Technical Terms

Acadian orogeny...

A middle Paleozoic mountain building episode, the climax of which was in the Late Devonian. The Acadian Orogeny occurred when the microcontinent of Avalonia collided with the eastern coast of Laurentia (North America). The Acadian orogeny was the second episode of mountain building that formed what are now known as the Appalachian Mountains, occurring after the Taconic Orogeny.

acanthostyles...

rod-like calcite spines that are found at the intersection of zooecial walls in some bryozoans.

accretion...

the process of growth or increase, typically by the gradual accumulation of additional concentric layers.

Anthozoa...

a class of the phylum Cnidaria that contain the corals, anenomes and their relatives. Most of the life cycle is spent in the polyp stage. Most corals secrete calcium carbonate skeletons and are classified into three main groups: Rugosa, Tabulata and Scleractinia.

anticline...

a fold in sedimentaryrocks that creates a dome or arch in which, with erosion, older rocks are exposed in the center and younger rocks along the margins. THe Cincinnati Arch is an example.

asthenosphere...

the layer of the upper mantle that lies below the lithosphere, or crust. The asthenosphere is molten, but high pressures give it a plastic, flowing quality that facilitates movement of crustal plates.

background extinction...

the stochastically constant loss of species through time due to causes that are more local than global. Unlike mass extinctions, the background extinction of one species is not usually related to extinctions of other species.

basalt...

fine-grained igneous rock formed by the extrusion of magma at the surface of the earth, usually in ocean spreading ridges but sometimes above sea level as continental flood basalts. Basalt is the main component of oceanic crust.

benthic...

living at the bottom of a water body, on or beneath the sediments.

biostratigraphy...

correlation of rocks using fossils. Because species each have finite time spans between their origination and extinction, they can be used as indicators that rock units containing a particular species are roughly the same age, within the limits of the range of time that the species persisted.

bioturbation...

reworking of sediments by the actions of benthic organisms (organisms that live on the bottom) that burrow into them, travel through them, or browsing them for food.

Borden Group...

a group of rock formations that formed in what is now Indiana during the Mississippian as part of a large delta system. The Borden Group outcrops in a band that includes Brown County just to the east of Bloomington. The Edwardsville Fm. represents the delta's topset beds, the Spickert Knob Fm.represents its foreset beds, and the New Providence Shale represents its bottomset beds.

Brachiopoda...

a phylum of shelled marine animals whose valves have a left-right symmetry, but whose top (dorsal) and bottom (pedical) valves are not symmetrical. Brachiopods are lophophorates, using their lophophores for filter feeding. Brachiopods were a diverse part of most marine faunas in the Paleozoic.

Bryozoa...

colonial marine organisms, similar to corals in having skeletons that unite members of a colony into a single unit, but differ from corals in being lophophorate filter feeders. Bryozoans have a more complicated anatomical structure than corals, possessing a mesodermal layer with a body cavity between the ectoderm and endoderm. Their geological range is from the Ordovician to the present day. The phylum Bryozoa is sometimes called Entoprocta.

calice (also spelled 'calyx')...

In corals, the cup shape depression in which the coral polyp sits. Solitary corals have only one calice, colonial corals have as many calices as they have polyps. In crinoids the calyx is the cup that contains most of the living animal and which is attached to the stem and arms.

carbonate rocks...

sedimentary rocks composed predominantly of carbonate minerals, especially calcium carbonate (calcite or aragonite), that are precipitated by organisms. The most common carbonate rocks are limestone and dolomite.

chemostratigraphy...

the study of correlations among rocks based on chemical signatures extracted from their sediments or fossils, especially including stable isotope stratigraphy.

chronostratigraphy and geochronology...

the study of the age of rock units. The interval of time to which a rock unit belongs is a geochronologic unit, which is what is shown on a geological time scale. A group of rocks that belong to the interval is the chronostratigraphic unit, which is what is usually shown on a stratigraphic column. For example, in Indiana the Cincinnatian Series is the rocks in the southeast part of the state, a chronostratigraphic unit, that belong to the Cincinnatian Epoch, a geochronological unit. In other words, chronostratigraphy is the study of the rocks, geochronology is the study of the time.

cirri...

Small side branches that form off of the columnals of some crinoids.

clade...

an ancestor and all of its descendants, or all the taxa deriving from a single node on a phylogenetic tree.

clastic sedimentary rocks...

rocks formed from fragments of other rocks that have been transported and cemented together (see siliciclastic rocks).

Cnidaria...

a phylum of aquatic animals that include the hydrozoans (hydras and their relatives), scyphozoans (jellyfish and their relatives) and anthozoans (corals and their relatives). Cnidarians have a simple tissue organization with ectodermal and endodermal layers, but no mesoderm. Cnidarians are typically predators who sting their prey with cnidoblast (or cnidocyte) cells located on their tentacles.

coenosteum...

the skeletal structure of a coral, bryozoan, or stromatoporoid that is made up of the individual skeletal components produced by the many members of the colony.

collar cells...

flagellated cells found in sponges that produce water currents that draw food particles into the ostium. The collar cells also filter particles from the water.

conodont...

Tiny, extinct, toothed chordates that vaguely resemble eels, classified in Class Conodonta. Conodonts are important as biostratigraphic markers, used to determine the age of rocks, and as indicators of metamorphism because their phosphatic dental elements change color in response to high temperatures. Conodonts are known from the Cambrian through the Triassic.

continental crust...

Felsic crust, composed dominantly of silicate rocks enriched in silicon, oxygen, aluminum, sodium, and potassium, is lighter than mafic oceanic crust, which makes it "float" higher to form continents.

convolute...

a form of gastropod shell in which all whorls lie in the same plane and each new whorl completely covers the previous one.

Cooksonia...

the first land plant, a psilopsid. These plants were small and simple, without leaves or roots, and reproduced by spores.

craniates...

the group of chordate animals that have evolved heads, including lampreys, jawless fishes, and gnathostomes.

craniids...

a group of inarticulate brachiopods (do not have a tooth hinged) that are usually small and live cemented to the substrate, often the shells of other organisms. The shell of caniids is held together by muscles and ligaments.

craton or cratonic shield...

the older, geologically stable part of a continental plate that has been in place since the Precambrian and unaffected by major folding or orogeny (mountain building) since that time.

Crinoidea...

"sea lillies", a group of pelmatozoan (stemmed) echinoderms.

Dearborn Upland...

the phyiographic province of the southeastern corner of Indiana which is underlain by Ordovician rocks and which is deeply dissected by streams and rivers flowing into the Ohio River.

denudation...

The removal of sediments from a particular location, often by water and wind.

dessication cracks...

Polygon-shaped cracks that form in mud as it dries in a terrestrial environment. Dessication cracks are most often preserved in the rock record when they fill with loose sand and are buried.

diagenesis...

the physical and chemical changes occurring during the conversion of sediment to sedimentary rock and, in some cases, into metamorphic rock.

doublure...

in a trilobite, the recurved margin of the dorsal exoskeleton that surrounds the animal.

electroreception...

the detection by an aquatic animal of electric fields or currents, common in sharks and other Paleozoic marine vertebrates.

enteron...

in corals, the digestive space inside the polyp that is lined with endodermal epithelium (gastrodermis). More generally, the enteron is the alimentary canal, or digestive tract of an organism, a term used mostly in relation to simple organisms or embryonic development.

eustasy...

change in global sea level, usually driven by either changes in the size of continental ice sheets, changes in the total area of the lithosphere taken up by continental plates, which changes the capacity of ocean basins, or changes in the rate of tectonic plate movements, which is associated with changes in sea floor elevation and thus the capacity of the ocean basins.

facies...

sedimentary package that has specific characteristics of the sedimentary conditions, sedimentary or faunal. For example, marine areas that are offshore and below wave base often have only fine particles of mud or silt depositied in them, representing a deep marine facies. Biofacies are facies of organisms rather than sediments.

fault...

a fracture or other junction in rocks, originating from strain. Motion between blocks of rock occur along faults, and the faults themselves can usually be detected by offset stratigraphy on either side of the fault.

fluvial...

related to a river or stream. Fluvial sediments include silts, muds and sands (sometimes gravels or larger clasts) that are transported by the stream waters. When fluvial systems meet marine environments they often result in the production of a delta.

flux...

rate at which a reservoir gains or loses its contents, therefore the rate at which it expands or contracts, especially in global cycles of rocks, water, or elements.

forearc basin...

a depression in the sea floor between the coast and a volcanic arc caused by the downwarping of the crust at a subduction zone. A foreland basin is a depression in the crust on the continental side of an orogeny.

fractionation...

the separation of heavier and lighter isotopes of an element, either naturally or in a laboratory setting.

glacial till...

poorly sorted, poorly consolidated sediments left by glaciers. The clasts of a till include everything from silt-sized particles to large boulders that have blown onto the glacier or scooped up as it flowed over the surface.

GOBE...

Great Ordovician Biodiversification Event. The increase in biodiversity that occurred during the Ordovician and ended with the Hirnantian extinction at the end of the Ordovician.

Gondwana...

the southernmost supercontinent the formed Pangaea, made up of what are today Australia, Antarctica, Africa, and South America.

holdfast...

the structure at the distal end of a crinoid's stem that attaches it to the substrate. Most often holdfasts have a branching, root-like structure, but sometimes they are highly modified into anchors or floats.

holochroal eyes...

in trilobites, the close packing of biconvex lenses underneath a single cornea.

inarticulate brachiopods...

a major group of brachiopods including the lingulids and craniids that have no teeth on the hinge between their two valves (shells). The valves are held together only by ligaments and muscle.

infaunal...

benthic organisms that live in the sediments of a sea, lagoon, or lake. Epifaunal organims live on the sediment surface.

Katian...

A global stage/aged for the period 445.6-445.8 MYA. The Cincinnatian stage/age, a specifically North American unit, belongs to the Katian.

lacustrine...

of or relating to lakes.

lithological units...

Mappable units of rock that have relatively homogeneous lithologies (in other words, are composed predominantly of a certain type of sedimentary rock). Formations are the primary formal lithological, or lithostratigraphic unit.

lithology...

The kind of rock that makes up a particular lithological unit. For example, the lithology of the Edwardsville Formation is predominantly silts and fine sands.

lophophorates...

a group of phyla containing Brachiopoda, Bryozoa and Phoronida, all of which possess a lophophore, which is a ring of ciliated tentacles that surrounds the mouth that is used in filter feeding.

lophophore...

a ring-shaped, horseshoe-shaped, or coiled structure with ciliated tentacles situated around the mouth that aids in suspension feeding. The cilia create currents that draw water toward the mouth where food particles can be removed. Lophophores are found in brachiopods and bryozoans.

metazoan...

multicellular animal life. The major divisions within Metazoa are the phyla, including Porifera, Cnidaria, Bryozoa, Brachiopoda, Arthropoda, Mollusca, and Echinodermata.

monocline...

a step-like fold in sedimentary rock layers, often caused by crustal extension that creates a staircase-like series of subsided blocks. Monoclines differ from anticlines, which are dome-like folds where the center is higher than the margins, or synclines, which are dish-like folds where the margins are higher than the centers.

monticule...

literally 'small mountain', a monticule is the term given to the raised areas on the surface of some colonial bryozoans.

myriapods...

an arthropod group that includes centipedes, millipedes and related animals. Myriapods typically have anywhere from 10 to more than 700 pairs of legs.

node...

a junction on a phylogenetic tree that represents the last common ancestor of the taxa stemming from it, diagnosed by anatomical or genetic features that evolved in that ancestor and which are (usually) found in the decendants.

oceanic crust...

Mafic crust, usually basalt, that forms the ocean floors and is continually being created at spreading ridges. It is uniformly thin and dense and is ultimately subducted convergent plate boundaries.

oncolites...

a sedimentary structure formed by layers of cyanobacterial growth, similar to stromatolites but forming spherical structures.

operculum...

the mineralized flap that closes the opening to a shell or chamber, including the covering of the opening in the zooecium in gymnolaemate bryozoans and the covering of the opening of the shells of some gastropods.

orogeny...

the process of mountain building, which normally involves the subduction of an oceanic crustal plate beneath a continental one. Molten material from the descending plate forms an igneous arc that usually has a forearc basin on the ocean side and a foreland basin on the continental side. As the plate collision progresses, thrust sheets are pushed ahead of the island arc onto the continent, all of which is often accreted to the continental plate.

ostium...

small openings in the wall of a sponge through which water is drawn in for filtering. The ostia have short pore canals that open into the spongocoel.

patch reef...

an isolated, comparatively small reef which may form within a lagoon or embayment. Modern patch reefs are often circular and surrounded by sand or seagrass.

pelagic...

an organism that lives in the water column between the surface and floor.

Pelmatozoa...

The group of stalked echinoderms, including crinoids, blastoids and a few other minor groups.

physiography...

physical geography and geomorphology, the study of landforms, ecological communities, water drainages, soils, and their relationship to the underlying bedrock geology , especially the investigation of the historical processes that created the landforms.

Porifera...

the phylum containing the sponges and their relatives. Porifera are filter feeds whose level of organization consists of differentiated cells that are only loosely organized into tissues. Their skeletons are usually composed of silicaceous or calcium carbonate spicules held together by the protein spongin. Stromatoporoids are an important group of Paleozoic poriferans.

progradation...

progradation accumulation of sediments farther and farther out from the original shore, growth of the shore. Progradation often happens at river mouths through the formation and growth of delta structures.

pseudoextinction...

the end of a named species when it speciates into two descendant species or changes so much that a new species name is applied. Pseudoextinction differs from ordinary extinction in that diversity does not decrease with a pseudoextinction and sometimes, in fact, increases.

regolith...

a layer of unconsolidated sediment covering the surface, often composed of clasts derived from the underlying rock. Sometimes the term regolith is restricted to only dry, abiotic accumulations, such as are found on the surface of the moon, but often the term is used more generally to include soils and alluvium.

regression...

a retreat of a shoreline toward the sea, usually caused by falling sea level. Regressions expose sediments subaerially, allowing erosional surfaces to form. In a stratigraphic section, regressions are indicated by shallower water facies being deposited over the top of deeper water facies.

Richmondian invasion...

the immigration of many species into the Cincinnati arch area from farther north (farther west in today's directions). The invasion happened because of a rise in sea level that flooded the transcontinental arch that had previously separated the Cincinnati arch basin from the source area of the invaders.

schizochroal eyes...

in trilobites, an aggregation of lenses, each with its own cornea.

sclerites...

individual pieces of the exoskeleton of a trilobite, often associated with moulting.

sequence stratigraphy...

an approach to the correlation of rocks and the study of the history of sea levels. In sequence stratigraphy the successive facies of rocks are studied in many individual rock sections across a wide geographic area, with particular attention paid to unconformities, transgressive sequences and regressive sequences. The sequences at different locations are correlated with one another to provide a regional picture of the sequence of sea level rise and fall, which helps determine which facies are lateral equivalents of one another (lateral equivalents are two or more rock units that were formed at the same time in different depositional environments, such as nearshore and offshore facies).

sequestration (carbon)...

removal of carbon from the atmosphere and depositing it in a reservoir. Carbon sequestration may happen naturally over geological time by the burial of organic material and carbonate rocks, or it may be done through human effort to reduce the amount of carbon dioxide emitted by power plants or to reverse the anthropogenic rise in carbon dioxide concentration in the atmosphere.

silicaceous pulse...

an influx of siliciclastic sediment into a marine basin from the continent, usually caused by flooding or other intense weathering and transport.

siliciclastic rocks...

clastic, non-carbonate sedimentary rocks, that are rich in silica minerals, especially quartz, but also feldspars, clay minerals, micas and feldspars, that form from the clasts of weathered igneous rocks (or other siliciclatic rocks). Siliciclastic rocks include conglomerates, sandstones, siltstones, and mudstones and that form from lithified sediments that have been transported by water, wind or ice.

spicules...

microscopic, mineralized structures, often silicaceous, that make up the skeletons of some invertebrate animals, especially sponges (Porifera).

spondylium...

a muscle platform in the beak area of the ventral (or pedicle) valve of a brachipod.

stromatoporoid...

an extinct group of sponges that produce calcareous skeletons that are layered like stromatolites. Stromatoporoids are similar, and perhaps related to living sclerosponges. Stromatoporoids lived from the Cambrian through Cretaceous and were especially numerous in the Silurian and Devonian.

subaerial...

exposed beneath the air, specifically meaning not submerged below sea level.

subduction zone...

the area where two plates come together and at least one, usually a plate of oceanic crust, is forced deep into the earth were it melts.

synapsids...

the group of amniote tetrapod vertebrates that are more closely related to living mammals than to living reptiles. Synapsids have one temporal fenestra in their skull.

syncline...

a fold in sedimentary rocks that creates a basin or trough in which, with erosion, younger rocks are exposed in the center and older rocks along the margins. The Illinois Basin is an example.

tabula...

horizontal layers in the skeletons of some corals that floor the calice, especially notable in Tabulata and Rugosa. As the coral gets older and grows outward from its original base, it deposits new tabulae.

Taconic orogeny...

the collision of plates along the eastern margin of Laurentia (the continent that was the precursor to North America) that occurred during the Cambrian and Ordovician. The Taconic orogeny was one of several orogenies that formed the Appalachian Mountain chain.

Taconic orogeny...

An early Paleozoic mountain building episode that was the first wave of mountain building that resulted in what are now known as the Appalachian Mountains. The Taconic orogeny occurred during the Cambrian and Ordovician, before the Acadian orogeny.

taxon...

a named group of organisms. A taxon can be a species, a genus, an order, a phylum, or any other level of group.

transgression...

movement of the strand line of a sea onto a continent. Transgression can be caused either by a rise in global sea level (eustasy) or the depression of the continental margin (isostasy). In a transgressive sequence, marine sediments build up over terrestrial sediments as marine facies migrate shoreward.

trilobites...

an extinct Class belonging to the phyum Arthropoda. Trilobites superficially resemble cockroaches, but are not directly related to insects. They were an important part of Cambrian faunas and the group persisted through the Paleozoic, the last trilobites becoming extinct in the end-Permian extinction.

trophic...

levels of the food web or trophic pyramid. The lowest tropic level consists of primary producers (autotrophs), such as plants, who do not ingest food but synthesize it through the process of photosynthesis. Herbivores, predators and apex predators. The earliest life logically consisted of only primary producers, after which first herbivores then predators be sustained in early earth ecosystems.

unconformity...

places in the rock record where there is a time gap in the successive layers due to erosion before overlying layers of sediments/rock were laid down.

unconsolidated...

loose sediments that are the uncemented, unlithified products of weathering or transport.

uplift...

the raising of rocks to higher elevation, usually directly as part of an orogeny, but sometimes more indirectly from shifts in blocks of crust during plate movement.

virgin forest...

forest that has never been logged or grazed. Also called old-growth forest, primary forest, ancient forest or woodland, or primeval forest.

zooecium...

the skeletal chamber of a bryozoan, which is the home to a single zooid. All of the zooecia of a bryozoan colony are collectively called the zooarium (plural, zooaria).