Pennsylvanian (geology)

"Pennsylvanian period" and "Late Carboniferous" redirect here. For the train, see Pennsylvanian (train).

The Pennsylvanian (/ˌpɛnsəlˈveɪni.ən/ pen-səl-VAYN-i-ən,^[4] also known as Upper Carboniferous or Late Carboniferous) is, on the ICS geologic timescale, the younger of two subperiods (or upper of two subsystems) of the Carboniferous Period. 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-producing beds of this age are widespread.^[5]

Pennsylvanian
323.2 ± 0.4 – 298.9 ± 0.15 Ma PreꞒ Ꞓ O S D C P T J K Pg N
Chronology
−360 — – −355 — – −350 — – −345 — – −340 — – −335 — – −330 — – −325 — – −320 — – −315 — – −310 — – −305 — – −300 — – Paleozoic Devonian Carboniferous Permian Mississippian Pennsylvanian Early Middle Late Early Mid Late Tournaisian Viséan Serpukhovian Bashkirian Moscovian Kasimovian Gzhelian     ← Carboniferous Rainforest Collapse ← Mazon Creek Fossils ← End of Romer's Gap ← Start of Romer's Gap Subdivision of the Carboniferous according to the ICS, as of 2021.^[1] Vertical axis scale: millions of years ago
Etymology
Name formality	Formal
Usage information
Celestial body	Earth
Regional usage	Global (ICS)
Time scale(s) used	ICS Time Scale
Definition
Chronological unit	Subperiod
Time span formality	Formal
Lower boundary definition	First appearance of the Conodont Declinognathodus nodiliferus.
Lower boundary GSSP	Arrow Canyon, Nevada, United States 36°44′00″N 114°46′40″W / 36.7333°N 114.7778°W / 36.7333; -114.7778
Lower GSSP ratified	1996^[2]
Upper boundary definition	First appearance of the Conodont Streptognathodus isolatus within the morphotype Streptognathodus wabaunsensis chronocline.
Upper boundary GSSP	Aidaralash, Ural Mountains, Kazakhstan 50°14′45″N 57°53′29″E / 50.2458°N 57.8914°E / 50.2458; 57.8914
Upper GSSP ratified	1996^[3]

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. Due in part to the high levels of oxygen, arthropods were far larger than modern ones. Arthropleura, a giant millipede relative, was a common sight and the giant dragonfly Meganeura "flew the skies".^[7]

Vertebrates

Amphibians were diverse and common; some were several meters long as adults. The collapse of the rainforest ecology in the mid-Pennsylvanian (between the Moscovian and the Kasimovian) removed many amphibian species that did not survive as well in the cooler, drier conditions. Amniotes, however, prospered due to specific key adaptations.^[8] One of the greatest evolutionary innovations of the Carboniferous was the amniote egg, which allowed for the further exploitation of the land by certain tetrapods. These included the earliest sauropsid reptiles (Hylonomus), and the earliest known synapsid pelycosaurs (Archaeothyris). Small lizard-like animals quickly gave rise to many descendants. Amniotes underwent a major evolutionary radiation, in response to the drier climate that followed the rainforest collapse.

For some reason, pelycosaurs were able to reach larger sizes before reptiles could, and this trend continued until the end of the Permian, during which their cynodont descendants became smaller and nocturnal, as the reptilian archosaurs took over, although dicynodonts would remain megafaunal until their extinction at the end of the Triassic.^[8][9] 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:^[10]

• Bashkirian (oldest)
• Moscovian
• Kasimovian
• Gzhelian (youngest)

North American subdivision is into five stages, but not precisely the same, with additional (older) Appalachian series names following:^[11][12]

• Morrowan stage, corresponding with the middle and lower part of the Pottsville Group (oldest)
• Atokan stage, corresponding with the upper part of the Pottsville group
• Desmoinesian stage, corresponding with the Allegheny Group
• Missourian stage, corresponding with the Conemaugh Group
• Virgilian stage, corresponding with the Monongahela Group (youngest)

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:^[13]

• Namurian (corresponding to Serpukhovian and early Bashkirian)
• Westphalian (corresponding to late Bashkirian, Moskovian and Kasimovian)
• Stephanian (corresponding to Gzelian).

References

1. "Chart/Time Scale". www.stratigraphy.org. International Commission on Stratigraphy.
2. Lane, H.; Brenckle, Paul; Baesemann, J.; Richards, Barry (December 1999). "The IUGS boundary in the middle of the Carboniferous: Arrow Canyon, Nevada, USA" (PDF). Episodes. 22 (4): 272–283. doi:10.18814/epiiugs/1999/v22i4/003. Retrieved December 8, 2020.
3. Davydov, Vladimir; Glenister, Brian; Spinosa, Claude; Ritter, Scott; Chernykh, V.; Wardlaw, B.; Snyder, W. (March 1998). "Proposal of Aidaralash as Global Stratotype Section and Point (GSSP) for base of the Permian System" (PDF). Episodes. 21: 11–18. doi:10.18814/epiiugs/1998/v21i1/003. Retrieved December 7, 2020.
4. "Pennsylvanian". Dictionary.com Unabridged (Online). n.d.
5. Gradstein, Felix M.; James G. Ogg; Alan G. Smith (2005). A Geologic Time Scale 2004. Cambridge University Press. p. 288. ISBN 978-0-521-78673-7.
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. Paul D. Taylor, David N. Lewis (2005). Fossil Invertebrates. The Natural History Museum; First North American edition. p. 160. ISBN 0565091832.
8. Sahney, S.; Benton, M.J.; Falcon-Lang, H.J. (2010). "Rainforest collapse triggered Pennsylvanian tetrapod diversification in Euramerica". Geology. 38 (12): 1079–1082. doi:10.1130/G31182.1.
9. Kazlev MA (1998). . Archived from the original on March 9, 2012. Retrieved March 30, 2012.
10. Cohen et al. 2013
11. Rice, Charles L. "Pennsylvanian system". Contributions to the geology of Kentucky. United States Geological Survey. Retrieved October 26, 2020.
12. 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.
13. Heckel, P.H.; Clayton, G. (2006). "The Carboniferous System. Use of the new official names for the subsystems, series, and stages" (PDF). Geologica Acta. 4 (3): 403–407. doi:10.1344/105.000000354. Retrieved October 26, 2020.

External links

• , Paleomap project. World map from this time period.
• The Carboniferous – 354 to 290 Million Years Ago, University of California Museum of Paleontology. Information on stratigraphies, localities, tectonics, and life.
• , Paleos.com
• US Geological Survey comparison of time scales