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CHAPTER 4 Marine Sediment. Classification: Shape, Size, Variation Formation Processes: Lithogenic (rock) Biogenic (organic based) Authogenic /Hydrogenous (precipitated from water) Volcanic Cosmogenic (outer space). Sediment Transport.
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CHAPTER 4 Marine Sediment Classification: Shape, Size, Variation Formation Processes: Lithogenic (rock) Biogenic (organic based) Authogenic/Hydrogenous (precipitated from water) Volcanic Cosmogenic (outer space)
Sediment Transport Fluid velocitydetermines thesize of theparticles thatcan be moved
Sediment Texture • Grain size sorting • Indication of selectivity of transportation and deposition processes • Textural maturity • Increasing maturity if • Clay content decreases • Sorting increases • Non-quartz minerals decrease • Grains are more rounded (abraded)
Sediments • Reflect composition of rock from which derived • Coarser sediments closer to shore • Finer sediments farther from shore • Mainly mineral quartz (SiO2)
Terrigenous & Lithogenic sediments (from land) • Rivers • Winds (aeolian) • Glaciers (ice-rafted debris, IRD) • Turbidites • Sea level changes
Terrigenous Sediments: • derived from weathering of rocks at or above sea level (e.g., continents, islands) • two distinct chemical compositions • ferromagnesian, or iron-magnesium bearing minerals • non-ferromagnesian minerals – e.g., quartz, feldspar, micas • largest deposits on continental margins (less than 40% reach abyssal plains) • transported by water, wind, gravity, and ice • transported as dissolved and suspended loads in rivers, waves, longshore currents
Sediment Distribution • Neritic • Shallow-water deposits • Close to land • Dominantly lithogenous • Typically deposited quickly • Pelagic • Deeper-water deposits • Finer-grained sediments • Deposited slowly
Neritic Lithogenous Sediments • Beach deposits • wave-deposited sand • Continental shelf deposits • Turbidite deposits • Glacial deposits • High latitude continental shelf • Currently forming by ice rafting
Pelagic Deposits • Fine-grained material • Accumulates slowly on deep ocean floor • Pelagic lithogenous sediment from • Volcanic ash (volcanic eruptions) • Wind-blown (aeolian) dust • Fine-grained material transported by deep sea currents
Dust (LANDSAT image). • Dust comprise much of the fine-grained deposits in remote open-ocean areas (red clays) • primary dust source is deserts in Asia and North Africa
Continental rise Continental slope Seafloor Features: Continental Margins Submarine canyons (cut into the c. slope) Abyssal plain Continental shelf Abyssal plain
boulder to clay size particles also eroded and transported to oceans via glacial ice • glacier termination in circum-polar oceans results in calving and iceberg formation • as ice (or icebergs) melt, entrained material is deposited on the ocean floor • termed 'ice-rafted' debris
Biogenic sediments(from living things) Calcareous (CaCO3)Foraminifera -- animalsCoccolithophores -- plants Siliceous (SiO2)Radiolaria -- animalsDiatoms -- plants Forams Diatoms Radiolarian
Biogenic Sediment • Two major types: • Macroscopic • Visible to naked eye • Shells, bones, teeth • Microscopic • Tiny shells or tests • Biogenic ooze • Mainly algae and protozoans
Biogenic Sediments: • composed primarily of marine microfossil remains • median grain size typically less than 0.005 mm (i.e., silt or clay size particles) • characterized as CaCO3 (calcium carbonate) or SiO2 (silica) dominated systems • sediment with biogenic component less than 30% termed calcareous, siliceous clay • calcareous or siliceous 'oozes' if biogenic component greater than 30%
siliceous oozes (primarily diatom oozes) cover ~15% of the ocean floor • distribution mirrors regions of high productivity • common at high latitudes, and zones of upwelling • radiolarian oozes more common in equatorial regions
calcareous oozes (foraminifera, coccolithophores) cover ~50% of the ocean floor • level below which no CaCO3 is preserved is the 'carbonate compensation depth‘ (CCD) • This change in dissolution rate is called the lysocline.Below the lysocline, more and more calcium carbonate dissolves, until eventually, there is none left. The lysocline typically occurs at a depth of 3000 to 4000 m
Temporal Succession of Pelagic Sediment at Spreading Centers
Cosmogenous Marine Sediments • Macroscopic meteor debris • Microscopic iron-nickel and silicate spherules (small globular masses) • Tektites • Space dust • Overall, insignificant proportion of marine sediments
Marine Sediment Mixtures Usually mixture of different sediment types Typically one sediment type dominates in different areas of the sea floor.
Distribution of Marine Sediments: • sediments thickest along continental margins, thin at mid-ocean ridges • coastlines • dominated by river-borne and wave reworked terrigenous sediments • shelf and slope characterized by turbidites and authigenic carbonate deposits • glacial deposits and ice-rafted debris common at high latitudes • high input of terrigenous sediments 'dilutes' biogenous components • deep-sea (pelagic) basins • abyssal clays (wind blown deposits) common • lower quantities of biogenic material • distribution of biogenous sediments dependent upon three primary factors • production in surface waters • dissolution in deep waters • dilution by other sediments types