GeoBrain — GSO L7 Cards

A metasomatic facies contact separating rocks that have undergone alteration of a particular facies from those that have undergone metasomatism of another facies. Alteration is a kind of metasomatism that does not introduce economically important minerals.

spaced cleavage domains branch and rejoin, creating lens-shaped microlithons.

An unconformable contact between two geological units in which the older, underlying rocks dip at an angle different from the younger, overlying strata, usually in which younger sediments rest upon the eroded surface of tilted or folded older rocks.

A fold whose core contains the stratigraphically older rocks

A convex-upward, concave downward fold.

A shape lineation defined by elongate augen.

Fabric defined by textural or mineralogic variations in sediment produced by depositional processes. May be manifested by lamination structure within the sediment, or by layering in which the individual layers (beds) are bounded by discontinuities related to events in the depositional history.

Lineation defined by the intersection of bedding surfaces and cleavage surfaces.

A surface internal to the containing sediment mass defined by textural or mineralogical variation, produced by sediment deposition process, and reflecting the orientation of the original depositional surface. Syn Laminated structure (NADM sedimentary rock vocabulary (https://pubs.usgs.gov/of/2004/1451/sltt/appendixC/appendixC_pdf.zip) SLTTs 2004).

Mineral lineation defined by aligned elongate biotite aggregates in a foliation surface. Biotite does not have an elongate (prismatic, acicular) mineral habit, so production of lineation must reflect elongate aggregates of biotite crystals.

An unconformity in which onlapping strata are truncated against a steep topographic scarp.

Ductile shear banding foliation defined by spaced, discrete planar zones of high strain less than 1mm thick. Commonly associated with a particle flattening ('S') fabric to form a mylonitic foliation.

A fold with straight limbs and sharp hinges. Well developed, these folds develop repeated set of v-shaped beds. Inter-limb angles are generally 60 degrees or less. Chevron folding preferentially occurs in well bedded units where bedding regularly alternates between contrasting competences.

A contact between bodies of material having different ages of origin. The temporal boundary represented by the zone contact is typically associated with some 'guide' event, such as a magnetic field reversal or fossil first appearance datum. If the event instance is implemented, link with Chronostratigraphic_Contact gsoc:isOutputOf ..event....

A tectonic foliation in a rock characterized by a tendency for the rock to split along a regular set of parallel or sub-parallel closely spaced surfaces. Cleavage is a more general term than schistosity because schistosity need not be present in order for a rock to display cleavage. Cleavage domains or parting surfaces are not spaced more than 5 cm apart on average (Borradaille et al., 1982)

Lineation defined by the intersection of two cleavages.

Composite fabric in which a cleavage is developed parallel to bedding.

Foliation defined by parting surfaces (cleavage domains) that have no apparent thickness, are spaced between 5 cm and 25 cm, and do not crenulate an older foliation. Fabric intermediate between typical cleavage and joints. Parting surfaces are regularly spaced, and penetrative on a 1-10 m scale. 5 cm upper limit on spacing of 'cleavage domains' in a 'cleavage 'fabric is suggested by Borradaile et al. [1982].

Layering fabric defined by layers that have internal comb structure. Layer boundaries are the termination surfaces for the constituent crystals.

Layering fabric defined by layers that have different mineralogic composition.

Foliation that includes fabric elements indicating classification with foliation types of different genetic origin, e.g. cleavage parallel to bedding is a compound fabric with a sedimentary foliation and a tectonic foliation. No connotation of genetic origin of fabric elements.

A compound foliation in which the constituent fabric elements are of metamorphic origin.

A geophysical contact between bodies of material distinguished based on electrical conductivity characteristics

A contact separating two geological units in which the layers are formed one above the other in order by regular, uninterrupted deposition under the same general conditions.

A surface that separates geologic units. Very general concept representing any kind of surface separating two geologic units, including primary boundaries such as depositional contacts, all kinds of unconformities, intrusive contacts, and gradational contacts, as well as faults that separate geologic units. (CGI ContactType vocabulary, adapted from Jackson, 1997, page 137, NADM C1 2004)

A cleavage that is statistically homogeneous down to the scale of individual mineral grains.

Cleavage defined by long, thin limbs of crenulation folds of pre-existing foliation, in which the boundaries between cleavage domains and lithons are gradational. Both the crenulation foliation and the crenulated (older) foliation are easily visible. Grades to spaced crenulation cleavage as boundaries of cleavage domains become sharp, and to schistosity or compositional layering as the crenulation foliation obscures the crenulated foliation to become the dominant fabric in the rock. In many rocks with continuous crenulation cleavage, the tendency to part along the cleavage may be weak, thus the rock may not technically meet the definition of 'cleavage as used in CGI foliationtype SKOS vocabulary 2018-08-03.

Cleavage that is overprinted on an older foliation that is folded to some degree in association with development of the younger cleavage. Cleavage domains commonly associated with long limbs of crenulation folds, and hinge surfaces of folds are roughly parallel. Wavelength of crenulation folds is less than or equal to 1 cm. Cleavage defined by limbs of microfolds coincident with zones of mineral differentiation

Lineation defined by small-scale wrinkles, typically of phylosillicate minerals, on another surface, typically a cleavage or schistosity. Use instead of intersection lineation if the wrinkles are the measured feature and the intersecting planar feature is not apparent.

Bedding defined by surfaces that are not distinct, e.g. by gradational grain size variations.

Fabric defined by fine laminae formed by the trapping of grains and lime precipitation in a microbial mat.

Layering in igneous rocks in which layers are characterized by variation in relative proportion of magmatically crystallized minerals. Typically a pattern of mineralogical variation will be repeated many times in a vertical section with layers of relatively consistent thickness. See photos in Best [1982] p. 176-177. Gravity-stratified layers typically have mafic minerals at the base and plagioclase at the top and are interpreted to form by crystal settling in magma.

A lithogenetic bundary separating rock masses that have different deformation structure, e.g. sheared rock against non sheared rock, brecciated rock against non-brecciated rock.

A geophysical contact separating bodies of material with different density characteristics, generally determined through measurement and modelling of gravity variations.

Lithogenetic contact at which a sedimentary or volcanic rock has been deposited on (or against) another rock body. The relationship between the older underlying rocks and younger overlying rocks is unknown or not specfied.

A regional-scale, large displacement, low-angle normal fault.

In plan view, the side opposite the observer is displaced to the right.

Fault with right-lateral strike-parallel displacement component of slip vector more than 10 times the dip-parallel component of the slip vector at at least one location along the fault, and right-lateral displacement over more than half the mapped trace of the fault.

A fault along which there is some separation parallel to the dip of the fault.

The net slip of the fault lies in the dip direction of the fault.

An unconformable contact between two geological units in which the bedding of the older, underlying unit is parallel to the bedding of the younger, overlying unit, but in which the contact between the two units is marked by an irregular or uneven surface of appreciable relief.

Spaced cleavage in which cleavage domains have sharply defined edges.

Crenulation cleavage in which the cleavage domains have discrete boundaries. Amplitude of crenulation folds tends to be small.

Disjunct spaced cleavage defined by discrete cleavage surfaces, typically in low-grade clastic rocks. Syn. Fracture cleavage.

A spaced cleavage independent of any pre-existing mineral orientation, cleavage in which there is no systematic relationship between a pre-existing preferred orientation and the superimposed cleavage. (Borradaile et al., 1982)

magnitude of slip or separation

Fabric in which domains of more strongly developed (closely spaced) cleavage are separated by lenses of weakly or non-cleaved rock. Typically observed on outcrop scale and used for geologic unit description

Foliation defined by regularly spaced ductile shear bands at the scale of descripiton.

a broadly planar zone of shear displacement within which deformation has occurred without loss of material continuity

Foliation defined by flattened pumice clasts or glass shards, aligned elongate lithic fragments, variations in composition, vesicularity, crystallinity, grain size, spherulite and lithophysae abundance, or the degree of devitrification in a welded tuff. This term denotes interpretation that foliation formed during compaction and welding of tuff.

Displacement across a fault is substantially in the direction perpendicular to the fault. The fault-parallel displacement is effectively zero.

A fault whose two sides have approached each other substantially in the direction perpendicular to the fault.

A discrete surface, or zone of discrete surfaces, with some thickness, separating two rock masses across which one mass has slid past the other and characterized by brittle deformation.

Quality that specifies the relative sense of displacement (right, left, up, down) between rocks on opposites of a fault.

A material spatial feature that contains one or more fault surfaces as well as deformed rocks related to the faults located between and adjacent to the fault traces

A contact separating two bodies of material across which one body has slid past the other.

Diffuse to distinct lamination in mudstones and mud, defined by the alignment of clay minerals. Lacks distinct very-fine scale layering and repetition of couplets that characterize varves. Essentially a continuous cleavage parallel to bedding, but considered a sedimentary structure related to sediment compaction during diagenesis.

Tectonic foliation defined by lenses and layers of original or relatively unaltered granular minerals surrounded by a matrix of highly sheared and crushed material. No connotation of metamorphic grade.

Layering produced by flow of magma, lava, or diapiric flow of sedimentary rock. Distinction from eutaxitic foliation may be difficult.

A linear alignment of fabric elements, especially elongate or rod-shaped minerals, interpreted to have been aligned by flow of magma, lava, pyroclastic material, or diapiric flow of sedimentary rock.

A curve or bend of a planar structure, such as rock strata, bedding planes, foliation or cleavage. A fold is usually the product of deformation, involving the compression of strata, but may include primary structures, as its definition is descriptive, not genetic. (Neuendorf et al., 2011).

Surface that contains the hinge lines in a stack of folded layers

the length of half the distance from the crest of a fold to the adjacent troughs.

Abstract surface that bisects the limbs of a fold or is the normal to a surface defined by the poles to the folded surface (typically visualized on a stereonet). The axial surface of a particular fold may be located based on observations of the folded geologic structure, but in general it has no direct physical manifestation. Contrast with hinge surface, which is defined as the surface containing a set of hinge lines in the stack of folded surfaces defining a fold structure. As a geologic surface, the axial surface has geometric properties, including orientation, which may be specified by observations at one or more locations, or generalized using terminology (upright, inclined, reclined, recumbent, overturned). (revised from GeoSciML 3.2)

the line linking points of maximum curvature on a folded surface (http://www.geosci.usyd.edu.au/users/prey/Teaching/Geos-2123/Folds/Sld22.html). A low-dimensional feature

Variation in orientation of fold hinge along trend of fold, distinguish sheath from cylindrical folds. Specify with terminology eg sheath, dome, basin, cylindrical.

Rounded vs. angular hinge zones; has to do with the proportion of the wavelength that is considered part of hinge

The generally planar region of a fold which lies between two adjacent hinge lines and is confined between the zones of maximum curvature. A role played by some layered rock reated to the adjacent fold hinges. Not necessarily a feature

The angle between adjacent limbs of a fold, normally determined by drawing tangents to the fold limbs at the inflection points.

Straight vs curved limbs, eg kink, chevron, sinusoidal, box

linear distance between inflection points in a single fold (GeoSciML v3.2)

Concordance or discordance of bisecting surface and axial surface, or ratio of length of limbs. Folded surface may have asymmetry defined by limb length ratio if inflection points are defined. Definition based on bisecting surface/axial surface angle depends on having multiple surfaces defined such that the axial surface may be identified. (symmetric, assymetric)

A collection of congruent folds (axis and axial surface are parallel) produced by the same tectonic event. Sometimes referred to as a \

The distance between adjacent crest or trough of a single fold, or the average distance between adjacent crests or troughs in a fold system.

boolean value, true if wavelength of folds in a fold system is approximately the same

A large-displacement (kilometers or tens of kilometers) shallowly dipping to subhorizontal fault or shear zone.

Foliation defined by the shapes of deformed mineral grains or grain aggregates having aspect ratios greater than 1.5:1, greater than 10 percent of the rock is composed of 'matrix' showing evidence of tectonic reduction in grain size, and the foliation and matrix are interpreted to be the product of continuous, crystal-plastic deformation processes. Generic class is used when data are insufficient to determine classification to protomylontic, mylonite, or ultramylonitc foliation, or to specify that any sort of mylontic foliation may be present.

A contact between regions characterised by their geological history or by similar structural, petrographic or stratigraphic features

A contact separating bodies of material in the earth that have different geophysical properties. Use for boundaries that are detected by geophysical sensor techniques as opposed to direct lithologic observation.

A boundary between a subglacial geomorphic unit and a periglacial geomorphic unit, marking the maximum extent of glacial cover. This can be thought of as the outcrop of the contact between a glacier and its substrate at some time at each point along the boundary. This contact type is included as an interim concept, assuming that in the future, there will be extensions to account better for geomorphic units and line types.

Compositional layering in a metamorphic rock, syn. gneissic banding

Foliation defined by the alignment of oblate particles, which may be detrital grains, crystals, or crystalline grain aggregates.

GSSP is dependent on some particular geologic event that is manifested globally in the stratigraphic record. At least one of the host Rock_Body_Boundary objects must be a participant in the host Geologic_Event

Fault that dips at least 45 degrees over more than half of its recognized extent, for which slip or separation is not explicitly specified.

Fault that dips at least 45 degrees over more than half of the recognized extent of the fault with the hanging wall displaced from a structurally higher position relative to footwall rocks.

Reverse fault that dips at least 45 degrees over more than half of its recognized extent, for which slip or separation is not explicitly specified.

Fault that dips less than 10 degrees over more than half the recognized extent of the fault.

Mineral lineation defined by aligned hornblende crystals.

Foliation interpreted to be due to flow in a body of magma or lava. Includes flow banding in lava, and foliation defined by aligned crystals in a phaneritic igneous rock..

An intrusive contact between a younger igneous rock and an older, pre-existing geological unit into which it has been intruded.

Foliation defined by surfaces of textural or mineralogical variation formed by igneous processes. If the lamination surfaces are regularly spaced, they may be used to define layers.

Layering that is the product of processes operating in magma or lava. syn. magmatic layering

Lineation defined by alignment of elongate fabric elements formed in lava or magma before complete crystallization. Some typical fabric elements are elongate phenocrysts and vesicles.

Lineation in igneous rock defined by aligned crystals where there is evidence that the crystal alignment is related to process occurring before the rock was solidified.

Lineation in an igneous rock, usually welded tuff, defined by elongate objects in the rock (usually pumice pads, also elongate crystals). Descriptive--elogation may be due to deformation or to rotation/alignment of originally elongate (prolate ellipsoid) objects in the rock.

A lithogenetic contact separating lithologically distinct phases of a single intrusive body. Does not denote nature of contact (intrusive or gradation).

Layering defined by grain size/ grain shape variations resulting from crystallization processes in igneous rock, most commonly observed in pegmatite/aplite dikes or bodies, and in Laramide leucogranites of Wilderness suite in Arizona.

lineation defined in a volcanic rock by aligned elongation direction of vesicles.

Fabric defined by long axis of tabular clasts stacked like shingles to define a surface that makes a small angle with the bedding surface. A depositional fabric formed by disk-shaped or elongate pebbles all tilted in the same direction, flat sides commonly dip upstream

surface that bounds a body of rock affected by an extraterrestrial impact event

Lamination defined by discontinuous surfaces

A lineation produced by the intersection of two planar fabrics.

Lamination fabric in which individual lamina or groups of lamina are warped in an irregular fashion, like a flattened peice of crumpled paper. A crude planar orientation is discernible.

Fabric defined by parting surfaces in rock that occur in crudely parallel orientation, spaced greater than 5 cm on average if in a very regular joint set. Spacing is more variable and alignment of surfaces is cruder that cleavage. Typically applies to geologic unit description.

Metamorphic layering in which the layers are less than 1 cm thick. See Weiss, L.E. [1972] plate 36 or Borraidaile et al [1982] plate 137A B (page 331), plate140A (page 337) for examples.

Layering formed by laminar lava flow, defined by variations in composition, vesicularity, crystallinity, grainsize, spherulite and lithophysae abundance, degree of devitrification, colour, and/or parting surfaces, syn. flow lamination, flow banding

Compound foliation in which mylonitic foliation is present in rock that has continuous compositional layering. Continuous means individual layers can be traced more than 1 m.

Foliation defined by stacked, differentiable, sheet-like masses of material (layers), with no denotation of the nature (composition, grain size, grain shape...) or origin (igneous, sedimentary, metamorphic) of the layers.

High angle fault with slip vector that has ratio of strike-parallel to dip-parallel displacement between 10 to 1 and 1 to 10 at at least one location along the mapped trace, with left-lateral strike-parallel component and normal dip-parallel component over at least half the mapped trace of the fault.

High angle fault with slip vector that has ratio of strike-parallel to dip-parallel displacement between 10 to 1 and 1 to 10 at at least one location along the mapped trace, with left-lateral strike-parallel component and reverse dip-parallel component over at least half the mapped trace of the fault.

A non-faulted contact separating bodies of material in the earth that have different lithologic character or geologic history.

Fault that dips less than 45 degrees over more than half of the recognized extent of the fault.

Fault that dips less than 45 degrees over more than half of the recognized extent of the fault with the hanging wall displaced from a structurally higher position relative to footwall rocks.

Foliation interpreted to be due to flow in a body of rock (typically mudrock, salt, or anhydrite) under low-temperature (non-metamorphic) conditions, typically related to diapirism.

A geophysical contact separating bodies of material distinguished based on properties related to magnetic fields.

A magentic contact between bodies of material with different polarity of remnant magnetization, e.g. between sections of ocean floor with different polarity.

A magnetic contact between bodies of material distinguished based on magnetic susceptibility characteristics.

A magnetic contact between bodies of material distinguished based on any aspect of magnetization of material in the units.

Lithogenetic contact separating rocks that have different lithologic properties related to metamorphism, metasomatism, alteration, or mineralization. Generally separates metamorphic rock bodies, but may separate metamorphosed (broadly speaking) and non-metamorphosed rock.

Layering defined by mineralogical variations in a rock body interpreted to be result of solid-state reactions in rock body (metamorphic segregation).

A metamorphic contact separating rocks that have undergone metamorphism of a particular facies from those that have undergone metamorphism of another facies.

Layering of unspecified origin in a metamorphic rock. Compositional or textural variations may be inherited from protolith, or result from metamorphic processes.

Metamorphic layering in which layer differntiation is relict of compositional variations in the protolith, typically heterogeneous sedimentary or volcanic rock.

A metamorphic contact separating rocks that have undergone metasomatism of a particular facies from those that have undergone metasomatism of another facies. Metasomatism is distinguished from metamorphism by significant changes in bulk chemistry of the affected rock.

Lineation defined by alignment of elongate crystals that have a prismatic crystal habit or of monomineralic grain aggregates.

A metasomatic facies contact separating rocks which have been mineralised and contain a particular mineral assemblage from those which contain a different assemblage. Mineralization is a kind of metasomatism that introduces ecomomically important minerals.

Generic layering defined by variations in mineralogy between individual sheets of material

An extraction fault with some displacement within the fault plane.

step-like fold in rock strata consisting of a zone of steeper dip within an otherwise horizontal or gently-dipping sequence.

Slip vector linking piercing point on opposite sides of fault, or separation vector linking offset surface along fault trace.

Generic mylonitic foliation in which 50-90 percent of rock is matrix due to tectonic grain size reduction processes. Planar fabric is very apparent due to flattening of mineral grains, development of shear surfaces, and alignment of tabular mineral grains. Lineation is typically present and easily observed.

A fold which closes laterally and is therefore neither antiformal nor synformal.

The fault-parallel displacement is effectively zero, as in an extraction fault.

An unconformable contact between an underlying, older nonstratified geological unit (usually intrusive igneous rocks or metamorphics) and an overlying, younger stratified geological unit.

The hanging wall has been displaced down relative to the footwall, dip of fault usually 45-90 degrees.

The movement sense includes both normal and dextral components.

Fault with dip-parallel displacement component of slip vector more than 10 times the strike-parallel component of the slip vector over more than half recognized extent of the fault, and for which the fault dips consistently in the same direction, and for which the hanging wall has been displaced down relative to the footwall.

The movement sense includes both normal and sinistral components.

The net slip of the fault lies between the strike and dip directions of the fault, the slip vector rakes between 10 and 80 degrees in the plane of the fault.

Fault with slip vector that has ratio of strike-parallel to dip-parallel displacement between 10 to 1 and 1 to 10 at at least one location along the mapped trace of the fault.

An unconformable contact between two geological units in which the bedding of the older, underlying unit is parallel to the bedding of the younger, overlying unit, in which the contact between the two units is planar, and may be coincident with a bedding plane.

Bedding defined by parallel surfaces. Bedding structure may be lamination or layering.

Bedding lamination structure in which all visible bedding surfaces are parallel.

Lineation defined by alignment of long axes of prolate-shaped particles such as clasts, fossils, crystals, or phenocrysts. Particles may be polycrystalline aggregates formed by deformation of pre-existing particles. General category does not specify genesis of particles or their alignment.

Lineation defined by tendency of rock to break into long, slender pieces resembling pencils. Typically produced by intesection of bedding and cleavage or intersection of two cleavages. Fabric is generally only observed in weakly metamorphosed rocks.

Continuous cleavage in phyllitic rock, phyllosilicate mineral grains just barely visible, grain size midway between slaty cleavage and schist, typically has a satiny lustre.

Lamination that is defined by planar bedding surfaces at the scale of description.

Foliation formed during original process of deposition or crystallization of an igneous or sedimentary material.

Foliation interpreted to be the product of igneous processes, formed in the rock while melt was still present..

Generic mylonitic foliation in which 10-50 percent of rock is matrix due to tectonic grain size reduction processes. Planar aspect of fabric may be quite subtle in weakly deformed rocks.

Chaotic and highly sinuous fold typically in an isolated layer within a more homogeneous rock body. Typical of sedimentary slump folding and veins or dikes in medium to high-grade metamorphic rocks

An extraction fault with no discernible displacement within the fault plane.

Aligned quartz fibres that define a measurable lineation

A geophysical contact separating bodies of material distinguished based on the characteristics of emitted of radiant energy related to radioactivity (e.g. gamma rays).

Surface dips between 0 and 10 degrees; typically used to describe orientation of fold hing surface or axial surface, use equivalent term 'Horizontal inclination' for other geologic surfaces.

A fold that has an essentially horizontal axial plane.

The hanging wall has been displaced up relative to the footwall, dip of fault usually greater than 45 degrees.

The movement sense includes both reverse and dextral components.

Fault with dip-parallel displacement component of slip vector more than 10 times the strike-parallel component of the slip vector at at least one location along the mapped trace of the fault, and the fault dips consistently in the same direction with the hanging wall displaced up relative to the footwall over at least half the mapped trace of the fault.

The movement sense includes both reverse and sinistral components.

Layering in igneous rock defined by repeated gravity-stratified layers of typically mafic minerals at the base and plagioclase at the top, formed by crystal settling

High angle fault with slip vector that has ratio of strike-parallel to dip-parallel displacement between 10 to 1 and 1 to 10 at at least one location along the mapped trace, with right-lateral strike-parallel component and normal dip-parallel component of slip over at least half the mapped trace of the fault

High angle fault with slip vector that has ratio of strike-parallel to dip-parallel displacement between 10 to 1 and 1 to 10 at at least one location along the mapped trace, with a right-lateral strike-parallel component and reverse dip-parallel component of slip over at least half the mapped trace of the fault.

Linear structure in metamorphic rocks in which the stronger parts have been shaped into parallel rods (eg. vein quartz)

Disjunct (Borradaile et al, 1990) cleavage characterized by short, discontinuous clavage surfaces, typically with concentrations of phyllosilicate minerals. Common in micaceous sandstone.

Foliation in mylonite defined by alignment of tabular crystals or deformed mineral grains, often with sigmoid shape, typically curving into an associated ductile shear banding foliation (C fabric) with a consistent sense.

Discrete, anastomosing spaced cleavage characterized by smooth and highly polished/slickensided cleavage surfaces that intersect with one another to form lensoid flakes, scales or chips. Common in pelitic rocks in shear zones, melange, or deformed accretionary complexes.

A fabric defined the parallel, planar arrangement of mineral grains having a platy, lamellar, or tabular crystallographic habit that are oriented in a continuous planar or rarely a linear fabric. Schistosity is commonly, but not necessarily, a crystalloblastic foliation. Platy mineral grains typically 1 to 10 mm across (Jackson, 1997), at smaller grain size grades into phyllitic cleavage. Schistosity is typically associated with a continuous cleavage due to the tendency to part parallel to the aligned mineral grains.

A fault on which there is increasing offset or separation along the strike from an initial point of no offset, with reverse offset in the opposite direction.

A fault on which there is increasing offset or separation along the strike from an initial point of no offset, with the opposite sense of offset in the opposite direction.

A lithogenetic contact separating essentially coeval sedimentary material bodies distinguished by characteristics reflecting different physical or chemical processes active at the time of deposition of the sediment.

An intrusive contact between a sedimentary rock unit and plastic sediment (e.g., clay, chalk, salt, gypsum, etc.), forced upward into it from underlying sediment

Layering resulting from primary sedimentary processes, in which the individual layers (beds) are bounded by discontinuities related to events in the depositional history.

A geophysical contact separating bodies of material defined based on their seismic character. Seismic character is based on transmission of vibrations (seismic waves) through a rock body, and relates to the velocity of transmission, and the nature of reflection, refraction, or transformation of seismic waves by inhomogeneities in the rock body.

a vector (magnitude and orientation) specifying the distance between the intersection of a surface on opposite sides of a displacment surface. In 3-D is the projection of a vector normal to the displaced surface into the displacment surface, but might also be specified as offset of the intersection of displacement surface and marker surface in some other profile view (e.g. horizontal/map view, or a cross section)

Mineral lineation defined by aligned sillimanite crystals.

In plan view the side opposite the observer is displaced to the left.

Fault with left-lateral strike-parallel displacement component of slip vector more than 10 times the dip-parallel component of the slip vector at at least one location along the fault, and left-lateral displacement over more than half the mapped trace of the fault.

Continuous cleavage defined by aligned fine to very-fine grained phylosilicate mineral grains. The individual grains defining the fabric are too small to be seen by the unaided eye. Grades into phyllitic cleavage as grain size increases. Cleavage domains typically less than 100 micrometres wide, rock easily splits into slabs and thin plates.

Lineation on a brittle slip surface defined by grooves, ridges, or striations

a vector (magnitude and orientation) that links a peircing point on opposite sides of a displacement surface.

Spaced cleavage forming an array of parallel to anastomosing, stylolitic to smooth, fracture-like partings formed by rock dissolution. Dissolution is indicated by discontinuity and offset of primary features that intersect cleavage surfaces, and typically by accumulation of insoluble residue along cleavage surface. Syn. stylolitic cleavage, pressure solution cleavage

Cleavage in which cleavage domains are spaced at finite intervals as the scale of description. Microlithons of uncleaved rock separate cleavage domains.

A spatially restricted part of a Contact feature in a particular stratigraphic section, typically located by a point location.

Lineation defined by elongate (prolate) fabric elements in which the alignment of the fabric elements, and the formation of prolate fabric elements is interpreted to be the product of crystal plastic deformation processes. Associated with mylontic foliation.

planar features indicate some displacement parallel to the strike of the fault.

The net slip of the fault (slip vector) is parallel to the strike of the fault.

Fault with strike-parallel displacement component of slip vector more than 10 times the dip-parallel component of the slip vector at at least one location along the mapped trace of the fault.

Tectonic layering in which variations that distinguish the layers are the result of melt segregation during high-grade metamorphism, some layers have magmatic/igneous mineralogy. Plates 143 and 144, Borradaile et al [1982] (page 344-347) Syn. Migmatitic layering, lit-par-lit layering

Lamination produced by sediment trapping, binding and or precipitation by cyanophytes (blue-green algae)

A fold of which the core contains the stratigraphically younger rocks

A convex-downward, concave upward fold.

Foliation in a rock body defined by physical components related to deformation subsequent to solidification of the rock.

Layering defined by mineralogical or textural variations in a rock body that are interpreted to be related to deformation or metamorphism, commonly associated with layers that have sharp boundaries. Also known as gneissic foliation. See plates 142-145 (p. 342-349) in Borradaile et al [1982] and plate 46A to 49A in Weiss [1972].

Penetrative linear structure in a rock body defined by fabric elements that are the product of tectonic processes. Linear is used in the sense that the orientation of the structure can be represented as a line in some sufficiently small neighborhood of any point in the material containig the fabric. Penetrative denotes that the fabric elements defining the structure are repeated at distances so small, compared with the scale of the whole that they can be considered to pervade it uniformly and be present at every point (paraphrase of Turner and Weiss, 1963, p. 21).

A regional-scale low-angle thrust fault.

Fault that dips less than 45 degrees over more than half of the recognized extent of the fault, with a hanging wall displaced from a structurally deeper position relative to footwall rocks.

A large scale strike-slip fault in which the fault surface is steeply inclined.

A variety of strike-slip fault along which the displacement suddenly stops or changes form, typically associated with mid-ocean ridges.

Layering interpreted to have originated as sedimentary bedding that has been transposed as a result of metamorphism and deformation.

Mylonitic foliation in which greater than 90 percent of rock is matrix due to tectonic grain size reduction processes. Typically rock is very-fine grained to aphanitic, with sparse porphyroclasts, and vague to prominent lamination on a mm scale.

A contact separating two geological units in which the younger unit succeeds the older after a substantial hiatus in deposition.

Gently curviplanar or wavy bedding lamination structure

Surface dips between 80 and 90 degrees, used to describe orientation of fold hinge surface or axial surface; use equivalent term 'Vertical inclination' for other geologic surfaces.

Metamorphic layering of uncertain origin, defined by subtle mineralogical or textural variations, with gradational layer boundaries. See plate 142 in Borradaile et al [1982].

Bedding defined by distinct, parallel laminae (layers less than 1 cm thick), typically occurring in sequences of distinct couplets (e.g. dark and light color). Generally interpreted as deposited from suspension in still water, with each lamina thought to be an annual sedimentation unit. Typically consists of mud-size sediment.

A fold for which the fold axis is vertical and axial surface is upright.

boundary around a body of rock that is within a zone of subsidence or cratering produced by volcanic activity.

A lithogenetic contact separating bodies of material differentiated based on lithologic properties related to weathering.

A strike slip fault in which the fault plane dips at least 45 degrees over more than half of the recognized extent of the fault.