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Quaternary Period


Abstract

This page describes the Quaternary Period, including stratigraphy, paleogeography, and famous lagerstätten, followed by a sketched outline of some of the major evolutionary events.

Keywords: Quaternary, Quaternary biota, fossil record, evolution

Introduction

The Quaternary Period comprises roughly the last two and a half million years of Earth history, up to and including the present. Globally, it is the most widely used unit in field mapping (Ogg et al. 2008) and is almost certainly the most intensively researched. Despite this, the definition and rank are highly controversial (see below) and many authorities do not recognise the Quaternary as a distinct geochronological unit at all, preferring to subsume the corresponding time interval within the Neogene.

 
 

Related Topics


Further Reading

  • Ogg et al. 2008: The Concise Geologic Time Scale. Cambridge.
       
       

      Stratigraphy

      Historical Development

      The following excellent account is quoted from Ogg et al. 2008, p. 149: ‘Despite being the most widely used unit in field mapping and having the greatest number of active researchers, the interval known as Quaternary is unique among chronostratigraphic subdivisions in having the most controversial definition and rank. The convoluted history and divergent concepts of Quaternary usage is fraught with opinionated debate, beginning with the early International Geological Congresses which considered relegating Quaternary to be an unranked synonym for a vaguely defined Pleistocene epoch (1894) or “Modern” period (1900). The association of Quaternary with the “Ice Ages” created another problem after the investigation of new regions, improved dating methods and deep-sea oxygen isotope records. The onset of these continental glaciations was discovered to begin much earlier in the Neogene than the ratified base of the Pleistocene Series.’

      Lower (Neogene–Quaternary) Boundary

      ‘In 1983, the base Pleistocene GSSP was ratified at Vrica, Italy, near the top of the Olduvai magnetic Subchron [2.58 Ma; Cohen et al. 2015], but the decision “was isolated from other more or less related problems, such as … status of the Quaternary.” The Gelasian Stage was later created (1996) to fill the “gap” between this GSSP and the “traditional” span of the Piacenzian Stage of the Pliocene Series’ (Ogg et al. 2008).

      Upper Boundary

      The Quaternary Period is unique in having no upper boundary as such; i.e., the upper boundary of the Quaternary is the present.

      Chronology

      The Quaternary is presently defined as the interval from 2.58 Ma to the present.

      Paleogeography

      Major Tectonic Events

      In general, the Quaternary world was little different from the present, tectonically. Changes in land and sea, the formation and inundation of land bridges between continents, for example, were more likely due to climate-induced sea level changes rather than to tectonism.

      One probable exception is the formation of the land bridge between North and South America, created by the emergence of the Isthmus of Panama. “Formation of the Isthmus of Panama involved subduction of the Pacific-Farallon Plate beneath the Caribbean and South American plates, ultimately driving the development of a volcanic arc on the trailing edge of the Caribbean Plate. This initial Panama Arc began to form approximately 73 Ma ... as the Caribbean Platemoved eastward, arriving at its current position by ~50 Ma. The North and South American plates continued to move westward past the Caribbean Plate after this time. In addition to their east-west (strike-slip) motion, the South American and Caribbean plates also acquired a north-south component of convergence, leading to the collision of the Panama Arc with South America” (O’Dea et al. 2016, p. 1).

      The isthmus is conventionally believed to have formed in the late Neogene, about 3 million years ago. An alternative and widely challenged theory argues for a land bridge as old as 15 Ma. However, a comprehensive, multidisciplinary analysis of geological, paleontological, and molecular records (O’Dea et al. 2016) confirmed the conventional wisdom and concluded that their “independent lines of evidence converge upon a cohesive narrative of gradually emerging land and constricting seaways, with formation of the Isthmus of Panama sensu stricto around 2.8 Ma. The evidence used to support an older isthmus is inconclusive, and we caution against the uncritical acceptance of an isthmus before the Pliocene” (abstract).

      The ecological effects from the the migration of plants and animals between the two continents, and the climatic changes arising from changed ocean currents, would profoundly shape the Quaternary world.

      Land and Sea

      In fossil sediments in the area around the Panama Canal, coral reefs, mangroves, and deltaic sediments ... demonstrate that parts of the Panama Arc were emergent since at least 30 Ma. [But,] until around 4 Ma, there was little taxonomic or ecological difference in shelf benthic and nektonic communities between the Tropical Eastern Pacific and the Caribbean..., demonstrating easy movement of water carrying larvae or adults between the oceans…. [However,] a regional extinction across the Caribbean between 4 and 2 Ma ... was highly selective against animals suited to high planktonic productivity..., implicating declining nutrients due to the restriction of Pacific waters entering the Caribbean, most likely caused by the emergence of the Panama Arc and formation of the Isthmus” (O’Dea et al. 2016, p. 4).

      Climate

      Paleontology

      General Characteristics

      In general, the Quaternary biota is little different from what we see around us today. The most familiar departures from extant living organisms are, of course, the large, specialised “ice age” animals such as mammoths, woolly rhinoceros, etc., comprising the Pleistocene megafauna. However, we should not forget all of the smaller plants and animals which have gone extinct in the past two and a half million years, many due to human predation or habitat destruction.

      Major Taxa

      Starter list:

      Mammut americanum (mastodon)

      Mammuthus primigenius (mammoth)

      Smilodon spp. (sabre-tooth cats)

      Coelodonta antiquitatis (woolly rhinoceros)

      Major Biotic Events

      Homonin Evolution

      The earliest fully bipedal human ancestor known is the 4 Ma old Australopithecus afarensis, first recognised from the famous fossil known as Lucy. Subsequently, two main lines of pre-human evolution diverged: the australopithecines, which eventually became extinct, and those given the genus name Homo, beginning with an unnamed ~2.5 Ma old fossil, rapidly succeeded by Homo rudolfensis. Two further species, Homo habilis and H. ergaster overlap through much of the interval 2 to 1.5 Ma; the latter seems more likely to have been the direct human ancestor.

      Homo erectus is the only recognised representative of the genus between about 1.2 and 0.7 Ma; some interpretations place it on the direct ancestral line to modern humans, others consider H. ergaster to have been directly ancestral to H. heidelbergensis, which first appears about 0.6 Ma, and from there to modern H. sapiens. However, if H. erectus is not directly ancestral to H. heidelbergensis and modern man, we are left with a ~900,000 year gap in which the true intermediaries are unknown.

      Anatomically modern H. sapiens first appears close to 200,000 years ago. The oldest well-dated fossils are the Omo I and Omo II fossils from Kibish, Ethiopia (McDougall et al. 2005).

      The Great American Biotic Interchange

      Some dispersal since at least the Miocene; probably dispersal by usual rafting etc. across narrow sea.

      “The Great American Biotic Interchange ... is characterized by a surge in successful dispersals in both directions beginning around 2.6 Ma, traditionally defined as beginning with the arrival of the South American porcupine Erethizon in North America..., and various members of the North American families Mustelidae, Canidae, and possibly Gomphotheriidae, along with the extinct horse Hippidion, successfully colonizing South America at the same time.... This wave of successful dispersals by many large mammals is widely considered convincing evidence that animals could, at this time, have walked dry-shod across a fully formed land bridge” (O’Dea et al. 2016, p. 6).

      Lagerstätten

      Rancho La Brea Tar Pits: Los Angeles, California; various taxa – Dire wolves are the most common large mammals, saber-toothed cats and coyotes also common; the animals were trapped in the asphalt mostly between about 50,000 and 11,000 years ago.

      Extinctions

      Two celebrated “mass” extinctions are associated with the Quaternary: the extinction of the Pleistocene megafauna, and the so-called “sixth extinction” which, its proponents believe, is going on around us right now.

      The iconic Pleistocene megafauna – including woolly mammoths, sabre-tooth tigers, etc. – became extinct at the end of the last glacial interval, the Würm glaciation. It is called the megafauna extinction because, at least in the Americas and northern Eurasia, it tended to be large animals that were most affected. Human impact (hunting) and climate change (global warming following the the Würm glaciation) have been implicated as major causes, although the relative importance of each is still being debated vigorously, and other contributing agents cannot be categorically ruled out either.

      Whole books have been written about the “sixth extinction” which, if it is real, is largely a consequence of habitat destruction by humans. The difficulty with recognising the modern world as a mass extinction in progress is that there is still relatively little detailed quantitative data to establish a reliable background level, or baseline, of what is “normal” species turnover of the millions of small plants and animals which, often, do not fossilise well. However, there can be little doubt that – again – large animals are going extinct at an unprecedented rate. It will be truly remarkable if people living in the next century will ever see a living black rhinoceros or an Amur leopard.

      New Zealand Occurrences

      Present day New Zealand is shaped by a tectonic regime comprising subduction to the north east (Hikurangi Trough), back arc extension through the Taupo Volcanic Zone, and crustal collision-driven mountain building in the southern axial range. Land area has generally increased over the past 5 million years, supplying “vast quantities of sediment to low-lying areas, the prograding inner continental shelf and offshore sedimentary basins” (Edbrooke 2017, p. 32).

      References

      Cohen, K.M.; Finney, S.C.; Gibbard, P.L.; Fan, J.X. 2015: The ICS international chronostratigraphic chart v 2015/01. Episodes 36: 199-204.

      Edbrooke, S.W. 2017: The geological map of New Zealand. GNS Science Geological Map 2: 1-183.

      McDougall, I.; Brown, F.H.; Fleagle, J.G. 2005: Stratigraphic placement and age of modern humans from Kibish, Ethiopia. Nature 433: 733-736. Nature.

      O’Dea, A.; Lessios, H.A.; Coates, A.G.; Eytan, R.I.; Restrepo-Moreno, S.A.; Cione, A.L.; Collins, L.S.; de Queiroz, A.; Farris, D.W.; Norris, R.D.; Stallard, R.F.; Woodburne, M.O.; Aguilera, O.; Aubry, M.-P.; Berggren, W.A.; Budd, A.F.; Cozzuol, M.A 2016: Formation of the Isthmus of Panama. Science Advances 2 (8): 1-11.

      Ogg, J.G.; Ogg, G.; Gradstein, F.M. 2008: The Concise Geologic Time Scale. Cambridge: 1-177.


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