This is a geochronolgy time spiral. Credit: United States Geological Survey.

Geochronology/Paleozoic is the science of applying dates in the past to Paleozoic rocks. In many situations fossils and artifacts may yield dates applicable to the rocks they occur in.

Notations

Let

1. ALMA represent the Asian Land Mammal Age,
2. b2k represent before AD 2000,
3. BP represent before present, as the chart is for 2008, this may require an added -8 for b2k,
4. ELMMZ represent the European Land Mammal Mega Zone,
5. FAD represent first appearance datum,
6. FO represent first occurrence,
7. Ga represent Gegaannum, billion years ago, or -10⁹ b2k,
8. GICC05 represent Greenland Ice Core Chronology 2005,
9. GRIP represent Greenland Ice Core Project,
10. GSSP represent Global Stratotype Section and Point,
11. HO represent highest occurrence,
12. ICS represent the International Commission on Stratigraphy,
13. IUGS represent the International Union of Geological Sciences,
14. LAD represent last appearance datum,
15. LO represent lowest occurrence,
16. Ma represent Megaannum, million years ago, or -10⁶ b2k,
17. NALMA represent the North American Land Mammal Age,
18. NGRIP represent North Greenland Ice Core Project, and
19. SALMA represent South American Land Mammal Age.

"The term b2 k [b2k] refers to the ice-core zero age of AD 2000; note that this is 50 years different from the zero yr for radiocarbon, which is AD 1950 [...]."^[1]

Chronostratigraphy

This is an International Chronostratigraphic Chart. Credit: K.M. Cohen, S. Finney, and P.L. Gibbard, International Commission on Stratigraphy.

Dates have been assigned to specific geologic stratigraphy frames, columns, or columnar units.

Paleozoic time frames

Permian

The Permian lasted from 299.0 ± 0.8 to 251.0 ± 0.4 Mb2k.

Late Paleozoic icehouse

The late Paleozoic icehouse, formerly known as the Karoo ice age, was the climate state 360–260 million years ago (Mya) in which large land-based ice-sheets were present on Earth's surface.^[5]

"The late Paleozoic icehouse was the longest-lived ice age of the Phanerozoic, and its demise constitutes the only recorded turnover to a greenhouse state."^[5]

Carboniferous

The Carboniferous began 359.2 ± 2.5 Mb2k and ended 299.0 ± 0.8 Mb2k.

Pennsylvanian

The Pennsylvanian lasted from 318.1 ± 1.3 to 299.0 ± 0.8 Mb2k.

Mississippian

The Mississippian lasted from 359.2 ± 2.5 to 318.1 ± 1.3 Mb2k.

Prolecanites gurleyi is an index fossil of the Mississippian.^[6]

Middle Mississippian

"This species has been consistently identified with the considerably younger, late Viséan (late Holkerian to Asbian [late Meramecian to early Chesterian]) genus Beyrichoceras Foord, 1903 (type species, Goniatites obtusus Phillips, 1836) (eg, Gordon, 1965, p. 284."^[7]

Visean

Detail of the Tournaisian/Visean boundary is arrowed in the Pengchong section. Credit: François-Xavier Devuyst, Luc Hance, Hongfei Hou, Xianghe Wu, Shugang Tian, Michel Coen, and George Sevastopulo.

"The first appearance of Eoparastaffella simplex in the lineage Eoparastaffela ovalis - Eoparastaffella simplex (foraminifers) [is] the new biostratigraphic criterion to define the base of the Viséan."^[8]

Lower Mississippian

Tournaisian

"The base of the Carboniferous System, Mississippian Sub-System and Tournaisian Stage is defined at the base of Bed 89 in Trench E' at La Serre, France. It coincides with the first appearance of the conodont Siphonodella sulcata within the evolutionary lineage from Siphonodella praesulcata to Siphonodella sulcata."^[9]

Devonian

The Devonian spanned 416.0 ± 2.8 to 359.2 ± 2.5 Mb2k.

Upper Devonian

Famennian

The diagram shows the detailed succession of beds around the GSSP level between beds 31g and 32a. Credit: G Klapper, R Feist, R T Becker and M R House.

Photograph of the succession shows that the GSSP lies between Bed 31g and 32a. Credit: G Klapper, R Feist, R T Becker and M R House.

Fossil is of Platyclymenia intracrostata Credit: Wikipek.

This is another example of Clymenia laevigata. Credit: Hectonichus.

"The boundary for the Frasnian/Famennian Stage Global Stratotype Section and Point (GSSP) [...] is drawn [above] in a section exposed [in the second image above] near the Upper Coumiac Quarry in the southeastern Montagne Noire, France."^[10]

A specimen of Clymenia laevigata from the Upper Devonian Famennian of Poland is on the right.

On the left is a fossil of Platyclymenia intracrostata also from the Famennian of Poland.

Frasnian

Early Devonian

Mimagoniatites is a genus of ammonites from the early Devonian.

"Shell [is] small to large size, evolute, thinly discoidal to discoidal. Whorl cross section of the first two whorls [is] approximately circular, in later whorls subtrapezoidal. Umbilicus [is] narrow to moderately wide, moderately large umbilical window (< 1 mm). Whorl expansion rate increases remarkably from the second whorl on (> 2.5, later up to 3.9). Growth line course [is] biconvex with prominent ventrolateral projection and deep ventral sinus."^[11]

The lower boundary of the genus is "LD3C--LD3D: Anetoceras Range Zone top, 405.5 million years" and the upper boundary is "CZB maureri--sulc.antiqua Zone [19,30], 398.5 million years".^[11]

Geographic distribution: "Devonian of Algeria (2 collections), Canada (1: Nunavut), China (7), the Czech Republic (5), Germany (3), Morocco (13), the Russian Federation (1), Spain (4), Turkey (3), United States (1: Pennsylvania)".^[12]

Silurian

The Silurian spanned 443.7 ± 1.5 to 416.0 ± 2.8 Mb2k.

Hexamoceras hertzeri is an index fossil for the Silurian.^[6]

Hexamoceras is a genus of the Nautiloidea.^[13]

"Rolfe made the important observation that 'Other genera are pre-Devonian and hence cannot be ammonoid aptychi, but Ruedemann's suggestion that aptychi "would naturally also have existed in the Ordovician and Silurian cephalopods" has been largely overlooked'."^[14]

Andean-Saharan glaciation

"A major glacial episode at c. 440 Ma, is recorded in Late Ordovician strata (predominantly Ashgillian) in West Africa (Tamadjert Formation of the Sahara), in Morocco (Tindouf Basin) and in west-central Saudi Arabia, all areas at polar latitudes at the time. From the Late Ordovician to the Early Silurian the centre of glaciation moved from northern Africa to southwestern South America."^[15]

The maximum extent of glaciation developed in Africa and eastern Brazil.^[16]

The Andean-Saharan was preceded by the Cryogenian ice ages (720–630 Ma, the Sturtian and Marinoan glaciations), often referred to as Snowball Earth, and followed by the Karoo Ice Age (350–260 Ma).^[17]

Telychian

Current Telychian GSSP is arrowed parallel to the bedding. Credit: Jeremy R. Davies, Richard A. Waters, Stewart G. Molyneux, Mark Williams, Jan A. Zalasiewicz, Thijs R. A. Vandenbroucke & Jacques Verniers.

On the right is an image of the type locality for the Telychian base GSSP indicated by an arrow which points parallel to the bedding. Older bedding of the Aeronian is to the right. The Telychian GSSP is in the Wormwood Formation, Cefn Cerig quarry.

In the section below for the Aeronian, the lower Telychian is marked with a Ⓣ.

Aeronian

Diagram has the Rhuddanian to early Telychian sea level curves where Ⓐ marks the horizon of the Aeronian GSSP. Credit: Jeremy R. Davies, Richard A. Waters, Stewart G. Molyneux, Mark Williams, Jan A. Zalasiewicz, Thijs R. A. Vandenbroucke & Jacques Verniers.

The arrow indicates the Aeronian lower GSSP perpendicular to the bedding. Credit: Jeremy R. Davies, et al.

The diagram above has the GSSP for the base of the Aeronian symbolized by a Ⓐ. The upper GSSP for the end of the Aeronian is symbolized by a Ⓣ.

On the right is the type locality for the base of the Aeronian indicated by the arrow. Actual beds are perpendicular to the arrow. The base of the Aeronian is in the Cefngarreg Sandstone Formation (formerly Trefawr Formation), Trefawr track section, Crychan Forest, Central Wales.

Ordovician

The Ordovician lasted from 488.3 ± 1.7 to 443.7 ± 1.5 Mb2k.

Upper Ordovician

This is an internal mold of a nautiloid from the Upper Ordovician of northern Kentucky. Credit: Wilson44691.

The image on the right is an over-encrusted, internal mold of a nautiloid from the Upper Ordovician of northern Kentucky.

Actonian

Geological map of the Onny Valley section is with the sample localities. Credit: Thijs R. A. Vandenbroucke, Antonio Ancilletta, Richard A. Fortey and Jacques Verniers.

The "Onny Valley [...] is the type locality for the Actonian and Onnian substages, and a [Site of Special Scientific Interest] SSSI."^[18]

On the right is a geological map of the Onny Valley section together with a strategraphic column, sample localities and the chrono- and lithostratigraphy of the southern Caradoc area (after Rushton et al. 2000).

Sandbian

Nemagraptus gracilis, Sandbian graptolites, are from the Caparo Formation, Venezuelan Andes. Credit: J.C. Gutiérrez-Marco, D. Goldman, J. Reyes-Abril, and J. Gómez.

"The Lower Sandbian Nemagraptus gracilis Zone comprises one of the most widespread, and easily recognizable graptolite faunas in the Ordovician System. The base of the N. gracilis Zone also marks the base of the Upper Ordovician Series, and is internationally defined by the FAD of the eponymous species, with the Global Stratotype Section and Point (GSSP) located at Fågelsång in Scania, southern Sweden (Bergström et al., 2000, 2009)."^[19]

Middle Ordovician

Darriwilian

Abereiddian

Ordovician chart illustrates the main regional series, stage and substage divisions. Credit: Hüseyïn Kozlu, M. Cemal Göncüoğu, Graciela N. Sarmiento & M. Alï Gül.

On the right is an Ordovician chart which illustrates the stratigraphic relationships between the Global Series, Stages and key faunal markers, and the main regional series, stage and substage divisions used in different parts of the world (after Webby 1988).

Here, the Abereiddian is the lower portion of the Llanvirn series, which in turn is the upper portion of Darriwilian Stage, of the upper Middle Ordovician.

Lower Ordovician

Cambrian

The Cambrian lasted from 542.0 ± 1.0 to 488.3 ± 1.7 Mb2k.

Furongian

The Furongian Series includes Cambrian Stage 10, Cambrian Stage 9, and the Paibian Stage.^[20]

Stage 10

The FAD of Lotagnosthus americanus is the primary stratigraphic tool for correlation of the base for Stage 10.^[20]

Stage 9

The FAD of Agnostotes orientalis is the primary stratigraphic tool for correlation of the base for Stage 10.^[20]

Paibian

The "FAD of Glyptagnostus reticulatus [is the primary stratigraphic tool for correlation of the base] for the Paibian Stage."^[20]

Guzhangian

The image shows exposure of the GSSP for the base of the Guzhangian Stage (coinciding with the FAD of Lejopyge laevigata) in the Huaqiao Formation, Luoyixi section, Guzhang County, Hunan Province, China. Credit: Shanchi Peng, Loren E. Babcock, Jingxun Zuo, Huanling Lin, Xuejian Zhu, Xianfeng Yang, Richard A. Robison, Yuping Qi, Gabriella Bagnoli, and Yong’an Chen.

The image shows an exoskeleton of the cosmopolitan agnostoid trilobite Lejopyge laevigata. Credit: Shanchi Peng et al.

"The Global boundary Stratotype Section and Point (GSSP) for the base of the Guzhangian Stage (Cambrian Series 3) is defined at the base of a limestone (calcisiltite) layer 121.3 m above the base of the Huaqiao Formation in the Louyixi section along the Youshui River (Fengtan Reservoir), about 4 km northwest of Luoyixi (4 km southeast of Wangcun), in northwestern Hunan, China."^[20]

"The GSSP level contains the lowest occurrence of the cosmopolitan agnostoid trilobite Lejopyge laevigata [in the image on the left] (base of the L. laevigata Zone)."^[20]

Drumian

Correlation chart of the Cambrian shows the new global chronostratigraphic stage (Drumian; column at left) compared to regional usage in major areas of the world. Credit: Loren E. Babcock, Richard A. Robison, Margaret N. Rees, Shanchi Peng, and Matthew R. Saltzman.

The "FAD of Ptychagnostus atavus [is the primary stratigraphic tool for correlation of the base (GSSP)] for the Drumian Stage".^[20]

"The Global boundary Stratotype Section and Point (GSSP) for the base of the Drumian Stage (Cambrian Series 3) is defined at the base of a limestone (calcisiltite) layer 62 m above the base of the Wheeler Formation in the Stratotype Ridge section, Drum Mountains, Utah, USA. The GSSP level contains the lowest occurrence of the cosmopolitan agnostoid trilobite Ptychagnostus atavus (base of the P. atavus Zone)."^[21]

Stage 5

Observed stratigraphic distribution of trilobites in the lower Wheeler Formation near the base of the Ptychagnostus atavus Zone, Stratotype Ridge section, Drum Mountains, Utah, USA, is modified from Babcock et al., 2004. Credit: Loren E. Babcock, Richard A. Robison, Margaret N. Rees, Shanchi Peng, and Matthew R. Saltzman.

Key agnostoid trilobite species are used for recognition of the base of the Drumian Stage. Credit: Loren E. Babcock, Richard A. Robison, Margaret N. Rees, Shanchi Peng, and Matthew R. Saltzman.

"The polymerid trilobites Ptychoparella (incorporating Elrathina as a junior synonym) and Elrathia have long stratigraphic ranges (Robison, 1964a, 1964b, 1976; Babcock, 1994a) that extend from stage 5 into the lower part of the Drumian Stage (White, 1973) and provide little help in constraining the base of the Drumian."^[21]

On the right are images of key agnostoid trilobite species used for recognition of the base of the Drumian Stage.

"A, Ptychagnostus gibbus (Linnarsson), dorsal exoskeleton in shale, x 8.4, from the Wheeler Formation, c. 25 m above base, south side of Swasey Peak, House Range, Utah (R. A. Robison locality 157); KUMIP 153949. B, Ptychagnostus atavus (Tullberg), cephalon in limestone showing scrobiculate genae, x 8.1, from the Wheeler Formation, 27 m above base, House Range, Utah (R. A. Robison locality 196); KUMIP 153830. C, P. atavus (Tullberg), pygidium in limestone, x 7.8, from same locality as specimen in Figure 6B; KUMIP 153933. D, P. atavus (Tullberg), dorsal exoskeleton from shale with cone-in-cone calcite encrusting ventral surface, x 8.1 from the Wheeler Formation, c. 100 below top, “Swasey Spring quarry”, east flank of House Range, Utah (R. A. Robison locality 114); KUMIP 153930."^[21]

The "Cambrian lobopodian (panarthropod) worm Hallucigenia sparsa [is] from the Burgess Shale (Cambrian Series 3, Stage 5)."^[22]

Stage 4

Stage 3

The FAD of trilobites is the primary stratigraphic tool for correlation of the base for Stage 3.^[20]

Terreneuvian

The Terreneuvian Series includes Cambrian Stage 2 and the Fortunian Stage.^[20]

Stage 2

Hallucigenia sparsa is from the Burgess Shale. Credit: Jean-Bernard Caron, Martin R. Smith, and Thomas H. P. Harvey.

"Hallucigeniids are [...] an important and widespread component of disparate Cambrian communities from late in the Terreneuvian (Cambrian Stage 2) through the ‘middle’ Cambrian (Series 3); their apparent decline in the latest Cambrian may be partly taphonomic. The cone-in-cone construction of hallucigeniid sclerites is shared with the sclerotized cuticular structures (jaws and claws) in modern onychophorans."^[22]

In the image on the right "Hallucigenia sparsa [is] from the Burgess Shale: (a,b) Smithsonian Institution, National Museum of Natural History (NMNH) 83935 (holotype), articulated specimen, showing seven pairs of spines, partially decayed towards the rear, presumed head to the right. (a) composite image of part and counterpart; (b) enlargement of the basal part of the spines; (c,d) Royal Ontario Museum (ROM) 61513, complete specimen showing seven pairs of spines and backscatter image of boxed area (d); (e–i) ROM 57776, backscatter images (overview and close-ups of boxed areas) of spine showing four internal cones and lineations; (g) ROM 61513, backscatter image showing lineations and a distal cone; (j–o) ROM 62269, backscatter images of several spines, showing elemental distribution of carbon (l) and phosphorous (m) and details of ornamentation near spines’ mid-length (n) and base (o) (arrows indicate local disturbances in the rhomboid pattern); (p) ROM 61513, backscatter image showing details of ornamentation showing scales in positive relief (top left) and negative relief below the carbon film. Ba, basal region of spines; C, cone; Li, lineations. Scale bars: (a–d) 1000 µm; (e,j–m) 100 µm; (f–i) 50 µm; (n–p) 10 µm."^[22]

Fortunian

The FAD of Trichophycus pedum is the primary stratigraphic tool for correlation of the base (GSSP) for the Fortunian Stage.^[20]

Precambrian

Def.

1. "the time and geology dated before the Phanerozoic"^[23] or
2. the "eon (or supereon) and rock formations dated before 541.0±1.0 million years ago, coinciding with the first appearance of the fossils of hard-shelled animals"^[23]

is called the precambrian.

Usage notes^[23]

• The International Commission on Stratigraphy, which attempts to standardize the vocabulary of the field, is revising the boundaries between time periods based on physical-science methods rather than the kinds of fossils present.
• The boundary between the Precambrian and the Phanerozoic has been changed from time to time and will be subject to change.

Hypotheses

1. Each time frame or span of time in geochronology has at least one dating technique.
2. Late Ordovician and Upper Ordovician are different time frames.

See also

References

External links

• Global Boundary Stratotype Section and Point (GSSP) of the International Commission on Stratigraphy

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