Arenigium

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system series step ≈ age ( mya )
higher higher higher younger
Ordovician Upper Ordovician Brain antium 443.4
⬍
445.2
Katium 445.2
⬍
453
Sandbium 453
⬍
458.4
Middle Ordovician Darriwilium 458.4
⬍
467.3
Dapingium 467.3
⬍
470
Lower Ordovician Floium 470
⬍
477.7
Tremadocium 477.7
⬍
485.4
deeper deeper deeper older

The Arenigium , also shortened to Arenig (English Arenig or Arenigian) is a chronostratigraphic period from the Ordovician to the lowest Middle Ordovician in the history of the earth . The term could not establish itself in international use and today corresponds to the global chronostratigraphic levels of the Floium , Dapingium and the lowest Darriwilium . The arenigium was most recently used as a period in the hierarchical rank of a series . The Arenigium follows the Tremadocium (regional series and global level) and is followed by the regional series (or level) of the Llanvirnium .

Naming and history

The term Arenig as a period in the history of the earth goes back to Adam Sedgwick , who first used it in a lithostratigraphic sense. In 1845 the "Porphyries of Arenig" are mentioned, in 1852 the "Arenig slates and porphyry" are mentioned, and in his "Synopsis" the relevant profile and time period is referred to as "Arenig porphyry". In all three works there is no clear reference to the introduction of a period, the terms denote a lithostratigraphic unit. Type locality of this unit is Arenig Fawr in Snowdonia ( North Wales ). Henry Hicks and John William Salter were the first authors to eliminate an "Arenig Group"; they too understood the term as a rock unit. They first divided the unit into three sub-units, in 1881 Henry Hicks restricted the Arenig to the lower two parts because the fauna of the upper part differed greatly from the two lower parts. Later the upper part of the "Tremadoc" was transferred to the Arenig in the sense of Hicks. The term Arenig Series has been in use at least since the work of Thomas McKenny Hughes in 1887 . Since then, the term has also been used as a term of time. At the beginning of the 20th century, Gertrude Lilian Elles established a graptolite stratigraphy of Arenig in several works. Four zones are generally recognized, a fifth, globally correlatable graptolite zone, the Tetragraptus approximatus zone, was inserted at the base, although it has not yet been detected in Wales.

For South Wales, Richard Fortey and Robert Owens divided the Arenig Series into three (regional) levels: Moridunian, Whitlandian and Fennian. These three tiers (and the Arenig series) comprise seven trilobite zones:

  • Fennian ( abyfrons , rushtoni and levigena zones)
  • Whitlandian ( radix and gibbsi zone)
  • Moridunian ( selwynii and rhyakos zone) (whereby the basis of the Moridunian level and the Arenig series was not defined)

In 1995 Richard Fortey and Robert Owens finally defined the base of the Arenig series and Moridunian level with the base of the Tetragraptus approximatus zone (although this zone has not been proven in Wales!). The authors defined the end of the Arenig series (and the beginning of the Llanvirn series) with the basis of the Didymograptus artus zone. This means that the beginning of the Arenig series coincides with the beginning of the global Floium stage. The beginning of the regional Llanvirn series is determined by these authors with the base of the Didymograptus artus zone (formerly D. bifidus ).

Correlation and absolute age values

In the course of the redefinition of the individual periods of the earth's history, the Arenigium (stage or series) was replaced by the global stages of Floium (2004), Dapingium (2007) and the lower Darriwilium (1997). The regional levels of the Moridunian and Whitlandian correspond to the Floium, the Fennian is equivalent to the Dapingium and the lower Darriwilium. In the overview and correlated with absolute age values:

  • Arenigium (477.7 ± 1.4 to 465.3 ma)
    • Fennian (470.0 ± 1.4 to 465.3 ma)
    • Whitlandian (473.2 ± 1.4 to 470.0 ma)
    • Moridunian (477.7 ± 1.4 to 473.2 ma)

literature

  • SM Bergström, A. Löfgren, J. Maletz: The GSSP of the Second (Upper) Stage of the Lower Ordovician Series: Diabasbrottet at Hunneberg, Province of Västergötland, Southwestern Sweden. In: Episodes. 27, No. 4, Beijing 2004, ISSN  0705-3797 , pp. 265-272.
  • Stig M. Bergström, Stanley C. Finney, Chen Xu, Daniel Goldman, Stephen A. Leslie: Three new Ordovician global stage names. In: Lethaia. 39, Oslo 2006, ISSN  0024-1164 , pp. 287-288.
  • Richard A. Fortey, Robert M. Owens: The Arenig Series in South Wales. Bulletin of the British Museum natural History. In: Geology. 41, No. 3, London 1987, ISSN  0007-1471 , pp. 69-307.
  • Richard A. Fortey, DAT Harper, JK Ingham, AW Owen, AWA Rushton: A revision of Ordovician series and stages from the historical type area. In: Geological Magazine. 132, 1995, ISSN  0016-7568 , pp. 15-30.
  • Felix M. Gradstein, Jim G. Ogg, Mark Schmitz, Gabi Ogg: The Geologic Time Scale 2012. 2-Volume Set, Volume 2, p. 501 ( books.google.de ).

Individual evidence

  1. ↑ Fortey et al. (1995: p. 15 ff.)
  2. ^ Adam Sedgwick: On the older Palaeozoic (Protozoic) rocks of Wales. In: Quarterly Journal of the Geological Society of London. 1, pp. 5–20, London 1845, here p. 8 ( Textarchiv - Internet Archive ).
  3. ^ Adam Sedgwick: On the classification and nomenclature of the Lower Palaeozoic rocks of England and Wales. In: Quarterly Journal of the Geological Society of London. 8, London 1852, pp. 136-168 ( biodiversitylibrary.org p. 147).
  4. ^ Adam Sedgwick, Frederick McCoy: A synopsis of the classification of the British Palæozoic rocks; With a systematic description of the British Palæozoic fossils in the Geological museum of the University of Cambridge. 2 volumes and a table volume, London 1851–1855, JW Parker and Son, S. XCV ( Textarchiv - Internet Archive ).
  5. ^ Henry Hicks, John William Salter: Second report on the "Menevian Group" and the other formations at St. David's, Pembrokeshire. In: Report of the British Association for the Advancement of Science, 1866. Nottingham 1867, pp. 182-186.
  6. ^ Henry Hicks: On the Tremadoc rocks in the neighborhood of St. David's, South Wales, and their fossil contents. In: Quarterly Journal of the Geological Society of London. 29, London 1873, pp. 39-52 ( biodiversitylibrary.org ).
  7. ^ Henry Hicks: On the succession of the ancient rocks in the vicinity of St. David's, Pembrokeshire, with special reference to those of the Arenig and Llandeilo groups, and their fossil contents. In: Quarterly Journal of the Geological Society of London. 31, London 1875, pp. 167-308 ( biodiversitylibrary.org ).
  8. ^ Henry Hicks: The classification of the Eozoic and Palaeozoic rocks of the British Isles. In: The Popular Science Review. New series, 5, No. 17, London 1881, pp. 290-308.
  9. ↑ T. M'Kenny Hughes: Notes on some sections in the Arenig Series of North Wales and the Lake District. In: Report of the fifty-sixth meeting of the British Association for the Advancement of Science, held in Birmingham in September 1886. John Murray, London 1887, p. 663 ( Textarchiv - Internet Archive ).
  10. ^ Gertrude Lilian Elles: Some graptolite zones in the Arenig rocks of Wales. In: Geological Magazine. 5th Series, No. 1, London 1904, pp. 199-211.
  11. ^ Gertrude Lilian Elles: The stratigraphy and faunal succession in the Ordovician rocks of the Builth-Llandrindod Inlier, Radnorshire. In: Quarterly Journal of the Geological Society of London. 95, London 1940, pp. 383-445.
  12. ↑ The absolute values ​​of the regional levels were determined using the Time Scale Creator 6.0 (October 2012) .

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