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14.3 Seafloor Sediments Section 14.3

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Section Objectives Key Concepts Vocabulary Reading Strategy 14.8 List the three types What are the three types ◆ terrigenous Summarizing Make a table like the one of ocean floor sediments. sediment of ocean-floor sediments? below that includes all the headings for the 14.9 Describe the formation of What does terrigenous ◆ biogenous section. Write a brief summary of the text for sediment consist of? sediment each heading. terrigenous, biogenous, and ◆ calcareous ooze What is the composition hydrogenous sediments. Actions at Boundaries of biogenous sediment? ◆ siliceous ooze ◆ hydrogenous I. Types of Seafloor Sediments How is hydrogenous sediment sediment formed? •Terrigenous sediments originated on land. Reading Focus • Biogenous sediments are biological in origin. Build Vocabulary L2 • ? Word Parts Have students break the words terrigenous, biogenous, and hydrogenous into parts, using a dictionary to find the meaning of each part. (terri- is from terra which means xcept for steep areas of the continental slope and the crest of the E “earth” or “ground”; bio- means “life”; mid-ocean ridge, most of the ocean floor is covered with sediment. hydro- means “water”; -genous means Some of this sediment has been deposited by turbidity currents. The “producing”, “yielding”, “origin.”) rest has slowly settled onto the seafloor from above. The thickness of ocean-floor sediments varies. Some trenches act as traps for sediment Figure 11 Distribution of Ocean-Floor Sediments Coarse- Reading Strategy L2 originating on the continental margin. The accumulation may grained terrigenous deposits approach 10 kilometers in thickness. In general, however, accumula- dominate continental margin Actions at Boundaries areas. Fine-grained clay, or mud, I. Types of Seafloor Sediments tions of sediment are much less—about 500 to 1000 meters. is more common in the deepest Generally, coarser sediments, such as sand, cover the continental areas of the ocean basins. • Terrigenous sediments originated on land. Infer Why is it more common to They come from minerals of continental shelf and slope while finer sediments, such as clay, cover the deep-ocean rocks. These sediments are composed of sand find fine-grained sediments in and gravel. floor. Figure 11 shows the distribution of the different types of ocean- the deepest areas of the ocean floor sediments. Various basins? • Biogenous sediments are biological in origin. types of sediment accumu- They come from shells and skeletons of marine animals and algae. These sediments late on nearly all areas of are composed of calcareous ooze, siliceous the ocean floor in the same ooze, and phosphate-rich material. way dust accumulates in all • Hydrogenous sediments originated in ocean water. They are crystallized through chemical parts of your home. Even reactions. These sediments are composed of the deep-ocean floor, far manganese nodules, calcium carbonates, and from land, receives small evaporites. amounts of windblown material and microscopic 2 INSTRUCT parts of organisms. Build Science Skills L2 Coarse nearshore Terrigenous deposits Fine clay (mud) Biogenous Calcareous ooze Siliceous ooze Predicting After students have read the introduction, ask: Why do sediment deposits near the continental margins The Ocean Floor 407 tend to be thicker than those on floor of the open ocean, far from land? (Water from rivers and runoff from coastal Facts and Figures land transports land sediments to margins. This sediment source does not exist in the open ocean.) Most seafloor sediments contain the remains of repository for sediments representing millions Logical, Verbal microscopic organisms that once lived near the of years of Earth’s history. They are useful ocean surface. When these organisms die, their recorders of climate change because the hard parts can settle onto the ocean floor, numbers and types of organisms living near where they may become buried and preserved the surface change with the climate. over time. The deep ocean floor has become a Answer to . . . Figure 11 They are less dense and transported further than coarser sediments that settle closer to shore.

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Section 14.3 (continued) Types of Seafloor Sediments Ocean-floor sediments can be classified according to their origin L1 Use Visuals into three broad categories: terrigenous sediments, biogenous Figure 11 Have students examine the Q Do we use diatoms in any sediments, and hydrogenous sediments. Ocean-floor sediments are products? map showing the distribution of marine usually mixtures of the various sediment types. sediments in the A Diatoms are used in filters for world’s oceans. Ask: refining sugar, straining yeast Terrigenous Sediment Terrigenous sediment is sediment that from beer, and cleaning swim- What kinds of ming pool water. They also are originates on land. Terrigenous sediments consist primarily of terrigenous sediments mild abrasives in household mineral grains that were eroded from continental rocks and trans- are shown on the cleaning and polishing products ported to the ocean. Larger particles such as gravel and sand usually map? (coarse nearshore deposits and fine and facial scrubs; and absorbents settle rapidly near shore. Finer particles such as clay can take years to for chemical spills. You use abyssal clay) How do the locations of diatoms in a variety of household settle to the ocean floor and may be carried thousands of kilometers by two types products such as toothpaste, ocean currents. Clay accumulates very slowly on the deep-ocean floor. of terrigenous deposits differ? (Fine- facial scrubs, and cleaning To form a 1-centimeter abyssal clay layer, for example, requires as grained clays are found farther from solutions. much as 50,000 years. In contrast, on the continental margins near the landmasses; coarser deposits are closer mouths of large rivers, terrigenous sediment accumulates rapidly and to landmasses.) According to the map, forms thick deposits. In the Gulf of Mexico, for instance, the sediment which type of biogenous sediment is many kilometers thick. appears to be more common? (biogenous calcareous ooze) Which type Biogenous Sediment Biogenous sediment is sediment that is of sediment is found along the west biological in origin. Biogenous sediments consist of shells and coast of North America? The east skeletons of marine animals and algae. This debris is produced coast of North America? (biogenous mostly by microscopic organisms living in surface waters. Once these siliceous ooze; terrigenous coarse organisms die, their hard shells sink, accumulating on the seafloor. nearshore deposits) The most common biogenous sediment is calcareous ooze. Visual, Logical Calcareous ooze is produced from the calcium carbonate shells of organisms. Calcareous ooze has the consistency of thick mud. When Types of Seafloor calcium carbonate shells slowly sink into deeper parts of the ocean, Sediments they begin to dissolve. In ocean water deeper than about 4500 meters, Build Science Skills L2 these shells completely dissolve before they reach the bottom. As a result, calcareous ooze does not accumulate in the deeper areas of Classifying Have students collect ocean basins. information about products that contain Other biogenous sediments include siliceous ooze and phosphate- diatomaceous earth. Suggest to rich material. Siliceous ooze is composed primarily of the shells of students to look for these products in diatoms—single-celled algae—and radiolarians—single-celled animals local grocery, hardware, auto supply, that have shells made out of silica. The shells of these organisms are pool supply, and garden supply stores. shown in Figure 12. Phosphate-rich biogenous sediments come from By reading the labels, students can collect data about the uses for each the bones, teeth, and scales of fish and other marine organisms. product. Challenge students to identify the general applications diatomaceous Name two types of biogenous sediments. earth is used for (filters, abrasives, absorbents) and classify each product they investigated according to its general application. (Sample answers: filters: pool cleaning equipment; abrasives: toothpaste, garden insect control; absorbents: materials for cleaning 408 Chapter 14 chemical spills) Logical, Interpersonal

Build Reading Literacy L1 Customize for English Language Learners Refer to p. 362D in Chapter 13, which provides the guidelines for this Use Prior Help students understand chemical terms in substances that contain the element carbon. Knowledge strategy. this section by explaining their derivations. Tell The term evaporites is derived from the word Use Prior Knowledge Before students students that sulfides are substances that evaporation. read this section, have them make a list contain the element sulfur. Carbonates are of the kinds of materials they think make up the sediment deposits on the ocean floor. After they have read the section, have students revise their lists. Logical, Intrapersonal

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Hydrogenous Sediment Hydrogenous sediment consists of minerals that crystallize directly from ocean water through various chemical reactions. Hydrogenous sediments Biogenous Deposits L2 make up only a small portion of the overall sediment in the Purpose Students observe similarities ocean. They do, however, have many different compositions and and differences among the types of are distributed in many different environments. Some of the organisms that form biogenous most common types of hydrogenous sediment are listed below. sediment deposits. •Manganese nodules are rounded, hard lumps of manganese, Materials prepared microscope slides iron, and other metals. These metals precipitate around an of diatoms, foraminifera, and radiolaria; object such as a grain of sand. The nodules can be up to or photographic slides of photomicro- 20 centimeters in diameter and are often scattered across graphs of these organisms and a slide large areas of the deep ocean floor. projector •Calcium carbonates form by precipitation directly from ocean water in warm climates. If this material is buried and Procedure Have students examine hardens, a type of limestone forms. Most limestone, how- prepared slides under the microscope ever, is composed of biogenous sediment. or view projected photographic slides. •Evaporites form where evaporation rates are high and there is Figure 12 Biogenous Inform students that these organisms restricted open-ocean circulation. As water evaporates from such Sediments The microscopic are single-celled members of the shells of radiolarians and phylum protista. Diatoms are algae areas, the remaining ocean water becomes saturated with dissolved foraminifers are examples of (plant-like protists) that make their minerals that then begin to precipitate. Collectively termed “salts,” biogenous sediments. This photomicrograph has been own food through photosynthesis. some evaporite minerals do taste salty, such as halite, or common enlarged hundreds of times. Foraminifera and radiolaria are animal- table salt. Other salts do not taste salty, such as the calcium sulfate like protists that feed on other minerals anhydrite (CaSO ) and gypsum. 4 microscopic organisms. Have students observe similarities and differences among the organisms shown. Expected Outcome Students will observe that these organisms all have Section 14.3 Assessment hard structures that vary in shape from species to species and can be preserved after the organisms’ soft tissues decay. Reviewing Concepts Visual 1. What are the three types of ocean floor sediments? Origin of Sediments An oceanographer 2. What does terrigenous sediment consist of? is studying sediment samples from the 3 3. What is the composition of biogenous Bahama Banks. The sediments have a high ASSESS sediment? amount of calcium carbonate. They are Evaluate 4. How is hydrogenous sediment formed? labeled biogenous but are later found to Understanding L2 contain no shells from organisms that typi- Critical Thinking cally make up calcareous ooze. What other Present students with a blank table explanation is there for the origin of these 5. Comparing and Contrasting Compare and that lists the three major categories of sediments? contrast calcareous ooze and siliceous ooze. seafloor sediments down the left 6. Predicting Would you expect to find more column. The center column should be evaporites in an area of warm water that titled Origin. The right column should receives large amounts of sunlight such as the be labeled Composition. Have students Red Sea or in an area of cold water that receives less sunlight such as the Greenland Sea? fill in the Origin and Composition columns.

The Ocean Floor 409 Reteach L1 Have each student write ten questions that cover the content of this section. Invite students to use their questions to Section 14.3 Assessment 5. Calcareous ooze and siliceous ooze both quiz each other. have the consistency of thick mud and are 1. terrigenous, biogenous, hydrogenous examples of biogenous sediments. Calcareous 2. mineral grains weathered from continental ooze is formed from the calcium carbonate rocks tests, or hard parts, of organisms. Siliceous They are hydrogenous, formed from 3. shells and skeletons of marine animals and ooze is formed from the siliceous tests of calcium carbonate precipitating directly algae organisms. Calcareous ooze is not found from seawater. 4. minerals crystallize directly from the water below depths of 4500 m. through chemical reactions 6. area of warm water with lots of sunlight Answer to . . . because these conditions are more favorable for evaporation calcareous ooze, siliceous ooze

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