the ordovician-silurian extinction event
DESCRIPTION
The Ordovician-Silurian mass extinction event; One of earths largest extinction events, wiping out approximately 60% of marine fauna. This event took place around 443.7 million years ago, in the late Ordovician period. This event is fairly loosely studied, current theories pointing towards possible causes being Gamma Ray burst, or the sheer amount of exposed rock; both theories leading to a glaciation event. But what else could have caused this? Well, looking at previous records we find that there is a large increase of atmospheric Carbon Dioxide, and then a period of abrupt cooling. There may have also been significant anoxification in the seas. To find an answer to this question, certain areas were closely studied such as algal populations, occurrences of certain minerals, such as potassium bentonite, and Iron Pyrite, along with other identifying characteristics such as oolites, and disturbances in certain layers. Through careful analysis of minerals, and organism populations; a few conclusions may be made. First off, there was a distinct layer of potassium bentonite, a mineral commonly associated with the presence of volcanic ash. Above the layer of bentonite, large portions of iron pyrite were found, indicating that there may have been an anoxification and even an introduction of sulphur to the environment. What was also found [above the K(Pottasium)-bentonite layer] were large populations of algae, such as Tetradium and Stromatolites, whom are opportunists, suggesting that that the environment may have been changed from what it originally may have been? From the data collecting, it may be concluded that the event may have been caused by super volcanism. To be specific, the volcanic arch off of Laurentia (present day Appalachian mountain range).TRANSCRIPT
Figure 1. Varying sea levels of the late Ordovician. http://insugeo.org.ar/libros/cg_17/077_1.jpg
Figure 2. The relation between Atmospheric CO2 and average global temperatures. http://stevengoddard.files.wordpress.com/2010/12/image002-3.gif
Figure 3. A global sea level fluctuation chart. http://www.agilegeoscience.com/storage/post-
images/Phanerozoic_Sea_Level.png?__SQUARESPACE_CACHEVERSION=1302539501583
Figure 4: A minor pyrite formation in the Gull River, indicating there were low
oxygen levels (in order for the pyrite to form there must be low amounts of
oxygen).
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