tangential cross-bedding (tan-gen'-tial). Cross-bedding in which the foreset beds appear in section as smooth arcs meeting the underlying surface at low angles; large-scale tangential cross-bedding is commonly believed to imply deposition by wind. Cf: angular cross-bedding.
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.
sillar (sil-lar'). (a) The deposit from a pyroclastic flow ( ignimbrite ) that became indurated by recrystallization due to escaping gases rather than by welding, as is the case with welded tuff; it is a type of ignimbrite. (b) A nonwelded ash-flow tuff. Etymol: Peruvian.
ocean current . (a) A permanent predominantly horizontal movement of the surface water of the ocean, constituting part of its general circulation. (b) Broadly, any current in the ocean tidal or nontidal, permanent or seasonal, horizontal or vertical characterized by regularity, either as a continuous stream flowing along a definable path, or less commonly of a cyclic nature.
cepstrum . The Fourier-transform of a log frequency distribution (Sheriff and Geldart, 1995, p.298, 554).
geocentric longitude . (a) geodetic longitude. (b) The celestial longitude of a body based on or as seen from the Earth's center.
food cycle . All the food chains in an association of organisms; the food relations between the members of a population that make it possible for the population to survive.
stibiomicrolite . A white or greenish-white cubic mineral of the pyrochlore group: (Sb,Ca,Na)2(Ta,Nb)2(O,OH,F)7.
inverse estuary . An "estuary" in which evaporation exceeds the influx of fresh water (land drainage and precipitation) so that the salinity of its water rises above that of seawater. Ant: positive estuary . Syn: negative estuary.
trapezohedron (tra-pe''-zo-he'-dron). (a) An isometric crystal form of 24 faces, each face of which is ideally a four-sided figure having no two sides parallel, or a trapezium. Syn: tetragonal trisoctahedron; leucitohedron; icositetrahedron. (b) A crystal form consisting of six, eight, or twelve faces, half of which above are offset from the other half below. Each face is, ideally, a trapezium. The tetragonal and hexagonal forms may be right- or left-handed.
hinge line [paleont] . (a) A line along which articulation takes place; e.g. the middorsal line of junction of two valves of a crustacean carapace, permitting movement between them, or the line along which the two valves of an ostracode articulate, seen when the carapace is complete. (b) The straight posterior margin of a brachiopod shell, parallel to the hinge axis. The term is also used as a syn. of cardinal margin. (c) A term applied loosely to the part of a bivalve-mollusk shell bordering the dorsal margin and occupied by or situated close to the hinge teeth and ligament. The term is sometimes used as a syn. of hinge axis. Syn: hinge [paleont].
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