JOHN DAY FOSSIL BEDS Geology and Paleoenvironments of the Clarno Unit John Day Fossil Beds National Monument, Oregon

acidic - with a low pH (<7), or abundance of hydronium ion (H⁺) in solution

aging upwards sequence - sedimentary succession including paleosols whose degree of development is generally stronger for paleosols higher within the succession than for those near the base

agglomeroplasmic - soil microfabric in which there is an incomplete or local fine-grained matrix to skeleton grains

agrotubule - tubular feature of soil filled with pellet-like clasts of and clastic grains

A horizon - surface horizon of a soil, commonly including organic matter

Albaqualf - kind of Alfisol that shows gley features and a sandy near surface horizon above the clayey subsurface horizon

albic horizon - light colored soil horizon characterized by less organic matter, less sesquioxides (Fe₂O₃ and Al₂O₃), or less clay than the underlying horizon. Its light color is due largely to quartz and feldspar.

Alfisol - fertile forest soil, with subsurface clayey, ferruginized or humic horizon

alkali elements - sodium (Na) and potassium (K)

alkaline - with a high pH (>7), and low activity of hydronium (H⁺) ions in solution

alkaline earth elements - calcium (Ca) and magnesium (Mg)

allophane - poorly ordered hydrous aluminum silicate

alluvial fan - large conical landform deposited by streams entering intermontane basins from narrow mountain valleys

alluvium - sedimentary deposits of rivers

alumina - aluminum oxide (Al₂O₃)

alveolar-septal structure - micromorphology of calcareous soils, with thin micritic compartments filled with sparry calcite, thought to form around fungi associated with roots

anaerobic decay - a metabolic reaction in which organic matter is broken down in the absence of oxygen into simpler compounds, including CO

andesite - silica saturated volcanic rock, often porphyritic with large crystals commonly plagioclase and groundmass; characteristic of volcanic arcs associated with subduction zones

andic - with properties like that of an Andisol

Andisol - Inceptisol-like soils formed on volcanic ash, with low bulk density, high porosity and great fertility

anthropic epipedon - surface horizon of a soil altered by human activity, such as habitation

Ap horizon - A horizon disrupted by plowing or other comparable disturbance

Aqualf - kind of Alfisol with gley features

Aquent - kind of Entisol with gley features

Aquept - kind of Inceptisol with gley features

aquic - showing gley features

Aquod - kind of Spodosol with gley features

Aquoll - kind of Mollisol with gley features

Aquox - kind of Oxisol with gley features

Aquult - kind of Ultisol with gley features

aragonite - mineral with the same chemical composition as calcite, but a different crystal structure, primarily found in skeletons of molluscs

Arent - kind of Entisol, with surface layers mixed by plowing or other human activity

Argid - kind of Andisol with argillic or natric horizons

argillan - cutan consisting of clay

argillasepic - soil microfabric mainly of clay and lacking highly birefringent streaks when viewed in thin section under crossed nicols

argillic horizons - soil horizon of clay enrichment, recognized in the field by oriented clay films that coat either mineral grains, small channels or ped surfaces. Compared with eluvial horizons argillic horizons have 3% more clay if eluvial horizon clay is 10-15%, 12% more clay if eluvial horizon clay is 15-40%, or 8% more if eluvial horizon clay is 40-100%.

Argiustoll - kind of Ustoll with a clayey subsurface horizon

Andisol - desert soil, usually thin profiles, commonly with calcareous nodules or salt crystals within a meter of the surface

anthropod - phylum of jointed legged animals, such as insects, spiders, and crayfish

asepic - soil microfabric lacking highly birefringent streaks (plasma separations) when viewed under crossed nicols

atomic absorption spectrometry - method of chemical analysis using light absorption wavelengths of flaming aerosol of sample

backfill structure - sinuous or simply curved layering within the filling sediment of a burrow produced by movement of an animal

badlands - erosional landform of deeply gullied sedimentary rocks too unstable and in too dry a climate to support a cover of vegetation

basaltic rocks - rocks like basalt, that are rich in iron and magnesium, fined grained and generally produced as volcanic flows

base - principal cations of soil solutions (Ca²⁺, Mg²⁺, Na⁺, K⁺)

base saturation - percentage of the cation exchange capacity due to bases

basket podzol - locally thickened sandy subsurface (E or eluvial) horizon under an individual tree

bauxite - highly weathered material rich in aluminum, and poor in humus, silica and bases, consisting mainly of gibbsite or similar minerals

Bc horizon - B horizon with concretions or nodules

Bg horizon - B horizon with strong gleying

B horizon - subsurface horizon of soil, often enriched in clay or carbonate

billet - small sawn slab of rock used to prepare a petrographic thin section

bimasepic - sepic plasmic fabric with a network of highly birefringent streaks in two preferred directions

biofunction - mathematical relationship between soil features and soil biota

biosequence - set of soils formed under similar climate, topographic setting, parent material and time, but different vegetation or other organisms

bioturbated - mixed and moved by the burrowing, rooting and other activities of organisms

birefringence - iridescent appearance of minerals when viewed in a microscope under cross-polarized light

birnessite - poorly crystalline mineral of dark iron and manganese oxides

Bk horizon - B horizon with accumulation of carbonates, usually calcite nodules

blocky peds - a form of ped that is polygonal and nearly equant in shape

Bn horizon - B horizon with accumulation of sodium

bog - general term for wetland vegetation, used especially for vegetation of mosses

Bo horizon - B horizon with residual accumulation of sesquioxides

Bonalf - a kind of Alfisol of cool to cold climates

Boroll - a kind of Mollisol of cool to cold climates

breccia - coarse grained rock with angular clasts

Bs horizon - B horizon with illuvial accumulation of sesquioxides

Bt horizon - B horizon with illuvial accumulation of clay

bulk density - a measure of mass in a given volume (grams per cubic centimeter); usually indicated by symbol ρ

burrow - tunnel or other excavation of a soil animal

butte - isolated hill or mountain with steep sides, usually having a smaller summit area than a mesa

Bw horizon - with colored or structural B horizon

By horizon - B horizon with accumulation of gypsum

Bz horizon - B horizon with accumulation of salts

calcareous - consisting largely of calcite

calciasepic - soil microfabric dominated by a mixture of clay and clay-sized carbonate, and lacking highly birefringent streaks when viewed in thin section under crossed nicols

calcic horizon - subsurface soil horizon enriched in calcite or dolomite in the form of coatings, wisps or nodules, and at least 15 cm thick with at least 5% more carbonate than underlying horizons.

calcification - soil building process of the accumulation of carbonate, usually as nodules in subsurface horizons

calcite - carbonate mineral (CaCO₃)

calcrete - rock cemented with calcium carbonate

caliche - pedogenic calcium carbonate nodules or layers

cambic horizon - subsurface soil horizon with at least enough pedogenic alteration to eradicate some rock structure, form some soil structure, and remove or redistribute primary carbonate. Their color has higher chroma or redder hue than does the color of the underlying horizons.

capillary action - tendency of fluids to rise in a small cylinder due to surface tension

carbonaceous - with abundant organic matter

carbonate - common anion (CO₃^2-) in soil solution and component of carbonate minerals such as calcite and siderite and skeletons such as mollusc shells

carboxyl - common radical of organic acids (COOH⁺)

caries texture - soil microfabric in which grains are deeply embayed because of local dissolution or hydrolysis

carnivore - animal that eats meat

carr - wetland vegetation of trees with alkaline groundwater

cation exchange capacity - measure of a soils exchangeable cations (mainly H⁺, Al³⁺, Ca²⁺, Mg²⁺, Na⁺, K⁺), usually by displacement with ammonium chloride and titration for its abundance

catena - A sequence of soils developed from similar parent material under similar climatic conditions but whose characteristics differ because of variations in relief and drainage.

celadonite - clay mineral {(K,Ca,Na)_-1.6(Fe³⁺, Al, Mg, Fe²⁺)₄Si_7.3Al_0.7O₂₀(OH)₄}

cement - fine grained binding substance that holds together rocks and firm parts of soil, typically silica or calcium carbonate

C horizon - subsurface soil horizon, excluding bedrock, with slightly more weathered material from which the soil formed or is presumed to have formed. Lacks properties of A and B horizons, but includes weathering as shown by mineral oxidation, accumulation of silica, carbonates or more soluble salts, and gleying.

chalcedony - microcrystalline quartz (SiO₂)

chaparral - synonym of fireprone shrubland, used mainly in California

charcoal - charred wood

chelate - a chemical compound capable of transporting elements or compounds by means of a particularly favorable site of attachment (from Greek chela for claw)

chlorite - clay like mineral {(Mg,Fe²⁺, Fe³⁺, Mn, Al)₁₂[(Si,Al)₈O₂₀](OH)₁₆}

chroma - purity of color, or degree to which a color is not masked by darkness or lightness in the Munsell system of color

Chromudert - a kind of Vertisol of humid seasonally dry climates, which has some horizons that are not black

chronofunction - mathematical relationship between soil features and the time over which they develop

chronosequence - set of soils formed under similar climate vegetation, topographic position and parent material but over varying lengths of time

clastic dike - crack in soil or sediment filled with contrasting material: silan in terminology of Brewer

clay skin - coating of clay along cracks or grains within a soil: argillan in terminology of Brewer

clinobimasepic - sepic plasmic farbic with a network of highly birefringent streaks in two preferred directions and at a low angle

clinometer - device for measuring angular deviation from horizontal

coal - black carbon-rich rock formed by burial alteration of peat

coalification - process forming coal from peat by expulsion of volatile materials and enrichment in carbon due to heat and pressure of deep burial

colloid - material that is too fine grained to be visible under the optical microscope, includes soil iron stain and clay colluvium. Soil materials that accumulate on and at the base of slopes by gravitational action.

complex-response - Change of the bedload transport rate in a fluvial system in response to a single external perturbation.

compression - form of fossil preservation in which the organic remains of the fossil are crushed and coalified between bedding planes

concretion - glaebule with concentric internal fabric, usually because of periodic addition of material. These are hard, locally cemented lumps of material with onion-skin internal layering.

cone - ellipsoidal structure of helically arranged reproductive organs of plants, found in conifers, lycopods and clubmosses

coprolite - fossil feces

corestone - spheroidally weathered remnant of parent material, least weathered toward the center, and usually within the C horizon of deep weathering profiles

cornstone - pedogenic calcium carbonate nodules of paleosols

cover slip - thin glass cover glued on top of a petrographic thin section

Cretaceous - period of geological time about 146-65 million years ago

cross bedding - sedimentary layering that is inclined to regional layering, commonly due to the formation of dunes with slip-faces at an angle to the ground surface

crystal chamber - irregular nodular masses of crystals

crystallaria - single crystals or groups of crystals in soils

crystallinity - degree of perfection of crystal structure, free of defects or other less regular arrangement of chemical constituents

crystallite - small crystal, beyond the size resolvable by optical microscopy

crystic - a soil microfabric dominated by crystals

cuirasse - indurated hardpan or crust exposed at the surface, usually lateritic

cumulic horizon - soil horizon that shows bedding or other evidence that it is accumulating in a sedimentary fashion on top of the soil

cutan - modified surface within a soil, formed at surface of a ped channel, grain or other feature of the soil

cuticle - tough, coating of hydroxy fatty acids and waxes that covers the leaves and other aerial parts of land plants

cutinite - a kind of exinite, formed from plant cuticles

Cv horizon - C horizon with plinthite

decalcification - soil-building process of leaching out carbonate from surface horizons

decarboxylation - chemical reaction removing carboxyl radical from organic matter

decomposition - decay, or breaking down of organic matter to simpler compounds such as carbon dioxide by decomposer microbes

dehydration - chemical reaction involving loss of water or hydroxyl

depth unction - common graphical presentation of chemical and petrographic data on soils and paleosols as a plot with one axis the depth from the surface of the profile

desert pavement - surface layer of stones, sometimes as closely interlocking as a cobblestone street

desert scrub - vegetation of widely scattered thorny shrubs and succulents such as cactus, with patches of bare ground

deviatoric - aligned in unpredictable and random directions

diagenesis - alteration of sediments after burial but before metamorphism: includes soil formation

diaspore - aluminum-rich mineral [AlO(OH)].

diffractogram - plot of the x-ray reflections produced for identification of minerals from an x-ray diffractometer

diffusion cutan - cutan formed by concentration at the surface of a material which becomes less prominent away from the surface for example the strong oxidation of the margins but not interior of peds

displacive fabric - a soil microfabric in which one mineral (usually calcite) fills cavities opened by the expansion or rotation of large clods of soil or the cracking out of clods or grains

dolomite - carbonate mineral (CaMg(CO₃)₂]

domed-columnar ped - ped in the form of a vertically-oriented prism, usually as thick as the whole B horizon and with its upper surface hemispherical: common in salt affected soils

drab-haloed root traces - root traces that are surrounded by soil of a gray and often also bluish or greenish color, compared with the yellow to red soil or paleosol away from the root trace

duricrust - hard cemented horizon of soil or deep weathering profile, includes laterite, bauxite, calcrete and silcrete

duripan - subsurface soil horizon cemented firmly by clay and silica

Dystrochrept - kind of Ochrept soil that is very low in weatherable bases

ecosystem - the complex of a community and its environment functioning as a unit in nature

Eh - electrode potential (usually in millivolts): for soils a measure of the degree of oxidation of the soil. Oxidized soils have a high positive Eh and reduced soils have a low negative Eh.

E horizon - soil horizon underlying O or A horizon, characterized by less organic matter, less sesquioxides (Fe₂O₃ and Al₂O₃) or less underlying horizon. Its light color is due largely to quartz and feldspar. Also known as an eluvial or albic horizon.

eluvial horizon - soil horizon characterized by less organic matter, less sesquioxides (Fe₂O₃ and Al₂O₃), or less clay than the underlying horizon. Its light color is due largely to quartz and feldspar

endocarp - interior woody part of a seed or fruit coat of plants, also known as a pit or stone, as in cherries and peaches

endolithic microrelief - system of surface cavities formed by microbes living within and on rocks

endoskeleton - internal skeleton, as in mammals

energy dispersive x-ray spectrometry - method of chemical analysis using x-rays emitted from sample in scanning electron microscope (EDAX)

Entisol - very weakly developed soils, usually with abundant sedimentary, igneous or metamorphic relicts from their parent material

Eocene - epoch of geological time about 57-33 million years ago

Ephemeral Stream - A stream that flows only briefly in direct response to rainfall or snowmelt.

epidermis - outer covering of cells of a plant or animal

estuary - that part of a river mouth that is influenced by marine tides

Eutrochrept - kind of Ochrept rich in bases

evaporite - sedimentary rock that forms by the accumulation of the evaporation of water, includes rock salt and gypsum

exoskeleton - skeleton, as in arthropods

extinction angle - angular difference between the orientation of a crystal and the point at which it can no longer transmit polarized light as viewed in petrographic thin section under a microscope, useful for identifying minerals such as feldspars

facies - an informal an rock unit, usually designated by features thought to be significant for interpreting sedimentary paleoenvironment

factor-function approach - study of environmental control in the expression of soil features, can be used also to infer paleoenvironmental conditions from paleosols

fecal pellet - small ovoid to spherical feces produced by small animals

feldspar - group of minerals including microcline and plagioclase

fen - wetland vegetation of grasses and other herbs with alkaline groundwater

ferran - cutan consisting of sesquioxides of iron

ferric iron - iron in the Fe³⁺ valence state, usually within red or yellow minerals or compounds

ferrous iron - iron in the Fe²⁺ valence state, usually within gray to green minerals or compounds

ferruginous rhizoconcretion - rhizoconcretion cemented by goethite, hematite or other iron hydroxides or oxides

fibric peat - peat with abundant recognizable plant material, not completely decayed

Fibrist - kind of Histosol consisting largely of plant remains so little decomposed that their botanical origin can be determined

fibrous roots - numerous fine (usually less than 2 mm diameter) roots radiating from the base of a plant, as in palms and grasses

fining upwards sequence - sedimentary layer that varies toward smaller grain size from the bottom to the top

fireprone shrubland - closely spaced woody shrubs, less than 2 m tall adapted to frequent burning

fission tracks - Imperfections in minerals and volcanic glass caused by spontaneous fission of unstable atomic nucleus, which propels energy particles through surrounding material. The density of tracks is a function of numbers of atoms that have undergone fission, and thus also of age.

flocculation - aggregation into a coherent mass from fine suspended particles, as can happen to clay particles in turbid water with changes in salinity

floodplain - frequently flooded, low lying region flanking large rivers

fluorescence - emission of electromagnetic radiation usually as a response to absorption of another form of radiation

Fluvent - kind of Entisol, those formed on silt and clay with conspicuous relict bedding

fluvial - relating to rivers

Folist - kind of Histosol, freely-drained, consisting primarily of organic horizons derived from leaf litter, twigs and branches resting on rock, gravel or boulders, the interstices of which are filled with organic material

footslope - lower convex part of a hill slope, between steeper backslope and more level toeslope

foraminfer - marine microorganisms that secrete or manufacture a small shell

forb - herbaceous plant other than grasses, found typically in rangeland

forest - vegetation of closely spaced trees more than 8 m tall

formation - The most fundamental local, rock division of stratigraphic classification, which has some distinctive homogeneity of lithology (color, texture, fossil content, etc.); generally named formally for some geographic locality (e.g. John Day Formation for the John Day region of Oregon).

fragipan - A hard and brittle subsoil horizon commonly cemented with amorphous silica and/or aluminum.

framboid - minute (10 microm to 1 mm diameter) round spherules or groups of spherules of pyrite, usually produced by anaerobic bacteria

freeze-thaw banding - structure of cracks and silty seams in pattern of brickwork, produced by frost heaving of soils

friable - easy to break into constituent grains: opposite of cemented or indurated

ganister - silicified sandstone, commonly containing root traces and underlying a coal seam. These are in most cases paleosol E or eluvial horizons.

geothermal gradient - variation in temperature of the Earth with depth into the crust

gibbsite - mineral rich in aluminum [Al₂(OH)₃]

gilgai microrelief - soil surface of ridges and swales or potholes produced by the shrinking and swelling of Vertisols

glaebule - segregations of materials distinct from other parts of the soil, including nodules, concretions, and septaria

gleization - process of gley formation

gley - soil that is blue-gray or green-gray colored, strongly mottled or with abundant iron-manganese nodules, usually due to waterlogging, but sometimes produced also by burial

glossic features - locally penetrating tongues or tubes of light-colored sandy material deep within a soil profile

glycolation - experimental, treatment of clays by exposure to open container of ethylene glycol at 80°C for 4 hours, used to study expansion of smectite clays

goethite - yellow to brown iron hydroxide mineral Fe₂O₃•H₂O)

graded bed - sedimentary bed that varies in gram size from the bottom to the top of the bed. Normally graded beds are finer grained to the top, and inversely, graded beds are coarser grained toward the top.

granotubule - tubular feature of soil filled with clastic grains and little clay

granular microfabric - soil microfabric in which skeleton grains are touching with little or fine grained matrix in the interstices

granular ped - a form of ped or clod that is small and rounded

grassland - vegetation of mainly grasses

"Green Clay" - kind of paleosol I found in Precambrian rocks, with unusual combination of indications of deep weathering (corestones, cracks) and gley colors (green gray with chemically reduced iron minerals)

groundwater calcrete - calcrete formed by precipitation of carbonate cement from groundwater

groundwater gley - gley features formed by the ponding of groundwater from an elevated water table

groveland - vegetation of clumps of trees separated by open grassland

guano - excrement of birds and bats

gypsic horizon - subsurface soil horizon with accumulation of gypsum

gypsum - evaporite mineral (CaSO₄•2H₂O)

hackly - having the appearance of something chopped or cut up

Haplaquept - typical Aquept, lacking distinguishing features of other kinds of Aquepts

Haplohumult - typical Humult, lacking distinguishing features of other kinds of Humults

Haplorthod - typical Orthod, lacking distinguishing features of other kinds of Orthod

Haploxerand - typical Xerand, lacking an especially dark surface horizon

Hapludalf - typical Udalf, lacking distinguishing features of other

Hapludoll - typical Udoll, lacking distinguishing features of other kinds of Udolls

Haplustalf - typeical Ustalf, lacking distinguishing features of other kinds of Ustalfs

Haplustoll - typical Ustoll, lacking distinguishing features of other kinds of Ustolls

halite - mineral of desert soils (NaCl)

halloysite - hydrated form of kaolinite

Harden index - quantitative measure of the degree of soil development, calculated by addition of scores for a variety of soil features thought to vary with time of formation

hardpan - A soil horizon cemented with silica, sesquioxides, calcium carbonate or organic matter.

hematite - red iron oxide mineral (Fe₂O₃)

hemic peat - peat in which some but not all of the plant material is so decayed as to be unrecognizable

Hemist - a kind of Histosoll in which organic matter is decomposed to the extent that as much as two-thirds of the plant material is unidentifiable

herbivore - animal that eats plants

histic epipedon - peat: a soil surface horizon with at least 18% organic matter if the mineral fraction contains more than 60% clay or 12% organic matter if the mineral fraction has no clay, for a depth of 20 cm.

Histosol - soil with peaty surface, which must be at least 40 cm thick if composed mainly of woody material

Holocene - epoch of geological time from 10,000 years ago to present

hornblende - a mineral of igneous and metamorphic rocks [(Na,K)_0-1Ca₂(Mg,Fe²⁺,Fe³⁺, Al)₅Si_6-7.5Al_2-0.5O₂₂(OH)₂]

hue - color, such as red, yellow or green, independent of lightness or darkness of the color, in the Munsell system of color classification

Humult - kind of Ultisol with a surface horizon rich in organic matter

humus - The well-dcomposed, relatively stable part of the organic matter found in aerobic soils.

hydrocarbon - compound mainly of hydrogen and carbon, including methane and paraffin

hydrolysis - common weathering reaction in soil solutions, converting aluminosilicate minerals to clay and cations in solution

hydronium - hydrogen ion (H⁺)

hydrothermal - related to groundwater of elevated temperature, commonly associated with volcanic activity

hydroxide - compound including hydroxyl

hydroxyl - chemical anion (OH^-)

ice wedge - vertical wedgelike disruption of a soil filled with horizontally layered material after melting of the ice that created it

ichnogenus - formal taxonomic category for a specific kind of trace fossil, similar to a genus of biological classification

ICP - inductively-coupled plasma emission spectrometry

illite - potassium-rich clay mineral {K_1.5-1.0Al₄[Si_6.5-7.0Al_1.5-1.0O₂₀](OH)₄}

illitization - common process during deep burial that converts smectite clays to illite

illuvial horizon - soil horizon enriched in clay by illuviation

illuviation - soil building process of enrichment of clay washed in from higher horizons

illuviation cutan - cutan formed by washing down of material from higher within a soil

impression - form of fossil preservation in which only an outline of the fossil remains with none of the original organic material

INAA - instrumental neutron activation analysis

Inceptisol - soils with some weathering and incipient development of a variety of different kinds of horizons, but none well-enough developed that the soil could be identified with another order

incisor - front tooth of mammals, greatly elongated in rodents

indurated - firm, hard, cemented

insepic - sepic plasmic fabric with small isolated patches of highly birefringent plasma

intercalary crystal - single crystal embedded in soil matrix

interstratified clays - clays with crystal layers of differing chemical composition

intertextic - soil microfabric in which skeleton grains are more prominent than fine grained matrix, which forms intergranular braces and fills local pockets

inundulic - soil microfabric similar to undulic, but cloudy, with large irregular isotropic patches which appear dark when viewed under crossed nicols

isotic - soil microfabric that is dark when viewed under crossed nicols because either isotropic, like opal, or opaque, like hematite

isotope - alternative forms of a chemical element that differ slightly in mass and sometimes also in other properties. Common isotopes of carbon are the very heavy radiogenic isotope ¹⁴C used for carbon dating, and the stable isotopes ¹³C and ¹²C.

isotopic dating - Mineral or rock dating using radioactive isotopes. Radioactive isotopes decay at constant rates therefore the ratio of daughter isotope to its unstable parent determines how long the radioactive parent has been in the mineral or rock.

isotropic mineral - a mineral whose crystal structure shows no preferred orientations: appears black in thin section under cross polarized light

isotubule - tubular feature of soil filled with mixed clay and clastic grains without any preferred orientation

Jacob staff - survey pole used for taking angular differences in elevation and horizontal differences in distance with clinometer

jarosite - powdery, yellow mineral smelling of rotten eggs [KFe₃(OH₆)(SO₄)₂], forms by oxidative weathering of pyrite

kandic horizon - subsurface soil horizon similar to argillic horizon in clay enrichment, but clays are kaolinitic and there are very few weatherable minerals remaining

kaolinite - base-poor clay mineral {Al₄{Si₄O₁₄](OH)₈}

karst - landform formed from the weathering and dissolution of limestone, often rugged with caves and pinnacles

karst bauxite - kind of bauxite formed within depressions of karst landscapes

kerogen - particulate organic matter lacking regular chemical structure and insoluble in organic solvents and mineral acids, present in sedimentary rocks

K horizon - subsurface soil horizon so impregnated with carbonate that its morphology is determined by the carbonate. Authigenic carbonate coats or engulfs all primary grains in a continuous medium and makes up 50% or more by volume of the horizon. The uppermost part of the horizon commonly is laminated. If cemented, the horizon corresponds with some caliches and calcretes.

krotovina - tubular feature in a soil filled with material from a higher soil horizon

Kubler index - measure of clay crystallinity using the width of x-ray diffractometer peaks

kunkar - pedogenic calcium carbonate nodules or layers

labile minerals - minerals such as olivine and pyroxene that are relatively easily weathered

lacustrine - relating to lakes

larval cell - chamber used for rearing young in the complex nests of social insects such as termites, bees and ants

laterite - highly weathered material rich in iron, and poor in humus, silica and bases

lattisepic - sepic plasmic fabric with a network of highly birefringent streaks in two preferred directions that are at a right angle

lentil ped - soil clods that are shaped like an elongate parallellogram, usually with slickensided faces and characteristic of Vertisols

lessivage - soil-building process of washing down of clay into subsurface cracks

lichen - plantlike organism formed by the symbiotic association of fungi and algae

ligament - tough tissue that connects bones or supports internal organs of animals

lime - calcium oxide (CaO)

limestone - rock formed mainly of calcite

linear gilgai - gilgai microrelief of elongate ridges and swales, usually running downslope

lithic sandstone - sandstone whose clasts are mainly rock fragments

lithofunction - mathematical relationship between soil features and parent material of the soil

lithorelict - rock fragment in a soil remaining from its parent material

lithosequence - set of soils formed under similar climate, vegetation, topographic setting and time, but varying parent material

litter - accumulation of leaves, wood and other decaying organic matter on the surface of soil

loess - deposits of wind-blown glacial dust

macronutrients - elements needed in large amounts for the nourishment of plants, including hydrogen (H), carbon (C), nitrogen (N), oxygen (0), magnesium (Mg), phosphorus (P), sulfur (S), potassium and calcium (Ca)

magnesia - magnesium oxide (MgO)

magnetite - an iron-rich mineral [Fe²⁺Fe³⁺₂O₄]

mangal - vegetation consisting of mangroves

mangan - cutan consisting of oxides or hydroxides of iron and manganese

mangrove - tree capable of living within the intertidal zone of the ocean

maquis - synonym of fireprone shrublands, used mainly for vegetation around the Mediterranean Sea

marsh - wetland vegetation of grasses and other herbs with acidic to neutral groundwater

masepic - sepic plasmic fabric with highly birefringent streaks forming an extensive criss-crossing network

megaspore - large (usually more than 60 microm diameter) spores of some kinds of ferns, lycopods and similar plants

member - Formal stratigraphic subdivisions of formations.

mesa - hill with a flat top

metaranotubule - tubular feature in a soil filled with sandy material from a higher soil horizon

metamorphism - alteration of rocks during deep burial and heating, generally to more than 200°C or greater than 7 km, whichever comes first

metasediment - metamorphosed sedimentary rock

metatubule - tubular feature of soil filled with material different from soil matrix and derived from some other soil horizon

micrite - very fine grained sediment of calcite and clay minerals

micritization - soil forming process whereby coarsely crystalline calcite or other materials are converted to micrite

microarthropod - microscopic arthropod, including springtails and mites

microbe - microscopic organism

microbial earth - vegetation of microbes living on and within a friable soil

microfabric - arrangement of constituents visible by microscopy

Milankovitch effect - Cyclic change of temperature of the earths surface due to combined effects of variations in the tilt of axis, wobble of axis (p recession), and ellipticity of the orbits.

mineral - Naturally occuring chemical element or compound with a definite composition, a characteristic crystal form, and other distinctive physical properties.

ministromatolite - small (often microscopic) domed structure with internal lamination, formed by the growth of microbial colonies

Miocene - epoch of geological time about 23-5 million years ago

moderately developed soil or paleosol - with surface rooted zone and obvious subsu ace clayey, sesquioxidic, humic or calcareous or surface organic horizons, qualifying as argillic, spodic or calcic horizons or Histosol and developed at least to the extent of nodules for calcic horizons

moder humus - organic matter consisting of a mix of recognizable plant material and other organic material completely decayed: intermediate between mor and mull humus

moisture equivalent - percentage moisture in a soil at "field capacity", which is the point at which water is no longer moving through or filling soil pores, but bound in immobile films to grains and roots

mole - mass in grams of Avogadro's number (6.022x10²³) of atoms or molecules of an element of compound, calculated by dividing weight percent of analyzed element or compound by its atomic weight

molecular weathering ratio - ratio of chemical constituents in moles, calculated in order to understand changing chemical proportions due to weathering

mollic epipedon - soil surface horizon of grassland soils, with fine structure (usually granular peds), dark color (chroma of 3 or less, value darker than 5 when dry), contains at least 1% organic matter (0.58% organic carbon), and has a base saturation of over 50%

Mollisol - grassland soil with a mollic epipedon at least 18 cm thick

monsoonal climate - climate of very marked seasonal rain fall, as in the Indian subcontinent

mor humus - organic material consisting of little decayed plant material, such as the dried pine needles commonly preserved under conifer forest

mosepic - sepic plasmic fabric with partly adjoining highly birefringent streaks

mottle - glaebules of very irregular shade and diffuse boundaries, usually expressed as different ore areas of soil

mucigel - gelatinous zone within the rhizosphere, rich in bacteria and fungi

mudflow - rapid downslope movement of a slurry of mud and boulders after rain storms or volcanic eruptions

mukkara structure - subsurface deformation of soil horizons, usually with the surface horizon festooned between ridges of exposed cracked subsurface horizon, produced by shrinking and swelling of Vertisols

mull humus - organic matter decayed so that plant structure is no longer visible, as in the surface horizon of grassland soils or Mollisols

murram - loose aggregate of pea-sized lateritic gravel used for road building

natric horizon - soil subsurface horizon more than 15% saturated with exchangeable sodium, commonly also with salts and prismatic or domed columnar peds

Natrustoll - kind of Ustoll, with abundant sodium or other indications of salt accumulation such as domed-columnar peds

needle fiber calcite - calcite crystals in the form of microscopic needles, commonly precipitated by soil fungi

neocutan - altered area within a soil at a surface as well as some distance in from the surface. These are unusually thick cutans.

neoferran - neocutan of iron oxides of hydroxides

neomorphism - change in form of crystals, including recrystallization

neutron activation analysis - method of chemical analysis using radiation induced after neutron irradiation in a nuclear reactor

nicols - polarizing light filters on a petrographic microscope

Nitosol - Ultisol or Oxisol with abundant slickensided clay skins in the F.A.O. soil classification

nodule - glaebule with an undifferentiated, massive internal fabric. These are usually local hard, cemented lumps of soil material.

normal fault - Fault along which the upper block has moved down relative to the lower block along a steeply inclined surface; characteristic of crust that has been subjected to tension.

normative mineral composition - estimate of the proportions of minerals present in a specimen calculated from the chemical composition of the specimen and ideal compositions of the minerals

Ochrept - kind of Inceptisol with ochric and cambic horizons, and sometimes also, poorly developed calcic horizons, fragipans or duripans.

ochric epipedon - soil surface horizon too light in color and low in organic matter to be mollic or umbric.

O horizon - surface accumulation of organic material overlying mineral soil

Oligocene - epoch of geological time about 33-23 million years

oligotrophic forest - forest living in low nutrient soil such as a Sodosol

olivine - a mineral of igneous rocks {Mg,Fe)₂[SiO₄]}

omnisepic - sepic plasmic fabric dominated by highly birefringent, oriented plasma, with a "woven" appearance

omnivore - animal that eats meat and plants

ooid - small (1-2 mm diameter) round grain with internal concentric structure

opal - silica mineral (SiO₂•nH₂O)

opalite - silica cemented shale or claystone

opaque - not pervious to light, and so black when viewed in a petrographic thin section

optical axis figure - arrangement of light interference bands seen when minerals are viewed in particular orientations within petrographic thin sections and useful for mineral identification

organan - cutan consisting of organic matter

Orthent - kind of Entisol, formed on erosional remnants such that hard bedrock, or relict soil material, is within 25 cm of the surface

Orthid - kind of Aridisol, lacking an argillic horizon

Orthod - kind of Spodosol, with a subsurface horizon including both sesquioxides and organic matter

orthotubule - tubular feature of soil filled with material of very similar fabric and composition to soil matrix

oxidation - chemical reaction in which electrons are lost to valence of elements with multiple valence states, for example Fe²⁺ to Fe³⁺, which commonly is achieved by means of oxygen as a electron sink

oxic horizon - highly weathered subsurface horizon characterized by hydrated oxides of iron and aluminum, 1:1 lattice clays, and low cation-exchange capacity. Few primary silicate minerals remain with the exception of quartz, which is quite resistant to weathering.

oxidized groundwater - water within soils and rocks that is rich in oxygen. Oxidizing groundwaters are rare, and largely found within actively-recharged, sandy aquifers, because of oxygen scavenging by microbes and by minerals

Oxisol - deeply weathered soils with kaolinitic clays, quartz and few weatherable minerals

oxygen-isotope analysis - Ration of ¹⁸O to ¹⁶O in shells composed of CaCO₃ provides indication of paleotemperature of seawater when the shell was formed.

Paleocene - epoch of geological time about 65-57 million years ago

paleochannel - former river channel, usually marked by an elongate deposit broadly lenticular in cross section, of cross bedded sandstone or conglomerate

paleoecology - study of the ecology of fossil organisms

paleomagnetism - former orientation of Earth's magnetic field as recorded in magnetic minerals in rocks

paleopedology - study of paleosols

paleosol - soil of a landscape of the past: a surficial region of a planet or similar body altered in place by biological, chemical or physical processes, or a combination of these

Paleudalf - kind of Udalf that is very strongly developed, usually over a long period of time (hundreds of thousands of years)

Paleudult - kind of Udult that is very strongly developed, usually over a long period of time (hundreds of thousands of years)

Paleustalf - kind of Ustalf that is very strongly developed, commonly with a continuous subsurface calcareous horizon

pallid zone - horizon of white clay and bleached or mottled rock beneath laterite in a deep weathering profile

palygorskite - mineral of desert soils [(OH₂)₄Mg₅Si₈O₂₀•4H₂O]

pampas - synonym of grassland, used mainly in South America

papule - glaebule of clay, a useful non-genetic term if one is not sure whether they are clay galls of the original parent material, void fills or segregations of clay

paratubule - tubular feature of soil filled with material different from soil matrix and unlike anything else within the profile

parent material - Initial material of a soil.

parkland - vegetation of woodland with numerous large grassy clearings

ped - natural aggregate of soil; that is, stable lumps or clods of soil between cracks, roots, burrows or other planes of weakness

pediment - An erosion surface formed by the retreat of an escarpment.

pedofacies - kind of sedimentary facies containing one or more paleosols and dominated by pedogenic features such as nodules, mottles and root traces

pedogenic - formed in association with soil

pedolith - sedimentary deposit composed of clasts that are clearly derived from soils, such as talus slopes of lateritic clasts below a laterite scarp

pedon - A single soil profile in a landscape; it is the smallest soil descriptive unit.

pedorelict - soil structure that formed in a different soil than the one in which it is found, for example a calcareous nodule within the gravelly parent material of a non-calcareous soil

pedotubule - tubular features of soils, including roots and burrows

pedotype - reference profile for definition of a soil or paleosol mapping unit

pegmatite - coarsely crystalline rock mainly of quatz and feldspar, usually forming veins within granitic rocks

peg root - short, bluntly-ending roots that protrude from the ground, as in mangroves

Pennsylvanian - period of geological time about 323-290 million years ago

perched water table - level of water ponded in soil by an impermeable subsurface layer

peridotite - rock formed mainly of olivine

periostracum - outer, thin, brown organic layer covering the shells of some molluscs, such as snails and freshwater clams

Permian - period of geological time about 290-250 million years ago

permineralized - infiltrated with cementing minerals, as in the silica that fills woody cell contents to create permineralized wood. Such wood is often incorrectly referred to as petrified, but the cellulose cell walls remain, and have not been turned to stone.

petrocalcic horizon - subsurface soil horizon cemented firmly with calcium carbonate

petroferric horizon - subsurface soil horizon cemented firmly with iron oxides and hydroxides

petrography - description of rocks, usually including study in thin section

petrogypsic horizon - subsurface soil horizon cemented firmly with gypsum

pH - negative logarithm of the activity of the hydronium ion (H+): soils a measure of acidity. Acidic soils have a low pH (<7) and alkaline soils have a high pH (>7), with a total observed range of 4.5-11, from a theoretical 1-14.

phenocryst - large crystals in a prophritic rock

phytolith - mineral particle made by a plant, such as opal bodies of grasses

pisolite - spherical concretions usually about 2 to 15 mm in diameter.

plagioclase - mineral of igneous rocks [Na(AlSi₃O₈)—Ca(AlSi₃O₈)]

plasma - fine grained material of soil microfabric, making up peds, including amorphous clay and iron stain

platy ped - form of ped that is thin but wide, often formed by weathering of sedimentary layers

playa lake - desert basin, rarely inundated, usually dry and covered in salt and clay

Pleistocene - epoch of geological time about 1.6 million to 10,000 years ago

plinthite - iron-rich, humus-poor clayey part of a soil, usually mottled red and yellow, and with the distinctive property of hardening irreversibly to an iron hardpan upon drying. This term is used or those kinds of laterites that are found within soil

Pliocene - epoch of geological time about 5 to 1.6 million years ago

podzolization - soil building process of acidic leaching into subsurface horizon of sesquioxides, organic matter or combinations of these

point-counting - systematic search and record of grain type or size made to determine mineral composition or grain size of paleosols

polygenetic Soil - A soil that has been formed by two or more different and contrasting processes so that the horizons are not genetically related.

porcellanous - with the appearance of china or porcelain

porosity - percent void space between grains and peds of soil; complement to solidity

porphyritic - crystalline texture of large crystals isolated within a fine grrained matrix

poyroskelic - soil microfabric in which grains are dispersed fine grained matrix, like phenocrysts in a porphyritic rock

potash - potassium oxide ([K₂O])

prairie - synonym of grassland, used mainly for vegetation in North America temperatures of about

pressure solution - process of dissolution of grains of rock by the pressures of deep burial focused at grain contacts

primary porosity - proportion of void space between grains and peds in the original soil or sediment

profile - A vertical section through a soil from the surface into the relatively unaltered material.

productivity - a measure of biological accumulation of organic matter, measured as grams of carbon or of dry organic matter per meter per year

"Protorendzina" - weakly developed soil with mollic surface horizon on limestone bedrock

Psamment - kind of Entisol, formed on sand, especially eolian dunes, with relict bedding

pseudoanticline - uparched bedding planes that are confined to a particular layer, and so thought to be due to local clay heave or crystallization rather than regional folding that produces anticlines

pseudomorph - mineral grain that has adopted the form of another mineral, usually as a result of replacement of that mineral, for example, chalcedony pseudomorphs of gypsum

pseudomycelium - fine irregular filaments of calcium carbonate in soil

ptygmatic - folded back on itself in a complex way

pyrite - common mineral of mangal and salt marsh soils (FeS₂)

pyroxene - mineral of igneous rocks {(Mg,Fe)Si₂O₆}

quartz - common mineral of soils (SiO₂)

quasicutan - altered area within a soil that is thick and shows a relationship to a surface, but is not right at the surface. Quasicutans form a kind of halo following the outline peds, grains and other features.

quasimangan - quasicutan of iron-manganese

Quaternary - period of geological time from 1.6 million years ago to present

radiogenic - prone to decay with the release of radioactivity

rain forest - forest living in a very humid climate

rangeland - region of open vegetation, including wooded grassland, grassland and desert scrub

rare earth elements - elements with atomic number 57-71, also known as lanthanides, of which lanthanum (La), cerium (Ce), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), ytterbium (Yb), and lutetium (Lu) are commonly analyzed in rocks and soils

recrystallization - process of forming new crystals without a change in chemical composition

red beds - sediments or sedimentary rocks that are largely red in color

reddening - change in color from brownish red (Munsell 10YR) to brick red (Munsell 5R) that occurs during soil formation and during burial of soils

reductant - chemical compound capable of inducing reduction

reduction - a chemical reaction in which electrons are donated to change the valence of elements with multiple valence states, for example converting ferric iron (Fe³⁺) to ferrous iron (Fe²⁺)

REE - rare earth elements

regolith - The unconsolidated mantle of weathered rock, soil and superficial deposits overlying solid rock.

relict structures - features persisting in soil from its parent material, including bedding, crystalline structure and schishosity

relief - degree to which the margins of a mineral grain stand out from its surroundings as viewed in thin section under a microscope

Rendoll - kind of Mollisol formed on limestone bedrock

replacive fabric - microfabric of soils in which one mineral is converted incompletely and over an irregular front into another mineral

residuum - material remaining after a long period of weathering

resistate minerals - minerals such as quartz and microcline that are resistant to weathering and tend to persist as other minerals are destroyed in soils

respiration - metabolic process of organisms, whereby organic food is converted into energy and carbon dioxide

reverse fault - Fault along which the upper block has moved down relative to the lower block; characteristic of crust that has been subjected to compression.

R horizon - consolidated or weathered bedrock underlying the soil

rhizoconcretion - concretion that forms by cementation of soil around a root

rhizoid - elongated epidermal cell that functions as a root, as in mosses, liverworts and primitive land plants

rhizome - a rootlike structure of plants which lies along or within the ground, but which is really a stem, as revealed anatomically and in its pattern of branching and budding

rizosphere - area of influence a root in the soil

rhyolite - silica rich volcanic rock

ripple mark - sedimentary structure of small scale undulations of a bedding plane: miniature dunelike forms produced by wind or water currents

rock varnish - thin crust of red to black iron and manganese oxides and clay formed on the surface of rocks in deserts, lakes and streams, largely as a result of microbial activity

root - branching subterranean structure of plants, often with some woody internal thickening

root hair - elongate cell erect on the surface of roots, most common a short distance behind the growing tip of roots.

rootlet - side branch from roots.

root trace - tubular cavity or irregular marking left in soils and paleosols by roots, recognized by irregular tubular shape, tapering downwards branching downward or outward from a center, and (for deeply buried paleosols) concertina-like shape due to compaction of surrounding sediment around the main lateral rootlets

saccharoidal - like sugar crystals

salic horizons - subsurface soil horizon with accumulations of salt

salinized - affected by salt accumulation

Salorthid - kind of desert soil or Aridisol, which has salts such as gypsum within the profile and lacks a subsurface horizon of clay enrichment

salt marsh - wetland vegetation of grasses and other herbs with saline groundwater, usually within the intertidal zone of bays

sand crystal - sand cemented into the shape of a crystal of cementing material, usually gypsum

sand wedge - vertically oriented wedgelike disruption of a soil filled with vertically banded sediments from opening and closing with freezing and thawing

sapric peat - peat in which organic matter has decayed to such an extent that little if any of the original plant components are recognizable

Saprist - kind of Histosol, consisting mainly of decomposed and unrecognizable plant mattes

saprolite - less altered lower portion of weathering profiles, showing some weathering, but much relict bedding, schistosity or crystalline structure remaining from parent material

savanna - commonly used as a synonym of wooded grassland, but also widely taken to include grassy woodland

scanning electron microscope - microscope that uses electron beams to create images

schist - metamorphic rock of clay grain size showing pronounced schistosity

schistosity - degree of development of planes of fissility and foliation characteristic of fine rained metamorphic rocks

sclerotia - rounded, woody bodies, with interlaced, elongate, hollows produced by the resting stages of fungi

secondary porosity - a system of tubes and vesicles developed in rock during deep burial associated with maturation of buried organic matter

sedimentary facies - Overall lithology of strata reflecting environment of deposition; characteristics of one environment such as beach sand, grade laterally into facies of another environment.

SEM - scanning electron microscope

sepic plasmic fabric - appearance of soil thin sections viewed under cross-polarized light of wisps or streaks of highly oriented and highly birefringent clay in a less organized dark matrix: a characteristic micro fabric of soils

sepiolite - mineral of desert soils [(OH₂)₄Mg₅Si₁₂O₃₀·8H₂O]

septarium (plural septaria) - glaebule with a complex system of internal cracks, usually due to shrinkage

sesquan - cutan consisting of sesquioxides of iron and aluminum

sesquioxides - alumina (Al₂O₃) and ferric iron (FeO₃)

shrubland - vegetation of low-growing woody shrubs, such as sagebrush and saltbush

siderite - carbonate mineral of waterlogged and organic rich soils (FeCO₃)

silan - cutan consisting of silica

silasepic - soil microfabric dominated by silt and sand grains, and lacking highly birefringent streaks when viewed under crossed nicols

silcrete - a silica cemented material associated with weathering profiles

silica - silicon dioxide (SiO₂)

siliceous - composed mainly of silica

silicified - cemented by silica

sinker - deeply-penetrating large root, that takes advantage of deep groundwater

sinter - silica-rich, often vuggy, deposits formed around volcanic hot springs

skeletan - cutan consisting of clastic grains such as quartz or feldspar

skeleton grains - clastic grains such as quartz and feldspar within the soil microfabric

skeletonized leaf - plant leaf decayed in such a way that cuticle and soft tissues have been removed to reveal the woody vascular traces or veins

skelsepic - sepic plasmic fabric with highly birefringent plasma associated with the outer surface of skeleton grains

slickenside - smooth to striated surface of a rock produced by shearing within soils, during burial crushing of soil peds and during faulting

slide - small glass pane used for supporting thin section of rock or soil

smectite - a base-rich clay mineral {1/2Ca,Na)_0.7(Al,Mg,Fe)_4-6[(Si,Al)₈O₂₀](OH)₄•nH₂O}

soil - The subaerial surface of the earth; a membrane between the lithosphere and atmosphere.

soil creep - downslope movement of hillside soils, as revealed by bending into the surface of near vertical veins and bedding planes

soil horizons - gradational changes in texture or mineral content down into parent material of a soil or paleosol from the truncated land surface

soil structure - three dimensional features characteristic of soils

solidity - percent solid grains or ped in a soil: complement to porosity

soluan - cutan consisting of soluble salts such as gypsum or calcite

solum - altered upper part of a weathering profile, including the various named soil horizons

sparry calcite - calcite crystals large enough to be discernable under an optical microscope

spherical microped - microscopic sphere-shaped soil clod, typical of tropical soils and produced as oral and fecal pellets of termites

spherulite - spherical aggregate of radiating crystals

spicule - small pointed mineral body made by an animal as part of its skeletal support, such as the opal bodies of freshwater sponges

spodic horizon - subsurface soil horizon formed by concentration of organic matter and sesquioxides that have been translocated downward from an E horizon

Spodosol - acidic sandy soil with B horizons enriched in organic matter, iron and aluminum or combinations of these, but not clay

sporinite - kind of exinite coal maceral, formed from spores and pollen

standard error - measure of the variation of a set of data points around a mean value or fitted curve, defined as the square root of variance after division by the number of data points

stele - central conducting strand of tracheids or xylem found within roots and stems of plants

steppe - synonym of grassland, used mainly for grasslands of Asia

stoichiometry - measurement of proportions of components for conservation of matter and energy in chemical equations and formulae

stone line - layer of pebbles or other large rock fragments confined to a narrow horizon, commonly an erosional plane, and conspicuous as the only large clasts in an otherwise one grained soil

stratovolcano - steep volcanic cone constructed by successive layers of ash and lava

stratigraphic sequences - Intervals of conformable strata bounded by unconformities.

stream terrace - Former level of a broad valley floor that was created by aggradation or by lateral fluvial erosion, but now is above the present floodplain because of incision by the stream. A terrace consists of a tread and a riser, which separates the tread from the stream or a lower terrace.

stress cutan - cutan formed by differential forces within the soil such as shearing due to swelling and shrinking induced by wetting and drying

striotubule - tubular feature of soil filled with mixed clay and clastic grains with curved internal layering

strongly developed soil or paleosol - with especially thick (2-3 m), sea, clayey or humic subsurface (B) horizons or surface organic horizons (coal or lignites) or especially well developed soil structure or calcic horizons as a continuous layer

subcutanic features - modifications of soil material that show a relationship to a surface, but do not occur only at that surface

Sulfaquent - kind of Aquent with common sulfur minerals such as pyrite or jarosite, commonly formed under salt marsh and mangal vegetation

Sulfaquept - kind of Aquept with common sulfur minerals such as pyrite or jarosite, commonly formed under salt marsh and mangal vegetation

sulfate - common anion (SO₄^2-) in soils, found in minerals such as gypsum

surface water gley - gley features formed by the ponding of water by impermeable soil layers above drier subsoil

swale - local elongate depression on the landscape, typically from abandoned flood channels

swamp - wetland vegetation of trees with acidic to neutral ground water

tap root - single, thick, vertical root, like that of a carrot

taxonomic uniformitarianism - assumption that soil types of the past formed under similar environmental conditions to taxonomically similar soils of the present

taxonomy - classification: for soils, used to distinguish the soil classification of the U.S. Soil Conservation Service (originally entitled "Soil Taxonomy") from other classifications

telinite - kind of vitrinite coal maceral, formed from wood fragments with some crushed, cellular structure remaining

tepee structure - inverted V-shaped local disruption of layering within a bed, due to action of roots or clay swelling

terrace - flat geomorphic surface representing the erosional remnant of a former land surface

Tertiary - period of geological time about 65-1.6 million years ago

thin section - transparent slice of rock or soil mounted between glass covers, used for microscopic examination

topofunction - mathematical relationship between soil features and topographic setting of soil

toposequence - set of soils formed under similar climate, vegetation, parent material and time, but varying topographic setting

Torrand - kind of Andisol of very dry climate, with little clay or colloidal material, and abundant salts and carbonate at shallow levels within the profile.

Torrox - kind of Oxisol of very dry climates

trace fossil - fossilized evidence of the activity of an organism, such as a fossil footprint or burrow

trachyte - volcanic intrusive and flow rock close to saturation with silica, consisting mainly of alkali feldspar

transform fault - A lateral or strike-slip fault characteristic of spreading ridges, which offsets the ridge axes as spreading progresses.

transpiration - evaporative by loss of water from leaves of plants

trimasepic - sepic plasmic fabric with a network of highly birefringent streaks in threep referred directions

Tropept - kind of Inceptisol found in intertropical regions.

tuber - potatolike underground storage organ of plants

Udifluvent - kind of Entisol, discernably decalcified and with clear relict bedding remaining from clayey alluvial parent material

Udalf - kind of Alfisol formed in a humid climate, usually non-calcareous

Udoll - kind of Mollisol formed in a humid climate, usually non-calcareous

Udult - kind of Ultisol formed in a humid climate, so deeply weathered and non-calcareous

Ultisol - acidic, deeply weathered forest soil, with clayey, ferric, aluminous or humic subsurface horizon

umbric epipedon - soil surface horizon similar to mollic except for platy to massive structure and base saturation less than 50%. They are generally associated with forest vegetation

unconformity - major temporal break in the accumulation of a sedimentary rock sequence, as indicated by fossils as evidence of age or by deformation of underlying layers before deposition of overlying layers

underclay - clayey paleosol beneath a coal seam

undulic - soil micro fabric that is almost but not quite isotropic, so very dark when viewed in thin section under crossed nicols

Ustalf - kind of Alfisol of dry summer-wet climates

Ustand - kind of Andisol of dry summer-wet climates

Ustochrept - kind of Ochrept formed in a dry climate, usually with carbonate nodules

Ustoll - kind of Mollisol of dry summer-wet climates

Ustox - kind of Oxisol of seasonally dry climates

Ustropept - kind of Tropept formed in a dry climate

valley calcrete - form of groundwater calcrete formed by precipitation from the water table near streams

value - the degree of lightness of a color in the Munsell system of color classification

vein - a narrow crack through rock, commonly filled with minerals such as quartz or calcite

vermicular - wormy, full of elongate cavities

vertic - showing some properties of Vertisols, such as slickensides and deep cracks

Vertisol - thick, very clayey, slickensided soil, often with internal deformation of horizons

very strongly developed - with unusually thick (3 or more m) subsurface (B) horizons or surface horizons (coal or lignites): such a degree of development is found mainly at major geological unconformities

very weakly developed soil or paleosol - with little evidence of soil development apart from root traces and abundant sedimentary, metamorphic or igneous textures remaining from parent material

vesicular - full of small, near-spherical cavities

Vitrand - kind of Andisol rich in glassy volcanic shards

vitrinite reflectance - measure of the shininess of the coal maceral vitrinite, the percentage of light reflected from the maceral

vitrain - bright coal: brilliant, black, non-laminated coal, clean to the touch and breaking with conchoidal fracture

vivianite - blue to white mineral of marsh soils [Fe₃(PO₄)₂&busll;8H₂O]

void - small open spaces within soil microfabric, generally crushed out of buried paleosols

volatile matter - easily moved materials: for coal, volatile material includes water, sulfur and nitrogen

volcanic arc - An arcuate chain of volcanic islands or volcanoes which erupt mainly andesitic lavas and ash but also including basalts and rhyolites; generally associated with trenches, seismicity and subduction.

volcanic ash - particles of volcanic sock, crystals and glass that settle out through the atmosphere after volcanic eruptions

volcaniclastic - formed from particles of volcanic rock

vosepic - sepic plasmic fabric with highly birefringent plasma associated with the walls of voids. May be difficult to recognize in paleosols with voids crushed during burial

vug - small unfilled cavity in rock or soil

Walkley-Black method - wet chemical titration method for the determination of abundance (weight percent) of soil organic carbon

waterlogged soil - soil that is saturated with water

water potential - negative water pressure maintained within tracheids that transports water through a plant

weakly developed soil or paleosol - with a surface rooted zone (A horizon), as well as incipient subsurface clayey, calcareous, sesquioxidic or humic or surface organic horizons, but none of these developed to the extent that they would qualify as argillic, spodic or calcic horizons or histic epipedons

weathering rind - thin outer zone of weathering found on rock and mineral grains within a soil.

Weaver index - measure of clay crystallinity using height of x-ray diffractometer peak

Weber index - measure of clay crystallinity using width of x-ray diffractometer peak of clay compared with that of quartz

wetland - part of the landscape that is waterlogged or inundated for a substantial part of the year

wooded grassland - trees giving 10-40% cover, isolated and scattered among grasses

wooded shrub land - trees giving 10-40% cover, isolated and scattered among grasses

woodland - vegetation of closely spaced trees 2-8 m tall

Xeralf - a kind of Alfisol of dry winter-wet climates

Xerand - a kind of Andisol of dry winter-wet climates

xeric - of dry winter-wet climates

Xeroll - kind of Mollisol of dry winter-wet climates

x-ray diffractometer - machine used to identify mineral by the angles at which their crystal faces reflect a focused beam of x-rays

x-ray fluorescence spectrometry - method of chemical analysis using wavelengths of secondary radiation.