The Neogene period is a unit of the geologic time scale starting 23.03 ± 0.05 million years ago (mya). It is the second of two periods that mark our current era, the Cenozoic, beginning at the end of the Paleogene period (and Oligocene epoch). Under the current proposal of the International Commission on Stratigraphy (ICS), the Neogene would consist of the Miocene, Pliocene, Pleistocene, and Holocene epochs and continue until the present (Lourens et al. 2004).
Traditionally, there was a recognition of Primary, Secondary, Tertiary, and Quaternary periods. The use of Primary and Secondary periods has been done away with. While the use of the Tertiary has been widespread and continues, the International Commission on Stratigraphy no longer endorses this term as part of the formal stratigraphic nomenclature, and it is generally considered a "sub-era" that includes the Paleogene and part of the the Neogene (Hinton 2006). In some classifications, the Quaternary likewise has been subsumed into the Neogene and considered a "sub-era," although this proposal remains quite controversial (Hinton 2006). There are proposals to recognize three periods of the Cenozoic, the Paleogene, Neogene, and Quaternary, with the Neogene ending at the close of the Pliocene.
This logical-scientific method of inquiry has been powerful in deducing the reality of our past Earth. In this process, an important scientific principle is a willingness to re-examine findings and hypotheses, as is reflected in the current Neogene-Quaternary controversy.
|Cenozoic era (65-0 mya)|
The Neogene traditionally ended at the end of the Pliocene epoch, just before the beginning of the Quaternary period—many time scales show this division. However, there is a movement among geologists (particularly Neogene Marine Geologists) to also include ongoing geological time (Quaternary) in the Neogene, while others (particularly Quaternary Terrestrial Geologists) insist the Quaternary to be a separate period of distinctly different record.
The somewhat confusing terminology and disagreement among geologists on where to draw what hierarchical boundaries is due to the comparatively fine divisibility of time units as time approaches the present. It is also a function of the geological preservation that causes the youngest sedimentary geological record to be preserved over a much larger area and reflecting many more environments, than the slightly older geological record. By dividing the Cenozoic era into three (arguably two) periods (Paleogene, Neogene, Quaternary) instead of seven epochs, the periods are more closely comparable to the duration of periods in the Mesozoic and Paleozoic eras.
The ICS has proposed that the Quaternary be considered a sub-era (sub-erathem) of the Neogene, with a beginning date of 2.588 mya—namely the start of the Gelasian Stage. The International Union for Quaternary Research (INQUA) has counterproposed that the Neogene and the Pliocene end at 2.588 Ma., that the Gelasian be transferred to the Pleistocene, and the Quaternary be recognized as the third period in the Cenozoic, citing the key changes in Earth's climate, oceans, and biota that occurred 2.588 mya and its correspondence to the Gauss-Matuyama magnetostratigraphic boundary (Clague et al. 2006). There is concern that there is no scientific justification or historical precedence for the changes the ICS proposes and that the placement of the Quaternary as a "sub-era" will lead to its demise as a term, particularly since Tertiary has been passing out of use leaving only the Quaternary as a "sub-era" (Clague et al. 2006).
|Tertiary sub-era||Quaternary sub-era|
Some continental motion took place during the Neogene, the most significant event being the connection of North and South America in the late Pliocene. Climates cooled somewhat over the duration of the Neogene culminating in continental glaciations in the Quaternary sub-era (or period, in some time scales) that follows, and that saw the dawn of the genus Homo.
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