Sedimentary Rocks

Sedimentary rocks form when sediment is compacted or cemented into solid rock Figure 3.2 Sedimentary layers of sandstone form steep cliffs above the San Juan River in Utah. Fig. 3-2, p.46

The Rock Cycle

Weathering Sediment becomes smaller, more rounded and more sorted silicate minerals react with water to form clay (a new solid mineral) and dissolved ions (quartz is the exception) Weathering agents: water (most important), wind, gravity, glaciers

Rock Cycle Processes - Lithification

Lithification: Turning sediment into sedimentary rock Compaction : wet, buried sediment is squeezed by overlying sediments, causing it to become more solid. Cementation minerals dissolved during the weathering process precipitate and act as a cement, e.g. calcite, silica, and iron oxide.

Sedimentary Rock Classification Based on sediment source Detrital Sedimentary Rocks Chemical Sedimentary Rocks Biochemical Sedimentary Rocks Organic Chemical Sedimentary Rocks

Detrital Sedimentary Rocks composed of solid sediment from weathered rocks conglomerate, sandstone, shale

Chemical Sedimentary Rocks Calcite CaCO3

Bio-

Chemical Sedimentary Rocks Composed of minerals precipitated from surface or ground water (chemical sediment) rock salt, rock gypsum Includes biochemical Sedimentary Rocks, composed of sediment of biological origin (e.g. shell fragments) Most common example is rock salt.

Organic sedimentary rocks Coal Different from other rocks because it is composed of organic material Stages in coal formation (in order) 1. Plant material 2. Peat 3. Lignite 4. Bituminous Coal 5. Anthracite (metamorphic)

Figure 6.13a,b

Figure 6.13b,c

Figure 6.13c,d

Sedimentary environments Sedimentary rocks contain evidence of past environments They provide information about climate (sediment size, presence or absence of water, sea level) Often contain fossils, which are indicators of both past climates and possible presence of fossil fuel.

Sedimentary environments Sedimentary environment or environment of deposition: A geographic setting where sediment is accumulating Determines the nature of the sediments that accumulate (grain size, grain shape, and other properties.) Today’s sedimentary rocks, tell us about past environments of deposition

Figure 6.5

Continental Sedimentary Environments Dominated by erosion and deposition associated with Streams Wind (eolian sandstones)

Continental Sedimentary Environments Glacial (morainal material) Alluvial fans (arkosic, feldspar-rich materials)

Shallow Marine Sedimentary Environments

Deep Marine Sedimentary Environments

Transitional Sedimentary Environments Tidal flats Lagoons Deltas

Sedimentary structures Provide information useful in the interpretation of Earth’s history Types of sedimentary structures Strata, or beds (most characteristic of sedimentary rocks) Cross-bedding Ripple marks Mud cracks

Figure 6.17

Figure 6.18a

Figure 6.18b

Figure 6.21a

Figure 6.21b