Early Jurassic

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Early/Lower Jurassic
201.3 ± 0.2 – 174.7 ± 0.8 Ma
Chronology

The Early Jurassic

Epoch (in chronostratigraphy corresponding to the Lower Jurassic Series) is the earliest of three epochs of the Jurassic Period. The Early Jurassic starts immediately after the Triassic–Jurassic extinction event, 201.3 Ma (million years ago), and ends at the start of the Middle Jurassic
174.7 ±0.8 Ma.

Certain rocks of marine origin of this age in Europe are called "Lias" and that name was used for the period, as well, in 19th-century geology.[4] In southern Germany rocks of this age are called Black Jurassic.

Origin of the name Lias

There are two possible origins for the name Lias: the first reason is it was taken by a

sloops from north Cornish ports such as Bude would sail across the Bristol Channel to the Vale of Glamorgan to load up with rock from coastal limestone quarries (lias and Carboniferous limestone from South Wales was used throughout North Devon/North Cornwall as it contains calcium carbonate to 'sweeten' (i.e.neutralise) the acidic Devonian and Carboniferous soils of the West Country); the Cornish would pronounce the layers of limestone as 'laiyers' or 'lias'; leac is Gaelic for "flat stone".[5]

Geology

Stratigraphy

Massive cliffs in Zion Canyon consist of Lower Jurassic formations, including (from bottom to top): the Kayenta Formation and the massive Navajo Sandstone

There has been some debate

ammonites has been used; but this depends on relatively complete ammonite faunas being present, a problem that makes correlation between sections in different parts of the world difficult. If this biostratigraphical indicator is used, then technically the Lias Group—a lithostratigraphical division—spans the Jurassic / Triassic
boundary.

United Kingdom

Lias formations at Lyme Regis, UK, known locally as Blue Lias

There are extensive Liassic outcrops around the coast of the

siltstones
, deposited under fully marine conditions.

Lias Group strata form imposing cliffs on the Vale of Glamorgan coast, in southern Wales. Stretching for around 14 miles (23 km) between Cardiff and Porthcawl, the remarkable layers of these cliffs, situated on the Bristol Channel are a rhythmic decimetre scale repetition of limestone and mudstone formed as a late Triassic desert was inundated by the sea.[7]

Life

Ammonites

During this period,

zone fossils. There were several distinct waves of ammonite evolution in Europe alone.[8]

Marine reptiles

The Early Jurassic was an important time in the evolution of the marine reptiles. The Hettangian saw the already existing

]

Terrestrial animals

Terrestrial environment of the Pliensbachian-Toarcian boundary Fennoscandinavia, with flora based on the Sorthat Formation. Dinosaurs are based on material found on various locations of the German realm of the Ciechocinek Formation and on lesser extent, footprints of the Drzewica Formation

On land, a number of new types of dinosaurs—the

sphenodonts, and early lissamphibians.[citation needed
]

See also

References

  1. ^ "International Chronostratigraphic Chart" (PDF). International Commission on Stratigraphy.
  2. S2CID 128552062
    .
  3. doi:10.18814/epiiugs/2001/v24i3/003. Retrieved 13 December 2020.{{cite journal}}: CS1 maint: numeric names: authors list (link
    )
  4. ^ Rudwick, M.J.S (1992): Scenes from Deep Time: Early Pictorial Representations of the Prehistoric World, University of Chicago Press, 280 pages. Except from Google Books
  5. ^ a b Chisholm, Hugh, ed. (1911). "Lias" . Encyclopædia Britannica. Vol. 16 (11th ed.). Cambridge University Press. p. 533.
  6. ^ International Subcommission on Jurassic Stratigraphy. Newsletter 35/1, December 2008, Edited by Nicol Morton and Stephen Hesselbo Archived 2015-01-28 at the Wayback Machine
  7. ^ Howe, S., Owen, G. & Sharpe, T. 2005 Walking the Rocks Geologists' Association - South Wales Group
  8. ^ See e.g. Davies, 1920, pp. 173–75

Sources

  • Davies, A. M., An Introduction to Palaeontology, Thomas Murby & Co., London
  • House, M.R. (1993) Geology of The Dorset Coast, The Geologists' Association.
  • Simms, M.J., Chidlaw, N., Morton, N. and Page, K.N. (2004) British Lower Jurassic Stratigraphy, Geological Conservation Review Series, No. 30, Joint Nature Conservation Committee, Peterborough.

External links