4/21/2016 Paleocene AccessScience from McGrawHill Education
Paleocene Article by: Haq, Bilal U. Division of Ocean Sciences, National Science Foundation, Arlington, Virginia. Publication year: 2014 DOI: http://dx.doi.org/10.1036/10978542.483400 (http://dx.doi.org/10.1036/10978542.483400)
Subdivisions Tectonics, oceans, and climate Life Bibliography Additional Readings
The oldest of the seven geological epochs of the Cenozoic Era, and the oldest of the five epochs that make up the Tertiary Period. The Paleocene Epoch represents an interval of geological time (and rocks deposited during that time) from the end of the Cretaceous Period to the beginning of the Eocene Epoch. Recent revisions of the geological time scales place the Paleocene Epoch between 65 to 55 million years before present (MYBP). See also: Cenozoic (/content/cenozoic/118600); Eocene (/content/eocene/236400); Geologic time scale (/content/geologictimescale/286500); Tertiary (/content/tertiary/686000)
The close of the Cretaceous Period was characterized by the disappearance of many terrestrial and marine animals and plants. The dawn of the Cenozoic in the Paleocene Epoch saw the establishment of new fauna and flora that have evolved into modern biota. The concept of the Paleocene as a separate subdivision of the Tertiary was introduced by the paleobotanist W. P. Schimper in 1874. He observed a distinctive assemblage of plant fossils in the http://www.accessscience.com/content/paleocene/483400 1/8 4/21/2016 Paleocene AccessScience from McGrawHill Education lower Eocene nonmarine sediments of the Paris Basin that he separated out as representing an independent epoch. In the older Lyellian classification, this interval was a part of the Eocene Epoch that constituted the oldest part of the Tertiary Period. The Paleocene deposits had lateral equivalents bearing early Tertiary mammals and were devoid of remains of dinosaurs, which had become extinct at the end of the Cretaceous Period. Schimper also noticed that the Paleocene flora contained numerous components that are now typical of Northern Hemisphere, in contrast to the Cretaceous when Southern Hemispheric floras prevailed.
Modern schemes of the Paleocene subdivide it into Lower and Upper series, and their formal equivalents, the Danian and Selandian stages. Some authors prefer to use a threefold subdivision of the Paleocene, adding the Thanetian at the top. The older, Danian lithofacies generally tend to be calcium carbonate–rich (pure chalk in the Danian type area), whereas the younger, Selandian and Thanetian facies have greater landderived components and are more siliciclastic (sand, sandstone, marl). See also: Chalk (/content/chalk/124200); Facies (geology) (/content/faciesgeology/250000); Marl (/content/marl/407400); Sand (/content/sand/600600); Sandstone (/content/sandstone/600900)
The Danian Stage was proposed by the French geologist E. Desor in 1847 with its type locality near Copenhagen, Denmark. Desor, however, regarded the Danian to be the youngest stage of the Cretaceous. He equated the Danian Chalk and Limestone at the Danish type localities of Faxe and Stevns Klint to the uppermost Cretaceous strata of the Paris Basin largely on the basis of similarities in lithology and the contained echinoidal fauna. It was not until 1897 that another French scientist, A. de Grossouvre, suggested that it would make more sense to place the upper limit of the Mesozoic at the base of the Danian and a major extinction level where ammonites, belemnites, rudistids, and dinosaurs disappeared. The Russian geologist P. Bezrukov in 1934 was the first to actually assign the Danian to the Tertiary, based on paleontological studies in the Ural River sections. In the 1960s the Danian Stage was formally placed in the lowermost Paleocene when it was demonstrated that these strata lacked diagnostic ammonites typical of the Late Cretaceous and contained a microfauna with greater affinity to those of the Tertiary. A major faunal break and hiatus below the Danian and equivalent strata in many sections in the world reinforced its definite Tertiary character.
The Selandian Stage was also defined based on sections in Zealand, near Copenhagen, by the Danish stratigrapher A. Rosenkrantz in 1924. Rosenkrantz, however, did not designate a formal type section for the stage. Later workers have amended the concept of standard Selandian to include all of the temporal equivalent interval of the Late Paleocene series, although the debate about the lithostratigraphic continuity within these sections continues. This stage is, nevertheless, preferable to the previously used upper Paleocene standard stage of Thanetian, which spans only the very upper part of Late Paleocene.
Regional subdivisions of the Paleocene include the Montian Stage, proposed by G. Dewalque in 1868, with a type locality near Mons, Belgium. Like the Danian, the Montian Stage has also been a subject of much discussion. It is now considered to be temporally equivalent to the youngest part of Danian and older part of Selandian (Fig. 1). The Thanetian Stage in Britain was based on the marine Thanet Sands of the Isle of Thanet in Kent. It was first raised to a stage level by E. Renevier in 1873 and is timeequivalent to the upper part of Selandian. The Landenian Stage was proposed by A. Dumont in 1839. It also has its type locality in Belgium and is often used in northwestern
http://www.accessscience.com/content/paleocene/483400 2/8 4/21/2016 Paleocene AccessScience from McGrawHill Education Europe as a stage younger than the Montian. Detailed studies have shown the Belgian Landenian also is equivalent to the British Thanetian. In the United States the Gulf coast Paleocene subdivisions include the Midwayan and the older part of the Sabinian stages. The base of the Midwayan shows a major faunal and lithological hiatus. In California, local stratigraphers have often used the Ynezian Stage to represent an informal equivalent of the upper Paleocene. In the former Soviet Union, the Kachinian Stage has been shown to encompass much of the Paleocene, extending slightly into the earliest Eocene. In New Zealand, the Teurian Stage spans most of the Paleocene, with the overlying Waipawan Stage ranging into the youngest Eocene. In Australia, the Late Paleocene strata are sometimes ascribed to the regional Wangerripian Stage. Paleontologists working with vertebrate fossils have often used their own informal age classifications for assemblage associations. In North American, they subdivide the Paleocene into the Puercan, Torrejonian, and Tiffanian ages, whereas in Europe the terms DanoMontian and Cernayasian have often been used to span the Paleocene in vertebrate paleontological literature. See also: Stratigraphy (/content/stratigraphy/659000)
Fig. 1 Standard Paleocene stages and their temporal equivalents in Europe, North America, and New Zealand.
Tectonics, oceans, and climate
Several major tectonic events that began in the Mesozoic continued into the Paleocene. For example, the Laramide Orogeny that influenced deformation and uplift in the North American Rocky Mountains in the Mesozoic continued into the Paleocene as a series of diastrophic movements, which ended abruptly in the early Eocene. See also: Orogeny (/content/orogeny/476700)
On the ocean floor the most notable tectonic events were the separation of the Seychelles from the rapidly northwardmoving Indian plate in the early Paleocene, and the initiation of seafloor spreading in the Norwegian Greenland Sea, between North America and Greenland in the late Paleocene. The Indian plate had broken away from eastern Gondwanaland in the Late Cretaceous and started moving relatively rapidly northward some 80 MYA. In the early Paleocene, the spreading ridge between Madagascar and India jumped northeastward toward India. This initiated the spreading between India and the Seychelles Platform and the formation of the ChagosLaccadive transform ridge.
During the Paleocene Epoch, the Indian plate continued its rapid flight across the eastern Tethys Ocean, the ancestral seaway that occupied the position of the modern northern Indian Ocean, to eventually collide with the Asian mainland in the midEocene around 50 MYA. In the Paleocene, the eastern Tethys was also characterized by
http://www.accessscience.com/content/paleocene/483400 3/8 4/21/2016 Paleocene AccessScience from McGrawHill Education another very active transform, the Ninetyeast Ridge. This ridge was formed when the Indian plate moved over a fixed mantle plume hot spot in the Late Cretaceous. See also: Plate tectonics (/content/platetectonics/527000)
The lowerlatitude shallowwater seas, as exemplified by the Tethys seaway, received thick deposits of calcium carbonates during the Paleocene. However, the seaway became progressively narrower and shallower, and the nature of carbonate accumulation changed correspondingly.
The sedimentary record of the Paleocene in the northwestern Atlantic indicates that a relatively calm regime of predominantly calcareous sediments typical of the Late Cretaceous was largely replaced by facies that represents more vigorous bottom waters that packed great erosive power due to increased convective overturn and dynamic ocean bottom currents. Although the deepwater connection between the North and South Atlantic was already established by the Early Paleocene, the South Atlantic sedimentary record indicates that in this basin the extensive erosion on the sea floor did not begin until the Late Paleocene. Sedimentary hiatuses representing this dynamic change in bottomwater regime during various times in the Paleocene are also common in other oceans. Thus, the Paleocene deep ocean can be said to have been characterized by extensive erosion and redeposition of sediments on the deep sea floor, reflecting expanded bottomwater activity, compared to the Cretaceous. See also: Basin (/content/basin/074100)
As a whole, the Cenozoic Era is characterized by a longterm withdrawal of the seas from coastal and inland oceans. In the latest Cretaceous, the global sea level had already begun to fall from the alltime Mesozoic high of the midCretaceous. The CretaceousTertiary boundary event is marked by a general transgression in the Danian, following a sealevel fall in the latest Cretaceous. This trend toward overall regressing seas was further accentuated in the later part of the Paleocene. Whereas the Danian is typified by relatively high sea levels, it is followed by a major fall in the early part of the Selandian that has been recorded in many parts of the world. The restriction of the seas in the Selandian is reflected in the sediment facies of the Paleocene, which changed from more carbonate dominated during the relatively higher sea levels of the Danian, to more terrigenous and siliciclastic in the Selandian. Latest Paleocene once again saw a sealevel rise that continued into the early Eocene. The Selandian sealevel fall, which is estimated at around 120 m, was large enough that it could have exposed extensive areas of the continental margins. Major coastline retreats are followed by stream incision of the shelf, and accordingly there is evidence that in the Selandian the sealevel fall is associated with major episodes of canyon formation, cut by rivers that migrated to the shelves during the eustatic drop. See also: Continental margin (/content/continental margin/159100)
Paleogeographicoceanographic considerations of the Paleocene record (Fig. 2) suggest that the western Tethyan seaway between Europe and Africa was open and a circumglobal Tethys current flowed through it, dominating the tropical oceanographic scene of the Paleocene. Toward the north a major epicontinental seaway, the Ural Sea, separated Asia from Europe through much of the Paleocene and Eocene. Epicontinental gulfs also existed on the Asian, African, and North and South American continents. These shallow interior seas were sites of extensive carbonate deposition, and also may have been prone to high production and preservation of organic matter that is important for hydrocarbon sourcerock accumulation.
http://www.accessscience.com/content/paleocene/483400 4/8 4/21/2016 Paleocene AccessScience from McGrawHill Education
Fig. 2 Paleogeography, oceans, and circulation patterns of the Paleocene. (After B. U. Haq and F. W. B. van Eysinga, Geological Time Table, Elsevier, Amsterdam, 1998)
The establishment of deeper connections between the North and South Atlantic in the Paleocene facilitated enhanced deepwater flow from the northern to the southern basin. Similar to the Cretaceous, the source of deep water in the Paleocene was most likely in the warm low and middle latitudes, rather than the cooler higher latitudes as in the Neogene. Warm saline bottom water was characteristic of this epoch. In the south, the Drake Passage between South America and Antarctica was still closed, although Australia had already separated from Antarctica by Paleocene time. The lack of circumAntarctic flow precluded the geographic isolation of Antarctica and the development of cold deep water from a southern source. See also: Paleoceanography (/content/paleoceanography/483300); Paleogeography (/content/paleogeography/483800)
The isotopic and paleontological climatic proxy indicators all point to an overall rise in global temperatures in the Paleocene that led to a period of peak warming in the latest Paleocene and Early Eocene. A mean seasurface temperature of around 10°C (50°F) in the higher latitudes is indicated by oxygen isotopic analysis of marine plankton. A prominent, relatively cooler interval that coincides with the major lowering of sea level has been recorded in the Late Paleocene. The marine microplankton (foraminifera and calcareous nannoplankton) exhibit latitudinal migrationary patterns that are consistent with major climatic fluctuations indicated by the Paleocene isotopic record. The Selandian sealevel lowering and concomitant climatic cooling is accompanied by a migration of highlatitude microplankton assemblage toward low latitudes in the Atlantic Ocean, while the latest Paleocene is characterized by a poleward migration of warm, lowlatitude assemblages. See also: Geologic thermometry (/content/geologicthermometry/286400); Marine sediments (/content/marinesediments/407000)
Terrestrial floras and faunas corroborate the peak warming in the latest Paleocene and Early Eocene and suggest that the warm tropicaltemperate belt may have been twice its modern latitudinal extent. The temperate floral and faunal elements extended to 60°N, which has been used as an argument to invoke a very low angle of inclination of the Earth's rotational axis in the PaleoceneEocene. Alternatively, the mild, equable polar climates and welladapted physiological responses of plants and animals of those times to local conditions may be enough to explain the
http://www.accessscience.com/content/paleocene/483400 5/8 4/21/2016 Paleocene AccessScience from McGrawHill Education presence of a rich vertebrate fauna on Ellesmere Island in arctic Canada. See also: Climate history (/content/climatehistory/140500); Paleobotany (/content/paleobotany/483200); Paleoclimatology (/content/paleoclimatology/483500)
At the close of the Paleocene Epoch, a prominent carbonisotopic (δ13C) shift occurred in the global carbonate reservoir that coincides with the peak warming at this time. Recent studies have ascribed this to the dissociation of sediments on continental margins that contained methane hydrates. When hydrates dissociate due to reduced hydrostatic pressure or increased temperature on the sea floor, large quantities of methane can be released into the water and atmosphere. In the latest Paleocene, bottomwater temperature increased rapidly with a coincident negative shift of δ13C in the global carbon reservoir by 2.5%. This isotopic change was accompanied by important biotic changes in the oceanic microfauna and was synchronous in the oceans and on land. The rapid (<10,000 years) and prominent 12C enrichment of the global carbon reservoir cannot be ascribed to increased volcanic emissions of carbon dioxide, changes in oceanic circulation, and/or terrestrial and marine productivity. The increased flux of methane from gashydrates into the oceanatmosphere system and its subsequent oxidation to carbon dioxide is held responsible for this isotopic excursion in the inorganic carbon reservoir. Highresolution data support the gashydrate connection to the latest Paleocene is abrupt climate change. Evidence from two widely separated sites, from the lowlatitude and southern highlatitude Atlantic Ocean, indicates multiple injections of methane with global consequences during the relatively short interval at the end of the Paleocene. See also: Hydrate (/content/hydrate/326400)
The Paleocene Epoch began after a meteorite struck the Earth, causing massive extinctions at the end of Cretaceous and decimating a large percentage of the terrestrial and marine biota. On land the last of the dinosaurs are the most familiar casualty of this event. In the oceans, all ammonites, genuine belemnites, rudistids, most species of planktonic foraminifera and nannoplankton, and marine reptiles disappeared at the close of the Cretaceous Period. Even though some groups, such as squids, octopus, nautilus, and a few species of marine plankton, survived, the genetic pool was relatively small at the dawn of the Tertiary Period. The recovery of the marine biota was, however, fairly rapid after the midPaleocene due to overall transgressing seas and ameliorating climates. By the Late Paleocene, the biota was well on its way to explosive evolutionary proliferation and high diversification of the Eocene. In the Paleocene, endemism in marine and terrestrial biota increased. For example, the larger foraminifera, Nummulites, thrived in the shallow seas of the Tethyan margins, but were excluded from the marginal seas of the New World. Planktonic microfauna also show increasing hemispheric and latitudinal provincialism. A new group of warmwater phytoplankton, the discoasters, made their first appearance in the Late Paleocene, and soon thereafter proliferated in the Eocene. The end of the Paleocene Epoch saw marked changes in deepwater circulation of the world ocean that resulted in a massive extinction of the benthic marine species. See also: Extinction (biology) (/content/extinctionbiology/249000)
On land the large dinosaurs, which had been on the decline for over 20 MY, died out at the close of the Cretaceous Period. However, smaller reptiles, including alligators and crocodiles, and some of the land flora escaped extinction and continued into the Paleocene. The Paleocene saw the first true radiation of mammals. The mammals of this epoch were characteristically primitive and small in size (50 cm or 20 in. or less). Their principal record is to be found in terrestrial deposits in Asia and North America. A typical example of Paleocene mammals is provided by the http://www.accessscience.com/content/paleocene/483400 6/8 4/21/2016 Paleocene AccessScience from McGrawHill Education condylarths (oddtoed ungulates), which evolved from a Late Cretaceous mammalian lineage. These small animals (Fig. 3) were ancestral to many carnivores as well as the important group of perissodactyls, which include horses, rhinos, and tapirs. The appearance of the first true grasses at the close of the Paleocene may have helped the later radiation of these animals. Ancestral insectivores, rodents, and primates also had their beginning in the Paleocene. During the early part of this epoch, North and South America were connected temporarily, allowing free migration of animals, but were separated soon thereafter. This led to evolutionary isolation of South America and survival of an archaic fauna dominated by anteaters, armadillos, and opossums, until the Pliocene when the isolation finally ended following the connection of the two continents at the Panama isthmus. Similarly, as the continent of Australia became more isolated geographically, its mammalian fauna, such as the marsupials, became sequestered and more specialized. See also: Dinosauria (/content/dinosauria/196800); Mammalia (/content/mammalia/402500); Paleontology (/content/paleontology/484100)
Bilal U. Haq
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