Pennsylvanian (geology)

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Pennsylvanian
323.2 ± 0.4 – 298.9 ± 0.15 Ma
Chronology
Subdivision of the Carboniferous according to the ICS, as of 2021.[1]

Vertical axis scale: millions of years ago
EtymologyName formalityFormalUsage informationCelestial body

The Pennsylvanian (

subperiods of the Carboniferous Period (or the upper of two subsystems of the Carboniferous System). It lasted from roughly 323.2 million years ago to 298.9 million years ago. As with most other geochronologic units, the rock beds that define the Pennsylvanian are well identified, but the exact date of the start and end are uncertain by a few hundred thousand years. The Pennsylvanian is named after the U.S. state of Pennsylvania, where the coal beds of this age are widespread.[5]

The division between Pennsylvanian and Mississippian comes from North American stratigraphy. In North America, where the early Carboniferous beds are primarily marine limestones, the Pennsylvanian was in the past treated as a full-fledged geologic period between the Mississippian and the Permian. In parts of Europe, the Mississippian and Pennsylvanian are one more-or-less continuous sequence of lowland continental deposits and are grouped together as the Carboniferous Period. The current internationally used geologic timescale of the ICS gives the Mississippian and Pennsylvanian the rank of subperiods, subdivisions of the Carboniferous Period.

Life

Generalized geographic map of the United States in middle Pennsylvanian time

Fungi

All modern classes of fungi have been found in rocks of Pennsylvanian age.[6]

Invertebrates

The major forms of life at this time were the arthropods. Arthropods were far larger than modern ones.

griffinfly Meganeura "flew the skies".[7] It is commonly considered that is because of high oxygen level, however some of those large arthropod records are also known from period with relatively low oxygen, which suggest high oxygen pressure may not have been a primary reason for their gigantism.[8][9]

Vertebrates

collapse
.

For some reason, pelycosaurs were able to reach larger sizes before reptiles could, and this trend continued until the

Most pre-rainforest collapse tetrapods remained smaller, probably due to the land being primarily occupied by the gigantic millipedes, scorpions, and flying insects. After the rainforest collapse, the giant arthropods disappeared, allowing amniote tetrapods to achieve larger sizes.

Subdivisions

The Pennsylvanian has been variously subdivided. The international timescale of the ICS follows the Russian subdivision into four stages:[12]

North American subdivision is into five stages, but not precisely the same, with additional (older) Appalachian series names following:[13][14]

The Virgilian or Conemaugh corresponds to the Gzhelian plus the uppermost Kasimovian. The Missourian or Monongahela corresponds to the rest of the Kasimovian. The Desmoinesian or Allegheny corresponds to the upper half of the Moscovian. The Atokan or upper Pottsville corresponds to the lower half of the Moscovian. The Morrowan corresponds to the Bashkirian.

In the European subdivision, the Carboniferous is divided into two epochs: Dinantian (early) and Silesian (late). The Silesian starts earlier than the Pennsylvanian and is divided in three ages:[15]

References

  1. ^ "Chart/Time Scale". www.stratigraphy.org. International Commission on Stratigraphy.
  2. . Retrieved December 8, 2020.
  3. . Retrieved December 7, 2020.
  4. ^ "Pennsylvanian". Dictionary.com Unabridged (Online). n.d.
  5. .
  6. ^ Blackwell, Meredith, Vilgalys, Rytas, James, Timothy Y., and Taylor, John W. Fungi. Eumycota: mushrooms, sac fungi, yeast, molds, rusts, smuts, etc., February 2008, Tree of Life Web Project
  7. .
  8. .
  9. .
  10. ^ .
  11. ^ Kazlev MA (1998). "Palaeos Paleozoic: Carboniferous: The Carboniferous Period". Archived from the original on March 9, 2012. Retrieved March 30, 2012.
  12. ^ Cohen et al. 2013
  13. ^ Rice, Charles L. "Pennsylvanian system". Contributions to the geology of Kentucky. United States Geological Survey. Retrieved October 26, 2020.
  14. ^ Kues, Barry S. (November 2001). "The Pennsylvanian System in New Mexico— overview with suggestions for revision of stratigraphic nomenclature" (PDF). New Mexico Geology: 103–122. Retrieved October 26, 2020.
  15. . Retrieved October 26, 2020.

External links