The basic concept here is that if your sample stays at the surface and experiences steady exposure with or without erosion, nuclide concentrations are confined to the “simple exposure region” highlighted with dark lines in the above figure.

In certain manifestations of this diagram (primarily when plotted with a log x-axis and a linear y-axis), the simple exposure region vaguely resembles a banana, for example: This resemblance, perhaps unfortunately, has resulted in the common use of the term “banana diagram.” Then the important aspect of this diagram is that if the sample gets buried after a period of surface exposure, both Al-26 and Be-10 concentrations decrease due to radioactive decay, and Al-26 decreases faster than Be-10.

cosmogenic dating group-24

I’ve done it this way in the version 3 online exposure age calculator, which will generate two-nuclide diagrams for all combinations of Ne-21, Be-10, Al-26, and C-14 in quartz, and also in the ICE-D database which makes use of the v3 calculator as a back end.

Summary: Draw two-nuclide diagrams so that burial always goes the same way.

High-energy cosmic rays shower the Earth's surface, penetrating meters into rock and producing long-lived radionuclides such as Cl-36, Al-26 and Be-10.

Production rates are almost unimaginably small - a few atoms per gram of rock per year - yet we can detect and count these "cosmogenic isotopes" using accelerator mass spectrometry, down to levels of a few thousand atoms per gram (parts per billion of parts per billion! The build-up of cosmogenic isotopes through time provides us with a way to measure exposure ages for rock surfaces such as fault scarps, lava flows and glacial pavements.

This is represented by a trajectory that goes down and to the left, as shown above in the Granger example.

So samples that are “below the banana” have experienced both a period of exposure and a period of burial.It also enabled workers to identify and fill gaps in this knowledge, and suggested avenues for new or further research, while retaining as a guiding principle and common denominator the decryption of the information contained in the caves of the Alps (Audra, 2004; Audra (i) Geometrical (Goran, 1992): The position and three-dimensional structure of cave systems can be determined by applying appropriate analytical techniques (Hobléa, 1999b) to data on the most voluminous parts of these cave systems, which are accessible to, and have been mapped by cavers.The results of such studies may then be combined with indicators such as palaeoflow paths (., 'chemin de drainage', Choppy, 1994.On the other hand, here is a Ne-21/Be-10 diagram from a very cool paper by Florian Kober and Vasily Alfimov: This figure has a lot of data in it that are beside the point from the perspective of this post, but the point is that it has the opposite axes: Be-10 concentration on the x-axis and Ne-21/Be-10 ratio on the y-axis. I think inverting the diagram so that burial goes up just confuses readers. Thus, I advocate always plotting the longer-lived nuclide of the pair on the x-axis, and the ratio of the shorter-lived to longer-lived nuclide on the y-axis. Of course, I am in the US, but I am not just cheering for my own team here.Thus, exposure still goes to the right (at least for a while), but burial goes UP. Not what we expect from our previous experience with the Al-26/Be-10 diagram. At present, the choice of axes in two-nuclide diagrams involving Ne-21 in the literature appears to reflect your position in relation to the Atlantic Ocean. It really does make more sense for two-nuclide diagrams to always behave the same way no matter what nuclide pair is involved.Where surfaces are gradually evolving, cosmogenic isotope measurements allow us to calculate erosion or soil accumulation rates.