GeoWord of the Day

The GeoWord of the Day is a free service of the American Geosciences Institute. All of the terms and definitions are from the Glossary of Geology, 5th Edition Revised.

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bed configuration . A group of bed forms, produced by flow and making up a particular bed geometry. Cf: bed phase.

pore system . All the openings in a rock or sediment, considered as a unit (Choquette and Pray, 1970, p.214).

periderm [paleont] . (a) The protein substances that compose the rhabdosome of a graptolite, consisting of an inner part (fusellar tissue) with growth increments and an outer part (cortical tissue) of layers of material (cortical fabric). (b) In fetal amniotes, a transitory cellular or keratinized tissue (generally lost shortly after hatching or birth) that protects immature openings of the eyes, external ears, and margins of the mouth from dessication and attack by microorganisms (in mammals, commonly known as epitrichium).

fixed blade . Portion of longitudinal axis on upper side of platformed pectiniform conodont elements between free blade and carina; fixed blade is flanked by platforms (TIP, 1981, pt. W, supp.2).

corrasion (cor-ra'-sion). (a) A process of erosion whereby rocks and soil are mechanically removed or worn away by the abrasive action of solid materials moved along by wind, waves, running water, glaciers, or gravity; e.g., the wearing-away of the bed and banks of a stream by the cutting, scraping, scratching, and scouring effects of a sediment load carried by the stream, or the sawing and grinding action of sand, gravel, and boulders hurled by waves and currents against a shore. The term has also been used for the loosening of rock material by the impact of rushing water itself, and was used by Penck (1953, p.112) for the "freeing of loosened rock fragments from their place of origin". The term "abrasion" is essentially synonymous. Syn: mechanical erosion. (b) A term sometimes used as a syn. of attrition. (c) A term formerly used as a syn. of corrosion, or as including the work of corrosion. The term was first used by Powell (1875, p.205) for channel cutting or the deepening of any valley floor and was extended by Gilbert (1877, p.101) to the work of all running water (including lateral corrasion). Verb: corrade.

plutonist (plu'-to-nist). A believer in the theory of plutonism as promulgated by Hutton. Ant: neptunist. Obsolete.

wetland . An area that is regularly wet or flooded and has a water table that stands at or above the land surface for at least part of the year (NOAA, 2004). The term has supplanted more colloquial terms such as swamp and marsh.

thermoelastic stress . Stress in a body caused by a local temperature gradient within the body.

entropy map . A facies map that is based on the degree of "mixing" of three end members (rock components) of a given stratigraphic unit, but that does not distinguish the natures of these end members (see Forgotson, 1960; Krumbein and Sloss, 1963). Cf: entropy-ratio map.

resolution [speleo] . The solution of speleothems that come into contact with undersaturated water, often during flooding; sometimes called "redissolving".


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