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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 37 (1953)

Issue: 10. (October)

First Page: 2407

Last Page: 2421

Title: Designation of Stratigraphic Units

Author(s): Harry E. Wheeler (2), V. Standish Mallory (3)


A utilitarian "stratigraphic code" should be sufficiently flexible to permit freedom in the selection and naming of units, and should encourage the designation of stratigraphic and map units which fulfill the needs of each field of specialization, but should employ terms with uniform connotation in all fields.

Cases involving designation of stratigraphic units from Cambrian to Tertiary are cited which indicate that the foregoing aims are attainable under the following conditions.

1. All stratigraphic units (lithic, biologic, or chronologic) are potentially employable as map units, and provision should be made for such application. However, only rock units, because of their objectivity, are recommended for general use as map units.

2. Geologic maps based on these various kinds of units (or their combinations) should be labeled as to type, and their units designated accordingly. Biostratigraphic units, for example, should not be called formations.

3. Rock units may effectively terminate laterally by gradation, pinch-out, faulting, transection by an intrusion, erosion, deep burial, and arbitrary cut-off (where a rock unit changes content and identity or rank without mappable lithologic contact). Recognition of the arbitrary cut-off as standard stratigraphic and mapping procedure would indicate acceptance of the following items.

4. A unit of one rank may retain its identity as parts of two or more units of greater rank.

5. Intertongued members should be assigned to one or the other of the formations involved--not alternately to each.

6. The term, tongue, should be abandoned for formal rock-unit designation.

7. Schemes of terminology employing vertically successive alternations of similar names (except in cases of structurally induced duplication) are unnecessary and needlessly compromise the law of superposition.

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