Paleogene

Last updated
Paleogene Period
66–23.03 million years ago
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FMIB 51606 Map of the Continents, Eocene time.jpeg

Map of Earth during the Eocene

Mean atmospheric O
2
content over period duration
c. 26 vol %
(130 % of modern level)
Mean atmospheric CO
2
content over period duration
c. 500 ppm
(2 times pre-industrial level)
Mean surface temperature over period durationc. 18 °C
(4 °C above modern level)
Key events in the Paleogene
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First Antarctic permanent ice-sheets [1]
An approximate timescale of key Paleogene events.
Axis scale: millions of years ago.

The Paleogene ( /ˈpæl.i.əˌn,-i.-,ˈp.li-,-li.-/ PAL-ee-ə-jeen, -ee-oh-, PAY-lee-, -lee-oh-; also spelled Palaeogene or Palæogene; informally Lower Tertiary or Early Tertiary) is a geologic period and system that spans 43 million years from the end of the Cretaceous Period 66 million years ago (Mya) to the beginning of the Neogene Period 23.03 Mya. It is the beginning of the Cenozoic Era of the present Phanerozoic Eon. The earlier term Tertiary Period was used to define the span of time now covered by the Paleogene and subsequent Neogene periods; despite no longer being recognised as a formal stratigraphic term, 'Tertiary' is still widely found in earth science literature and remains in informal use. [2] The Paleogene is most notable for being the time during which mammals diversified from relatively small, simple forms into a large group of diverse animals in the wake of the Cretaceous–Paleogene extinction event that ended the preceding Cretaceous Period. [3] The United States Geological Survey uses the abbreviation PE for the Paleogene, [4] [5] but the more commonly used abbreviation is PG with the PE being used for Paleocene.

Contents

This period consists of the Paleocene, Eocene, and Oligocene epochs. The end of the Paleocene (55.5/54.8 Mya) was marked by the Paleocene–Eocene Thermal Maximum, one of the most significant periods of global change during the Cenozoic, which upset oceanic and atmospheric circulation and led to the extinction of numerous deep-sea benthic foraminifera and on land, a major turnover in mammals. The term 'Paleogene System' is applied to the rocks deposited during the 'Paleogene Period'.

Climate and geography

The global climate during the Paleogene departed from the hot and humid conditions of the late Mesozoic era and began a cooling and drying trend which, despite having been periodically disrupted by warm periods such as the Paleocene–Eocene Thermal Maximum, [6] persisted until the temperature began to rise again due to the end of the most recent glacial period of the current ice age. The trend was partly caused by the formation of the Antarctic Circumpolar Current, which significantly lowered oceanic water temperatures. A 2018 study estimated that during the early Palaeogene about 56-48 million years ago, annual air temperatures, over land and at mid-latitude, averaged about 23–29 °C (± 4.7 °C), which is 5–10 °C higher than most previous estimates. [7] [8] Or for comparison, it was 10 to 15 °C higher than current annual mean temperatures in these areas; the authors suggest that the current atmospheric carbon dioxide trajectory, if it continues, could establish these temperatures again. [9]

During the Paleogene, the continents continued to drift closer to their current positions. India was in the process of colliding with Asia, forming the Himalayas. The Atlantic Ocean continued to widen by a few centimeters each year. Africa was moving north to meet with Europe and form the Mediterranean Sea, while South America was moving closer to North America (they would later connect via the Isthmus of Panama). Inland seas retreated from North America early in the period. Australia had also separated from Antarctica and was drifting toward Southeast Asia.

Flora and fauna

Mammals began a rapid diversification during this period. After the Cretaceous–Paleogene extinction event, which saw the demise of the non-avian dinosaurs, mammals transformed from a few small and generalized forms that began to evolve into most of the modern varieties we see today. Some of these mammals would evolve into large forms that would dominate the land, while others would become capable of living in marine, specialized terrestrial, and airborne environments. Those that took to the oceans became modern cetaceans, while those that took to the trees became primates, the group to which humans belong. Birds, which were already well established by the end of the Cretaceous, also experienced adaptive radiation as they took over the skies left empty by the now extinct pterosaurs.

Pronounced cooling in the Oligocene led to a massive floral shift and many extant modern plants arose during this time. Grasses and herbs such as Artemisia began to appear at the expense of tropical plants, which began to decline. Conifer forests developed in mountainous areas. This cooling trend continued, with major fluctuation, until the end of the Pleistocene. [10] This evidence for this floral shift is found in the palynological record. [11]

Geology

Oil industry relevance

The Paleogene is notable in the context of offshore oil drilling, and especially in Gulf of Mexico oil exploration, where it is commonly referred to as the "Lower Tertiary". These rock formations represent the current cutting edge of deep-water oil discovery.

Lower Tertiary rock formations encountered in the Gulf of Mexico oil industry usually tend to be comparatively high temperature and high pressure reservoirs, often with high sand content (70%+) or under very thick evaporite sediment layers. [12]

Lower Tertiary explorations include (partial list):

Related Research Articles

Cretaceous Third and last period of the Mesozoic Era 145-66 million years ago

The Cretaceous is a geological period that lasted from about 145 to 66 million years ago (mya). It is the third and final period of the Mesozoic Era, as well as the longest. The name is derived from the Latin creta, "chalk". It is usually abbreviated K, for its German translation Kreide.

Cenozoic Third era of the Phanerozoic Eon 66 million years ago to present

The Cenozoic Era meaning "new life" is the current and most recent of the three geological eras of the Phanerozoic Eon. It follows the Mesozoic Era and extends from 66 million years ago to the present day. It is generally believed to have started on the first day of the Cretaceous–Paleogene extinction event when an asteroid hit the Earth.

The Eocene Epoch is a geological epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period in the modern Cenozoic Era. The name Eocene comes from the Ancient Greek ἠώς and καινός and refers to the "dawn" of modern ('new') fauna that appeared during the epoch.

The Mesozoic Era is an interval of geological time from about 252 to 66 million years ago. It is also called the Age of Reptiles and the Age of Conifers.

Neogene Second geologic period in the Cenozoic Era 23-2.6 million years ago

The Neogene is a geologic period and system that spans 20.45 million years from the end of the Paleogene Period 23.03 million years ago (Mya) to the beginning of the present Quaternary Period 2.58 Mya. The Neogene is sub-divided into two epochs, the earlier Miocene and the later Pliocene. Some geologists assert that the Neogene cannot be clearly delineated from the modern geological period, the Quaternary. The term "Neogene" was coined in 1853 by the Austrian palaeontologist Moritz Hörnes (1815–1868).

The Oligocene is a geologic epoch of the Paleogene Period and extends from about 33.9 million to 23 million years before the present. As with other older geologic periods, the rock beds that define the epoch are well identified but the exact dates of the start and end of the epoch are slightly uncertain. The name Oligocene was coined in 1854 by the German paleontologist Heinrich Ernst Beyrich; the name comes from the Ancient Greek ὀλίγος and καινός, and refers to the sparsity of extant forms of molluscs. The Oligocene is preceded by the Eocene Epoch and is followed by the Miocene Epoch. The Oligocene is the third and final epoch of the Paleogene Period.

The Phanerozoic Eon is the current geologic eon in the geologic time scale, and the one during which abundant animal and plant life has existed. It covers 541 million years to the present, and began with the Cambrian Period when animals first developed hard shells preserved in the fossil record. The time before the Phanerozoic, called the Precambrian, is now divided into the Hadean, Archaean and Proterozoic eons.

Tertiary is a widely used, but obsolete term for the geologic period from 66 million to 2.6 million years ago. The period began with the demise of the non-avian dinosaurs in the Cretaceous–Paleogene extinction event, at the start of the Cenozoic Era, and extended to the beginning of the Quaternary glaciation at the end of the Pliocene Epoch. The time span covered by the Tertiary has no exact equivalent in the current geologic time system, but it is essentially the merged Paleogene and Neogene periods, which are informally called the Lower Tertiary and the Upper Tertiary, respectively.

Placentalia Infraclass of mammals in the clade Eutheria

Placentalia is one of the three extant subdivisions of the class of animals Mammalia; the other two are Monotremata and Marsupialia. The placentals are partly distinguished from other mammals in that the fetus is carried in the uterus of its mother to a relatively late stage of development. The name is something of a misnomer considering that marsupials also nourish their fetuses via a placenta, though for a relatively briefer period, giving birth to less developed young who are then kept for a period in the mother's pouch.

Paleocene–Eocene Thermal Maximum Rapid (in geological terms) global warming, profound changes in ecosystems, and major perturbations in the carbon cycle which started about 55.0 million years ago

The Paleocene–Eocene Thermal Maximum (PETM), alternatively "Eocene thermal maximum 1" (ETM1), and formerly known as the "Initial Eocene" or "Late Paleocene Thermal Maximum", was a time period with more than 5–8 °C global average temperature rise across the event. This climate event occurred at the time boundary of the Paleocene and Eocene geological epochs. The exact age and duration of the event is uncertain but it is estimated to have occurred around 55.5 million years ago.

The Late Cretaceous is the younger of two epochs into which the Cretaceous geological period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous series. The Cretaceous is named after the white limestone known as chalk which occurs widely in northern France and is seen in the white cliffs of south-eastern England, and which dates from this time.

The Maastrichtian is, in the ICS geologic timescale, the latest age of the Late Cretaceous epoch or Upper Cretaceous series, the Cretaceous period or system, and of the Mesozoic era or erathem. It spanned the interval from 72.1 to 66 million years ago. The Maastrichtian was preceded by the Campanian and succeeded by the Danian.

The Danian is the oldest age or lowest stage, of the Paleocene epoch or series, of the Paleogene period or system, and of the Cenozoic era or erathem. The beginning of the Danian age is at the Cretaceous–Paleogene extinction event 66 Ma. The age ended 61.6 Ma, being followed by the Selandian age.

Seymour Island island

Seymour Island is an island in the chain of 16 major islands around the tip of the Graham Land on the Antarctic Peninsula. Graham Land is the closest part of Antarctica to South America. It lies within the section of the island chain that resides off the west side of the peninsula's northernmost tip. Within that section, it is separated from Snow Hill Island by Picnic Passage, and sits just east of the larger key, James Ross Island, and its smaller, neighboring island, Vega Island.

Lukas Hottinger was a paleontologist, biologist and geologist. Hottinger collaborated with the Natural History Museum of Basel (Switzerland).

The natural history of New Zealand began when the landmass Zealandia broke away from the supercontinent Gondwana in the Cretaceous period. Before this time, Zealandia shared its past with Australia and Antarctica. Since this separation, the New Zealand biota and landscape has evolved in near-isolation. The exclusively natural history of the country ended in about 1300 AD, when humans first settled, and the country's environmental history began. The period from 1300 AD to today coincides with the extinction of many of New Zealand's unique species that had evolved there.

Cool tropics paradox

The cool tropics paradox is the apparent difference between modeled estimates of tropical temperatures during warm, ice-free periods of the Cretaceous and Eocene, and the colder temperatures which proxies suggested were present. The long-standing paradox was resolved when novel proxy derived temperatures showed significantly warmer tropics during past greenhouse climates. The low-gradient problem, i.e. the very warm polar regions with respect to present day, is still an issue for state-of-the-art climate models.

The Paleocene, or Palaeocene, is a geological epoch that lasted from about 66 to 56 million years ago (mya). It is the first epoch of the Paleogene Period in the modern Cenozoic Era. The name is a combination of the Ancient Greek palæo- meaning "old" and the Eocene Epoch, translating to "the old part of the Eocene".

The climate across the Cretaceous–Paleogene boundary is very important to geologic time as it marks a catastrophic global extinction event. Numerous theories have been proposed as to why this extinction event happened including an asteroid known as the Chicxulub asteroid, volcanism, or sea level changes. While the mass extinction is well documented, there is much debate about the immediate and long-term climatic and environmental changes caused by the event. The terrestrial climates at this time are poorly known, which limits the understanding of environmentally driven changes in biodiversity that occurred before the Chicxulub crater impact. Oxygen isotopes across the K–T boundary suggest that oceanic temperatures fluctuated in the Late Cretaceous and through the boundary itself. Carbon isotope measurements of benthic foramifinera at the K–T boundary suggest rapid, repeated fluctuations in oceanic productivity in the 3 million years before the final extinction, and that productivity and ocean circulation ended abruptly for at least tens of thousands of years just after the boundary, indicating devastation of terrestrial and marine ecosystems. Some researchers suggest that climate change is the main connection between the impact and the extinction. The impact perturbed the climate system with long-term effects that were much worse than the immediate, direct consequences of the impact.

Cretaceous–Paleogene extinction event End of the era of non-avian dinosaurs

The Cretaceous–Paleogene (K–Pg) extinction event, also known as the Cretaceous–Tertiary(K–T)extinction, was a sudden mass extinction of three-quarters of the plant and animal species on Earth, approximately 66 million years ago. With the exception of some ectothermic species such as the leatherback sea turtle and crocodiles, no tetrapods weighing more than 25 kilograms survived. It marked the end of the Cretaceous period, and with it the end of the entire Mesozoic Era, opening the Cenozoic Era that continues today.

References

  1. Zachos, J. C.; Kump, L. R. (2005). "Carbon cycle feedbacks and the initiation of Antarctic glaciation in the earliest Oligocene". Global and Planetary Change. 47 (1): 51–66. Bibcode:2005GPC....47...51Z. doi:10.1016/j.gloplacha.2005.01.001.
  2. "GeoWhen Database - What Happened to the Tertiary?". www.stratigraphy.org.
  3. Robert W. Meredith, Jan E. Janecka, John Gatesy, Oliver A. Ryder, Colleen A. Fisher, Emma C. Teeling, Alisha Goodbla, Eduardo Eizirik, Taiz L. L. Simão, Tanja Stadler, Daniel L. Rabosky, Rodney L. Honeycutt, John J. Flynn, Colleen M. Ingram, Cynthia Steiner, Tiffani L. Williams, Terence J. Robinson, Angela Burk-Herrick, Michael Westerman, Nadia A. Ayoub, Mark S. Springer, William J. Murphy. 2011. Impacts of the Cretaceous Terrestrial Revolution and KPg extinction on mammal diversification. Science 334:521-524.
  4. https://ngmdb.usgs.gov/fgdc_gds/geolsymstd/fgdc-geolsym-sec32.pdf
  5. https://pubs.usgs.gov/fs/2007/3015/fs2007-3015.pdf
  6. Wing, S. L. (2005-11-11). "Transient Floral Change and Rapid Global Warming at the Paleocene-Eocene Boundary". Science. 310 (5750): 993–996. doi:10.1126/science.1116913. ISSN   0036-8075. PMID   16284173.
  7. Naafs et al. (2018). "High temperatures in the terrestrial mid-latitudes during the early Palaeogene" (PDF). Nature Geoscience. 11 (10): 766–771. doi:10.1038/s41561-018-0199-0. hdl:1983/82e93473-2a5d-4a6d-9ca1-da5ebf433d8b.CS1 maint: uses authors parameter (link)
  8. University of Bristol (30 July 2018). "Ever-increasing CO2 levels could take us back to the tropical climate of Paleogene period". ScienceDaily.
  9. "Ever-increasing CO2 levels could take us back to the tropical climate of Paleogene period". University of Bristol. 2018.
  10. 1925-, Traverse, Alfred (1988). Paleopalynology. Unwin Hyman. ISBN   978-0045610013. OCLC   17674795.CS1 maint: numeric names: authors list (link)
  11. Muller, Jan (January 1981). "Fossil pollen records of extant angiosperms". The Botanical Review. 47 (1): 1–142. doi:10.1007/bf02860537. ISSN   0006-8101.
  12. "Lower Tertiary". Halliburton. Archived from the original on 2011-09-29. Retrieved 2011-07-13.