,17(51$7,21$/ 675$7,*5$3+,& &+$57 - sgs · i saudi arabian code of stratigraphic...

A new Geological Time Scale, with special reference to Precambrian and Neogene

by F.M. Gradstein et al., 2004. Episodes, vol.27, no.2

INTERNATIONAL STRATIGRAPHIC CHART

SAUDI ARABIAN CODE OFSTRATIGRAPHIC CLASSIFICATION AND NOMENCLATURE

SAUDI STRATIGRAPHIC COMMITTEESPECIAL PUBLICATION

SGS-SP-2012-2FIRST EDITIONA.H. 1434 - A.D. 2013

www.sgs.org.sa

من إصدارات هيئة املساحة اجليولوجية السعودية

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saudi arabian code of stratigraphicclassification and nomenclature

SAUDI STRATIGRAPHIC COMMITTEE MEMBERS

SAUDI GEOlOGICAl SURvEy

Dr. Zohair A. Nawab (Chairman)Mohammed A. Halawani

SAUDI ARAMCO

Abdulazziz A. Al-DuaijiBassam H. Bahabri

KInG ABDUlAzIz UnIvERSITy

Prof. Mohammed H. Basyoni

KInG SAUD UnIvERSITy

Dr. Mohammed E. Al Dabbagh

KInG FAHD UnIvERSITy OF PETROlEUM AnD MInERAlS

Dr. Khalid Al Ramadan

MInISTRy OF WATER AnD ElECTRICITy

Hussain F. Al Ajmi

KInG ABDUlAzIz CITy FOR SCIEnCE AnD TECHnOlOGy

Dr. Abdullah K. Al Mahri

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TABlE OF COnTEnTS

Background ................................................................................................................................................. iii

Rules and Regulation .................................................................................................................................. 1

General Definitions ..................................................................................................................................... 3

Articles ........................................................................................................................................................ 6

Purpose .................................................................................................................................................. 6

General Procedures ................................................................................................................................ 6

Definitions of Formal Units ............................................................................................................. 6

Redifinition, Revision, and Abandonment ....................................................................................... 10

Lithostratigraphic Units ......................................................................................................................... 11

Nature ............................................................................................................................................. 11

Boundaries ....................................................................................................................................... 12

Ranks ............................................................................................................................................... 12

Nomenclature .................................................................................................................................. 16

Lithodemic Units ................................................................................................................................... 17

Nature ............................................................................................................................................. 17

Boundaries ....................................................................................................................................... 17

Ranks ............................................................................................................................................... 17

Nomenclature .................................................................................................................................. 20

References Consulted .................................................................................................................................. 21

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bacKgroundActing on the initiative of the Deputy Ministry of Mineral Resources (DMMR) for the creation of the Saudi Stratigraphic Committee (SSC), which was mandated to create and maintain a unified Saudi Arabian Stratigraphic Code based on international practice, the Ministry of Petroleum and Mineral Resources of the Kingdom of Saudi Arabia appointed its first members in 1977. The Saudi Stratigraphic Committee was reactivated by the Saudi Geological Survey (SGS) in 2001 and since then chaired by the SGS President. The committee is composed of representatives from Saudi Aramco, King Abdulaziz University, King Saud University, King Fahd University, King Abdulaziz City for Science and Technology, and Ministry of Water and Electricity.

The first version of the Stratigraphic Code was published as DGMR TM-1979-1 which was applied only within the Directorate General of Mineral Resources and other related agencies working for it. These regulations contained no element of obligation to be used as a national code, although the interests of uniformity and ease of communication would have been clearly best served if they were followed.

The Code was re-issued with significant modifications in 2004, as Data-File Report SGS-DF-2004-7 of the Saudi Geological Survey. That version was based mainly on the International Stratigraphic Guide (Salvador, 1994) and the North American Stratigraphic Code (1983), in addition to modifications designed to make it as suitable as possible for application in Saudi Arabia and particularly, in the highly contrasting settings of the mostly Precambrian terrains of the Arabian Shield and the surrounding Phanerozoic cover rocks.

In this edition, procedures, definitions, classification, nomenclature and other provisions were adopted from the North American Stratigraphic Code (The North American Commission on Stratigraphic Nomenclature, 2005) and International Stratigraphic Guide (ISSC, 1994). Categories of formal stratigraphic units fall into 3 classes. Lithostratigraphic, lithodemic, magnetopolarity, biostratigraphic, and pedostratigraphic units belong to class I, the rock-material category based on content, inherent attributes, or physical limits. Chronostratigraphic and polarity-chronostratigraphic units belong to class IIA, the material category used as standards for defining spans of geologic time. Non-material and temporal categories of class IIB include geochronologic, polarity-chronologic, diachronic, and geochronometric untis. Since the Code was intended to be flexible enough to provide changes and revisions, only lithostratigraphic and lithodemic units are included in this edition. As the Code evolves, other formal stratigraphic units may be added in future editions.

The significant modifications that were made in the second edition and that have been maintained in this third edition are as follows:

1. Separate provisions were made for (1) sedimentary, extrusive, and/or low-grade metamorphic rocks derived from them, and (2) intrusive and/or high-grade metamorphic rocks.

2. Provision was made for the use of the terms “member” and “layer” for divisions of units of intrusive and/or high-grade metamorphic rocks of formational rank.

3. The inadmissibility of knowingly combining (1) sedimentary, extrusive, and/or low-grade metamorphic rocks with (2) intrusive and/or high-grade metamorphic rocks in any single unit is emphasized. Provision was made for units that can be traced through various metamorphic zones.

4. The requirement for a formal group to have a type area has been removed.

5. The need for informal classification and nomenclature to follow the rules for formal classification and nomenclature as closely as possible, in order to facilitate possible formalization in the future, is emphasized.

6. Emphasis is therefore made that the regulations to be obligatory hereafter.

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mohammed halawaniHead of Secretary and SGS RepresentativeSaudi Stratigraphic Committeec/o Saudi Geological SurveyP.O. Box 54141, Jeddah 21514Kingdom of Saudi Arabia

Comments on the regulations and rules of the Code are welcomed. They should be forwarded to:

Saudi Arabian Code of Stratigraphic Classification and Nomenclature

1Saudi Stratigraphic Committee

regulations for official use of the saudi arabian stratigraphic code

1. These regulations for official use of the Saudi Arabian Code of Stratigraphic Classification and Nomenclature, hereafter referred to as “the Code”, are issued with the authority of the Saudi Stratigraphic Committee.

2. The stratigraphic classification and nomenclature of rock units in all published reports, such as Technical Reports, Open-File reports, and Geologic Maps by members of Saudi Arabian geosciences community, whether issued officially or by an outside organization, and whether resulting in whole or only in part from official work, shall conform with the Code or as subsequently amended with authority of the Saudi Stratigraphic Committee.

3. Responsibility for examining reports and maps for conformity with the Code shall fall on the Saudi Stratigraphic Committee, hereafter called “the Committee.” With respect to reports and maps to be issued internally, this responsibility can be delegated to any operating technical editor(s) in the Saudi Arabian geoscience’s community under the general direction of the Committee.

4. The Code shall be administered by the Committee as follows:

(a) The classification and nomenclature of rock units in reports and maps submitted for publication, or for issue as Technical Report, shall be in accordance with the Code. Author(s) may express personal opinion at variance with it.

(b) The classification and nomenclature of rock units in reports and maps submitted for external publication shall generally accord with the Code. They may differ from it, with the approval of the Chairman of the Saudi Stratigraphic Committee.

(c) The classification and nomenclature of rock units in reports and maps that embody the results of cooperative investigations with outside organizations shall accord with the Code, except that if such material is published by a cooperating organization that uses a different code, the classification and nomenclature of the cooperating organization may be used; but in that case, the departure from the Saudi Arabian Code shall be indicated in a footnote or elsewhere in the report or map.

(d) All reports and maps that are submitted for publication and resulting in whole or in part from official work and containing stratigraphic names shall be submitted to the Committee before publication.

When major departures from the Code occur in such material, the Committee shall consider whether they should be adopted as new official usage, or be approved for use in the particular report or map without prejudice to official usage, or be disallowed.

The Committee shall also consider and rule on all proposals for new names or redefinition of old names, and on the geographic extension or restriction of old names.

Minor departures from the Code need not be brought to the attention of all Committee members, but may be considered and ruled upon by the Chairman and one other member of the Committee.

(e) No changes in usage, classification, or nomenclature shall be made in a report or map after it has been reviewed, without further reference to the reviewer.

5. The Saudi Stratigraphic Committee shall keep this Code constantly under review with the object of recommending publication of any necessary amendments with authority of the Chairman, and may issue provisional instructions on such matters through a Technical Circular.

6. An agenda shall be submitted to members of the Committee before each of their meetings on the matters to be discussed.

7. The approved minutes of all Committee meetings shall be made available for consultation to all interested parties upon request to the Secretary of the Committee.

8. The Committee shall act in an advisory capacity to the Saudi Arabian geosciences community and other geologists, upon request to the Secretary of the Saudi Stratigraphic Committee.

9. Services offered shall include provision of information on the following:

(a) The nomenclature of rock units (for example, whether a particular geographic name has been used

2 Saudi Stratigraphic Committee


previously in a stratigraphic name).

(b) The original and current definitions of any particular unit.

(c) The currently acted rank of any particular unit.

(d) Reservation of new names for stratigraphic units.

(e) Interpretation of the Code.

(f ) General or specific matters in the Committee’s records.

10. If an author in any of the operating units of the Saudi Arabian geosciences community, or in any other geologic organization requests the reservation of an available name for a stratigraphic unit, an informal record of that author’s intentions shall be preserved by the Committee for the information of others who may inquire about the name. The Committee shall not, however, presume to pass judgment on the validity or use of any name outside the reports and maps over which it is given jurisdiction by this Code, nor shall its suggestions, recommendations, or instructions contain any element of obligation for other authors.



general definitionsStratigraphy, from the Latin “stratum” and the Greek “graphia”, has traditionally been considered as the descriptive science of rock strata. The definition of stratigraphy has been broadened to include 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. Stratigraphic procedures include the description, classification, naming, and correlation of these units for the purpose of establishing their relationship in space and their succession in time. All classes of rocks- igneous, metamorphic, and sedimentary, consolidated as well as unconsolidated- fall within the general scope of stratigraphy and stratigraphic classification.

stratum (plural=strata): A geologic stratum is a layer (a generally tabular body) of rock characterized by certain lithologic properties or attributes that distinguish it from adjacent layers.

lithostratigraphic classification: The systematic organization of the Earth’s rock bodies, as they are found in their original relationships, into units based on their lithologic properties.

lithostratigraphy: The element of stratigraphy that deals with the description and systematic organization of the rocks of the Earth’s crust into distinctive, named units based on the lithologic character of the rocks and their stratigraphic relations.

lithostratigraphic unit: A body of rocks that is defined and recognized as a unit (distinct entity) in the classification of Earth’s rocks, based on its observable and distinctive lithologic properties or combination of lithologic properties and its stratigraphic relations.

Stratigraphic Terminology: The total of unit-terms used in stratigraphic classification, such as group, formation, member. Stratigraphic terminology is either formal or informal.

the code emphasizes formal categories of geologic units, but informal nomenclature is highly useful in stratigraphic work.

formal lithostratigraphic nomenclature uses unit terms that are defined and named according to an established or conventionally agreed scheme of classification and nomenclature, such as this Saudi Arabian Code. The initial letter of all words in the formal geologic unit name is capitalized, as in “Qasim Formation” or “Wajid Sandstone.” Formalization is appropriate for those units requiring stability of nomenclature in economic or scientific purposes.

Informal lithostratigraphic nomenclature uses unit terms only as ordinary nouns. The initial letter of an informal unit term is written or printed in lower case, as in “Hijaz formation” or “Murbat sandstone”. These informal unit terms are not protected by the stability provided by proper formalization and recommended classification procedures.

informal terms are appropriate for casually mentioned, innovative, and most economic units, those defined by unconventional criteria, and those that may be too thin to map at usual scales.

casual units are mentioned for insufficient need or information, or perhaps an inappropriate basis for formal designations.

Most economic units, such as aquifers, oil sands and ore-bearing beds are informal.

Innovative approaches in regional stratigraphic studies have resulted in the recognition and definition of units best left as informal. Units bounded by major regional unconformities on North American Craton were designated “sequences” by Sloss (1963) and “synthem” by Chang (1975).

The formal use of informal stratigraphic terms (formation, member) in published documents is strongly discouraged.

No geologic unit should be established and defined, whether formally or informally, unless its recognition serves a clear purpose.

stratigraphic nomenclature: The system of proper names given to specific stratigraphic units.

correlation is a procedure to show correspondence in character and/or in stratigraphic position between geographically separated parts of a geologic unit. There are different kinds of correlation depending on the feature to be emphasized. Lithological correlation (lithocorrelation) demonstrates correspondence in lithologic properties and lithostratigraphic position.



facies: The term “facies” means “aspect”, “nature”, or “manifestation of character” of rocks or specific constituents of rocks. It is used to mean “the expression of lateral change in lithologic aspect and the environment of deposition or formation (deltaic facies, marine facies), lithologic composition (sandstone facies), geographic or climatic association (Tethyan facies), fossil content (graptolitic facies), tectonic association (orogenic facies), and metamorphic grade.

diastem: A minor break or hiatus in a stratigraphic section, due largely to oscillation in the intensity of climatic factors, or it is a short interruption in deposition with little or no erosion of previously deposited material before resumption of sedimentation.

unconformity: A surface of erosion separating two rock bodies of different ages, indicating that sediment deposition was not continuous. The interval of geologic time not represented is called a hiatus. Unconformities result from the subaerial or subaqueous exposure of rocks below the unconformity and erosion with loss of part of the older rocks.

Types of unconformities (fig.1):

a. disconformity: is an unconformity between parallel layers of sedimentary rocks which represents a period of erosion or non-deposition. Disconformities are marked by features of subaerial erosion. This type of erosion can leave channels and paleosols in the rock record. The two common disconformities are paraconformity and blended unconformity.

A paraconformity is a type of disconformity in which the separation is a simple bedding plane with no obvious buried erosional surface. Paraconformity is a type of unconformity in which strata are parallel; there is little apparent erosion and the unconformity surface resembles a simple bedding plane. It is also known as nondepositional unconformity or pseudoconformity.

A blended unconformity is a type of disconformity or nonconformity with no distinct separation plane or contact, sometimes consisting of soils, paleosols, or beds of pebbles derived from the underlying rock.

b. nonconformity: exists between sedimentary rocks and metamorphic or igneous rocks when the sedimentary rock lies above and was deposited on the pre-existing and eroded metamorphic or igneous rock. If the rock below the break is igneous or has lost its bedding by metamorphism, the plane of juncture is a nonconformity.

c. angular unconformity: is an unconformity where horizontally parallel strata of sedimentary rock are deposited on tilted and eroded layers, producing an angular discordance with the overlying horizontal layers. The whole sequence may later be deformed and tilted by further orogenic activity.



Figure 1. Type of unconformities (modified from www.2.sunysolfolk.edu).

A

B

C



articles

purpose

Article 1. Purpose

The Saudi Stratigraphic Code seeks to describe explicit practices for classifying and naming all defined rock units in Saudi Arabia. It provides the basis for formulation of language designed to promote standardized classification and formal nomenclature of rock units in Saudi Arabia. To be effective, a code must be widely accepted and used; geologic organizations may adopt its recommendations for nomenclature procedure. Because the code embodies only current concepts and principles, it should have the flexibility to provide for both changes and additions to improve its relevance to new scientific problems.

general procedures

Article 2. Procedures

This Code describes explicit stratigraphic procedures for classifying and naming geologic units accorded formal status. Such procedures, if widely adopted, assure consistent and uniform usage in classification and terminology and therefore, promote unambiguous communication.

DEFInITIOn OF FORMAl UnITS

Article 3. Requirements for formal name of unit

The proposal of a new formal unit requires a statement of intent to introduce the new unit and the reasons for doing so. To be valid and useful, a new unit must be duly proposed and duly described. Naming, establishing, revising, redefining, and abandoning formal units require publication in a recognized scientific medium of a comprehensive statement which includes:

- intent to designate or modify a formal unit

- designation of category and rank of unit

- selection and derivation of name.

- specification of stratotype (where applicable)

- description of unit

- definition of boundaries

- historical background

- dimensions, shape, and other regional aspects

- geologic age

- correlation

- genesis (where applicable)

Article 4. Publication

“Publication in a recognized scientific medium” means that a work, when first issued, must: (1) be reproduced in ink on paper, be reproduced electronically on CD-ROM or by some other method that assures numerous identical copies and wide distribution, (2) be issued for the purpose of scientific, public, and permanent record, (3) be readily obtained by purchase or free distribution, and (4) have undergone adequate peer review.

The following are inadequate and do not constitute publication within the meaning of this Code: (1) distribution of microfilms or similar methods, (2) distribution to colleagues or students of a note, (3) distribution of proof sheets, (4) open-file release, (5) theses, dissertations, and dissertation abstracts, (6) mention at a scientific or other meetings, (7) mention in an abstract, map explanation, or figure caption, (8) labeling of a rock specimen in a collection, (9) mere deposit of a document in a library, (10) anonymous publication, (11) mention in the popular press, (12) distribution by an author by posting on the internet.



Article 5. Intent and utility

To be valid, a new unit must serve a clear purpose and be duly proposed and duly described, and the intent to establish it must be specified.

Article 6. Category and rank

The category and rank of a new or revised unit must be specified.

Article 7. Name

The name of a formal unit is compound. It should consist of a geographic name combined with an appropriate rank (Khuff Formation) or descriptive term (Saq Sandstone). The first letters of all words used in the names of formal geologic units are capitalized. The derivation of the geographic component of the name should be explained, and the kind and rank of the unit should be specified.

Geographic names should be derived from permanent natural or artificial features at or near which the stratigraphic unit is present. Names derived from such impermanent sources as farms or small communities are not entirely satisfactory but are acceptable if no others are available.

The name of a new unit should be unique. Therefore, before attempting to establish a new formal unit, authors should refer to national, region, or provincial records of stratigraphic names to determine whether a name has been used previously.

Use of geographic name for a stratigraphic unit should be subject to approval by the Committee.

Two names should not be derived from the same geographic feature.

Responsibility for avoiding duplication, either in use of the same name for different units (homonymy) or in use of different names for the same unit (synonymy), rests with the proposer.

Stability of nomenclature is maintained by use of the rule of priority and by preservation of well-established names. A geographic name may be used in a formal lithostratigraphic name only: (1) if it cannot be regarded as reserved for future formal definition of another unit, for example, by well-established use in reports or maps of the Saudi Geological Survey, and (2) if no other unit has been given the same name and no other name has been given to the same unit in published literature, except that a name that has been formally abandoned may be used again if alternative names are lacking and no confusion is possible. Names should not be modified without explaining the need.

Priority in publication is to be respected, but the critical factors in selecting names to be preserved should always be the usefulness of the unit, adequacy of definition, and freedom from ambiguity. Priority alone does not justify preservation of a name that has been only occasionally used or has been inadequately established. No priority is established unless a unit is formally named and defined in accordance with the rules of this Code.

If different names have been given to the same unit, the first established name should adhere, and if more than one unit has been given the same name, the name should adhere to the earliest established unit.

The geographic component of a well-established stratigraphic name is not changed due to differences in spelling or changes in the name of a geographic feature. The geographic component of a name should not be altered by translation into another language, while lithologic or rank terms can be translated. Spelling of the geographic component of a lithostratigraphic name should conform with accepted principles of transliteration, except that a name that has become well established with a different spelling in publications, open-file reports, or maps should nevertheless be preserved or, if it has been spelled variously, its spelling should be made uniform by adopting the form used by the majority, whatever the original spelling in geologic literature.

Stratigraphic units are not limited by international frontiers, and effort should be made to use only a single name for each unit regardless of political boundaries.

Articles and those parts of geographic names, such as “Jabal” and “Wadi”, that are in common use throughout Saudi Arabia should preferably be omitted from lithostratigraphic names, although the full topographic name should be specified in the definition of the unit concerned.

After the completed name of a unit has been mentioned in a given text, part of it may be omitted in a



discussion to avoid cumbersome repetition if omission is compatible with clarity; for example, Shammar Group may be called “the Shammar” or “the Group.”

When uncertainty exists with respect to the assignment of rocks to a named unit, arbitrary assignment should be avoided and the uncertainty indicated by a query, for example, “Murdama Group?” or by the use of such terms as “probably,” “presumably,” and “maybe.”

Nothing in the foregoing rules restricts the informal lithostratigraphic use of any term, except terms reserved for other types of stratigraphic nomenclature, but informal classification and nomenclature should follow the rules laid down in this Code for formal terms as far as possible.

The names listed in the Saudi Arabian Stratigraphic Lexicon (Fitch, 1980), Stratigraphic Column for Phanerozoic Rocks of Saudi Arabia (Halawani, 2001), and other compilations on Saudi Arabian stratigraphic successions within the geoscience community, should be used informally until they are formally established in accordance with this Code and the Saudi Stratigraphic Committee has declared them to have been so established.

The following usages are considered informal:

- The term “group” for a unit that is not composed wholly of established units or has no regional significance.

- Identical geographic names for the whole and (or) a part or parts of one unit or for units of different rank(s) in different areas.

- Designation of members or beds solely by letter or number.

- The plural of the term “bed”.

- The term “lentil” or “lens” for a geographically restricted member that terminates on all sides within a formation.

- The term “tongue” for a member that extends outward beyond the main body of a formation.

- The term “lamina” for a layer too thin to be appropriately called a bed.

- The term “basement complex”.

- The term “lithozone” for a body of rocks that is unified in a general way by lithologic features but for which the need or justification for designating a formal unit is lacking.

Article 8. Stratotypes (type section)

The designation of a unit or boundary stratotype (type section or type locality) is essential in the definition of the formal units. A stratotype is the standard (original or subsequently designated) for a named unit or boundary and constitutes the basis for definition or recognition of that unit or boundary; therefore, it must be illustrative and representative of the unit or boundary being defined.

A unit stratotype is the type section for a stratiform deposit or the type area for a nonstratiform body that serves as the standard for definition and recognition of a unit.

A boundary stratotype is the type locality for the boundary reference point for a stratigraphic unit. Both boundary stratotypes for any unit need not to be in the same section or region.

A type locality is the specified geographic locality where the stratotype of a formal unit or unit boundary was originally defined and named. A type area is the geographic territory encompassing the type locality.

A composite-stratotype consists of several reference sections (which may include a type section) required to demonstrate the range or totality of a unit. A stratotype of a higher rank formed by the combination of the stratotypes of its component units of lower rank is also a composite-stratotype. Thus, the stratotype of a group may be a composite of the stratotypes of its constituent formations.

- Holo-, Para-, Neo-, Lecto, and Hypostratotypes are common terms in designating the stratotypes of layered stratigraphic units. Holostratotype is the original stratotype designated by the original author at the time of proposing a stratigraphic unit or boundary. Parastratotype is a supplementry stratotype used in the original definition by the original author to illustrate the diversity or heterogeneity of the defined stratigraphic unit. Lectostratotype is a stratotype for a previously described stratigraphic unit selected later in the absence of an adequatly designated original stratotype (holostratotype).



Neostratotype is a new stratotype selected to replace an older one which has been destroyed, covered, or otherwise made inaccessible. Hypostratotype (called reference section) is a stratotype proposed after the original designation of the holostratotype in order to extend knowledge of the unit or boundary to other geographic areas.

- Reference sections may serve as invaluable standards or revisions of formal units. Reference sections may be designated for well-established units never specified with type section before, and for units whose stratotypes have been destroyed, covered, or otherwise made inaccessible. Supplementary reference sections often are designated to illustrate the diversity or heterogeneity of a defined unit or some critical feature not evident or exposed in the stratotype. Once a unit or boundary stratotype section is designated, it is never abandoned or changed; however, if a stratotype proves inadequate, it may be supplemented by a principal reference section or by several reference sections that may constitute a composite-stratotype.

- Stratotypes should be described both geographically and geologically. Geographic details must be included to enable others to find the stratotype in the field. Geologic information should include lithologic properties, the thickness or size of the rock body, structural attitude, geomorphic expression, unconformities or hiatuses, nature of boundaries of the unit (sharp, transitional, unconformable, etc.), relation of unit to other units in the area, and distinguishing and identifying features charcterizing the unit at the stratotype or type locality.

- Stratotypes should be clearly marked and its boundaries should be based on a single point in a designated sequence of rock strata.

- Stratotypes should be situated in an area geographically accessible to all who are interested, regardless of political or other circumstances, and it should offer reasonable assurance of long-range preservation.

- Requirements for the proper selection of type localities and reference localities for nonlayered igneous and metamorphic rock bodies are similar to those that apply to the selection of stratotypes (type sections) of layered stratigraphic units.

Article 9. Unit description

A unit proposed for formal status should be described and defined so clearly that any subsequent investigator can recognize that unit unequivocally. The amplified description should cover any such characteristics or features that are not intended as essential parts of the definition, details of any measured sections and of any lateral variations (preferably including designated reference sections), supplementary chemical data, structure, geomorphic expression, secondary surface form, possible correlations, any age indications, and any other relevant considerations or interpretations. When possible, such a description should be illustrated by graphic profiles, columnar sections, structural sections, photographs, and any other material likely to assist in recognition of the unit elsewhere. Distinguishing features that characterize a unit may include any or several of the following: composition, texture, primary structures, structural attitudes, biologic remains, readily apparent mineral composition, geochemistry, geophysical properties, geomorphic expression, unconformable or cross-cutting relations, and age, in addition to such supplementary features as ripple marks, mud cracks, cross-bedding and the presence of uncommon minerals.

Article 10. Boundaries

The criteria specified for the recognition of boundaries between adjoining units are of paramount importance. Lithostratigraphic boundaries are placed at positions of discernible lithologic change. Thay are usually designated at sharp lithologic contacts but also may be placed arbitrarily within zones of lithologic gradation, for example, at the top of the highest traceable bed of one of the component rock types. The degree of change in lithology required to justify the establishment of distinct formations is not amenable to strict and uniform rules; it may vary with the complexity of the geology and the details required to portray it satisfactorily.

Article 11. Historical background

A proposal for a new name must include a nomenclatorial history of constituent rocks assigned to the



proposed unit, describing how they were treated previously and by whom (references), as well as such matters as priorities, possible synonymy, etc.

Article 12. Dimensions and regional relations

A perspective on the magnitude of a unit should be provided by such information as may be available on the geographic extent of a unit: thickness variation observed, composition, relations to other units, and correlations with other nearby units. A unit and its boundaries may be extended away from its type section or locality, only as far as the essential lithologic features and lithostratigraphic relationship on which it is based are known with certainty to exist, or through indirect evidence that are justifiably or assumed to continue. Sometimes, a single unit may be composed of a series of isolated bodies having essentially the same lithology and lithostratigraphic position.

Article 13. Age

Age plays no proper role in the definition of units. Nevertheless, the age as well as the basis for its assignment, are important features of the unit and, where possible, should be stated.

Article 14. Correlation

The spatial and temporal counterparts of a newly defined unit beyond the type area are needed.

Article 15. Genesis

Observations and inferences that bear on genesis are of great interest and should be disscussed.

Article 16. Subsurface unit

Many useful units are based on subsurface (well, mine or tunnel) sections. If adequate sample information is available, such subsurface sections can be used legitimately for proposing, defining, and describing new stratigraphic units. The same general rules of procedure used for outcrop sections apply to subsurface units. In proposing a new subsurface unit, the well or mine in which the type section is present becomes the type locality. In well sections, stratotypes need to be designated by well depths and on log rather than by markers at the surface, and geological information for these stratotypes will be based largely on well samples and well logs.

The following data are desirable for establishing subsurface units:

- Designation of well or mine. Name of type well or mine; location of the well or mine by written description, map, exact geographic coordinates; name of the operating agency or individual.

- Geologic logs. Lithologic logs of the well and maps in written and graphic form are needed.

- Geophysical logs. Electrical or other wireline logs and seismic profiles are desirable.

- Depositories. It is essential, that sets of cores, cuttings or other samples, fossil material, logs, and so on covering the type section of a subsurface unit, be readily available for study. Such materials should be placed at an institution with proper curatorial facilities such as the Saudi Geological Survey, universities or museums. The location of the depository should be given.

REDEFInITIOn, REvISIOn, AnD ABAnDOnMEnT OF FORMAl UnITS

Formally defined and named units may be redefined, revised, or abandoned, but revision and abandonment require as much justification as establishment of a new unit.

Article 17. Redefinition

Redefinition of a unit involves changing the view of the content of the unit without changing the boundaries or rank; for example, if a limestone unit changed laterally to a unit in which shale is prominent. Redefinition may be justified to make a unit more useful or easier to recognize, map, and extend throughout its area of occurrence. Redefinition is particularly justifiable if a minor change in boundary could make the unit conform more closely to the criteria for defining and describing a unit without its name having to be changed. Redefinitions should include a statement of intent to revise an existing unit and the reasons for doing so.

The lithologic term in an established lithostratigraphic name may be changed if it is found to be significantly



inaccurate and if the change may be made without modifying the geographic name.

Article 18. Revision

Revision involves either minor changes in the definition of one or both boundaries or in the rank of a unit; for example, a member may become a formation or vice versa.

Article 19. Abandonment

Abandonment involves abandoning of an improperly defined unit by demonstration of synonymy (use different names for same unit) or homonymy (use same name for different units), of assignment to an improper category, or the lack of need or useful purpose for a unit. If reference needs to be made to a name that has been formally abandoned, its abandonment should be mentioned or be indicated by quoting the name of its originator, for example, “the Hijaz Formation of Thompson (1954).”

lithostratigraphic units

nATURE

Article 20. Nature of lithostratigraphic units

A lithostratigraphic unit is a defined body of sedimentary, extrusive igneous, metasedimentary, or metavolcanic strata which is distinguished and delimited on the basis of lithic characteristics and stratigraphic position. A lithostratigraphic unit generally conforms to the Law of Superposition and commonly is stratified and tabular in form.

Basic units

Lithostratigraphic units are the basic units of general geologic work and serve as the foundation for delineating strata, local and regional structure, economic resources, and geologic history in regions of stratified rocks. They are recognized and defined by observable rock characteristics; boundaries may be placed at clearly distinguished contacts or drawn arbitrarily within a zone of gradation. Unconsolidated deposits may constitute valid lithostratigraphic units.

Extension of a unit

Unit may contain a greater or lesser thickness and may span a greater or lesser time interval than the unit as exposed in its type section or locality.

Type section and locality

The definition of lithostratigraphic unit should be based, if possible, on a stratotype consisting of readily accessible rocks in place (outcrop, mine, drill hole). Even where remote methods are used, definitions must be based on lithic criteria including descriptions of actual rock material and not geophysical characteristics. The establishment of subsurface reference sections for units originally defined in outcrop is encouraged.

Type section never changed

The definition and name of a lithostratigraphic unit are established at a type section (or locality) that, once specified, must not be changed. If the type section is poorly designated or delimited, it may be redefined subsequently. If the originally specified stratotype is incomplete, poorly exposed, structurally complicated, or unrepresentative of the unit, a principal reference section or several reference sections may be designated to supplement, but not to replace, the type section.

Independence from inferred geologic history and time concepts

Inferred geologic history, depositional environment, biological sequence and time have no place in the definition of a lithostratigraphic unit, which must be based on composition and other lithic characteristics. Fossils may be valuable during mapping in distinguishing between two lithologically similar, noncontiguous lithostratigraphic units. Although concepts of time or age play no part in defining lithostratigraphic units nor in determining their boundaries, evidence of age may aid recognition of similar lithostratigraphic units at localities far removed from the type sections or areas.

Surface form

Because the surface expression of lithostratigraphic units is an important aid in mapping, it is commonly



advisable, but properly should play a minor part at most in the definition of such units.

Economically exploited units

Aquifers, oil sands, coal beds, and quarry layers are, in general, informal units even though named.

Instrumentally defined units

The boundaries of subsurface units should be defined so as to correspond to useful geophysical markers.

The term “zone”

If applied to the designation of lithostratigraphic unit as, for example, in “producing zone”, it is informal. Cyclic or rhythmic sequences named “cyclothems” if named, are informal, too.

Soils and paleosols

These are layers composed of the in-situ products of weathering of older rocks which may be of diverse composition and age and should not be treated as lithostratigraphic units.

Depositional facies

These are informal units, whether objective (black shale, graptolitic) or genetic and environmental (turbiditic, fluvial).

BOUnDARIES


Boundaries of lithostratigraphic units are placed at positions of lithic change. Boundaries are placed at distinct contacts or may be selected at some arbitrary level within zones of gradation. Both vertical and lateral boundaries are based on the lithic criteria that provide the greatest unity and utility.

A named lithostratigraphic unit is preferably bounded by a single lower and a single upper surface so that the name does not recur in a normal stratigraphic succession. Where a rock unit passes vertically into another by intergrading or interfingering of two or more kinds of rock, unless the gradational strata are sufficiently thick to warrant designation of a third, independent unit, the boundary is necessarily arbitrary and should be selected on the basis of practicality.

Where a unit changes laterally through gradation into, or intertongues with, a markedly different kind of rock, a new unit should be proposed for the different rock type. An arbitrary lateral boundary may be placed between the two equivalent units.

Key beds may be used as boundaries for a formal lithostratigraphic unit where the internal lithic characteristics of the unit remain relatively constant.

Unconformities, where recognizable objectively on lithic criteria, are ideal boundaries for lithostratigraphic units (fig. 2).

RAnKS OF lITHOSTRATIGRAPHIC UnITS

Article 22. Formation

The formation is the fundamental unit in lithostratigraphic classification. A formation is a body of rock identified by lithic characteristics and stratigraphic position; it is prevailingly but not necessarily tabular and is mappable at the Earth’s surface or traceable in the subsurface.

Fundamental unit

Formations are the basic lithostratigraphic units used in describing and interpreting the geology of a region. The limits of a formation normally are those surfaces of lithic change that give it the greatest practicable unity of constitution. A formation may represent a long or short time interval, may be composed of materials from one or several sources, and may include breaks in deposition. A sequence of rocks of closely similar lithology, but including a local or minor hiatus or a disconformity or unconformity, should not be separated into more than one formation merely because this type of stratigraphic break occurs. However, adjacent strata separated by a minor hiatus or by a regional unconformity should not knowingly be combined in a single formation.



Content

A formation should possess some degree of internal lithic homogeneity or distinctive lithic features. It may contain between its upper and lower limits: (i) rock of one lithic type, (ii) repetitions of two or more lithic types, or (iii) extreme lithic heterogeneity which in itself may constitute a form of unity when compared to the adjacent rock units.

Lithic characteristics

Distinctive lithic characteristics include chemical and mineralogical composition, texture, and such supplementary features as color, primary sedimentary or volcanic structures, fossils (viewed as rock-forming particles), or other organic content (coal, oil-shale). A unit distinguishable only by the taxonomy of its fossils is not a lithostratigraphic but a biostratigraphic unit. Rock type may be distinctively represented by electrical, radioactive, seismic, or other properties, but these properties by themselves do not describe adequately the lithic character of the unit.

Mappability and thickness

The proposal of a new formation must be based on tested mappability. Well-established formations

Figure 2. Diagramatic example of lithostratigraphic boundaries and classification (from The North American Commission on Stratigraphic Nomenclature, 2005).



commonly are divisible into several widely recognizable lithostratigraphic units; where formal recognition of these smaller units serves a useful purpose, they may be established as members and beds, for which the requirement of mappability is not mandatory. A unit formally recognized as a formation in one area may be treated elsewhere as a group, or as a member of another formation, without change of name. Thickness is not a determining parameter in dividing a rock succession into formations; the thickness of a formation may range from a feather edge at its depositional or erosional limit to thousands of meters elsewhere. No formation is considered valid that cannot be delineated at the scale of geologic mapping practiced in the region when the formation is proposed.

Interbedded volcanic and sedimentary rock.

Sedimentary rock and volcanic rock that are interbedded may be assembled into a formation under one name which should indicate the predominant or distinguishing lithology.

Volcanic rock

Mappable distinguishable sequences of stratified volcanic rock should be treated as formations or lithostratigraphic units of higher or lower rank.

Metamorphic rock

Formations composed of low-grade metamorphic rock (defined for this purpose as rock in which primary structures are clearly recognizable) are, like sedimentary formations, distinguished mainly by lithic characteristics. The mineral facies may differ from place to place, but these variations do not require definition of a new formation. High-grade metamorphic rocks whose relation to established formations is uncertain are treated as lithodemic units.

Article 23. Member

A member is the formal lithostratigraphic unit next in rank below a formation and is always a part of some formation. It is recognized as a named entity within a formation because it possesses characteristics distinguishing it from adjacent parts of the formation. A formation need not be divided into members unless a useful purpose is served by doing so. Some formations may be divided completely into members; others may have only certain parts designated as members; still others may have no members. A member may extend laterally from one formation to another.

Mapping of member

A member is established when it is advantageous to recognize a particular part of a heterogeneous formation. A member, whether formally or informally designated, need not be mappable at the scale required for formations. Even if all members of a formation are locally mappable, it does not follow that they should be raised to formational rank, because proliferation of formation names may obscure rather than clarify relations with other areas.

Lens and tongue

A geographically restricted member that terminates on all sides within a formation may be called a lens (lentil). A wedging member that extends outward beyond a formation or wedges (“pinches”) out within another formation may be called a tongue. Lenses and tongues may be named.

Division of members

A formally or informally recognized division of a member is called a bed or beds, except for volcanic flow rocks, for which the smallest formal unit is a flow. Members may contain beds or flows, but may never contain other members.

Laterally equivalent members

Although members normally are in vertical sequence, laterally equivalent parts of a formation that differ recognizably may also be considered members.

Article 24. Bed(s)

A bed, or beds, is the smallest formal lithostratigraphic unit of sedimentary rocks.

Limitations



The designation of a bed or a unit of beds as a formally named lithostratigraphic unit generally should be limited to certain distinctive beds whose recognition is particularly useful. Coal beds, oil sands, and other beds of economic importance commonly are named, but such units and their names usually are not a part of formal stratigraphic nomenclature.

Key or marker beds.

A key or marker bed is a thin bed of distinctive rock that is widely distributed. Such beds may be named, but usually are considered informal units. Individual key beds may be traced beyond the lateral limits of a particular formal unit. Key or marker bed may be used as a formation boundary but only over an area in which the essential lithologic characerstics of the formation continue. Even though such beds be traceable beyond the area of diagnostic overall lithology, this alone does not justify geographic extension of the formation.

Article 25. Flow

A flow is the smallest formal lithostratigraphic unit of volcanic flow rocks. A flow is a discrete, extrusive, volcanic body distinguishable by texture, composition, order of superposition, paleomagnetism, or other objective criteria. It is part of a member and thus is equivalent in rank to a bed or beds of sedimentary-rock classification. Many flows are informal units. The designation and naming of flows as formal rock-stratigraphic units should be limited to those that are distinctive and widespread.

Article 26. Group

A group is the lithostratigraphic unit next higher in rank to formation; a group may consist entirely of named formations, or alternatively, need not be composed entirely of named formations.

Use and content

Groups are defined to express the natural relationships of associated formations. They are useful in small-scale mapping and regional stratigraphic analysis. In some reconnaissance work, the term “group” has been applied to lithostratigraphic units that appear to be divisible into formations, but have not yet been so divided. In such cases, formations may be erected subsequently for one or all of the practical divisions of the group. Extentions of a group may consist of informal or unnamed units and (or) units whose names are the same as those used in the group original area or that are wholly or partly different. A group preferably not contain a major hiatus or regional unconformity.

Change in component formations

The formations making up a group need not necessarily be everywhere the same. However, a formation or its parts may not be assigned to two vertically adjacent groups.

Change in rank

The wedge-out of a component formation or formations may justify the reduction of a group to formation rank, retaining the same name. When a group is extended laterally beyond where it is divided into formations, it becomes in effect a formation, even if it is still called a group. When a previously established formation is divided into two or more component units that are given formal formation rank, the old formation, with its old geographic name, should be raised to group status. Raising the rank of the unit is preferable to restricting the old name to a part of its former content, because a change in rank leaves the sense of a well-established unit unchanged.

Article 27. Supergroup

A supergroup is a formal assemblage of related or superposed groups, or of groups and formations. Such units have proved useful in regional and provincial syntheses. Supergroups should be named only where their recognition serves a clear purpose.

Although “series” is a useful general term, it is applied formally only to a chronostratigraphic unit and should not be used for a lithostratigraphic unit. The term “series” should no longer be employed for an assemblage of formations or an assemblage of formations and groups, as it has been, especially in studies of the Precambrian. These assemblages are groups or supergroups.



lITHOSTRATIGRAPHIC nOMEnClATURE

Article 28. Compound character

The formal name of a lithostratigraphic unit is compound. It consists of a geographic name combined with a descriptive lithic term or with the appropriate rank term, or both. It is preferable to use the unit-term rather than the lithologic term in combination with the geographic term for the name of a layered sedimentary lithostratigraphic unit. The use of both lithologic term and the unit-term (for example, Saq Sandstone Formation) should be discouraged. Initial letters of all words used in forming the names of formal rock-stratigraphic units are capitalized.

Omission of part of a name

Where frequent repetition would be cumbersome, the geographic name, the lithic term, or the rank term may be used alone, once the full name has been introduced; as “the Saq,” “the sandstone,” or “the formation,” for the “Saq Sandstone”.

Use of simple lithic terms.

The lithic part of the name should indicate the predominant or diagnostic lithology, even if subordinate lithologies are included. Where a lithic term is used in the name of a lithostratigraphic unit, the simplest generally acceptable term is recommended (for example, limestone, sandstone, shale, tuff, quartzite). Compound terms (for example, clay shale) and terms that are not in common usage (for example, calcirudite, orthoquartzite) should be avoided. Combined terms, such as “sand and clay,” should not be used for the lithic part of the names of lithostratigraphic units, nor should an adjective be used between the geographic and the lithic terms. The terms “lower”, “middle”, and “upper” should not be used for formal subdivisions of lithostratigraphic units.

Group names

A group name combines a geographic name with the term “group,” and no lithic designation is included; for example, Tabuk Group.

Formation names

A formation name consists of a geographic name followed by a lithic designation or by the word “formation.” Examples: Saq Sandstone or Saq Formation.

Member names

All member names include a geographic term and the word “member;” some have an intervening lithic designation, if useful. Members designated solely by lithic character (for example, siliceous shale member), by position (upper, lower), or by letter or number, are informal.

Names of reefs

Organic reefs identified as formations or members are formal units only where the name combines a geographic name with the appropriate rank term.

Bed and flow names

The names of beds or flows combine a geographic term, a lithic term, and the term “bed” or “flow”.

Informal units

When geographic names are applied to such informal units as oil sands, coal beds, mineralized zones, and informal members, the unit term should not be capitalized. A name is not necessarily formal because it is capitalized, nor does failure to capitalize a name render it informal. Geographic names should be combined with the terms “Formation” or “Group” only in formal nomenclature.

Informal usage of identical geographic names

The application of identical geographic names to several minor units in one vertical sequence is considered informal nomenclature. The application of identical geographic names to several lithologic units constituting a cyclothem likewise is considered informal.

Metamorphic rock

Metamorphic rock recognized as a normal stratified sequence, commonly low-grade metavolcanic or



metasedimentary rocks, should be assigned to named groups, formations, and members. High-grade metamorphic and metasomatic rocks are treated as lithodemes and suites.

Misuse of well-known name

A name that suggests some well-known locality, region, or political division should not be applied to a unit typically developed in another less well-known locality of the same name.

lithodemic units

nATURE

Article 29. Nature

A lithodemic unit is a defined body of predominantly intrusive, highly deformed, and/or highly metamorphosed rock, distinguished and delimited on the basis of rock characteristics. In contrast to lithostratigraphic units, a lithodemic unit generally does not conform to the Law of Superposition. Its contacts with other rock units may be sedimentary, extrusive, intrusive, tectonic, or metamorphic (fig. 3).

Recognition and definition

Lithodemic units are defined and recognized by observable rock characteristics. They are the practical units of general geological work in terranes in which rock bodies generally lack primary stratification. In such terranes they serve as the foundation for studying, describing, and delineating lithology, local and regional structure, economic resources, and geologic history.

Type and reference localities

The definition of a lithodemic unit should be based on as full knowledge as possible of its lateral and vertical variations and its contact relationships. For purposes of nomenclatural stability, a type locality and, wherever appropriate, reference localities should be designated.

Independence from inferred geologic history

Concepts based on inferred geologic history properly play no part in the definition of a lithodemic unit. Nevertheless, where two rock masses are lithically similar but display objective structural relations that preclude the possibility of their being even broadly of the same age, they should be assigned to different lithodemic units.

Use of “zone”

As applied to the designation of lithodemic units, the term “zone” is informal. Examples are: “mineralized zone,” “contact zone,” and “pegmatitic zone.”

BOUnDARIES


Boundaries of lithodemic units are placed at positions of lithic change. They may be placed at clearly distinguished contacts or within zones of gradation. Boundaries, both vertical and lateral, are based on the lithic criteria that provide the greatest unity and practical utility. Contacts with other lithodemic and lithostratigraphic units may be depositional, intrusive, metamorphic, or tectonic.

Boundaries within gradational zones.

Where a lithodemic unit changes through gradation into, or intertongues with, a rock mass with markedly different characteristics, it is usually desirable to propose a new unit. It may be necessary to draw an arbitrary boundary within the zone of gradation. Where the area of intergradation or intertonguing is sufficiently extensive, the rocks of mixed character may constitute a third unit.

RAnKS OF lITHODEMIC UnITS

Article 31. Lithodeme

The lithodeme is the fundamental unit in lithodemic classification. A lithodeme is a body of intrusive, pervasively deformed, or highly metamorphosed rock, generally non-tabular and lacking primary depositional



Figure- 3. Lithodemic (upper case) and lithostratigraphic (lower case) units. A lithodeme of gneiss (A) contains an intrusion of diorite (B) that was deformed with the gneiss. A and B may be treated jointly as a complex. A younger granite (C) is cut by a dike of syenite (D), that is cut in turn by unconformity I. All the foregoing are in fault contact with a structural complex (E). A volcanic complex (G) is built upon unconformity I, and its feeder dikes cut the unconformity. Laterally equivalent volcanic strata in orderly, mappable succession (h) are treated as lithostratigraphic units. A gabbro feeder (G’), to the volcanic complex, where surrounded by gneiss is readily distinguished as a separate lithodeme and named as a gabbro or an intrusion. All the foregoing are overlain, at unconformity II, by sedimentary rocks (j) divided into formations and members (from The North American Commission on Stratigraphic Nomenclature, 2005).

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.

Content

A lithodeme should possess distinctive lithic features and some degree of internal lithic homogeneity. It may consist of (i) rock of one type, (ii) a mixture of rocks of two or more types, or (iii) extreme heterogeneity of composition, which may constitute in itself a form of unity when compared to adjoining rock-masses.

Lithic characteristics

Distinctive lithic characteristics may include mineralogy, textural features such as grain size, and structural features such as schistose or gneissic structure. A unit distinguishable from its neighbors only by means of chemical analysis is informal.

Mappability

Practicability of surface or subsurface mapping is an essential characteristic of a lithodeme.

Units below the rank of lithodeme are informal.

Article 32. Suite

A suite (metamorphic suite, intrusive suite, plutonic suite) is the lithodemic unit next higher in rank to lithodeme. It comprises two or more associated lithodemes of the same class (e.g., plutonic, metamorphic). For cartographic and hierarchical purposes, suite is comparable to group.

Purpose: Suites are recognized for the purpose of expressing the natural relations of associated lithodemes having significant lithic features in common, and of depicting geology at compilation scales too small to allow delineation of individual lithodemes. Ideally, a suite consists entirely of named lithodemes, but may contain both named and unnamed units.

Change in component units

The named and unnamed units constituting a suite may change from place to place, so long as the



original sense of natural relations and of common lithic features is not violated.

Change in rank

Traced laterally, a suite may lose all of its formally named divisions but remain a recognizable, mappable entity. Under such circumstances, it may be treated as a lithodeme but retain the same name. Conversely, when a previously established lithodeme is divided into two or more mappable divisions, it may be desirable to raise its rank to suite, retaining the original geographic component of the name. To avoid confusion, the original name should not be retained for one of the divisions of the original unit.

Article 33. Supersuite

A supersuite is the unit next higher in rank to a suite. It 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.

Article 34. Complex

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) and, although unranked, commonly is comparable to suite or supersuite and is named in the same manner.

Use of “complex”

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. “Complex” is unranked but commonly comparable to suite or supersuite; therefore, the term may be retained if subsequent, detailed mapping distinguishes some or all of the component lithodemes or lithostratigraphic units.

Volcanic complex.

Sites of persistent volcanic activity commonly are characterized by a diverse assemblage of extrusive volcanic rocks, related intrusions, and their weathering products. Such an assemblage may be designated a volcanic complex.

Structural complex.

In some terranes, tectonic processes (e.g., shearing, faulting) have produced heterogeneous mixtures or disrupted bodies of rock in which some individual components are too small to be mapped. Where there is no doubt that the mixing or disruption is due to tectonic processes, such a mixture may be designated as a “structural complex”, whether it consists of two or more classes of rock, or a single class only. A simpler solution for some mapping purposes is to indicate intense deformation by an overprinted pattern.

Misuse of “complex”.

Where the rock assemblage to be united under a single, formal name consists of diverse types of a single class of rock, as in many terranes that expose a variety of either intrusive igneous or high-grade metamorphic rocks, the term “intrusive suite,” “plutonic suite,” or “metamorphic suite” should be used, rather than the unmodified term “complex.” Exceptions to this rule are the terms structural complex and volcanic complex.

Misuse of “Series” for Suite, Complex, or Supersuite.

The term “series” has been employed for an assemblage of lithodemes or an assemblage of lithodemes and suites, especially in studies of the Precambrian. This practice now is regarded as improper; these assemblages are suites, complexes, or supersuites. The term “series” also has been applied to a sequence of rocks resulting from a succession of eruptions or intrusions. In these cases a different term should be used; “group” should replace “series” for volcanic and low-grade metamorphic rocks, and “intrusive suite” or “plutonic suite” should replace “series” for intrusive rocks of group rank.



lITHODEMIC nOMEnClATURE

Article 35. Compound character

The formal name of a lithodemic unit is compound. It consists of a geographic name combined with a descriptive or appropriate rank term. The principles for the selection of the geographic term, concerning suitability, availability, priority, etc, follow those established before in naming formal units, where the rules for capitalization are also specified.

Article 36. Lithodeme names

The name of a lithodeme combines a geographic term with a lithic or descriptive term, e.g., Killarney Granite, Adamant Pluton, Manhattan Schist, Skaergaard Intrusion, Duluth Gabbro. The term formation should not be used.

Lithic term.

The lithic term should be a common and familiar term, such as schist, gneiss, gabbro. Specialized terms and terms not widely used, such as websterite and jacupirangite, and compound terms, such as graphitic schist and augen gneiss, should be avoided.

Intrusive and plutonic rocks

Because many bodies of intrusive rock range in composition from place to place and are difficult to characterize with a single lithic term, and because many bodies of plutonic rock are considered not to be intrusions, latitude is allowed in the choice of a lithic or descriptive term. Thus, the descriptive term should preferably be compositional (e.g., gabbro, granodiorite), but may, if necessary, denote form (e.g., dike, sill), or be neutral (e.g., intrusion, pluton). In any event, specialized compositional terms not widely used are to be avoided, as are form terms that are not widely used, such as bysmalith and chonolith. Terms implying genesis should be avoided as much as possible, because interpretations of genesis may change.

Article 37. Suite names

The name of a suite combines a geographic term, the term “suite, “ and an adjective denoting the fundamental character of the suite; for example, Idaho Springs Metamorphic Suite, Tuolumne Intrusive Suite, Cassiar Plutonic Suite. The geographic name of a suite may not be the same as that of a component lithodeme. Intrusive assemblages, however, may share the same geographic name if an intrusive lithodeme is representative of the suite.

Article 38. Supersuite names

The name of a supersuite combines a geographic term with the term “supersuite.”



references consulted Chang, K.H., 1975, Unconformity-bounded stratigraphic units, Geological Society of America Bulletin, v. 86,

no. 11, p. 1544-1552.

Code-Committee der Stratigraphischen Kommission der DUGW, 1977, Stratigraphic Guidelines –Recommendations of the Stratigraphic Commission of the Deutche Union der Geologischen Wissenschaften regarding the use of stratigraphic methods (in German, English, and French): Newsl. Stratigr., v. 6, no. 3, p. 131-151.

Commission for the Stratigrahic Code of Indonesia, 1975, Stratigraphic Code of Indonesia, revised edition (in Indonesian and English), S. Martodjojo, ed.: Association Geologists, 19 p.

Fitch, F., H, 1980, Saudi Arabian Stratigraphic Lexicon: Saudi Arabian Deputy Ministry for Mineral Resources, Technical Record DM-TR-01-1.

Halawani, M.A., 2001, Stratigraphic Column for the Phanerozoic Rocks of Saudi Arabia, A compilation and Synthesis with Comments, Kingdom of Saudi Arabia: Saudi Geological Survey Technical Report SGS-TR-2001-3, (A reprint of BRGM-TR-2000-3).

India Geological Survey, 1971, Code of Stratigraphic Nomenclature of India, Miscellaneous Publication, no. 20, 28 p.

International Sub-commission on Stratigraphic Classification of IUGS International Commission on Stratigraphy, 1974, International Stratigraphic Guide (A guide to stratigraphic classification, terminology, and procedure), 2nd ed., Salvador, A. (Editor), 214 p.

International Subcommission on Stratigraphic Classification of IUGS International Commission on Stratigraphy, 1994, International Stratigraphic Guide (2nd edition, Amos Salvador, ed.): Trondheim, Norway, International Union of Geological Sciences, and Boulder, Colorado, Geological Society of America, 214 p.

Norwegian Committee on Stratigraphy, 1989, Rules and recommendations for naming geological units in Norway, J.P. Nystuen, ed.: Norwegian Journal of Geology, v. 69, supplement 2, 111 p.

Sloss, L.L., 1963, Sequences in the cratonic interior of North America, Geological Society of America Bulletin, v. 74, no.2, p. 94-114.

South Africa Committee for Stratigraphy, 1977, South African Code of Stratigraphic Terminology and Nomenclature, revised edition (in English and Afrikaans): Department of Mines, Geological Survey Special Publication 20, 22 p.

Stratigraphic Code of Pakistan (2nd ed.), 1967, Memoirs of the Geological Survey of Pakistan, v. 4, pt. 1, p. 1-7.

Stratigraphic Code Sub-Committee, 1969, Recommendation for Stratigraphical Usage: Geological Society of London Proceedings, p. 139 – 166 (second version of the 1967 Report).

Stratigraphic Committee of Geological Society of London, 1991, A Guide to Stratigraphic Procedure: Geological Society of London Journal, v. 148, p. 813-824.

Stratigraphic Committee of the Directorate General of Mineral Resources, 1979, Saudi Arabian Code of Lithostratigraphic Classification and Nomenclature: Saudi Arabian Ministry of Petroleum and Mineral Resources Technical Manual TM-1979-1, 15 p.

Stratigraphic Committee, 1984, Saudi Arabian Code of Lithostratigraphic Classification and Nomenclature: Second Edition: Saudi Arabian Deputy Ministry for Mineral Resources Technical Manual DM-TM-04-1 (Reissued as Saudi Geological Survey Data- File Report SGS-DF-2004-7, 16 p.).

The North American Commission on Stratigraphic Nomenclature, 2005, North American Stratigraphic Code: American Association of Petroleum Geologists Bulletin, v. 89, no. 11, p. 1547-1591.

The North American Commission on Stratigraphic Nomenclature, 2003, North American Stratigraphic Code: American Association of Petroleum Geologists Bulletin, v. 67, no. 5, p. 841-875.

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