Physical Geology Chapter 7

Clastic

taken from Greek word meaning "broken". Rocks that contain discrete fragments and particles that are cemented in and compacted together.

Fossils

the remains or traces of pre-historic life, are important inclusions in sediment and sedimentary rock. Also, important tools for interpreting the geological past.

Understand the use of the term fossil fuel.

Coal is commonly called a fossil fuel. When coal is burned, energy from the sun that has stored by plants many millions of years ago is being used, hence the actual burning of "fossil."

Environment of deposition

: Each environment is characterized by certain physical, chemical, and biological conditions.

Diagenesis

A collective term for all of the chemical, physical, and biological changes that take place after sediments are deposited and during and after lithification.

What are the two primary ways that sediments are lithified into sedimentary rocks?

Diagenesis: When sediments are buried to relatively shallow depths they undergo a variety of processes collectively called diagenesis. Lithification: The transformation of sediments into sedimentary rock is called lithification. The two main processes that contribute to lithification are compaction (a reduction in pore space by packing grains in more tightly together) and cementation (a reduction in pore space by adding new mineral material that acts as rock a "glue" to bind the grains to each other).

Mud-cracks

Indicate that the sediment in which they were formed was alternately wet and dry. When exposed to air, wet mud dries out and shrinks, producing cracks. Associated with tidal flats, shallow lakes, and desert basins.

Detrital sedimentary rocks

Rocks that form from the accumulation of materials that originate and are transported as solid particles derived from both mechanical and chemical weathering.

Well sorted

Rocks with particles that are nearly all the same size.

Chemical sedimentary rocks

Sedimentary rock consisting of material that was precipitated from water by either inorganic or organic means.

Cross-bedding

Sediments accumulate horizontally. Most characteristic of sand dunes, river deltas, and certain stream channel deposits.

Poorly sorted

Sediments where there is a wide range of different sizes

Bedding planes

Separates each strata. Relatively flat surfaces along which rocks tend to separate.

Be prepared to distinguish between shale, sandstone, conglomerate, breccia, limestone, coquina, chalk, travertine, dolostone, chert, evaporites, and coal based on the information provided in your text. Understand the conditions under which each of these rocks formed.

Shale is made mostly of small grains of clay minerals. It accumulates in low-energy depositional environments such as the deep sea, lake bottoms, and floodplains adjacent to rivers. Shale is fissile due to the alignment of microscopic clay flakes parallel to bedding. Contain a lot of organic material accumulates in low-oxygen environments and is characterized by a black color. Sandstone is dominated by sand-sized grains. Sandstones may exhibit various degrees of sorting, in which similar-sized grains are deposited together Conglomerate and breccia are characterized by a high portion of gravel-sized grains. If deposited by water, a conglomerate implies a very energetic current, one capable of moving gravel. Grains in a breccia are angular, indicating that the material was deposited closer to its source area. Conglomerate is made of rounded grains, implying a significant amount of transport before deposition. Limestone is the most common chemical sedimentary rock. It forms mainly in shallow, warm ocean settings. Limestone is dominated by calcium carbonate. This is the material from which corals construct reefs. Coquina and chalk are also examples of biochemical limestone. Travertine and oolitic limestone are examples of inorganic limestone. Dolostone is a chemical sedimentary rock that is dominated by the mineral dolomite. Like calcite, dolomite is a carbonate mineral, but about half of ots calcium ions have been replaced by magnesium ions. Chert is the general term for rocks made of microcrystalline silica. If the chert is red, it is called jasper. Black chert is flint. Agate is multicolored. Evaporate deposits form when minerals precipitate from an ever-more-concentrated solution of dissolved ions. This is how the vast salt flats of American West formed. Coal forms from the burial of large amounts of plant matter in low-oxygen depositional environments such as swamps and bogs. Through compression, the peat becomes compressed into low-grade form of coal called lignite.

Ripple marks

Small waves of sand that develop on the surface of a sediment layer through the action of moving water or air.

Graded beds

Special type of bedding, the particles within the a single sedimentary layer gradually change from coarse at the bottom to fine at the top. Are most characteristic of rapid deposition of water containing sediment of varying sizes.

Sorting

The degree of similarity in particular size in sediment in sedimentary rock.

Nonclastic

The minerals form a pattern of interlocking crystals. The crystals might be microscopically small or large enough to be visible without magnification

Lithification

The process, generally involving cementation and/or compaction, of converting sediments to solid rock.

Strata or beds

The single most common characteristic feature of sedimentary rocks. Sedimentary rocks form as layer upon layer of sedimentary accumulates in various dispositional environments

Understand the process that forms coal and be prepared to distinguish between peat, lignite, bituminous coal, and anthracite.

Through compression, the peat becomes compressed into a low-grade form of coal called lignite, Lignite can be compressed further, driving out volatile components and concentrating carbon to make higher-grade bituminous coal. Metamorphism accompanying mountain building can take this concentration proceed even further, producing the highest grade coal, anthracite.