Both particles are small enough that they get transported to deep ocean floor • Transportation?? How did they get there what was the Transport Agent… • Rivers – Clay  Sand • Mississippi River Delta: Birds Foot • Trapped Near the Continents

14. How sediments reach deep ocean • Turbidity Currents • Density and Gravity pull particles down Slope • Causes flatness of the abyssal plains • Resistant sandstone - rubble • Turbidity current deposit rubble

16. Terrigenous Particles • Wind (Eolian) • Covers Long Distances • Small Grain Sizes • Slow Accumulation

17. Africa's West Coast: Sediments that wind transports from the Sahara Desert

19. Terrigenous Particles • Transportation • Glaciers • Deposits of sediment only happens when glaciers reach sea level • Iceberg Rafting • Rivers and streams • Eloation

20. Coccolithophorid Biogenous Particles • 2nd Most abundant source for sediments • Skeletal Components • Sediment Rich in skeletal material “ooze” • Sample must contain more than 30% biogenic material • Two Major Players • CaCO3 Calcium Carbonate: Plants • Foraminifera: Animals • To make an “ooze” • Production ~ Same everywhere • Preservation ~ More soluble at high pressure and low temperature • As it sinks carbonate needs shallower waters ~ 3500 – 4500 m starts to dissolve • When carbonate no longer can be preserved = CCD carbonate compensation depth • Little Dilution – Rapid input of Something else • Get away from terrigenous areas Foraminifera

21. Foraminifera (zooplankton with CaCO3 shell)

22. White Cliffs of Dover

23. Biogenous Particles • Silica • Opal – SiO2 . n H2O • Zooplankton • Diatoms – Plants • Radiolarians • Zooplankton • To make a Siliceous “ooze” • Production ~ High Productivity Zones they Do Well • Preservation ~ Entire Ocean is Under saturated with Silica • Once animal dies it starts to be dissolved • Preservation takes place with over whelming the system • Make a lot so a Few can Survive • Getting to the sediment is the key • Micro environment once diatom reaches sediment won’t dissolve because others already have been and water is saturated with silica

24. Diatoms (phytoplankton with SiO2 shell)

25. Cleaning agents and toothpaste often contain diatoms because of their sharp surfaces

27. Biogenous Sediments • Soft Tissue • Gas Hydrates • Near continental Margins • A lot of methane stored in sediments • Might be a useful source of fuel • Possible Problems • Limited Stability Range • Methane is much greater green house gas = AGGRESSIVE • Large Gaseous Emissions!

31. Hydrogenous/Authigenic Sediments • Formed by chemical or biochemical reactions on ocean floor/ formed in the place they now occupy • Nodules of ferromanganese (Fe and Mn) or phosphorite (P). • Mn found deep sea beds • P found continental margins • Concentric layers of metal oxides accrete on particles over millions of years (1-4 mm per 106 y). • Contain economically important metals Cu, Zn, Co and Pb. (but too expensive to harvest). • Origin uncertain (biological?)

32. Ferromanganese nodules Floor of South Pacific Ocean. Nodule size 1-5 cm diameter

33. Ferromanganese nodules Cross-section

34. Hydrogenous • Pebble like • Manganese Nodules • mm per million years, they grow slow • Evaporites – Hydrogenous deposit, precipitates out as water evaporates • Salts: Evaporates from isolated arms of the ocean • Sea salts • Red sea • Persian Gulf • Gypsum • Oolite sands – Calcium carbonate precipitates from shell fragments, white and rounded • Abundant in many warm, shallow waters • Bahamas

36. Deep Sea Sedimentation Process

37. Distribution of Sea Sediments • Neritic sediments: consist of primary terrigenous material • Found normally along continental shelf's

38. Distribution of Deep Sea Sediments • Pelagic sedimentation: Sediments of the slope, rise, and deep-ocean that originate in the ocean • Pelagic: • Inorganic red or brown clays and silt • Fine-grained (0.0002 – 0.0004 mm) • Dominate below waters with little planktonic production.

39. Deep Sea Sedimentation • Pelagic: • Oozes • Deep ocean sediment that has at least 30% of debris from planktonic organisms • Named after the dominate remnant organism • Calcareous oozes (CaCO3) • Shells of foraminifera & pteropods (zooplankton) and coccolithophorids (phytoplankton). • Accumulate on seafloor aboveCCD. • Forms hard limestone under pressure • Siliceous oozes (SiO2) • Shells of radiolaria (zooplankton) and diatoms (phytoplankton). • Accumulate on seafloor belowCCD. • Accumulate below regions of high diatom production (equator, poles, upwelling areas)

42. Deep Sea Sedimentation Distribution

43. Atlantic Basin • Sediments as thick as 1 km (3,300 feet) • Small area • Great numbers of rivers spilling sediments into ocean

44. The Atlantic basin contains a “two-layer-cake” stratigraphy–a thick basal layer of carbonate ooze overlain by a layer of mud.

45. Pacific Basin • Less than .5 km in thickness • Large area • Pacific has many trenches that the sediment gets trapped

46. Pacific plate moves across latitudes…

47. The Pacific basin contains a “five-layer-cake” stratigraphy, because unlike the Atlantic its sea floor as it spreads crosses the equator where the CCD is lowered to the ocean bottom.

48. Continental Margins • Rivers and Erosion allow for a lot of the terrigenous sediment transported to the margins • Orderly sorting of particles from finest to large grains • Large grains stay near shore • Small grains get carried into the deep ocean • Biogenous Sediments also accumulate in this region • Productivity of near shore waters is normally high • Some sediments are lithified due to the pressure of overlying sediments.

49. Exceptions • Shelf deposits are subject to erosion as the sea level fluctuates. • Ice ages • Exposed shelf leads to further erosion

50. Studying Sediments • Clamshell sampler - Shallow sediment sampler