Chapter 4

Chapter 4 - Intro to Oceanography: Chapter 4 I. What Is...

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Intro to Oceanography : Chapter 4 I. What Is Lithogenous Sediment? Lithogenous sediment is derived from preexisting rock materials Also called terrigenous sediment because most lithogenous sediment comes from the landmasses a. Origin i. Begins as rocks on continents or islands ii. Weathering agents such as water, temp extremes, and chemical effects break rocks into smaller pieces – easier to erode and transport iii. Eroded material is carried to oceans by streams, wind, glaciers, and gravity iv. Deposited in environments such as bays or lagoons, beaches, or the continental margin (most of them) b. Composition i. All rockets are composed f discrete crystals called minerals ii. Most abundant, chemically stable, and durable minerals in Earth’s crust is quartz, composed of silicon and oxygen (same composition as glass) iii. Majority of lithogenous deposits such as beach sands are composed primarily of quartz. c. Sediment Texture i. Grain size and texture are important properties of lithogenous sediment ii. Wentworth scale of grain size indicates that particles can be classified as boulders (largest), cobbles, pebbles, granules, sand, silt, or clay (smallest). iii. Size is proportional to the energy needed to lay down a deposit. iv. Texture depends on sorting – a measure of the uniformity of grain sizes and indicates the selectivity of the transportation process v. Maturity (texture depends on) increases as 1. clay content decreases 2. sorting increases 3. non-quartz minerals decrease 4. grains within the deposit become more rounded vi. A poorly sorted glacial deposit, which contains relatively large quantities of clay-sized particles and poorly rounded larger particles, is immature vii. Well-sorted beach sand, on the other hand, which contains well-rouded particles and very little clay, is a mature sedimentary deposit d. Distribution i. Marine sedimentary can be categorized as neritic or pelagic. 1. Neritic deposits are found along continental margins and near islands. a. Beach Deposits
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i. Made of whatever materials are locally available. Mostly composed of quartz-rich sand and is transported by the waves that crash against the shoreline during storms. b. Continental Shelf Deposits i. Relict sediments – sediments that cover the continental shelf c. Turbidite Deposits i. Turbidity currents also carry vast amounts of neritic material, which spreads out as deep-sea fans, comprises the continental rise, and gradually thins toward the abyssal plains. ii. Composed of characteristic layering called graded bedding d. Glacial Deposits i. Laid down during the most recent ice age and are currently forming around the continent of Antarctica and around Greenland by ice rafting. ii.
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Chapter 4 - Intro to Oceanography: Chapter 4 I. What Is...

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