Sediments

Sediment particles that accumulate in a loose, unconsolidated form.

Originate fromweathering and erosion of rocks

activity of living organisms

volcanic eruptions

chemical processes in the water

space

Broad range of sizes and typesBeach sand is sediment

Mud in quiet bays is sediment

What do sediments look like?

• Surface– Could be smooth– May be rippled where there is a strong current

• Color– Biological sediments are white or cream-colored– Clays range in color from tan to chocolate brown– Nearshore sediments are dark and contain organic

matter and smell of hydrogen sulfide (rotten eggs)

Classification by Source

Classifying Sediment by Particle Size

• Particle size is used to classify sediments– Marine sediments are made of sand, silt and

clay• The smaller the particle the more easily it can be

transported by streams, waves and currents.• Transportation tends to sort sediments by size

– Coarser grains tend not to travel as far as finer grains.– Clays may be transported great distances

Sorting of sizes depends on the energy of the environment

• Well-sorted :particles of one size – occur where energy fluctuates little

• deep ocean sediments

• Poorly-sorted: mixture of sizes – found where energy fluctuates a lot

• rubble at the base of shore cliff

Terrigenous Sediments

• Most abundant – 15 billion tons/year transported in rivers

• 100 million tons/year transported by air

• Originate on continents or islands

• Two most common components• granite, the source of quartz • clay, the of terrigenous sediments

Biogenous Sediments

• Next most abundant

• Come from the living organisms– Plants and animals precipitate siliceous and

calcareous compounds to form their shells and skeletons.

– Most abundant in areas of high productivity• Continental Shelves

– Over millions of years they can form oil and natural gas

Making Fossil Fuels

Hydrogenous Sediments

• Minerals precipitate directly from water– sources

• submerged rock and sediment• leaching of the fresh crust at oceanic ridges• material issuing from hydrothermal vents • substances flowing in river runoff

– Called authigenic because they were formed in the place they currently occupy

– Example: Manganese Nodules

Cosmogenous Sediments

• Are of extraterrestrial origin and are the • Least abundant

– Interplanetary dust • Silt and sand sized micrometeoroids that come from

asteroids and comets or from collisions between asteroids– About 15,000 to 30,000 metric tons of interplanetary dust

enters earth’s atmosphere every year

– Rare impacts by large asteroids and comets• 65 million years ago an asteroid 10 km in diameter struck

earth on what is now the northern coast of the Yucatan.

Global Sediment Thickness

Sediments Distribution by Source

Neritic and Pelagic Sediments

• Sediments on continental shelves are often different from those on basin floors

– Continental shelf sediments, neritic sediments are primarily terrigenous

• 72% of all marine sediment is on continental slopes and rises

– Deep ocean floors are covered by finer sediments than those of the continental margins.

• Pelagic sediments come from the sea

Deep Ocean Sediments

• Thickness varies greatly from place to place– Atlantic = 1 km deep, Pacific = 0.5 km deep

• Atlantic is smaller in area• Atlantic is fed by a greater number of rivers laden with

sediment• Pacific has many trench that trap sediments moving

toward basins

– Sediments are thickest on the abyssal plains and thinnest (or absent) on ridges

– Turbidites, Clays and Oozes

Turbidites

Calcium Carbonate Compensation Depth (CCD)

Sampling Sediments

• Historically sampled by clamshell samplers and deeper samples by piston corers

– Pretty straightforward and dirty

Sediments as Historical Records

• Stratigraphy - older sediments are below younger ones– Determine a historical record of events that

happened in the distant past. – Analyze different layers, strata, in the

sediments and determine what ocean conditions were when the sediments were laid down.

• historical record of global climate or productivity.