Geology Essay

2509 WordsFeb 26, 201511 Pages
Name: 1 GEOL 104 Dinosaurs: A Natural History Geology Assignment DUE: Mon. Sept. 18 Part I: Environments of Deposition Geologists can use various clues in sedimentary rocks to interpret their environment of deposition: that is, the type of conditions that were present when they were laid down. Some aspects of the environment of deposition are revealed by the type of sedimentary rock. Carbonate rocks are composed of calcium carbonate, like limestone (including chalk): these form almost exclusively in saltwater (marine) environments. Coal, compressed plant material that was buried so fast it did not have time to decay, indicates the presence of swamps. On the other hand, sandstones and mudstones (like shale) can form in a variety of environments, so we need additional information. Another aspect of the environment recorded in the sedimentary rocks is the energy of the environment: that is, how fast the water (or wind) was moving. Essentially, the higher the energy, the larger the size of the particles of sediment. Slow moving water can only move extremely fine (small) particle sizes: silt, clay, and mud. This slow moving water might be the still water of lake or lagoon or the slowly moving water of a river at flood stage that has overflowed its banks. Moderately quick moving water (or fast moving wind) can move sand. Only the fast moving water can move gravel: these conditions are found in mountain streams or the deepest parts of the channels of rivers. Note that the energy of environment can affect the type of fossils preserved. Higher energy often means that the animal bodies will get buried faster, and so have a greater chance of being fossilized. However, higher energy also means that the bodies (especially of small animals) will tend to be torn apart and the edges of the fossils will be rounded by rolling. In contrast, large bodied animals

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