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

Abstract The whole Earth is stratified, in a broad sense, so that all rocks and all classes of rocks—sedimentary, igneous, and metamorphic—fall within the scope of stratigraphy and of stratigraphic classification. Rocks have many different properties, and it is possible to classify them according to any of these properties: lithology, fossil content, magnetic polarity, electrical properties, seismic response, chemical or mineralogical composition, and many others. Rocks can also be classified according to such attributes as their time of origin or their environment of genesis. The stratigraphic position of change for any one property or attribute does not necessarily coincide with that for any other. Consequently, units based on one property do not generally coincide with units based on another, and their boundaries commonly cut across each other. It is not possible, therefore, to express all of the different properties with a single set of stratigraphic units; different sets of units are needed (see Figure 1 ). At the same time, the general unity of stratigraphy should be emphasized. While many different kinds of units are needed to express the variations in all of the many different properties and attributes of the rocks, still, these units are closely related. They concern only different aspects of the same rocks, and they are intimately involved with one another in achieving the same major goals of stratigraphy—to improve our knowledge and understanding of the Earth's rock bodies and their history.

Abstract Stratigraphy, from the Latin stratum and the Greek graphia, has traditionally been considered the descriptive science of rock strata. In the last few decades, the critical value to stratigraphy of the information provided by nonlayered rock bodies—sedimentary as well as intrusive igneous rocks and massive metamorphic rocks of undetermined origin—has become evident. Non-layered rock bodies not only are the source of geochronometric (numerical) ages determined by isotopic methods, but they also provide crucial age information through the establishment of their cross-cutting and boundary relationships with layered and/or nonlayered rocks with which they are associated. The definition of stratigraphy should, therefore, be 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. As such, stratigraphy is concerned not only with the original succession and age relations of rock bodies, but also with their distribution, lith-ologic composition, fossil content, and geophysical and geochemical properties—indeed, with all observed properties and attributes of rock bodies and their interpretation in terms of environment or mode of origin and of geologic history. All classes of rocks—igneous and metamorphic as well as sedimentary, unconsolidated as well as consolidated—fall within the general scope of stratigraphy and stratigraphic classification.

Abstract Stratigraphy makes use of numerous named divisions of the rock bodies making up the Earth's crust. It is essential that these named units have their attributes clearly stated and their boundaries clearly defined so that all who use them will start with the same basic understanding of their meaning and so that there will be a common standard for their identification away from the place where they were defined and named. An area of exposure (or a well, or mine) that may be examined and studied by those interested provides an essential part of the establishment of a stratigraphic unit and a useful aid to its identification—a stratotype (type section) for layered sedimentary and volcanic sequences, a type locality for units composed of nonlayered igneous or meta-morphic rocks.

Abstract Lithostratigraphic units are bodies of rocks, bedded or unbedded, that are defined and characterized on the basis of their observable lithologic properties. All stratigraphic units are composed of rock and thus have “rock character,” but only lithostratigraphic units are differentiated on the basis of the kind of rock: limestone, sandstone, sand, tuff, claystone, basalt, granite, schist, marble, and so on. The recognition of such units is useful in visualizing the physical picture of the Earth's rocks, in working out rock sequences, in determining local and regional structure, in investigating and developing natural resources, and in determining the origin of rocks. Lithostratigraphic units are the basic units of geologic mapping and are an essential element of the stratigraphy of the area. Lithostratigraphic classification is usually the first approach in stratigraphic work in any new area and is always an important key to geologic history even if no ages are available from either fossils or isotopic age determinations (Figure 3 ).

Abstract Unconformity-bounded units are bodies of rocks bounded above and below by significant unconformities. Unconformity-bounded units are generally composed of diverse types of any kind or kinds of rocks (sedimentary, igneous, metamorphic, or any combination of two or more of these kinds). Unconformity-bounded units are mappable stratigraphic units differentiated and set apart from underlying and overlying units only by being separated from them by their bounding stratigraphic discontinuities. Lithologic properties, fossil content, and chronostratigraphic span of the rocks on either side of a bounding unconformity are significant for the recognition of an unconformity-bounded unit only to the extent that they serve to recognize the boundary unconformity. Lithostratigraphic, biostratigraphic, and chronostratigraphic units will continue to be those most frequently used in stratigraphic work, but in certain areas and for certain purposes, unconformity-bounded units are invaluable stratigraphic units, almost “natural” units, which the stratigrapher may be able to use for a clear and pragmatic approach to stratigraphic analysis and for a descriptive, lucid interpretation of geologic history. Unconformity-bounded units lend themselves, for instance, to the expression of those aspects of the geologic development of the Earth dealing with its orogenic episodes, its epeirogenic cycles, and its phases of eustatic sea-level changes. These geological events are commonly recorded by unconformities in the stratigraphic succession. Unconformity-bounded units, for this reason, have sometimes been considered to be equivalent to “sedimentary cycles” or tectonically controlled stratigraphic units: stratotec-tonic, tectostratigraphic, tectonostratigraphic, or tectogenic units; tectonic cycles; tectosomes; structural or tectonic stages; and so on. All of these types

Abstract Biostratigraphic units (biozones) are bodies of rock strata that are defined or characterized on the basis of their contained fossils. Biostratigraphic units exist only where the particular diagnostic biostratigraphic feature or attribute on which they are based has been identified. Biostratigraphic units are, therefore, descriptive units based on the identification of fossil taxa. Their recognition depends on the identification of either their defining or characterizing attributes. Biostratigraphic units may be enlarged to include more of the stratigraphic record, both vertically and geographically, when additional data are obtained. In addition, since they depend on taxonomic practice, changes in their taxonomic base may enlarge or reduce the body of rocks included in a particular biostratigraphic unit. Biostratigraphic units are geographically as extensive as their particular diagnostic taxa. A biostratigraphic unit may be based on a single taxon, on combinations of taxa, on relative abundances, on specified morphological features, or on variations in any of the many other features related to the content and distribution of fossils in strata. The same interval of strata may be zoned differently depending on the diagnostic criteria or fossil group chosen. There are thus several kinds of biostratigraphic units. Because of this diversity of possible biostratigraphic units, gaps or overlaps frequently occur both vertically and laterally between the different kinds of biozones, between biozones based on different fossil groups, or even between biozones of the same kind or based on the same fossil group. Biostratigraphic units are distinct from other kinds of stratigraphic units in that the

Abstract Measurable magnetic properties of rocks, such as magnetic susceptibility and the intensity and direction of natural remanent magnetization (NRM), can be used in stratigraphic classification. NRM may indicate a number of useful properties of the magnetic field: reversals of polarity, the dipole-field-pole position (which shows apparent polar wander due to plate motions), nondipole components (secular variation), and variations in field intensity. Where any of these characters vary stratigraphically, they may be the bases for related but different kinds of stratigraphic units known collectively as magnetostratigraphic units (magnetozones). The magnetic property most useful in stratigraphic work is the change in the direction of the remanent magnetization of the rocks, caused by reversals in the polarity of the Earth's magnetic field. Such reversals of the polarity have taken place many times during the geologic history of the Earth. They are recorded by the rocks because the rocks become magnetized in the direction of the Earth's magnetic field at the time of their formation. If it can be demonstrated that the direction of the magnetic polarity as measured today in the rocks is indeed the direction originally acquired by those rocks, rather than the result of later remagnetization, then the changes of the direction of the magnetic polarity recorded in a stratigraphic sequence can be used as the basis for the subdivision of the sequence into units characterized by their magnetic polarity. Such units are called magnetostratigraphic polarity units. A magnetostratigraphic polarity unit is present only where this property can be identified in the rocks.

Abstract Chronostratigraphic units are bodies of rocks, layered or unlayered, that were formed during a specified interval of geologic time. The units of geologic time during which chronostratigraphic units were formed are called geochronologic units. The relation of chronostratigraphic units to other kinds of stratigraphic units is discussed in Chapter 10.

Abstract The categories within stratigraphic classification are all closely related. All deal with the rocks of the Earth's crust, with the picture of the stratified Earth as it presently exists, and with the history of the Earth as interpreted from its rocks. Each category, however, is concerned with a different property or attribute of the rocks and a different aspect of Earth history. The relative importance of the different categories varies with circumstances. Each is important for particular purposes. Lithostratigraphic units are the basic units of geologic surface or subsurface mapping, and lithostratigraphic classification is usually the first approach in stratigraphic work in any new area. Wherever there are rocks, it is possible to develop a lithostratigraphic classification even when no other stratigraphic procedures are feasible. Lithostratigraphic units are based primarily on the lithologic properties of rocks—sedimentary, igneous, and metamorphic. The fossil content of lithostrati-graphic units may in certain cases be an important distinguishing element in their recognition, not because of the age significance of the fossils but because of their diagnostic lithologic (physical) properties. Coquinas, algal reefs, radio-larites, oyster beds, and coal beds are good examples. Inasmuch as each lithostratigraphic unit was formed during a specific interval of geologic time, it has not only lithologic significance but also chrono-stratigraphic significance. The concept of time, however, properly plays little part in establishing or identifying lithostratigraphic units and their boundaries. Lithologic character is generally influenced more strongly by conditions of formation than by time of origin; similar rock types are repeated

Abstract This reprint of the 1994 volume was produced at the request of the IUGS International Commission on Stratigraphy. The purpose of the 1994 volume was to promote international agreement on principles of stratigraphic classification and to develop an internationally acceptable stratigraphic terminology and rules of stratigraphic procedure. At the time of its first printing, this second edition was the most up-to-date statement of international agreement on concepts and principles of stratigraphic classification and a guide to international stratigraphic terminology. The first edition, published in 1976, was a significant contribution toward international agreement and improvement in communication and understanding among earth scientists worldwide. The revised, second edition updated and expanded the discussions, suggestions, and recommendations of the first edition, expansions necessitated by the growth and progress of stratigraphic ideas and the development of new stratigraphic procedures since release of the first edition.

Abstract Because energy is essential to provide the basic needs of humanity, namely food, clean fresh water, fuel for transportation, the generation of electricity, and the production of heat, it is at the core of economic and social activity; and because energy is consumed by people, estimates of the consumption of energy during the 21st century need to be based on projections of the size, composition, and mode and amount of energy use of the human population of the world. Estimates of the possible supply of energy are based on the availability of the presently known sources: principally oil, natural gas, coal, and hydroelectric and nuclear power. The development of these estimates is the objective of this study. They support the conclusion that, although the global distribution of energy sources is obviously uneven, during the 21st century, there will be sufficient sources to adequately satisfy the demand for energy of a human population whose growth rate shows signs of starting to level off.

Abstract The rate of growth of the world’s human population, alarmingly rapid during the last couple of centuries, slowed down appreciably in the late 20th century in the developing and developed countries alike. However, the human population continues to grow slowly in the developed countries and faster in the Third World, particularly in sub-Saharan Africa. The developing countries increased their share of the total world population from 67% in 1950 to 79% in 2000. Total energy consumption, as a result, also increased faster in the developing than in the developed countries. The fossil fuels (oil, natural gas, and coal) provided the bulk of the energy consumed in the world in the last 50 years. Only hydroelectric power and, since 1950, nuclear power contributed additional, albeit smaller, amounts of energy. Energy consumption per capita rose worldwide since the mid-20th century until the early 1970s. Since then, it has grown at a much lower rate everywhere, even remaining essentially unchanged in some countries. Energy consumption per capita in the developed countries in the last 50 years has been much higher (7–10 times higher) than that in the developing countries and 2–4 times higher in the United States than in the rest of the developed countries.

Abstract The growth rate of the world’s human population decreased during the late 20th century. It should be expected to continue to decrease during the 21st century. Three projections are favored that show the world’s population increasing from 6 billion at the end of the 20th century to either 10, 11, or 12 billion by 2100. In all three projections, it is estimated that the percentage of the world’s population living in the developing countries will reach about 90% in 2100. Energy consumption per capita in the 21st century is predicted to decrease in the developed countries, probably to increase moderately in the developing countries, and, as a result, to increase in the world as a whole. Given that the developing countries will contain the great majority of the world’s people during the 21st century, the correct estimation of their future energy consumption will be critical in forecasting the total energy consumption in the world. Even a modest increase in the energy consumption per capita in the developing countries will result in their total energy consumption surpassing that of the developed countries during the first half of the 21st century; by 2100, the developing countries could be consuming three times as much energy as the developed countries. Will this be possible?