GL 107 Earth Systems Science
K. Hannula
Discussion questions for 9/21/07
1. What are the differences between the places where the sediments that become conglomerate, sandstone, and shale are deposited?
Conglomerate can be deposited by fast-moving water: mountain streams, or on alluvial fans (where mountain streams flow onto valley floors). Conglomerate can also be deposited by glaciers or by landslides.
Sandstone can be deposited by wind, or by water than moves moderately fast. Rivers, beaches, and shallow ocean bottoms (where waves can move sand around) are places where sandstone can be deposited.
Shale is deposited in very still water -- water that does not move at all. Deep lake bottoms, or deeper parts of the ocean floor (too deep for waves to move sediment) are places where shale can form.
2. What kinds of information about a rock's history can you get from limestone?
Limestone can either be deposited chemically (say, from hot springs), or biochemically (as shells of organisms, both large and microscopic). Most biochemical limestone is deposited in oceans, although it can possibly form in lakes as well. Fossils found in limestone can provide a lot of information about a rock's history -- they can be used to tell how old the rock is, they tell about the biological communities that lived in the area (and the biological communities tell about the environment -- how deep was the water, how fast did it move, how warm was it, did light reach the ocean floor).
3. What kinds of information about the depositional environment can you get from rock salt and gypsum?
Rock salt and gypsum form by chemical precipitation from evaporating water. In order to form rock salt and gypsum, you need a hot, dry climate. Rock salt and gypsum can form in desert lakes (such as in Death Valley), or in tidal flats in hot, dry climates (such as along the Persian Gulf).
4. What kinds of information about a rock's history can you get from coal?
Coal forms from land plants, so coal tells you that the area was above sea level.