bentonite debris flow . A debris flow associated with the seasonal freezing and thawing and extreme cold of the arctic region, formed where easily hydrated bentonite-rich sediments are exposed to surface water (in moderate quantities for at least several weeks) on slopes of 5-30°, and developed in a smooth-sided, fluted, leveed, and U-shaped mudflow channel. Term proposed by Anderson et al. (1969, p.173) for such features near Umiat, Alaska.
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.
carbon-14 dating . A method of determining an age in years by measuring the concentration of carbon-14 remaining in an organic material, usually formerly living matter, but also dissolved bicarbonate, etc. The method, worked out by Willard F. Libby, U.S. chemist, in 1946-1951, is based on the assumption that assimilation of carbon-14 ceases abruptly upon removal of the material from the Earth's carbon cycle (i.e., on the death of an organism) and that it thereafter remains a closed system. Most carbon-14 ages are calculated using a half-life of 5,730 ± 40 years or 5,568 ± 30 years. Thus the method is useful in determining ages in the range of 500 to 30,000 or 40,000 years, although it may be extended to 70,000 years by using special techniques involving controlled enrichment of the sample in carbon-14. Syn: radiocarbon dating; carbon dating.
stibiopalladinite (stib''-i-o-pal-la'-di-nite). A metallic silver-white to steel-gray hexagonal mineral: Pd5Sb2 . Syn: allopalladium.
circle of longitude . A circle, parallel to the plane of the Earth's equator; along which longitude is measured.
internal sedimentation . Accumulation of clastic or chemical sediments derived from the surface of, or within, a more or less consolidated carbonate sediment (mud or silt), and deposited in secondary cavities formed in the host rock (after its deposition) by bending of laminae or by internal erosion or solution (Bathurst, 1958, p.31).
photointerpretation (pho''-to-in-ter''-pre-ta'-tion). The extraction of information from aerial photographs and images for a particular purpose, such as mapping the geologic features of an area. Also spelled: photo interpretation. Syn: photographic interpretation.
diffraction [waves] . The bending of a water wave around an obstacle, e.g., the bending of waves into the wave shadow behind an island.
stellate element . A pectiniform conodont element with four primary processes, one of which is anterior and another posterior (TIP, 1981, pt. W, supp.2).
chatoyancy (cha-toy'-an-cy). An optical phenomenon, possessed by certain minerals in reflected light, in which a movable wavy or silky sheen is concentrated in a narrow band of light that changes its position as the mineral is turned. It results from the reflection of light from minute, parallel fibers, cavities or tubes, or needlelike inclusions within the mineral. The effect may be seen on a cabochon-cut gemstone, either distinct and well-defined (as the narrow, light-colored streak in a fine chrysoberyl cat's-eye) or less distinct (as in the usual tourmaline or beryl cat's-eye). Var: chatoyance.
brandholzite . A vitreous colorless trigonal mineral: MgSb2(OH)12•6H2O.
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