Cambrian (geology): Difference between revisions
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The name is derived from ''Cambria'', the Roman word for ''Wales'', the area where the rocks of the Cambrian was first studied.<ref>[http://www.isgs.uiuc.edu/glossary.htm Glossary] Illinois State Geological Survey</ref> | The name is derived from ''Cambria'', the Roman word for ''Wales'', the area where the rocks of the Cambrian was first studied.<ref>[http://www.isgs.uiuc.edu/glossary.htm Glossary] Illinois State Geological Survey</ref> | ||
(''See main article'' [[Geologic ages of earth history]]) | |||
==Boundaries== | ==Boundaries== | ||
Revision as of 23:53, 24 April 2007
The Cambrian is both a system of strata and a period of time. The name refers to a chronostatrigraphic or a geochronological unit of geological measure. The Cambrian is roughly the period between 543 to 490 million years ago in the Paleozoic Era of the Phanerozoic Eon. It encompasses four chronostatrigraphic series and ten epochs and correspondingly, four geochronological stages and ten ages.
| Erathem/Era | System/Period | Series/Epoch | Stage/Age |
|---|---|---|---|
| Paleozoic | Cambrian | Furongian | Unnamed |
| Unnamed | |||
| Paibian | |||
| Unnamed | Unnamed | ||
| Drumian | |||
| Unnamed | |||
| Unnamed | Unnamed | ||
| Unnamed | |||
| Unnamed | Unnamed | ||
| Unnamed |
The name is derived from Cambria, the Roman word for Wales, the area where the rocks of the Cambrian was first studied.[1]
(See main article Geologic ages of earth history)
Boundaries
The Cambrian is recognized by the ICS geochronologically as the period from 542 million years ago (with an error factor plus or minus 1.0 mya) to 488.3 (plus or minus 1.7 mya).[2] The lower boundry[3] is characterised by trace fossils, the lowest occurrence of Treptichnus (Phycodes) pedum and a near base of negative carbon-isotope excursion. The end or lower boundry is characterised by Conodont fossils, and the lowest occurrence of Iapetognathus fluctivagus; just above the base of Cordylodus lindstromi conodont Zone, and just below lowest occurrence of planktonic graptolites.
The Cambrian strata is distinctive for a large increase in the fossil record indicating a significant increase in plant and animal life during that time (also referred to as the "Cambrian Explosion") [4]
Historically it has been subdivided into three epochs (not recognized by the ICS)
- Early Cambrian (542 - 513 mya)
- Middle Cambrian (513 - 501 mya)
- Late Cambrian (501 - 488.3 mya)
Regional variations are also in use. An example of the Laurentian Timescale from the Geological Society of America: Laurential Regional Designations[5]
- D Epoch
- Sunwaptan (495 – 490 mya)
- Steptoean (500 – 545 mya)
- C Epoch
- Marjuman (506 – 500 mya)
- Delamaran (512 – 516 mya)
- B Epoch
- Dyeran (516 – 512 mya)
- Montezuman (520 – 516 mya)
- A Epoch (543 – 520 mya)
Currently the Furongian Series (or Epoch) and the Paibian and Drumian Stages (or Ages) are defined and designated by name. [6] The earliest undefined series (unamed) encompasses the as yet unamed Stage 1 and Stage 2 (earliest to latest). Series 2 extends from 521 mya to 510 mya with two stages. Series 3 (from 510 to 501 mya) is composed of Stage 5, the Drumian Stage (or Age). and Stage 7. The final and last series to be created in the Cambrian, the Furongian, encompasses the Paibian Stage, Stage 9 and Stage 10 [7][8][9][10]
| System/Period | Series/Epoch | Stage/Age | Span in millions of years ago |
|---|---|---|---|
| Cambrian | Furongian | ||
| Unnamed | |||
| 492 to 488.3 mya | |||
| 496 to 492 mya | |||
| Unnamed | |||
| Paibian | |||
| 501 to 496 mya |
| System/Period | Series/Epoch | Stage/Age | Span in millions of years ago |
|---|---|---|---|
| Cambrian | Series 3 | ||
| Stage 7 | |||
| 503 to 501 mya | |||
| 506 to 503 mya | |||
| Drumian | |||
| Stage 5 | |||
| 510 to 506 mya |
| System/Period | Series/Epoch | Stage/Age | Span in millions of years ago |
|---|---|---|---|
| Cambrian | Series 2 | ||
| Stage 4 | |||
| 517 to 510 mya | |||
| 521 to 517 mya | |||
| Stage 3 |
| System/Period | Series/Epoch | Stage/Age | Span in millions of years ago |
|---|---|---|---|
| Cambrian | Series 1 | ||
| Stage 2 | |||
| 534.6 to 531 mya | |||
| 542 to 534.6 mya | |||
| Stage 1 |
GSSP
In accordance with ICS rules, a period is defined by an event recorded in rock formations termed the global stratotype section and point (GSSP). The GSSP is the reference point that defines the international “standard” for recognition of the base, or lower boundary, of the period. The initial GSSP of the beginning of the Cambrian Period is in Newfoundland, Canada.[11]
Sources
- Proposed Global Standard Stratotype-Section and Point for the Paibian Stage and Furongian Series (Upper Cambrian) International Subcommission on Cambrian Stratigraphy, International Commission on Stratigraphy (ICS), International Union of Geological Sciences (IUGS).
- Subcommission on Neoproterozoic Stratigraphy International Commission on Stratigraphy (ICS), International Union of Geological Sciences (IUGS).
- EarthTime
References
- ↑ Glossary Illinois State Geological Survey
- ↑ All ICS chronological data are given with boundaries of plus or minus millions of years ago (mya).
- ↑ At the upper most boundary of the Ediacaran system/period in the Neoproterozoic Erathem/Era in the Proterozoic Eonothem/Era of the Precambrian
- ↑ Geologists seek to put an end to blind dates Tom Clarke (2003) Nature|Vol 425: 9 October. Reprinted from www.nature.com/nature
- ↑ 1999 Geologic Time Scale The Geological Society of America. Compilers: A. R. Palmer, John Geissman. Note: Only a few internationally defined ages have been established. These are regional (Laurentian) only. Limits (referred to a "Boundary Picks") were based on dating techniques and fossil records current in 1999. Sources for nomenclature and ages:
- Primarily from Gradstein, F., and Ogg, J., 1996, Episodes, v. 19, nos. 1 & 2; Gradstein, F., et al., 1995,
- SEPM Special Pub. 54, p. 95–128; Berggren, W. A., et al., 1995,
- SEPM Special Pub. 54, p. 129–212; Cambrian and basal Ordovician ages adapted from Landing, E., 1998, Canadian Journal of Earth Sciences, v. 35, p. 329–338; *Davidek, K., et al., 1998, Geological Magazine, v. 135, p. 305–309.
- Cambrian age names from Palmer, A. R., 1998, Canadian Journal of Earth Sciences, v. 35, p. 323–328.
- ↑ Note: All other series and stages are as yet unmamed and referred to simply as "Series" or "Stage", by the ICS.
- ↑ Cambrian Period GeoWhen
- ↑ International Stratigraphic Chart International Commission on Stratigraphy (ICS), International Union of Geological Sciences (IUGS).
- ↑ Subcommission on Neoproterozoic Stratigraphy International Commission on Stratigraphy (ICS), International Union of Geological Sciences (IUGS)
- ↑ Evolving Time Scale EarthTime
- ↑ A new period for a geological time scale Andrew H. Knoll, Malcolm R.Walter, Guy M. Narbonne, Nicholas Christie-Blick (2004) Science. vol. 305, July