|Peripatus Home Page Paleontology >> Neogene Period||Updated: 25-Jun-2018|
AbstractThis page describes the Neogene Period, including stratigraphy, paleogeography, and famous lagerstätten, followed by a sketched outline of some of the major evolutionary events.
Keywords: Neogene, Neogene biota, fossil record, evolution
Hörnes 1853 proposed combining Lyell’s original (1833) Miocene and Pliocene epochs into a new unit, the Neogene, based on his interpretation of mollusc faunas (Steininger et al. 1997). In this original proposal, the Neogene did not include the Quaternary. Various proposals have been advanced at different times to include the Quaternary within the Neogene, and numerous articles can be found which assume just that. To be clear, the current position is that the Neogene does not include the Quaternary: the Cenozoic Era is formally divided into three periods – Paleogene, Neogene and Quaternary – and the Neogene comprises the Miocene and Pliocene epochs only (Cohen et al. 2015).
The Neogene System does not have a type section, as such, because it was not originally conceived as a unit in its own right. Instead, it is an aggregate unit, comprising the Miocene and Pliocene series (epochs) which had been defined much earlier – at least as far back as the eleventh edition of Lyell’s Principles (Lyell 1872, table on p. 135) which in turn refers to an earlier source (Elements of Geology, 6th edition, p. 102).
Lower (Paleogene–Neogene) Boundary
The Paleogene-Neogene boundary is coincident with the base of the Aquitanian Age which in turn defines the base of the Miocene Epoch. The Aquitanian GSSP is formally defined in the Lemme-Carrosio section in northern Italy, located at the 35 m level as measured downward from the top of the section. The horizon corresponds closely with the first appearance of the calcareous nannofossil Sphenolithus capricornutus and with the C6Cn.2n(o) reversal boundary (after Gradstein et al. 2012, p. 925-926).
Upper (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).
Today, the International commission on Stratigraphy places the base of the Neogene at 23.03 Ma and the top at 2.58 Ma (Cohen et al. 2015).
Major Tectonic Events
Isthmus of Panama
“Tectonic collision between South America and Panama began at 23–25 Ma. The collision is significant because it ultimately led to development of the Panamanian Isthmus, which in turn had wide-ranging oceanic, climatic, biologic, and tectonic implications” (Farris et al. 2011, p. 1007).
“Between 25 and 23 Ma, the type of volcanic arc activity underwent a distinct change from hydrous mantle wedge–derived magmatism to localized extensional magmatism, indicating that the arc had impinged on South America … By 15 Ma, continued collision led to a transition from generally deepwater biogenic to siliciclastic sedimentation.... Between 9 and 6 Ma, rates of paleobathymetric change in sedimentary sequences reveal significant deepening across the Panama Arc.... Eustatic sea-level rise could in part be the cause of the deepening during the 9 to 8 Ma interval ..., but later deepening cannot be explained by sea-level change and must therefore have been due to subsidence. … At around 6 Ma, the Panama Arc began rising again … and has continued to do so until the present day. Arc uplift combined with sea-level falls driven by the expansion of the Greenland ice sheet around 3 Ma ... and the establishment of repeated Pleistocene glaciations beginning at 2.6 Ma ... resulted in the land bridge connecting North and South America” (O’Dea et al. 2016, p. 1-2; also see further discussion on the Quaternary page).
“In the deep ocean, divergences in neodymium isotopes … and benthic foraminifera δ13C ... between Caribbean and Pacific sites, as well as an abrupt increase in the Pacific carbonate compensation depth, provide strong evidence that deepwater connection was shut off between 12 and 9.2 Ma. At this time, the deepest part of the sill of the Panama Arc must have shoaled to less than 1800 m and was perhaps as shallow as 1200 m … [W]estern Atlantic surface water salinity began to diverge from eastern Pacific values about 4.6 Ma and reached modern Caribbean values by about 4.2 Ma.... Deep Caribbean δ13C increased toward modern values at the same time, in response to flooding of the Caribbean by nutrient-poor North Atlantic Deep Water.... Finally, Caribbean carbonate preservation improved at 4.6 Ma, likely reflecting the replacement of corrosive Antarctic Intermediate Water by North Atlantic Deep Water as overturning increased in the northern North Atlantic.... The development of a large salinity contrast between the Caribbean and eastern Pacific ... is a particularly strong indication that the Panama Arc was mostly emergent by 4.2 Ma.... Nonetheless, vigorous exchange of near-surface waters between the oceans continued as demonstrated by similarities in the radiolarian..., foraminiferal..., and nannoplankton coccolithophore ... communities of the Caribbean and Tropical eastern Pacific…. Our reviews and new analyses show that, before isthmus formation, the Panama Arc existed as a semi-emergent island chain through which abundant seawater flowed from the Pacific into the Caribbean since at least 30Ma. The arc collided, initially underwater, with South America around 24 Ma and has continued to do so to this day.... Meanwhile, the largest of the interoceanic straits were more than 1200 m deep, permitting massive interoceanic seawater exchange until these deepwater passages were extinguished by 9.2 Ma..., after more than 15 My of collision and uplift. Proximity of emergent land on the Panama Arc to South America increased the probability that terrestrial animals and plants could disperse between the continents across the seaways. Land mammal dispersals began ~20 Ma and trickled on for a further 17 My,most likely via rafting. Shallowseawater continued to be exchanged between the oceans until ~4 Ma whereupon the number of diverging marine species peaked..., and the Caribbean underwent a profound environmental, ecological, and evolutionary transformation ... resulting from significant constriction of the interoceanic seaways. Despite the near completion of a land bridge, ample interoceanic gene flow continued until at least ~3.2 Ma, suggesting that strong currents passed through the straits into the Caribbean, as suggested by models of the shoaling Panama Arc” (O’Dea et al. 2016, p. 3 & 6).
Land and Sea
|Ron Blakey (Northern Arizona University) paleogeographic reconstruction)|
The first recognisable apes had evolved by about 20 Ma ago with the appearance of Dryopithecus (formerly Proconsul) africanus, which may have been ancestral to humans. A great variety of forms appeared shortly after Dryopithecus, particularly in Africa, but with a few exceptions the fossil record becomes more than usually poor between about 14 and 4 Ma ago, and little is known from this period. Molecular evidence suggests that it was during this period, between 5 and 10 Ma ago, that the evolutionary line of humans diverged from that of the other apes.
Major Biotic Events
Molecular evidence suggests that the evolutionary line of humans diverged from that of the other apes sometime between 10 and 5 million years ago. The recently described, 6-7 Ma Sahelanthropus tchadensis discovered at Toros-Menalla in Chad, is the oldest plausible human ancestor known to date. Not much younger, ~6 Ma, is Orrorin tugensis, discovered at Lukeino in Kenya. Together, the two fossil discoveries hint at a diverse and perhaps geographically widespread homonid ancestry, and an older divergence between men and apes than is indicated by most molecular studies. For the present, there is insufficient evidence to be sure.
The earliest fully bipedal human ancestor known is the 4 million year 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.
In the late Neogene, the first of what would later, in the Quaternary, become a major migration of animals, began to leak across the narrow sea separating South and North America. “Around 9 to 8.5 Ma, the sloths Thinobadistes and Pliometanastes, derived from South American ancestors, appeared in North America.... Their success in the north, along with the arrival of the first South American edentate genera Glossotherium and Plaina in Mexico around 4.8 to 4.7 Ma..., is suggestive of their ecological, and therefore competitive, distinction from already established herbivorous mammals in North America.... The first record of North American immigrants in South America is the omnivorous endemic procyonid carnivore Cyonasua at ~7 Ma..., followed by the endemic sigmodontine rodent Auliscomys at ~5 Ma..., both of which are likely to represent much earlier migrations that have yet to be revealed in the fossil record. The South American flightless terror bird Titanis occurred in Texas between about 5.0 and 4.7 Ma.... A close relative of the capybara, Neochoerus, is first recorded present in Mexico around 3.8 Ma, and Glyptotherium is also recorded in Mexico around the same time...” (O’Dea et al. 2016, p. 5).
Foulden Maar: Foulden Maar is an early Miocene volcanic crater lake deposit, and the first lagerstätte to be described from New Zealand. The fossils include leaves, flowers, fish and insects.
The end of the Pliocene marked the beginning of a period of great climatic variability and sea-level oscillations. A study by Pimiento et al. 2017 estimated extinction rates among marine megafauna (mammals, seabirds, turtles and sharks) during this time to be three times higher than in the rest of the Cenozoic, with 36% of Pliocene genera failing to survive into the Pleistocene.
New Zealand Occurrences
Beginning in the latest Oligocene, increased tectonism led to the development of the subduction zone running between north and south Zealandia which separates the Australian and Pacific tectonic plates. Obducted ocean-basin crust was over-thrust onto what is now Northland and Raukumara Peninsula before late Miocene time, when the subduction zone moved eastward towards its present position. Most sedimentary basins around New Zealand accumulated thick mudstones during the Miocene. From the late Miocene, oblique crustal convergence across the Alpine Fault led to rapid uplift of the Southern Alpine range. (After Edbrooke 2017, p. 32.)
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).
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.
Farris, D.W.; Jaramillo, C.; Bayona, G.; Restrepo-Moreno, S.A.; Montes, C.; Cardona, A.; Mora, A.; Speakman, R.J.; Glascock, M.D.; Valencia, V. 2011: Fracturing of the Panamanian Isthmus during initial collision with South America. Geology 39 (11): 1007-1010.
Gradstein, F.M.; Ogg, J.G.; Schmitz, M.D.; Ogg, G.M. 2012: The Geologic Time Scale 2012. Elsevier 1-2.
Hörnes, M. 1853: Mitteilung an Prof. Bronn gerichtet: Wien, 3. Okt., 1853. Jahrbuch für Mineralogie, Geognosie, Geologie und Petrefakten-Kunde: 806-810.
Lyell, C. 1833: Principles of geology, being an attempt to explain the former changes of the Earth's surface, by reference to causes now in operation (First Edition). John Murray, London 3.
— 1872: Principles of Geology (eleventh edition). John Murray, London (2 vols.).
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.
Pimiento, C.; Griffin, J.N.; Clements, C.F.; Silvestro, D.; Varela, S.; Uhen, M.D.; Jaramillo, C. 2017: The Pliocene marine megafauna extinction and its impact on functional diversity. Nature Ecology & Evolution 1: 1100-1106.
Steininger, F.F.; Aubry, M.P.; Biolzi, M.; Borsetti, A.M.; Cati, F.; Corfield, R.; Gelati, R.; Iaccarino, S.; Napoleone, C.; Rögl, F.; Rötzel, R.; Spezzaferri, S.; Tateo, F.; Villa, G.; Zevenboom, D. 1997: Proposal for the global stratotype section and point (GSSP) for the base of the Neogene (the Palaeogene/Neogene boundary). In Montanari, A.; Odin, G.S.; Coccioni, R. (ed.) 1997: Miocene stratigraphy - an integrated approach. Developments in Paleontology and Stratigraphy 15. : 125-147.
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