1. Stratigraphy. Stratigraphy, from Latin stratum + Greek graphia, is the description of all rock bodies forming the Earth's crust and their organization into distinctive, useful, mappable units based on their inherent properties or attributes in order to establish their distribution and relationship in space and their succession in time, and to interpret geologic history.
2. Stratum (plural=strata). Layer of rock characterized by particular lithologic properties and attributes that distinguish it from adjacent layers.
3. Stratigraphic classification. The systematic organization of the Earth's rock bodies, as they are found in their original relationships, into units based on any of the properties or attributes that may be useful in stratigraphic work.
4. Stratigraphic unit. A body of rock established as a distinct entity in the classification of the Earth's rocks, based on any of the properties or attributes or combinations thereof that rocks possess.
5. Stratigraphic terminology. The total of unit-terms used in stratigraphic classification.It may be either formal or informal.
a. Formal stratigraphic terminology uses unit-terms that are defined and named according to guidelines conventionally established.
b. Informal stratigraphic terminology uses unit-terms as ordinary nouns in a descriptive sense, not as a part of a specific scheme of stratigraphic classification.The use of informal terms in published documents is strongly discouraged.
6. Stratigraphic nomenclature. The system of proper names given to specific stratigraphic units.
7. Zone.Minor body of rock in many different categories of stratigraphic classification. The type of zone indicated is made clear by a prefix, e.g., lithozone, biozone, chronozone.
8. Horizon. An interface indicative of a particular position in a stratigraphic sequence.
The type of horizon is indicated by a prefix, e.g., lithohorizon, biohorizon, chronohorizon.
9. Correlation. A demonstration of correspondence in character and/or stratigraphic position. The type of correlation is indicated by a prefix, e.g., lithocorrelation, biocorrelation, chronocorrelation.
10. Geochronology. The science of dating and determining the time sequence of the events in the history of the Earth.
11. Geochronologic unit. A subdivision of geologic time.
12. Geochronometry. A branch of geochronology that deals with the quantitative (numerical)measurement of geologic time. The abbreviations ka for thousand (103), Ma for million (106), and Ga for billion (milliard of thousand million, 109) years are used.
13. Facies. The term "facies" originally meant the lateral change in lithologic aspect of a stratigraphic unit. Its meaning has been broadened to express a wide range of geologic concepts: environment of deposition, lithologic composition, geographic, climatic or tectonic association, etc.
14. Caution against preempting general terms for special meanings. The preempting of general terms for special restricted meanings has been a source of much confusion.
The preferable procedure is to conserve the original general meaning of a term and to seek a more precise and less
ambiguous word for the special meaning.
B. Procedures for Establishing and Revising Stratigraphic Units.
The proposal of a new formal stratigraphic unit requires a statement of intent to introduce the new unit and the reasons for the action. A new unit must be duly proposed and duly described. This includes:
2. Special requirements for establishing subsurface units. The same rules of procedure used for outcrop sections apply to subsurface units established on the basis of exposures in mines, tunnels or from sections penetrated in wells. Stratotypes in well sections are designated by well depths and on well logs and in cores, if available. The following data are desirable for establishing subsurface units:
3. Naming of stratigraphic units. The names of most formal stratigraphic units consist of an appropriate geographic name combined with an appropriate term indicating the kind and rank of the unit, e.g. La Luna Formation, except for some terms that were established in the early history of stratigraphy.
i. Source. Geographic names should be derived from permanent natural or artificial features at or near which the stratigraphic unit is present.A name should be on standard published maps of the pertinent political jurisdiction.
ii. Spelling of Geographic Names. The spelling of the geographic component of the name of a stratigraphic unit should conform to the usage of the country of origin.
iii. Changes in Geographic Names. The change in the name of a geographic feature does not affect the name of the associated stratigraphic unit nor does disappearance of the geographic feature require a new name.
iv. Inappropriate Geographic Names. A geographic name should not be misleading, e.g. London Formation for a unit in Canada, although a city with that name exists in Canada.
v. Duplication of Geographic Names. The name of a new stratigraphic unit should be unique in order to prevent ambiguity.The IUGS Lexique Stratigraphique International and national and regional lexicons contain lists of previously used names and inquiry to geological surveys and other regional organizations is recommended to discover previously used names not yet published in the lexicons.
vi. Names for subdivisions of Stratigraphic Units. If a unit is divided into two or more formal
component units, the geographic name of the original unit should not be employed for any of the subdivisions.
i. Capitalization. The first letters of all words used in the names of formal stratigraphic units are capitalized (except for the trivial names of species and subspecies rank in the names of biostratigraphic units). Informal terms are not capitalized.
ii. Hyphenation. Compound terms for most kinds of stratigraphic units, in which two common words are joined to give a special meaning, should be hyphenated, e.g. concurrent-range zone, normal-polarity zone. Exceptions are adjectival prefixes or combining forms that are generally combined with the term-noun without a hyphen, e.g. biozone.
iii. Repetition of the Complete Name. After the complete name of a stratigraphic unit has been referred to
once in a publication, part of the name may be omitted for brevity if the meaning is clear, e.g., the Oxfordian Stage
may be referred to as "the Oxfordian", or "the Stage".