{"id":326,"date":"2018-08-24T15:10:35","date_gmt":"2018-08-24T19:10:35","guid":{"rendered":"https:\/\/opentextbc.ca\/physicalgeologyh5p\/chapter\/9-4-depositional-environments-and-sedimentary-basins-2\/"},"modified":"2023-07-04T12:53:47","modified_gmt":"2023-07-04T16:53:47","slug":"depositional-environments-and-sedimentary-basins","status":"publish","type":"chapter","link":"https:\/\/opentextbc.ca\/physicalgeologyh5p\/chapter\/depositional-environments-and-sedimentary-basins\/","title":{"raw":"9.4 Depositional Environments and Sedimentary Basins","rendered":"9.4 Depositional Environments and Sedimentary Basins"},"content":{"raw":"The setting in which sediments are accumulated is called a depositional environment<\/strong>. (Some of the more important of these environments are illustrated in Figure 9.19.) Thus far you've seen that some types of sedimentary rocks\u2014coal, and gypsum, for example\u2014require very specific conditions to form because particular biological processes or chemical reactions are necessary. Different types of clastic sedimentary rocks also form in particular depositional environments. In the case of clastic rocks, the key environmental conditions are related to the amount of energy available to transport sediments, and how far the sediments get from their source before being deposited.\r\n\r\nBroadly, depositional environments can be said to be terrestrial, marine, or to reflect a transitional zone between the two. Terrestrial<\/strong> refers to depositional environments on land. These may be depositional environments such as deserts, found on dry land, but they could also be environments such as freshwater lakes or rivers. Marine<\/strong> refers to environments associated with saltwater seas and oceans. Transitional depositional environments include environments such as deltas, where freshwater rivers empty into saltwater seas or oceans.\r\n\r\n[caption id=\"attachment_324\" align=\"aligncenter\" width=\"1024\"]\"\" Figure 9.19<\/strong> Some of the important depositional environments for sediments and sedimentary rocks. Source: Karla Panchuk (2021) CC BY-SA 4.0. Modified after Mike Norton (2018) CC BY-SA 3.0. Image source.<\/a>[\/caption]\r\n\r\nTables 9.1 and 9.2 provide a summary of the processes and sediment types that pertain to the various depositional environments illustrated in Figure 9.19. The types of sediments that accumulate in these environments are examined in more detail in the last section of this chapter.\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n
Table 9.1 Terrestrial Depositional Environments. Source: Karla Panchuk (2018), CC BY 4.0. Modified after Steven Earle (2015), CC BY 4.0. Data source<\/a>.<\/em><\/caption>\r\n
Environment<\/th>\r\nKey Transport Processes<\/th>\r\nDepositional Settings<\/th>\r\nTypical Sediments<\/th>\r\n<\/tr>\r\n
Glacial<\/td>\r\nGravity, moving ice, moving water<\/td>\r\nValleys, plains, streams, lakes<\/td>\r\nGlacial till, gravel, sand, silt, clay<\/td>\r\n<\/tr>\r\n
Alluvial<\/td>\r\nGravity, moving water<\/td>\r\nWhere steep-sided valleys meet plains<\/td>\r\nCoarse angular fragments<\/td>\r\n<\/tr>\r\n
Fluvial<\/td>\r\nMoving water<\/td>\r\nStreams<\/td>\r\nGravel, sand, silt, organic matter<\/td>\r\n<\/tr>\r\n
Aeolian<\/td>\r\nWind<\/td>\r\nDeserts and coastal regions<\/td>\r\nSand, silt<\/td>\r\n<\/tr>\r\n
Lacustrine<\/td>\r\nMoving Water<\/td>\r\nLakes<\/td>\r\nSand, silt, clay, organic matter<\/td>\r\n<\/tr>\r\n
Evaporite<\/td>\r\nStill water<\/td>\r\nLakes in arid regions<\/td>\r\nSalts, clay<\/td>\r\n<\/tr>\r\n<\/tbody>\r\n<\/table>\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n
Table 9.2 Marine & Transitional Depositional Environments Source: Karla Panchuk (2018), CC BY 4.0. Modified after Steven Earle (2015), CC BY 4.0. Data source<\/a><\/em><\/caption>\r\n
Environment<\/th>\r\nKey Transport Processes<\/th>\r\nDepositional Settings<\/th>\r\nTypical Sediments<\/th>\r\n<\/tr>\r\n
Deltaic<\/td>\r\nMoving water<\/td>\r\nDeltas<\/td>\r\nSand, silt, clay, organic matter<\/td>\r\n<\/tr>\r\n
Beach<\/td>\r\nWaves, long-shore currents<\/td>\r\nBeaches, spits, sand bars<\/td>\r\nGravel, sand<\/td>\r\n<\/tr>\r\n
Tidal<\/td>\r\nTidal currents<\/td>\r\nTidal flats<\/td>\r\nFine-grained sand, silt, clay<\/td>\r\n<\/tr>\r\n
Reef<\/td>\r\nWaves, tidal currents<\/td>\r\nReefs and adjacent basins<\/td>\r\nCarbonates<\/td>\r\n<\/tr>\r\n
Shallow marine<\/td>\r\nWaves, tidal currents<\/td>\r\nShelves, slopes, lagoons<\/td>\r\nCarbonates in tropical climates; sand\/silt\/clay elsewhere.<\/td>\r\n<\/tr>\r\n
Lagoonal<\/td>\r\nLittle transportation<\/td>\r\nLagoon bottom<\/td>\r\nCarbonates in tropical climates, silt, clay<\/td>\r\n<\/tr>\r\n
Submarine fan<\/td>\r\nUnderwater gravity flows<\/td>\r\nContinental slopes, abyssal plains<\/td>\r\nGravel, sand, silt, clay<\/td>\r\n<\/tr>\r\n
Deep water<\/td>\r\nOcean currents<\/td>\r\nDeep-ocean abyssal plains<\/td>\r\nClay, carbonate mud, silica mud<\/td>\r\n<\/tr>\r\n<\/tbody>\r\n<\/table>\r\n
\r\n\r\n<\/a>Practice with Depositional Environments<\/strong>\r\n\r\n[h5p id=\"108\"]\r\n\r\n<\/div>\r\n

Sedimentary Basins Are Needed to Collect Sediment<\/h1>\r\nMost of the sediments that you might see around you, including talus on steep slopes, sand bars in streams, or gravel in road cuts, will never become sedimentary rocks. This is because they've only been deposited relatively recently\u2014perhaps a few centuries or millennia ago\u2014and will be re-eroded before they are buried deep enough beneath other sediments to be lithified. In order for sediments to be preserved long enough to be turned into rock (a process that takes millions or tens of millions of years) they need to have been deposited in a basin in which sediments can be preserved for that long. Most such basins are formed by plate tectonic processes (Figure 9.20).\r\n\r\n[caption id=\"attachment_325\" align=\"aligncenter\" width=\"650\"]\"\" Figure 9.20 <\/strong>Some types of tectonically produced basins: (a) trench basin, (b) forearc basin, (c) foreland basin, and (d) rift basin. Source: Steven Earle (2015), CC BY 4.0. Image source.<\/a>[\/caption]\r\n\r\nTrench basins<\/strong> form where a subducting oceanic plate dips beneath the overriding continental or oceanic lithosphere. They can be several kilometres deep, and in many cases, host thick sequences of sediments from nearby eroding coastal mountains. There is a well-developed trench basin off the west coast of Vancouver Island.\r\n\r\nA forearc basin<\/strong> lies between the subduction zone and the volcanic arc, and may be formed in part by friction between the subducting plate and the overriding plate, which pulls part of the overriding plate down. The Strait of Georgia, the channel between Vancouver Island and the BC mainland, is a forearc basin.\r\n\r\nA foreland basin<\/strong> is caused by the mass of a mountain range depressing the crust. A rift basin<\/strong> forms where continental crust is being pulled apart, and the crust on both sides the rift subsides. If rifting continues this will eventually becomes a narrow sea, and then an ocean basin. The East African rift basin represents an early stage in this process.\r\n
\r\n\r\n<\/a>Practice with Types of Sedimentary Basins<\/strong>\r\n\r\n
\r\nFill in the missing words to complete the descriptions of the different types of sedimentary basins.<\/strong>\r\n\r\nOne type of sedimentary basin forms when continental crust begins to split apart and sag downward. This is a\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0<\/span> basin.\r\n\r\nOther types of sedimentary basins are related to subduction zones. The deepest type, a \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0<\/span> basin, occurs right where subduction is happening.\r\n\r\nIf a subducting plate drags down the front edge of the plate with which it's colliding, a \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0<\/span> basin could form between the subduction zone and a chain of volcanic mountains.\r\n\r\nThanks to isostasy, the weight of the mountains themselves can flex the lithosphere downward into a \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0<\/span> basin.\r\n\r\nTo check your answers, navigate to the below link to view the interactive version of this activity.<\/strong>\r\n<\/div>\r\n[h5p id=\"109\"]\r\n<\/div>","rendered":"

The setting in which sediments are accumulated is called a depositional environment<\/strong>. (Some of the more important of these environments are illustrated in Figure 9.19.) Thus far you’ve seen that some types of sedimentary rocks\u2014coal, and gypsum, for example\u2014require very specific conditions to form because particular biological processes or chemical reactions are necessary. Different types of clastic sedimentary rocks also form in particular depositional environments. In the case of clastic rocks, the key environmental conditions are related to the amount of energy available to transport sediments, and how far the sediments get from their source before being deposited.<\/p>\n

Broadly, depositional environments can be said to be terrestrial, marine, or to reflect a transitional zone between the two. Terrestrial<\/strong> refers to depositional environments on land. These may be depositional environments such as deserts, found on dry land, but they could also be environments such as freshwater lakes or rivers. Marine<\/strong> refers to environments associated with saltwater seas and oceans. Transitional depositional environments include environments such as deltas, where freshwater rivers empty into saltwater seas or oceans.<\/p>\n

\"\"
Figure 9.19<\/strong> Some of the important depositional environments for sediments and sedimentary rocks. Source: Karla Panchuk (2021) CC BY-SA 4.0. Modified after Mike Norton (2018) CC BY-SA 3.0. Image source.<\/a><\/figcaption><\/figure>\n

Tables 9.1 and 9.2 provide a summary of the processes and sediment types that pertain to the various depositional environments illustrated in Figure 9.19. The types of sediments that accumulate in these environments are examined in more detail in the last section of this chapter.<\/p>\n\n\n\n\n\n\n\n\n\n
Table 9.1 Terrestrial Depositional Environments. Source: Karla Panchuk (2018), CC BY 4.0. Modified after Steven Earle (2015), CC BY 4.0. Data source<\/a>.<\/em><\/caption>\n
Environment<\/th>\nKey Transport Processes<\/th>\nDepositional Settings<\/th>\nTypical Sediments<\/th>\n<\/tr>\n
Glacial<\/td>\nGravity, moving ice, moving water<\/td>\nValleys, plains, streams, lakes<\/td>\nGlacial till, gravel, sand, silt, clay<\/td>\n<\/tr>\n
Alluvial<\/td>\nGravity, moving water<\/td>\nWhere steep-sided valleys meet plains<\/td>\nCoarse angular fragments<\/td>\n<\/tr>\n
Fluvial<\/td>\nMoving water<\/td>\nStreams<\/td>\nGravel, sand, silt, organic matter<\/td>\n<\/tr>\n
Aeolian<\/td>\nWind<\/td>\nDeserts and coastal regions<\/td>\nSand, silt<\/td>\n<\/tr>\n
Lacustrine<\/td>\nMoving Water<\/td>\nLakes<\/td>\nSand, silt, clay, organic matter<\/td>\n<\/tr>\n
Evaporite<\/td>\nStill water<\/td>\nLakes in arid regions<\/td>\nSalts, clay<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n\n\n\n\n\n\n\n\n\n\n\n
Table 9.2 Marine & Transitional Depositional Environments Source: Karla Panchuk (2018), CC BY 4.0. Modified after Steven Earle (2015), CC BY 4.0. Data source<\/a><\/em><\/caption>\n
Environment<\/th>\nKey Transport Processes<\/th>\nDepositional Settings<\/th>\nTypical Sediments<\/th>\n<\/tr>\n
Deltaic<\/td>\nMoving water<\/td>\nDeltas<\/td>\nSand, silt, clay, organic matter<\/td>\n<\/tr>\n
Beach<\/td>\nWaves, long-shore currents<\/td>\nBeaches, spits, sand bars<\/td>\nGravel, sand<\/td>\n<\/tr>\n
Tidal<\/td>\nTidal currents<\/td>\nTidal flats<\/td>\nFine-grained sand, silt, clay<\/td>\n<\/tr>\n
Reef<\/td>\nWaves, tidal currents<\/td>\nReefs and adjacent basins<\/td>\nCarbonates<\/td>\n<\/tr>\n
Shallow marine<\/td>\nWaves, tidal currents<\/td>\nShelves, slopes, lagoons<\/td>\nCarbonates in tropical climates; sand\/silt\/clay elsewhere.<\/td>\n<\/tr>\n
Lagoonal<\/td>\nLittle transportation<\/td>\nLagoon bottom<\/td>\nCarbonates in tropical climates, silt, clay<\/td>\n<\/tr>\n
Submarine fan<\/td>\nUnderwater gravity flows<\/td>\nContinental slopes, abyssal plains<\/td>\nGravel, sand, silt, clay<\/td>\n<\/tr>\n
Deep water<\/td>\nOcean currents<\/td>\nDeep-ocean abyssal plains<\/td>\nClay, carbonate mud, silica mud<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n
\n

<\/a>Practice with Depositional Environments<\/strong><\/p>\n

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