Glossary
The following definitions are from several sources in
total or in part, but the main reference is: Bates, R.L.,
and J.A. Jackson, editors, 1987, Glossary of Geology:
American Geological Institute, Alexandria, VA, 3rd
edition, 788 p. © 2003 American Geological Institute
and reprinted with their permission. For more information,
log on to
www.agiweb.org.
Stratigraphic definitions come from: Handbook of
Illinois Stratigraphy, H.B. Willman, Elwood Atherton,
T.C. Buschbach, Charles Collinson, J.C. Frye, M.E.
Hopkins, J.A. Lineback, J.A. Simon, 1975. 261 p.
A | B |
C | D |
E | F |
G | H |
I | J |
K | L |
M | N |
O | P |
Q | R |
S | T |
U | V |
W | X |
Y |
Z
A
Separation and removal of rock material and formation of deposits, especially by wind
action or the washing away of loose and soluble materials.
An interval of geologic time; a division of an epoch.
One that is actively depositing sediment in its channel or floodplain because it is
being supplied with more load than it can transport.
One that has been at least partially filled with sand, silt, and mud by flowing water.
A general term for clay, silt, sand, gravel, or similar unconsolidated sorted or
semi-sorted sediment deposited during comparatively recent time by a stream or other body
of running water.
A convex upward rock fold in which strata have been bent into an arch; the strata on each
side of the core of the arch are inclined in opposite directions away from the axis or
crest; the core contains older rocks than does the perimeter of the structure.
A geologic formation that is water-bearing and which transmits water from one point
to another.
Said of rock or sediment that contains, or is composed of, clay-sized particles or clay
minerals.
A relatively clean quartz sandstone that is well sorted and contains less than 10%
argillaceous material.
Formed or generated in place; specif. said of rock constituents and minerals that have
not been transported or that crystallized locally at the spot where they are now found, and
of minerals that came into existence at the same time as, or subsequently to, the formation
of the rock of which they constitute a part. The term, as used, often refers to a mineral
(such as quartz or feldspar) formed after deposition of the original sediment.
The Aux Vases Sandstone is named for the Aux Vases River in Ste. Genevieve County, Missouri,
and the type section consists of outcrops in the Mississippi River bluffs at the mouth of
the Aux Vases River. The Aux Vases consists of sandstone, siltstone, and minor amounts of
shale and, locally, dolomite and limestone. It occurs in much of the area of the Chesterian
Series. It crops out along the Mississippi River Valley in St. Clair, Monroe, and Randolph
Counties, being particularly well exposed in the bluffs 2-3 miles southeast of Prairie du
Rocher, Randolph County. In southern Illinois it crops out principally in Union, Johnson,
and Hardin Counties.
B
Lower limit of erosion of the land's surface by running water. Controlled locally and
temporarily by the water level of stream mouths emptying into lakes, or more generally
and semi-permanently by the level of the ocean (mean sea level).
The suite of mostly crystalline igneous and/or metamorphic rocks that generally underlies
the sedimentary rock sequence.
A topographic or structural low area that generally receives
thicker deposits of sediments than adjacent
areas; the low areas tend to sink more readily, partly because of the weight of the thicker
sediments; the term also denotes an area of relatively deep water adjacent to shallow-water
shelf areas.
A naturally occurring layer of earth material of relatively greater horizontal than
vertical extent that is characterized by physical properties different from those of
overlying and underlying materials. It also is the ground upon which any body of water
rests or has rested, or the land covered by the waters of a stream, lake, or ocean; the
bottom of a stream channel.
The solid rock (sedimentary, igneous, or metamorphic) that underlies the unconsolidated
(non-indurated) surface materials (for example, soil, sand, gravel, glacial till, etc.).
A drainageway eroded into the solid bedrock beneath the surface materials. It may be
completely filled with unconsolidated (non-indurated) materials and hidden from view.
A calcarenite containing abundant fossils or fossil fragments.
A low-gradient, low-volume stream flowing through an intricate network of interlacing
shallow channels that repeatedly merge and divide, and are separated from each other by
branch islands or channel bars. Such a stream may be incapable of carrying all of its load.
Most streams that receive more sediment load than they can carry become braided.
The Burlington Limestone is named for the city of Burlington, Des Moines County, Iowa,
where the formation is well exposed and about 70 feet thick. In Illinois, the Burlington extends from
Henderson County in the northwest across a roughly triangular area southward to Jackson
County and eastward to Iroquois County. Good outcrops are found in the Mississippi River
bluffs from Quincy, Adams County, to near Alton, Madison County. In the vicinity of Quincy
the lower 25 feet is relatively pure and is quarried as the “Quincy Lime". In the
southern area the Burlington and the overlying Keokuk can be distinguished only by their
fossils and are generally referred to as the Burlington-Keokuk Limestone.
C
Describes a limestone composed of more or less worn fragments of shells or pieces of
older limestone. The particles are generally sand-sized.
Said of a rock containing as much as 50% of calcium carbonate (CaCO3), but
also composed of something else (synonym: limy).
The heating of calcite or limestone to its temperature of dissociation so that it loses
its carbon dioxide; also applied to the heating of gypsum to drive off its water of
crystallization to make plaster of paris.
A common rock-forming mineral consisting of CaCO3; it may be white, colorless,
or pale shades of gray, yellow, and blue; it has perfect rhombohedral cleavage, appears
vitreous, and has a hardness of 3 on the Mohs' scale; it effervesces (fizzes) readily in
cold dilute hydrochloric acid. It is the principal constituent of limestone.
The earliest period of the Paleozoic, thought to have covered the span of time between 543
and 490 million years ago; also, the corresponding system of rocks. It is named after
Cambria, the Roman name for Wales, where rocks of this age were first studied.
A cavity in the earth large enough for a human to enter. Caves can form as a result of
physical and chemical weathering of rock. Physical weathering usually produces shelter-type
caves that extend into the rock for only a few feet. Chemical weathering of rock can produce
caves (solution channels along fractures and bedding planes) that extend for many miles into
the rock.
An era of geologic time, from the beginning of the Tertiary period to the present. (Some
authors do not include the Quaternary, considering it a separate era.) It is characterized
paleontologically by the evolution and abundance of mammals, advanced mollusks, and birds;
paleobotanically, by angiosperms. The Cenozoic is considered to have begun about 65 million
years ago.
Silicon dioxide (SiO2); a compact, massive rock composed of minute particles of
quartz and/or chalcedony; it is similar to flint but lighter in color.
The Chesterian Series, the uppermost series of the Mississippian System, is named for
Chester, Randolph County, where it is well exposed in the bluffs of the Mississippi River.
The Chesterian Series consists of limestone-shale formations alternating with
sandstone-shale formations. It extends from the major unconformity at the base of the
Pennsylvanian System (sub-Absaroka unconformity) down to the base of the Shetlerville Member
of the Renault Formation, which is the top of the Valmeyeran Series. Many of the Chesterian
limestones and shales are abundantly fossiliferous. The sandstones are much less
fossiliferous, but can contain some plant fossils. Coals, a few inches thick at most, occur in
some of the Chesterian sandstones. Many of the limestones contain abundant crinoidal
fragments, and the series is characterized by the presence of Talarocrinus which
distinguishes it from the underlying Valmeyeran containing Platycrinites penicillus.
Blastoids and the corkscrew bryozoan, Archimedes, are common and characteristic.
Chitin: A resistant organic compound with the same basic carbohydrate structure as
cellulose, but nitrogenous because some hydroxyl groups are replaced by ascetamide groups.
It is a common constituent of various invertebrate skeletons such as insect exoskeletons
and foraminiferal inner test, and also occurs in hyphae and spores of fungi.
Said of rocks composed of particles of other rocks or minerals, including broken organic
hard parts as well as rock substances of any sort, transported and deposited by wind,
water, ice, or gravity.
A low, roughly concave topographic feature in a landscape. Rain falling within the
boundaries of the depression would be channeled toward its lowest part (usually near its
center).
The difference in altitude between the crest of a dome or anticline and the lowest
structural or elevation contour that completely surrounds it.
A graphic representation, in the form of one or more vertical column(s), of the vertical
succession and stratigraphic relations of rock units in a region.
(a) A hard, compact mass or aggregate of mineral matter, normally subspherical, but
commonly oblate, disk-shaped, or irregular with odd or fantastic outlines; formed by
precipitation from aqueous solution about a nucleus or center, such as a leaf, shell, bone,
or fossil, in the pores of a sedimentary or fragmental volcanic rock, and usually of a
composition widely different from that of the rock in which it is found and from which it is
rather sharply separated. It represents a concentration of some minor constituent of the
enclosing rock or cementing material, such as silica (chert), calcite, delimite, iron oxide,
pyrite, or gypsum, and it ranges in size from a small pellet-like object to a great
spheroidal body as much as 3 m in diameter. Most concretions were formed during diagenesis,
and many (especially in limestone and shale) shortly after sediment deposition. (b) A
collective term applied loosely to various primary and secondary mineral segregations of
diverse origin, including irregular nodules, spherulities, crystalline aggregates, geodes,
septaria, and related bodies.
Said of strata deposited one upon another without interruption in accumulation of sediment;
beds parallel.
The final period of the Mesozoic era (after the Jurassic and before the Tertiary period of
the Cenozoic era), thought to have covered the span of time between 144 and 65 million years
ago; also, the corresponding system of rocks. It is named after the Latin word for chalk
(creta) because of the English chalk beds of this age.
D
A low, nearly flat, alluvial land form deposited at or near the mouth of a river where it
enters a body of standing water; commonly a triangular or fan-shaped plain extending beyond
the general trend of a coastline.
Pertaining to or formed from detritus; said esp. of rocks, minerals, and sediments.
The term may indicate a source outside the depositional basin or a source within it.
Loose rock and mineral material produced by mechanical disintegration and removed from its
place of origin by wind, water, gravity, or ice; also, find particles of organic matter, such
as plant debris.
A period of the Paleozoic era (after the Silurian and before the Mississippian), thought to
have covered the span of time between 400 and 345 million years ago; also, the corresponding
system of rocks. It is named after Devonshire, England, where rocks of this age were first
studied.
An unconformity marked by a distinct erosion-produced, irregular, uneven surface of
appreciable relief between parallel strata below and above the break; sometimes represents a
considerable interval of nondeposition.
A mineral, calcium-magnesium carbonate (Ca,Mg[CO3]2); also the name
applied to sedimentary rocks composed largely of the mineral. It is white, colorless, or tinged
yellow, brown, pink, or gray; has perfect rhombohedral cleavage; appears pearly to vitreous;
and effervesces feebly in cold dilute hydrochloric acid.
All rock material transported by a glacier and deposited either directly by the ice or
reworked and deposited by meltwater streams and/or the wind.
A 10,000-square-mile area in northeastern Iowa, southwestern Wisconsin, and northwestern
Illinois where the absence of glacial drift suggests that the area may not have been glaciated.
E
An adjective describing geologic features that are in an overlapping or staggered arrangement.
Each is relatively short but collectively they form a linear zone.
A ridge or series of ridges formed by accumulations of drift built along the outer margin
of an actively flowing glacier at any given time; a moraine that has been deposited at the
lower or outer end of a glacier.
An interval of geologic time; a division of a period. (Example: Pleistocene Epoch).
A unit of geologic time that is next in magnitude beneath an eon; consists of two or more
periods. (Example: Paleozoic Era).
A long, more or less continuous cliff or steep slope facing in one general direction; it
generally marks the outcrop of a resistant layer of rocks, or the exposed plane of a fault
that has moved recently.
F
A fracture surface or zone of fractures in Earth materials along which there has been
vertical and/or horizontal displacement or movement of the strata on opposite sides relative
to one another.
A mnemonic adjective derived from feldspar + lenad (feldspathoid) +
silica + c, and applied to an igneous rock having abundant light-colored
minerals in its mode; also, applied to those minerals (quartz, feldspars, feldspathoids,
muscovite) as a group. It is the complement of mafic.
Containing iron and magnesium; applied to mafic minerals.
[sed] Any sediment deposited by an agent so as to fill or partly fill a valley, a sink or
other depression.
A general term for the property possessed by some rocks of splitting easily into thin
layers along closely spaced, roughly planar, and approximately parallel surfaces, such as
bedding planes in shale or cleavage planes in schist; its presence distinguishes shale from
mudstone. The term includes such phenomena as bedding fissility and fracture
cleavage.
A relatively wide planar opening in bedrock that originated as a fracture or fault. The
opening may be partially or totally filled with soil or, if open, can act as a conduit for
flowing water.
Said of rock that tends to split into layers of suitable thickness for use as flagstone.
The surface or strip of relatively smooth land adjacent to a stream channel produced by the
stream's erosion and deposition actions; the area covered with water when the stream
overflows its banks at times of high water; it is built of alluvium carried by the stream
during floods and deposited in the sluggish water beyond the influence of the swiftest current
Of or pertaining to a river or rivers.
(a) A very common mineral of the apatite group: Ca5(PO4) 3F.
It is a common accessory mineral in igneous rocks. Syn: apatite. (b) An apatite mineral in
which fluorine predominates over chlorine and hydroxyl.
Sedimentary deposits formed by a combination of fluvial (river) and lacustrine (lake)
conditions.
The basic rock unit distinctive enough to be readily recognizable in the field and
widespread and thick enough to be plotted on a map. It describes the strata, such as
limestone, sandstone, shale, or combinations of these and other rock types. Formations
have formal names, such as shale, or combinations of these and other rock types formations
have formal names, such as Joliet Formation or St. Louis Limestone (Formation), generally
derived from the geographic localities where the unit was first recognized and described.
Any remains or traces of a once-living plant or animal preserved in rocks (arbitrarily
excludes Recent remains); any evidence of ancient life. Also used to refer to any object that
existed in the geologic past and for which evidence remains (for example, a fossil waterfall).
Said of a rock or mineral that crumbles naturally or is easily broken, pulverized, or reduced
to powder, such as a soft and poorly cemented sandstone.
G
Ordovician age groups of rock which are largely dolomite with a shaly zone near the middle and some
limestone beds in the lower portion.
Computer software used to input, store, retrieve, manipulate,
analyze and output geographically referenced data or geospatial data,
often in the form of maps, in order to support decision making for
planning and management of land use, natural resources, environment,
urban facilities, transportation, and other administrative records.
The study of the planet Earth that is concerned with its origin, composition, and form; its
evolution and history; and the processes that acted (and act) upon it to control its historic
and present forms.
Study of the Earth with quantitative physical methods. Application of the principles of
physics to the study of the earth, especially its interior.
A collective term for the geologic processes of glacial activity, including erosion and
deposition, and the resulting effects of such action on the Earth's surface.
A large, slow-moving mass of ice formed on land by the accumulation, compaction, and recrystallization of
snow.
The Glenwood formation is a characteristically poorly sorted sandstone, impure dolomite, and
green shale of Ordovician age. It overlies the Ordovician-age St. Peter Sandstone in
northern Illinois. The St. Peter consists of well sorted, frosted, friable quartz sand.
A part of a surface feature of the Earth that slopes upward or downward; the angle of slope,
as of a stream channel or of a land surface, generally expressed by a ratio of height versus
distance, a percentage or an angular measure from the horizontal.
A plutonic rock in which quartz constitutes 10 to 50 percent of the
felsic components and in which the alkali feldspar/total feldspar
ratio is generally restricted to the range of 65 to 90 percent.
Water present below the water table in small, often microscopic, interconnected pore spaces
between grains of soil, sand and/or gravel, and in open fractures and/or solution channels in
rock.
I
Said of a rock or mineral that solidified from molten or partly molten material, (that is
from magma).
Pertaining to the classical third glacial stage of the Pleistocene Epoch in North America,
between the Yarmouthian and Sangamonian interglacial stages.
Said of a compact rock or soil hardened by the action of pressure, cementation, and
especially, heat.
Cambrian age sandstone formations occurring under northern and central Illinois which are
clean, white, coarse to fine grained. Neither outcrop in Illinois. Thin dolomite beds may
occur in upper part of the Ironton.
J
A fracture or crack in rocks along which there has been no movement of the opposing sides
(see also Fault).
K
Collective term for the land forms and subterranean features found in areas with relatively
thin soils underlain by limestone or other soluble rocks; characterized by many sinkholes
separated by steep ridges or irregular hills. Tunnels and caves formed by dissolution of the
bedrock by groundwater honeycomb the subsurface. Named for the region around Karst in the
Dinaric Alps of Croatia where such features were first recognized and described.
Pertaining to the classical second glacial stage of the Pleistocene Epoch in North America,
after the Aftonian interglacial stage and before the Yarmouthian.
An aquifer whose porosity and permeability is dominated by connected conduits (for example,
joints, fractures, caves, tubes) that were enlarged by dissolution of rock. Karst aquifers
have extremely rapid recharge and relatively large hydraulic conductivities (greater than
10-4 cm/s) and a turbulent groundwater flow regime (as opposed to laminar flow).
An area or region of the surface of the earth whose landscape is characterized by sinkholes,
caves, springs, disrupted land drainage, and an underground drainage system. Karst terrains
form in areas with carbonate rock (limestone and dolomite), and areas underlain by other types
of soluble rock (for example, salt or gypsum).
The Keokuk Limestone is named for Keokuk, Lee County, Iowa. At the type locality about 70 feet
of Keokuk Limestone overlying the Burlington Limestone is well exposed along Soap Creek and in
the Mississippi River bluff near the mouth of the creek. Like the Burlington, the Keokuk is
primarily a biocalcarenite. In the type region the lower 30 feet
is very cherty and is differentiated as the Montrose Chert Member. The part of the Keokuk
above the Montrose is composed of beds of fossiliferous, crinoidal limestone interbedded with
fine-grained limestone, argillaceous dolomite, and calcareous gray shale. The limestone is
light gray, speckled with darker gray, brown, or black, and contains beds and nodules of chert.
It is generally thinner bedded and darker than limestone of the Burlington, and the shale
partings are more numerous. In contrast to the crinoidal limestone of the Burlington, the Keokuk
shows a great heterogeneity of skeletal remains, with abundant bryozoans, corals and brachiopods.
L
Produced by or belonging to a lake.
A protocontinent of the Northern Hemisphere, corresponding to Gondwana in the Southern
Hemisphere, from which the present continents of the Northern Hemisphere have been derived by
separation and continental displacement. The supercontinent from which both were derived is
Pangea. Laurasia included most of North America, Greenland, and most of
Eurasia, excluding India. The main zone of separation was in the North Atlantic, with a branch
in Hudson Bay; geologic features on opposite sides of these zones are very similar.
The LaSalle Anticlinal Belt is the most prominent anticlinal feature in the Illinois Basin.
It is actually a complex structure of en echelon folds, asymmetrical
anticlines, and monoclines stretching from Stephenson County in
northern Illinois through Lawrence County in southeastern Illinois.
Molten, fluid rock that is extruded onto the surface of the Earth through a volcano or
fissure. Also the solid rock formed when the lava has cooled.
A sedimentary rock consisting primarily of calcium carbonate (the mineral, calcite). Limestone
is generally formed by accumulation, mostly in place or with only short transport, of the shells
of marine animals, but it may also form by direct chemical precipitation from solution in hot
springs or caves and, in some instances, in the ocean.
To change to stone, or to petrify; especially to consolidate from a loose sediment to a
solid rock.
The description of rocks on the basis of color, structure, mineral composition, and grain
size; the physical character of a rock.
The vertical difference in elevation between the highest and lowest points of a land surface
within a specified horizontal distance or in a limited area.
A homogeneous, unstratified accumulation of silt-sized material deposited by the wind.
M
Said of an igneous rock composed chiefly of one or more ferromagnesian,
dark-colored minerals in its mode; also, said of those minerals. The term was proposed
by Cross, et al. to replace the term femag, which they did not consider to be
euphonious. Etymol: a mnemonic term derived from magnesium + ferric + ic.
It is the complement of felsic.
Naturally occurring molten rock material generated within Earth and capable of intrusion
into surrounding rocks or extrusion onto the Earth's surface. When extruded on the surface
it is called lava. The material from which igneous rocks form through
cooling, crystallization, and related processes.
The Maquoketa Shale Group is Ordovician in age, with green to blue shale with limestone
and dolomite beds in lower portion. The group has been eroded over part of northern Illinois,
but underlies most of the rest of the state.
One of a series of somewhat regular, sharp, sinuous curves, bends, loops, or turns produced
by a stream, particularly in its lower course where it swings from side to side across its
valley bottom.
Crescent-shaped, swales and gentle ridges along a river's flood plain that mark the positions
of abandoned part of a meandering river's channel. They are generally filled in with sediments
and vegetation and are most easily seen in aerial photographs.
An era of
geologic time, from the end of the Paleozoic to the beginning of the Cenozoic, or from
about 248 to about 65 million years ago.
Any rock derived from pre-existing rocks by mineralogical, chemical, and
structural changes, essentially in the solid state, in response to marked changes in
temperature, pressure, shearing stress, and chemical environment at depth in Earth's
crust (for example, gneisses, schists, marbles, quartzites, etc.).
A naturally formed chemical element or compound having a definite chemical composition,
an ordered internal arrangement of its atoms, and characteristic crystal form and
physical properties.
A period of the Paleozoic era ( after the Devonian and before the
Pennsylvanian), thought to have covered the span of time between 354 and 323 million
years ago; also, the corresponding system of rocks. It is named after the Mississippi
River valley, where rocks of this age are well exposed. It is the approximate
equivalent of the Lower Carboniferous of European usage.
A local steeping of an otherwise uniform gentle dip.
(a) A piece of unfractured bedrock, generally more than a few meters across.
(b) A large upstanding mass of rock
A mound, ridge, or other distinct accumulation of glacial drift, predominantly
till, deposited in a variety of topographic landforms that are independent of
control by the surface on which the drift lies.(see also
End Moraine)
The scientific study of form, and of the structures and development that
influence form; term used in most sciences.
Cambrian sandstone with with a few thin red shale beds.
N
Pertaining to the first classical glacial stage of the Pleistocene
Epoch in North America, followed by the Aftonian interglacial stage.
One of several kinds of measurements of rock characteristics taken by lowering
instruments into cased or uncased, air- or water-filled boreholes. Elevated natural
gamma radiation levels in a rock generally indicate the presence of clay minerals.
A place
with an abrupt inflection in a stream profile, generally formed by the presence of a
rock layer resistant to erosion; also, a sharp angle cut by currents at base of a cliff.
An unconformity resulting from deposition of sedimentary strata on massive crystalline
rock.
O
The Ordovician age Oneota Dolomite underlies all of Illinois except the northmost
part of the state. It ranges in thickness from 100 feet in the north to over 500
feet in the south. This formation consists of fine- to coarse-grained, light gray
to brownish gray, cherty dolomite that contains minor amounts of sand and, at its
base, thin shaly beds.
The second earliest period of the Paleozoic era (after the Cambrian and before
the Silurian), thought to have covered the span of time between 490 and 443
million years ago; also, the corresponding system of rocks. It is named after a
Celtic tribe called the Ordovices. In the older literature the Ordovician is
sometimes know as the Lower Silurian.
An aerial photograph or satellite scene that has been transformed by the orthogonal projection, yielding a map
that is free of most significant geometric distortions.
Stratified glacially derived sediment (clay, silt, sand, gravel) deposited by
meltwater streams in channels, deltas, outwash plains, on flood plains, and in
glacial lakes.
The surface of a broad body of outwash formed in front of a
glacier.
The loose soil, silt, sand, gravel or other unconsolidated material overlying
bedrock, either transported or formed in place.
A crescent-shaped lake in an abandoned bend of a river channel. A precursor of
a meander scar.
P
An era of geologic time, from the end of the Precambrian to the beginning of the
Mesozoic, or from about 543 to about 248 million years ago.
The
supercontinent that existed from 300 to 200 million years ago. It combined
most of the continental crust of the Earth, from which the present continents
were derived by fragmentation and movement away from each other by means of
plate tectonics. During an intermediate stage of the fragmentation, between
the existence of Pangea and that of the present widely separated continents,
Pangea was split into two large fragments, Laurasia on the north and Gondwana
in the southern hemisphere.
A naturally
formed unit of soil structure, (for example, granule, block, crumb, or
aggregate).
A land surface of regional scope worn down by erosion to a nearly flat or
broadly undulating plain.
A period of the Paleozoic era (after the Mississippian and before the Permian),
thought to have covered the span of time between 323 and 290 million years ago;
also, the corresponding system of rocks. It is named after the state of
Pennsylvania in which rocks of this age are widespread and yield much coal. It
is the approximate equivalent of the Upper Carboniferous of European
usage.
An interval of geologic time; a division of an era (for example, Cambrian, Jurassic, Tertiary).
The last period of the Paleozoic era (after the
Pennsylvanian), thought to have covered the span of time between 290 and 248 million
years ago; also, the corresponding system of rocks. The Permian is sometimes considered
part to the Carboniferous, or is divided between the Carboniferous and Triassic. It is
named after the province of Perm, Russia, where rocks of this age were first studied.
The study and classification of the surface features of Earth
on the basis of similarities in geologic structure and the history of
geologic changes.
(a) A region, all parts of which are similar in geologic structure
and climate and which has consequently had a unified
geologic history. (b) A region whose pattern of relief features or landforms
differs significantly from that of adjacent regions.
An epoch of the Quaternary period, after the Pliocene of the
Tertiary and before the Holocene; also, the corresponding worldwide
series of rocks. It began one to two million years ago and lasted
until the start of the Holocene, some 10,000 years ago. When the
Quaternary is designated as an era, the Pleistocene is considered
to be a period.
A low arcuate ridge of sand and gravel developed on the inside of a stream
meander by accumulation of sediment as the stream channel migrates toward the
outer bank.
Ordovician age group of dolomites and sandstones underlying the the
Glenwood-St.Peter formations, but is missing in parts of northern Illinois. It
thickens considerably to the south.
All geologic time, and its corresponding rocks, before the beginning
of the Paleozoic; it is equivalent to about 90% of geologic time.
Precambrian time has been divided according to several different systems,
all of which use the presence or absence of evidence of life as a
criterion.
Q
The second period of the Cenozoic era, following the Tertiary; also, the
corresponding system of rocks. It began two to three million years ago and extends
to the present. It consists of two grossly unequal epochs: The Pleistocene, up to
about 8,000 years ago, and the Holocene since that time. The Quaternary was
originally designated an era rather than a period, with the epochs considered to
be periods, and it is still sometimes used as such in the geologic literature.
The Quaternary may also be incorporated into the Neogene, when the Neogene is
designated as a period of the Tertiary era.
R
Any of several types of geophysical measurements taken in bore holes using either the
natural radioactivity in the rocks, or the effects of radiation on the rocks to
determine the lithology or other characteristics of the rocks in the walls of the
borehole. (Examples: Natural gamma radiation log; neutron density log).
(a) A term
used loosely for the actual physical shape, configuration, or general unevenness of a
part of Earth's surface, considered with reference to variations of height and slope or
to irregularities of the land surface; the elevations or differences in elevation,
considered collectively, of a land surface (frequently confused with topography). (b)
The vertical difference in elevation between the hilltops or mountain summits and the
lowlands or valleys of a given region; high relief has great variation; low relief has
little variation.
A long narrow
trough, generally on a continent, bounded by normal faults, a graben with regional
extent. Formed in places where the forces of plate tectonics are beginning to split a
continent. (Example: East African Rift Valley).
S
A medium-grained sedimentary rock composed of abundant rounded or angular fragments of
sand size set in a fine-grained matrix (silt or clay) and more or less firmly united by
a cementing material (commonly silica, iron oxide, or calcium carbonate); the
consolidated equivalent of sand, intermediate in texture between conglomerate and shale.
The sand particles usually consist of quartz, and the term sandstone, when used without
qualification, indicates a rock containing about 85-90% quartz (Krynine, 1940). The rock
varies in color, may be deposited by water or wind, and contains numerous primary
features (sedimentary structures and fossils). Sandstones may be classified according to
composition of particles, mineralogic or textural maturity, fluidity index,
diastrophism, primary structures, and type of cement (Klein, 1963). (b) A field term for
any clastic rock containing individual particles that are visible to the unaided eye or
slightly larger.
Solid fragmental matter, either inorganic or organic, that originates from
weathering of rocks and is transported and deposited by air, water, or ice, or
that is accumulated by other natural agents, such as chemical precipitation from
solution or secretion from organisms. When deposited, it generally forms layers of
loose, unconsolidated material (for example, sand, gravel, silt, mud, till, loess,
alluvium).
A rock resulting from the consolidation of loose sediment that has
accumulated in layers (e.g., sandstone, siltstone, limestone).
A
fine-grained detrital sedimentary rock, formed by the
consolidation (esp. by compression) of clay, silt, or mud. It is characterized by
finely laminated structure, which imparts a fissility
approximately parallel to the bedding, along which the rock breaks readily into
thin layers and that is commonly most conspicuous on weathered surfaces, and by
an appreciable content of clay minerals and detrital quartz; a thinly laminated
or fissile claystone, siltstone, or mudstone. It normally contains at least 50%
silt, with 35% clay or fine mica fraction and 15% chemical or
authigenic materials. Shale is generally soft but
sufficiently indurated so that it will not fall apart on wetting; it is less firm
than argillite and slate, commonly has a splintery fracture and a smooth feel,
and is easily scratched. Its color may be red, brown, black, or gray.
Said of an ocean or lake bottom that becomes progressively
shallower as a shoreline is approached. The shoaling of the ocean
bottom causes waves to rise in height and break as they approach the
shore.
An indurated silt having the texture and composition of silt
but lacking its fine lamination or fissility; a massive
mudstone in which silt predominates over clay; a non-fissile silt shale.
A period of the Paleozoic, thought to have covered the span of time between 443 and 417
million years ago; also, the corresponding system of rocks. The Silurian follows the
Ordovician and precedes the Devonian; in the older literature, it was sometimes
considered to include the Ordovician. It is named after the Silures, a Celtic tribe.
Any
closed depression in the land surface formed as a result of the collapse of the
underlying soil or bedrock into a cavity. Sinkholes are common in areas where bedrock
is near the surface and susceptible to dissolution by infiltrating surface water.
Sinkhole is synonymous with doline, a term used extensively in Europe. The essential
component of a hydrologically active sinkhole is a drain that allows any water that
flows into the sinkhole to flow out the bottom into an underground conduit.
Long, low, gentle slope on the inside of a stream meander. The slope on which the
sand that forms point bars is deposited.
The movement and entrainment of soil along an initially small pathway in the soil.
As water moves along the pathway, the pathway enlarges and the velocity of the flow
may increase proportionally, thus, entraining more soil. The result is the formation
of an ever enlarging cavity along the flow path. At some point, structural support
may be lost and the ground surface or structures on the surface may collapse into
the cavity.
The St. Louis Limestone is named for St. Louis, Missouri, where it is extensively
exposed. No type section was designated. The St. Louis is typically exposed in
Illinois in the Mississippi River bluffs at Alton, Madison County. It is also well
exposed in the Mississippi and Illinois Valleys in western and southern Illinois and
along the Ohio River in Hardin County. The St. Louis is 500 feet thick in
southeastern Illinois and thins north-westward to less than 200 feet before being
truncated by pre-Pennsylvanian erosion. The St. Louis Limestone in Illinois is
characterized by fine-grained, micritic to lithographic, cherty limestone, but it
contains beds of dolomite, crystalline limestone, fossiliferous limestone, and
evaporites.
Geologic time-rock units; the strata formed during an age or subage, respectively.
Generally applied to glacial episodes (for example, to the Woodfordian Substage of
the Wisconsinan Stage).
The study, definition, and description of major and minor natural divisions of
rocks, particularly the study of their form, arrangement, geographic distribution,
chronologic succession, classification, correlation, and mutual relationships of
rock strata.
A stratum or body of strata recognized as a unit in the classification
of the rocks of Earth's crust with respect to any specific rock character, property,
or attribute or for any purpose such as description, mapping, and correlation.
A tabular
or sheet-like mass, or a single, distinct layer of material of any thickness, separable
from other layers above and below by a discrete change in character of the material or
by a sharp physical break, or by both. The term is generally applied to sedimentary
rocks, but could be applied to any tabular body of rock. (see also
Bed)
A small interval of geologic time; a division of an age.
A convex-downward fold in which the strata have been bent to form a trough; the strata
on either side of the core of the trough are inclined in opposite directions toward
the axis of the fold; the core area of the fold contains the youngest rocks. (see also
Anticline).
A
fundamental geologic time-rock unit of worldwide significance; the strata of a system
are those deposited during a period of geologic time (for example, rocks formed during
the Pennsylvanian Period are included in the Pennsylvanian System).
T
Pertaining to the global forces that cause folding and faulting of the Earth's crust.
Also used to classify or describe features or structures formed by the action of those
forces.
The branch of geology dealing with the broad architecture of the upper (outer) part
of Earth; that is, the major structural or deformational features, their origins,
historical evolution, and relations to each other. It is similar to structural
geology, but generally deals with larger features such as whole mountain ranges, or
continents.
A borehole log, run only in water-filled boreholes,
that measures the water temperature and the quality of groundwater in the well.
An abandoned flood plain formed when a stream flowed at a level above the level of its
present channel and flood plain.
Sediment eroded from the land, or a continent, and deposited in water
(generally in a marine environment).
Unconsolidated,
nonsorted, unstratified drift deposited by and underneath a glacier and consisting
of a heterogenous mixture of different sizes and kinds of rock fragments.
The undulating surface of low relief in the area underlain by ground moraine.
The natural or physical surface features of a region, considered collectively as to
form; the features revealed by the contour lines of a map.
The first period of the Mesozoic era (after the Permian of the Paleozoic era, and before
the Jurassic), thought to have covered the span of time between 225 and 190 million
years ago; also, the corresponding system of rocks. The Triassic is so named because
of its threefold division in the rocks of Germany. Syn: Trias.
U
Said of strata that do not succeed the underlying rocks in immediate order of age or
in parallel position. A general term applied to any strata deposited directly upon
older rocks after an interruption in sedimentation, with or without any deformation
and/or erosion of the older rocks.
A surface of erosion or nondeposition that separates younger strata from older strata;
most unconformites indicate intervals of time when former areas of the sea bottom were
temporarily raised above sea level.
Nonlithified sediment that has no mineral cement or matrix binding its
grains.
V
The accumulations of outwash deposited by rivers in their valleys downstream from a
glacier.
The Valmeyeran Series is named for Valmeyer, Monroe County, near which much of the series
is exposed. It is the middle series of the Mississippian System and includes
formations assigned to two series (Osagian and Meramecan) in other areas. The
Valmeyeran Series underlies most of central and southern Illinois and includes strata
from the top of the Chouteau Limestone upward to the base of the Shetlerville Member
of the Renault Limestone. The series is thickest, over 1800 feet, in southeastern
Illinois, and it thins to 600 feet or less before being truncated by erosion in
northern Illinois.
W
The Warsaw Shale is named for Warsaw, Hancock County, and the exposure in Geode
Glen at Warsaw has become the type section. The Warsaw is widely present in the
bluffs of the Mississippi and Illinois Valleys in western and southwestern
Illinois. It consists of as much as 300 feet of siltstone in west-central
Illinois, but it thins to less than 100 feet in the outcrop area, where it
consists of gray shale containing beds of argillaceous
limestone. Quartz geodes are common and locally abundant; some are replacements
of fossils. Some contain petroleum. The Warsaw is fossiliferous, with
brachiopods, bryozoans, and crinoids especially common.
The point in a well or opening in the Earth where groundwater begins. It generally
marks the top of the zone where the pores in the surrounding rocks are fully saturated
with water.
The group of processes, chemical and physical, whereby rocks on exposure to the weather,
change in character, decay, and finally crumble into soil.
Pertaining to the classical fourth glacial stage (and the last
definitely ascertained, although there appear to be others) of the Pleistocene Epoch
in North America, following the Sangamonian interglacial stage and preceding the
Holocene.
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