Marine Science - Sternschein Chapter 5 Sediments Marine Science - Sternschein

Sediments Vary In Appearance Sediments – particles of organic or inorganic matter Originate mainly from weathering and erosion of rocks and activity of living organisms Ocean floor slowly dusted by continuous rain of sediments Marine sediments have broad range of sizes/types Colors vary from white/creams to red/browns Very few areas of sea bed are free of overlying sediment

Sediments by Size

Sediments – by Particle Size Particle size frequently used to classify sediments. The smaller the particle, the more easily it can be transported (via streams/waves/currents) Coarser grains tend not to travel as far as finer grains Clays can remain suspended for long periods of time over great distances Well-sorted sediments = particles of mostly one size, form in environment where energy fluctuates in narrow limits Poorly-sorted sediments = mixture of sizes, form in environments where energy fluctuates over a wide spectrum

Sediments by Source

Classification by Source cont. Can be classified by origin; 4 categories Terrigenous sediments = most abundant, originate on continents/islands from erosion, volcanic eruptions, and blown dust Rocks of Earth’s crust are made up of minerals, inorganic crystalline materials with specific chemical compositions

Classification by Source cont. Biogenous sediments = next most abundant marine sediment, silicon-containing/calcium carbonate- containing compounds, making sediments of biological origin Over millions of years can form fossil fuels Hydrogenous sediments = minerals that precipitated directly from seawater Cosmogenous sediments = extraterrestrial origin, least abundant Two major sources: interplanetary dust and rare impacts by large asteroids/comets

Cycling of Sediments

Sediment by location Sediments on ocean floor rarely come from a single source; most sediment deposits are mixtures Neritic sediments (neritos, “of the coast”) consist primarily of terrigenous material Greater proportion of deep-sea sediment is biogenous Pelagic sediment = sediments of the slope/rise/deep-ocean floor, originate in the ocean

Location cont. Currents distribute sand/larger particles along the coast, while wave action carries silts/clays to deeper water Finest sediment may come to rest or continue to be transported by the turbulence of deep currents Leads to sorting of particles: Large grains near the coast to relatively small grains near shelf break. Lithification = conversion of sediments into sedimentary rock by pressure-induced compaction or by cementation

Different types of pelagic sediments Thickness of pelagic sediments are highly variable Atlantic Ocean bottom – covered by sediments to a thickness of about 1km (3,300ft), while Pacific floor has an average thickness of less than 0.5km (1,650ft) Atlantic Ocean is fed by greater number of rivers, and is smaller in area, thus getting more sediment for its size Dilute mixtures of sediment/water periodically rush down the continental slope in turbidity currents Turbidity currents are thought to help cut submarine currents, moving onto adjacent abyssal plains before eventually coming to rest, making deposits called turbidites Turbidites = graded layers of terrigenous sand imbedded with finer pelagic sediments typical of deep-sea floor

Oozes Ooze = deep-ocean sediment containing at least 30% biogenous material Named after dominant remnant organisms constituting them When these organisms die, their shells settle slowly toward the bottom, mingle with fine-grained terrigenous silts and clays, and accumulate as ooze

Coccoliths (top right) contribute to calcareous ooze, such as that on Dover’s cliffs. Figure 5.14 Dover’s famous white cliffs are uplifted masses of lithified coccolithophores. This chalk-like material was deposited on the sea-bed around 100 million years ago, overlain by other sediments, and transformed into soft limestone by heat and pressure.

Nodules Hydrogenous sediments also accumulate on deep- sea floors Most famous hydrogenous sediments = manganese nodules, consist primarily of manganese and iron oxides

Oolites Molecules of calcium carbonate may precipitate around shell fragments or other particles Oolite sands = sands comprised of ooliths

Tools used to study sediments Cameras – actual views but limited visibility Clamshell sampler – collects & retrieves sediment (limited depth) Piston corer – collects intact samples at greater depths Seismic profiling – computer-aided images produce a more detailed image

Sampling tools

Importance of Sediments Reveals clues to the past (paleontologist) Substantiated theory of plate tectonics Sediments are used in building materials Petroleum is extracted from sediments A source of manganese and iron