DEEP-SEA SEDIMENTSPart II

GEOL 1033

Lessons 14, 15, & 37

TYPES OF MODERN OCEAN FLOOR SURFACE SEDIMENTS

• 1. Terrigenous – last lecture – lesson 14• 2. Biogenic – last lecture – lessons 15 & 37

• CCD

• 3. Authigenic – lesson 14• 4. Clays – lesson 14• 5. Volcanic – lesson 14

Deep-Sea Calcium Carbonate Accumulation• Below the CCD, cold water holds more CO2, which

results in more carbonic acid [ H2CO3 ], that dissolves CaCO3 faster (by forming bicarbonate ions [ HCO3- ].

Carbonate Compensation Depth (CCD) in the Atlantic

• Calcareous oozes occur at shallower depths (<3 500 to 4 000 m)

• Siliceous oozes occur at deeper depths (> 3 500 to 4 000 m)

Carbonate Sediments Accumulate in Shallower Deep-Sea Areas

• At mid-ocean ridges

Solution of Silica and Calcium Carbonate with Depth

• Lysocline – significant increase in rate of solution

• CCD

3. Authigenic Sediments

• Manganese nodules & crusts:– Common on deep seafloor– Abundant over 25% of seafloor– Slow sedimentation rates– Grow around a nucleus

• Economic importance– Future source of many metals

• Mn• Fe• Co• Zn• Others

– Technology needs to be developed– Expensive now– But, the price of land-based ores

will someday rise as they become mined out and harder to find

MANGANESE NODULES & CRUSTS• Crusts from Western Pacific Ocean floor

• Cut nodule from the Blake Plateau, western North Atlantic Ocean

4. DEEP-SEA CLAYS

• Clays:– Deep ocean– Below CCD– Very fine-grained

• Settled from suspension

• Some may be authigenic

– Red & brown coloured– Mottled due to burrowing

invertebrates, such as worms– Slow sedimentation rates

5. Volcanic Sediments• Volcaniclastics

– Ash = as fine as icing sugar used for making cake frosting

– Lapilli = pebble-sized ejecta

– Restricted to local distribution around volcanic islands

DISTRIBUTIONS OF DEEP-SEA SEDIMENTS

• Terrigenous:– Nearshore areas– Continental margins

• Shelf• Slope• Rise

– Polar glacial regions (and former glaciated coasts)

• Calcareous oozes:– Less deep areas above CCD– Especially Atlantic Ocean,

So. Pacific, & W. Indian

• Siliceous oozes:– Below CCD– Diatom oozes:

• No. Pacific• Antarctic Ocean

– Radiolarian oozes• Equatorial Pacific• Antarctic Ocean

DISTRIBUTIONS OF DEEP-SEA SEDIMENTS

• Manganese nodules:– Common in deep seafloor

– Abundant 25% of seafloor

– Slow sedimentation rates

• Clays:– Red & brown coloured

– Deep ocean (abyssal plains)

– Below CCD

– Slow sedimentation rates

H

DISTRIBUTIONS OF DEEP-SEA SEDIMENTS• Thicknesses:

– Thickest beneath continental shelves, lower cont. slopes & cont. rises– Thinnest on the flanks of mid-ocean ridges

• Areas:– Calcareous oozes = 48%– Siliceous oozes = 14%– Clays = 38%

• Age:– No seafloor crust is older than about 180 to 200 Ma (Jurassic or younger)

• Why?

– Total area of sedimentary sequences decreases as age increases• Why?

• Depth:– Younger sedimentary sequences are in less deep ocean

• Why?

– Older sedimentary sequences are in deeper oceans• Why?

age

area

age

dep

th

Basal Sediment Ages of Pacific Ocean Basin

DISTRIBUTIONS OF DEEP-SEA SEDIMENTS• Oceanic cross section summarizing sediments

MODERN DEEP-SEA OOZES

• Deep-sea oozes– Fine-grained

– At least 30% microfossil skeletons

• Carbonate compensation depth (CCD)– Calcium carbonate dissolves in deeper, colder waters

• Sea-floor distributions– Calcareous oozes cover ~ 48% of seafloor

• Plate tectonic influences– Increased amounts of calcium carbonate have been recycling

into the mantle since the mid- Mesozoic (Jurassic Period)

END OF FILE

READING ASSIGNMENTS• 7th Edition, 2003, Sverdrup & others:

(Pages correspond to the lesson topics in the Study Guide)– Lesson 1 page 2– Lesson 2 p. 29-38, 45-51– Lesson 8 p. 54-59 (Q7 assigned)– Lesson 3 p. 38-42 (E3 assigned)– Lesson 4 p. 2-21, 24-26 (Q3 assigned)– Lesson 5 p. 40-45; 3(bottom+fig)-4(fig); 259(bottom)-260(top) (Q4 assigned)– Lesson 6 p. 42-45, 87-89, 364(gases)– Lesson 7 p. 99-101(top),108-109,143-144(sound),120(bottom)-124 (Q6 assigned)– Lesson 9 p. 62-63, 101(bathymetry)-112(fig)– Lesson 10 p. “ “ “ “ – Lesson 11 p. “ “ “ “ (Q9 assigned)– Lesson 12 p. “ “ “ “ , 107(fig+bottom)-110(top), 464-465– Lesson 13 p. “ “ “ “– Lesson 14 p. 112(sediments)-127 (Q11 assigned)– Lesson 15 p. 393-413– Lesson 37 p. 393-413, 374-379 (Q27 assigned)– Lesson 16 p. 53-61, 65 (E9 assigned)– Lesson 17 p. 64(fig), 66, 73-75, 127(Min Dep), 87, 90-96, 468-469– Lesson 18 p. 71-79, 81(hot spots)-83

• 6th edition, (2000), or 5th edition, (1997) may be used. See handout for pages.

Since mid-Mesozoic, calcareous oozes on the deep-sea floor have caused a major change in Earth chemical cycles, e. g., new recycling into the mantle. Calcareous are oozes “scraped” from the seafloor and squeezed down into the mantle at subduction zones formed where lithospheric plates collide.