Lesson 15 Sediments Geological Oceanography Sediments are important

Lesson 15: Sediments Geological Oceanography

Sediments are important to marine scientists 2 l Did you know that ocean sediments hold clues about the earth? l They can provide information on earth’s past climate, the location of oil and natural gas resources, seafloor age, pollution patterns and many other processes l There are many types of sediments and we will learn different ways to classify them

How are sediments classified? l 3 By grain size Classification Grain Diameter Clay <0. 004 mm Silt 0. 004 -0. 0625 mm Sand 0. 0625 -2 mm Granule 2 -4 mm Pebble 4 -64 mm Cobble 64 -256 mm Boulder >256 mm l By origin – Where do you think sediment comes from?

Where does sediment come from? l Lithogenous sediments come from land – – l Biogenous sediments come from organisms – – 4 Rivers, wind, ice and other geologic processes erode and transport rocks and minerals into the sea Also called “terrigenous, ” these particles make up most of the sediment near islands and continents They come from the shells and exoskeletons of marine organisms They cover most of the area of the sea floor

Where does sediment come from? l Hydrogenous sediments come from chemical reactions in the water – – l Cosmogenous sediments come from space – – 5 Sources may include minerals or chemicals that dissolve in seawater, river runoff or hydrothermal vent water They make up less than 1% of seafloor sediments and tend to form slowly Sources may include meteorites and cosmic dust Least abundant of the four types of marine sediments

Can you name some common examples? Lithogenous ? Red Clay ? Quartz 6 Photos: USGS, USDA

Can you name some common examples? Biogenous 7 Plankton ? remnants silica or calcite Cosmogeneous Tektites ? Photos: USGS

Do you think sediment is uniformly distributed throughout the ocean? l l 8 No! Even though most sediment contains a mixture of types, one typically dominates depending where you are in the ocean

Distribution: Biogenous sediment l l l 9 The biogenic material in the ocean comes primarily from the breakdown of plankton skeletons Deep ocean sediments are usually high in biogenic material Ooze is deep-ocean sediment that has more than 30% biogenic material – calcareous ooze: composed mostly of calcium carbonate plankton skeletons – siliceous ooze: composed mostly of silica plankton skeletons

Distribution: Lithogenous (terrigenous) sediment l l l 10 Lithogenous sediments are generally found close to shore except for clay particles Thus, sediments near the shore tend to be dominated by lithogenous material, while deep-ocean sediment tends to be dominated by biogenic material Lithogenous clay particles are relatively light, so they can be carried further from shore by wind, forming pelagic red clay accumulations

Sediment thickness in the deep ocean 11 l Sediment layering is not the same across all of Earth’s ocean l Do you think the Atlantic or Pacific ocean basin has greater sediment thickness? Why?

Let’s look at a global map of ocean thickness 12

The Atlantic Ocean Basin has greater sediment thickness 13 l Sediment thickness on the Pacific Ocean floor is about half that of the Atlantic Ocean l Rivers flowing into the Atlantic cover more land than those flowing into the Pacific, so they bring more sediment

Exploring sediment distribution In today’s activity, we will analyze maps of sediment distribution 14