Geoscience Ontology, Geologic Unit

Geologic unit defined by bounding surfaces. Not necessarily stratified. Donovon (2004, IUGS abstract Florence) makes good case for use of a noncommittal term for the bounding surface. While there may be no agreement that a given stratal boundary is a discontinuity, there is consensus that all the identified boundaries are stratal surfaces. Includes: 1. Unconformity bounded units (Salvador 1994), defined by bounding stratigraphic discontinuities ('significant unconformities', unconformity is defined as surface of erosion in Salvador 1994). 2. Sequence stratigraphic unit, an allostratigraphic unit that is used to interpret the depositional origin of sedimentary strata and assumes, though this is not always stated, an implicit connection to base level change. It does this by establishing how the sequence of strata accumulated in order in the sedimentary section over a subdividing framework of surfaces.

Geologic unit defined by alteration process.

Metamorphic facies characterized in rocks of basaltic composition by hornblende-plagioclase (plagioclase more calcic than An17).

Geologic unit defined by genesis involving direct human action to deposit or modify material.

Geologic unit defined based on fossil content. Five kinds of biozones are recognized by the revised NACSN (Lenz et al., 2000, Note 64, a recommended complete replacement of Articles 48 through 54 of the North American Stratigraphic Code (NACSN, 1983) accepted for publication 2000.): range biozone, interval biozone, lineage biozone, assemblage biozone, and abundance biozone. These represent different approaches to defining and recognizing biozones.

A body of rocks that includes all rocks, layered or unlayered, formed during a specific interval of geologic time, and only those rocks formed during that time span. Chronostratigraphic units are bounded by synchronous horizons. The rank and relative magnitude of the units in the chronostratigraphic hierarchy are a function of the length of the time interval that their rocks subtend, rather than of their physical thickness. (http://www.stratigraphy.org/upload/bak/chron.htm)

An assemblage or mixture of rocks of two or more genetic classes, i.e., igneous, sedimentary, or metamorphic, with or without highly complicated structure, may be named a complex. The term "complex" takes the place of the lithic or rank term (for example, Boil Mountain Complex, Franciscan Complex) and, although unranked, commonly is comparable to suite or supersuite and is named in the same manner. Identification of an assemblage of diverse rocks as a complex is useful where the mapping of each separate lithic component is impractical at ordinary mapping scales. The term may be retained if subsequent, detailed mapping distinguishes some or all of the component lithodemes or lithostratigraphic units.

Lithotectonic unit defined by deformation style or characteristic geologic structure observable in outcrop.

Omphacite-garnet-quartz (no plagioclase, olivine stable with garnet), assemblage for rocks of basaltic composition

Hornblende-albite-epidote(-chlorite), assemblage for rocks of basaltic composition

Geologic unit defined by human-made genesis involving excavation. Not necessarily defined by landform (a hole...), as they could have been subsequently filled/landscaped etc. If the excavation is filled becomes an excavation with artificial ground wholly or partly superimposed on it. This sort of thing can become quite important in urban geology where an excavation can be filled and landscaped.

how material is exposed at Earth surface, e.g. poorly exposed, well exposed.

Represents a particular body of rock that is a lateral variant of a lithostratigraphic unit, or a variant of a lithodemic unit. Contrast with lithosome in being a particular, connected body of rock, as opposed to a kind of rock body that is repeated in many places in a unit.

Geologic unit defined by its geophysical characteristics. Denotes that the properties used to define the unit are measured by intrumental techniques, not directly observable by humans, e.g. density, magnetic susceptibility, magnetization, electrical conductivity.

Metamorphic facies characterized in rocks of basaltic composition by glaucophane-epidote (-garnet), glaucophane-lawsonite, or glaucophane-lawsonite-jadeite.

Metamorphic facies characterized in rocks of basaltic composition by the mineral assemblage clinopyroxene-orthopyroxene-plagioclase (olivine not stable with plagioclase or with garnet), or especially high-temperature varieties or polymorphs of minerals

Metamorphic facies characterized in rocks of basaltic composition by actinolite-albite-epidote-chlorite (an epidote group mineral is the diagnostic Ca-Al silicate rather than prehnite or pumpellyite).

a lithologic facies within an igneous rock body. Sometimes called 'phase', e.g. porphyritic facies, fine-grained facies.

dct:Source -- based on Gillespie, M R, Stephenson, D, and Millward, D. 2008. BGS classification of lithodemic units: Proposals for classifying units of intrusive rock. British Geological Survey Research Report, RR/08/05. 31pp.

a part that occurs as beds distributed within a stratigraphic unit.

dct:Source -- based on Gillespie, M R, Stephenson, D, and Millward, D. 2008. BGS classification of lithodemic units: Proposals for classifying units of intrusive rock. British Geological Survey Research Report, RR/08/05. 31pp.

Describes the nature of outcrops formed by a Rock Body. Examples: bouldery, cliff-forming, ledge-forming, slope-forming. Assign free text string value for now, controlled vocabulary is the goal.

A body of intrusive, pervasively deformed, or highly metamorphosed rock, generally non-tabular and lacking primary depositional structures, and characterized by lithic homogeneity. It is mappable at the Earth's surface and traceable in the subsurface. For cartographic and hierarchical purposes, it is comparable to a formation

Lithodemic unit is not recognized by the international Stratigraphic code (Salvador, 1994) {@en} The 'Guide for geological nomenclature in Sweden', RA Kumpulainen, 2017 adopts the NACSN 2005 terminology. The British Geological survey defines a vocabulary of subdivisions of the 'lithodeme' defined by NACSN to reflect common geologic field usage (Gillespie, M R, Stephenson, D, and Millward, D. 2008. BGS classification of lithodemic units: Proposals for classifying units of intrusive rock. British Geological Survey Research Report, RR/08/05. 31pp.). The BGS terminology is partially adopted here.

Rock object defined by a specific genesis AND surrounding rocks, e.g. Metamorphic Unit, Sedimentary Unit. This differs from a unit such as 'Metamorphic Unit created by Event X', which is not defined by bounding rocks, but only by a specific genesis (Event X) and which is not a Geologic Unit, but is a Situated Rock Object. It also differs from a unit such as 'Metamorphic Rock' (a Generic Rock Object), which includes metamorphic rocks regardless of originating process or event, and without regard to surrounding rocks: i.e. all rocks (possibly in an area) created by any metmorphic event or process

A rock body defined by lithology independent of relationships to other units. Denotes a 'kind' of rock body characterized by lithology, e.g. basaltic rocks. Does not necessarily represent a single genetically related or connected package of material.

Geologic unit defined on the basis of observable and distinctive lithologic properties or combination of lithologic properties and stratigraphic relationships. Denotes a particular body of rock.

Geologic unit defined by magnetic characteristics.

Stratigraphic part that is a thin laterally continuous bed within another unit.

Geologic unit produced by gravity driven, down-slope displacemnt of material, and characterized by the type of movement giving rise to the deposit, and by how the individual movement types present in the deposit are related in time and space.

Categories that characterize mineral assemblages indicative of certain metamorphic P-T conditions. Examples include Barrovian metasedimentary zones (eg: biotite facies, kyanite facies) or assemblages developed in rocks of more mafic composition (eg: greenschist facies, amphibolite facies).

explicit statement that is not metamorphosed

A geologic uint that is not stratigrpahic, that is not existentially dependent on its surrounding rocks.

Geologic unit that represents a single pedologic horizon in a sequence of strata (consolidated or non-consolidated). The presence of an overlying geologic unit is required, but locally the soil horizon may be at the Earth surface (in which case is may be coincident with a Pedoderm). See discussion at https://www.seegrid.csiro.au/twiki/bin/view/CGIModel/PedostratigraphicUnit

a body of intrusive rock, generally with a simple, regular margin, the whole being kilometre-scale or larger and with a cylindrical, lenticular or tabular shape; a pluton might consist of essentially one intrusion, or be a composite of two or more spatially associated intrusions that are inferred to be related genetically.

Geologic unit defined by primary magnetic-polarity record imposed whien the rock was deposited or crystallized during a specific interval of geologic time. Kind of chronostratigraphic unit and kind of geophysical unit.

Metamorphic facies characterized in rocks of basaltic composition by clinopyroxene-orthopyroxene-plagioclase (olivine stable with plagioclase).

distinguished from the pyroxene hornfels facies by the occurrence of especially high-temperature varieties and polymorphs of minerals (eg. pigeonite, K-rich labradorite), assemblage for rocks of basaltic composition

a lithologic variant in a sedimentary unit, typically related to spatial variation in the original depositional environment or subsequent diagenetic environment.

The stage includes all rocks formed during an age. A stage is normally the lowest ranking unit in the chronostratigraphic hierarchy that can be recognized on a global scale. The stage has been called the basic working unit of chronostratigraphy because it is suited in scope and rank to the practical needs and purposes of intraregional chronostratigraphic classification. It is a subdivision of a series.

A geologic unit that occupies a particular stratigraphic position as part of a stratigraphic unit.

A geologic unit and (the amount of) its rock material are co-located, but different entities. They can share properties, e.g. porosity, thickness, density, but also have differences: - different persistence conditions: the material can exist without the unit; e.g. a unit can be cease to exist due to natural (seismic) or artificial (explosion) means, but the material can persist - different parthood conditions:
-- a unit can be part of a collection of units (e.g. a stratigraphic lexicon), but its material cannot. -- parts of the unit are not parts of the material, e.g. the western arm of formation X is not a part of its sandstone - the sandstone making up the western part of X is a part of the sandstone -- different identity conditions: a unit can have some material added or removed and retain identity, but the material changes identity with the addition or removal of some material

Metamorphic facies characterized in rocks of basaltic composition by prehnite-pumpellyite, pumpellyite-actinolite, prehnite-actinolite (prehnite and pumpellyite are the diagnostic Ca-Al silicates rather than minerals of the epidote or zeolite groups).

A geologic unit that comprises two or more associated Lithodemes, Plutons, Intrusions, or Igneous_Swarms of the same class (e.g., plutonic, metamorphic) that are interpreted to be genetically related. For cartographic and hierarchical purposes, suite is comparable to group

A geologic unit that comprises two or more Suites or Complexes having a degree of natural relationship to one another, either in the vertical or the lateral sense. For cartographic and hierarchical purposes, supersuite is similar in rank to supergroup

Geologic unit defined defined on basis of structural or deformation features, mutual relations, origin or historical evolution. Contained material may be igneous, sedimentary, or metamorphic.

Metamorphic facies characterized in rocks of basaltic composition by zeolite minerals such as laumontite and heulandites (in place of other Ca-Al silicates such as prehnite, pumpellyite and epidote).