UCMP Glossary: Geology
| Phylogenetics | Geology | Biochemistry | Cell biology | Ecology | Life
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abyssal plain -- The ocean floor offshore from the continental margin, usually
very flat with a slight slope.
accrete -- v. To add terranes (small land masses or pieces of crust) to
another, usually larger, land mass.
alkaline -- Term pertaining to a highly basic, as opposed to acidic, subtance.
For example, hydroxide or carbonate of sodium or potassium.
allochthonous -- Refers to something formed elswhere than its present location.
Antonym of autochthonous.
alluvial fan -- n. A fan-shaped deposit of sand, mud, etc. formed by a stream
where its velocity has slowed, such as at the mouth of a ravine or at the foot
of a mountain.
alluvium -- n. a deposit of sand, mud, etc., formed by flowing water; alluvial
- adj.
amber -- Fossilization where the organism is entrapped in resin and preserved
whole.
andesite -- Igneous volcanic rock, less mafic than basalt, but more mafic than
dacite; rough volcanic equivalent of diorite.
anticline -- A fold of rock layers that is convex upwards. Antonym of syncline.
archipelago -- n. A group of islands; an expanse of water with scattered
islands.
asphalt -- A dark bituminous substance found in natural beds. Residue from
petroleum distillation.
autochthonous -- Refers to something formed in its present location. Antonym of
allochthonous.
Banded Iron Formation -- n. Rock consisting of alternating light and dark
layers of iron-rich chert (the dark layers have more iron minerals) formed from
3.8 to 1.7 billion years ago.
barrier island -- n. A long, narrow island that runs parallel to the mainland
and is separated from it by a lagoon.
basalt -- Highly mafic igneous volcanic rock, typically fine-grained and dark
in color; rough volcanic equivalent of gabbro.
basement rock -- n. The oldest rocks in a given area; a complex of metamorphic
and igneous rocks that underlies the sedimentary deposits. Usually Precambrian
or Paleozoic in age.
basin -- n. Any large depression in which sediments are deposited.
Basin and Range Province -- n. One of the most extensive systems of
fault-bounded mountains separated by sediment-filled valleys, extending across
Idaho, Oregon, Nevada, Utah, Arizona, New Mexico, California, and northern
Mexico. Basin and Range topography The surface features typical of the Basin
and Range Province.
bedrock -- n. The general term referring to the rock underlying other
unconsolidated material, i.e. soil.
biostratigraphy -- n. The study of rock layers (e.g., distribution, environment
of deposition, age) based on their fossils; biostratigraphic- adj.
biostratinomy -- The study of what happens between the death of an organism and
burial. Part of taphonomy.
bioturbation -- n. The disturbance of sediment by organisms, e.g. burrows,
trails, or complete mixing.
blueschist -- Metamorphic rock formed under great pressures, but not so great
temperatures.
brackish -- adj. Slightly salty.
braided river -- n. A river characterized by a network of channels that split
and entwine, rather than a single channel for water and sediment. Braided
rivers are common in upland areas closer to mountain fronts where the slope,
and consequently water velocity, lessens and the river begins to deposit
sediment. Braiding is the result of the channel becoming clogged with sediment.
breccia -- n. A rock composed of angular fragments of older rocks;
distinguished from a conglomerate in that the component rocks are not rounded
and worn.
calcareous -- adj. Term used to describe a structure, secreted by an organism,
that consists of or contains calcium carbonate (CaCO3), e.g., the shell of a
bivalve.
caldera -- n. A large circular volcanic depression, often originating due to
collapse.
caliche -- n. A sedimentary deposit commonly made of calcium carbonate and
formed from the leaching of minerals from the top layers of soil. Caliche
deposits characterize arid and semi-arid environments.
carbon film -- Thin layer of carbon remains of past life found in sedimentary
rocks.
carbonate -- n. A mineral composed mainly of calcium (Ca) and carbonate (CO3)
ions, may also include magnesium (Mg), iron (Fe) and others. n. Rock or
sediments derived from debris of organic materials composed mainly of calcium
and carbonate (e.g., shells, corals, etc.) or from the inorganic precipitation
of calcium (and other ions) and carbonate from solution (seawater). For
example, limestone or dolomite. carbonate platform - n. A broad (hundreds of
meters), flat, shallow submarine expanse of carbonate rock, more common in the
early-middle Paleozoic. carbonate bank – n. A narrow (tens of meters), fairly
flat, shallow, submarine plateau of carbonate rock, more common from the
middle-late Paleozoic to the present, e.g., the Bahama Banks.
casts -- Fossils formed when water containing minerals leaks into a mold. The
minerals harden to form a copy of the original structure or organism.
cenote -- n. Mayan word for a sinkhole formed when fresh water dissolves
limestone below the surface and the overlying rocks collapse.
chalk -- A soft compact calcite, CaCO3, with varying amounts of silica, quartz,
feldspar, or other mineral impurities, generally gray-white or yellow-white and
derived chiefly from fossil seashells.
chert -- Hard, dense sedimentary rock, composed of interlocking quartz crystals
and possibly amorphous silica (opal). The origin of the silica is normally
biological, from diatoms, radiolaria or sponge spicules. Synonymous with flint.
clast -- n. An individual grain or constituent of a rock; clastic- adj.
Describes a rock or sediment composed mainly of fragments of preexisting rocks
or minerals that have been transported some distance from their place of origin,
e.g., sandstone, shale.
compactions -- Fossils that have undergone some degree of flattening of their
three-dimensional structure.
compression -- Fossil formed when an organism is flattened (compressed) and a
thin film of organic material from its body is left in the rock.
concretion -- n. A hard, rounded mass, commonly of silica, calcite, dolomite,
iron oxide, pyrite, or gypsum, that formed within a rock from the precipitation
of these minerals around a nucleus, such as a leaf, bone, shell, or fossil, and
ranging in diameter from centimeters to meters.
conglomerate -- A coarse-grained sedimentary rock, with clasts larger than 2
mm.
continental crust -- The Earth's crust that includes both the continents and
the continental shelves.
continental margin -- n. The ocean floor from the shore of continents to the
abyssal plain.
continental rise -- n. Part of the continental margin; the ocean floor from the
continental slope to the abyssal plain. The continental rise generally has a
gentle slope and smooth topography.
continental shelf -- n. The part of the continental margin from the coastal
shore to the continental slope; usually extending to a depth of about 200
meters and with a very slight slope, roughly 0.1 degrees; includes conetinental
and oceanic sediments down to the ocean floor.
continental slope -- n. Part of the continental margin; the ocean floor from
the continental shelf to the continental rise or oceanic trench. Usually to a
depth of about 200 meters. The continental slope typically has a relatively
steep grade, from three to six degrees.
copal -- Brittle aromatic yellow to red resins of recent or fossil origin,
obtained from tropical trees.
coprolites -- Fossilized feces.
core -- That portion of the interior of the Earth that lies beneath the mantle,
and goes all of the way to the center. The Earth's core is very dense, rich in
iron and the source of the magnetic field.
craton -- n. A part of the Earth's crust that has attained stability and has
been little deformed for a long period of time, refers only to continents;
cratonic- adj.
cross-bedding -- n. The arrangement of sedimentary beds tilted at different
angles to each other, indicating that the beds were deposited by wind or
flowing water.
crust -- n. The outermost layer of the Earth, varying in thickness from about
10 kilometers (6 miles) below the oceans, to 65 kilometers (about 40 miles)
below the continents; represents less than 1 percent of the Earth's volume.
dacite -- Igneous volcanic rock, less mafic than andesite, typically
fine-grained and light in color; rough volcanic equivalent of granodiorite.
delta -- n. A low, nearly flat accumulation of sediment deposited at the mouth
of a river or stream, commonly triangular or fan-shaped; deltaic– adj.
dendrites -- n. Small branching patterns on rocks made of iron and manganese
oxides that show the passage of fluids through the rock.
deposition -- Any accumulation of material, by mechanical settling from water
or air, chemical precipitation, evaporation from solution, etc.
diagenesis -- n. Any sort of chemical, physical, or biogenic change that occurs
in fossils and sediments after their deposition. Physical erosion of a shell in
a river, dissolution of carbonate in acidic conditions, and microbial invasion
of a bone are all forms of diagenesis. adj. diagenetic
diatomite -- Diatomite, or diatomaceous earth, is a siliceous sedimaentary rock
formed from the accumulations of diatoms or other nanoplankton.
diorite -- Igneous plutonic rock, less mafic than gabbro, but more mafic than
granite and granodiorite; rough plutonic equivalent of andesite.
dip -- The angle that a bedding plane or fault makes with the horizontal when
measured perpendicular to the strike of the bedding plane or fault.
dolomite -- A carbonate sedimentary rock composed of more than 50 percent of
the mineral calcium-magnesium carbonate (CaMg(CO3)2).
drill core -- n. A column of material (e.g., mud, ice, rock) removed from the
earth by drilling. Often used as a tool for exploration of natural resources.
drumlin -- n. Elongated mound of glacial sediment deposited parallel to ice
flow.
epicenter -- Point on the Earth's surface directly above the focus of an
earthquake.
erosion -- n. The processes by which materials of the Earth's crust are worn
away, loosened, or dissolved while being transported from their place of
origin.
erratic -- n. A large, isolated boulder left behind by a glacier.
escarpment -- n. A steep or vertical cliff, either above or below sea level.
esker -- n. A ridge of glacial sediment deposited by a stream flowing in and
under a melting glacier.
estuary -- n. An area where fresh water comes into contact with seawater,
usually in a partly enclosed coastal body of water; a mix of fresh and salt
water where the current of a stream meets the tides; estuarine– adj.
evaporite -- n. a deposit of salt minerals (e.g., halite, gypsum, anhydrite)
left behind by the evaporation of seawater, usually forms within a restricted
basin.
extrusive -- Igneous. Antonym of intrusive.
fault -- n. (v.) A fracture, or large crack, in the Earth's crust where one
side moves up/down/sideways relative to the other; fault block- n. pieces of
crust that have slipped into or alongside a fault; fault zone- n. an area with
multiple faults.
felsic -- Term used to describe the amount of light-colored feldspar and silica
minerals in an igneous rock. Complement of mafic.
fiord -- A steep-sided, drowned coastal valley carved by glacial action. Also
spelled 'fjord.'
floodplain -- n. The flat area on either side of an active river channel that
can be covered in water when the river is in flood. When the channel is
breached, sediment-laden waters spread across the floodplain. When the waters
recede, a layer of sediment is left behind. When the floodplain is not covered
with water, it commonly supports vegetation and soil formation.
focus -- The initial point within the Earth that ruptures in an earthquake,
directly below the epicenter.
fold -- Bent rock strata.
fossil -- Any evidence of past life, including remains, traces, imprints as
well as life history artifacts. Examples of artifacts include fossilized bird's
nests, bee hives, etc.
fossil record -- All of the fossils that have existed throughout life’s
history, whether they have been found or not.
fossiliferous -- adj. Rich in fossils.
freezing -- To preserve an organism without any significant alteration to its
chemical composition by subjecting it to freezing temperatures.
gabbro -- Highly mafic igneous plutonic rock, typically dark in color; rough plutonic
equivalent of basalt.
gastroliths -- n. Fossilized gizzard stones, usually only applicable in the
study of fossil reptiles.
geologic maps -- Maps that show the types and ages of rock of an area. These
maps are used by paleontologists to find areas that are likely to contain
fossils they are interested in.
glass -- A non-crystaline rock that results from very rapid cooling of magma.
granite -- Highly felsic igneous plutonic rock, typically light in color; rough
plutonic equivalent of rhyolite. Granite is actually quite rare in the U.S.;
often the term is applied to any quartz-bearing plutonic rock.
granodiorite -- Igneous plutonic rock, less felsic than granite, typically
light in color; rough plutonic equivalent of dacite.
graywacke -- Sandstone composed of poorly sorted angular clasts.
hotspot -- n. A localized, somewhat persistent (tens of millions of years), and
relatively fixed zone of mantle melting, inferred from surface volcanic
activity. Evidence of a hotspot's existence is left behind as tectonic plates
move across it, for example, the Hawaiian Islands.
hydrothermal vent -- n. A place on the seafloor, generally associated with
spreading centers, where warm to super-hot, mineral-rich water is released; may
support a diverse community of organisms.
hypersaline -- adj. Extremely salty, having much more salt than normal
seawater.
Ichnology -- The study of trace fossils.
igneous rock -- Any rock solidified from molten or partly molten material.
impressions -- Prints or marks made when an organism’s body has been compressed
(flattened). Impressions are different from compressions because no thin
organic material is left behind.
interbedded -- adj. Describes beds (layers) of rock lying between or
alternating with beds of a different kind of rock.
intrusion -- n. Magma (and the rock it forms) that has pushed into pre-existing
rock; intrusive- adj.; plutonic- syn. extrusive- ant.
island arc -- n. A curved chain of islands that rise from the sea floor,
usually near a continent. The convex side usually faces the open ocean, while
the concave side usually faces the continent, e.g., the Aleutian Islands in
Alaska; volcanic arc- syn.
isotope -- One of two or more variations of the same chemical element,
differing in the number of neutrons not the number of protons.
kame -- n. A short, steep-sided knoll of glacial sediment.
karst -- n. A type of topography formed by dissolution of rocks like limestone
and gypsum that is characterized by sinkholes, caves, and subterranean
passages.
kettle lakes -- n. Lakes formed as water fills a hole formerly occupied by a
block of stranded ice.
lava -- Any molten material that is extrusive or volcanic, or the rock that
forms from a molten extrusive.
limestone -- A carbonate sedimentary rock composed of more than 50 percent of
the mineral calcium carbonate (CaCO3).
limy -- adj. Describes sediments, soils, or rocks that contain a significant
amount of lime (calcium oxide, CaO).
loess -- n. A widespread, loose deposit consisting mainly of silt; most loess deposits
formed during the Pleistocene as an accumulation of wind-blown dust carried
from deserts, alluvial plains, or glacial deposits.
lowland -- n. (adj.) Large area of relatively low relief, usually applied to
coastal regions that do not rise high above sea level. upland, highland – ant.
mafic -- Term used to describe the amount of dark-colored iron and magnesium
minerals in an igneous rock. Complement of felsic.
magma -- n. Molten rock generated within the Earth; forms intrusive (solidifies
below the surface) and extrusive (solidifies above the surface) igneous rocks.
mantle -- That portion of the interior of the Earth that lies between the crust
and the core.
marine terrace -- n. A platform of marine deposits (typically sand, silt,
gravel) sloping gently seaward. Such a platform may be exposed along the coast,
forming cliffs, due to uplift and/or the lowering of sea level, e.g., marine
terraces of coastal Southern California.
marl -- n. A loose, crumbly deposit consisting of clay and calcium carbonate and
formed in marine or freshwater conditions.
melange -- A body of rocks consisting of large blocks (mappable size) of
different rocks jumbled together with little continuity of contacts.
metamorphic rock -- Any rock derived from other rocks by chemical, mineralogical
and structural changes resulting from pressure, temperature or shearing stress.
metamorphism -- n. The process of altering the chemical or mineralogical
composition of a rock through different amounts of heat and pressure below the
surface of the Earth; metamorphose- v; metamorphic - adj.
microfossil -- n. A very small fossil, best studied with the aid of a
microscope, e.g. foraminifera, radiolarians, and small vertebrate fossils such
as teeth. macrofossil– ant.
mid-oceanic ridges -- Elongated rises on the ocean floor where basalt
periodically erupts, forming new oceanic crust; similar to continental rift
zones.
mineralization -- The process of replacing any organism’s original material
with a mineral.
molds -- Fossils formed when the sediment surrounding a buried organism
hardens. When the organism decays, its impression is left in the rock and can
be seen if the rock is broken open.
moraine -- n. A mound or ridge of sediment deposited by a glacier; lateral
moraine- n. deposited to the side of a glacier; terminal moraine- n. deposited
to the front of a glacier; ground moraine- n. deposited on the land surface.
oceanic crust -- n. The Earth's crust which is formed at mid-oceanic ridges,
typically 5 to 10 kilometers thick with a density of 3.0 grams per centimeter
cubed.
oceanic trench -- Deep steep-sided depression in the ocean floor caused by the
subduction of oceanic crust beneath either other oceanic crust or continental
crust.
orogeny -- n. The tectonic processes of folding, faulting, and uplifting of the
earth’s crust that result in the formation of mountains.
outcrop -- n. Any place where bedrock is visible on the surface of the Earth.
v. The exposing of bedrock at the Earth's surface.
paleosol -- Soil horizon from the geologic past.
peat -- n. A deposit of partly decayed plant remains in a very wet environment;
marsh or swamp deposit of plant remains containing more than 50 percent carbon.
permineralization -- Fossilization process that occurs when minerals, carried
by ground water, enter and harden in the pores of an organism’s structures.
Phanerozoic -- n. The geologic eon that includes the interval of time from
approximately 543 million years ago to the present, comprising the Paleozoic,
Mesozoic, and Cenozoic eras.
pillow lava -- Lava extruded beneath water characterised by pillow-type shapes.
plate -- n. Rigid parts of the Earth's crust and part of the Earth's upper
mantle that move and adjoin each other along zones of seismic activity. The
theory that the crust and part of the mantle are divided into plates that
interact with each other causing seismic and tecotnic activity is called plate
tectonics.
pluton -- n. Any body of igneous rock that solidified below the earth’s
surface.
plutonic -- Applies to igneous rocks formed beneath the surface of the Earth;
typically with large crystals due to the slowness of cooling. Synonym of
intrusive. Antonym of volcanic.
radio-carbon dating -- Method for determining the age of an organic substance
by measuring the amount of the carbon isotope, carbon-14, remaining in the
substance; useful for determining ages in the range of 500 to 70,000 years.
rebound -- v. To spring back after a weight has been removed.
red bed -- n. Sedimentary layers composed primarily of sandstone, siltstone,
and shale, that are predominantly red in color due to the presence of iron
oxides; often used in reference to the Permian or Triassic sediments of the
western U.S.
reef -- n. A large ridge or mound-like structure within a body of water that is
built by calcareous organisms such as corals, red algae, and bivalves; barrier
reef- n. A reef growing offshore from a land mass and separated by a lagoon or
estuary, e.g, the Great Barrier Reef of Australia; patch reef- n. A
discontinuous reef growing in small areas, separated by bare areas of sand or
debris, often part of a larger reef complex.
regression -- (n) A drop in sea level that causes an area of the land to be
uncovered by seawater.
replacement -- Fossilization process in which the original material in an
organism is broken down and replaced by different minerals.
rhyolite -- Highly felsic igneous volcanic rock, typically light in color;
rough volcanic equivalent of granite.
rift -- n. A long, narrow crack in the entire thickness of the Earth's crust,
which is bounded by normal faults on either side and forms as the crust is
pulled apart; v. To split the Earth's crust; rift zone- n. The area on
continents where a trough bounded by normal faults is forming; the site of
crustal extension, similar to that which occurs at mid-oceanic ridges; rift
basin or rift valley- n. The long, and fairly wide trough that has formed as a
section of the Earth's crust has dropped down along faults, e.g., African Rift
Valley in East Africa.
rock cycle -- The process through which one type of rock (igneous, sedimentary,
or metamorphic) is converted into another.
salt lick -- n. A natural or artificial deposit of exposed salt that animals
lick for nutrients.
sandstone -- Sedimentary rock composed of sand-sized clasts.
sea-floor spreading -- n. The process of adding to the Earth's crust at
mid-ocean ridges as magma wells up and forces previously formed crust apart.
sediment -- Any solid material that has settled out of a state of suspension in
liquid.
sedimentary rock -- Any rock resulting from the consolidation of sediment.
siderite -- Also called ironstone, that is a concretion of iron carbonate.
Common in the Mazon Creek fossil beds.
silicification -- Process whereby silica replaces the original material of a
substance. For example, silicified wood.
sill -- n. A sheet-like igneous intrusion that parallels the plane of the
surrounding rock.
sinkhole -- n. A natural depression in the surface of the land caused by the
collapse of the roof of a cavern or subterranean passage, generally occurring
in limestone regions.
soil -- Unconsolidated materials above bedrock.
stratigraphy -- n. The study of rock layers, especially their distribution,
environment of deposition, and age; stratigraphic, adj.
stratum -- A layer of sedimentary rock; plural is strata.
strike -- The direction or trend of a bedding plane or fault, as it intersects
the horizontal.
subduction -- n. A geologic process in which one edge of one crustal plate is
forced below the edge of another; subduct– v.; subduction zone- n. A long
narrow area in which subduction is taking place, e.g. the Peru-Chile trench,
where the Pacific Plate is being subducted under the South American Plate.
subsidence -- n. The sudden sinking or gradual downward settling of the Earth’s
surface with little or no horizontal motion.
syncline -- A fold of rock layers that is convex downwards. Antonym of
anticline.
taphonomy -- n. The study of the death, decay, burial, and fossilization of an
organism. Essentially, taphonomy describes everything that happens to an
organism between the time it dies and the moment its remains are discovered.
Understanding why organisms are or are not preserved over time helps explain
the biases seen in the fossil record. Taphonomy is often broken into two parts,
biostratinomy and diagenesis.
tectonic -- adj. Describing the forces that cause the movements and deformation
of Earth’s crust on a large scale, also describes the resulting structures or
features from these forces.
terrane -- n. A general term used to refer to a piece of the crust that is
usually smaller than a continent but larger than an island; exotic terrane- n.
terrane that has an unknown origin or a different origin than its surrounding
rocks.
till -- n. unstratified glacial drift consisting of clay, sand, gravel, and
boulders
topography -- n. The relief features of the Earth's surface, above and below
sea level; the set of landforms in a region.
trace fossil -- Evidence left by organisms, such as burrows, imprints,
coprolites, or footprints. Trace fossils are not preserved parts of the
organism.
transgression -- (n) A rise in sea level relative to the land.
tuff -- n. A general term for consolidated rocks made of material ejected from
volcanic explosions.
turbidite -- n. The sediments or rocks that formed as a result of a turbidity
flow.
turbidity current -- n. A bottom fast-flowing current that moves down a slope,
depositing suspended sediments over the floor of a body of water
turbidity flow -- n. A flow of dense, muddy water moving down a slope due to a
turbidity current
unconformity -- Any interruption of the continuity of a depositional sequence.
undifferentiated -- adj. Unable to distinguish between. Undifferentiated rocks:
rocks for which it is not possible to specify finer age divisions.
upland -- n. (adj.) An area that is higher relative to the surrounding areas,
but not mountainous; highland– syn.; lowland– ant.
uplift -- n. (v.) The process or result of raising a portion of the Earth’s
crust through different tectonic mechanisms.
volcanic -- adj. Describes the action or process of magma and gases rising to
the crust and being extruded onto the surface and into the atmosphere; also
applies to the resulting igneous rocks that cool on the surface of the Earth,
including beneath water, which typically have small crystals due to the
rapidity of cooling. volcanically - adv. extrusive - syn. plutonic - ant.
volcanic arc -- n. A curved chain of islands that rise from the sea floor,
usually near a continent. The convex side usually faces the open ocean, while the
concave side usually faces the continent; island arc - syn.
volcanism -- n. The process by which magma and associated gases rise to the
Earth’s crust and are extruded, or expelled, onto the surface and into the
atmosphere.
weathering -- n. The physical, chemical, and biological processes by which rock
is broken down into smaller pieces.
Last updated:2009-11-12
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