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Paleontology, basis of practical geochronology

Jurjiz Alexander Jeletzky
Paleontology, basis of practical geochronology
Bulletin of the American Association of Petroleum Geologists (April 1956) 40 (4): 679-706


The all-embracing abstract time exists only as an unknowable, theoretical concept. All practically useful time standards, including that of the everyday physical ("absolute") time, are partial time standards derived from the abstract time and only approaching this latter more or less closely. The term absolute time, as used now, is incorrect and highly misleading; it should be replaced by the term-physical time. Only biological (paleontological) and radioactive partial time standards are available for the deciphering of geological history. The radioactive standard provides the measurable (calibrated) physical ("absolute") time values; the biological standard is non-calibrated and unrelated to the former. Barring locally geochronologically useful bentonitic beds, lava flows, and rhythmic sediments, all physical-stratigraphical criteria are only locally stratigraphically valuable and devoid of any geologic time significance. The geochronological uses of fossils and radioactive processes form the subject of geochronology, which is an independent branch of geology and should not be confused with stratigraphy proper. It is proposed to limit the use of stratigraphy to strictly local or areal arrangement of rock units by physical-stratigraphical criteria; so defined it would lack any geochronological connotation. All hitherto known methods of the physical age determination of the layered rocks are either too crude, or too local in their applicability, or both, to be available for the purposes of the everyday practical geochronology. This situation is not likely to change radically in the near future. Consequently, paleontology is, for the time being, the only basis of practical everyday geochronology. Its units become objective and purely empirical in their nature once they are thoroughly tested. Furthermore, the precision of the paleontological clock is far greater than it is generally realized. The possibility of an unrecognizable homotaxis on the scale materially affecting the reliability of paleontological correlation is denied. The so-called stratigraphical nomenclature now in vogue is confused and over-refined. Only the scales of the practical rock-stratigraphical and geochronological units are fundamentally distinct and practically important. The so-called ideal time stratigraphic (actually geochronological) units are only theoretically valuable, and unimportant as compared with the practical geochronological units; therefore, the ideal geochronological units do not deserve formal recognition. The so-called biostratigraphical units are completely synonymous with the so-called time-stratigraphic units as long as the latter remain practically useful geochronological units. Both terms being misleading, it is proposed to replace them by the term-biochronological units. There are only two minor theoretical, and at that largely semantic, distinctions between the biochronological and the so-called geologic time units, which are not worth formal recognition. As the dual nomenclature of the relative (paleontological) geochronological units is deeply rooted throughout the world, however, the geologic time units (here renamed relative geologic time units) are provisionally retained as a subcategory of the biochronological scale. It is hoped, however, that it shall be possible to abolish this subcategory through international channels. The possible use of the geologic time units as ideal geologic time units is discussed and rejected. A separate category of the physical ("absolute") time units is proposed within the frame of the geochronological classification. Paleontology being the only basis of the practical geochronology, obviously no practically valuable regional or world-wide geochronological subdivision is now possible either in pre-Cambrian rocks or in the great masses of Phanerozoic rocks whose relationships to the nearest fossiliferous rocks are unknown. All geochronological units named in pre-Cambrian are either entirely ideal in their nature or are only local rock-stratigraphical units in disguise. Stage and zone are better considered units of the biochronological than of the relative geologic time subcategory, should the distinction between the two be considered worth formal recognition.

ISSN: 0883-9247
Serial Title: Bulletin of the American Association of Petroleum Geologists
Serial Volume: 40
Serial Issue: 4
Title: Paleontology, basis of practical geochronology
Pages: 679-706
Published: 195604
Text Language: English
Publisher: American Association of Petroleum Geologists, Tulsa, OK, United States
Accession Number: 1959-015687
Categories: GeochronologyStratigraphy
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: table
Source Note: discussion by R. M. Stainforth, p. 2289-2290, Sept. 1956.
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2019, American Geosciences Institute. Reference includes data from Bibliography and Index of North American Geology, U. S. Geological Survey, Reston, VA, United States
Update Code: 1959
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