burial metamorphism . A type of low-grade regional metamorphism affecting sediments and interlayered volcanic rocks in a geosyncline without any influence of orogenesis or magmatic intrusion. Original rock fabrics are largely preserved but mineralogical compositions are generally changed (Coombs, 1961). Cf: dynamothermal metamorphism.
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.
stomatal index . In paleobotany, the ratio of the number of epidermal cells to the number of stomata in a given area of a leaf, times 100. The index is used to compensate for the differences in stomatal density between sun and shade leaves, dry-climate and wet-climate leaves of the same species, and in the reconstruction of past levels of CO2. Cf: stomatal density.
exotic stream . A stream that derives much of its waters from a drainage system in another region; e.g. a stream that has its source in a humid or well-weathered area but that flows across a desert before reaching the sea. Example: the Nile. Cf: indigenous stream.
autocyclicity (au''-to-cy-clic'-i-ty). The state of cyclothemic deposition that requires no change in the total energy and material input into a sedimentary system but involves simply the redistribution of these elements within the system (Beerbower, 1964, p.32). It involves such mechanisms of deposition as channel migration, channel diversion, and bar migration. Cf: allocyclicity.
tiptopite (tip'-top-ite). A colorless hexagonal mineral: K2(Li,Na,Ca)6Be6(PO4)6(OH)2•H2O . It is structurally related to the cancrinite group.
striation (stri-a'-tion). (a) stria. (b) One of multiple scratches or minute lines, generally parallel, inscribed on a rock surface by a geologic agent, e.g., glaciers ( glacial striation ), streams (cf: drag mark ), or faulting (cf: slickenside ). Syn: scratch. (c) The condition of being striated; the disposition of striations. Adj: striated; striate.
linkage [geomorph] (link'-age). The joining at a sharp angle of two branches of a mountain range, as shown in plan view. Cf: deflection [geomorph].
acute bisectrix (a-cute'). In optically biaxial minerals, the direction bisecting the acute angle between optic axes. Cf: obtuse bisectrix.
confining bed (con-fin'-ing). A body of relatively impermeable or distinctly less permeable material stratigraphically adjacent to one or more aquifers. Cf: aquitard; aquifuge; aquiclude. Syn: confining unit .
tracheophyte (tra'-che-o-phyte''). A vascular plant; includes all plants that have a vascular system, i.e. xylem and phloem (Swartz, 1971, p.477).
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