Sediments Sediment particles that accumulate in a loose, unconsolidated form. Originate from weathering and erosion of rocks activity of living organisms volcanic eruptions chemical processes in the water space Broad range of sizes and types Beach 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.