Most such basins are formed by plate tectonic processes, and some of the more important examples are shown in Figure 6.3.2. 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 that will last that long. Most 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 because they have only been deposited relatively recently-perhaps a few centuries or millennia ago-and are likely to be re-eroded before they are buried deep enough beneath other sediments to be lithified. Sand, silt, clay, and organic matter (in swampy parts only)Ĭarbonates in tropical climates, sand/silt/clay elsewhere Table 6.5 The important marine depositional environments and their characteristics Environment Sand (near the edges only), silt, clay, and organic matter Gravel, sand, silt, and organic matter (in swampy parts only) Glacial till, gravel, sand, silt, and clay Table 6.4 The important terrestrial depositional environments and their characteristics Environment

The characteristics of these various environments, and the processes that take place within them, are also discussed in later chapters on glaciation, mass wasting, streams, coasts, and the sea floor. We’ll look more closely at the types of sediments that accumulate in these environments in the last section of this chapter. Table 6.4 provides a summary of the processes and sediment types that pertain to the various depositional environments illustrated in Figure 6.3.1. Figure 6.3.1 Some of the important depositional environments for sediments and sedimentary rocks. Some of the more important of these environments are illustrated in Figure 6.3.1. Sediments accumulate in a wide variety of environments, both on the continents and in the oceans. Chapter 6 Sediments and Sedimentary RocksĦ.3 Depositional Environments and Sedimentary Basins

Sandstone depositional environment