# 6.7: Volume and Distribution of Marine Sediments

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## Volume and Distribution of Marine Sediments

Of the 4 types of sediments, lithogenous and biogenous sediments are the most abundant on Earth today. Lithogenous sediment dominate the regions adjacent to continental landmasses (continental margins). The lithogenous sediment accumulations along continental margins can be many miles thick, especially where rivers have dumped large quantities of sediments for long periods of geologic time. Biogenous sediments accumulations can also be massive, particularly in locations where warn, shallow seas allow massive reef tracts to persist for long periods of time, such as with the Australian Great Barrier reef. Planktonic remains blanket the seafloor in large regions of the world's oceans. In contrast, cosmogenous and hydrogenous sediments are generally insignificant in comparison, but have important scientific and economic significance where they occur.

Sedimentary rocks are exposed throughout the world's continents, covering about half of the exposed land on the earth surface. This sedimentary cover blanketing continental areas was originally deposited mostly in coastal environments, in shallow seas flooding shallow continental basins, on continental shelves and in ocean basins along the margins of continents. Most of these sedimentary rocks that blanket much of the continents formed in the last several hundred million years. Even more massive quantities of sediments occur along continental margins in ocean basins. In many places around the world the thickness of sediments eroded from continental landmasses and volcanic chains and deposited in the adjacent ocean basin can be many miles thick! Sediments are thinnest or nonexistent on new ocean crust forming along mid-ocean ridges.

Most lithogenous sediments are on or near a landmass
• Coarser sediments accumulate closer to shore,
• Finer sediments are winnowed by waves and currents and are transported farther from shore to quieter water settings where they can settle out.

 Figure 6.17. Thickness of sedimentary deposits along continental margins. Figure 6.18. Distribution of sediments on the seafloor by type. Figure 6.19. Continental margins are places where large quantities of lithogenous and biogenous sediments accumulate. They are thinnest or missing on new ocean crust forming on mid-ocean ridges. Figure 6.20. Map of geologic provinces of the world. Sediments and sedimentary rocks not only cover much of the world's seabed but also cover large regions of the continents that were once under water.

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