CHAPTER 4 Marine Sediments Fig CO4 Marine sediments

CHAPTER 4: Marine Sediments Fig. CO-4

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

Classification of marine sediments Classified by origin n Lithogenous (derived from land) n Biogenous (derived from organisms) n Hydrogenous (derived from water) n Cosmogenous (derived from outer space) n

Lithogenous sediments n n n Eroded rock fragments from land Reflect composition of rock from which derived Transported from land by Water (e. g. , river transported sediment) n Wind (e. g. , windblown dust) n Ice (e. g. , ice-rafted rocks) n Gravity (e. g. , turbidity currents) n

Lithogenous sediments Fig. 4. 5

Lithogenous sediments n n Most lithogenous sediments at continental margins Coarser sediments closer to shore Finer sediments farther from shore Mainly mineral quartz (Si. O 2)

Relationship of fine-grained quartz and prevailing winds Fig. 4. 6 b

Sediment texture n Grain size n Proportional to energy of transportation and deposition Table 4. 2

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

Sediment maturity Fig. 4. 7

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

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

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

Biogenous marine sediments n Hard remains of once-living organisms n Shells, bones, teeth n Macroscopic (large remains) n Microscopic (small remains) n Tiny shells or tests settle through water column n Biogenic ooze (30% or more tests) n Mainly algae and protozoans

Biogenous marine sediments Commonly either calcium carbonate (Ca. CO 3) or silica (Si. O 2 or Si. O 2. n. H 2 O) n Usually planktonic (free-floating) n

Silica in biogenic sediments n Diatoms (algae) n Photosynthetic n Diatomaceous earth n Fig. 4. 8 a Radiolarians (protozoans) n Use external food n Siliceous ooze Fig. 4. 8 b

Siliceous ooze n n Seawater undersaturated with silica Siliceous ooze commonly associated with high biologic productivity in surface ocean Fig. 4. 12

Calcium carbonate in biogenous sediments n Coccolithophores (algae) n n n Photosynthetic Coccoliths (nano-plankton) Rock chalk Fig. 4. 9 a

Calcium carbonate in biogenous sediments n Foraminifera (protozoans) n Use external food n Calcareous ooze Fig. 4. 9 c

Distribution of biogenous sediments Most common as pelagic deposits n Factors controlling distribution n Productivity n Destruction (dissolution) n Dilution n

Carbonate deposits Limestone (lithified carbonate sediments) n Stromatolites n Warm, shallowocean, high salinity n Cyanobacteria Fig. 4. 11 b

Calcareous ooze and the CCD Warm, shallow ocean saturated with calcium carbonate n Cool, deep ocean undersaturated with calcium carbonate n n Lysocline--depth at which Ca. CO 3 begins to dissolve rapidly n Calcite compensation depth CCD--depth where Ca. CO 3 readily dissolves

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 n n

Distribution of calcareous oozes in surface sediments of modern seafloor Fig. 4. 14

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

Iron-manganese nodules n n n Fist-sized lumps of manganese, iron, and other metals Very slow accumulation rates Why are they on surface seafloor? Fig. 4. 15 a

Hydrogenous marine sediments n Phosphates n Phosphorous-bearing n Occur beneath areas in surface ocean of very high biological productivity n Economically useful: fertilizer n Carbonates n Aragonite n Oolites and calcite

Hydrogenous marine sediments n Metal sulfides n Contain iron, nickel, copper, zinc, silver, and other metals n Associated with hydrothermal vents n Evaporites n Minerals that form when seawater evaporates n Restricted open ocean circulation n High evaporation rates n Halite (common table salt) and gypsum

Cosmogenous marine sediments Macroscopic meteor debris n Microscopic iron-nickel and silicate spherules n n Tektites n Space n dust Overall, insignificant proportion of marine sediments

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

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

Distribution of neritic and pelagic marine sediments Fig. 4. 19

How sea floor sediments represent surface ocean conditions Microscopic tests sink slowly from surface ocean to sea floor (10 -50 years) n Tests could be moved horizontally n Most biogenous tests clump together in fecal pellets n n Fecal pellets large enough to sink quickly (10 -15 days)

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

Retrieving sediments n n Dredge Gravity corer Rotary drilling n n Deep Sea Drilling Program Ocean Drilling Program Integrated Ocean Drilling Program Studies reveal support for plate tectonics, drying of the Mediterranean Sea, global climate change

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

Salt deposits Fig. 4. 25

Manganese nodules Fig. 4. 26

End of CHAPTER 4 Marine Sediments Fig. 4 E