Dating glacial deposits
It is not clear whether this implies a global glaciation, or the existence of localized, possibly land-locked, glacial regimes. Radiocarbon dating dates the decay of Carbon within organic matter. This is caused by a number of factors, including variations in solar radiation, magnetic storms, and internal geophysical factors. This information is vital for numerical models, and answers questions about how dynamic ice sheets are, and how responsive they are to changes in atmospheric and oceanic temperatures. Uranium-series uses the decay of uranium and thorium isotopes U, U and Th in calcites in particular, such as stalactites and stalagmites in caves.
Unfortunately, glacial sediments are typically difficult to date. Leave a Reply Your email address will not be published. Potassium-argon and argon-argon dating can be used to date the formation of volcanic rocks. It is effective for hundreds of thousands of years, and dates how long the sediment has been buried.
Older marine sediments can be dated using palaeo-magnetism. The first of these discoveries was published in by J. These minerals are magnetised during formation.
However, evidence of sea-level glaciation in the tropics during the Sturtian is accumulating. Amino Acid Racemisation dates the decay and change in proteins in organisms such as shells. Alternatively, Earth's dipolar field could have been oriented such that the poles were close to the equator.
Scientists dating Quaternary glacial sediments in Antarctica most commonly use one of the methods outlined below, depending on what kind of material they want to date and how old it is. It is effective on timescales of several millions of years. When sedimentary rocks form, magnetic minerals within them tend to align themselves with the Earth's magnetic field. Organic matter needs to have been buried and preserved for this technique. It assumes that organic material is not contaminated with older radiocarbon which, for example, is a common problem with organic material from marine sediment cores around Antarctica.
This last point is very difficult to prove. The radiation emanates from radioactive grains within the sediment, such as zircons. Unconsolidated sediments contain magnetic minerals, such as those on the continental shelf and slope. Therefore, the presence of glacial deposits within the tropics suggests global ice cover. Other methods of dating glacial sediments There are so many other methods of dating Quaternary sediments and organic material that it is impractical to cover them all here in detail.
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