The main objective of my Ph D is to reconstruct the retreat of the Uummannaq Ice Stream System, a large system of coalescent ice streams in West Greenland.To constrain the timing of the retreat of this ice, we are using a technique known as cosmogenic nuclide dating.Radiocarbon dating is abundantly used and offers very high precision dates, but we often want to date an event that is either too far in the past, or without the right type of organic matter, to be dated by C.While there is a slew of other dating techniques to choose from, cosmogenic nuclide exposure dating is useful for relatively young (~100 to 10 million years old) samples.Surface exposure dating using terrestrial cosmogenic nuclides (TCN) is an established and reliable method to date landforms and has been applied for dating glacial advances and retreats, erosion history, lava flows, meteorite impacts, fault scarps, and other geological events.Within landslide studies, NGU applies TCN dating to determine ages of rockslide events and the age of sliding surfaces in order to determine past long-term displacement rates Earth is constantly bombarded with cosmic rays that are high-energy charged particles.This provides an ideal method for determining when a glacier retreated from a region, hence exposing the ground beneath.
Using certain cosmogenic radionuclides, scientists can date how long a particular surface has been exposed, how long a certain piece of material has been buried, or how quickly a location or drainage basin is eroding.
Under these conditions, surface cosmogenic 21 Ne concentrations should be a function only of the erosion rate and the 21 Ne production rate.
Geologic evidence as well as cosmogenic 10 Be and 26 Al concentrations indicate that i) these sites have experienced millions of years of surface exposure at low erosion rates, and ii) steady erosion has been sustained long enough that surface 10 Be and 26 Al concentrations have reached equilibrium with the erosion rate.
If we are particularly interested in the timing of the uncovering of a surface—say, bedrock that had been covered by ice, or sediments that had been revealed by the incision of a stream—we can employ cosmogenic nuclide surface exposure dating to study that uncovering process.
This is different from techniques (like Ar, or U/Th) that date the formation of a rock itself.