The Triassic-Jurassic

The Triassic-Jurassic

Boundary Extinction

There have been five major extinction events in geologic history. The largest of which was the Permian-Triassic extinction that occurred approximately 251 million years ago. During this extinction, 96% of marine species and 70% of terrestrial vertebrate species went extinct. Other extinction events include the Cretaceous- Tertiary and the End Ordovician. The Triassic-Jurassic boundary extinction occurred 200 million years ago during the Phanerozoic eon. The extinction occurred just before Pangaea broke apart. This extinction affected land, sea and faunal species like the Permian-Triassic extinction.

There is a lot of evidence supporting the extinction at the Triassic-Jurassic boundary. The hypothesis of Sudden Productivity Collapse Associated with the Triassic-Jurassic Boundary Mass Extinction is that many species of the Triassic Period did not survive the mass extinction between the Triassic and Jurassic Periods and that this extinction was very quick and detrimental to many species. P.D. Ward suggests that this extinction was similar to but not as extreme as the Permian-Triassic and the Cretaceous-Tertiary extinctions.

The research conducted by P.D. Ward and his team of scientists is supported mainly by carbon isotope evidence collected from the Queen Charlotte Islands, British Colombia, Canada. The evidence of the carbon isotopes that were unaffected by diagenesis is synchronized with the sudden extinction of marine plankton which leads one to infer that the two extinctions happened around the same time. The scientists also collected “bulk samples of black shale (Ward, 2001).” These samples varied from location to location which also contributes to the hypothesis that extinction occurred. Another piece of evidence recorded is the fact that monotid bivalves went extinct in the lower Kennecott Point section where the researchers also studied.

The Triassic-Jurassic extinction was also marked by certain faunal extinctions. J.C. McElwain reported in Fossil Plants and Global Warming at the Triassic-Jurassic Boundary that the “greenhouse” warming from 3Ð'oC to 4Ð'oC was indicated by a “fourfold increase in atmospheric carbon dioxide concentration (McElwain, 1999). McElwain reports that a temperature increase in one degree Celsius could have led to 95% of the fauna during this time going extinct. Evidence to support McElwain’s hypothesis comes from “sedimentary facies, paleosols, sea-level change, and flood basalt volcanism (McElwain, 1999). Leaf temperatures were calculated and fossil-leaf width and stomatal density and size were recorded. There was two test groups in this study: one was with typical end-Triassic climate and CO2 and the other with variable warming and variable CO2 (McElwain, 1999). Summed up, the Fossil Plants and Global Warming at the Triassic-Jurassic Boundary article states that leaf width and a quadruple increase in CO2 levels caused the faunal extinction.

Jozef Palfy and James K. Mortensen discovered that the marine and terrestrial extinction events during the Triassic-Jurassic boundary probably did not occur simultaneously. They believe that the land extinction occurred first and the marine extinction followed several hundred thousand years later. The marine sedimentary rock from the boundary was analyzed and yielded a “U-Pb zircon age of 199.6 Ð'± .3 million years (Plafy, 2000).” And according to previously recorded data, the terrestrial vertebrates went extinct before the recorded age of the marine sedimentary rocks.

It has been highly noted that during the time of the Triassic-Jurassic extinction event, there was a major increase in the level of volcanism. Terrestrial and marine extinction at the Triassic-Jurassic boundary synchronized with major carbon-cycle perturbation: A link to initiation of massive volcanism? relates data found from the United Kingdom and Greenland that apparently demonstrate the extinction of terrestrial and marine species as well as certain faunal species coincides with one of the largest volcanic eruptions, which characterized the Central Atlantic magmatic province.

The intense volcanism that is associated with the Triassic-Jurassic boundary extinction is also noted in Carbon isotope anomaly and other agrochemical changes at the Triassic-Jurassic boundary from a marine section in Hungry. This article states that the volcanism of the Central Atlantic magmatic province “may have induced climatic and oceanographic changes that triggered gas hydrate dissociation, which in turn accelerated environmental change, contributing to the biotic turnover around the Triassic-Jurassic boundary (Palfy, 2001).” It is thought that the intense volcanism and the productivity collapse led to the mass extinction during this