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Abstract

The first edition of the International Stratigraphic Guide was prepared by the International Subcommission on Stratigraphic Classification (ISSC)* of the International Commission on Stratigraphy. The Subcommission was created in 1952 by the 19th International Geological Congress (Algiers). It first worked under the aegis of the International Geological Congresses, and then, since 1965, under the International Union of Geological Sciences (IUGS). The publication of an international stratigraphic guide was the principal objective of the Sub-commission since its inception.

As mentioned in the Introduction of the first edition of the Guide, many de-veloping fields of stratigraphy, such as those dealing with electrical and other kinds of well logs, seismic stratigraphy, magnetic reversals, geochemical zonation, soils, volcanogenic strata, igneous and metamorphic rocks, unconformity-bounded units, eustatic cycles, oceanic stratigraphy, ecostratigraphy, the Quaternary, and the Precambrian were barely touched in the first edition. These were expected to be the subject of future studies by the Subcommission.

Consequently, soon after the first edition of the Guide was published in 1976, the ISSC began to investigate these developing fields of stratigraphy and to determine if they should be included in a second edition of the Guide.

This revised second edition of the International Stratigraphic Guide includes new chapters on unconformity-bounded units and magnetostratigraphic polarity units, and updates the discussion of several subjects, particularly the stratigraphic treatment of igneous and metamorphic rock bodies.

For this second edition of the Guide, the Subcommission decided against establishing new kinds of stratigraphic units based exclusively on

Origin and Purposes of the Guide

The first edition of the International Stratigraphic Guide was prepared by the International Subcommission on Stratigraphic Classification (ISSC)* of the International Commission on Stratigraphy. The Subcommission was created in 1952 by the 19th International Geological Congress (Algiers). It first worked under the aegis of the International Geological Congresses, and then, since 1965, under the International Union of Geological Sciences (IUGS). The publication of an international stratigraphic guide was the principal objective of the Sub-commission since its inception.

As mentioned in the Introduction of the first edition of the Guide, many de-veloping fields of stratigraphy, such as those dealing with electrical and other kinds of well logs, seismic stratigraphy, magnetic reversals, geochemical zonation, soils, volcanogenic strata, igneous and metamorphic rocks, unconformity-bounded units, eustatic cycles, oceanic stratigraphy, ecostratigraphy, the Quaternary, and the Precambrian were barely touched in the first edition. These were expected to be the subject of future studies by the Subcommission.

Consequently, soon after the first edition of the Guide was published in 1976, the ISSC began to investigate these developing fields of stratigraphy and to determine if they should be included in a second edition of the Guide.

This revised second edition of the International Stratigraphic Guide includes new chapters on unconformity-bounded units and magnetostratigraphic polarity units, and updates the discussion of several subjects, particularly the stratigraphic treatment of igneous and metamorphic rock bodies.

For this second edition of the Guide, the Subcommission decided against establishing new kinds of stratigraphic units based exclusively on wireline well logs and seismic reflection profiles. While extremely useful in stratigraphic work, the information supplied by wireline logs and seismic reflection profiles is not recorded in the rocks; it is only a graphic (or electronic) record of remote measurements of certain physical properties of the rocks. Rock types are only identified broadly and by inference, and formal stratigraphic units should not be established on the basis of these remote measurements.

Special chapters dealing with the Precambrian and the Quaternary were judged to be unnecessary. However, brief mention of the special problems that arise in subdividing the Precambrian and the Quaternary into chronostratigraphic units is made in sections 9.F and 9.G. The Guide deals with principles and procedures of stratigraphic classification and nomenclature. The same principles and procedures applied to other rocks can also be applied to Precambrian and Quaternary rocks.

Soils and soil-stratigraphic units have not been covered in this second edition of the Guide. The stratigraphic treatment of soils needs additional consideration before attempting to formalize principles and procedures and to incorporate soil-stratigraphic units into the Guide. These units may be the subject of future discussion by the ISSC.

The purposes of this revised second edition of the Guide are the same as those of the first edition: to promote international agreement on principles of stratigraphic classification and to develop an internationally acceptable stratigraphic terminology and rules of stratigraphic procedure—all in the interest of improved international communication, coordination, and understanding and thus of improved effectiveness in stratigraphic work throughout the world.

The recommendations of this second edition of the International Stratigraphic Guide are based on the current consensus of a substantial majority of members of the Subcommission. Future editions undoubtedly will introduce yet additional changes dictated by the tests of time and usage and will incorporate worthy new views and methods.

The Subcommission welcomes criticism and alternative proposals, and it invites suggestions from all geologists for improving this second edition of the Guide.

Composition of Subcommission

The membership of the Subcommission has evolved over a 35-year period, beginning in 1954 with invitations to some 300 members of the Commission on Stratigraphy to join the Subcommission. Twenty-five accepted, and with the addition of a few other stratigraphers, the charter membership of the Subcommission amounted to 32 individuals. Membership now stands at about 75 and represents a worldwide geographic spread of stratigraphers and stratigraphic organizations and a wide spectrum of stratigraphic interests, traditions, and philosophies. Three classes of members are presently recognized:

Individual Members: This group is composed of individual stratigraphers throughout the world chosen because of their interest in and genuine dedication to matters of stratigraphic classification and nomenclature and their interest in the work of the ISSC.

Individual Members ex officio: This group includes the Chairman, Vice Chairmen, Past Chairman, and Secretary-General of the IUGS International Commission on Stratigraphy and the chairmen or secretaries of each of the subcommissions, regional committees, and working groups of that Commission.

Organizational Members: This group is composed of representatives of every active national or multinational stratigraphic committee and commission, and stratigraphic committees of geological societies, and national geological surveys. It includes every active stratigraphic organization in the world.

With these three kinds of membership, the Subcommission is considered representative, especially since it also has frequently gone to stratigraphers beyond its membership to solicit views on special problems.

Preparation and Revision of the Guide

Because of the size and international nature of its membership, the Sub-commission has operated largely by correspondence, supplemented by meetings at all International Geological Congresses since the Subcommission was created in 1952. It has particularly used the procedure of written questionnaires, responses, discussion, and conclusions.

Since the publication of the first edition of the Guide in 1976, the ISSC published three notes, covering particular subjects of stratigraphic classification and nomenclature:

  1. Magnetostratigraphic polarity units—a supplementary chapter of the ISSC International Stratigraphic Guide (in cooperation with the IUGS/IAGA Sub-commission on a Magnetic Polarity Time Scale): Geology, v. 7, p. 578-583, December, 1979.

  2. Unconformity-bounded stratigraphic units: Geological Society of America Bulletin, v. 98, p. 232-237, February, 1987.

  3. Stratigraphic classification and nomenclature of igneous and metamorphic rock bodies: Geological Society of America Bulletin, v. 99, p. 440–142, September, 1987.

These notes were the basis for the preparation of two new chapters of the Guide and the revision of the chapter on lithostratigraphic units.

The second edition of the International Stratigraphic Guide contains a Glossary of Stratigraphic Terms and an updated Bibliography of published literature on principles and concepts of stratigraphic classification, terminology and procedure.

Spirit of the Guide

The Subcommission offers its International Stratigraphic Guide as a recommended approach to stratigraphic classification, terminology, and procedure—not as a “code.” Individuals, organizations, or nations should not feel compelled to follow it, or any part of it, unless convinced of its logic and value. Stratigraphic classification, terminology, and procedure should not be legislated. Real and lasting progress will be achieved only as geoscientists voluntarily agree on the validity and desirability of certain principles, procedures, and terms. The purpose of the Guide is to inform, to suggest, and to recommend; it must continually evolve in keeping with the growth of geologic knowledge.

Because of the great diversity of stratigraphic views, the Guide favors a broad and unrestrictive approach in defining principles, proposing rules, and recommending procedures. Where two important lines of stratigraphic thought conflict, the Guide generally favors the less prohibitive one—the one that allows the greater freedom for both points of view. Ultimately, conflicting views will probably be settled by the test of usage. Terms that are not useful will die out; procedures that are not useful will be abandoned.

Furthermore, the Guide recognizes that there are stratigraphic situations where hard and fast rules cannot be applied and that common sense may best indicate what will most effectively promote clarity, understanding, and progress.

The Guide reflects a belief that the ideal concepts behind stratigraphic clas-sification and terminology should be maintained, even if in practice the ideal can only be approached and not perfectly achieved. If compromises must be made in practice they should be recognized for what they are.

National and Regional Stratigraphic Codes

The ultimate goal of the Subcommission is a single set of common worldwide principles and rules of stratigraphic classification, terminology, and procedure, rather than many diverse national and regional schemes. The Subcommission has, however, always supported the development of national and regional stratigraphic codes. Those that have come to the attention of the Subcommission are listed in order of their date of publication at the back of this Guide. These codes have helped in developing principles, in promoting awareness of the need for rules, and in providing a testing ground for various proposals. Ultimately, the Subcommission is committed to improving a single body of international rules rather than on developing numerous more or less conflicting local or national codes.

Alternative or Dissenting Views

Geologists worldwide have many different views on stratigraphic classification and stratigraphic terminology. Many of these views have been discussed thoroughly during the last 40 years in the Circulars of the Subcommission.

The Subcommission considered during the preparation of the first edition of the Guide the possibility of publishing dissenting comments and alternative views. It was soon realized that it would be impossible to devote adequate space to include all possible qualifying or conflicting ideas and replies to them and that it would be unfair to select some views and neglect others. Summaries are commonly unsatisfactory, and dissenting views are best kept in the author's own words. It was also recognized that most alternative views had already been published independently and that references to those that had been published would be contained in the bibliography accompanying the Guide, where they would be available to all who were interested. The same policy was followed in the preparation of this second edition.

Despite the diversity of views on stratigraphic principles in the world today, the approach of the Guide is believed to be sufficiently broad and tolerant so that it will not be found unduly restrictive to anyone in its application to practical problems of stratigraphy.

*Originally International Subcommission on Stratigraphic Terminology (ISST).

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