Triassic–Jurassic extinction event(Redirected from Triassic-Jurassic extinction event)
The Triassic–Jurassic extinction event marks the boundary between the Triassic and Jurassic periods, , and is one of the major extinction events of the Phanerozoic eon, profoundly affecting life on land and in the oceans. In the seas, a whole class (conodonts) and 23-34% of marine genera disappeared. On land, all archosaurs other than crocodylomorphs (Sphenosuchia and Crocodyliformes) and Avemetatarsalia (pterosaurs and dinosaurs), some remaining therapsids, and many of the large amphibians became extinct.
About 42% of all terrestrial tetrapods went extinct. This event vacated terrestrial ecological niches, allowing the dinosaurs to assume the dominant roles in the Jurassic period. This event happened in less than 10,000 years and occurred just before Pangaea started to break apart. In the area of Tübingen (Germany), a Triassic-Jurassic bonebed can be found, which is characteristic for this boundary.
The extinction event marks a floral turnover as well. About 60% of the diverse monosaccate and bisaccate pollen assemblages disappear at the T-J boundary, indicating a major extinction of plant genera. Early Jurassic pollen assemblages are dominated by Corollina, a new genus that took advantage of the empty niches left by the extinction.
Several explanations for this event have been suggested, but all have unanswered challenges:
- Gradual climate change, sea-level fluctuations or a pulse of oceanic acidification during the late Triassic reached a tipping point. However, this does not explain the suddenness of the extinctions in the marine realm.
- Asteroid impact, but so far no impact crater of sufficient size has been dated to coincide with the Triassic–Jurassic boundary.
- The unconfirmed Wilkes Land crater is of sufficient size and falls within the correct age range at 100 million to 500 million years old and 2.5x the size of the Chicxulub crater.
- The eroded Rochechouart crater in France has most recently been dated to 201 ±2 million years ago, but at 25 km (16 mi) across (possibly up to 50 km (30 mi) across originally), appears to be too small. The impact responsible for the annular Manicouagan Reservoir occurred about 12 million years before the extinction event - the Rochechouart crater is now thought to have been caused by part of the same fragmented impactor.
- Massive volcanic eruptions, specifically the flood basalts of the Central Atlantic Magmatic Province (CAMP), would release carbon dioxide or sulfur dioxide and aerosols, which would cause either intense global warming (from the former) or cooling (from the latter). The record of CAMP degassing shows several distinct pulses of carbon dioxide immediately following each major pulse of magmatism, at least two of which amount to a doubling of atmospheric CO2.
- The isotopic composition of fossil soils of end Triassic and Early Jurassic has been tied to a large negative carbon isotope excursion (Whiteside et al. 2010). Carbon isotopes of lipids (n-alkanes) derived from leaf wax and lignin, and total organic carbon from two sections of lake sediments interbedded with the CAMP in eastern North America have shown carbon isotope excursions similar to those found in the mostly marine St. Audrie’s Bay section, Somerset, England; the correlation suggests that the end-Triassic extinction event began at the same time in marine and terrestrial environments, slightly before the oldest basalts in eastern North America but simultaneous with the eruption of the oldest flows in Morocco (Also suggested by Deenen et al., 2010), with both a critical CO2 greenhouse and a marine biocalcification crisis.
- Contemporaneous CAMP eruptions, mass extinction, and the carbon isotopic excursions are shown in the same places, making the case for a volcanic cause of a mass extinction. The catastrophic dissociation of gas hydrates (suggested as one possible cause of the largest mass extinction of all time, the so-called "Great Dying" at the end of the Permian Period) may have exacerbated greenhouse conditions.
- Other scientists reject the volcanic eruption theory, because the Newark Supergroup, a section of rock that records the Triassic-Jurassic boundary, contains no ash-fall horizons and the first basalt flows lie ~10 meters above the transition zone.
- Some sources (Whiteside et al 2010) give a date 201.4 Ma.
- The extinction of conodonts —in terms of discrete elements— at the Triassic-Jurassic boundary
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