The Lower Triassic is the first of three epochs of the Triassic period. It lasted from about 252.2 million years ago (mya) to ~247.2 mya. The Lower Triassic is the oldest epoch of the Mesozoic era. These rocks were laid down just after the great Permian–Triassic extinction event.
The Lower Triassic was called the Scythian stage, which can be found in older literature. In Europe, most of the Lower Triassic is composed of sandstone. It is a lithostratigraphic unit of continental red beds. They were formed on land under desert conditions.
Fauna[change | change source]
The massive extinctions that ended the Paleozoic era caused extreme hardship for the surviving species. Many types of corals, brachiopods, molluscs, echinoderms, and other invertebrates had completely disappeared. The most common hard-shelled marine invertebrates were bivalves, gastropods, ammonites, echinoids, and a few articulate brachiopods. The most common land animal was the herbivorous synapsid Lystrosaurus.
The first ichthyosaurs evolved in this epoch.
The climate during the Lower Triassic (especially in the interior of the supercontinent Pangaea) was generally dry. Deserts were widespread. The poles had a temperate climate. The relatively hot climate of the epoch may have been caused by widespread volcanic eruptions.
References[change | change source]
- Sahney S. and Benton M.J. (2008). "Recovery from the most profound mass extinction of all time" (PDF). Proceedings of the Royal Society: Biological 275 (1636): 759–65. doi:10.1098/rspb.2007.1370. PMC 2596898. PMID 18198148. http://journals.royalsociety.org/content/qq5un1810k7605h5/fulltext.pdf.
|Precambrian (4.567 gya – 541 mya)|
|In the left column are Eons, bold are Eras, not bold are Periods. gya = billion years ago, mya = million years ago|
|Hadean (4.567 gya – 4 gya)|
|Archaean (4 gya – 2.5 gya)||Eoarchaean (4 gya – 3.6 gya)|
|Proterozoic (4 gya – 2.5 gya)||Palaeoproterozoic (2.5 gya – 1.6 gya) Siderian (2.5 gya – 2.3 gya) Rhyacian (2.3 gya – 2.05 gya) Orosirian (2.05 gya – 1.8 gya) Statherian (1.8 gya – 1.6 gya)|
|Phanerozoic (541 mya – today)|
|In the left column are Eras, bold are Periods, not bold or italics are Epochs, Italics are stages. kya = thousand years ago, mya = million years ago|
|Palaeozoic (541 mya – 252.17 mya)||Cambrian (541 mya – 485.4 mya)|
|Mesozoic (252.17 mya – 66.0 mya)||Triassic (252.17 mya – 201.3 mya) Lower Triassic (252.17 mya – 247.2 mya) Middle Triassic (247.2 mya – 237 mya) Upper Triassic (237 mya – 201.3 mya)|
|Cainozoic (66.0 mya – today)||Palaeogene (66.0 mya – 23.03 mya) Palaeocene (66.0 mya – 56 mya) Eocene (56 mya - 33.9 mya) Oligocene (33.9 mya – 23.03 mya)|
|Source||International Chronostratigraphic Chart 2013. International Commission on Stratigraphy, retrieved 8 April 2013. Divisions of geologic time – major chronostratigraphic and geochronologic units USGS, retrieved 8 April 2013.|