User:Miadaks/sandbox

Larger Benthic Foraminifera as a Means of Dating

Scientists are attempting to use the Larger Benthic Foraminifera as a means of dating. The Tanzanian Drilling Project (TDP for short) is focused on extracting these Foraminifera and analyzing their size, intactness, change in formation and change in coil patterns. Scientists were able to create comparison by setting up three different sites, each of which were approximately three kilometers apart, along the south coast of the Rufiji River. The site at the Kilwa Peninsula was found most useful as it contained complete sequences throughout the Eocene – Oligocene extinction. They found that there were both clay beds and limestone beds which both contained some Foraminifera. The limestone beds, however, contained more Foraminifera which, due to the compactness of the limestone beds themselves, were all mainly intact and analyzable. The few broken Foraminifera fossils found in the limestone beds were compared to the findings in the clay successions for identification of species. The clay beds contained fewer Foraminifera but were able to preserve them much better. It is thus ideal that the researchers came upon both clay and limestone beds because together they give a lot more information to the possible causes and date of the extinction. Since there were some that were in pieces, for example, researchers came to a conclusion that the Foraminifera were transported due to large storms or hurricanes at the time. They also concluded that different lights and energy played a big role in where the Foraminifera were found.

The process of biostratigraphy was used as a way of dating because scientists use the fossils found to analyse the age of the rock they were found in. There were two zones being analysed, the Shallow Benthic and the Indo – Pacific. What researchers were looking for was a correlation between these two zones, and with this correlation they could see how the Foraminifera were differently and similarly affected in the two regions. For something to qualify as a mass extinction it must be widespread and affect a multitude of different species, therefore the correlation was important for further arguing whether the Eocene-Oligocene was a mass extinction or not. For the Shallow Benthic Zone, the Tethys, a former tropical body of salt water, was examined at its shallower parts. Researchers discovered that out of the 20 divisions, the Eocene Oligocene transition was between the 20th and 21st division. However, the East Indian Letter Classification, which was analysed in the Indo- Pacific region, was a little different. This region was divided by groups of the Larger Benthic Foraminifera (unlike with the Tethys where it was simply divided into zones), however it lacked a lot of correlation between its sections and the Tethyan region. Majority of the zones showed important carbon successions, which indicate the major sea-level falls thus providing more backbone to the argument that sea-level falls caused the extinction. As a result of not finding a correlation between these two zones, researchers were unable to directly pinpoint a time for the extinction and a potential cause.

Lastly, researchers used sedimentology, the study of modern sediments, to analyse two different types of beds – Type I and Type II. The Type I beds were approximately 0.1-1.5 meters thick and are found about two meters above the Eocene Oligocene boundary. They contain a lot of the Larger Benthic Foraminifera and are rich in bioclast and quartz packstones. However, they are also victim of a high level of wearing away. This potentially backs up the hypothesis of large storms or hurricanes which transported the Foraminifera therefore increasing fragmentation and separation of the fossils. The Type II beds were almost opposite. They contained very few Foraminifera and were lacking bioclast and quartz packstones. When researchers were analyzing the Type II beds they realized the significant lack in diversity, when comparing to the Type I beds. Through this the hypothesis that there were decreases in sea-level were further backed up.