Copy of `Illinois State Geological Survey - Geological terms`

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Illinois State Geological Survey - Geological terms
Category: Sciences > Geological Terms
Date & country: 25/07/2013, US
Words: 50

An interval of geologic time; a division of an epoch.

One that is actively depositing sediment in its channel or floodplain because it is being supplied with more load than it can transport.

A convex upward rock fold in which strata have been bent into an arch; the strata on each side of the core of the arch are inclined in opposite directions away from the axis or crest; the core contains older rocks than does the perimeter of the structure.

A geologic formation that is water-bearing and which transmits water from one point to another.

A relatively clean quartz sandstone that is well sorted and contains less than 10% argillaceous material.

The suite of mostly crystalline igneous and/or metamorphic rocks that generally underlies the sedimentary rock sequence.

A drainageway eroded into the solid bedrock beneath the surface materials. It may be completely filled with unconsolidated (non-indurated) materials and hidden from view.

A calcarenite containing abundant fossils or fossil fragments.

Describes a limestone composed of more or less worn fragments of shells or pieces of older limestone. The particles are generally sand-sized.

The heating of calcite or limestone to its temperature of dissociation so that it loses its carbon dioxide; also applied to the heating of gypsum to drive off its water of crystallization to make plaster of paris.

A cavity in the earth large enough for a human to enter. Caves can form as a result of physical and chemical weathering of rock. Physical weathering usually produces shelter-type caves that extend into the rock for only a few feet. Chemical weathering of rock can produce caves (solution channels along fractures and bedding planes) that extend for m...

The difference in altitude between the crest of a dome or anticline and the lowest structural or elevation contour that completely surrounds it.

Said of strata deposited one upon another without interruption in accumulation of sediment; beds parallel.

All rock material transported by a glacier and deposited either directly by the ice or reworked and deposited by meltwater streams and/or the wind.

A ridge or series of ridges formed by accumulations of drift built along the outer margin of an actively flowing glacier at any given time; a moraine that has been deposited at the lower or outer end of a glacier.

An adjective describing geologic features that are in an overlapping or staggered arrangement. Each is relatively short but collectively they form a linear zone.

An interval of geologic time; a division of a period. (Example: Pleistocene Epoch).

A unit of geologic time that is next in magnitude beneath an eon; consists of two or more periods. (Example: Paleozoic Era).

A fracture surface or zone of fractures in Earth materials along which there has been vertical and/or horizontal displacement or movement of the strata on opposite sides relative to one another.

Containing iron and magnesium; applied to mafic minerals.

Said of rock that tends to split into layers of suitable thickness for use as flagstone.

The surface or strip of relatively smooth land adjacent to a stream channel produced by the stream's erosion and deposition actions; the area covered with water when the stream overflows its banks at times of high water; it is built of alluvium carried by the stream during floods and deposited in the sluggish water beyond the influence of the swift...

(a) A very common mineral of the apatite group: Ca5(PO4) 3F. It is a common accessory mineral in igneous rocks. Syn: apatite. (b) An apatite mineral in which fluorine predominates over chlorine and hydroxyl.

Of or pertaining to a river or rivers.

Sedimentary deposits formed by a combination of fluvial (river) and lacustrine (lake) conditions.

Ordovician age groups of rock which are largely dolomite with a shaly zone near the middle and some limestone beds in the lower portion.

A plutonic rock in which quartz constitutes 10 to 50 percent of the felsic components and in which the alkali feldspar/total feldspar ratio is generally restricted to the range of 65 to 90 percent.

A fracture or crack in rocks along which there has been no movement of the opposing sides (see also Fault).

Collective term for the land forms and subterranean features found in areas with relatively thin soils underlain by limestone or other soluble rocks; characterized by many sinkholes separated by steep ridges or irregular hills. Tunnels and caves formed by dissolution of the bedrock by groundwater honeycomb the subsurface. Named for the region aroun...

Produced by or belonging to a lake.

The vertical difference in elevation between the highest and lowest points of a land surface within a specified horizontal distance or in a limited area.

A local steeping of an otherwise uniform gentle dip.

Cambrian sandstone with with a few thin red shale beds.

An unconformity resulting from deposition of sedimentary strata on massive crystalline rock.

The surface of a broad body of outwash formed in front of a glacier.

A crescent-shaped lake in an abandoned bend of a river channel. A precursor of a meander scar.

A land surface of regional scope worn down by erosion to a nearly flat or broadly undulating plain.

The study and classification of the surface features of Earth on the basis of similarities in geologic structure and the history of geologic changes.

A low arcuate ridge of sand and gravel developed on the inside of a stream meander by accumulation of sediment as the stream channel migrates toward the outer bank.

Said of an ocean or lake bottom that becomes progressively shallower as a shoreline is approached. The shoaling of the ocean bottom causes waves to rise in height and break as they approach the shore.

An indurated silt having the texture and composition of silt but lacking its fine lamination or fissility; a massive mudstone in which silt predominates over clay; a non-fissile silt shale.

A small interval of geologic time; a division of an age.

A convex-downward fold in which the strata have been bent to form a trough; the strata on either side of the core of the trough are inclined in opposite directions toward the axis of the fold; the core area of the fold contains the youngest rocks. (see also Anticline).

Pertaining to the global forces that cause folding and faulting of the Earth's crust. Also used to classify or describe features or structures formed by the action of those forces.

An abandoned flood plain formed when a stream flowed at a level above the level of its present channel and flood plain.

The undulating surface of low relief in the area underlain by ground moraine.

A surface of erosion or nondeposition that separates younger strata from older strata; most unconformites indicate intervals of time when former areas of the sea bottom were temporarily raised above sea level.

Nonlithified sediment that has no mineral cement or matrix binding its grains.

The accumulations of outwash deposited by rivers in their valleys downstream from a glacier.

The point in a well or opening in the Earth where groundwater begins. It generally marks the top of the zone where the pores in the surrounding rocks are fully saturated with water.