Geological Time Units Research Articles

Simplifying the stratigraphy of time

We propose ending the distinction between the dual stratigraphic terminology of time-rock units (of chronostratigraphy) and geologic time units (of geochronology). The long-held, but widely misunderstood, distinction between these two essentially parallel time scales in stratigraphy has been rendered unnecessary by the widespread adoption of the global stratotype sections and points (GSSP-golden spike) principle in defining intervals of geologic time within rock strata. We consider that the most appropriate name for this stratigraphic discipline is chronostratigraphy, which would allow geochronology to revert to its mainstream and original meaning of numerical age dating. This in turn makes the little- used formal term geochronometry redundant. The terms eonothem, erathem, system, series, and stage would become redundant, in favor of eon, era, period, epoch and (disputably) age. Our favored geologic time units may be qualified by early and late, but not by lower and upper. These suggested changes should simplify stratigraphic practice, encompass both stratified and nonstratified rocks, and help geologic understanding, while retaining precision of meaning

Simplifying the stratigraphy of time: Comments and Reply

[Zalasiewicz et al. (2004)][1] have proposed fundamental changes in the definition and application of stratigraphic terminology involving time-rock and geologic-time units that fly in the face of widely accepted principles that have been tried and tested in establishing an international unified

Discussion and reply: Notes on geochronologic and chronostratigraphic units - Discussion

We welcome Walsh's contribution to the discussion of geologic time units and their relevance in regional and international stratigraphic codes. At this time, we do not want to engage in a debate of the merits of his proposals, but we do want to comment on some of the references made to various

The end of the Pleistocene: a general critique of chronostratigraphic classification

Formal Chronostratigraphic Units are defined in theInternational Stratigraphic Guideon the basis of boundary stratotypes and then extended globally as isochronous units. They are unrealistic for application to late‐Quaternary history, which involves events that are demonstrably time‐transgressive owing to measurable lags between the causative force and the geologic response. Natural geologic time units that are diachronous globally are preferred because they represent events identifiable in the stratigraphic record. A similar objection is raised against formal Chronostratigraphy for the pre‐Quaternary: recognizable biostratigraphic or lithostratigraphic units on which the geologic time scale has been built are diachronous globally, for they depend on slow evolutionary or tectonic processes. The imposition of Chronostratigraphic Units that are unrecognizable stratigraphically at a distance away from the type locality introduces an unnecessary terminology in the efforts of stratigraphers to econstruct the geologic history.

Eustasy and Geoid Changes

The real ocean surface-the equipotential surface of the geoid or the geodetic sea level-is rough and uneven and characterized by humps and depressions of several meters. The present geoid configuration cannot have remained stationary back in time. The main question is over what time units geoid changes may have played a significant role. The instability of the geoid configuration has not been considered previously. The geoid may change both horizontally (geographical dislocation of the geoid relief) and vertically (magnitudinal changes in relief). There are numerous variables (during different geological time units) that must have affected the geoid. Geoid changes must certainly have occurred during the Phanerozoic and the Late Quaternary. Holocene data also yield indication of geoid changes. Tide gauge data and Holocene eustatic short-period fluctuations seem to indicate geoid changes even during short-period time units. Geoid changes are related to fundamental geophysical-astronomical problem...

Inherent instability of biostratigraphic zonal schemes

Abstract Biostratigraphic zones other than assemblage zones are absolutely defined by and tied to the taxonomic concepts of their index fossils. They cannot, therefore, be defined by reference to sequences of strata in that they are only as stable as the taxonomy of the zonal fossils. With the proliferation of independent zonal schemes the importance of stages as unifying correlation units grows and so does the need to fix their boundaries in sequences of strata. Increased interest in type and parastratotype sections and boundary sections for both European and New Zealand stages can be expected. The objectives and practice of stratigraphic correlation are not merely to match up strata containing similar fossils but to match strata deposited contemporaneously, and so long as correlation approaches this objective nearly enough for the practical purposes of stratigraphy, and stages are defined in type and standard or parastratotype sequences, the terms timestratigraphic or chronostratigraphic are appropriate. International geological time units are useful and necessary.

Palynological study of the Neogene deposits of the Mecsek Mountains (Hungary)

In the course of the palynological analysis of samples taken from both vertical and horizontal sections across a series of Neogene basins around the Mecsek Mountains, 424 species of 185 genera were described. Palynological data made it possible to reconstruct the succession of subtropical vegetation patterns in relation to geological time units from the Helvetian to the Pannonian. The palaeoclimatological results deduced from each vegetation pattern suggest a change from the warm subtropical climate to a cold subtropical one, a change influenced by local and microclimatic factors. Besides permitting other conclusions to be drawn, the vegetation patterns also support the established stratigraphic subdivision.

Paleontology, Basis of Practical Geochronology

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, an 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. End_Page 679------------------------------

Report 3--Nature, Usage, and Nomenclature of Time-Stratigraphic and Geologic-Time Units as Applied to the Precambrian: STRATIGRAPHIC COMMISSION

Report 3--Nature, Usage, and Nomenclature of Time-Stratigraphic and Geologic-Time Units as Applied to the Precambrian: STRATIGRAPHIC COMMISSION