Indiana Geology Glossary

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Glossary

Indiana Geology Glossary

Select a letter from the list below or scroll downward.

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

ablation: Loss of ice in a glacier or ice sheet from melting, sublimation, or calving of bergs into a body of water.
ablation complex: Assemblage of sediments deposited during the ablation of a glacier, generally by being let down from at or near the glacier surface by melting of underlying ice.
ablation hummock: Mound of till-like sediment deposited in a depression in the ice. The sediment becomes a positive topographic feature after the surrounding ice has melted.
Aboite aquifer system: Complex of sand and gravel aquifers centered in Aboite Township in western Allen County.
alluvial valley: River or stream valley flanked by floodplains that are frequently inundated by seasonal floods and underlain by alluvium.
alluvium: Sand, gravel, silt, and clay deposited adjacent to modern streams and derived from erosion of surface sediments elsewhere in the watershed or from valley walls.
anastomosing: Branching and reconnecting of stream-channel segments, separated by small islands of sediment.
anhydrite: A mineral, calcium sulfate (CaSO4), that is usually massive or in crystalline masses. Anhydrite is often associated with the mineral gypsum; however, it is not as common as gypsum. The name is of Greek origin meaning without water, in contrast to gypsum, which contains water.
anion: Negatively charged ion in solution. When minerals dissolve in water, they form ions that have a tiny positive or negative electrical charge.

John Comer, Indiana Geological Survey.
annular seal: Cement or bentonite clay pumped into the space between the borehole wall and well casing to seal out water and contaminants.
annular space: The space between a well casing pipe and the drilled borehole into which the casing is inserted.; See: well
anticline: A fold where the rocks are bent convex upward.
aquifer: A permeable body of rock, such as fractured bedrock or glacial till, that is saturated with ground water and is capable of providing significant quanties of water to wells and springs.

Modified from Glossary of Geology, 4th Edition, 1997, American Geological Institute.
aquitard: Slowly permeable stratum that retards water movement into and out of adjacent or underlying aquifers .; See: confining unit
arch: A broad open anticlinal fold on a regional scale.
artesian: Condition in which water levels in wells stand above the top of the aquifer. A "flowing artesian well" discharges to the surface under its own hydraulic head.
arthropod: A large group of invertebrate animals having segmented bodies, jointed legs, and exoskeleton (e.g., insects, trilobite).
attenuation: The chemical, physical, and(or) biological processes that restrict the migration of contaminants through geologic media.

B

basal outwash: Sand and gravel that were deposited as outwash in front of an advancing glacier and subsequently overridden by the ice and buried by other kinds of deposits. Basal outwash commonly forms the base of glacial depositional sequences.; See: outwash
basal till: Glacial till deposited by melting of ice at the base of a glacier and little reworked by meltwater or mass movement.
basin: A low area on the earth's crust where sediments have accumulated. These sediments may be consolidated or unconsolidated.
beach ridge: An arcuate ridge of sand that parallels or sub-parallels a coast. Beach ridges are formed by fluctuation in water level that create the core of the ridge. Later they increase in size by the addition of dune sand.
bedding plane: Surface marking the break between two distinct pulses (beds) of sediment deposition.
bedrock: Consolidated rock composed of cemented or lithified sediments (such as sandstone, shale, limestone) or crystalline rock (such as granite or slate). Underlies all surficial soil, sand, gravel, clay, and other material.
bentonite: Type of clay derived from weathered volcanic ash that expands when wet; commonly used as well drilling mud and annular seal.
biodegradable: Subject to decomposition by biological means, especially by micro-organisms.
bivalve: Any mollusk having a shell in two parts, hinged together so it will open and close like a book.
blow count: The unit of measure for the standard penetration test and representing the number of blows required to drive a 2-inch diameter core sampler one foot through unconsolidated material by dropping a 140-pound hammer from a distance of 30 inches.
brachiopod: A group of sea animals with hinged half shells and a soft body.
brackish: Containing salt, brine.
bulk permeability: Ease with which gases, liquids, or plant roots penetrate or pass through a bulk mass of soil.

C

calcareous shale: A shale containing at least 20 percent calcium carbonate in the form of finely precipitated materials or small organically fixed particles.
calcite: A common rock-forming mineral; CaCO3.
calcium carbonate: Chemical compound (CaCO3) in limestone and marble. Common component of sea water and may precipitate on the bottom of a sea, lake, etc.
carbonate bedrock: Rocks composed of limestone (calcium carbonate) and dolomite (calcium-magnesium carbonate).
carbonate rock: A sedimentary rock composed of more than 50 percent by weight of carbonate minerals.
cation: Positively charged ion in solution. When minerals dissolve in water, they form ions that have a tiny positive or negative electrical charge.

John Comer, Indiana Geological Survey.
channel: Typically a linear sag, stream course, or meltwater conduit with a V-shaped or U-shaped cross section. Channels in the glacial environment are commonly filled with sand and gravel deposited by meltwater.
Cincinnati Arch: A broad (elongate) structural high of regional scale where the sedimentary bedrock has been gently bent into a convex shape. The arch trends north-south from the southeast corner of the state to the east-central part where it divides into the Kankakee and Findlay Arches. The Kankakee Arch extends to the northwest and the Findlay Arch trends northeast into Ohio. To the west and southwest of these structural highs the rocks dip gently and thicken southwestward into the Illinois Basin. To the north of these structures the rocks dip northward into the Michigan Basin. Some of the oldest rocks exposed at the surface in Indiana are found along the axis of the Cincinnati Arch in the southeast corner of the state. See Tectonic Features of Indiana for a diagram illustrating the arch.
climate: The kind of weather a location has over a period of years.
cold-blooded: Animals with a body temperature that changes with the external environment.
cone of depression: Area below a well or dewatering site where the water table or potentiometric surface is drawn down below its natural (static) level due to removal of ground water.
confined aquifer: Saturated body of permeable rock or sediment overlain by a less permeable unit and characterized by hydraulic head higher than the top of the aquifer.
confining unit: Rock or unconsolidated material, generally of low permeability, that restricts ground-water flow.
conformable: Said of strata or groups of strata (such as formations) that are generally parallel to each other.
conifer: A cone-bearing tree that has needles as leaves (pine, fir, and cedar).
conodont: An extinct marine, wormlike chordate that existed during the Cambrian and into the Triassic. Only the microscopic toothlike phosphatic hard parts found in the head are commonly preserved.
continental drainage divide: A line of elevated terrain that separates two or more watersheds emptying into oceans or other bodies of water on different sides of the continent.
continental drift: A scientific theory of the slow movement of rock plates of oceanic and continental crust.
core: A sample or rock produced by drilling into the earth. Commonly, cores are cylindrical in shape.
craton: Part of the earth's crust that has been stable and little deformed for a prolonged period of time.
crevasse: Large near-vertical fracture open at the surface of a glacier and commonly a route for meltwater flow.
cross section: A diagram illustrating earth materials as if a large ditch was dug into the ground and the materials are viewed from within the ditch.

D

debris flow: Mass of rock and(or) sediment that becomes unstable and moves downslope under its own weight.
delta: Wedge-shaped mass of sediment deposited where a river or stream empties into a standing body of water such as a lake.
Devonian: Period of geologic time from about 410 to 360 million years ago.
diamicton: A descriptive, nongenetic term for poorly sorted sediments.
diffusion: The outward spreading of a plume of liquid or gas from areas of greater concentration to areas of lesser concentration.
dip: Refers to the angle at which the bedrock strata are inclined from the horizontal. Dip on bedrock surfaces may be caused by forces that bend the rock mass or by a variety of mechanisms active when sediments that make up the rock were accumulating.
discharge area: Region where ground water is moving toward, and generally appearing at the land surface or in a surface-water body.
dolostone or dolomite: Sedimentary rock composed of calcium magnesium carbonate (dolomite) that formed from the chemical alteration of limestone. Fossils are typically absent as a result of the dolomitization process.
drainage basin: An area bounded by a drainage divide that gathers water originating as precipitation and contributes it to a particular stream channel or system of channels, or to a lake, reservoir, or other body of water. A drainage basin can be small, such as one that contributes water to a small pond, or large, such as the one that contributes water to the Wabash River.

Modified from Glossary of Geology, 4th Edition, 1997, American Geological Institute.; See: drainage divide
drainage divide: The boundary between adjacent drainage basins.

Modified from Glossary of Geology, 4th Edition, 1997, American Geological Institute.; See: drainage basin

E

epicenter: Point on the Earth's surface that is directly above an earthquake's center within the Earth.

Jeff Kirby, Indiana Geological Survey.
Erie Interstadial: A period of ice lobe retreat from northeastern Indiana beginning around 17,000 B.P., followed by the readvance of ice.
Erie Lobe: Last ice lobe active in eastern Indiana and western Ohio during the late Wisconsin glaciation. Axis developed according to the orientation of Lake Erie as continental ice sheet advanced into the Great Lakes Region
erosion: Mechanical abrasion of material on the Earth's surface by glaciers, water, and wind.
esker: Linear type of ice-contact stratified deposit formed in subglacial channels and commonly having a sharply peaked ridgelike profile in cross section.
evaporite: A sedimentary rock that is formed through precipitation from evaporating sea water. Gypsum, anhydrite, and halite (rock salt) are examples of evaporites.
extinct: Plants and animals that no longer exist.

F

fabric: Structure in a rock or unconsolidated sediment produced by the parallel orientation of individual mineral grains, inclusions, or elongate rock fragments.
fan: Wedge-shaped body of sediment (usually sand and gravel) with a roughly semicircular map pattern and a gentle to steep upper surface that slopes away from the head or apex of the body.
fault: A discrete surface across which rocks move relative to each other; a planar break in the rocks.
fine grained: A relative or absolute grain size term. Relatively, it means any size smaller than the most common size. Absolutely, it refers to grains from 0.35 to 0.275 mm in diameter (Wentworth scale).
flow system: The cycle of ground water flow in an aquifer system including recharge, lateral and vertical flow, and discharge.
fluvial: Produced by the action of rivers or streams.
Fort Wayne Moraine: A large curved ridge composed of clayey till of the Lagro Formation centered on the City of Fort Wayne in northeastern Indiana. This ridge was deposited as an end moraine of the Erie Lobe of the late Wisconsin ice sheet before it retreated from Indiana approximately 12,000 years ago.
fossil: The remains or traces of an animal or plant of a former time; e.g., trilobite.
fracture flow: Ground-water flow controlled predominantly by a network of fractures, bedding planes, or other planar structures in a rock or sediment.

G

gamma-ray logs: Gamma-ray logging measures natural gamma radiation received by a detecting crystal over a specified time period. Gamma radiation of interest in logging is emitted during the radioactive decay of potassium, uranium, and thorium. Gamma-ray logs have three fundamental benefits: they provide an indicator of relative clay content because clays are generally higher in potassium than other common minerals, they provide a more precise resolution of boundaries between different geologic units than the SP log, and they can be collected from cased and open boreholes, both above and below the water table because gamma radiation easily passes through all these materials.
geologic period: A fixed span of geologic time that includes many kinds of igneous, metamorphic, and sedimentary rock that correlate one with another on a variety of criteria, but mainly on the basis of their geologic age.
geologist: A scientist skilled in studying earth materials and history.
geophysical logs: Geophysical logs are paper or digital records produced by a variety of instruments that are lowered on an electrical cable into a hole that has been drilled in the ground. These holes are drilled through both unconsolidated and bedrock materials for geologic information (corehole or boring), as a source of ground water (water wells), or for petroleum exploration (natural gas or oil well).
Glacial Lake Maumee: The name historically applied to the phase of ancestral Lake Erie that existed immediately following the retreat of the latest Erie Lobe ice.
glacial material: Sediment ranging in size from clay to large boulders that was transported, mixed, and deposited by glaciers and their meltwaters.
glacial terrain: Geographic region characterized by a distinctive landscape whose morphology reflects a particular series of glacial and postglacial events and which is underlain by a particular sequence of sediments that are directly related to those events.
glacial terrain map: A map that depicts the geographic distribution and characteristics of different glacial terrains.; See: glacial terrain
glacier: Mass of ice that flows under its own weight by internal deformation of ice, basal sliding, or other mechanisms.
glaciolacustrine: Associated with a lake environment formed in, on, or proximal to glacial ice.
glaciotectonic stress: System of forces acting on a body of rock or sediment owing to overriding by active glacial ice.
Gowganda Tillite: Till originally deposited during Precambrian glaciation approximately 1.8 billion years ago, and subsequently lithified and metamorphosed at low grade to a distinctive rock, typified by white and pink granite pebbles and boulders embedded in a fine-grained, green-gray matrix. Type locality is north of Lake Huron.
ground water: All water present below the surface of the Earth.
grout: Material, typically cement or bentonite slurry, used to seal the annular space of a well.
gypsum: Mineral composed of calcium sulfate, typically produced in hyper-saline basins characterized by the evaporation of water that causes concentration of salts.

H

heterogeneity: Spatial variation in physical attributes, such as grain-size, of a rock or sediment.
high-capacity well: Typically a large-diameter (8 inches or more) well capable of producing more than 70 gallons per minute.
Holocene: The more recent of the two epochs of the Quaternary Period; 10,000 B.P. is widely accepted as the start of the Holocene, which is characterized by the dramatic change (and explosion) of vertebrate life as the ice sheets retreated. This change occurred at different times at different places (for example, much of North America was still covered with ice 10,000 to 11,000 B.P.), hence 10,000 is the agreed-upon arbitrary starting point globally.
Huntertown aquifer system: Complex of sand and gravel aquifers and associated till-confining units in northern Allen County, best developed in the general vicinity of the Town of Huntertown.
Huntertown Formation: Sequence of outwash sand, till, ice-contact stratified deposits, and lacustrine sediments deposited by the Saginaw Lobe and its meltwaters in northern Allen County.
Huron-Erie Lobe: Ice lobe active in eastern Indiana and western Ohio during the late Wisconsin glaciation. Axis of flow developed parallel to the orientation of the basins and major bays of Great Lakes Huron and Erie.
hydraulic communication: Ease with which changes in hydraulic head are transmitted between different geologic units or different parts of an aquifer system.
hydraulic conductivity: Ability of a rock or sediment to transmit water under a unit hydraulic gradient.
hydraulic gradient: In an aquifer, the rate of change of total hydraulic head over the length of a flow path; for purposes of measurement and analysis, hydraulic gradient is commonly divided into two components: horizontal and vertical.
hydraulic head: The elevation that water rises to in a well open to a specific point in the subsurface. Consists of two components: 1) pressure head, and 2) elevation head.
hydrogeology: The science of ground water and its interaction with the geologic environment.
hydrothermal: Produced by extremely hot water. Hydrothermal fluids, typically 100 to 300 degrees celsius, are the last watery remnants of molten rock that solidified deep in the Earth's crust.

John Comer, Indiana Geological Survey.

I

Ice Age: The popular name for the most recent period of glacial activity, also known as the Pleistocene Epoch, which began some 2 million years ago and is still in progress. That period which continental glaciers overspread vast regions of northern North America.
ice-contact fan: Fan deposited against the front of a glacier or atop and amidst blocks of ice.; See: fan
ice-contact stratified deposits: Glacial sediment composed primarily of sand, gravel, and debris flows that were deposited on, against, or within glacier ice.
ice-marginal channel: Channel cut by a meltwater stream flowing along the margin of a glacier.; See: channel
ice-walled channel: Channel within a glacier whose walls are largely formed by glacier ice.; See: channel
Illinoian: A period of major glacial activity that took place from about 300,000 to 140,000 years ago. Deposits from this period are exposed at the modern land surface in southeastern and southwestern Indiana, beyond the limit of the Wisconsin ice sheets. They also occur in the subsurface throughout much of the rest of the state, beneath the overlying Wisconsin deposits.
illite: A hydrous, nonexpanding, potash-bearing clay mineral derived mainly from the weathering or alteration of mica and other aluminosilicate minerals.
induced recharge: The increased downward flow of water that occurs above a cone of depression as a result of pumping.
interlobate: Located between or affected by two lobes of glacier ice.
invertebrate: An animal without a backbone.
ion: An atom or group of atoms that has a net positive or negative charge.

From Introductory Chemistry, A Foundation, 1990, D.C. Heath and Company.

J

joint: Crack or fracture in a rock or sediment.

K

kaolinite: A clay mineral of the kaolin group derived from weathering of feldspars and montmorillonite clay; extremely stable high-alumina crystal lattice that does not greatly expand under varying water content and does not exchange iron or magnesium.
karst: A type of topography that is formed typically on limestone, primarily by dissolution, and that is characterized by sinkholes, caves, and underground drainage. The topography of the Mitchell Plateau region of Indiana, which extends from Owen and Monroe Counties to Harrison County, is mostly karst.

Modified from Neuendorf, K. K. E., Mehl, J. P., Jr., and Jackson, J. A., eds., 2005, Glossary of Geology: Alexandria, Virginia, American Geological Institute, 5th Edition, 779 p.
kettle: Depression caused by collapse of sediment due to the melting of buried blocks of ice.
kettle lake: A kettle lake is a kettle that is filled with water.; See: kettle

L

lacustrine sediment: Sediment deposited in lakes. Most commonly composed of silt and clay, but locally may consist of fine sand and gravely beach sediments.
Lagro Formation: The youngest sequence of glacial deposits in Allen County, composed mainly of clay-rich glacial till deposited during the most recent ice advances out of the Lake Erie basin.
landform: A natural feature of the landscape.
late Wisconsin: The most recent period of major glacial activity during the ongoing Ice Age, from about 22,000 to 10,000 years ago.
limestone: A sedimentary rock composed primarily of calcite. The calcite may be in the form of crystals, fossil fragments, or other fragments such as pellets and oolites.
lithology: The physical character of a rock or sediment. Refers primarily to the composition and texture of the material.
lithostratigraphy: Refers to the physical arrangement, in three dimensions, of different geologic materials and formations.; See: stratigraphy
loamy: Texture description for a soil having moderate amounts of sand (7-27 percent), silt (23-52 percent), and clay (28-50 percent).
local flow system: Very shallow ground-water flow between relatively nearby recharge and discharge areas.; See: flow system
Loraine Conglomerate: Metamorphosed glacial outwash composed of distinctive red pebbles of jasper in a white quartzitic matrix. Closely associated with Gowganda Tillite in the Lake Huron basin and in glacial deposits derived therefrom.

M

macropore: Large opening in a rock or sediment, such as a fracture or root channel that can act as a pipe to conduct ground water.
mammal: Class of vertebrate animals which give milk to their young; mammals are warm-blooded.
manganese oxide: A mineral compound formed through the oxidation of manganese (MnO2) by ground water discharging to the surface.
Maumee Lacustrine Plain: The former bottom of ancestral Lake Erie, represented by the flat landscape of eastern Allen County and adjacent parts of Ohio.
Maumee Torrent: Massive flood caused by the catastrophic drainage of Glacial Lake Maumee when the Erie Lobe readvanced slightly and meltwater overtopped a sag in the Fort Wayne Moraine. The flood greatly altered the upper Wabash River drainage and cut the vastly oversized Wabash-Erie Channel between Fort Wayne and Huntington, now occupied by the Little River.
MCL: Maximum Contaminant Level. The highest concentration allowed by the federal government in public drinking water supplies. MCLs are set using the best available treatment technology and taking cost into consideration.

John Comer, Indiana Geological Survey.
megasequence: Assemblage of sediments associated with one or more successive advances of a particular glacial lobe.
meltwater channels: Channels that carry flowing water from melting glacier ice.
mg/L: Milligrams per Liter. Unit of concentration used to quantify the amount of a constituent dissolved in a given volume of water.

John Comer, Indiana Geological Survey.
Michigan Basin: Structural basin centered on southern Saginaw Bay and characterized by Mesozoic rocks at the center, ringed by progressively older Paleozoic rocks.
Mississippian: Pertaining to the Mississippian Period, which began 340 million years ago and ended 320 million years ago.
moraine: Broadly arcuate to linear hummocky ridge deposited where an ice margin became stationary for a protracted period of time.
mud flow: Unsorted mixture of sediment that ranges from clay to boulders in size, and was deposited by the gravity flowage of unstable, oversaturated sediment.; See: till

N

nearshore: Area of a beach from the upper limit of swash to the lower limit of storm-wave base.
nonpoint-source pollution: Pollution from sources that cannot be defined as discrete points, such as areas of crop production, timber, surface mining, disposal of refuse, and construction.

From Glossary of Geology, 4th Edition, 1997, American Geological Institute.

O

Ordovician: Rocks pertaining to the Ordovician Period, which dates from 510 million to 439 million years ago. The oldest rocks that crop out in Indiana are Ordovician in age.
organism: Any living plant or animal.
outwash: Sediment deposited by meltwater out in front of an ice margin. Usually composed of sand and(or) gravel.
outwash fans: A fan-shaped accumulation of mostly sand and gravel deposited by glacial meltwater streams, and typically radiating from one or more distinct apexes along a moraine or other ice marginal position.
outwash train: Body of outwash sand and gravel in linear form that typically extends along a major river valley that drained one or more former ice margins.; See: outwash
outwash valleys: A valley underlain by glacial outwash. May be oriented parallel or perpendicular to a former ice margin, and may or may not be occupied by a modern stream.
overconsolidated: Refers to a sediment that is denser or harder than would be expected based on its depth of burial by younger sediments. For example, glacial till is commonly overconsolidated because of the great weight of the ice that once was above it.
oxidation haloes: Zone up to several inches wide around a fracture, void, or other permeable feature in which oxygen-bearing ground water has oxidized iron- and manganese-bearing minerals to a yellow, brown, or reddish color.

P

paleontologist: Scientist skilled in studying fossils and their history.; See: fossil
Paleozoic: Of, belonging to, or designating the era of geologic time that includes the Cambrian, Ordovician, Silurian, Devonian, Mississippian, Pennsylvanian, and Permian Periods. The time span is between approximately 542 and 251 Ma.

From Gradstein, F. M., Ogg, J. G., and Smith, A. G., 2004, A geologic time scale, 2004: Cambridge, UK, Cambridge University Press, 589 p.
palimpsest: Refers to a landscape in which most of the topographic features are not related to the materials at the land surface but are inherited from a buried surface at depth.
palustrine: Material growing or deposited in a marsh or related wetland environment.
Pennsylvanian: Pertaining to the Pennsylvanian Period, which began 320 million years ago and ended 290 million years ago.
permeability: The ability of geologic material to transmit water. In this report, the term is used in the same sense as "hydraulic conductivity."; See: hydraulic conductivity
pH: Negative logarithm of the hydrogen ion concentration. Water with low pH (<7) is an acid, water with high pH (>7) is a base, and water with pH=7 is neutral. A pH of 7 is equal to a hydrogen ion concentration of 10^-7 (or 0.0000001) mg/L.

John Comer, Indiana Geological Survey.
photon: The quantum electromagnetic energy, regarded as a discrete particle having zero mass and no electrical charge.
physiographic region: Geographic locales of similar topographic expression.
pitted: Refers to a landscape composed of outwash with numerous depressions caused by rafted blocks of ice that subsequently melted after being deposited with the outwash.
Pleistocene: Geologic epoch corresponding to the most recent ice age, and beginning about 2 million years ago.
plume: Mass of liquid or gas moving through a different medium. Most commonly refers to a mass of contaminants or contaminated ground water migrating through the subsurface geologic environment.
potassium-40, ⁴⁰K: A radioactive isotope of potassium having an atomic mass number of 40 and a half-life of approximately 1.31 × 109 years.
potentiometric surface: The surface defined by contouring the elevations of water levels tapping a confined aquifer system. This surface represents a map of hydraulic head in the aquifer system and defines the general direction of horizontal ground-water flow.

R

recessional margin: Location where an ice front stood for a significant period of time during the general retreat of the glacier and which is commonly marked by ridges or other accumulations of sediment deposited at the ice margin.
recessional moraine: A moraine that formed where the ice margin stabilizes during a general retreat of the glacier; See: moraine
recharge area: Region where significant percent of precipitation and surface water reaches the zone of saturation via infiltration. Commonly occurs by a combination of high potentiometric surface elevation, downward hydraulic gradients, and permeable surface sediments.
recharge potential: Comparative term that refers to the likelihood or ease with which ground water is likely to be recharged in a particular geologic or geographic region, relative to other regions having different conditions.
resistivity logs: Resistivity logging is important in the evaluation of sediment and rock materials, as well as fluids contained in the pore spaces of these materials. Resistivity is the measurement of the degree to which materials and their contained fluids impede the flow of electric current and is the inverse of conductivity, which is the property that is actually measured. Materials containing clay minerals or water with dissolved salts (commonly sodium chloride) conduct electricity readily and will have lower resistivity than porous nonclay-bearing clean materials or nonporous materials. Resistivity logging is most commonly used for evaluating formations to detect the presence of hydrocarbons in petroleum wells, but is sometimes also used in mineral exploration. Hydrocarbons and fresh water are poor conductors of electricity in contrast with salty formation water, which is a good conductor. Therefore, a resistivity log will show a difference between the resistivity of rocks filled with hydrocarbons and those filled with salty formation water.
rift: An elongate trough in the earth's crust formed by tension and defined by normal faults.
rock cycle: Processes where older rocks are made into new rocks through erosion and deposition, temperature and pressure, or melting and cooling.

S

Saginaw Lobe: Ice lobe active in far northern Indiana and southern Michigan during the late Wisconsin glaciation. Axis of flow developed parallel to the orientation of Saginaw Bay of Lake Huron.
sandstone: Sedimentary rock made of sand-size (0.06-2 mm) particles, usually of the mineral quartz, but other minerals or rock fragments may also be present.
saturated zone: All of the subsurface below the water table, and characterized by having all of the pore spaces filled with ground water.
secondary permeability: Permeability caused by post-depositional modification of a rock or sediment, such as fracturing or the development of solution features.
sediment load: The amount of fragmental rock material carried in suspension in a stream as clay, silt, sand, or coarser material. Darker colored, muddier water in streams after heavy rains shows the increase in sediment load.
sedimentary rock: A rock formed from particles that were eroded from a previous rock, then transported, deposited, and lithified. Also includes rock that accumulated as chemical precipitates.
seismic risk: A statistical or nonstatistical assessment of the potential for an area to experience ground shaking.
shale: Fissile sedimentary rock formed from mud (silt and clay). Where organic compounds are abundant, the shale is black whereas lower organic content results in lighter colors.; See: sedimentary rock
siltation: The deposition or accumulation of silt, or similar sized rock material, from suspension in a standing or slowly moving body of water.
siltstone: Sedimentary rock composed of silt-size (0.004-0.06 mm) particles (i.e., silt is coarser than clay, but finer than sand and has a slightly gritty feel when rubbed between the fingers or placed between the front teeth and lightly ground).; See: sedimentary rock
Silurian: Period of geologic time from about 440 to 410 million years ago.
sinkhole: A depression in a karst area, commonly having a circular pattern. Its drainage is subterranean, its size is measured in meters or tens of meters, and it is commonly funnel shaped.

From Neuendorf, K. K. E., Mehl, J. P., Jr., and Jackson, J. A., eds., 2005, Glossary of Geology: Alexandria, Virginia, American Geological Institute, 5th Edition, 779 p.; See: karst
sinking stream: A surface stream that disappears underground in a karst region.

From Glossary of Geology, 4th Edition, 1997, American Geological Institute.; See: karst
sluiceway: Valley or channel that conducted large amounts of glacial meltwater that may or may not be occupied by a modern stream; commonly associated with one or more ice margins.
SMCL: Secondary Maximum Contaminant Level. SMCLs are set so that drinking water will not have unpleasant taste, odor, appearance, or side effects. SMCLs are not enforcible and drinking water that exceeds them is not considered dangerous to human health.

John Comer, Indiana Geological Survey.
solution feature: Any type of secondary opening in limestone or dolomite caused by the dissolution of the rock in ground water. Caves, enlarged joints, and sinkholes are among the more common forms.
specific conductivity: With reference to the movement of water in soil, a factor expressing the volume of transported water per unit of time in a given area.

From Glossary of Geology, 4th Edition, 1997, American Geological Institute.
spontaneous potential logs: Spontaneous potential (SP) logging measures naturally occurring small electrical potentials (in millivolts) existing between an electrode in the borehole and a grounded electrode at the surface. These potentials or electrical fields develop in the borehole because of differences in ionic concentrations (primarily of sodium chloride and referred to as “salinity”) between the fluid in the borehole, the interstitial fluid in porous formations, and the shale or clay layers that are adjacent to the porous formation. SP response is related to the strength of the electrical fields in the borehole as well as the direction or polarity of the fields. The magnitude of the SP response depends on the amount of the contrast in salinity between the interstitial water and the borehole water as well as in the amount of permeability of the porous formation. With greater salinity contrast or greater permeability or both, the SP response will be larger. The polarity of that response (positive or negative) will depend on whether the borehole water contains more or less salt than the formation water. Changes in the amplitudes of the SP response can vary from one formation to another or from one location to another within the same formation. SP data can be used to detect permeable formations, the boundaries of these formations, the values for the formation-water resistivity, and to provide qualitative indications of the shale content of the bed.
spring: Any place where ground water discharges onto the land surface due to the intersection of the water table with the ground.
stratigraphy: The arrangement of geologic materials, and the depositional environments they represent, in both time and space.
suspended load: The part of the total stream load that is carried for a considerable period of time in suspension, free from contact with the stream bed; it consists mainly of clay, silt, and sand.

From Glossary of Geology, 4th Edition, 1997, American Geological Institute.
synodic month: The time it takes for the moon to go from new moon to 1st quarter phase to full moon to 3rd quarter phase and return to new moon. Currently this takes 29.53 days.

T

tectonic features: The structures or features resulting from the forces that produce movement and deformation of the Earth's crust.
terminal moraine: A moraine that marks the maximum extent of the ice margin.; See: moraine
texture: The relative proportions of particles of different sizes in a sediment, such as pebbles, sand, silt, and clay.
thorium: A silvery-white metallic radioactive element. Its longest-lived and only naturally occurring isotope is thorium-232.
till: Unsorted sediment deposited directly from glacier ice with little or no reworking by meltwater or mass movement. Usually contains particles ranging in size from clay to boulders, and may be partially consolidated depending on the geologic history.; See: mudflow
Tipton Till Plain: Physiographic region characterized by flat to gently rolling terrain, the result of continental glaciation during which glacial till and outwash were deposited as the ice advanced and melted from Indiana more than eight times.
topographic expression: Pertaining to the elevation, form, and dimensions of land forms; elevation typically being measured in relation to sea level.
trace element: An element that is not essential in a mineral but that is found in small quantities in its structure or adsorbed on its surfaces. Although not quantitatively defined, it is conventionally assumed to constitute significantly less than 1.0% of the mineral.

From Glossary of Geology, 4th Edition, 1997, American Geological Institute.
Trafalgar Formation: Assemblage of sediments representing the first known incursion of late Wisconsin ice into northeastern Indiana.
transpiration: The process by which water absorbed by plants, usually through the roots, is evaporated into the atmosphere from the plant surface.

From Glossary of Geology, 4th Edition, 1997, American Geological Institute.
tunnel valley: Hummocky to flat-bottomed, channel oriented perpendicular to an ice margin and eroded into the substrate below the ice sheet. A tunnel valley typically represents a major route for meltwater draining part of an ice sheet, and exiting the front of the ice.

U

unconformity: Large gap in the rock record, typically represented by a surface that bounds two rock or sediment bodies of vastly different ages.
unconsolidated: Refers to sediment that is not generally cemented or otherwise bound together by some type of chemical cement (such as limestone) within the pore spaces or by intense compaction from deep burial.
underflow: Ground-water flow that is generally below and parallel to the direction of surface water flow in a river valley.
unsaturated zone: All of the subsurface above the water table where pores are filled in part by water and in part by air.
uranium: A heavy silvery-white metallic radioactive element having 14 known isotopes, of which uranium-238 is the most abundant in nature.

V

vertebrate: An animal with a backbone.
vertical sequence: Refers to either a real or artificially constructed sequence of rocks or unconsolidated sediments.

W

Wabash Moraine: A large curved ridge composed of clayey till of the Lagro Formation located west of the St Joseph and St. Mary’s Rivers in northeastern Indiana. This ridge was deposited as an end moraine of the Erie Lobe of the late Wisconsin ice sheet before it retreated from Indiana approximately 12,000 years ago.
warm blooded: An animal that maintains an integral body temperature that is relatively constant; e.g., birds, mammals.
water table: The interface between the saturated and unsaturated zones.; See: saturated zone
well: Borehole drilled to produce water for consumption or to monitor water quality.
well casing: Plastic or metal pipe used above the water-producing zone of a well to keep the well shaft open and to prevent entry of sediment or contaminants.
well screen: Slotted pipe installed in the water-producing zone of a sand and gravel well to allow water to enter the well while keeping sediment out.
wellhead protection area: Zone around a public water supply wellfield identified by geologic and hydraulic factors that is managed to prevent contamination of the water supply.
Wisconsin: Most recent period of major glacial activity during the ongoing Ice Age, from about 75,000 to 10,000 years ago. Nearly the entire modern landscape of the northern two-thirds of Indiana, and a large part of the deposits beneath, are the product of this stage.
Wisconsinan glacial boundary: The southernmost extent of the Wisconsinan glaciation; in Indiana the southernmost extent of Wisconsinan glaciation dates from about 22,000 years ago, although older Wisconsin-age deposits are known to exist north of that margin.

Z

zone of influence: Land area directly above a cone of depression that is at increased risk because most of the water (and contaminants) that infiltrate this area will be "captured" by the cone of depression and eventually be drawn into the well.
zone of saturation: All subsurface rocks and soil below the water table characterized by having all pores, fractures, and other openings filled with ground water.

Glossary

Indiana Geology Glossary

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

ablation

ablation complex

ablation hummock

Aboite aquifer system

alluvial valley

alluvium

anastomosing

anhydrite

anion

annular seal

annular space

anticline

aquifer

aquitard

arch

artesian

arthropod

attenuation

B

basal outwash

basal till

basin

beach ridge

bedding plane

bedrock

bentonite

biodegradable

bivalve

blow count

brachiopod

brackish

bulk permeability

C

calcareous shale

calcite

calcium carbonate

carbonate bedrock

carbonate rock

cation

channel

Cincinnati Arch

climate

cold-blooded

cone of depression

confined aquifer

confining unit

conformable

conifer

conodont

continental drainage divide

continental drift

core

craton

crevasse

cross section

D

debris flow

delta

Devonian

diamicton

diffusion

dip

discharge area

dolostone or dolomite

drainage basin

drainage divide

E

epicenter

Erie Interstadial

Erie Lobe

erosion

esker

evaporite

extinct

F

fabric