boring porosity . Porosity resulting from organisms boring into lithified substrate.
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.
paleic surface (pa-le'-ic). A smooth preglacial erosion surface, such as widely developed in Scandinavia.
Mangapanian (Man-ga-pa'-mi-an). South Pacific stage: middle Pliocene (above Waipipian, below Nakamaruan).
jaspery (jas'-per-y). Resembling or containing jasper; e.g. "jaspery iron ore" (impure hematite interbedded with jasper), or "jaspery chert" (a silicified radiolarian ooze associated with volcanic rocks in Ordovician strata of southern England). Syn: jaspidean.
bedding-plane cave . (a) A cave with passages, generally much wider than high, that have developed along a bedding plane, usually by dissolution of one of the beds. (b) A passage formed along a bedding plane, especially when there is a difference in susceptibility to corrosion in the two beds.
uniformity coefficient (u-ni-form'-i-ty). A numerical expression of the variety in particle sizes in mixed natural soils, defined as the ratio of the sieve size through which 60% (by weight) of the material passes to the sieve size that allows 10% of the material to pass. It is unity for a material whose particles are all of the same size, and it increases with variety in size (as high as 30 for heterogeneous sand).
brecciation (brec-ci-a'-tion). Formation of a breccia, as by crushing or breaking a rock into angular fragments.
zone of accumulation [mass move] . The area of a landslide within which the displaced material lies above the original ground surface (Varnes, 1978). Cf: zone of depletion.
desmid (des'-mid). One of a family of unicellular, microscopic green algae, commonly composed of semicells that are mirror images of each other.
core and mantle structure . The microstructure consisting of a central core of original grain grading outward into subgrains and/or newly recrystallized grains. It is indicative of subgrain rotation recrystallization.
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