Marine Sediments Some Important Concepts In Chapter 5

See Fig. 5.7, p. 107“When I think of the floor of thedeep sea, the single, overwhelmingfact that possesses my imaginationis the accumulation of sediments. Isee always the steady, unremitting,downward drift of materials fromabove, flake upon flake, layer uponlayer For the sediments are thematerials of the most stupendoussnowfall the Earth has ever seen.”—Rachel Carson, The Sea Around Us (1956)Marine SedimentsBased on data from core samples, scientists have determined theage of portions of the Pacific floor, measured in millions of years.Some Important Concepts in Chapter 5* Ocean sediment includes particles from land, fromchemical processes, from biological activity, andfrom space.* Ocean sediment is thickest over continentalmargins and thinnest over active oceanic ridges.* Sediment deposited on a quiet seafloor can providea sequential record of recent events in the watercolumn above. Sediments may be recycled into theEarth at subduction zones.* Sediments are an important source of crude oil andnatural gas, food materials, and manganese andother economically important materials.1

Marine Sediments! What is sediment?! “Who cares?”cares?”! Types of sediment– By particle size/texture– By origin/formationWhat is sediment, and who cares?" Sediment Layers of loose material onocean bottoms (or elsewhere). “Marine snow”." Records Earth history (mineral composition,sediment texture). “Forensics”.– Past climate– Age of seafloor– Plate motions – Fossil evolution & extinction! How is it transported?! Where is it distributed?All made with diatomsStudying Sediments:Underwater Cameras2

Can be used to obtain a relatively undisturbed sediment sample.See Fig. 5.17, p. 115Fig. 5.18b-e, p. 115Studying Sediments:Piston CorersStudying Sediments:Clam-shell SamplersFig. 5.18a, p. 115Fig. 5.19, p. 1163

A cylinder of sedimentis taken for analysis.! Age of the material,density, strength,composition, etc.Distribution of SedimentsThe sediment ofcontinental shelves iscalled neritic ( “ofthe coast”) sediment,and contains mostlyterrigenous material.Sediments of theslope, rise, and deepocean floors arepelagic ( “of the deepsea”) sediments, andcontain a greaterproportion ofbiogenous material.Table 5.3, p. 107Types of Sediment By particle size (texture) By origin (formation):– Terrigenous (Lithogenous)– Biogenous (Biogenic)– Hydrogenous (Authigenic)– Cosmogenous (Cosmogenic)4

Classifying Sediment (a) By Particle SizeSediment size indicatesenergy of transport & deposition.Waves & currents generallytransport smaller particles fartherthan larger particles.Table 5.1, p. 103Textural Maturity5

Mature Quartz SandClassifying Sediment (b) By urces: Kennett, 1982; Weihaupt, 1979; Sverdrup, Johnson, Fleming, 1942.1. Terrigenous (Lithogenous)Table 5.2, p. 104Rivers transport a lot of sediment Rock fragments from land Transported to oceans by:– Rivers– Wind– Ice–!Gravity flows Mainly quartz (SiO2)– Chemically stable– Abrasion resistant Most accumulates near continentalmargins Wind-blown dust makes abyssal clay6

Saharan Dust Storm, 2/26/00, SeaStar SeaWiFS SatelliteFig. 5.5a, p. 105Wind-derived quartz in oceansediments(Outlined area is shown in 2/26/00 photo)Fig. 5.5b, p. 1057

Distribution of Terrigenous Sediments Neritic near-shore– Mainly from breakdown of continental rocks– Coarser particles closer to shore– Beach sands, continental shelf deposits, turbiditedeposits, glacial deposits– Shelf sediments may be converted to rock vialithification Pelagic deep ocean– Finer particles farther from land– Wind blown or distal turbidite2. Biogenous (Biogenic) Hard parts of once-living organisms(shells, teeth, bones, and even poop!)Microscopic Siliceous (SiO2) TestsDiatomRadiolarianOoze Calcareous (CaCO3) calcium carbonate Siliceous (SiO2) silica “Ooze” is 30% biogenic material(by weight)8

Microscopic Calcareous (CaCO3) TestsCoccolithophores (with a diatom)ForaminiferaWhite Cliffs of Dover (England) Chalk CoccolithsOozeSee Fig. 5.11, p. 111Distribution of Biogenous Sediments Neritic near-shore– Carbonates in shallow, warm ocean Coral reefs, ooid shoals, beach sands– Stromatolites (carbonate, cyanobacteria, algae) Pelagic deep ocean– SiO2 ooze under areas of surface oceanupwelling (high biologic productivity)– CaCO3 ooze on seafloor 4500 m deep CaCO3 dissolves in cold seawaterCarbonate CompensationDepth (CCD)The depth below whichcarbonate readily dissolves.Only non-calcareous sedimentsaccumulate below the CCD.Abyssal hillsSee Fig. 5.12, p. 1119

Factors in distribution of biogenous sediments:–Biologic productivity–Dissolution as shells settle through ocean–“Dilution” by non-biogenic materialShells and silt-clay fall through seawatercolumn to seafloor3. Hydrogenous (Authigenic)Dissolved ions precipitate from seawater– Manganese nodules– Inorganic carbonates– Phosphates– Metallic sulfides– EvaporitesManganese Nodules Very slow rate ofaccumulation Larger nodulesgrow larger faster Origin is unknown10

Microtektites4. Cosmogenous (Cosmogenic(Cosmogenic))Extraterrestrial fragments– Glassy tektites– Fe-Ni micrometeorites– Found in deep ocean where othersediments accumulate very slowlyFig. 5.6, p. 106Scanning electron micrograph (SEM) imageof an Fe,Ni-rich spherule of cosmic dustMeteorite Impact K-T* meteorite crater off Yucatan Peninsula Tektites & spherules found in marine sediments Shocked quartz in marine sediments*Cretaceous-Tertiaryboundary(65 Myr ago)11

Mixtures of Sediment Types Most marine sediments aremixtures of the 4 types ofsediment Usually one sediment type isdominantDistance Rate x Time12

Distribution of Marine SedimentsWhat differences in the type and distribution of sedimentsdo you note between the Atlantic Ocean and the Pacific Ocean?Fig. 5.8, p. 10813

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! 5-Minu" Wri" # Summarize the main points oftoday’today’s lecture. List 3 to 5 questions you have, basedon today’today’s lecture. What did you find most interestingabout today’today’s lecture? How was the lecture relevant to you?15

Distribution of Sediments The sediment of continental shelves is called neritic ( Òof the coastÓ) sediment, and contains mostly terrigenous material. Sediments of the slope, rise, and deep-ocean ßoors are pelagic ( Òof the deep seaÓ) sediments, and contain a greater proportion of bi