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AAPG Bulletin


(Begin page 366)

AAPG Bulletin, V. 85, No. 2 (February 2001), P. 366-371.

Copyright ©2001. The American Association of Petroleum Geologists. All rights reserved.


NOTE 63--Application for amendment of the North American Stratigraphic Code concerning consistency and updating regarding electronic publishing (NORTH AMERICAN COMMISSION ON STRATIGRAPHIC NOMENCLATURE)

Ismael Ferrusquía-Villafranca, Instituto de Geología Universidad Nacional Autónoma de México, Ciudad Universitaria, México D.F. 45100; R. Michael Easton, Precambrian Geoscience Section, Ontario Geological Survey, 933 Ramsey Lake Road, Sudbury, Ontario, P3E 6B5, Canada; Lucy E. Edwards, U.S. Geological Survey, 926A National Center, Reston, Virginia, 20192; Robert H. Fakundiny, New York State Geological Survey/State Museum, 3140 Cultural Education Center, Empire State Plaza, Albany, New York, 12230; and James O. Jones (deceased), Department of Geology, University of Texas, San Antonio, Texas, 78249-0663

Manuscript received October 13, 1999; revised manuscript received April 15, 2000; final acceptance June 30, 2000.


We are indebted to the fellow members of the North American Commission on Stratigraphic Nomenclature who served during the period 1995-1998, William R. Arnott, Benoit Beauchamp, John P. Bluemle, Emiliano Campos-Madrigal, Carlos Manuel Cantu-Chapa, A. (Tony) Davidson, Robert J. Fulton, A. P. (Tony) Hamblin, Ardith Hansel, Lee C. Gerhard, W. Burleigh Harris, Robert R. Jordan, David T. King Jr., Norman P. Lasca, Alfred C. Lenz, Susan A. Longacre, Ernest A. Mancini, Randall Orndorff, Donald E. Owen, John Pojeta Jr., Terry Poulton, Brian J. Pratt, James Robertson, Paul R. Seaber, Bruce R. Wardlaw, and Ray W. Yole, for their kind comments and criticisms of the ideas expressed in the NACSN ad hoc Committee Reports, as well as their encouragement to put together and publish this proposed Amendment. Also we thank the Association of Earth Sciences Editors for their proposed changes to Article 4 on the issue of electronic publication.


The North American Stratigraphic Code, hereafter referred to as the Code, "represents but a stage in the evolution of scientific communication" (North American Commission on Stratigraphic Nomenclature, 1983, p. 841). It requires continued revision to adapt and better meet the present and emerging needs of the profession. The North American Commission on Stratigraphic Nomenclature (NACSN) is the body of scientists entrusted with the responsibilities of recommending procedures for classifying and naming stratigraphic and related units and of considering proposal for amendment to the Code.

In 1994, the NACSN decided to address various inconsistencies and imperfections detected in the Code. Chairman Donald G. Cook appointed an ad hoc committee consisting of Lucy E. Edwards, Robert H. Fakundiny, R. Michael Easton, and Ismael Ferrusquía, chaired by the latter, to look into consistency, clarity, and simple updates and to make recommendations. At about the same time, the Association of Earth Sciences Editors proposed updating of the Code with respect to electronic publishing. Another ad hoc committee of the NACSN was appointed in 1996 to deal with biostratigraphic units (Note 64, this volume). An additional ad hoc committee has been appointed to consider diachronic units.

The work of the present committee involves the Scope and Overview sections of the Code, 19 of the Articles, 1 figure caption, 2 of the figures, and 2 tables. Most proposed modifications attempt to improve the consistency and clarity of the Code. A significant change in this Note of Amendment is in the area of publication, namely, Article= 4.


In compliance with Article 21 (NACSN, 1983, p. 855), "changes of this code may be proposed in writing to the Commission by any geoscientist at any time. If accepted for consideration by a majority vote of the Commission, they may be adopted by a two-thirds vote of the Commission at an annual meeting not less than a year after publication of the proposal," we recommend that the Code be amended as proposed, and we invite comments from the geologic community on this proposal. These comments should be directed to Bruce R. Wardlaw, Chairman, NACSN, U.S. Geological Survey, 926A National Center, Reston, Virginia, 20192; e-mail: <[email protected]>.

Proposed additions are in boldface type (except in the title of articles, remarks or in the figure captions where the additions, for contrast, are written in normal type, to ease their detection). Proposed deletions are in strikethrough type. In the section on Article 4, an asterisk (*)at the beginning of a paragraph indicates modifications proposed by the Association of Earth Sciences Editors. In the list of references cited, an asterisk at the beginning of an entry indicates a reference to be added to the Code if this proposed change is approved.

(Begin page 367)

SCOPE [p. 847, right column, 6th paragraph]

The term stratigraphic unit may be defined in several ways. Etymological emphasis requires that it be a stratum or assemblage of adjacent strata distinguished by any or several of the many properties that rocks may possess (ISSC, 1976, p 13; 1994, p. 13). The scope of stratigraphic classification and procedures, however, suggests a broader definition: a naturally occurring body of rock or rock material distinguished from adjoining bodies of rock on the basis of some stated property or properties. Remainder of paragraph unchanged.

TABLE 1 [p. 848]

A new version is proposed (Table 1).

Table 1 Classes and Categories of Units Defined*

     Lithostratigraphic (22)
     Lithodemic (31)**
     Magnetopolarity (44)
     Biostratigraphic (48)
     Pedostratigraphic (55)
     Allostratigraphic (58)

     A. Material Categories Used to Define Temporal Spans
          Chronostratigraphic (66)
          Polarity-Chronostratigraphic (83)
     B. Temporal (Non-Material) Categories
          Geochronologic (80)
          Polarity-Chronologic (88)
          Diachronic (91)
          Geochronometric (96)

*Numbers in parenthesis are the numbers of the Articles where
units are defined.
**Italicized categories are those introduced or developed since
publication of the previous coed (ACSN, 1970).

OVERVIEW [p. 849, right column, 1st & 2nd paragraphs]

Despite admonitions in previous American codes and the International Stratigraphic Guide (ISSC, 1976, p. 81; 1994, p. 87) that similar procedures should be applied to the Precambrian, no comparable chronostratigraphic units, or geochronologic units derived therefrom, proposed for the Precambrian have yet been accepted worldwide. Instead, the IUGS Subcommission on Precambrian Stratigraphy (Sims, 1979) and its Working Groups (Harrison and Peterman, 1980) recommend division of Precambrian time into geochronometric units having no material referents.

FIGURE 1 [p. 850]

A new version is proposed (Fig. 1).

aapg8502_0960_01.jpg (68160 bytes)

Figure 1--Relation of geologic time units to the kinds of rock-units material-referents on which most are based. Numbers in parentheses refer to the number of the article in which each kind of unit is defined.


Article 2.--Categories. Categories of formal stratigraphic units, though diverse, are of three classes (Table 1). The first class (I on Table 1)[tn1] is of rock-material categories based on content, inherent attributes, or physical limits content and stratigraphic position, and includes lithostratigraphic, lithodemic, magnetopolarity, biostratigraphic, pedostratigraphic, and allostratigraphic units. The second class (IIA on Table 1) is of material categories used as standards for defining spans of geologic time, and includes chronostratigraphic and polarity-chronostratigraphic units. The third class (IIB on Table 1) is of nonmaterial temporal categories and includes geochronologic, polarity-chronologic, diachronic, and geochronometric, and diachronic units.

*Article 4.--Publication.4 "Publication in a recognized scientific medium" in conformance with this Code means that a work, when first issued, must (1) be reproduced in (Begin page 368) ink on paper or by some method that assures numerous identical copies and wide distribution;; be reproduced electronically on CD-ROM, on the Internet, or by another electronic method widely accepted by the scientific community; or be reproduced by some method that assures numerous identical copies and wide distribution; (2) be issued for the purpose of scientific, public, permanent record; and (3) be readily obtainable by purchase or free distribution; and (4) have undergone adequate peer review.

*Remarks. (a) Inadequate publication.--The following do not constitute publication within the meaning of the Code: (1) distribution of microfilms, microcards, or matter reproduced by similar methods; (2) distribution to colleagues or students of a note, even if printed, in explanation of an accompanying illustration; (3) distribution of proof sheets; (4) open-file release; (5) theses, dissertations, and dissertation abstracts; (6) mention at a scientific or other meeting; (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; or (11) mention in the popular press or in a legal document; or (12) distribution by an author by posting on the Internet, or by another electronic medium, a document that has not undergone the procedures stated below (Remark c).

(b) Guidebooks.--A guidebook with distribution limited to participants of a field excursion does not meet the test of availability. Some organizations publish and distribute widely large editions of serial guidebooks that include referred regional papers; although these do meet the tests of scientific purpose and availability, and therefore constitute valid publication, other media are preferable.

*(c) Electronic publication.--Publication in this medium, which has become widespread since distribution of the Code in 1983, is confined to publication in a journal or other publication series by a widely recognized (1) scientific society, (2) government agency, (3) academic institution, or (4) other respected scientific publisher. All versions distributed must be the same, whether in paper or electronic form, without alteration. Other requirements are as follows: (1) archival practices adequate for future availability; (2) suitable typography; (3) coding and markup practices that adhere to accepted standards; (4) database preparation that includes satisfactory search and retrieval tools, as well as the capability for downloading to a researcher's local printer; and (5) adequate copyediting standards.

TABLE 2 [p. 852]

A new version is proposed (Table 2).

Table 2. Categories and Ranks of Units Defined in This Code*

366_t2.jpg (93775 bytes)

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, and other pertinent considerations. Consideration of the historical background of an older unit commonly provides the basis for justifying definition of a new unit.

Article 13.--Age. For most formal material geologic units, other than chronostratigraphic and polarity-chronostratigraphic, inferences regarding geologic age play no proper role in their definition. Nevertheless, the age, as well as the basis for its assignment, are important features of the unit and, where possible, should be stated. For many lithodemic units, the age of the protolith should be distinguished from that of the metamorphism or deformation. If the basis for assigning an age is tenuous, a doubt should be expressed.

Article 19.

Remarks. (a) Boundary change.--Revision is justifiable if a minor change in boundary or content will make a unit more natural and useful. If revision modifies only a minor part of the content of a previously established unit, the original name may be retained.

Article 22.

Remarks. (e) Independence from time concepts.--The boundaries of most lithostratigraphic units may transgress time horizons are time independent, but some may be approximately synchronous. Inferred time-spans, however measured, play no part in differentiating or determining the boundaries of any lithostratigraphic unit. Remainder of paragraph unchanged.

Article 23.--Boundaries. Boundaries of lithostratigraphic units are placed at positions of lithic change. Boundaries are placed at distinct contacts or may be fixed arbitrarily selected at some arbitrary level within zones of gradation (Fig. 2a). Both vertical and lateral boundaries are based on the lithic criteria that provide the greatest unity and utility.

Remarks. (b) Boundaries in lateral lithologic change.--Where a unit changes laterally through abrupt gradation into, or intertongues with, a markedly different kind of rock, a new unit should be proposed for the different rock type. Remainder of paragraph unchanged.

Article 31.

Remarks. (a) 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 rocks 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.

Article 41.--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 (Begin page 369) Suite, Cassiar Plutonic Suite. The geographic name of a suite may not be the same as that of a component lithodeme (see Article l9f). Intrusive assemblages, however, may share the same geographic name if an intrusive lithodeme is representative of the suite. (e.g., the Methuen Plutonic Suite may include the Methuen, Deloro, Abinger, and Addington Granites, [Easton, 1992]. As the Methuen Granite, a lithodeme, is typical of the suite, the duplication of names is permissible).

Article 44.--Definition of Magnetopolarity Unit. A magnetopolarity unit is a body of rock unified by its remanent magnetic polarity and distinguished from adjacent rock bodies that has have different polarity.

Article 46.

Remarks. (c) Ranks.--When continued work at the stratotype for a polarity zone, or new work in correlative rocks rock bodies elsewhere, reveals smaller polarity units, these may be recognized formally as polarity subzones. If it should prove necessary or desirable to group polarity zones, these should be termed polarity superzones. The rank of a polarity unit may be changed when deemed appropriate. (Begin page 370)

Article 55.

Remarks (e) Distinction from pedologic soils.--Pedologic soils may include organic deposits (e.g., litter zones, peat deposits, or swamp deposits) that overlie or grade laterally into differentiated buried soils. The organic deposits are not products of pedogenesis, and therefore, O horizons are not included in a pedostratigraphic unit (Fig. 6[ln6]); they may be classified as biostratigraphic or lithostratigraphic units. Pedologic soils also include the entire C horizon of a soil. The C horizon in pedology is not rigidly defined; it is merely the part of a soil profile that underlies the B horizon. Remainder of paragraph unchanged.

FIGURE 6 [p. 865]

A new version is proposed (Fig. 6).

aapg8502_0960_06.jpg (47711 bytes)

Figure 6--Relationship between pedostratigraphic units and pedologic profiles. The base of a geosol is the lowest clearly defined physical boundary of a pedologic horizon in a buried soil profile. In this example it is the lower boundary of the B horizon because the base of the C horizon is not a clearly defined physical boundary. In other profiles the base may be the lower boundary of a C horizon. (*Modified from Ruhe, 1965; Pawluk, 1978.)

Article 57.

Remarks (c) Procedures for establishing formal pedostratigraphic units.--A formal pedostratigraphic unit may be established in accordance with the applicable requirements of Article 3, and additionally by describing major soil horizons in each soil facies. The definition should include a description of major soil horizons and their lateral variations.

Article 58.

Remarks. (a) Purpose.--Formal allostratigraphic units may be defined to distinguish between different (1) superposed discontinuity-bounded deposits of similar lithology (Figs. 7, 9), (2) contiguous discontinuity-bounded deposits of similar lithology (Fig. 8), or (3) geographically separated discontinuity-bounded units of similar lithology (Fig. 9), or. Formal allostratigraphic units may also be defined to distinguish as single units discontinuity-bounded deposits characterized by lithic heterogeneity (units 1-4 in Fig. 8 7). Allostratigraphic units are distinguished by bounding discontinuities. The lithology of an allostratigraphic unit plays no part in its definition.


Nature and Types Kinds

Article 61.--Types Kinds. Geologic-time units are conceptual rather than material, in nature. Two types kinds are recognized: Those based on material standards or referents (specific rock sequences or bodies), and those independent of material referents (Fig. 1[ln1]).

Article 62.--Types Kinds Based on Referents. Two types kinds of formal geologic-time units that are based on material referents are recognized: they are isochronous and diachronous units.

Article 66.--Definition. A chronostratigraphic unit is a body of rock established to serve as the material reference for all constituent rocks formed during the same span of time. Each of its boundaries boundary is synchronous. The body also serves as the basis for defining the specific interval of time, or geochronologic unit (Article 80), represented by the referent.

Article 75.--Chronozone. A chronozone is a nonhierarchical, but commonly small, formal chronostratigraphic unit, and its boundaries may be independent of those of ranked chronostratigraphic units such as stage or series. Although a chronozone is an isochronous unit, it may be based on a biostratigraphic unit (example: Cardioceras cordatum Biochronozone), a lithostratigraphic unit (Begin page 371) (Woodbend Lithochronozone), or a magnetopolarity unit (Gilbert Reversed-Polarity Chronozone). Modifiers (litho-, bio-, polarity) used in formal names of the units need not be repeated in general discussions where the meaning is evident from the context, e.g., Exus albus Chronozone.

Article 96.--Definition. Geochronometric units are units established through the direct division of geologic time, expressed in years. Like geochronologic units (Article 80), geochronometric units are abstractions, i.e., they are not material units. Unlike geochronologic units, geochronometric units are not based on the time span of designated chronostratigraphic units (stratotypes), but are simply time divisions of convenient magnitude for the purpose for which they are established (e.g., Hofmann, 1990), such as the development of a time scale for the Precambrian. Their boundaries are arbitrarily chosen or agreed-upon ages in years.


*Easton, R. M., 1992, The Grenville Province and the Proterozoic history of central and southern Ontario, in P. C. Thurston, H. R. Williams, R. H. Sutcliffe, and G. M. Stott, eds., Geology of Ontario, Ontario Geological Survey Special Volume 4, part 2, p. 713-904.

*Hofmann, H. J., 1990, Precambrian time units and nomenclature--the geon concept: Geology, v. 18, p. 340-341.

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

North American Commission on Stratigraphic Nomenclature, 1983, North American Stratigraphic Code: AAPG Bulletin, v. 67, p. 841-875.

4This article is modified slightly from a statement by the International Commission of Zoological Nomenclature (1964, p. 7-9). Footnote unchanged.

Ismael Ferrusquía-Villafranca, R. Michael Easton, Lucy E. Edwards, Robert H. Fakundiny, and James O. Jones (deceased)

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